Anton de Kom Universiteit van Suriname

Photovoltaic-Thermal (PVT) Solar System;

Technical Feasibility Study of PVT applications for

Courtyard Marriott Hotel Paramaribo

Student: Svasti M Ramratan

Enrollment Number: 09WB1024

Supervisor: ir. P. Deosarran

Reviewer: ir. J. Narain

Date: December 7, 2016

STUDIERICHTING

Wb WERKTUIGBOUWKUNDE

2

Svasti M Ramratan (09WB1024)

Photovoltaic-Thermal (PVT) Solar System; Technical Feasibility Study of PVT applications for Courtyard Marriott Hotel

Paramaribo

Paramaribo, December 7, 2016

Supervisor: ir. P. Deosarran

Reviewer: ir. J. Narain

Anton de Kom University of Suriname

Faculty of Technology

Mechanical Engineering Dicipline

Leysweg 86, P.O.B. 9212 Paramaribo, Suriname

Keywords: Photovoltaic-Thermal Systems, Types of Solar PVT-systems, Energy efficiency, Feasibility

Report Number: 02PD2016

3

Anton de Kom Universiteit van Suriname

Photovoltaic-Thermal (PVT) Solar System;

Technical Feasibility Study of PVT applications for

Courtyard Marriott Hotel Paramaribo

Report submitted for the conclusion of the

Mechanical Engineering course at the Anton

de Kom University of Suriname, as a partial

requirement for obtaining the title Bachelor

of Science in Mechanical Engineering.

Svasti M Ramratan

Supervisor: ir. P. Deosarran Reviewer: ir. J. Narain

Mechanical Engineering discipline Mechanical Engineering discipline

Anton de Kom University of Suriname Anton de Kom University of Suriname

December 7, 2016

STUDIERICHTING

Wb WERKTUIGBOUWKUNDE

4

Acknowledgement

The completion of this thesis report would not have been possible without the support of many

people. My gratitude goes to the owner of Marriott Hotel Paramaribo, Arun Hindori, and the

managing director, Egon Von Foidl, for granting permission to conduct the project and Marriott

Hotel. And to the maintenance manager of Marriott Hotel, Mariano Alidikromo, and

maintenance second in command, Mike Rachman, for providing all the needed data and assisting

with the needed measurements to conduct the research of this project. My gratitude also goes to

my supervisor, ir. P. Deosarran, for all his feedback, guidance, for always being supportive, and

for always delivering quick responses during the development of the thesis project. I would like

to thank the Manager of the Mechanical Engineering division, ir. J. Narain, for providing his

guidance to correctly formulate this thesis report. I would also like to thank the manager of Blik

Bruining and Partners N.V., Vernon Bruining, for also providing information for the thesis report.

Many people have also provided needed literature and technical advices to formulate this report

which is greatly valued. My gratitude for this goes to Harrol Seepaul, Corrado Sirianni, Robbin

Gajadin, Atish Bisseswar, and Clint Ally. I would also like to thank all my friends, fellow students,

and every other faculty member who have supported me.

The love of my family has been the pillar that supported me through the mechanical engineering

bachelor course. In my life so far, nothing has exceeded the feeling of coming home and seeing

them smile.

Svasti M Ramratan

December 7, 2016

5

List of Symbols

Standard Nomenclature

Symbol Description Unit

Absorber thickness m Absorptivity -

Angle of incidence rad

A Area m2 𝐹′ Collector efficiency (modified) -

𝑛 Declination angle rad

𝑚 Defined variable -

𝑥 Dryness factor - Dynamic viscosity pa s Efficiency %

𝐾 Extension coefficient m-1 𝐹 Fin efficiency -

𝑢 Flow velocity m/s ℎ Fluid to tube heat transfer

coefficient

W/m2K

𝐿 Glass cover thickness m 𝐶𝑝 Heat capacity J/kg K 𝐹𝑅 Heat removal factor (modified) -

Hour angle rad �� Mass flow m3/h 𝑆 Modified solar radiation W

𝑈𝐿 Overall loss coefficient

(modified)

W/m2K

𝑈𝐿 Overall loss coefficient W/m2K Reflectance -

𝑟 Reflection -

𝑛 Reflection index cover glass -

G Sun Irradiance W 𝑆 Solar radiation per unit area W

𝑇 Temperature C

Temperature coefficient - Thermal conductivity W/mK 𝑘 Thermal conductivity of

absorber

W/mK

Transmissivity -

() Transmissivity-absorptivity

product

-

𝐷 Tube diameter m 𝑊 Tube spacing m 𝑄𝐿 Useful thermal energy W/s

V

6

Superscripts and Subscripts

(Super/Sub) Script Description

1 incident

2 refracted

// parallel perpendicular

a ambient

b beam

d diffusion

el electrical

i inside

L loss

PV photovoltaic

r refrigerant

ref reference

t total

th thermal

WD width and depth

VI

7

List of Abbreviations and Acronyms

D Dimensional

PV Photovoltaic

PVT Photovoltaic-Thermal

RPVT Refrigerant-based Photovoltaic-Thermal

SDG Sustainable Development Goals

UN United Nations

VRF Variable Refrigerant Flow

WPVT Water-based Photovoltaic-Thermal

VII

8

Table of Contents

Acknowledgement ........................................................................................................................... IV

List of Symbols ................................................................................................................................... V

List of Abbreviations and Acronyms ............................................................................................ VII

1 Introduction ................................................................................................................................ 10

1.1 Background ............................................................................................................................... 10

1.2 Problem Statement and Objectives .......................................................................................... 11

1.3 Project work activities to fulfill the objective .......................................................................... 12

1.4 Outline ....................................................................................................................................... 12

2 Solar Technology in Suriname .................................................................................................... 13

2.1 Solar Energy .............................................................................................................................. 13

2.2 Renewable Energy in Suriname ............................................................................................... 14

2.3 Solar Projects in Suriname ........................................................................................................ 14

2.4 Solar Energy for Courtyard Marriott Hotel Paramaribo .................................................. 15

3 Overview of PVT-Systems........................................................................................................... 16

3.1 Basic Concept of PVT-Systems................................................................................................. 16

3.2 Water based and Refrigerant based PVT-systems.................................................................. 18

4 Performance Analysis of the PVT-System ................................................................................. 20

4.1 Florschuetz Model .................................................................................................................... 20

4.2 Energy Coverage ....................................................................................................................... 23

4.3 Used Data .................................................................................................................................. 23

4.3.1 Measurements .................................................................................................................... 24

4.3.2 PVT Panel Design ............................................................................................................... 24

4.3.3 Expected Model Performance ........................................................................................... 26

4.4 Methodology of the performance analysis ............................................................................. 28

VIII

9

5 Model Analysis ............................................................................................................................... 30

5.1 Mathematical Model ................................................................................................................. 30

5.2 Model Results ...................................................................................................................... 36

5.3 Model Validation ...................................................................................................................... 41

6 Analysis of PVT applications for Marriott Hotel ...................................................................... 43

6.1 Analyzed PVT applications ...................................................................................................... 43

6.2 Results of the WPVT-system .................................................................................................... 44

6.3 Results of the RPVT-system ..................................................................................................... 47

6.4 Energy Coverage of the PVT-system ....................................................................................... 50

6.5 Discussion of the PVT-systems ................................................................................................ 52

7 Conclusion and Recommendations ............................................................................................. 54

7.1 Conclusions ............................................................................................................................... 54

7.2 Recommendations .................................................................................................................... 55

Appendixes......................................................................................................................................... 56

A Complete set Equations ............................................................................................................ 56

B Marriott Hotel with Solar Panels.............................................................................................. 58

C WPVT and RPVT-system Comparison.................................................................................... 61

References........................................................................................................................................... 62

IX

10

1 Introduction

“I’d put my money on the sun and solar energy. What

a source of power! I hope we don’t have to wait until oil

and coal run out before we tackle that. I wish I had

more years left.

—Thomas Edison, 1931

(Inventor, Businessman)

1.1 Background

The electricity demand of the building sector is rising due to the effect of increased living

standards. This development also takes place in Suriname. Within the building sector,

commercial buildings such as hotels use an estimated 45% of the total energy usage for cooling

in tropical regions and an estimated 15% for water heating [1, 2]. Next to the increasing electricity

demand, electricity grid prices in Suriname currently also continue to rise. A solution to reduce

the energy costs from the electricity grid, is to utilize renewable energy for water heating and

cooling. In the hotel industry solar energy is presently the most used renewable energy. Solar

panels can be conveniently integrated within buildings [3]. It can be used by photovoltaic systems

to generate electricity or by thermal solar systems for thermal energy. Another method is

combining solar photovoltaic and thermal technology, which has shown to have many benefits.

These photovoltaic-thermal solar systems (PVT-systems) produce electricity and heat

simultaneously and deliver a higher overall efficiency. This combined system also delivers a

higher electricity performance due to the thermal collector that is able to actively cool down the

photovoltaic solar cells that operate better at lower temperatures [4]. In executed studies the PVT-

system has reached thermal and electrical efficiencies of approximately 70% and 14% [21].

Different types of PVT-applications can be used when integrating this system into a building.

Depending on what the building requirements are, the system can be designed as a PVT air -,

water- or refrigerant based system. Focus can also be lain on either increasing the electricity

production or the thermal production of the PVT-system [5]. A mathematical model was

developed by Florschuetz [17] to analyze the performance of PVT-systems. The performance of

this system can be assessed in terms of the electrical and thermal output and efficiency of the

system [22]. The information that is needed to analyze this system is the solar panel environment

condition, its location, and the panel design specifications. The main input data to analyze this

system are the electrical- and thermal load, the sun radiation and the ambient temperature.

Currently Energiebedrijven Suriname (EBS) is the only utility grid in Suriname generating

electricity, and for a certain amount by means of fossil fuel [6]. Corporate Marriott has also set

environment goals for their hotels stating: “Our sustainability strategy supports business growth

and reaches beyond the doors of our hotels to preserve and protect our planet’s natural

resources”. One of the environment goals of Corporate Marriott is to further reduce energy and

11

water consumption with 20% for their hotels by 2020 [9]. Since March, 2016 it is also stated in the

Constitution of Suriname that individuals producing electricity by means of on-grid renewable

energy can redeliver excess electricity to the utility grid at closeout prices [10].

1.2 Problem Statement and Objectives

Marriott Hotel in Paramaribo uses electricity from the utility grid of Suriname to provide for

water heating and air cooling for the comfort of its guests. Using energy from the utility grid is

related to the increased costs of cooling and heating appliances due to higher electricity prices.

Marriott Hotel aims to reduce its energy usage [9] and using renewables, such as the PVT system,

can contribute to that goal. Integrating a PVT system can reduce the energy cost from the grid by

partially generating the electricity and heat that is needed for cooling and water heating. PVT-

systems can reach higher efficiencies than the conventional photovoltaic system and can cover

the energy usage of both cooling and water heating appliances, but the application of this system

is not yet tested for the environment conditions in Suriname. For the research in this thesis project

different types of PVT-systems are reviewed that can be integrated in commercial buildings and

the technical feasibility of the PVT-systems, which are applicable for Marriott Hotel Paramaribo,

is assessed.

The objective of this report can be split in two sections which are:

1. Investigating and gathering information on PVT-systems. The focus is lain on the

performance of applicable building integrated PVT-systems. The considered PVT-systems

are:

Water based PVT-system (WPVT-system)

Refrigerant based PVT-system (RPVT-system)

2. Investigating the performance of PVT-systems for Marriott Hotel as a case study. The

performance is analyzed to determine a monthly average yield of the system. The

analyzed aspects for the case study are:

The electrical and thermal power output and efficiency of the PVT-systems

The amount of energy that can be covered by the PVT-systems

12

1.3 Project work activities to fulfill the objective

The executed steps to fulfill the stated objectives were the following:

Gathering information on different types of building integrated PVT-systems namely the

water-, and refrigerant based PVT-systems. The focus is lain on the performance, built,

and thermal energy usage of the PVT-systems.

