High Efficiency Heat Pumps for lowTemperature Lift Applications
12th IEA Heat Pump Conference 2017 Rotterdam, May 17th, 2017
Prof. Dr. Beat WelligLucerne University of Applied Sciences and ArtsCC Thermal Energy Systems & Process Engineering
Outline
1. Motivation
2. Design rules for low-lift heat pumps
3. Prototypes and experimental results
4. Examples for building heating and cooling
5. Conclusions
2
Temperature Lifts for Building Heating
3
50
40
30
20
10
0
-10
-20
Evap
orat
ing
/ con
dens
ing
tem
p. [°
C]
15 K
75 K
Radiators
Underfloor heating
Geothermal heat probes / ground water
Ambient air
Temperature lift for highly efficient building heating (e.g. geothermal heat probe and low-temperature underfloor heating system): 15–30 K
(constant evap. temp. of 10°C)
Temperature Lifts for Building Cooling
4
Temperature lift for high efficient building cooling (e.g. highly efficient fan coilunits and efficient hybrid recooling systems): 10–20 K
50
40
30
20
10
0
-10
Evap
orat
ing
/ con
dens
ing
tem
p. [°
C]
10 K
55 K
Air-cooled condenser,
recooler
Cooling tower
Space cooling
Dehumidification
Ice storage
(constant evap. temp. of 14°C)
Why do we need Low-lift Heat Pumps?In many applications a temperature lift of 10–30 K is sufficient.
Standard HPs § are designed for higher lifts and § exhibit poor Carnot efficiencies if they are
operated at low lifts.
The potential for high efficient heating/cooling systems is not fully exploited!
Goal:Development of heat pumps and chillers specifically designed for low temperature lifts.
5
6
5
4
3
2
chill
er C
OP
40302010temperature lift [K]
one compressor
two compressors
Chilled Water System A (screw compressor) chiller COP = Qevap / Pel, comp
Example of field measurement:Chiller in office building in ZurichCarnot efficiency at low lift: 32–35%
Design Rules for Low-Lift Applications
§ Expansion valve-- Small and stable superheatingØ Electronic expansion valve
§ Compressor- Low internal pressure ratioØ Oil free turbo compressor
§ Heat exchangers- Minimize the required DTØ «thermally long» brazed plate
heat exchangers§ Refrigerant
- High volumetric capacity- High isentropic efficiency
Ex open Exp pD < D
Condenser
Evaporator
Expansion valve
Compressor
p,T
DpC
DpEx
Dp
E
DpEx
ope
n
6
Low-Lift Heat Pump Prototypes
Heat pump with reciprocating compressor
Refrigerant R290Heating capacity 16 kW(in cooperation with BMS Energietechnik AG, Wilderswil, Switzerland)
7
Low-Lift Heat Pump PrototypesHeat pump with oil-free radial turbo compressor
Refrigerant R600Heating capacity 9–20 kW (in cooperation with BS2 AG, Schlieren, Switzerland and Celeroton AG, Volketswil, Switzerland)
8
Experimental Results: Heating Mode
Carnot efficiency decreases at temperature lifts below 20 K
Carnot efficiency remainsconstantly above 60%
20
15
10
5
CO
P HP
3025201510Temperature lift [K]
70
60
50
40
Car
not e
ffici
ency
[%]
n = 142 krpm
n = 177 krpm
n = 200 krpm
Low-lift heat pump with turbo compressor: COPHP Carnot efficiency
Heating mode
9
(constant evap. temp. of 10°C)
Experimental Results: Cooling Mode
Carnot efficiency decreases at temperature lifts below 20 K
Carnot efficiency remainsconstantly near/above 60%
20
15
10
5
CO
P Ch
3025201510Temperature lift [K]
70
60
50
40
Car
not e
ffici
ency
[%]
n = 142 krpm
n = 177 krpm
n = 200 krpm
Low-lift chiller with turbo compressor: COPCh Carnot efficiency
Cooling mode
10
(constant evap. temp. of 10°C)
Turbo-HP: Application for Building Heating
B35 Building, Zurich(Prof. Dr. H. Leibundgut, ETH Zurich)§ Apartment building § Two geothermal heat probes
(380 m und 300 m) § Heating water temperature 28°C
at design temperature –8°C § Temperature lift around 20 K and
lowerGeothermal heat probes(380 m and 300 m)
Low-lift heat pump
20°C
-8°C
28°C
24°C12°C
9°C
11
Geothermal heat probes(380 m and 300 m)
Low-lift heat pump
20°C
-8°C
28°C
24°C12°C
9°C
28°C
8°C
9°C
28°C
12°C
24°C
TC
Condensation
Evaporation
T
Heating water
TE
Geothermal heat probe water
Tem
pera
ture
lift
(20
K)
Turbo-HP with same operating conditions: § COPHP » 9.7, Carnot eff. » 63%§ COSPHS » 8.8, incl. both circulation pumps
Turbo-HP: Application for Building Heating
12
Building cooling Distribution ProductionChiller Free cooling
Standard chillerOptimized chiller
High-efficient fan coil unitPel < 1% QR(4 Wel/m2)
Circulationpump
Pel < 1% QR
Evaporativecooler
Pel ≈ 3% QR
Evaporator
Condenser
13
Turbo-HP: Application for Building CoolingChilled water system in an office building in Zurich
28
26
24
22
20
18
16
14
12
10
tem
pera
ture
[°C
]
06:00 09:00 12:00 15:00
Free Cooling Chiller
recoolercondenser
evaporator
recooler in reccoler out building out building in
wet bulb temperature
Temperature profiles for a summer day:
7-8
K14
Turbo-HP: Application for Building Cooling
External temperature lift 7–8 KExpected inner temperature lift of Turbo-HP approx. 10 K
Expected efficiency:§ COP » 16, Carnot eff. » 62% § COSP » 9, incl. all pumps & fans
§ Considerable energy savings by consistent use of low temperature lifts
§ Standard HPs cannot exploit the efficiency potential § HP must be specifically designed for these conditions
§ Experimental results for Turbo-HP:§ building heating: COP > 9 for lift of 20 K, § building cooling: COP > 15 for lift of 10 K, § with Carnot efficiencies > 60%
§ Mandatory requirement: suitable low-lift building technology systems are needed!
Conclusions
15
16
Financial Support:§ Commission for Technology and Innovation CTI§ Lucerne University of Applied Sciences and Arts
Project Partners:§ BMS Energietechnik AG, Wilderswil, Switzerland§ BS2 AG, Schlieren, Switzerland§ Celeroton AG, Volketswil, Switzerland
Thank you for your attention!
Acknowledgement