Air-Source vs. Water/Ground-Source Heat Pump Systems ...

CoolEnergy.dk – March 6-7 th, 2013 – Odense, Denmark 

Air-Source vs. Water/Ground-Source 

Heat Pump Systems – Operational 

Characteristics 

Jørn Stene PhD 

Specialist – COWI AS, Division Buildings 

Associate professor II – NTNU 

1 

MARCH 7TH, 2013 

COWI POWERPOINT PRESENTATION


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2 




NTNU 

› NTNU – The Norwegian University of Science and Technology 

› Main responsibility for higher technological education in Norway 

› 7 faculties, 52 departments 

› 22,000 students, half of them in technical studies 

› Annual graduation – 3200 Master and 330 PhD stud. 

› Approx. foreign students 

› Close cooperation with SINTEF 

› www.ntnu.no 

› NTNU, Department of Energy and Process Engineering 

› Thermal Energy, Industrial Process Engineering, Fluid Flow Engineering 

and "Heating, Cooling and Ventilation in Buildings" 

› Applied Heat Pump Technology, TEP4260 and TEP16 

› www.ntnu.no/ept 

3 




Classification – Air-to-Water Heat Pumps 

A1.1 – Direct system design 

Outdoor 

Indoor 

› Evaporator, compressor etc. – outdoor 

› Circulation of refrigerant in a pipeline 

circuit between air-source evaporator 

and indoor water-cooled condenser 

Air 

Evaporator 

Condenser 

Heating 

system 


Heat Pump Unit 

› Heat pump unit – outdoor 

› Circulation of water in a closed pipeline 

circuit between condenser or gas cooler 

in indoor heat pump and heating system 


Evaporator 

Condenser 

Gas cooler 


system 


› Heat pump unit – indoor 




system 

› Circulation of ambient air in ducts through 

the wall to/from the indoor evaporator 

Evaporator 

Condenser 

4 




Classification – Air-to-Water Heat Pumps 

A2.1 – Indirect system design 

› Reversible air-to-water heat pump and 

chiller unit located outdoor 

› A 4-way valve switches between 

heating and cooling mode 

› Secondary circuit with circulating antifreeze 

fluid between outdoor condenser 

and indoor heat exchanger 

A2.2 – Indirect system design 

› Indoor brine-to-water heat pump unit 

located indoor 

› Secondary circuit with circulating antifreeze 

fluid between outdoor air cooler 

and indoor evaporator 



Evaporator, 

condenser 

Outdoor 


Air cooler 

(heat exchanger) 

Condenser, 

evaporator 

Secondary 

Circuit 

Secondary 

circuit 

Evaporator 

Indoor 

Heat 

exchanger 


Condenser 


system 


system 

5 




Classification – Brine-to-Water Heat Pumps 

B1.1 – Direct system design 

› The heat pump evaporator is in direct 

contact with the heat source (seawater, 

groundwater, sewage etc.) 

› The evaporator must be designed and 

operated to prevent corrosion, fouling, 

clogging and frost formation 

› Achieves a higher evaporation temp. 

than a direct heat source system, B2.1 

B2.1 – Indirect system design 

› Heat from the heat source is transferred 

from the outdoor heat exchanger to 

the indoor evaporator via a secondary 

circuit with circulating anti-freeze fluid 

› Standard heat pumps can be used 

Heat source 

Source 

Outdoor 

Heat exchanger 

Secondary 

circuit 

Evaporator 

Indoor 


Evaporator 

Condenser 


Condenser 


system 


system 

6 




Factors that Affects Heat Pump Operation 

› Heat source system 

› Heat source temperature level – variations 

› Direct / indirect system design – heat exchanger design 

› Corrosion – material selection 

› Pollution, fouling – cleaning requirements 

› Volumetric transport capacity (kJ/m 3 K) 

› Frosting – defrosting (air-source systems) 

› Heat pump unit 

› Refrigerant (working fluid) 

› Type of compressor – pressure rating, part load capacity control etc. 

› Design – single-stage, cascade, two-stage, economizer, EVI etc. 

