seasonal performance factor and monitoring for heat pump...

1

Project

SEasonal PErformance factor and MOnitoring for

heat pump systems in the building sector

(SEPEMO-Build)

Contract No.: IEE/08/776/SI2.529222

Deliverable 3.1 Survey of completed and ongoing field measurements of

air-to-air heat pumps

Coordinator: Philippe Rivière, Armines

Main authors

Philippe Rivière, Armines Christine Arzano-Daurelle, Toan Cong Tran, EdF R&D

Roger Nordman, SP

The sole responsibility for the content of this document lies with the authors. It does not necessarily reflect the opinion of the European

Communities. The European Commission is not responsible for any use that may be made of the information contained therein.

2

CONTENTS

INTRODUCTION 4

1. AIR TO AIR HEAT PUMPS 4

1.1 PRINCIPLE OF OPERATION 4 1.2 DIFFERENT PRODUCT TYPES 5 1.3 PRODUCTS TARGETED IN THE SEPEMO STUDY 9

2. HSPF MEASUREMENT 10

2.1. HSPF DEFINITION 10 2.2. HSPF MEASUREMENT PRINCIPLES 10

3. SWEDEN 11

INTRODUCTION 11 3.1. MEASUREMENT METHOD 1: SP METOD NR 1721 11

3.2. PERFORMANCE CALCULATION METHOD 13

3.3. MEASUREMENT RESULTS 14

4. FRANCE 17

INTRODUCTION 17

4.1. MEASUREMENT METHOD 17 4.2. PERFORMANCE CALCULATION METHOD 18 4.3. MEASUREMENT RESULTS 18

5. JAPAN 19

INTRODUCTION 19 5.1. MEASUREMENT METHOD 19 5.2. CALCULATION METHOD 19 5.3. MEASUREMENT RESULTS 20

DISCUSSIONS AND CONCLUSIONS 24

VERY FEW FIELD MEASUREMENTS WITH LARGELY VARIABLE PERFORMANCES 24 POTENTIAL ISSUES WITH IDENTIFIED HSPF MEASUREMENT METHODS 24

POSSIBLE ALTERNATIVE INTERNAL METHODS 24 THE DIFFICULT CHOICE OF A METHODOLOGY FOR THE SEPEMO PROJECT 25

REFERENCES 26

LIST OF FIGURES 27

LIST OF TABLES 27

4

Introduction

Before to describe the on-going and achieved field measurements, this document first gives an

overview of the air-to-air heat pump principles, technologies and main products sold in Europe.

Then, the different possible in-situ measurement methods of the heating seasonal performance

factor (HSPF) are briefly described.

In only 3 countries, past and on-going field measurements were identified, France, Japan and

Sweden; these are presented by country. In each case, the method used is described along with

the field results when available.

1. Air to air heat pumps 1.1 Principle of operation

An air/air heat pump (HP) is a thermodynamic machine to transfer heat from a colder

environment to a warmer environment while heat is naturally transferred from the hot to the

cold environment until both temperature sources are equal.

Figure 1. Operation principle of air to air heat pump

All air to air heat pumps on the EU market are of the vapour compression type: the refrigerant

captures energy from the outdoor air while evaporating. A compressor driven by an electric or a

gas/liquid combustible motor raises the refrigerant vapor temperature. The heat is then

transferred into the house while the refrigerant condenses to liquid before reaching the

expansion valve and cooling down again to capture outdoor heat.

The thermodynamic cycle is divided into four main steps:

Evaporation: the refrigerant is evaporated at low pressure and low temperature by

absorbing heat of external air.

Compression: the refrigerant gas is compressed to high pressure, resulting in an

increase in temperature

Condensation: the refrigerant gas at high pressure is condensed at high temperature by

transferring heat to the inner air.

Expansion: the refrigerant liquid is expanded to low pressure. The fluid follows a sharp

drop in temperature before repeating its circuit.

5

HP can also be used for cooling application. Reversible HP can deliver heating power or

cooling power according to the selected operating mode. When the end-user selects the desired

mode, the refrigerant flow direction is reversed thanks to a four-way valve. The refrigerant

circuiting in both operation modes are shown hereunder.