Performing the needed measurements and gathering relevant data to analyze the

performance of PVT-systems applicable for Marriott Hotel. The measurements which are

conducted are the ambient temperature and the electrical usage of the cooling and water

heating system from Marriott Hotel. The data which is gathered includes the architect

model of Marriott Hotel and the electrical and thermal energy usage of its cooling and

water heating appliances.

Analyzing the Florschuetz model [17] in Microsoft Excel and determining its validity by

implementing research data from Gaurracino et al. [22] and Ji et al. [23].

Analyzing the performance of PVT-systems for Marriott Hotel through the Florschuetz

model [17] in Microsoft Excel at steady state conditions.

Comparing the energy performance of the WPVT and RPVT- system.

Investigating the amount of energy that can be covered by the WPVT and RPVT-system

for Marriott Hotel.

1.4 Outline

The document is structured as follows. In chapter 2 the status of solar energy usage in Suriname

is given. This is followed by chapter 3 which gives general information on different types of PVT-

systems. In this chapter the different types of PVT-systems are explained based on the built,

performance and the practical uses of the system. Chapter 4 gives the method of how the energy

performance and how the energy coverage are analyzed. The Florschuetz model [17] is explained

in this chapter and the used data for the analysis of the PVT-system is given. The elaboration of

the Florschuetz model [17], which is also written in Microsoft Excel, is given in chapter 5 where

the research data from Gaurracino et al. [22] and Ji et al. [23] is used to test the validity of the

model. Chapter 6 gives the analysis of a WPVT and RPVT-application for Marriott Hotel by using

the Florschuetz model [17] and the panel design requirements that comply for Marriott Hotel.

The report is concluded with chapter 7 stating the conclusions and recommendations which are

drawn from the conducted research.

13

2 Solar Technology in Suriname

“Don’t you know yet? It’s your light that lights up

the world.

—Rumi, 1273

(Poet, Jurist, Islamic scholar, Theologian)

Current developments of solar energy in Suriname are given in this chapter. The relevance of this

information is: By knowing where Suriname stands today on solar technology, research can be

done from that point towards innovation. This chapter gives an indication of the sun irradiance

in Suriname, constitution agreements, executed projects and indicates the benefits of solar

technology for a hotel.

2.1 Solar Energy

Suriname has favorable environmental conditions for the use of solar as an energy source

according to the Investment and Development Corporation Suriname (IDCS). Suriname receives

large amounts of sunlight, with an average of 7.2 hours of sunshine per day and an average daily

solar irradiation of 5 kWh per square meter [16]. Figure 2.1 gives averaged hourly sun radiation

data measured at Anton de Kom Universiteit van Suriname within a time period of 6.00 to 19.00

[41].

FIGURE 2.1 Average irradiance data over a time period between 6.00 and 19.00 [41].

18.40

137.10

326.50

450.94

569.06

678.35709.16688.19629.54596.33

362.15

182.98

35.93

0.00

100.00

200.00

300.00

400.00

500.00

600.00

700.00

800.00

IRR

AD

IAN

CE

(W/M

2)

HOURLY TIME PERIOD

Average Hourly Radiation

14

In figure 2.1 the pattern of the irradiance throughout the day follows a sine function. This is a

general irradiation pattern during Earth’s rotation followed by a location close to the equator

such a Suriname. The radiation from the sun has specific wavelength characteristics depending

on the temperature within the atmosphere (at different geographic locations) and outside the

earth’s atmosphere [42]. Part of the solar radiation that enters the Earth’s atmosphere is absorbed

by it or the radiation is scattered by atmospheric constituents, which is called diffuse radiation.

Another part of the radiation arrives directly at the Earth’s surface, which is called beam or direct

radiation. Both are needed to determine the amount of solar radiation absorbed by a solar panel

[51].

2.2 Renewable Energy in Suriname

Recently renewable energy has gained more acknowledgement by the Suriname government

creating more opportunities and providing additional benefits for using renewables. Within the

Budgetary of Natural Resources of Suriname it is included that the ministry sets it as a priority to

stimulate the use of renewable energy in 2016 [11]. It is also stated in the Constitution of Suriname

that incoming March, 2016 individuals using renewables will be able to redeliver excess electricity

to the electricity grid at closeout prices if the yearly kWh production of the generated renewable

electricity exceeds the yearly kWh required amount of electricity [10]. Suriname also takes part of

the Sustainable Development Goals (SDG) of the United Nations (UN) that supports renewable

energy projects [8], hereby also motivating further research of renewable energy applications.

2.3 Solar Projects in Suriname

In Suriname many photovoltaic (PV) solar projects and thermal solar projects have been executed

and are still being carried out. The largest PV solar project in Suriname is a 5 MW solar plant of

IAMGOLD at its Rosebel open pit mine with 16000 solar panels and an estimated cost of $14

million [12]. This solar plant provides electricity that the mines use. Staatsolie Maatschappij

Suriname N.V. launched a 30 kW solar energy pilot project that is operational since 2015 to obtain

more information on solar technology for future large scale applications [13]. In 2014 EBS

Energiebedrijven Suriname received finances through the government of Suriname from the

Inter-American Development Bank (IDB) as part of a payment for a solar project of 500 kW at the

village of Atjoni [14].

A few companies/initiatives in Suriname that provide services for and products of solar

technology are Kapasi Solar N.V., Multi Solar, Marsol N.V., Guguplex Technologies. The types of

solar technologies that are offered range from PV panels (imported and made from PV cells) for

electricity generation and thermal solar panels for hot water usage.

15

2.4 Solar Energy for Courtyard Marriott Hotel Paramaribo

Courtyard by Marriott Paramaribo hotel opened in June 2009 and is located on the Suriname

River. The hotel has 140 hotel rooms which are air conditioned by means of Toshiba Carrier

Variable Refrigerant Flow (VRF) cooling systems. There are 29 active VRF units which use an

estimated 44% of the total electricity usage of the hotel (see table 2.1). The consumption water

heater of Marriott Hotel is a gas fired water heater of the manufacturer Lochinvar which uses an

approximately 12% of the total energy usage. The occupancy rate varies from 70% to 100% which

effects the energy usage of the hotel [15].

Average kWh/day Average kWh/Month

VRF (29 Units) 1247 37398

Water Heater 17.6 528

Electricity usage

of Marriott Hotel

- 85481

TABLE 2.1 The average measured daily VRF energy usage and estimated monthly usage with the entire

electricity load of Marriott Hotel.

Solar energy can be utilized for both the cooling and heating requirements by means of

photovoltaic and thermal solar panels. Applying solar energy for heating and cooling in a

commercial building, such as a hotel, has a high return on investment cost because of the high

electricity usage of heating and cooling. Hotels being one of the main attractions for tourists

makes a green initiative in a hotel also good for the tourism in a country. Brebbia et al. [29]

presented a study with economic benefits that can be gained in hotels through implementing

environmental initiatives. Along with the economic benefits there are also other factors that are

influenced in a positive manner with an environment strategy, which are:

Gaining competitive advantage by being a leader in the sector

Customer loyalty

Employee retention

Awards and recognition

Regulatory compliance

Risk management

Increased brand value

16

3 Overview of PVT-Systems

“It always seems impossible until it’s done.

—Nelson Mandela, 2013

(Activist, Politician, Philanthropist, Lawyer)

In this chapter information is given on PVT-systems and general information on the thermal effect

of photovoltaics. An overview is given on how a PVT-system is built, previous done studies on

the system and how these systems can be categorized.

3.1 Basic Concept of PVT-Systems

PVT-systems are combined photovoltaic and thermal collectors that produce both electricity and

thermal energy. Theoretical and experimental research has been documented on PVT-systems

since mid-1970s. By combining the photovoltaic and thermal collectors the system generates more

energy than the individual systems of the same size. The thermal collector also lowers the

operating temperature of the system which results in a higher electricity production [5]. Installed

PV panels reach temperatures as high as 50 to 60C. The electrical efficiency of individual PV

modules vary from 10.2 to 11.5% at high temperatures. Only 6 to 20% of the sun irradiance that

is absorbed by a PV module is converted into electricity and the remaining solar energy is

converted into heat, which increases the PV module temperature and reduces the efficiency [19].

The efficiency of a PV module is reduced by an average of 0.45% for each degree over 25C [20].

PV cells are made from semiconductor materials such as, polycrystalline silicon (p-Si),

monocrystalline silicon (c-Si), and amorphous silicon (a-Si) [31]. The upper and lower layer of the

cell are doped with different dopants which can modulate the electrical properties. This occurs

when the solar cells are exposed to sunlight and the electrons excite from the valence band, which

is the highest range of electron energies, to the conduction band, which is the lowest range of

vacant electron states, creating charged particles. High temperatures (above 25C) reduce the

band gap of the cell which effects the electrical parameters and hereby reduces the electrical

efficiency of the cell. [45]

Florschuetz [17] presented an equation set to determine the performance analysis of the PVT-

system by modifying the Hottel-Whillier model [25] that is used to analyze flat plate collectors.

This method can be used on different types of PVT-systems to determine the energy performance.

17

PVT-systems can generally be categorized by the medium of the thermal collector. Different types

of mediums that can be used for PVT-systems are air, water and refrigerant. Studies have been

conducted on these types of PVT-systems (Guarracino et al., 2016; Ji et al., 2009) and the

efficiencies of these systems have also been compared with each other [18]. The research of Zhang

et al. [18] indicated that air-based PVT-systems have a lower thermal removal effectiveness than

fluid-based PVT-systems. And between water-and refrigerant-based PVT-system, refrigerant-

based systems showed a higher performance. Air-based and water-based PVT-systems have

already made it on the market, while refrigerant-based systems are still in the experimental stage.

The air-based system has lower thermal performance characteristics compared to a water based

system due to lower heat capacity and thermal conductivity of air compared to water. The low

density of air causes the heat transfer volume to be at a larger size compared with the water based

system if it were to be used for water heating. This makes the system more suitable for air heating

requirements [49]. Refrigerant based PVT-systems have shown potential for building integration

but there are still technical and economic barriers that prohibit a wide application [18]. Other

PVT-systems that have also been researched on are heat pipe, dual fluid- and concentrator PVT-

systems [33]. The research of C. Good et al. [34] presented an estimated approach to determine

the range of how qualified a type of PVT-system is for building integration. The extent of the

research done in this project does not cover the other possible PVT-systems (such as concentrating

PVT Etc.), but focusses mainly on systems that have been considered promising for building

integration based on the research done by C. Good et al. [34]. A market survey of Task 35, 2008

[26] showed a list of manufacturers with PVT commercial products such as PowerTherm and

PowerVolt. The market of PVT-systems is still small, according to a technical report by J.

Ruschenburg in 2013 [27], only 4% of the total solar market contained PVT products. Figure 3.1

indicates the components of the PVT panel from PowerVolt [22]. In the cross section the placing

of the PV module and absorber, the copper piping construction, the insulation and the aluminum

frame built can be seen. The PV module is fastened to the absorber, which consists of copper

pipes, by means of an adhesive. The complete collector together with an insulation layer is placed

in an aluminum frame with a case around the panel.

FIGURE 3.1 Partial Cross section PVT-water based solar panel from PowerVolt.

18

3.2 Water based and Refrigerant based PVT-systems

Water-based PVT-system (WPVT-System)

The build of the WPVT-system is similar to conventional flat plate collectors. The absorber is

constructed with PV cells that can be connected in series, with the tubing of the medium placed

underneath. The fluid is forced through the tubes and cools the PV panels which leads to a higher

efficiency. The water extracts the heat and can directly be used as domestic water (open loop), or

the heat can be extracted for heating services and the water can return to the panel providing

cooling once again (closed loop). Guarracino et al. [22] presented a dynamic model of a WPVT-

system with a sheet and tube thermal collector for domestic water heating and electricity

generation. In the research of Guarracino et al. [22] it is given that the efficiency of the WPVT-

system dropped with 4% from the given nominal efficiency of 12.6% without water flow, and

with water cooling the efficiency stayed above the nominal efficiency. A schematic of the

experimental setup from research done by Haurant et al. [30] is given in figure 3.5. The

components in the figure are the PVT panels (1), the pump (2), the water tank (3), an axillary

heater (4), and micro inverters (5). Water flows to the PVT-panel from a pump that causes the

forced circulation of the water through the system. From the PVT-panel the water goes to the tank

and then through a valve before going back to the pump. In the water tank the heat is used to

warm up the domestic water which flows through the tank to be consumed. Before going to the

consumer it also goes through an axillary heater to reach the required temperature of 60C.

