Research on Compound Condensation / Evaporation of Four Functional Heat Pump Performance

Xiaoheng Zhang1,a,*, Guangcai Gong1,b, Jianyong Zhou2,c

1Civil Engineering College, Hunan University, Changsha，Hunan，China

2 Huahui Engineering Design Group CO. LTD, Shaoxing, Zhejiang, China

azhangxiaoheng2008@126.com,bgcgong2000@yahoo.com.cn,czjyong2009@126.com

Keywords: compound condensation / evaporation of four functional heat pump; experimental test; coefficient of performance.

Abstract. Compound condensing heat pump combines the advantages of heat pump technology and

condensing heat recovery technology. It takes full account of the common infrastructure in the

cooling and heat source system and greatly increases equipment utilization ratio. It also recycles

condensing heat to produce sanitary hot water efficiently while ensuring cooling and heating of heat

pump to achieve the same effect. The distinctive technical features of the compound condensation /

evaporation of four functional heat pump ensure its efficient and reliable operation. This heat pump

system runs in several models throughout the year,which include the refrigeration mode,

refrigeration&domestic hot water mode, domestic hot water mode and heating mode. The

performance in refrigeration mode and refrigeration&domestic hot water mode is studied by a

designed experiment is done and the an explicit analysis is made.

By comparing the results of simlation and experiment,an agreement can be shown clearly.

Therefore,the final conclusion is drawn:the performance of compound condensation / evaporation of

four functional heat pump is improved over the traditional heat pump.It is worthy to further promote

for the sake of energy saving.

Introduction

Since the beginning of 20th century,there has been a substantial increase in the energy consumption

around the world.The energy crisis human facing is getting worse nowadays[1,2].China is the second

largest energy consuming country in the world and its energy supply and demand imbalance is acute.

It can be shown by some Relevant data that building energy consumption accounts for 20.7% of the

total social consumption and HVAC energy consumption accounts for 50%～60% of the building

energy consumption[3,4].Therefore, the research on the new energy-saving technology in the HVAC

field is very important.

Air source heat pump is widely used owing to its initial investment, convenient installation and

suitability for medium and small public buildings[5].However, the condensing heat exhausted from

the air-source heat pump directly into the atmosphere in the summer is not only a waste of energy, but

also causes the city's heat pollution. In addition, the heat pump will result in unsatisfactory heating

effect while its air-cooled evaporator frosts extremely in the low temperature and high humidity

weather condition [6]. Compound condensing heat pump combines the advantages of heat pump

technology and condensing heat recovery technology. It takes full account of the common

infrastructure in the cooling and heat source system and greatly increases equipment utilization ratio.

It also recycles condensing heat to produce sanitary hot water efficiently while ensuring cooling and

heating of heat pump to achieve the same effect. The design of the compound condensation /

evaporation of four functional heat pump can be seen as the following figure.

The technical characteristics of the compound condensation / evaporation of four functional heat

pump unit are as follows:the condensing heat recovery is carrid out by the heat recovery plate heat

exchanger which is connected in series between the outlet of compressor and the inlet on the

high-pressure side of four-way directional control valve;the hot water in which the water is heated

recurrently by the water pump is adopted to supply domestic hot water ;The fluid bypass pneumatic

Key Engineering Materials Vol. 517 (2012) pp 875-880Online available since 2012/Jun/26 at www.scientific.net© (2012) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/KEM.517.875

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control pipe is adpoted to ensure the four-way directional control valve a normal working position in

the condition that the heat recovery device is added into the unit;in the summer working condition, air

cooled heat exchanger with control solenoid valve connected on its two terminals and heat recovery

plate heat exchanger constitute air &water cooled compound condensation module;in the winter

heating condition, the air &water cooled compound evaporation module consists of the heat

exchanger on the ground-source side and air cooled heat exchanger which is connected in parallel

with it by a solenoid valve; variable condition by-pass pipe I and II make the whole unit transform

various working conditions flexibly and ensure the high efficiency and reliability of the unit

operation[7].

Fig.1. Structure schematic diagram of compound condensation / evaporation of four functional

heat pump

1-compressor;2,3,6,7,8,11,12- two-way solenoid valve;4- heat recovery plate heat exchanger；5-

four-way directional control valve；9-(ground-source side)plate heat exchanger；10- air cooled heat

exchanger；13- thermal expansion valve；14-(air conditioner water side)plate heat exchanger；15-

hot water tank；16,17,18- water pump；19- one-way valve；20- flash chamber；21- dry filter；22-

buried pipe heat exchanger；23- bypass pneumatic control pipe；24- pilot valve；I,II- variable

condition by-pass pipe. Annotation: two-way solenoid valve 2 and 6 never open simultaneously; two-way solenoid valve

group (7,12), two-way solenoid valve group(8,11) and two-way solenoid valve 6 never open

simultaneously.

The compound condensation / evaporation of four functional heat pump unit has four kinds of

operation modes all the year round.