Figure 2. Reversible circuit of HP – Heating mode (Source Costic)

Figure 3. Reversible circuit of HP - Cooling mode (Source Costic)

1.2 Different product types

The more popular type of air to air heat pump is the reversible split air conditioner or heat

pump. It is made of one or several indoor unit and one or two outdoor units. Each indoor unit is

connected directly to an outdoor unit. When several indoor units are connected to one or two

outdoor units, then the split system is called a multisplit system.

Figure 4. Multi-split air conditioners (source LG)

6

Products in this range are partly in the residential and commercial areas. Reversibility of these

air conditioners is growing rapidly. There are different indoor unit types, ducted or non ducted

(non ducted units can be located outside the space to be heated). Non ducted indoor units can be

wall mounted, cassettes, ceiling mounted cassette units, concealed ceiling, wall mounted,

ceiling suspended and floor standing.

Figure 5. Types of indoor units (source Mitsubishi Electric)

Wall Floor type Ceiling mounted

cassette units Cassette

Floor standing Concealed ceiling

(ducted) Ducted units

For split systems, there is a large variation of possible configurations the final sold products

being a combination between the outdoor and indoor unit for a specific building.

Outdoor unit is generally air cooled but can be sometimes water cooled.

The new products include the following components:

Refrigerant fluid used: R410A mainly

Compressor type: rotary and scroll

Compressor control type: inverter is dominant in Western Europe.

Expansion valve: electronic

Indoor heat exchanger: tube and fin coil with different types of fans

Outdoor heat exchanger: tube and fin coil with axial or centrifugal fan if air cooled.

The VRF (Variable Refrigerant Flow) system is similar in shape to multisplit heat pumps.

Nevertheless, in a multisplit unit, the expansion occurs in the outdoor unit. On the contrary, the

expansion valve is located in the terminal unit in VRF systems.

VRF 2 pipes: the refrigerant network can be made of 2 pipes. When heating, one duct contains

high pressure and high temperature refrigerant vapor. This vapor is cooled down in terminal

units and brought back at low temperature low pressure in diphasic state. When cooling,

7

diphasic low temperature high pressure refrigerant is circulated and expanded in terminal units

where it is used to cool the air in the terminal units and low pressure low temperature is brought

back to the compressor located in the outside unit.

VRF heat recovery: a heat recovery version is able to offer both cooling and heating for

different zones of the building. Heat recovery is achieved by diverting heat from indoor units in

cooling mode to those areas requiring heating. According to EN14511:2007 definitions, this

may be achieved by a gas/liquid separator or a third line in the refrigeration circuit.

For VRF systems, there is a large variation of possible configurations the final sold products

being a combination between the outdoor and indoor unit for a specific building, with different

possible circuiting depending on the possible simultaneity of heating and cooling requirements.

Figure 6. VRF systems (left - source Daikin outdoor units, right – source Toshiba

system overview)

These new products include the following components:

Refrigerant fluid used: R410A

Compressor type: scroll

Expansion valve: electronic


Outdoor heat exchanger: tube and fin coil with axial or centrifugal fan if air cooled and

plate heat exchanger if water cooled.

These systems are generally air cooled although some can be water cooled.

The capacity range of these solution extended with groups of outdoor units now being able to

supply up to 150 kW cooling capacity. With smaller indoor unit size being 2 kW capacity, this

enables to connect more than 50 indoor units on an outdoor unit type. This is scalable with a

capacity ratio that enables to take into account the fact that all thermal zones do not require

their design capacity at the same time so that more indoor units can be connected to the same

outdoor unit.

In general, the ventilation system is kept separate but VRF systems can also be coupled with a

centralized air system that enables to precondition centrally the air entering terminal units,

filtering, controlling fresh air renewal, etc… Hence, manufacturers tend to offer systems that

cover more and more functions.

8

Figure 7. Daikin VRF complete solution for heating, cooling, ventilation and air curtain

management

The VRF systems integrate progressively more control options and manufacturers also offer

integrated controls that can enable to control up to 2000 indoor units of different types and to

optimize jointly air renewal, heat recovery and the air conditioning system (in its broader

acceptance here).

Package reversible heat pumps can be located either into the room to treat or into another

room or outside – Window/Wall reversible air conditioner, rooftop - providing the air by ducts

and grilles for a better temperature homogenization. It is the same working principle as the split

air conditioner but with higher capacities. It can be coupled with air ducts, as rooftops, to

distribute air to several rooms. Rooftop combines the cooling/heating and ventilation function.