FIGURE 3.5 Schematic setup of a (closed loop) water-based PVT-system [30]

Refrigerant-based PVT-system (RPVT-system)

The RPVT-system is built by placing direct expansion evaporator coils under PV modules. This

allows the refrigerant to be evaporated when it passes through the PV modules in the tubes. The

coils under the PV module act as the evaporator, which allows the refrigerant to reach low

19

temperatures (0-20C). The refrigerant can flow through a heat pump system and be used for

domestic water heating [18]. Tsai [24] presents a study of a RPVT-system assisting a heat pump

water heater with electricity and thermal energy under real weather conditions. The behavior of

the system is theoretically and experimentally analyzed in this study. The results of this research

showed that the performance of the system was only for a small amount effected by weather

change. Figure 3.7 shows the schematic structure of the system used by Tsai [24]. The refrigerant

flows from the expansion valve through the PVT panel and evaporates going from liquid to vapor

phase due to the thermal energy transfer from the panel to the refrigerant pipes. The vaporized

refrigerant is then compressed in the compressor and brought to higher temperatures qualified

to heat the consumption water. The flow continues through the condenser in the tank and the

heat is extracted by the water in the tank. The refrigerant is cooled down and goes through a

valve and back to the PVT panel.

FIGURE 3.7 Schematic structure of a RPVT-panel [24].

20

D x 𝑊 − 𝐷

2

4 Performance Analysis of the PVT-System

“Sometimes the questions are complicated, but the

answers are simple.

—Theodor Seuss Geisel, 1991

(Writer, Cartoonist, Animator, Artist)

In this chapter a method is given to determine the performance for PVT-systems namely the

Florschuetz model [17]. Section 4.1 states the approach of the model followed by section 4.2 which

gives how the energy coverage is determined. The used data for the Florschuetz [17] model

analysis and of the PVT-application for Marriott Hotel is also given. The executed methodology

is stated in section 4.4.

4.1 Florschuetz Model

For a performance analysis of the PVT-system the electrical output, thermal output and total

efficiency are determined based on the modified equations of Florschuetz [17] on the Hottel-

Whillier model given in Duffie and Beckman [25]. This model is chosen because the sheet and

tube configuration that is used in the Florschuetz model [17] also applies for the PVT application

requirements in this project (See figure 4.1). This is one of the panel configurations which can be

integrated into a building. A steady state approach, which was given in Florschuetz [17], is

applied for this model to deliver a daily average yield of the PVT-system. This application is only

applicable for the specific given location and its steady state conditions over a certain time period.

Since this project aims for the daily average yield of one case study and only uses one type of PVT

collector configuration for all applications, a steady state approach is assumed to be acceptable

[35].

FIGURE 4.1 Cross section of the sheet and tube collector configuration [17]

W

Glass Cover

Collector Plate

dx

PV +

Thermal

cells

Tube

21

The section dx of figure 4.1 is given in figure 4.2 with the configuration of the PV and thermal

cells to indicate the local steady state energy balance of the panel.

FIGURE 4.2 Local energy balance of the absorber of the PVT collector [17]

Following figure 4.2 the local energy balance is given as

𝑑2𝑇

𝑑𝑥2=

1

𝑘 [𝑈𝐿(𝑇𝑃𝑉 − 𝑇𝑎) − 𝑆 + 𝑞𝐸] (4.1)

In this equations k is the thermal conductivity, is the thickness of the collector, UL is the thermal

loss coefficient, TPV and Ta are the PV- and ambient temperatures, and S is the absorbed irradiance.

It is assumed that the underside of the plates and tubes is well insulated. It is also assumed that

the temperature gradients that are transverse to the fluid flow direction are independent from the

temperature gradients parallel to the fluid flow. Temperature gradients across the thickness are

neglected in this analysis. It is also assumed that the thermal resistance across the adhesive is

negligible. This indicates that no energy transfer occurs across the surfaces that are normal to the

flow direction [17]. When the equations are applied the following boundary conditions are stated,

𝑑2𝑇

𝑑𝑥2|

𝑥=0

= 0 and 𝑑2𝑇

𝑑𝑥2|

𝑥=𝑊−𝐷

2

= 𝑇𝑃𝑉 (4.2)

The electrical efficiency 𝑒𝑙 is assumed to decrease linearly with the photovoltaic panel

temperature [17] and is determined by

𝑒𝑙

= 𝑟𝑒𝑓

(1 − 𝑟𝑒𝑓

(𝑇𝑃𝑉 − 𝑇𝑟𝑒𝑓 )) (4.3)

In this equation 𝑟𝑒𝑓 is the reference efficiency at the reference temperature 𝑇𝑟𝑒𝑓 of the panel. And

𝑟𝑒𝑓 is the reference temperature coefficient.

By defining the electrical efficiency as a ratio of the local electrical output and the incident energy,

the local electrical output can be stated as

𝑞𝐸 = 𝑒𝑙

𝑆

(4.4)

dx

PV Module

Adhesive

Absorber

qEdx

UL(TPV -Ta)

Sdx

−𝑘𝑑𝑇

𝑑𝑥|

𝑥

−𝑘

𝑑𝑇

𝑑𝑥|

𝑥+𝑑𝑥

22

In equation 4.4 stands for the absorptivity of the collector. By combining the equations 4.1 till

4.4 and rearranging the parameters the modified overall loss coefficient is obtained, which is

𝑈𝐿 = 𝑈𝐿 −

𝑆

𝑟𝑒𝑓

𝑟𝑒𝑓= 𝑈𝐿 −

𝑟𝑒𝑓

𝑟𝑒𝑓𝐺 (4.5)

With G as the incident irradiation. And rearranging again the modified equation to determine the

absorbed solar radiation per unit area is given as

𝑆 = 𝑆 (1 −

𝑒𝑙

) (4.6)

The thermal efficiency of the PVT-system can be determined with

𝑡ℎ

= 𝐹𝑅 ((1 −

𝑒𝑙) − 𝑈𝐿

(𝑇𝑖−𝑇𝑎

𝐺)) (4.7)

In equation 4.7 𝐹𝑅 stands for the modified heat removal factor, which is obtained by the

conventional matter of the Hottel-Whillier model but instead of 𝑈𝐿 the modified parameter 𝑈𝐿 is

used. The transmissivity-absorptivity product used is given by , and 𝑇𝑖 stands for the inlet

cooling medium temperature of the PVT-panel.

The useful thermal energy can be determined by

𝑄𝑢 = 𝐴𝑃𝑉𝐹𝑅

(𝑆 − 𝑈𝐿 (𝑇𝑖 − 𝑇𝑎) (4.8)

And the electrical output of the PVT panel is

𝑄𝑒 =𝐴𝑃𝑉 𝑆

𝑒𝑙

[1 −

𝑟𝑒𝑓

𝑟𝑒𝑓

𝑒𝑙

(𝐹𝑅 (𝑇𝑖 − 𝑇𝑎) +

𝑆

𝑈𝐿

(1 − 𝐹𝑅 ))] (4.9)

The overall steady state energy balance can be given as

𝑄𝑆 = 𝑄𝑢 + 𝑄𝐿 + 𝑄𝑂𝐿 + 𝑄𝑒 (4.10)

In equation 4.10 QL stands for the overall thermal losses and QOL stands for the optical losses. The

overall efficiency of the PVT-panel is simply determined by the sum of the thermal efficiency and

the electrical efficiency given in equation 4.11.

𝑡

= 𝑒𝑙

+ 𝑡ℎ

(4.11)

Besides the modified equations by Florschuetz [17] of the Hottel-Whillier model, determining the

performance of the PVT-system follows the same mathematical steps and assumptions as the

conventional Hottel-Whillier method given in Duffie and Beckman [25]. The complete

mathematical procedure that is followed for this project is given in Chapter 5.

23

4.2 Energy Coverage

To make an assessment on the amount of energy that can be covered by the PVT-system the

method of Herrande et al. [28] is used.

The percentage of the electrical energy demand that is covered by the PVT-system can be

determined by equation 4.12.

𝐷𝐶𝐸(%) =𝐸𝑃𝑉𝑇 − 𝐸𝑙𝑜𝑠𝑠

𝐸𝑇

. 100 (4.12)

Here 𝐸𝑃𝑉𝑇 stands for the gross electrical energy produced by the PVT panel and 𝐸𝑙𝑜𝑠𝑠 stands for

the electrical energy consumed by the pump or compressor that circulates the medium. 𝐸𝑇 stands

for the annual electrical consumption. The research done in this project is done for the VRF

electricity demand by substituting the VRF demand for ET. The total demand of the hotel is also

determined using equation 4.12 by substituting the total electricity demand of the hotel for ET.

The percentage of the thermal energy demand covered is determined by

𝐷𝐶𝐻𝑊(%) =𝑄𝑃𝑉𝑇

𝑄𝑇

. 100 (4.13)

In this equation 𝑄𝑃𝑉𝑇 stands for the net thermal energy output of the PVT system and 𝑄𝑇 stands

for the total hot water demand.

The average percentage of energy demand covered is determined by

𝐷𝐶𝑎𝑣(%) =𝐷𝐶𝐸 + 𝐷𝐶𝐻𝑊

2 (4.14)

And the weighted average percentage over the time period of the annual electrical demand is

determined by

𝐷𝐶𝑤𝑎𝑣(%) =𝐸𝑇 𝐷𝐶𝐸 + 𝑄𝑇𝐷𝐶𝐻𝑊

𝐸𝑇 + 𝑄𝑇

(4.15)

4.3 Used Data

The data that was gathered for this project are: Measurements that were conducted at Marriott

Hotel for a case study of the PVT applications with environment conditions of Suriname;

Averaged hourly sun radiation data measured at Anton de Kom Universiteit van Suriname [41];

and panel design specifications of Gaurracino et al. [22] and Ji et al. [23]. The latitude of Anton de

Kom Universiteit is 5.8129° N and the latitude of Marriott Hotel is 5.8326° N. Based on a 1%

difference between the latitudes, the assumption is made that the difference of the irradiance from

Anton de Kom Universiteit and Marriott Hotel is negligible. For Marriott Hotel, WPVT and

RPVT-panel design specifications are used that comply with the hotel’s needs.

24

4.3.1 Measurements

The measured parameters were the ambient temperature, the VRF electrical usage, and the gas

fired water heater electrical usage. The measurements were conducted in March and April 2016.

VRF electricity measurements

The electrical usage of each individual VRF unit was measured to determine the average daily

usage of the systems. Then the overall usage off the 29 VRF units was determined. The electricity

measurements were conducted with an OM-DVCV Omega data logger from the maintenance

department of Marriott Hotel. The current and voltage accuracy of the instrument is 1.0 A and

0.4 V. To test how long the VRF units operated till reaching the desired room temperature

(which is set at 21C), the temperature of the hotel rooms were also measured. The average

operating duration of a VRF unit was one hour before reaching the desired room temperature.

Temperature measurements

The ambient temperatures and hotel room temperatures were measured with a Temperature and

Humidity USB Data Logger from the maintenance department of Marriott Hotel. The

temperature accuracy of the instrument is 2 C. The ambient temperature was measured from

the roof level of Marriott Hotel.

4.3.2 PVT Panel Design

For the analysis and validation of the Florschuetz model [17] written in Microsoft Excel the

research data of Gaurracino et al. [22] and Ji et al. [23] was used. These research papers

determined the performance of a PVT-system and had the availability of sufficient data to

conduct a performance analysis with the Florscheutz model [17]. The PVT-systems of Gaurracino

et al., [22] and Ji et al. [23] also had the ability for building integration which is needed to obtain

the objective of this project.

In table 4.1 and 4.2 the specifications of PVT panel obtained from Gaurracino et al. [22] and Ji et

al. [23] are given. In table 4.3 the specifications of the PVT applications suitable for Marriott Hotel

are given. Gaurracino et al. [22] used the design specifications from PowerTherm of the

manufacturer Solimpeks for a WPVT-system. And Ji et al. [23] used an experimental setup to

conduct the research for a RPVT-system.

