XV EUROPEAN CONFERENCE MILANO 7th-8th JUNE 2013 CSG

Latest Technology in Refrigeration and Air Conditioning Under the Auspices of the PRESIDENCY OF THE COUNCIL OF MINISTERS

Performance and economy analysis of a R744 heat pump system with an ambient air-cooled gas cooler

and a ground heat exchanger under different climatic conditions

Haitao HU, Ph.D.,

Visiting researcher (Norwegain Universiyt of Science and Technology)

Lecturer (Shanghai Jiao Tong University)

Contents

1. Background

2. Existing method to decrease earth energy unbalance for HP

3. New concept to decrease earth energy unbalance using R744 heat pump system

4. Performance and economy analysis of R744 system

5. Conclusions

1. Background: Motivation

Energy load balance for Earth???

R134a system R744 system

Q1: The optimized air cooling load proportion?Q2: The influences of different factors on system performance? Earth energy balance, Investment cost, operation cost, Operation condtion?

Air cooling load=

Heat recovery system

2. Existing Method to decrease energy unbalance

Typical building in China (archives building)

Basic design parameter of the building

Parameters Values Parameters ValuesBuilding area 8000m2 Indoor design temperature 20 oCNumber of floors 4 Indoor design humidity 50%Heat transfer coefficient of exterior walls

0.46W/ m2K Heating load 238.0 kW

Heat transfer coefficient of exterior windows

1.18W/ m2K Cooling load 545.6 kW

with heatrecovery system

Unbalance degree is 30% Unbalance degree is 16%

Q: 1. 30%16%, 0??2. 90% 0????

2. Existing Method to decrease energy unbalanceUnbalance of earth energy for GSHP:

3. New concept to decrease energy unbalance ------(CO2 gas cooler + ground HX)

Air-cooledGas cooler

3. New concept to decrease energy unbalance ------ Mathematic modeling

2,isen 1

totcomp

cm h hW

2 2 4

2 2 2 2tot

1 1 1 1

0.26 0.7952 0.2803 0.0414 0.0022P P P P

P P P P

Compressor:

S vol 1m V N

Gas cooler:

3/1PrRe jNu 428.04

t

l32

l

p1D )()(tan)(Re324.0

CN

P

P

P

Fj jjjj

11

2 2

1210

1

2

f

A

AGP

mc

c

0916.03796.1

c

h35.5

t

0e

3

t

P21D )())((log)()(tanRe01915.0

C

ND

D

A

A

P

Ff fff

Ground Heat exchanger:

2

1cos sin

1 1cos 1 sin11 cos sin1

Ph h Z

PZ h Z P h ZPP h h ZP

3. New concept to decrease energy unbalance -----Validation of modeling

Ambient Temp.

Inlet Pres.

Inlet Temp.

Outlet Temp.

Mass Flow of R744

Pressure Drop of R744

Exp. heat capacity

Predicted heat capacity

oC Bar oC oC kg/h Bar kW kW 25 75 88 27 2641.54 0.03 171 187

25 75 88 25.4 2565.98 0.028 171 161

30 78.5 88 32 6046.27 0.12 342 362

30 78.5 88 30.4 5704.51 0.11 342 331

35 92 88 37 11184.38 0.3 570 583

45 85 88 47 30857.14 237 395 370

45 120 88 47 11074.29 50 240 258

45 120 140 45.4 18120 38 335 319

Deviation is Within 10%

1) Comparison between different operation methods[Alternate or coupled operation of gas cooler and GX]

4. Performance and economy analysis of R744 system

2) Effect of indoor temperature

3) Effect of air cooling load proportion

4) Effect of climates

5) Effect of ground heat exchanger depth

6) Comparison between R744 heat pump system and the existing R134a system

1) Comparison between different operation methods [Shanghai, China]

Operation method (alternate operation)

4. Performance and economy analysis

Coupled Operation of GC+GX:

  GX cooling loadGJ

GX heating loadGJ

Unbalance GX Max. cooling load

kW

GX Max. heating

loadkW

Operation cost

(X104 RMB)

GX 3445.5 2430.6 29.5% 545.6 238.0 41.12

GX+Gas cooler[Alternate operation] 2430.6 2430.6 0 545.6 238.0 39.67

GX+Gas cooler[Coupled operation]

2430.6 2430.6 0 212.8 238.0 38.69Decrease 60%

Investment X104 RMB

Cooling system +Boiler

Air source heat pump

R134aGround source

heat pump

R744 Ground source heat

pump with gas cooler [alternate operation]

R744 Ground source heat

pump with gas cooler [Coupled operation]

Instrument 123.02 159.76 124.68 149.00 140.00

Transformer device 14.54 11.56 7.05 7.50 7.1

Installation 33.91 49.13 37.40 38.50 38.0

Natural Gas 8.74 0 0 0 0

Ground HX 0 0 134.40 134.40 58.63

Total 183.21 219.25 316.23 330.20 260.43

Decrease 18%

4. Performance and economy analysis 1) Comparison between different operation methods [Shanghai, China]

  GX cooling loadGJ

GX heating loadGJ

Unbalance GX Max. cooling load

kW

GX Max. heating

loadkW

Operation cost

(X104 RMB)

GX 3445.5 2430.6 29.5% 545.6 238.0 41.12

GX+Gas cooler[Alternate operation] 2430.6 2430.6 0 545.6 238.0 39.67

GX+Gas cooler[Coupled operation]

2430.6 2430.6 0 212.8 238.0 38.69

Decrease 6%

4. Performance and economy analysis 2) Effect of indoor temperature on earth energy unbalance and investment cost

4. Performance and economy analysis 3) Effect of air cooling load proportion on earth energy unbalance, investment cost and operation cost

Recommended operation condition:20 oCAir cooling load proportion is 30%

4. Performance and economy analysis

4) Effect of climates on earth energy unbalance, investment cost and operation cost

Climate System GX Max. cooling

loadkW

GX Max. heating

loadkW

ShanghaiOriginal 545.6 238.0

GX+GX 212.8 238.0

Guangzhou

Original 554.4 221.2

GX+GX 27.4 221.2

New Delhi Original 775.5 237.3

GX+GX 154.0 237.3

4. Performance and economy analysis

5) Effect of ground heat exchanger depth on system investment cost

Reason:The heat flux per meter of heat exchanger decreases with the increasing depth.

In a long heat exchanger, temp. difference between fluid and backfill in the lower part of GX decreases, resulting in less heat transferred from water to backfill for per meter of heat exchanger.

6) Comparison between R744 heat pump system and the existing R134a system

4. Performance and economy analysis

R744 heat pump system R134a heat pump system

Shanghai:30%

Guangzhou:90%

0%

0%

Investment cost:Shanghai: Decrease 18%; Guangzhou: Decrease 14%

Operation cost:Shanghai: Decrease 6%Guangzhou: unchangeable

1) Numerical model for CO2 heat pump with gas cooler and ground heat exchanger was developed.

2) Trough adjusting the air cooling load proportion, the unbalance of earth energy can always be decreased to zero.

3) By using air-cooled gas cooler, the investment cost and operation cost can be decreased.

4) With the increase of tube depth of GX, the investment cost will be increased.

5. Conclusion

Thank you very much!