These products are generally air cooled although some can be water cooled.

The new rooftop products include the following components:

Refrigerant fluid used: R410A, R407C

Compressor type: scroll

Expansion valve: thermostatic and electronic


Outdoor heat exchanger: tube and fin coil with axial or centrifugal fan if air cooled and

plate heat exchanger if water cooled.

Figure 8. Roof top air conditioner (source Carrier)

Water to air package reversible heat pumps are mostly used in water loop heat pump

systems, typically in hotels and shopping centers.

9

Air to air heat recovery heat pumps are alternatives to heat recovery heat exchangers for

ventilation. As their heat exchangers are located in the airstreams, these heat pumps are ducted

on both sides.

1.3 Products targeted in the SEPEMO study

In this study, we focus on the most common type of residential installations in Europe (by far),

i.e. free duct mini-split reversible air conditioners.

10

2. HSPF measurement

2.1. HSPF definition

The heating seasonal performance factor of air/air based HP is defined as the ratio of the heat

supplied at the condenser by the electricity consumption of the whole system during a given

period:

(1)

With:

PH: the heating capacity

And PE: the electric consumption

2.2. HSPF measurement principles

The electric power PE is measured by an electric meter. Major devices consuming electricity are

compressor and indoor and outdoor fans.

In order to measure the heat energy supplied, there are several ways based on air measurement

or refrigerant measurement.

When the heat measurement is based upon air: the heat supplied is defined by multiplying air

flow and air enthalpy variation at the condenser, as follows.

( )

So it’s necessary to measure the air flow rate and air enthalpies input and output. For this type

of method, measuring the air flow rate of the non ducted air to air units is the main challenge.

When the heat measurement is based upon refrigerant: the heat supplied is defined by

multiplying refrigerant mass flow and refrigerant enthalpy variation at the condenser. So it’s

necessary to measure the refrigerant flow rate and enthalpies input and output. Here again, the

main challenge is to measure the flow.

All completed and ongoing field measurements are based on air enthalpy measurement

methods.

dt).t(P

dt).t(PHSPF

E

H

11

3. Sweden

Introduction

This part regarding past and on-going field measurement in Sweden is based upon the national

report for Sweden for air-to-air heat pumps established in the frame of the SEPEMO project [1].

According to this report, only one field measurement of A/A heat pumps has been made in

Sweden in recent years. The measurement methodology used in this study consists of a

combination of capacity tests at certain conditions and full year electricity measurements

according to SP method 1721 [2].

3.1. Measurement method 1: SP metod nr 1721

SP method nr 1721 is a field measurement method for field testing of electrically driven air to

air heat pumps in heating or cooling mode. The method includes heating capacity, electric

power input and coefficient of performance. Instructions of how the measurements shall be

performed are stated. If the test is conducted in accordance with the measuring requirements of

the method, the coefficient of performance can be determined with an uncertainty of

measurement lower than 10 %. The method is validated in a combination of laboratory and field

measurements.

The system boundaries are specified in the method. The measurements can either be carried out

for a single heat pump or for the entire heat pump system, see Figure 9 below.

12

Figure 9. Boundaries of the HP system, SP metod nr 1721

Figure 10. Example of the arrangement of the measurement equipment according to

SP method 1721.

13

No examples or recommendations of operating points for the tests are stated in the method

itself.

The total electricity consumption during the test is measured by attaching an electrical power

meter or an integrated electrical energy meter to the supply cable of the heat pump.

The emitted heat effect is decided by measurements in the circulation flow. A volume or a mass

flow meter (installed according to the manufacturer’s instructions) is used to measure the air

flows in the heat transfer medium circuit. To minimize effects at the air flow, the meter is not

allowed to affect the static pressure at the outflow of the heat pump more than ±3Pa. Therefore

it is often necessary to include an extra fan.

The temperatures that shall be measured are: incoming cooling medium temperature, incoming

heating medium and leaving heat transfer medium temperature. The temperature of the

incoming cooling medium is measured by one sensor placed in the center of the air intake. The

temperature of the incoming heating medium is measured by at least four temperature sensors

evenly spread over the air intake. The variation between the highest and lowest temperature

indication shall be lower than 1 K.