The design specifications for Marriott Hotel are determined by using the parameters applicable

for water as a medium (such as mass flow and pipe diameter) from Gaurracino et al. [22] and the

design parameters applicable for refrigerant as a medium from Ji et al. [23]. The design of the

WPVT and RPVT-system are then equally sized to conduct a comparison study.

25

Specifications WPVT-system

Parameter Value

Nominal Power (W) 180

Total Surface Area (m2) 1.427

Total Aperture Area (m2) 1.42

Panel Dimensions (mm) 870x1640x150

Cell (mm) 125x125

Voltage at Maximum Power Point (MPP) (V) 4.98

Current at MPP (A) 36.16

Open circuit voltage (V) 5.4

Short circuit current (A) 44.46

Maximum operating pressure (bar) 4.15

Flow rate (m3/h) 0.0065

Reference PV module efficiency (%) 17.8

Reference temperature coefficient 0.00375

Reference temperature (C) 25

Type of solar cell Monocrystalline (c-Si)

Internal Piping Copper

Fluid medium Water

TABLE 4.1 Specifications WPVT-system from the research conducted by Gaurracino et al. [22]

Specifications RPVT-system

Parameter Value

Nominal Power (W) 300

Total Surface Area (m2) 5.49

Total Aperture Area (m2) 4.59

Voltage at Maximum Power Point (MPP) (V) 0.53

Current at MPP (A) 4.58

Open circuit voltage (V) 0.63

Short circuit current (A) 5.12

Maximum operating pressure (bar) 7

Flow rate (m2/h)) 0.0019

Reference PV module efficiency (%) 12

Reference temperature coefficient 0.0045

Reference temperature (C) 25

Type of solar cell Monocrystalline (c-Si)

Internal Piping Copper

Fluid medium R-22

TABLE 4.2 Specifications RPVT-system from the research conducted by Ji et al. [23]

26

Specifications of the WPVT and RPVT-system for Marriott Hotel

Parameter WPVT-System RPVT-System

Nominal Power (W) 200 200

Total Surface Area (m2) 1.37 1.37

Total Aperture Area (m2) 1.36 1.36

Voltage at Maximum Power Point (MPP) (V) 36.8 36.8

Current at MPP (A) 5.43 5.43

Open circuit voltage (V) 46.8 46.8

Short circuit current (A) 5.67 5.67

Operating pressure (bar) 10 4

Flow rate (m3/h) 0.0065 0.0019

Tube outside diameter (m) 0.01 0.007

Tube inside diameter (m) 0.008 0.006

Tube spacing (m) 0.095 0.130

Fluid to tube heat transfer coefficient (W/m2K) 500 76

Reference PV module efficiency (%) 12 12

Reference temperature coefficient 0.0045 0.0045

Reference temperature (C) 25 25

Fluid to tube heat transfer coefficient (W/m2K) 500 76

Type of solar cell Monocrystalline

c-Si

Monocrystalline

c-Si

Internal Piping Copper Copper

Panel Design Sheet and tube Sheet and tube

Fluid medium Water R-22

TABLE 4.3 Specifications WPVT and RPVT-system for Marriott Hotel

The differences between the WPVT and the RPVT-system specifications are the fluid properties

and the parameters which are influenced by the fluid properties. Such as the heat transfer

coefficient, mass flow rate, tube dimensions, and operating pressure.

Since the specifications of Marriott Hotel are chosen to comply with the requirements of the hotel,

the electrical output is taken as the parameter that is most needed and the thermal output is the

parameter which is an added value to the complete energy output of the PVT system. This is

chosen because the electrical cost of Marriott Hotel exceeds the thermal costs.

4.3.3 Expected Model Performance

The expected performances of the PVT-systems and used environment data of Gaurracino et al.

[22] and Ji et al. [23] are given in figure graphs 4.3, 4.4 and 4.5 which are used for the model

analysis and validation in chapter 5.

In the performance analysis done by Ji et al. [23] the ambient temperature range was

approximately 7-13 C. The results of the electrical efficiency given in a graph of Ji et al. [23]

27

showed a steady flow of approximately 13% over the time period between 9.00 and 15.00 (see

figure 4.3). The graph shows a slight reduction of electrical efficiency after 15.00. It is stated in the

research of Ji et al. [23] that electrical and thermal efficiencies of 12% and 50% have been reached

with the analyzed model.

FIGURE 4.3 Performance analysis from Ji et al. [23]. Left is the electrical output of the PVT system and

right is the heat gain from the PVT system.

The solar irradiance and ambient temperature used from the research by Ji et al., [23] is given in

figure 4.4. This research was done in China, Hefei.

FIGURE 4.4 Solar irradiance and ambient temperature data from Ji et al., [23]

Guarracino et al. [22] presented a dynamic model of a water based PVT collector with a sheet and

tube thermal absorber. The obtained electrical efficiency in this study is approximately 12 to 14 %

within the time period 7.00 and 17.00.

28

FIGURE 4.5 Performance analysis of Guarracino et al. [22] indicating the electrical efficient, PV panel

temperature and fluid flow into the panel, over the measured ambient temperature within the time

period of a day.

For the WPVT and RPVT implementations of Marriott Hotel (which is given in chapter 6), it is

expected that the RPVT-system reaches a higher performance compared with the WPVT-system

[18]. The performance is also estimated to be higher than the obtained research from Gaurracino

et al. [22] (which is conducted in UK, London) and Ji et al. [23] (which is conducted in Hefei,

China) due to environment conditions of Suriname, which are more ideal to utilize solar energy

compared with the environment conditions of Gaurracino et al. [22] and Ji et al. [23].

The flow patterns of the graphs given in figure 4.3 and 4.5 are approximately the same flow

patterns that the WPVT and RPVT for Marriott Hotel are expected to have. The parameters that

will be analyzed are: Electrical Efficiency; Thermal Efficiency; Electrical output power; Useful

thermal heat; and Total Efficiency.

4.4 Methodology of the performance analysis

This section contains a methodology that will be followed to determine the performance analysis

of the PVT-systems. The mentioned WPVT and RPVT-systems in chapter 3 are applied for

Marriott Hotel through the given model in section 4.1 to obtain the performance of a PVT-system

case study with environment conditions of Suriname for a hotel. All the PVT-systems are

analyzed based on their performance by using the PVT model of Florschuetz [17]. When

analyzing the performance of the WPVT and RPVT systems for conditions of Marriott Hotel, a

systematic approach is taken. This methodology can be given by the following 4 steps in figure

29

4.6. In step one the specifications will be given of the PVT system. Step 2 will give a schematic of

how the PVT system looks like with the medium flow and boundaries explained. The relevant

assumptions of the model will be given in step 3 followed by the actual analysis of the PVT system

in step 4, in which the results will be given and discussed afterwards.

FIGURE 4.6 Methodology to determine the PVT-system performance.

•Specifying what the inputs are of the PVT-system. With this the design conditions ofthe PVT-system are stated that will be used to determine the performance of thesystem.

Step 1

•Giving a schematic of the PVT-system and stating the boundary of the systemindicating towhat extend andwhichcomponents of the systemwill be analyzed.

Step 2

•Stating the relevant assumptions to reduce the model to a manageable state thatfitswith the objective of this study.

Step 3

•Analyzing the PVT system based on the information gathered in steps 1 to 3 andapplying the Florschuetz model [17] to determine the performance of the system. Inthis step the results are givenand discussed.

Step 4

30

5 Model Analysis

“Respect is based on the awareness that everyone has

value.

—Brahma Kumaris

In this chapter the written Microsoft Excel model of the Florschuetz method [17] to determine the

PVT performance is explained and validated. The validations are done for the WPVT-system and

the RPVT-system by using Gaurracino et al. [22] and Ji et al. [23]. The Florschuetz model [17] will

be elaborated within the mathematical analysis, but only the direct application the conventional

Hottel-Whillier method will be given because the Hottel-Whillier model has already been

researched on in Suriname [40].

5.1 Mathematical Model

As was given in chapter 3, Zang et al. [18] indicated that the heat extracted from the air-based

PVT-system can mostly be used for room heating. Since Suriname has a warm tropical climate

this would not be useful for Marriott Hotel. Using the air-based system would mean sending out

the heated air into the atmosphere after heat extraction, which is loss of thermal energy delivering

a low overall efficiency. The thermal energy extracted from the WPVT and the RPVT-systems are

usable for water heating which is a need at Marriott Hotel.

The mathematical steps that have been executed for the WPVT and RPVT-systems are conducted

per hourly averaged time period. The basic assumptions that apply for the Hottel-Whillier [25]

model also count for this model. For the Florschuetz [17] model, the assumption is made that the

local electrical conversion efficiency of the solar cell array (absorber) can be represented as a linear

decreasing function of the local absorber operating temperature [17].

The applied mathematical model to obtain the performance of the WPVT and RPVT panel is

analyzed by determining the following:

1. Environment and location conditions for the WPVT and RPVT panels.

2. The radiation transmission and the absorption

3. The modified absorbed irradiance per unit area ��

4. The modified heat removal factor 𝐹𝑅 and modified overall loss coefficient 𝑈𝐿

5. The electrical 𝑄𝑒𝑙 and thermal 𝑄𝑢 output of the PVT panel and the total PVT panel efficiency

31

1. Environment and location conditions for the WPVT and RPVT panels.

Water-based PVT-system (WPVT-System)

Table 5.1 states the location’s conditions for the PVT panel of Guarracino et al. [22].

PVT panel state conditions

Location UK, London

Latitude 51.5074° N

Longitude 0.1278° W

Tilt Angle 31, 24, 16

Day # 244, 240, 198

TABLE 5.1 PVT panel state conditions of the WPVT-system, Guarracino et al. [22]

The solar panel tilt angle for a latitude greater that 50 can be determined by the rule of thumb:

For winter: 𝑇𝑖𝑙𝑡𝑊 = 90 − (𝐿𝑎𝑡𝑖𝑡𝑢𝑑𝑒) + 23 (5.1𝑎)

For summer: 𝑇𝑖𝑙𝑡𝑆 = 90 − (𝐿𝑎𝑡𝑖𝑡𝑢𝑑𝑒) − 23 (5.1𝑏)

The PVT panel analysis has been done for 3 days of the year: 1 September, 28 August and 17 July

(Day#: 244, 240 and 198). The optimum solar tilt angle of these days are: 31, 24, and 16. [39]

Refrigerant-based PVT-system (RPVT-System)

Table 5.2 states the location’s conditions for the PVT panel of Ji et al. [23].

PVT panel state conditions

Location China, Hefei

Latitude 31.87 N

Longitude 117.23 E

Tilt Angle 27.32

Day # -

TABLE 5.2 PVT panel state conditions of the RPVT-system, Ji et al. [23]

The solar panel tilt angle for the latitude between 25 and 50 can be determined by the rule of

thumb: 𝑇𝑖𝑙𝑡 = 0.76(𝐿𝑎𝑡𝑖𝑡𝑢𝑑𝑒) + 3.1 (5.2𝑎)

32

For locations at a latitude smaller than 25 the following rule of thumb is used:

𝑇𝑖𝑙𝑡𝑆 = 0.87(𝐿𝑎𝑡𝑖𝑡𝑢𝑑𝑒) (5.2𝑏)

2. The radiation transmission () and the absorption ()

The transmission and absorption (given in figure 5.1) are needed to determine the transmissivity-

absorption product (). This parameter is used in equation 4.7 to determine the thermal

efficiency. Before the absorption and transmission are determined, the optical properties of the

cover system must be determined along with the reflection of the radiation, and the absorbance

of the glazing which is fully described in Duffie and Beckman [25]. The transmittance, absorbance

and reflectance of the solar radiation by the solar collector are needed to determine the

performance of the collector. The assumption is made that the properties of the cover (which is

taken as iron glass) are independent of the wavelength.

FIGURE 5.1 Absorption of solar radiation (Under the absorber plate of the PVT panel) [25]

The transmissivity-absorption product () can be determined by

() =

1 − (1 − )𝑑

(5.3)

To obtain this parameter the following parameters, such as the angle of incidence, refraction,

refraction and transmission must first be determined.