1. Refrigeration mode:condesation is implemented by air cooled condensation module in this mode

which serves when buildings need cool capacity.In this condition, air conditioning cooling water is

prepared by plate heat exchanger(14).The flow path of refrigerant is:

1→5→10→19→13→20→21→19→14→5→1.

2. Refrigeration&domestic hot water mode: condesation is implemented by air &water cooled

compound condensation module.During some time in summer,when buildings need air conditioning

refrigeration as well as some domestic hot water,the unit can make full use of condesation heat to

prepare the sanitary hot water. The flow path of refrigerant is:

1→4→5→10→19→13→20→21→19→14→5→1.

Meanwhile, the high pressure and high temperature refrigerant gas discharged from compressor

directly goes into heat recovery plate heat exchanger(4)and heat the sanitary hot water to the

demanded temperature by pump(16).Then the prepared domestic hot water is provided to the user by

the hot water tank (15).

876 Novel and Non-Conventional Materials and Technologies for Sustainability

3. Domestic hot water mode：water cooled condensation module is adopted in the mode which is

applied to the situation that buildings need cooling capacity as well as a lot of domestic hot water in

summer or buildings need no cooling capacity but a lot of domestic hot water in transition season. The

flow path of refrigerant is:

1→4→5→19→13→20→21→19→14→5→1.

At this time,the fan of air cooled heat exchanger is turned off. After the high pressure and high

temperature refrigerant gas discharged from compressor condenses in the heat recovery plate heat

exchanger(4),it directly goes into variable condition by-pass pipe II.Then it is throttled down at

thermal expansion valve and goes back into compressor after exchanging heat in the plate heat

exchanger on the air conditioner water side. Under the condition that there is no need for air

conditioning water,the air conditioning water can exchange heat with soil by the heat exchanger on

the ground source side and the cooling capacity is discharged to the soil.

4. Heating mode:this mode is applied to builings only with the heating need.It has two working

conditions.One is air cooled evaporative pattern which is suitable to the situation that the air

temperature is higher than apparatus dew point.There is no frost on the air cooled heat exchanger at

the time. The flow path of refrigerant is:

1→5→14→19→13→20→21→19→10→5→1;

The other is water cooled evaporative pattern with the flow path of refrigerant:

1→5→14→19→13→20→21→19→9→5→1.

When the air temperature is lower than apparatus dew point,the air cooled heat exchanger is prone

to frosting and have an adverse impact to the unit efficiency.Therefore,evaporating heat exchange is

implement by ground source heat exchanger.

Experimental platform

The compound condensation / evaporation of four functional heat pump consists of air handling

system, water sysstem and control system.

Air handling system.This system is acquire by making a technological transformation to a

CXAH0125A type air cooled heat pump unit according to the structure schematic diagram. Its main

technichal specification is shown by table1.

Table1 CXAH0125A type air cooled heat pump unit technichal specification Item Unit /type Paramater

R capacity kW 32

H capacity kW 38.5

Compressor

type Hermetic scroll

quantity 1

Input power(R/ H)(kW) 11.2/10.7

runcurrent(R/ H)(A) 19.2/18.8

Starting Current (A) 135

Chilled water pump

type multiple centrifugal

Input power (kW) 1

delivery lift(mH2O） 18

Evaporator type multiple centrifugal

flow capacity(R/ H) (L/min) 91.7/110

Frozen oil type / filling volume (L) 160P/3.3

Cooling medium type / filling volume（kg） HCFC-22/8.15

Turnover pipe（PT） 1-1/4 ——

R:refrigeration H:heating

Key Engineering Materials Vol. 517 877

Heat recovery plate heat exchanger:MTB100 type plate heat exchanger;65 heat tablets, 50℃ outlet

water temperature; coefficient of heat transmission 948w/m2℃; 7.2℃log-heat transfer temperature

difference;5.5 m2 heat transfer area.

Water cooled evaporating plate heat exchanger: MTL035 type plate heat exchanger;39 heat tablets;

7℃outlet water temperature; coefficient of heat transmission 932.7w/m2 ℃;5.1℃log-heat transfer

temperature difference;1.3 m2 heat transfer area.

Solenoid valve: II-two normally closed solenoid valve of Svseries;temperature range -40℃～110℃;

Coil voltage 220V.

Water system. Cold water tank.Inner pot:volume 2 m3; wall thickness 0.08m;material SUS304;

outward pot: wall thickness 0.05m, insulation:Polyurethane foaming layer.The drainage pipe is near

to the bottom of inner pot and the overflow pipe is near to the top.The buried pipe heat exchanger is

designed to uint type exchanger with 3 parts.Its two terminals are static pressure current tanks and the

middle is the heat exchange pipe whose length is determined according to the specific situation. The

rest main eqipments of the water system are listed in the table2.