The temperature of the leaving heat transfer medium circuit is measured by at least four sensors

evenly spread out at a point where the air is mixed. The mixing device is not allowed to affect

the static pressure of the outflow of the heat pump more than ±3Pa, whereupon it is often

necessary to include an extra fan. Heat exchange between the mixing device and the

surroundings shall be taken into account. The variation between the highest and lowest

temperature indication shall be lower than 1 K.

The data collection starts when “the plant” has operated at least five minutes at steady state

conditions, within the required permissible deviations, see Table 1. The stability is controlled

by continuous measurement at intervals shorter than 1/5 of the stability period, maximum one

minute interval.

Table 1. Maximum permissible deviations from mean value for measured temperatures

and flow rates, SP metod nr 1721

The sampling period shall be at least 10 minutes and the collection of data shall be either

continuous register or measuring by intervals more frequent than 1/5 of the measuring period

(<2 mn). The operation shall be stable also during the measurement period.

When the heat pump operates during conditions where frosting occurs, the capacity test is

performed after a defrost period at the most stable 10-minutes period possible (at least five

minutes after the defrost period).

3.2. Performance calculation method

A bin method is used. The outdoor temperature is measured on site and the temperature

chronicle is binned.

Temperature, flow Maximum permissible deviations from mean

value

tvbin ± 1 K

tvbut ± 1 K

qvvb, qmvb ± 5 %

14

The capacity and electricity consumption of the heat pump is measured with the measurement

method above several times during the heating season. This enables to draw the variation of the

heating capacity of the heat pump with the outdoor temperature.

Measurements are spread across the heating season in order to cover all heating conditions from

more to less rigorous conditions.

3.3. Measurement results

The field study, performed by SP, included a three step procedure consisting of:

1. Questionnaire to about 450 households all over Sweden to gain knowledge about householders’

experiences and perceived appreciation of these units.

2. From the questionnaires, 25 householders were chosen for a thorough investigation of their

heating systems, and an in-depth interview.

3. Five sites were chosen for a one year field monitoring project.

The results from the one year field monitoring study shows that A/A heat pumps perform

relatively well in cold climates that Sweden represents.

The results show that the efficiency of air-to-air heat pump systems lies within a range, with

some corrections, corresponding to earlier data from SP's laboratory tests. The heat pumps in

the investigation returned annual COPs of between 2.3 and 2.6, with an average of 2.5. It is

likely that the annual COP would be higher if also part-load performance was included.

Outdoor temperatures were not greatly different between one site and another, but were

generally higher than for a statistically average year. As far as indoor temperatures were

concerned, it was noted that most of the system owners wanted slightly higher temperatures in

bathrooms and preferably slightly lower temperatures in bedrooms. It was also found that the

temperature in 1½-storey houses was higher on the upper floor than on the lower floor, and that

it was the energy awareness of owners and their tolerance of different temperatures in different

parts of the house that largely determined the overall amount of energy use.

SP's previous experience of laboratory tests show that there may be short-circuiting effects from

outgoing air to incoming air for indoor and outdoor units. It is also known that the indoor unit is

most sensitive to temperature variations. This investigation found that the outdoor unit was also

adversely affected under certain conditions. Air flows can be affected, for example, by bushes

or foliage close to the outdoor unit, while phenomena such as the formation of cold zones

around the outdoor unit on calm winter days were also observed.

One of the points noted in connection with the various field measurements was that the air

filters and the indoor and outdoor units’ heat exchangers needed cleaning. After a simple

control measurement of two systems, with and without air filters, it is expected that the air flow

through the indoor unit will increase by about 10-20%, and performance and efficiency of the

heat pump will increase by about 5-10%, after the air filters and heat exchangers has been

cleaned. The user’s energy awareness together with service and maintenance of a heat pump is

essential for correct operation, good performance and high efficiency.

