Presentazione dell'Ing. Nicolandrea Calabrese (ENEA) al XVI Convegno Europeo il 12 giugno 2015 - 2a sessione

1. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
“Development of CO2 heat pump for DHW production”
CASE STUDY: CO2 heat pump tested at ENEA CASACCIA Research Centre (ROMA)
XVI EUROPEAN CONFERENCE Milan, June 12th 2015
Scientific referents:
Eng. Nicolandrea Calabrese
Eng. Paola Rovella
Eng. Raniero Trinchieri
Info: andrea.calabrese@enea.it
www.climatizzazioneconfontirinnovabili.enea.it

2. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
EUROPEAN PROJECT: Next Heat Pump Generation working with natural fluids
R&D WORKING ORGANIZATION: 13 partners
CASES STUDY OF THE PROJECT: three R290 HPs AND two CO2 HPs
(Project duration from December 2012 to December 2016)
“This project has received funding from the European Union’s Seventh Programme for research, technological development and demonstration
under grant agreement No [307169]”.
Coordinator:

3. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
THE CO2 HPs PROTOTYPE
OBJECTIVES OF THE PROJECT FOR CO2 HPs DEVELOPMENT:
• Diffusion of Natural Refrigerant: (CO2 has ODP = 0 and GWP = 1) alternative according to the
European Regulation (UE) N° 517/2014 (F-Gas Regulation);
• low Carbon footprint (20% improvement in TEWI);
• high efficiency (10-20% more than the current state of the art HFCs/HFOs or sorption heat pumps);
• costs very similar or only slightly higher than existing systems (10%).
• high capacity heat pump;

4. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
THE HP TEST FACILITY: ENEA CALORIMETER
MAIN TECHNICAL FEATURES
• temperature range: -15°C/+35°C (± 1°C);
• relative humidity range: 10% - 95% R.H. (into the
range +10°C÷+35°C with precision: ±3%…± 5% R.H);
• mobile pedestal to support the control probes;
• pressure compensating valve;
• maximum thermal power: 50 kW;
• Test according UNI EN 14511.
DIMENSIONS: 4900x5700x4800 mm;
VOLUME: 120 m3.
30 kW CO2 PROTOTYPE (AIR-WATER)
FOR DHW IN TEST

5. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
30 kW CO2 PROTOTYPE FOR DHW: EXPERIMENTAL RESULTS
0.58
0.6
0.62
0.64
0.66
0.68
0.7
0.72
0.74
-10 0 10 20 30 40
10
15
20
30
40
50

g
[-]
T
amb
[°C]
T
in water
[°C]
Global efficiency ηg vs. ambient temperature
(parameter inlet water temperature)
0.75
0.8
0.85
0.9
0.95
1
1.05
200 400 600 800 1000 1200 1400
80
85
90
95
100
105

GC
[-]
G
water
[kg/h]
P
oCP
[bar]
Gas cooler efficiency εGC vs. water mass flow rate
Gwater (parameter compressor discharge pressure)
ηg = [GCO2 (houtCPis – hinCP)]/Wel
Minimum and maximum values of the main experimental and calculated parameters.
Ambient
Temp.
Tamb
Water Temp.
GC inlet
Tin water
Water Temp.
GC outlet
Tout water
Water Mass
flow
Gwater
CO2 Temp.
GC inlet
TCO2inGC
Low
pressure
pev
High
pressure
poCP
Gas cooler
efficiency
εGC
Thermal
capacity
QGC
[°C] [°C] [°C] [l/h] [°C] [bar] [bar] [-] [kW]
MIN -10 10 55 250 100 23 76 0.78 11
MAX +35 55 80 1400 167 47 106 1.00 32
εGC = (hinGC-hoGC) / (hinGC-homin)

6. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
30 kW CO2 PROTOTYPE FOR DHW: EXPERIMENTAL RESULTS
ToCP vs. CO2 suction superheating
(parameter IHE efficiency) The ToCP increases with superheat as it is
shown; in particular in some tests ToCP
reaches very high values, higher than
compressor maximum operating
conditions, when the efficiency of
regenerative IHE, εIHE, is very high too
and very close to 1. This very high εIHE
caused the compressor working with
high superheating.
Reduction of IHE efficiency (εIHE)

7. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
30 kW CO2 PROTOTYPE FOR DHW: EXPERIMENTAL RESULTS
Tev vs. Tamb
(parameter inlet water temperature)
-15
-10
-5
0
5
10
15
-10 -5 0 5 10 15 20
10
15
20
30
40
50
T
ev
[°C]
T
amb
[°C]
T
water in
[°C]
Possible FAN
modulation
ABOUT FANS : The speed modulation occurs only at high ambient
temperatures. At these temperatures, their speed decreases to allow the
machine to have an evaporation temperature below 12 ° C
Tin water [°C]

8. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
30 kW CO2 PROTOTYPE FOR DHW: IMPROVEMENTS OF EVAPORATOR
The EVAPORATOR must be optimized improving the air
distribution, using fan-shroud facing upwards, and reducing the
electrical fan consumption using EC motor fan.

9. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
30 kW CO2 PROTOTYPE FOR DHW: COMPRESSOR
The COMPRESSOR shows high mass flow
and consequent high input power in many
operating conditions so the improvements
focus on the electric motor, the suction
reeds, the valve plate, the discharge port
and extension of application range.
EXPERIMENTAL RESULTS IMPROVEMENTS
In order to obtain high COP at high ambient
temperature the suction pressure at compressor could
be increased because actually the application envelop
of the compressor permits a max CO2 evaporation
temperature up to 12°C (pressure about 47 bar); the
required extension of application range means that the
increasing of the maximum suction pressure at
compressor should be up to 50 bar.
Increasing of
compressor
working range
over Te = 12°C.

10. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
30 kW CO2 PROTOTYPE FOR DHW: PROTOTYPE IMPROVEMENTS
The CONTROLLER of the gas cooler pressure poCP must be improved because
at this moment it is optimized only for water temperature at Gas Cooler inlet
lower than 30°C.

11. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
30 kW CO2 PROTOTYPE FOR DHW: PERFORMANCES AND STATE OF ART
BETTER performances
at LOW ambient
temperatures.
WORSE performances
at HIGH ambient
temperatures.
HP IMPROVEMENTS ESPECIALLY AT HIGH AMBIENT TEMPERATURES

12. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
30 kW CO2 PROTOTYPE FOR DHW: SIMULATION FOR THE IMPROVEMENTS
 Utilization of a MATLAB code
to evaluate the effects of
possible modifications on
performances of Heat Pump.
 The performance, in terms of
COP, are greatly improvable
when the ambient temperature
is greater than 2 ° C: the
simulation shows how much
the COP could increase
reducing the IHE efficiency
and increasing the
evaporation temperature.
 The possible effects of
improvements, reported in the
table, were not all considered
(thermal dispersions and
reduction of pressure drops
etc.) in the graph.
Heat pump COP improvements according the simulations.
Ambient Temperature [°C] -7 2 7 16
T in water [°C] 10 10 10 17
T out water [°C] 60 60 60 65
Pgc_opt [%] 1.5 3.0 0.4 6.2
Tev improvement and εIHE opt (IHE in the graph) [%] 3.5 4.6 10.3 4.7
Pressure drop (suction line), reduction of thermal losses [%] 1.9 2.1 2.4 1.8
Reduction of Wfan [%] 6.7 6.7 6.8 6.4
Other improvements (evaporator pressure drop, etc) [%] 1.7 3.2 1.7 1.6
TOTAL improvement [%] 15.3 19.6 21.6 20.7
TARGET LINE

13. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
30 kW CO2 PROTOTYPE FOR DHW: CONCLUSIONS
 Very good results with ambient temperature lower than 2 °C: performance
target reached
 Modifications needed to improve performances when ambient
temperature is greater than 2°C:
 Optimization of gas cooler pressure by internal control
 Reduction of IHE efficiency
 Optimization of heat transfer at Evaporator
 Improvements of the Compressor.
 Matlab simulation shows the possibility to reach the performance target
also with these boundary conditions through the modifications above
described.

14. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
Our research and development activities:
Thanks for your attention
Scientific referent: Eng. N. Calabrese
andrea.calabrese@enea.it
www.climatizzazioneconfontiirinnovabili.enea.it

15. Latest Technologies in Refrigeration and Air Conditioning - XVI European Conference Milano, 12th - 13th June 2015
Thank you for your attention