› Heat distribution system 

› Temperature level variations, heat load variations etc. 

7 




Heat Source – Temperature Level – Norway 

HEAT SOURCE Temperature Level During the Heating Season 

-20ºC -10ºC 0ºC 10ºC 20ºC 

 

 

 

 

 

 

 

 

 

Ambient air 

Seawater 

Groundwater 

Bedrock 

Lake water 

Soil (ground) 

Ventilation air 

Sewage 

Grey water 

-40 to 10°C 

3-8°C 

4-8°C 

-4 to 8°C 

0-5°C 

-5 til 0°C 

4-12°C 

10-25°C 

20°C 

8 




Heat Sources – Monthly Mean Temperatures 

› Ambient air 

› Large temp. variations 

during the year and 

between climatic zones 

› Seawater 

› Relative moderate 

temperature variations, 

1-3 months temperature 

delay vs. ambient 

air 

Temperature (°C) 

A 

B 

C 

D 

E 

› Groundwater – rock 

› Relatively moderate 

temperature variations 

during the year and 

between climatic zones 

A – Air Bergen, B – Air Trondheim, C – Air Røros 

D – Seawater, -20 m, Bergen, E – Groundwater, Elverum 

9 




Important Operational Aspects for HPs 

› Energy Saving 

› Seasonal Performance Factor (SPF net ) 

› Heat pump units incl. fans and pumps 

› Coverage factor of annual heating demand 

› Reference system wrt. primary energy demand 

› Lifetime 

› El.boiler, oil-fired boiler, gas-fired boiler, bio-fired boiler, district heating or other heat pump 

› Mechanical wear and tear for the heat source system 

› Corrosion on heat exchangers, pipelines etc. 

› Wear and tear for compressors, motors, valves etc. 

› Maintenance 

› Components 

› Leakage testing etc. 

10 




Heating Cap. vs. Evaporation Temperature, t E 

Relative Relativ heating kondensatoreffekt capacity (-) (-) 

1,8 

1,6 

1,4 

1,2 

1,0 

0,8 

0,6 

0,4 

0,2 

R410A 

R407C 

R134a 

R744 (CO2) (CO2) 

R717 (NH3) (NH3) 

R290 (propan) (propane) 

-30 -25 -20 -15 -10 -5 0 5 10 15 20 

Evaporation Fordampningstemperatur Temperature, (°C) t E (°C) 

Single-stage unit – t C =45 °C – compressor efficiencies not incl. 

› The heating capacity 

drops 3-4 % for each 

°C reduction in t E 

› Reduced vapour density 

of the suction gas and 

with that lower mass 

flow rate, m R (kg/s), at 

reduced t E 

› Decreasing compressor 

efficiency (λ) at increasing 

pressure ratio (π) 

› Lowest relative drop in 

heating capacity for: 

› R744 (CO 2 ), R410A and 

R290 (propane) 

11 



0 

5 


Performance – Air-to-Water CO 2 Heat Pump 

R744 Ref :W.C.Reynolds: Thermodynamic Properties in SI 

100,00 

DTU, Department of Energy Engineering 

s in [kJ/(kg K)]. v in [m^3/kg]. T in [ºC] 

M.J. Skovrup & H.J.H Knudsen. 12-03-15 

90,00 

80,00 

90 

80 

10°C 

A 

30°C 

0,0015 

B 

s = 1,45 

s = 1,45 

0,0020 

40°C 

s = 1,50 

s = 1,55 

C 

s = 1,60 

s = 1,65 

50°C 

0,0030 

s = 1,70 

0,0040 

D 

0,0050 

0,0060 

0,0070 

0,0070 

0,0080 

0,0090 

0,0090 

Pressure [Bar] 

70,00 

Pressure (bar) 