The measurements included for example the quantities listed below:

• Total electrical energy input to the house (power supply meter from the electricity

supply company

• Electrical energy input to heat pump

15

• Electrical energy input for the additional heaters, also known as supplementary

heating

• Heat power input from the indoor unit and total electrical energy input to the heat

pump on five different occasions

• Indoor air temperature in three different rooms and outdoor temperature

The existing electric meters in the households were utilized for determining the total electrical

energy input to the house. Readings were to some extent made by the home owners, but data

was also provided by the electricity supplier. An electricity meter with a logger was installed to

measure the electrical energy input to the heating system with direct electricity and one for

measuring the in electrical energy input to the heat pump. Data for electric energy was logged

every 5 minutes. Indoor and outdoor temperature was logged continuously every 20 minutes for

all items other than house B, where data was logged every 5 minutes.

Performance tests according to SP method No 1721 were performed on five different occasions.

Measurements were supposed to take place at various outdoor temperatures twice during

spring, twice during autumn and once in winter to give a good spread in outdoor temperature.

Performance testing of air/air heat pumps in field, SP Method No 1721, includes determining

the following quantities in steady state:

• Air flow over the indoor unit

• Air temperature before and after the indoor unit

• electrical energy input

• Air pressure

When the test meets the requirements of the measurement method the heat factor method can

generally be determined with an uncertainty less than 10%. When the measurement period is at

least 10 minutes, with specified settings of the air conditioner, the energy output from the heat

pump on an annual basis can be determined with an uncertainty less than 20%.

Results from measurements and calculations with the annual average during the current period

are shown in the table below. The result is partly dependent on that the data submitted by the

home owners are correct.

Table 2. Result summary, yearly average

Measured magnitudes

A B C D E

Electrical energy input the house WT

[MWh] 17,6 16,5

a. 17,4 9,16 19,2

Electrical energy input to heat pump

Wvpa [MWh] 3,75 2,65

a. 3,96 3,15 3,72

Electrical energy input to additional

heater Wtva

[MWh]

3,28 3,10a. 3,09 0,74 1,00

Air flow over indoor unit [l/s] 103 142 147 124 109

Outdoor temperature, tu

[°C] 7,4 7,8 6,6 8,0 6,8

Indoor temperature, tisov

[°C] 21,7 21,1 19,4 20,1 20,7

Calculated magnitudes

A B C D E

Estimated yearly heat factor, SPFvpa 2,6 2,7 2,5 2,6 2,4

Energy coverage ratio, ETG [%] 75 70 76 92 90

Input electrical energy per m2 c.

98 110 125 53 128

Thermal energy per m2 d.

73 69 95 52 66

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a. Object B is based on readings performed by the power supply company and the home owner, some estimates are made during the performance period.

c. The ratio of the total electrical energy input to the house and the heated surface.

d. The sum of the thermal energy output from the heat pump and additional heat divided by the heated house surface.

Figure 11. Heat pump coefficient of performance, heat capacity and electrical power

input as a function of temperature for object B, measured under maximum capacity

conditions.

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

-10 -5 0 5 10 15

CO

P

0

500

1000

1500

2000

2500

3000

3500

4000

4500

Eff

ekt

(W)

COP

PE

PH

17

4. France

Introduction

Within the framework of the Sepemo projet, several field measurements of field performances

of duct and multi split HP are being carried out by the MD3E company for the French energy

agency ADEME.

The descriptions of the on-going field measurements as well as the results of the monitoring

campaign are not yet available to the SEPEMO project.

4.1. Measurement method

Figure 12. Diagram of MD3E air enthalpy measurement method

In order to compute a seasonal performance factor, the following quantities are measured:

Indoor and outdoor air temperature

Air temperature on inlet and outlet veins of each indoor unit

Humidity on inlet and outlet veins of each indoor unit (necessary to establish the cooling

capacity for reversible units)

Air velocity on inlet vein of each indoor unit (via a hot wire air speed measurement

device)

Electricity consumption

VentilateurCompresseur

Console 1

autres

composants

V

T

T

T T

electricité

V débit

HR Hygrométrie

T température

Unité

extérieure

Pompe

Légende

HR

HR

Console 2...

V

T

T

HR

HR

18

These quantities are measured every 5 or 10 second, then the average values are saved every 10

minutes.

4.2. Performance calculation method

A preparation phase before the test is intended to determine the ratio velocity distribution at the

inlet side of the indoor unit through a multi point measurement. During tests, the multi point

measurement system is removed and the ratio velocity measurement is assumed to be constant.