The angle of Incidence (1) is determined by,

𝑐𝑜𝑠1 = 𝑠𝑖𝑛(sin 𝑐𝑜𝑠 + cos cos cos sin) + cos (cos cos cos − sin cos sin) +

(cos sin sin sin) (5.4)

In this equation is the declination angle, the slope of the collector, the surface azimuth

angle, the hour angle, and is the latitude.

33

The angle of Refraction (2) which is determined by

2 = 𝑠𝑖𝑛−1 (𝑠𝑖𝑛1

𝑛) (5.5)

With a reflection index of n = 1.52 for Iron tempered cover glass.

The reflectance (r) of the incident solar angle is

𝑟 =1

2(

𝑠𝑖𝑛2(2 − 1)

𝑠𝑖𝑛2(2 + 1)+

𝑡𝑎𝑛2(2 − 1)

𝑡𝑎𝑛2(2 + 1)) (5.6)

The perpendicular reflectance (r) of the incident solar angle is

𝑟 = (𝑠𝑖𝑛2(2 − 1)

𝑠𝑖𝑛2(2 + 1)) (5.7)

The parallel reflectance (rII) of the incident solar angle is:

𝑟|| = (𝑡𝑎𝑛2(2 − 1)

𝑡𝑎𝑛2(2 + 1)) (5.8)

Transmissivity obtained by absorption (a):

𝑎 = 𝑒−(

𝐾𝐿𝑐𝑜𝑠2

) (5.9)

In this equations L is the glass cover thickness and K is the extinction coefficient.

Transmittance obtained by radiation (r):

𝑟 =1

2(

1 − 𝑟1 + (2 − 1)𝑟

+1 − 𝑟||

1 + (2 − 1)𝑟||

) (5.10)

From the above mentioned equations the following can be obtained: The transmittance of the

collector ():

= 𝑎𝑟 (5.11)

The absorbance of the collector ():

= 1 − 𝑎 (5.12)

And the reflectance of the collector (d):

𝑑

= 𝑎 − (5.13)

3. The modified absorbed irradiance per unit area ��

The modified absorbed solar radiation per unit area is determined by equation 4.9 given in

chapter 4. The absorbed solar radiation S is determined by,

34

𝑆 = 𝐼𝑏𝑟𝑏()𝑏 + (𝐼𝑏𝑟𝑑 + (𝐼𝑏 + 𝐼𝑑)𝑟𝑟)()𝑑 (5.14)

The beam reflectance for the absorbed solar radiation is determined by

𝑟𝑏 =𝑐𝑜𝑠1

𝑐𝑜𝑠2

(5.15)

And the diffuse reflectance is determined by

𝑟𝑑 =(1 + 𝑐𝑜𝑠)

2 (5.16)

With

𝑟𝑟 =(1 − 𝑐𝑜𝑠)

2 (5.17)

Where is the reflectivity of the surrounding surfaces and is the slope of the collector. The

parameter ()b is the transmissivity-absorption product determined at the beam angle of the

incident solar irradiance (1) and ()d is the transmissivity-absorption product determined at the

diffuse angle of the incident solar irradiance. The diffuse angle is taken as 60 [42].

The beam irradiance 𝐼𝑏 is taken as the direct solar irradiance that is measured [41] and the diffuse

irradiance 𝐼𝑑 is estimated with the following [50]: 𝐼𝑑 = 𝐼𝐺 − 𝐼𝑏 (5.18)

Here 𝐼𝐺 is the global irradiance. The global irradiance is obtained from Solargis [43] for the

specified location. And of equation 5.14 can be determined with equation 5.12.

The electrical efficiency of the PVT-collector is assumed to decrease linearly with the temperature

of the absorber. It is determined by equation 4.3 that is given in chapter4.

To obtain the reference parameters the Evans-Florschuetz PV efficiency correlation coefficients

are used from Dubey et al., 2012 [44].

𝑇𝑃𝑉 is the PVT-panel temperature and 𝑇𝑟𝑒𝑓 stands for the panel reference temperature. The panel

temperature for pc‐Si PV modules (used in Guarracino et al. [22]) can be obtained with

𝑇𝑝𝑣 = 30 + 0.0175(𝐺 − 300) + 1.14(𝑇𝑎 − 25) (5.19)

The temperature for a-Si PV modules (used in Ji et al. [23]) can be obtained with

𝑇𝑝𝑣 = 30 = 0.0175(𝐺 − 150) + 1.14(𝑇𝑎 − 25) (5.20)

Here G stands for the sun irradiance and 𝑇𝑎 stands for the ambient temperature or environment

temperature. a-Si PV modules have a lower electrical efficiency resulting a slightly higher PV

temperature compared with pc-Si PV modules [31].

35

4. The modified heat removal factor 𝑭𝑹 and modified overall loss coefficient 𝑼𝑳

The modified heat removal factor is determined by

𝐹𝑅 =

��𝐶𝑝

𝐴𝑃𝑉 𝑈𝐿

(1 − exp (−𝐴𝑃𝑉 𝑈𝐿

𝐹′

��𝐶𝑝

)) (5.21)

In equation 4.4 the mass flow of the cooling medium is given by ��. And 𝐶𝑝 stands for the heat

capacity. The PV area is given by 𝐴𝑃𝑉 and 𝐹′ stands for the modified collector efficiency.

The modified collector efficiency is determined with the same method to determine the collector

efficiency as given by Duffie and Beckman [25] but instead of the overall loss coefficient, the

modified overall loss coefficient by Florschuetz [17] is used. The modified collector efficiency is

given in equation 5.22.

𝐹′ =1 𝑈𝐿

⁄

𝑊 [1

𝑈𝐿 [𝐷 + (𝑊 − 𝐷)𝐹𝑊𝐷

+1𝐶𝑏

+1

𝜋𝐷𝑖 ℎ𝑓𝑖]

(5.22)

From this equation FWD is determined by

𝐹𝑊𝐷 = (1 −𝐷

𝑊) 𝐹 +

𝐷

𝑊 (5.23)

The coefficient F is determined by

𝐹 =tanh (

𝑚(𝑊 − 𝐷)2 )

𝑚(𝑊 − 𝐷)/2 (5.24)

And the dimensionless parameter m is determined by

𝑚 = √𝑈𝐿

𝑘 (5.25)

In this equation is the absorber thickness, k is the thermal conductivity of absorber, D is the

outside tube diameter, Di is the inside tube diameter, hfi is the fluid to tube heat transfer

coefficient, W is the tube spacing for tube and sheet collector configuration, and Cb is the bond

(adhesive) conductance which can be determined by

𝐶𝑏 =𝑘𝑏 𝑏

(5.26)

With b as bond width, as the average bond thickness and kb as the bond thermal conductivity.

The modified overall loss coefficient is determined by equation 4.5 given in chapter 4. The

reference values, irradiance and transmittance have been explained in the previous equations.

The overall loss coefficient 𝑈𝐿 is determined by using the cover system parameters of Florscheutz

[22] given in table 5.3. The analyzed systems have one collector cover.

36

Number of Collector Covers 𝑼𝑳 [W/m2K]

None (Wind 5 m/s) 1 30

None (Wind 2.5 m/s) 1 30

one 0.92 7

two 0.84 3.5

TABLE 5.3 PVT panel cover system overall loss coefficient [17]

5. The electrical 𝑸𝒆𝒍 and thermal 𝑸𝒖 output of the PVT panel and the total PVT panel

efficiency

The power output and panel efficiency ultimately determine the performance of the PVT panel.

These parameters are plotted over a given time period to analyze and validate the model. The

equations of these parameters are given in chapter 4. The thermal- and, electrical efficiency, and

useful thermal energy of the PVT-system can be determined with equation 4.7 and equation 4.8

from chapter 4.

From the useful thermal energy the outlet temperature of the fluid medium can be determined

with

𝑄𝑢 = ��𝐶𝑝(𝑇𝑜 − 𝑇𝑖) (5.27)

With all the needed parameters determined with the above mentioned equation set the

performance of the PVT system can be analyzed.

5.2 Model Results

The WPVT and RPVT-system results are given in table 5.4 and 5.5. The performance graphs of

the WPVT-system are given in figure 5.2 till 5.5 and the graphs of the RPVT-system are given in

figure 5.6 and 5.9. The electrical output, panel temperature, and efficiency of the WPVT-system

is validated.

The WPVT graphical results

In figure 5.2 the results of the electrical efficiency of the WPVT are graphed. The graph flow

decreases from 12.14 % to 11.24% with an increase of the ambient temperature. The ambient

temperature increases between 9.00 and 12.00 which reduces the band gap of the cells within the

panel. This reduces the electrical efficiency (See chapter 3). With a decrease of the ambient

temperature from 13.00 to 16.00 the electrical efficiency increases again.

37

FIGURE 5.2 Electrical efficiency WPVT model

FIGURE 5.3 Thermal efficiency WPVT model

The thermal efficiency of the WPVT model analysis is given in figure 5.3. The graph holds a steady

flow with a slight increase of efficiency at midday. The flow increases from 31.82 % to 34.16 %

before 12.00 then decreases to 27.66 % after 12.00. This can be related to the amount of irradiance

that is available during midday and which can be absorbed by the panel.

0.1214

0.1161

0.1132 0.1124 0.11320.1143

0.1182

0.1202 0.1202

0.10600.10800.11000.11200.11400.11600.11800.12000.12200.1240

9 10 11 12 13 14 15 16 17

Effi

cie

ncy

Time/h

WPVT Electrical Efficiency

0.3182 0.3207 0.3375 0.3416 0.3375 0.33200.3038

0.2766

0.0000

0.0500

0.1000

0.1500

0.2000

0.2500

0.3000

0.3500

0.4000

8 9 10 11 12 13 14 15

Effi

cie

ncy

Time (h)

WPVT Thermal Efficiency

38

FIGURE 5.4 Thermal Output WPVT model

The thermal output of the WPVT system is given in figure 5.4. The thermal heat increases with

an increase of irradiance and ambient temperature and decreases with a decrease of these input

parameters. The generated thermal energy goes from 372 W to 701 W, then decreases to 205 W.

The dependence on the amount of irradiance can clearly be seen in this graph.

FIGURE 5.5 Electrical Output WPVT model

In figure 5.5 the results of the electrical output are graphed. The electrical output is lower than

the thermal energy output. The flow pattern is similar to the thermal heat flow pattern with an

increase of energy before 12.00-13.00 and a decrease of energy after 12.00-13.00. The effect the

irradiance has on the power output can also be seen in this graph.

372

620680 701 680

632

330

205

0

100

200

300

400

500

600

700

800

8 9 10 11 12 13 14 15

Po

we

r (W

)

Time (h)

WPVT Thermal Output

246

364409 424 409

380

201

122

0

50

100

150

200

250

300

350

400

450

9 10 11 12 13 14 15 16

Po

we

r (W

)

Time (h)

WPVT Electrical Output

39

The RPVT graphical results

FIGURE 5.6 Electrical Efficiency RPVT model

In figure 5.6 the results of the electrical efficiency of the RPVT are graphed. The graph flow

decreases from 12.98 % to 11.85% with an increase of the ambient temperature. The effect of a

temperature increase on the efficiency which is explained in chapter 3 is also shown here. The

obtained efficiency percentages are still higher than a conventional PV system, which reduces

with 0.45% for every degree above 25C.

FIGURE 5.7 Thermal Efficiency RPVT model

The thermal efficiency of the RPVT model analysis is given in figure 5.7. There is an increase of

efficiency when the irradiance and ambient temperature increase. The flow increases from 54.52%

to 60.41 % before 12.00 then decreases to 56.15 % after 12.00.