60,00 

50,00 

40,00 

30,00 

20,00 

70 

60 

50 

40 

30 

20 

-15 

-10 

-5 

10 

15 

20 

25 

v= 0,0030 

v= 0,0040 

30 

30 

25 

20 

x = 0,10 0,20 0,30 0,40 0,50 0,60 0,70 0,80 0,90 

s = 1,00 1,20 1,40 1,60 1,80 

v= 0,0060 

v= 0,0080 

v= 0,010 

140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 

Enthalpy [kJ/kg] 

v= 0,015 

s = 1,75 

s = 1,80 

s = 1,80 

15 

⎛ Q& 

COP = ⎜ 

10 

⎝ W 

5 

Specific Enthalpy (kJ/kg) 

GC 

s = 1,85 

⎞ 

⎟ 

⎠ 

s = 1,90 

s = 1,95 

s = 1,95 

s = 2,00 

0 

-5 

-10 

-15 

-10 

0 

10 

20 

30 

s = 2,05 

Q GC-A =100% 

Q GC-B = 83% 

Q GC-C = 56% 

s = 2,10 

s = 2,10 

Q GC-D = 34% 

s = 2,15 

s = 2,20 

s = 2,20 

s = 2,25 

s = 2,30 

s = 2,35 

s = 2,35 

40 50 60 70 80 90 100 110 

0,010 

0,015 

0,015 

COP A =4.3 (100%) 

0,020 

0,020 

COP B =3.5 (71%) 

COP C =2.4 (58%) 

COP D =1.5 (31%) 

0,030 

› Heating capacity and COP decline rapidly at increasing inlet water temperature 

in the gas cooler → hot water heating and low-temp. space heating 

12 




COP vs. Evaporation Temperature, t E 

Effektfaktor COP (-) (-) 

10,0 

R410A R410A 

8,0 

6,0 

4,0 

2,0 

R407C 

R134a 

R744 (CO2) (CO2) 

R717 (NH3) (NH3) 


-30 -25 -20 -15 -10 -5 0 5 10 15 20 



› The COP drops 2-3 % 

for °C reduction in t E 

› Increasing temperature 

lift (∆t) for the heat 

pump at decreasing t E 


efficiency (η is ) at increasing 


› Highest cycle COP 

› R717 (ammonia), R134a 

and R290 (propane) 

› R744 (CO 2 ) heat pumps 

may achieve high COP at 

low return temperature 

in the heating system 

13 




Discharge Gas Temp. vs. Evaporation Temp., t E 

Discharge Trykkgasstemperatur Gas Temp. (°C) (°C) 

150 

140 

130 

120 

110 

100 

90 

80 

70 

60 

50 

-30 -25 -20 -15 -10 -5 0 5 10 15 20 


R410A 

R407C 

R134a 

R744 (CO2) (CO2) 

R717 (NH3) (NH3) 


› Disch. gas temp. increases 

with decreasing t E 

› Increasing temperature 

lift (∆t) for the heat 

pump at decreasing t E 


efficiency (η is ) at increasing 


› High discharge gas 

temp., thermal load 

› Lubricant carbonization, 

decomposition of refrigerant 

and leakage risk 


› Increase wear and tear, 

compressor failure 

14 




Pressure Ratio vs. Evaporation Temperature, t E 

Pressure Trykkforhold Ratio (-) (-) 

12 

11 

R410A 

10 

R407C 

9 

R134a 

8 

R744 (CO2) 

7 

R717 (NH3) 

6 


5 

4 

3 

2 

1 

-30 -25 -20 -15 -10 -5 0 5 10 15 20 



› Pressure ratio increases 

with decreasing t E 

› Increased pressure 

difference (∆p) at 

decreasing t E 


efficiencies at increasing 


› High pressure ratio, 

mechanical load 

› Increased wear and 

tear, compressor failure 

› Max. pressure ratio 

1:10 for reciprocating 

and scroll compressors 

15 




Air-to-Water Heat Pump – Operational Map 

Ambient air temp. (°C) 

Heating mode 

Example 

20 

10 

0 

-10 

-12 

Temperature 

limitations 

30 35 40 45 50 

Outlet water temp. (°C) 

› Standard reversible R410A 

heat pump / chiller unit 

› Nom. heating cap. – 150 kW 

› Stop temperature: -12 °C 

› t water = 40°C at t air = -12 °C 

› t water < 50°C at t air ≥ 0 °C 

› The pressure ratio and discharge gas temp. limits the operational map 

› Limited water temp. from cond. → limited heat supply at high temp. req. 