Flow volume is calculated thank to a velocity-flow volume table which is built at the beginning

of the measurement campaign.

Air velocity is measured at only one point and velocities of all other points are revealed thanks

to the ratio distribution. The air flow rate variations can then be computed from measurements.

Heating energy is computed thanks to the inlet and outlet temperature measurement (and

humidity ratios for the cooling mode).

According to response time of humidity sensor, there are 2 ways for thermal flow calculation.

If the response time is long (more than 1 minute), air enthalpy is calculated every 10 minutes by

using average value of air temperature, humidity and air velocity during this period.

If the response time is short (less than 1 minute), air enthalpy is calculated every 5 or 10

seconds by using measured value o f air temperature, humidity and air velocity. A sum of

calculated air enthalpies during 10 minutes delivers average air enthalpy. This average value is

saved.


The measurement results are not yet available.

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5. Japan Introduction

Only one campaign was identified for Japan for a long term monitoring of the seasonal

performance of heat pumps. The results were published by Tokyo Gas [X].

5.1. Measurement method

The field measurement was realized by Tokyo Gas [X] to measure the heating and cooling

seasonal performance of a split type air to air heat pump with 6 indoor units and 1 outdoor unit

installed in a university campus in suburban Tokyo. The rated COP measured in normative

condition is 2.64 for cooling and 2.9 for heating.

The summer measurement (for cooling COP or EER) was conducted with the indoor setting

temperature of 27 °C, and winter measurement with the temperature of 24 °C during the 3 first

days, then 22°C during the 3 next days and finally 20 °C during the 3 last days. Throughout

measurement, airflow was set in the “strong” mode while ventilation direction was set in the

“no swing” condition.

Dry-bulb and wet-bulb temperature of the inlet and the outlet air flow were measured at all

indoor units with thermocouple (Figure 13) while the air speed was measured with an

experimental set up developed for this study.

Figure 13. Temperature and humidity measurement points in a test by Tokyo gas

Electricity consumption was measured every minute. Acquisition time of temperature, humidity

and velocity measurement is not given.

During the tests, the air flow rate and direction are fixed. On indoor air unit, multi point

measurement of air temperature, humidity and velocity is performed at the outlet and the inlet.

5.2. Calculation method

Heat exchange quantity was calculated by multiplying the inlet and outlet enthalpy difference

and the air flow rate. The air flow rate was calculated by integrating the airflow distribution

according to the speed profile presented for both indoor and outdoor unit below in Figure 14.

20

Velocity measurement is used to determine the ratios of velocity at each point to velocity at

center point, also called the ratio velocity distribution. The air velocities are then corrected, by

maintaining the ratio velocity distribution so that the air flow rate obtained from velocities

integration matches the value given by the manufacturer. By combining measured temperatures

and humidity ratios, the heating energy calculation is then performed.

SCOP was obtained by dividing the heat exchange quantity by the electric power consumption

of indoor and outdoor units.

Figure 14. Wind velocity distribution of air outlet and air inlet.

Air flow rate inlet and outlet distribution were measured to establish an air flow rate ratio at any

point of the inlet/outlet grill to the central point. Air flow of each measured point and its

representing area were calculated. The sum of the calculated airflow rates was adjusted to

match the rated air flow rate for “strong wind” mode.


Results of winter measurements are shown in Figure 15 and in Figure 16 below.

21

Figure 15. Electricity consumption (winter measurement, Indoor: 6F; Outdoor: 9F)

.

Figure 16. Change of COP (winter measurement).

The average SCOP during this test is 0.6. Part load factors are mostly below 20 % of the heat

pump capacity (Figure 17). This is certainly the cause of the very low performance in heating

mode.

22

Figure 17. Relation between outdoor temperature and load factor (winter

measurement).

Results of summer measurement are shown in

Figure 18 and Figure 19 below.

Figure 18. Electricity consumption (summer measurement, Indoor: 6F; Outdoor: 9F)

23

Figure 19. EER (cooling COP) versus time (summer measurement).

The calculated SEER is 1.74. This SEER is low again but better than the heating SCOP. The

part load factors are below 30 % of the heat pump rated capacity (Figure 20).

Figure 20. Relationship between outdoor temperature and load factor (summer

measurement).

