1. 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)

2. 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

3. 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=

4. 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 Values
Building area 8000m2
Indoor design temperature 20 o
C
Number of floors 4 Indoor design humidity 50%
Heat transfer coefficient
of exterior walls
0.46W/ m2
K Heating load 238.0 kW
Heat transfer coefficient
of exterior windows
1.18W/ m2
K Cooling load 545.6 kW

5. with heat
recovery system
Unbalance degree is 30% Unbalance degree is 16%
Q:
1. 30%16%, 0??
2. 90% 0????
2. Existing Method to decrease energy unbalance
Unbalance of earth energy for GSHP:

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

7. 3. New concept to decrease energy unbalance
------ Mathematic modeling
( )2,isen 1
tot
comp
cm h h
W η
−
=
g
g
2 2 4
2 2 2 2
tot
1 1 1 1
0.26 0.7952 0.2803 0.0414 0.0022
P P P P
P P P P
η
       
= − + − + − ÷  ÷  ÷  ÷
       
Compressor:
S vol 1m V Nη ρ= × × ×
g
Gas cooler:
3/1
PrRe⋅⋅= jNu
428.04
t
l32
l
p1
D )()(tan)(Re324.0 C
N
P
P
P
F
j jjjj
θ=
( ) 











−++⋅=∆ 11
2 2
1210
1
2
ρ
ρ
σ
ρ
ρ
ρ
f
A
AG
P
mc
c
0916.03796.1
c
h35.5
t
0
e
3
t
P21
D )())((log)()(tanRe01915.0 C
−−
= N
D
D
A
A
P
F
f fff
θ
Ground Heat exchanger:
( ) ( )
( ) ( )
( ) ( )
( )2
1
cos sin
1 1cos 1 sin
11 cos sin
1
P
h h Z
PZ h Z P h Z
PP h h Z
P
β β
θ β β
β β
 −
− 
+ = − × −
− − + + 

8. 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
o
C Bar o
C o
C 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%

9. 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

10. 1) Comparison between different operation methods [Shanghai, China]
Operation method (alternate operation)
4. Performance and economy analysis
Coupled Operation of GC+GX:
GX cooling
load
GJ
GX heating
load
GJ
Unbalance GX Max.
cooling load
kW
GX Max.
heating
load
kW
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 60%

11. Investment
X104
RMB
Cooling
system
+Boiler
Air source
heat pump
R134a
Ground 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
load
GJ
GX heating
load
GJ
Unbalance GX Max.
cooling load
kW
GX Max.
heating
load
kW
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%

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

13. 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 o
C
Air cooling load proportion is 30%

14. 4. Performance and economy analysis
4) Effect of climates on earth energy unbalance, investment cost and operation cost
Climate System GX Max.
cooling
load
kW
GX Max.
heating
load
kW
Shanghai
Original 545.6 238.0
GX+GX 212.8 238.0
Guangzho
u
Original
554.4 221.2
GX+GX
27.4 221.2
New Delhi
Original 775.5 237.3
GX+GX 154.0 237.3

15. 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.

16. 6) Comparison between R744 heat pump system and the existing R134a system
4. Performance and economy analysis
R744 heat pump systemR134a heat pump system
Shanghai:
30%
Guangzhou:
90%
0%
0%
Investment cost:
Shanghai: Decrease 18%; Guangzhou: Decrease 14%
Operation cost:
Shanghai: Decrease 6%
Guangzhou: unchangeable

17. 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

18. Thank you very much!