16 




Air-to-Water Heat Pump – Performance 

Heating Avgitt capacity varmeeffekt (kW) 

210 

190 

170 

150 

130 

110 

90 

30°C 

40°C 

50°C 

-15 -10 -5 0 5 10 15 4,520 

Amb. air temperature Utelufttemperatur (°C) 

› Both heating capacity and 

COP drop at decreasing 

ambient air temperature 

Effektfaktor, COP (-) 

6,0 

5,5 

5,0 

4,0 

3,5 

3,0 

2,5 

2,0 

1,5 

Example 

› Standard reversible R410A 

heat pump / chiller unit 

› Nom. heating cap. – 150 kW 

30°C 

40°C 

50°C 

-15 -10 -5 0 5 10 15 20 

Amb. air Utelufttemperatur temperature (°C) (°C) 

17 




Power and Energy Coverage vs. Heat Source 

Net Power Demand(%) 

P N 

Q HP – annual heat supply from heat pump 

Annual Heat supply from peak load unit 

Heat pump 

capacity curves 

Q HP 

Air: α=70-80 % 

Rock, water: α=85-95 % 

Relative power demand 

› Available heating cap. 

› Water, rock – rel. stable 

source temperature and 

flat capacity curve 

› Ambient air – large 

temperature variations 

and steep capacity curve 

› Temp. limitation for the 

heat pump unit will limit 

energy coverage factor, α 

Duaration (days) 

Principle power demand duration curve - hot water heating not incl. 

α 

⎛ Q 

= 

⎜ 

⎝ Q 

HP 

total 

⎞ 

⎟ ⋅100 % 

⎠ 

18 




COP, SPF and Relative Energy Saving – ∆E 

COP (-) 

Theoretical (max.) COP 

Real COP 

Prosentvis energisparing, ∆E 

50% 

67% 

75% 

80% 83% 

Temperature Difference, ∆t Seasonal Performance Factor, SPF (-) 

› Percentage energy saving ∆E compared to direct electric heating system 

› Non-linear relationship between SPF and energy saving ∆E 

19 




SPF and Energy Coverage – ∆E 

Rel. Energy Relativ energisparing, Saving, ∆E (%) (%) 

80 

70 

60 

50 

40 

30 

20 

10 

0 

5,0 

4,0 

SPF=2,0 

3,5 

SPF=2,5 

3,0 

2,5 

SPF=3,0 

SPF=3,5 

2,0 

SPF=4,0 

SPF=5,0 

0 10 20 30 40 50 60 70 80 90 100 

Heat Pump Varmepumpens Energy energidekning, Coverage, ∆Q (%) α (%) 

Electric Peak Load – Elecric Heating as Reference System 

› Relative energy saving 

of a heat pump system 

∆E (%) determined by: 

› Seasonal perf., SPF 

› Energy coverage fact., α 

› Mean efficiency for peak 

load system, η 

⎡ 

∆E 

= ⎢1 

− 

⎣ 

α 

SPF 

(1 − α) ⎤ 

+ ⎥ ⋅100% 

η ⎦ 

› Annual energy saving 

significantly affected 

by energy coverage, α 

20 




Air-to-Water Heat Pumps – Main Properties 

› Installation – possibilities and limitations 

› Ambient air is the most available heat source 

› Heating capacity and COP is affected by the ambient air temp. 

› Evaporator requires defrosting – energy use and possible problems 

› Fans generates noise – challenges wrt. location, use ”low noise” techn. 