24

Discussions and conclusions

Very few field measurements with largely variable performances

Very few field measurements could be identified. In addition, regarding the on-going field

measurements in France, the results are not yet available.

The performances of the air-to-air heat pumps measured vary greatly according to the test

campaign. In Sweden, over 5 air-to-air heat pumps, it was estimated that the HSPF value,

including the electric backup heater lied between 2.4 and 2.7. It is also estimated that this

performance could be slightly undervalued as the part load performance impact is not taken into

account in the methodology used for the in-situ measurement.

Regarding the tests performed in Japan on a commercial split system, very low seasonal

performance values were identified in both cooling and heating mode. The split systems was

largely oversized in both cooling and heating mode and worked all the time at very low load

ratios. In addition, it was not using an inverter controlled compressor to match efficiently the

capacity to the load.

All long term field measurements identified use the air based measurement method with the

measurement of indoor air flow rate at indoor unit(s). In the case of the French and Japanese

field measurements, the measurement of the air flow at indoor units can be done in continuous

but measurement is reputed uncertain while for the method used in Sweden, measurement

cannot be done continuously as the air flow measurement apparatus cannot be left in the living

area (being very cumbersome) but is probably more accurate than the use of hot wires.

Potential issues with identified HSPF measurement methods

Measurement methods for HSPF of air-to-air HP in real life conditions can be classified in two

categories [4]: external and internal methods. In the former, the heating capacity measurement

is based on those of the air flow rate and of the air enthalpy. In the latter, it is based on the

measurements of the refrigerant fluid flow and properties.

The main limitation of the external methods used in France and in Japan is the unknown

accuracy. It is thought to be low, as the heating capacity is proportional to the air flow which is

determined via the air velocity measurement, a measure which uncertainty is supposed to be

relatively high.

On the reverse, the method used in Sweden is thought be relatively accurate as regards the air

flow measurement at the indoor unit and thus regarding the heating capacity. Nevertheless, the

accuracy of the method to compute the HSPF is less certain as the measurement cannot be done

continuously because of the cumbersome apparatus to make the precise air flow measurement.

Possible alternative internal methods

An internal method tested in the laboratory is presented in [5]. The refrigerant flow rate is

measured by a Coriolis flow meter installed at the exhaust side of the condenser (in heating

mode). The refrigerant enthalpies are computed from the measurement of the temperatures and

pressures at the supply and exhaust of the condenser. Two air-to-air HPs were tested in the

25

laboratory in steady-state conditions. In comparison with the calorimeter method, the internal

method gives relatively good accuracy. The maximal relative difference between these two

methods is about 6.8 % in heating mode. Measurement uncertainties of both methods are not

shown. The main drawback of this method is the difficult installation of the flow meter in situ :

this method cannot be envisaged for existing heat pumps.

In order to avoid the installation of a coriolis flowmeter, which cannot be done in-situ, it is also

possible to use the compressor to determine the refrigerant flow rate by using the energy

balance of the compressor. The compressor heat loss factor is assumed to be constant and

known. The refrigerant flow rate can then be computed as:

1

, , , ,

com

r

r com ex r com su

Pm

h h

where P is the electric power, h is the specific enthalpy, subscripts r, com, ex, and su refer to

refrigerant, compressor, exhaust side and supply side respectively. The enthalpies are

determined via measurements of pressure and temperature.

[6] provides examples using this "internal" method. 110 tests on 13 water-to-water or air-to-

water HPs were tested either in the laboratory or in situ. Accuracy is better than ±15 %

compared with the enthalpy measurements on the water side. The main advantage of this

method is to eliminate the need for a flow meter. But the drawbacks are that (1) accuracy is

low, especially in dynamic conditions, due to the unmeasured factor ; (2) the method cannot

be used for HP with a gas injection compressor; (3) the difficulty of the installation of the

pressure sensor in situ for residential HPs which usually do not have pressure plugs at both high

and low pressure sides.

The difficult choice of a methodology for the SEPEMO project

The review of the possible HSPF in-situ methods shows that there is no fully satisfying in situ

measurement method for the HSPF of residential air-to-air heat pumps. On the one hand,

external methods may be used for the HSPF test in the field over a long time period but their

accuracy has been unknown. On the other hand, internal methods using a refrigerant flow meter

provide acceptable accuracy in steady state conditions but it is difficult to apply these methods

in the field and, in addition, their accuracy in dynamic conditions is unknown.