Table2 The rest main eqipments of the water system Item Type Number Item Type Number

Water pump Y80-22/1.1KW 1 Galvanizedironpipe DN25 120 m

Water pump PH-40E/90W 1 Galvanizedironpipe DN32 2 m

Water pump JY7112/370W 1 flowmeter mechanicalDN40 9

Copper valve DN20 4 Flange DN40 43

Copper valve DN25 10 Flange DN25 56

Copper valve DN40 9 insulation Armaflex&reg 1.2m3

Automatic vent DN20 4 BVwire 10mm2 100m

Copper model Y

filter DN25 1 BVwire 10mm

2 100m

Copper model Y

filter DN40 3 nonreturn valve DN25 1

Sluice valves DN15 2 nonreturn valve DN40 2

Results and discussion

Experimental study on the performance of compound condensation / evaporation of four functional

heat pump in refrigeration & domestic hot water operating mode is conducted in this paper.

Changes in parameter such as compressor suction and discharge gas temperature, omestic hot

water temperature, coefficient of refrigeration performance (COPa), coefficient of domestic hot water

performance (COPw),coefficient of combined performance(COPa+w) is acquired by the experimental

test. In this paper, the unit coefficient of performance is defined as follows [8]:

powrerInput

capacityCoolingCOPa = (1)

powerInput

gainheatwaterhotDomesticCOPw = (2)

powerInput

gainheatwaterhotDomesticcapacityCoolingCOP

wa

+=

+ (3)

878 Novel and Non-Conventional Materials and Technologies for Sustainability

Unit test in the refrigeration mode.Test conditions: Chilled water pump flow capacity

101.1L/min;water quantity of cold water tank 2t;outdoor temperature tw=32.8℃;outdoor relative

humidityФw=67.5%.

Fig.2. Time-varying compressor suction and

discharge gas temperature in refrigeration mode

gragh

Fig.3. Time-varying COPa in refrigeration mode

temperature gragh

Unit test in refrigeration&domestic hot water mode. Test conditions: Chilled water pump flow

capacity 101.1L/min;hot water pump loop flow capacity 60L/min;hot water tank initial temperature

24.1℃,water quantity 0.8t;outdoor temperature tw=30.5℃;outdoor relative humidityФw=69.1%.

Fig.4. Time-varying compressor suction and

discharge gas temperature in refrigeration

&domestic hot water mode gragh

Fig.5. Time-varying hot water tank

temperature in refrigeration &domestic hot

water mode gragh

Fig.6. Time-varying temperature difference of inlet

and outlet in the heat recovery plate exchanger in

refrigeration &domestic hot water mode gragh

Fig.7. Time-varying coefficient of performance

in refrigeration &domestic hot water mode

gragh

Discussion on the results.By the figures we can see:

1. Refrigeration mode.Compressor discharge gas temperature is around 95℃ and suction gas

temperature is around 25℃.They are not varying over time. (Fig.2)Therefore,the added heat recovery

plate heat exchanger has no adverse impact to the normal refrigeration of the unit.The coefficient of

the unit performance maintains around 2.85(Fig.3) and the refrigerating effect of the unit is good.

Key Engineering Materials Vol. 517 879

2. Refrigeration &domestic hot water mode . Compressor discharge gas temperature is low in the

beginning and then rises gradually.It tends to stabilize finally. Compressor suction gas temperature

declines slightly over time. (Fig.4)

The temperature of domestic hot water in the tank rises fast at first.Then the rising turns slower. It

tends to stabilize finally. Besides,in this operating mode,it only takes 1 hour to heat 0.8t hot water

from 24℃ to around 50℃.This can meet well the need of domestic hot water.It indicated that the

recovered heat comprises not only sensible heat of overheating zone but aslo some hidden heat in

mushy zone. (Fig.5)

During the short beginning time,the temperature difference of inlet and outlet in the heat recovery

plate exchanger becomes larger gradually owing to the increased exchanging heat.And it diminishes

over time with the rising temperature of domestic hot water. It is can be seen from the graph that the

largest temperature difference comes to 5.5℃ when the loop flow capacity of hot water pump is

60L/min. (Fig.6)

The COPa maintains around 3.Contary to Fig.3, when the unit operates in this mode, it improves

slightly in contrast to the refrigeration mode.It is because that subcooling phenomenon makes the

compressor input power reduce when the heat recovery condensor is added to the unit. The

coefficient of refrigeration performance goes down with the rising temperature of water in the hot

water tank. The COPw is around 1.3 and up to 1.8.Its change trend complies with the temperature

difference of inlet and outlet in the heat recovery plate exchanger.The COPa+w improves by 50% than

the coefficient of performance in the refrigeration mode.The time-varying reduction of COPa leads to

its reduction.

Summary

In this paper,an explicit introduction is made to the compound condensation / evaporation of four

functional heat pump unit involving its structure design, technical characteristics and the four kinds of

operating mode.A test experiment is done for t compound condensation / evaporation of four

functional heat pump and a detailed anynasis of the performance characteristics of the refrigeration

operating mode and the refrigeration&domestic hot water mode in the experimental platform which

consists of air handling system, water sysstem and control system is made. On basis of all the above,it

is can be drawn that compound condensation / evaporation of four functional heat pump unit

improves the traditional heat pump not only in the added function but aslo in the coefficient of

performace.If it’s technique can be promoted further,it will be very helpful to mitigate energy crisis.

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880 Novel and Non-Conventional Materials and Technologies for Sustainability

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