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