0.1257

0.1217

0.12000.1185

0.11930.1204

0.1241

0.1258

0.1140

0.1160

0.1180

0.1200

0.1220

0.1240

0.1260

0.1280

8 9 10 11 12 13 14 15

Effi

cie

ncy

Time (h)

RPVT Electrical Efficiency

0.5452

0.5806

0.59340.6041

0.59840.5912

0.57350.5615

0.5000

0.5200

0.5400

0.5600

0.5800

0.6000

0.6200

8 9 10 11 12 13 14 15

Effi

cie

ncy

Time (h)

RPVT Thermal Elfficiency

40

FIGURE 5.8 Thermal Output RPVT model

The thermal output of the RPVT system is given in figure 5.8. The thermal heat increases with an

increase of irradiance and ambient temperature and decreases with a decrease of these input

parameters. The generated thermal energy goes from 970 W to 1750 W, then decreases to 626 W.

FIGURE 5.9 Electrical Output RPVT model

In figure 5.9 the results of the electrical output from the RPVT-system are graphed. The electrical

output is also lower than the thermal energy output. The flow pattern is similar to the thermal

heat flow pattern with an increase of energy before 12.00-13.00 and a decrease of energy after

12.00-13.00.

970

15711690 1750 1700

1590

908

626

0

500

1000

1500

2000

8 9 10 11 12 13 14 15

The

rmal

Ou

tpu

t (W

)

Time (h)

RPVT Thermal Output

171

271292 304 295

277

166

116

0

50

100

150

200

250

300

350

8 9 10 11 12 13 14 15

Ele

ctri

cal

Po

we

r (W

)

Time (h)

RPVT Electrical Output

41

5.3 Model Validation

The margin for error is very large when verifying the model data with the graphed researched

data from Guarracino et al. [22] and Ji et al. [23] because the scaling from the graphs that are given

are between the 100 W and 500 W. And the scale size for the efficiency graphs are 1%. Hereby

the validation of the model is conducted by:

1. Following the flow pattern of the obtained graphs and analyzing if there are deviations

compared with the graphs of Guarracino et al. [22] and Ji et al. [23].

2. Comparing the given average performance of the research from Guarracino et al. [22] and Ji

et al. [23] with the averaged analyzed performance of the Florschuetz model which is executed

in Microsoft Excel.

The flow patterns of the efficiency and power output graphs from the model analysis (figure 5.2

till 5.9) can be considered as similar to the flow patterns from the graphs of Gaurracino et al. [22]

and Ji et al. [23] in chapter 4 (figure 4.3 and figure 4.5). The flow pattern of the electrical efficiency

indicates the dependence it has on the efficiency drop with an increasing ambient temperature,

which is explained in chapter 3. And the sine flow pattern of the electrical and thermal power

output indicates the dependence of these factors on the irradiance (given in chapter 2) which also

gives a sine flow pattern. The equations that relate the electrical and thermal power output and

thermal efficiency with the irradiance are given in section 4.1 and elaborated in section 5.1.

Table 5.4 gives the average performances of the analyzed Florschuetz model and the research

data from Guarracino et al. [22] and Ji et al. [23].

WPVT-System RPVT-System

Averaged Values Analyzed

Model

Guarracino

et al. [22]

Difference

%

Analyzed

Model

Ji et al.

[23]

Difference

%

Electrical Efficiency 0.1161 0.131 6 0.1219 0.12 0.7

Thermal Efficiency 0.3210 0.362 9 0.5810 0.50 7

Electrical energy

(Wh)

290.18 203.2 18 236.54 300 12

Thermal heat (Wh) 492.25 - - 1350.50 1750 13

TABLE 5.4 Average performances from obtained data and research data

The differences at the RPVT model analysis can have occurred due to a difference in fluid to tube

heat transfer coefficient (hfI):

The properties of R-22 for the analyzed Florschuetz model [17] are determined by the online Fluid

Properties calculator [37]. In the research by Ji et al. [23] a numerical simulation program written

42

in C++ language has been used to solve the complete set of equations. The use of different

methods to obtain the fluid properties can also have led to a difference in the fluid to tube heat

transfer coefficient (hfI) between the model and the research done by Ji et al. [23]. This parameter

is needed for the modified heat removal factor (𝐹𝑅 ) which is used to determine the thermal

efficiency, electrical output and thermal heat output. See the performance equations 4.7, 4.8 and

4.9. And the modified heat removal factor is given in equations 5.21-5.22. The difference in the

electrical efficiency is below 1% and can be accepted as accurate.

The differences at the WPVT model analysis can have occurred due to a difference in the inlet

fluid temperature (Ti):

The research from Guarracino et al. [22] indicated a temperature range and its average of the inlet

fluid temperature (Ti) of the cooling medium. The input values were an estimation based on that

information for every time period of the model computation. These estimations differed with a

certain percentage, hereby causing a difference within the analyzed performance. The inlet fluid

temperature is used for the thermal efficiency and for the electrical and thermal energy output

(See equations 4.7, 4.8 and 4.9). The ambient temperature (Ta) could not be read from the graph

to a 0.01 certainty. Inaccurate readings of the ambient temperature could have had an effect on

the electrical efficiency analysis. See equation 4.3 and equations 5.19-5.20.

43

6 Analysis of PVT applications for Marriott Hotel

“Once we accept out limits, we go beyond them.

—Albert Einstein, 1955

(Theoretical Physicist)

The given methodology in chapter 4 is applied in this chapter to determine the performance of

PVT applications for Marriott Hotel. The Microsoft Excel model explained in chapter 5 is used to

analyze the PVT-systems with the location conditions of Marriott Hotel. These steps are applied

for the WPVT and RPVT-system and documented in section 6.2 and 6.3. The chapter is concluded

with a discussion section by analyzing the performances of the WPVT and RPVT-system.

6.1 Analyzed PVT applications

The model analysis for Marriott Hotel is conducted over a time period between 9.00 and 17.00.

The performance is determined by using averaged hourly measured data within the given time

period. The performance of each averaged hour between 9.00 and 17.00 is determined in

Microsoft Excel for the WPVT and RPVT-system. This delivered eight efficiency and power

output results for each of the analyzed systems. The PVT panel is analyzed at the state conditions

mentioned in table 6.1. The panel design specifications given in table 4.3 of chapter 4 are used.

PVT panel state conditions

Establishment Courtyard Marriott Hotel Paramaribo

Location Anton Dragtenweg/ Paramaribo/Suriname

Latitude 5.8326° N

Longitude 55.1351° W

Tilt Angle 5

Azimuth 0

Day # 117

Time interval 9.00-17.00

TABLE 6.1 PVT panel state conditions

The sun irradiance and ambient temperatures are given in table 6.2. The table shows averaged

measured values within time periods of one hour. In this application the results of the

44

performance is given for the WPVT and RPVT implementation at Marriot Hotel’s environment

conditions.

Time-

Period

# Hour

Sun

Irradiance

(G, W/m2)

Ambient

Temperature

(Ta, °C)

1 9.00-10.00 450.94 28.97

2 10.00-11.00 569.06 29.30

3 11.00-12.00 678.35 28.73

4 12.00-13.00 709.16 30.13

5 13.00-14.00 688.19 30.73

6 14.00-15.00 629.54 30.67

7 15.00-16.00 596.33 29.73

8 16.00-17.00 362.15 28.23

TABLE 6.2 Sun Irradiance and ambient temperature

6.2 Results of the WPVT-system

The results of the performance analysis by following the given methodology of chapter 4 and

chapter 5 of the WPVT-system for Marriott Hotel is given in this section. A schematic of the

experimental setup from Guarracino et al. [22] is given in figure 6.1. In the figure a red boundary

is dashed around the PVT panel. Only this component will be analyzed on its efficiency.

FIGURE 6.1 Schematic of the PVT water-based system [22]

A simplified model is considered for the method of Florscheutz [17]. The main assumptions

made for the PVT- system are:

The system will be modelled with a one-dimensional, steady-state heat transfer [31].

45

The thermal capacities of the collector components, and the heat transfer from the

absorber to the conductive plate and the pipes for the PVT- system are negligible [31].

The top optical losses are accounted by the product (τα), where τ is the transmittance of

the front protective glass of the PVT module and α is the absorbance of solar radiation by

the cells [31].

The optical losses are subtracted from the incident solar radiation to get the net energy

available for conversion into heat and electricity [31].

The node temperatures of the PVT-collector are assumed to be uniform throughout the

respective surfaces [31].

The collector aperture area is equal to the front area of the PV module [31].

The fluid flow-rate is evenly distributed between the pipes and the thermal losses and

mixing effects at the inlet and outlet manifolds are negligible [22].

It is assumed that there is no dust or partial shading on the collector. (Losses due to cloud

shading is neglected).

The electrical resistances are neglected when evaluating the electrical energy output and

the electrical efficiency [22].

The reflection, absorption and transmission factors are calculated only for the incident

solar irradiance [22].

The changes in kinetic energy and potential energy are ignored in the energy equation set

[23].

The equations of the Florschuetz model which are used which have been explained in chapter 4

and elaborated in chapter 5 to obtain the results. The model has been used to determine the

performance of the WPVT-system, which is graphed in figure 6.2 till 6.5.

FIGURE 6.2 Electrical efficiency of the WPVT-system

In figure 6.2 the results of the electrical efficiency of the WPVT-system for Marriott Hotel are

graphed. The graph flow decreases from 12.14 % to 11.24% with an increase of the ambient

temperature.

0.1214

0.1161

0.1132 0.1124 0.1132 0.1143

0.11820.1202

0.1050

0.1100

0.1150

0.1200

0.1250

9 10 11 12 13 14 15 16

Effi

cie

ncy

time (h)

WPVT Electrical Efficiency

46

FIGURE 6.3 Thermal efficiency of the WPVT-system

The thermal efficiency of the WPVT-system analysis is given in figure 6.3. There is a slight

increase of efficiency when the irradiance and ambient temperature increase. The flow increases

from 31.82% to 34.16 % before 12.00 then decreases to 27.66 % after 12.00.

FIGURE 6.4 Thermal energy of the WPVT-system

The thermal output of the WPVT system is given in figure 6.4. The thermal heat increases with

an increase of irradiance and ambient temperature and decreases with a decrease of these input

parameters. The generated thermal energy goes from 371.67 W to 701.28 W, then decreases to

205.37 W.

0.3182 0.3207 0.3375 0.3416 0.3375 0.33200.3038

0.2766

0.0000

0.0500

0.1000

0.1500

0.2000

0.2500

0.3000

0.3500

0.4000

9 10 11 12 13 14 15 16

the

rmal

eff

icie

ncy

time (h)

WPVT Thermal Efficiency

371.67

620.09679.77 701.28 679.77

632.33

330.39

205.37

0.00

100.00

200.00

300.00

400.00

500.00

600.00

700.00

800.00

9 10 11 12 13 14 15 16

Po

we

r (W

)

Time (h)

WPVT Thermal Output

47

FIGURE 6.5 Electrical output of the WPVT-system

In figure 6.5 the results of the electrical output from the WPVT-system are graphed. The electrical

output is also lower than the thermal energy output. The flow pattern is similar to the thermal

heat flow pattern with an increase of energy before 12.00-13.00 and a decrease of energy after

12.00-13.00.

6.3 Results of the RPVT-system

In this section the refrigerant based PVT application is analyzed based on the methodology of

chapter 4. The PVT panel state conditions of table 6.1 and the sun irradiance and ambient

temperature of table 6.2 also comply for the RPVT-system. The PVT panel characteristics are

given in table 4.3 of chapter 4. The refrigerant used for the PVT-system is R-22. The refrigerant at

the inlet of the PVT panel is in liquid state, through the PVT panel in liquid-vapor state, and when

the refrigerant exits the PVT panel it is in vapor state. The characteristics needed for the analysis

of the PVT panel is of the refrigerant in liquid-vapor state when it goes through the PVT panel.

In Appendix A the additional heat calculations are given to determine the fluid to tube heat

transfer coefficient for R-22 in liquid-vapor phase. The properties of R-22 are determined with the

thermodynamic data given in Moran and Shapiro [36] and the online Fluid Property Calculator

[37]. A schematic of the refrigerant based system is given in figure 6.6. The system boundary is

once more placed with the panel considered, only this component will be analyzed based on its

performance.