As a conclusion, it has been decided, for the SEPEMO project, to use the measurement on

available air based measurement methods. In the meanwhile, Armines, EdF R&D and SP have

been working in order to establish the accuracy of all possible measurement methods in view of

elaborating an accurate and convenient measurement method for in-situ measurement.

Laboratory work [3] and [7] are the first steps in that direction.

26

References [1] Roger Nordman, SP Technical research institute of Sweden, Experiences from field measurements

on Air-air heat pumps in Sweden, National report to Deliverable 3.1 of the SEPEMO build project.

[2] Per Fahlén, Christer Kjellgren, Performance testing of air- to air heat pumps in field applications,

SP metohd nr 1721, Issue 2: 1995-10-03, SP AP 1994:51

[3] Toru, Ichikawa, Won, Anna et Yoshida, Satoshi, Tokyo Gas, Study on Running Performance of a

Split-type Air conditioning System Installed on a University Campus in Subruban Tokyo. 2007. Climat

2007 WellBeing Indoors.

[4] C.T. Tran, P. Rivière, D. Marchio, C. Arzano-Daurelle, Refrigerant-based measurement method of

heat pump seasonal performances, International Journal of Refrigeration, Available online 30 March

2012, ISSN 0140-7007, 10.1016/j.ijrefrig.2012.03.010.

[5] Teodorese, V., Detroux, L., & Lebrun, J. (2007). Testing of a room air conditioner - High

class RAC test results-Medium class RAC test results. Liège: Université de Liège.

[6] Fahlén, P. (2004). Methods for commissionning and performance checking of heat pumps

and refrigeration equipment. Gothenburg: Chalmers University of Technology.

[7] Jactard A., Li Z., Investigation of field methods for evaluation of air-to-air heat pump

performance, Department of Energy and Environment, Division of Building Services

Engineering, Chalmers University of Technology, Göteborg, Sweden 2011.

27

List of figures

Figure 1. Operation principle of air to air heat pump .................................................................... 4

Figure 2. Reversible circuit of HP – Heating mode (Source Costic) ............................................ 5 Figure 3. Reversible circuit of HP - Cooling mode (Source Costic)............................................. 5 Figure 4. Multi-split air conditioners (source LG) ........................................................................ 5 Figure 5. Types of indoor units (source Mitsubishi Electric) ....................................................... 6 Figure 6. VRF systems (left - source Daikin outdoor units, right – source Toshiba system

overview) ....................................................................................................................................... 7 Figure 7. Daikin VRF complete solution for heating, cooling, ventilation and air curtain

management .................................................................................................................................. 8 Figure 8. Roof top air conditioner (source Carrier) ...................................................................... 8

Figure 9. Boundaries of the HP system, SP metod nr 1721 ........................................................ 12 Figure 10. Example of the arrangement of the measurement equipment according to SP method

1721. ............................................................................................................................................ 12

Figure 11. Heat pump coefficient of performance, heat capacity and electrical power input as a

function of temperature for object B, measured under maximum capacity conditions. ............. 16 Figure 12. Diagram of MD3E air enthalpy measurement method .............................................. 17 Figure 13. Temperature and humidity measurement points in a test by Tokyo gas ................... 19

Figure 14. Wind velocity distribution of air outlet and air inlet. ................................................ 20 Figure 15. Electricity consumption (winter measurement, Indoor: 6F; Outdoor: 9F) ................ 21

Figure 16. Change of COP (winter measurement). ..................................................................... 21 Figure 17. Relation between outdoor temperature and load factor (winter measurement). ........ 22

Figure 18. Electricity consumption (summer measurement, Indoor: 6F; Outdoor: 9F) ............. 22 Figure 19. EER (cooling COP) versus time (summer measurement). ........................................ 23 Figure 20. Relationship between outdoor temperature and load factor (summer measurement).

..................................................................................................................................................... 23

List of tables

Table 1. Maximum permissible deviations from mean value for measured temperatures and

flow rates, SP metod nr 1721 ...................................................................................................... 13

Table 2. Result summary, yearly average ................................................................................... 15

seasonal performance factor and monitoring for heat pump...

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