› Max. water temp. 40-50 °C – limitation at high temp. requirements 

› Some heat pump units can supply 55-80 °C max. water temperature 

› May provide cooling, but limited free cooling 

› Investment, energy saving and lifetime 

› Rel. low investment costs since the evaporator is an integrated part 

› Moderate energy saving due to moderate energy coverage and SPF 

› Moderate lifetime due to large temp. variations (wear and tear) 

21 




Air-to-Water Heat Pumps – Problems 

› Compressor 

› Mechanical/thermal stress – wear and tear, compressor failure 

› Low compressor efficiency – reduced performance 

› Air cooler 

› Corrosion – refrigerant leakage, reduced performance etc. 

› Fatigue fractures – refrigerant leakages 

› Defrosting – extensive energy use, reduced performance etc. 

› Fans – noise, vibrations etc. 

› Recirculation of air – reduced performance 

› Operating limitations and problems 

› Limited outlet water temperature – reduced annual heat supply 

› High stop-temperature – reduced annual heat supply 

› 4-way valve malfunction etc. 

22 




Ground/Water-Source HPs – Main Properties 

› Installation – possibilities and limitations 

› Heating capacity/COP not affected by the ambient air temperature 

› Heat source/sink – may supply considerable free (renewable) cooling 

› The heat source system is hidden – no or minimal noise 

› Max. water temp. 50-60 °C – limitation at high temp. requirements 

› Two-stage plants may supply heat at 70-80 °C – expensive 

› Limitation for heat source system – availability, uncompacted material 

and lack of free space for GSHPs, polluted water (ground/seawater) 

› Important with correct design/operation of the heat source system 

› Investment, lifetime and energy saving 

› Relatively high investment costs due to separate heat source system 

› Monitoring and maintenance of heat source system important 

› High energy saving & long lifetime when correctly designed/operated 

23 




Water/Ground-Source HPs – Problems 

› Compressor 

› Mechanical/thermal stress – wear and tear, compressor failure 

› Low compressor efficiency – reduced performance 

› Heat source system – heat exchangers, pumps, tubing etc. 

› Corrosion – leakage, reduced performance, malfunction 

› Fouling – reduced performance, malfunction 

› Clogging – reduced performance, malfunction 

› Pump cavitation – reduced performance, malfunction 

› Gradual temp. drop in energy wells – reduced performance 

› Freezing of energy wells – severe settings, pipe rupture etc. 

› Operating limitations and problems 

› Limited outlet water temperature – reduced annual heat supply 

24 




Example – Air-Water vs. Ground-Source HP 

› Heat supply to an existing, non-residential building 

› Dominating space heating demand, some hot water demand (DHW) 

› Goal – replace existing oil-fired boiler with renewable heat source 

› Data 

› Climate – Trondheim, DOT=-19 °C og t A = 4.9 °C 

› Heating demand 

› Net power demand, space heating: 450 kW 

› Annual heating demand, space heating: 900,000 kWh/y 

› Annual heating demand, DHW: 100,000 kWh/y 

› Heat distribution system 

› Temperature requirement – 60/40 °C or 80/60 °C at DOT 

› Energy price – interest rate – mainenance 

› El.price: 0,8 NOK/kWh (about 10 Eurocent) 

› Interest rate: 7 % 

› Maintenance: 3 % of the investment costs for the heat pump system 

25 




Example – Air-to-Water vs. Ground-Source HP 

Thermal power demand (kW) 

Effekt (kW) 

500 

450 

400 

350 

300 

250 

200 

150 

100 

50 

0 

55 % 

Diagram – Geir Eggen, COWI 

Tilsatsvarme 

Effekt biobrenselanlegg 

Varighetskurve for 

effektbehov 

Space heating and 

heating Energidekning of ventilation fra pelletsanlegg air 

Hot water heating 


utetemperatur 

Ambient air temp. 