245.64

364.46409.18 423.84 409.18

380.31

201.41

121.75

0.00

50.00

100.00

150.00

200.00

250.00

300.00

350.00

400.00

450.00

9 10 11 12 13 14 15 16

Po

we

r (W

)

Time (h)

WPVT Electrical Output

48

FIGURE 6.6 Schematic illustration of the refrigerant based PVT-system from Chow et al. [32]

The refrigerant based PVT-system has the same simplified assumptions as the water based

PVT-system given in section 6.3 of step 3 along with the following additional assumptions:

The refrigerant flow inside the evaporator tubing is one dimensional and homogeneous.

The liquid and vapor refrigerant have the same average transport velocity, i.e. the slip

between liquid and vapor is neglected [23].

The liquid and vapor phases are in saturated thermal equilibrium and the pressure of the

liquid and vapor at the same cross-section are equal [23].

The influence of the pressure drop on the physical properties of the liquid and vapor

refrigerant, such as temperature, density and enthalpy, has not been taken into account.

The applied equations for the RPVT-system are given in table 6.3. The obtained performance for

the RPVT-system is graphed in figure 6.7 till 6.10.

FIGURE 6.7 Electrical efficiency of the RPVT system

0.1257

0.1217

0.12000.1185

0.11930.1204

0.1241

0.1258

0.1140

0.1160

0.1180

0.1200

0.1220

0.1240

0.1260

0.1280

9 10 11 12 13 14 15 16

ele

ctri

cal e

ffic

ien

cy

time (h)

RPVT Electrical Efficiency

49

In figure 6.7 the results of the electrical efficiency of the RPVT-system for Marriott Hotel are

graphed. The graph flow decreases from 12.57% to 11.85% with an increase of the ambient

temperature. The RPVT graph flow is similar to the WPVT electrical graph flow.

FIGURE 6.8 Thermal efficiency of the RPVT system

The thermal efficiency of the RPVT-system analysis is given in figure 6.8. There is an increase of

efficiency when the irradiance and ambient temperature increase. The flow increases from 54.52%

to 60.41 % before 12.00 then decreases to 56.15 % after 12.00.

FIGURE 6.9 Thermal output energy from the RPVT system

The thermal output of the RPVT system is given in figure 6.9. The thermal heat increases with an

increase of irradiance and ambient temperature and decreases with a decrease of these input

parameters. The generated thermal energy goes from 970.24 W to 1749.55 W, then decreases to

625.98 W.

0.5452

0.5806

0.5934

0.60410.5984

0.5912

0.5735

0.5615

0.5100

0.5200

0.5300

0.5400

0.5500

0.5600

0.5700

0.5800

0.5900

0.6000

0.6100

9 10 11 12 13 14 15 16

the

rmal

eff

icie

ncy

time (h)

RPVT Thermal Efficiency

970.24

1570.581689.86 1749.55 1699.56

1589.84

908.40

625.98

0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

1400.00

1600.00

1800.00

2000.00

9 10 11 12 13 14 15 16

Po

we

r (W

)

Time (h)

RPVT Thermal Output

50

FIGURE 6.10 Electrical output from the RPVT system.

In figure 6.10 the last obtained result is given which is the electrical output from the RPVT-system.

The electrical output here is also lower than the thermal energy output of this system. The flow

pattern is similar to the thermal heat flow pattern with an increase of energy before 12.00-13.00

and a decrease of energy after 12.00-13.00. The electrical output goes from 438.14 W to 671.07 W

and then decreases to 352.44 W at 16.00.

6.4 Energy Coverage of the PVT-system

The energy coverage is executed according to the procedure given in chapter 4. The results are

given in table 6.5. The average energy demand data of Marriott Hotel and the average energy

output data of the PVT-systems is given in table 6.4. Data of the WPVT and RPVT-system has

been used for the analysis. The assessment is done for a PVT system of 264 panels that can cover

the roof area of Marriott Hotel. In Appendix B an estimation of the solar panel system sizing for

Marriott Hotel is given. The size of the system is determined by using the maximum of roof area

that can be covered with solar panels. The electrical output is assumed to increase linearly with

the amount of panels. And according to the PVT panel characteristics of the company SmartClima

[47] the thermal output also linearly increases with the increase of panels. The total power output

is determined by multiplying the amount of panels with the average electrical and thermal output

of one panel and determining the monthly output. The average electrical and thermal output of

the WPVT are 3.49 kWh and 3.87 kWh per panel per day. And the average electrical and thermal

output of the RPVT are 4.45 kWh and 9.49 kWh per panel per day. It is assumed that the electricity

through a large inverter can cause an electrical energy reduction of approximately 15% [48] which

his included in the electricity output power of the WPVT and RPVT systems in table 6.4.

438.14

542.66

641.46 671.07 656.70593.07 559.22

352.44

0.00

100.00

200.00

300.00

400.00

500.00

600.00

700.00

800.00

9 10 11 12 13 14 15 16

Po

we

r (W

)

Time (h)

RPVT Electrical Output

51

Parameter Averaged Energy per month (250 panels) (kWh)

WPVT-System RPVT-System

PVT Electrical output 𝐸𝑃𝑉𝑇 23494.8 29957.4

Pump/Compressor

electrical usage

𝐸𝑙𝑜𝑠𝑠 528 14400

VRF electrical usage 𝐸𝑉𝑅𝐹 37398 37398

Total Electricity demand

Marriott

𝐸𝑇 85481 85481

PVT Thermal output 𝑄𝑃𝑉𝑇 30650 75160.8

Thermal demand 𝑄𝑇 174084 174084

TABLE 6.4 Energy demand of Marriott Hotel and energy output of the PVT systems

The total amount of operating hours of the units is taken as an average of 20 hours per day.

Parameter Equation WPVT % RPVT %

-VRF electricity

demand covered 𝐷𝐶𝐸_𝑉𝑅𝐹 (%) =

𝐸𝑃𝑉𝑇 − 𝐸𝑙𝑜𝑠𝑠

𝐸𝑉𝑅𝐹

. 100 (4.12𝑎) 61.41 0.42

-Total electricity

demand covered 𝐷𝐶𝐸_𝑇(%) =

𝐸𝑃𝑉𝑇 − 𝐸𝑙𝑜𝑠𝑠

𝐸𝑇

. 100 (4.12𝑏) 26.87 0.18

-Thermal energy

demand covered 𝐷𝐶𝐻𝑊(%) =

𝑄𝑃𝑉𝑇

𝑄𝑇

. 100 (4.13) 17.6 43.18

-Average covered

energy 𝐷𝐶𝑎𝑣(%) =

𝐷𝐶𝐸_𝑇 + 𝐷𝐶𝐻𝑊

2 (4.14)

22.24 21.68

-Average covered

energy in time

period

𝐷𝐶𝑤𝑎𝑣(%) =𝐸𝑉𝑅𝐹 𝐷𝐶𝐸_𝑇 + 𝑄𝑇𝐷𝐶𝐻𝑊

𝐸𝑉𝑅𝐹 + 𝑄𝑇

(4.15) 19.24 35.62

TABLE 6.5 Energy coverage of the WPVT-system and the RPVT-system

In table 6.5 is given that the WPVT covers 61.41% of the VRF demand and 17.6 of the thermal

demand. And the RPVT covers 78.69% of the VRF demand and 43.18 of the thermal demand. It

should be noted that the thermal energy usage of the water heater was determined based on the

maximum that the heater can use. Due to insufficient information, and proper measuring

equipment, the exact amount of thermal energy demand of the water heater could not be

determined.

52

6.5 Discussion of the PVT-systems

Table 6.6 gives the average performance and the generated energy difference between the WPVT

and the RPVT system. The applied Florschuetz model [17] was limited to a qualitative analysis

because the model was only successfully validated based on the flow patterns of the performance

graphs in chapter 5. The qualitative analysis was done by analyzing the flow patterns and

comparing the estimated performance increases.

Averaged Values WPVT-System RPVT-System Difference (%)

Electrical Efficiency 0.1100 0.1200 1

Thermal Efficiency 0.4165 0.5190 11

Total Efficiency 0.5264 0.6290 8

Electrical (Wh) 435.63 556.84 12

Thermal heat (Wh) 483.80 1186.32 42

TABLE 6.6 Averaged performance and difference % of the WPVT and the RPVT performance

Table 6.6 shows that the RPVT-system reached a higher performance compared with the WPVT-

system which was the expected result that was indicated from previous conducted research [18].

The results also show higher power output values compared with the WPVT and RPVT system

of the research done by Gaurracino et al. [22] and Ji et al. [23] given in figure 5.4 of chapter 5,

which was also expected considering that the applied environment conditions of Suriname where

more favorable for solar energy utilization. The thermal and electrical energy flow graphs of

figure 6.11 and 6.12 also indicate higher performances for the RPVT-system compared with the

WPVT-system. The figures 6.11 till 6.12 show the power outputs of the WPVT and the RPVT

system graphed together to indicate the differences over the time period.

FIGURE 6.11 RPVT and WPVT Thermal Output

970.24

1570.581689.86 1749.55 1699.56

1589.84

908.40

625.98

371.67

620.09 679.77 701.28 679.77 632.33

330.39205.37

0.00

500.00

1000.00

1500.00

2000.00

9 10 11 12 13 14 15 16

Po

we

r (W

)

Time (h)

Thermal Output

RPVT

WPVT

53

FIGURE 6.12 RPVT and WPVT Electrical Output

The PVT panel of the RPVT system acts as an evaporator coil which allows the refrigerant to

evaporate when it passes through the module. This allows the refrigerant to evaporate at very

low temperatures (0-20C). The PV cells reduce to a similar temperature hereby also reducing the

temperature effect on the PV panel that is explained in chapter 3. This results that the PV panels

can than operate at higher efficiencies compared with the WPVT-system. Next to that is the effect

of the compressor which increases the pressure of the vapor and delivers it to the condensing unit

that can provide heating at a higher temperature compared with the WPVT-system [18]. The

refrigerant goes through the compressor which increases the temperature before entering the

water tank. This gives a higher overall performance of the RPVT compared with the WPVT-

system. It also causes a higher energy coverage of the RPVT compared with the WPVT-system

for the energy demand of Marriott Hotel.

It should be noted that although the RPVT-system reaches a higher performance, it still comes

with the technical limits that need to be addressed before integrating it to buildings [18]. The

technical aspects which are still being researched on are the refrigerant piping cycle that needs a

perfect seal to maintain high or low pressures at different sections and to prevent air from being

sucked into the system. There is also a high risk that needs to be investigated of refrigerant

leakage and achieving a balanced refrigerant distribution across multiple coils which are installed

at large PV panel areas [18]. And the WPVT-system is already commercially available and capable

for building integration [34], but only the knowledge of maintenance and operation lack.

171.43

271.06292.05 303.84 294.91

276.79

166.00

116.26

245.64

364.46

409.18 423.84 409.18380.31

201.41

121.75

0.00

50.00

100.00

150.00

200.00

250.00

300.00

350.00

400.00

450.00

9 10 11 12 13 14 15 16

Po

we

r (W

)

Time (h)

Electrical Output

RPVT

WPVT

54

7 Conclusion and Recommendations

“Women like men should try to do the impossible.

And when they fail, they’re failure should be a

challenge to others.

—Amelia Earhart, 1939

(Aviation Pioneer and Author)

7.1 Conclusions

The PVT-system which can generate electricity and heat from solar energy is the main subject of

this study. The system can be categorized in different types of designs and the focus was lain on

the WPVT-system and the RPVT-system. This system has been investigated on its performance

for environment conditions in Suriname. For this investigation Marriott Hotel Paramaribo was

approached as a case study. The objective by implementing the system for Marriott Hotel was to

reduce the amount of energy used by the utility grid. The system was investigated for the VRF

cooling system and gas fired water heating system of Marriott Hotel. The PVT-system can be

mathematically analyzed by the Florschuetz model [17]. This model was written in Microsoft

Excel and used to analyze the performance of the PVT-system at steady state conditions. The

model was first tested on its validity by implementing research data of Gaurracino et al. [22] and

Ji et al. [23]. The output of the model validation was qualitatively analyzed by comparing the

performance of the system which indicated similarities. The model was then used to analyze a

WPVT and RPVT-application with the environment conditions of Marriott Hotel.

The electrical and thermal energy generated by the WPVT-system per panel are 435 Wh and 485

Wh. And the electrical and thermal energy output of the RPVT-system are 556 Wh and 1186 Wh.