0 50 100 150 200 250 300 350 

Duration Varighet (døgn (days) 

-20 

-15 

-10 

-5 

0 

5 

10 

15 

Ambient Air Temperature (°C) 

Temperatur (°C) 

› Heat pump dimensioning – 40-70% of net power demand for space heating 

› Carry out a technical/economical optimization incl. sencivity analysis 

26 





› Ground-source heat pump – 225 kW 

› Standard brine-to-water chiller unit 

› Refrigerant R407C, max. outlet water temperature 50 °C 

› Investments 

› Brine-to-water heat pump/chiller unit 500,000 NOK 

› Energy wells in bedrock 2,000,000 NOK 

› Tubing, machinery room, el.installation etc. 800,000 NOK 

› Engineering and unforeseen costs (20 %) 660,000 NOK 

TOTAL 

3,960,000 NOK 

› Lifetime heat pump unit 15 years 

› Lifetime other installations 20 years 

› Lifetime energy wells 40 years 

› Energy coverage factor (α) To be calculated 

› Seasonal performance factor (SPF) To be calculated 

27 





› Air-to-water heat pump – 225 kW 

› Standard reversible chiller with indirect system design 

› Refrigerant R410A, max. water temp. 40/50 °C at -10/0 °C 

› Investments 

› Air-to-water heat pump/chiller unit 700,000 NOK 

› Noise reduction for evaporator 200,000 NOK 

› Container, tubing, el. installation etc. 800,000 NOK 

› Design and unforeseen costs (20 %) 340,000 NOK 

TOTAL 

2,040,000 NOK 

› Lifetime heat pump unit 10 years 

› Lifetime other installations 20 years 

› Energy coverage factor (α) To be calculated 

› Seasonal Performance Factor (SPF) To be calculated 

28 





500 

-20 

GSHP 1 (60/40 °C) 

Effekt (kW) 

450 


400 

350 

300 

250 

200 

150 

100 

50 

Tilsatsvarme 



effektbehov 

Energidekning fra pelletsanlegg 


utetemperatur 

-15 

-10 

-5 

0 

5 

10 

15 


• Energy coverage HP 89 % 

• SPF heat pump 3.8 

• SPF incl. peak loak 2.9 

• Energy saving 65 % 

• Costs (NOK/kWh) 0.83 

GSHP 2 (80/60 °C) 



• SPF incl. peak load 1.9 

0 

0 50 100 150 200 250 300 350 




› Considerable reduction in the annual heat supply from the heat pump and 

energy saving when using standard HP unit and high temp. heating system! 

29 





500 

-20 

Air HP 1 (60/40 °C) 

Effekt (kW) 

450 


400 

350 

300 

250 

200 

150 

100 

50 

Tilsatsvarme 



effektbehov 

Energidekning fra pelletsanlegg 


utetemperatur 

-15 

-10 

-5 

0 

5 

10 

15 







Air HP 2 (80/60 °C) 




0 

0 50 100 150 200 250 300 350 




› Considerable reduction in the annual heat supply from the heat pump and 

energy saving when using standard HP unit and high temp. heating system! 

30 




Field Monitoring – Residential Heat Pumps 

› New field monitoring 

project in 

Norway with 18 

air-water and 

brine-water HPs 

› HVAC association 

› Governm. support 

Air-to-water Brine-to-water – relative energy saving in % 

› New field monitoring 

project in 

Sweden with 20 

GSHP systems 

› Several other 

field studies in EU 

› Field monitoring 

shows real energy 

saving for the heat 

pump system 

31 




Example 1 – W/W heat Pump in Passive House 

› Prototype heat pump designed by D. Zijdemans 

› Installation in a passive house 

› Single-family house – 172 m 2 (2007) 

› Location – Flekkefjord (Sourthern Norway) 

› Heat pump covers the entire heating demand 

› Domestic hot water – 65 °C 

› Space heating – floor heating – 35 °C 

› Advanced water-to-water heat pump 

› 2.9 kW nominal heating capacity 

› Heat source – lake water 

› Working fluid – propane (R290) 

› Low- and high-temperature storage tanks 

› Especially designed for efficient DHW heating 

32 




Optimum HP Design for Hot Water Heating 

5°C 

70°C 

SG 

CONDENSER 

EVAPORATOR 

DSH 


5°C 

70°C 

Relative HX position (-) 