The RPVT-system reached a higher overall performance compared with the WPVT-system, but

the RPVT-system also still has its technical limits which needs to be researched if it were to be

used for large appliances and building integration [18]. The electrical energy usage of Marriott

Hotel that can be covered by the WPVT-system is 26% and the thermal energy which can be

covered is 17%. And with the RPVT-system, 0.18% of the electrical energy can be covered and

43% of the thermal energy based on the research of this project. The WPVT-system could cover a

higher electrical demand and the RPVT-system could cover a higher thermal demand based on

the research of this project.

55

7.2 Recommendations

A study should be conducted for different PVT collector configurations with environment

conditions of Suriname. It should be noted that the one dimensional steady state

application is not qualified for other PVT collector configurations. The steady state one

dimensional approach in this qualified for the panel configuration mentioned in Chapter

4. But a two dimensional study is needed to analyze other panel configurations. And a

dynamical model is needed for an in depth performance analysis which includes the

temperature distribution analysis and an analysis of the instantaneous yield for dynamic

conditions [35].

Research on the yearly performance of a PVT-system should be conducted through a pilot

project, hereby better predicting the performance of the PVT-system for commercial

applications in Suriname. Through an experimental study more reliable data can be

obtained, which also could be used to study the technical barriers that exist with the RPVT

system.

The complete PVT-system needs to be analyzed that can lead to a more accurate approach

when executing an experimental research. The PVT-system also consists of a

compressor/pump, tank, valve, auxiliary heater and condenser.

Before implementing renewables it is important to investigate if possibilities exists to

reduce the overall energy usage of Marriott Hotel beforehand.

A study should be done on an economic assessment of the PVT-system. This can deliver

a full feasibility report of a PVT-system implementation for Marriott Hotel.

For a continuation of this study, factors such as the landscape, and wind speed differences

that have an effect on the sun irradiance should be included for the analysis of this project.

And irradiance data measured at Marriott Hotel should be used. The exact thermal

demand data of the water heater should also be included.

For this analysis of the RPVT-system the refrigerant R-22 is used. It is recommended that

a study is conducted with an environmental friendly refrigerant such as R134a or R-104

for conditions in Suriname. This study would support reducing the usage of products and

systems which have high environmental impacts such as global warming.

A study should be done to investigating if the possibility exists to directly apply the DC

wattage generated by the PVT panel to the VRF system of Marriott Hotel (which has a DC

compressor), hereby being able to cover more energy with the PVT system by eliminating

the use of inverters which cause electrical energy losses.

56

Appendixes

A Complete set Equations

In this appendix the complete set of equations used are given in table A.1. And the additional

equations needed to calculate the heat transfer coefficient of the refrigerant R-22 through the PVT

panel is given.

Equations to determine the Energy Performance

Electrical efficiency 𝑒𝑙

= 𝑇𝑟𝑒𝑓

(1 − 𝑟𝑒𝑓

(𝑇𝑃𝑉 − 𝑇𝑟𝑒𝑓 )) (1)

PV temperature 𝑇𝑝𝑣 = 30 + 0.0175(𝐺 − 300) + 1.14(𝑇𝑎 − 25) (2)

Thermal efficiency

𝑡ℎ= 𝐹𝑅

((1 − 𝑒𝑙

) − 𝑈𝐿 (

𝑇𝑖 − 𝑇𝑎

𝐺)) (3)

Heat removal factor (modified) 𝐹𝑅 =

��𝐶𝑝

𝐴𝑃𝑉 𝑈𝐿 (1 − exp (−

𝐴𝑃𝑉 𝑈𝐿 𝐹′

��𝐶𝑝

)) (4)

Collector efficiency (modified) 𝐹′ =

1 𝑈𝐿 ⁄

𝑊 [1

𝑈𝐿 [𝐷 + (𝑊 − 𝐷)𝐹𝑊𝐷

+1𝐶𝑏

+1

𝜋𝐷𝑖ℎ𝑓𝑖]

(5)

1st Fin efficiency 𝐹𝑊𝐷 = (1 −

𝐷

𝑊) 𝐹 +

𝐷

𝑊 (6)

2nd Fin efficiency

𝐹 =tanh (

𝑚(𝑊 − 𝐷)2 )

𝑚(𝑊 − 𝐷)/2 (7)

Dimensionless parameter

𝑚 = √𝑈𝐿

𝑘 (8)

Overall loss coefficient (modified) 𝑈𝐿 = 𝑈𝐿 −

𝑟𝑒𝑓

𝑟𝑒𝑓𝐺 (9)

Transmissivity-absorptivity product () =

1 − (1 − )𝑑

(10)

Transmissivity = 𝑎𝑟 (11)

Absorptivity = 1 − 𝑎 (12)

Reflectance 𝑑

= 𝑎 − (13)

Transmissivity considering absorption 𝑎 = 𝑒

−(𝐾𝐿

𝑐𝑜𝑠2) (14)

Transmissivity considering reflectance 𝑟𝑁 =

1

2(

1 − 𝑟1 + (2𝑁 − 1)𝑟

+1 − 𝑟||

1 + (2𝑁 − 1)𝑟||

) (15)

TABLE A1 Complete set of Equations for the energy performance of the PVT-system

57

Equations to determine the Energy Performance

Useful thermal energy 𝑄𝑢 = 𝐴𝑐𝐹𝑅 (𝑆 − 𝑈𝐿

(𝑇𝑖 − 𝑇𝑎) (16)

Electrical Output 𝑄𝑒 =

𝐴𝑃𝑉𝑆𝑒𝑙

[1 −

𝑟𝑟

𝑒𝑙(𝐹𝑅

(𝑇𝑖 − 𝑇𝑎) +𝑆

𝑈𝐿 (1 − 𝐹𝑅

))] (35)

Solar radiation per unit area 𝑆 = 𝐼𝑏𝑟𝑏()𝑏 + (𝐼𝑏𝑟𝑑 + (𝐼𝑏 + 𝐼𝑑 )𝑟𝑟)()𝑑 (17)

Modified solar radiation 𝑆 = 𝑆 (1 −

𝑒𝑙

) (18)

Beam reflection 𝑟𝑏 =

𝑐𝑜𝑠1

𝑐𝑜𝑠2

(19)

Diffusion reflection 𝑟𝑑 =

(1 + 𝑐𝑜𝑠)

2 (20)

Reflection of radiation 𝑟𝑟 =

(1 − 𝑐𝑜𝑠)

2 (21)

Refraction angle 2 = 𝑠𝑖𝑛−1 (𝑠𝑖𝑛

1

𝑛) (23)

Perpendicular reflection 𝑟 = (

𝑠𝑖𝑛2(2 − 1)

𝑠𝑖𝑛2(2 + 1)) (24)

Parallel reflection 𝑟|| = (

𝑡𝑎𝑛2(2 − 1)

𝑡𝑎𝑛2(2 + 1)) (25)

Reflection of radiation 𝑟 =

1

2(

𝑠𝑖𝑛2(2 − 1)

𝑠𝑖𝑛2(2 + 1)+

𝑡𝑎𝑛2(2 − 1)

𝑡𝑎𝑛2(2 + 1)) (26)

Angle of incidence 𝑐𝑜𝑠 = 𝑠𝑖𝑛(sin 𝑐𝑜𝑠 + cos cos cos sin)+ cos (cos cos cos − sin cos sin)+ (cos sin sin sin) (27)

Total energy efficiency 𝑡

= 𝑒𝑙

+ 𝑡ℎ

(28)

Declination angle

𝑛= 23.45 (sin (

360

365×

284

𝑛)) (29)

TABLE A1 (continued) Complete set of Equations for the energy performance of the PVT-system

58

Table A2 gives additional equations needed to determine the characteristics of the liquid, vapor

and liquid-vapor state of the refrigerant R-22 through the PVT-system. The temperature and

pressure at the inlet is 12C and 800 kPa in a liquid state from Ji et al. [23]. The properties of R-22

are determined with the thermodynamic data given in Moran and Shapiro [36] and the online

Fluid Property Calculator [37]. The fluid to tube heat transfer coefficient (ℎ𝑓𝑖) is determined with

the equation given in the research of H. Chen et al. [52].

Additional equations

Heat transfer coefficient (2-phase region) (𝒉𝒇𝒊) ℎ𝑓𝑖 = 𝑙 ((1 − 𝑥)0.8 +

3.8𝑥0.76(1 − 𝑥)0.04

𝑃𝑟0.38) (30)

Prandtl number (0.8414) 𝑃𝑟 =

𝑟

𝐶𝑝𝑟

𝑟

(31)

Heat transfer coefficient of liquid phase

a= 0.3 liquid phase

a= 0.4 vapor phase

𝑙 = 0.023𝑅𝑒0.8𝑃𝑟𝑎

𝐷𝑖

(32)

Reynolds number 𝑅𝑒 =

𝑟

𝑢𝑟𝐷𝑖

𝑟

(33)

Mass flow (5.26 *10-4 kg/s) �� = 𝑟𝑢𝑟𝐴 (34)

Additional Parameters

Dryness factor 𝑥 = 0.323

Specific heat at constant pressure (J/kgK) 𝐶𝑝𝑟 = 5000

Thermal conductivity (W/mK) 𝑟 = 0.0174

Dynamic viscosity (pa s) 𝑟 = 12.1 *10-6

Flow velocity (m/s) 𝑢𝑟 = 0.2065

Density (kg/m3) 𝑟 = 90

Copper pipe Area (m2) A = 2.83 *10-5

TABLE A2 Additional equations and parameters for the refrigerant based PVT-system

B Marriott Hotel with Solar Panels

The total estimated roof area available for the placing of solar panels is 450 m2, figure B2. Because

Solar panels are assumed to need large amounts of space, the Solar system sizing is made by

estimating how many panels can cover the roof of Marriott Hotel for the electricity need of the

VRF cooling system. An estimated 80% of the roof area can be used for panes. This gives,

𝑆𝑜𝑙𝑎𝑟 𝑃𝑎𝑛𝑒𝑙 𝑅𝑜𝑜𝑓 𝐴𝑟𝑒𝑎 = 0.8 × 450𝑚2 = 360 𝑚2

59

From that is determined what amount of energy a system of that size can cover of the energy

demand from Marriott Hotel and if there is extra energy generated that can be sold to the grid.

The amount of solar panels that can be placed on that area are,

𝑆𝑜𝑙𝑎𝑟 𝑃𝑎𝑛𝑒𝑙 𝑅𝑜𝑜𝑓 𝐴𝑟𝑒𝑎

𝑃𝑉𝑇 𝑃𝑎𝑛𝑒𝑙 𝐴𝑟𝑒𝑎=

360𝑚2

1.36𝑚2= 264 𝑝𝑎𝑛𝑒𝑙𝑠

An illustration of how the panels can be integrated is given in this appendix. There must be noted

that more presentable methods need to be analyzed before implementing the panels, see figure

B2. The panels will be integrated with a tilt of 5 towards the southern direction. The Hotel has a

steep roof of 35, figure B1. The panels will have to be implemented with a construction below to

obtain the needed tilt of 5.

FIGURE B1 Marriott Hotels’ front view with the roof steepness given.

60

FIGURE B2 Marriott Hotel roof area (left) and the roof area available for solar panels (right) in dark blue.

61

C WPVT and RPVT-system Comparison

WPVT-System RPVT-System

Electrical Coverage X

Thermal Coverage X

Experimentally tested X X

Commercially Available X

Existing barriers no yes

TABLE C. WPVT and RPVT- Comparison overview

In table C a comparison between the WPVT-system and the RPVT-system is given based on the

research of this project. The WPVT-system can deliver a higher electrical energy coverage for

Marriott Hotel compared with the RPVT-system and the RPVT-system can deliver a higher

thermal energy coverage compared with the WPVT-system. Both systems have already been

experimentally tested and delivered the expected performances within the research done [18].

The WPVT-system is already on the market today whereas the RPVT-system is still only in the

experimental phase. There still exists technical and economic barriers for the RPVT-system that

need to be researched on before building integration [18], whereas the WPVT-system is already

being applied for building integration.

62

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