› Suction gas heat exchanger (SG) – increases gas temp. and superheat 

› Desuperheater (DSH) – hot discharge gas for reheating of DHW 

› SG + DSH – leads to lower condensation temp. and increased COP 

33 




Example 1 –W/W Heat Pump in Passive House 

Heat pump 

Pump HT 

Floor 

heating 

LT 

HT 

DSH 

Pump LT 

Compressor 

Condenser 

SG 

Evaporator 

Heat source 

Ref. – David Zijdemans, Oso Hotwater 

› LT storage tank – 35°C – floor heating system + preheating DHW 

› HT storage tank – 65 °C – reheating of DHW 

34 




Example 1 – W/W Heat Pump in Passive House 

COP – heat pump 

unit COP – total 

SPF – heat pump 

unit SPF – total 

Measurements – D. Zijdemans 

› Average COP 3.2 + 100 % coverage factor = 70 % energy saving 

› Increased COP by optimization and improved measuring equipment 

35 




CO₂ Heat Pump Water Heaters (HPWH) 

› CO 2 (R744) – environmentally benign refrigerant 

› GWP = 0, non-flammable, non-toxic 

› Technology developed at NTNU-SINTEF, Trondheim 

› Properties of the CO 2 heat pump cycle 

› Heat rejection at gliding temp. in a gas cooler 

› Can supply high temperature heat 

› Excellent energy-efficiency for components 

› Properties of CO 2 heat pump water heaters 

› The most energy efficient cycle 

› Domestic hot water (DHW) heating up to 95 °C 

› No DHW reheating required 

› Tank system etc. must be optimized for the CO 2 cycle 


Gas cooler 

Compressor 

Evaporator 

Specific enthalpy (kJ/kg) 

36 




CO₂ Heat Pump Water Heaters (5 to 100 kW) 

37 




Example 2 – CO₂ B/W HPWH in Block of Flats 

› Tveita borettslag (housing cooperative), Oslo 

› 3 large block of flats from 1969 with 819 apartments 

› Extensive refurbishing – various measures 

› Investments 40 mill. € 

› Energy reduced use from 280 to 140 kWh/(m 2 y) 

› CO 2 heat pump installation (2011) 

› The first large capacity CO 2 heat pump in NO 

› Exhaust air 22 °C as heat source 

› Heating of DHW for each block of flats (x 3) 

› Hot water tanks – 1000 litres – serial connection 

› CO 2 heat pump units of 3 x 100 kW from Green & 

Cool (SE) – designed by Kuldeteknisk AS, Tromsø 

› Measured COP approx. 4.0 incl. pumps 

38 




Example 2 – CO₂ B/W HPWH in Block of Flats 

12°C 

12°C 

9°C 

9°C 

22°C 

Heat exchangers 

22°C 

CO 2 heat pump 

GC 

E 

12°C 

Secondary circuit 

with anti-freeze 

Hot water tanks 

55°C 

9°C 

70°C 

Hot water 

70°C 70°C 10°C 

39 




Example 3 – A/W HP in Passive Office Bldg. 

› GK Norway, new head office – completed June 2012 

› http://hjemme.enova.no/sitepageview.aspx?articleID=4013 

› Passive house standard (class A) – calculated values: 

› Net energy demand: 67 kWh/(m 2 år) 

› Supplied energy: 52 kWh/(m 2 år) 

› BREEAM classification: ”Very good” 

› BRA 14,300 m 2 with workshop and stockroom 

› Annual heating demand – approx. 45,000 kWh/y 

› GK Norway contractor for e.g.: 

› Ventilation and AC system 

› Air-to-water heat pump and cooling system 

› Hydronic system and sanitary installations 

40 





› Air-to-water heat pumps – base load 

› Cooling power 500 kW – heating power 200 kW 

› Indirect system design with secondary circuit 

› Provides either heating or cooling 

› 2 units, each 4 scroll compressors and 2 circuits 

› Expected stop-temperature approx. –15 °C 

› Electric heating system – peak load 

› Electric boiler + electric heaters in the rooms (200 W) 

› Computer cooling 

› Water chiller – max. 50 kW (50 % utilization) 

› District heating and GSHP – not selected 

› No available district heating network – expensive tubing 

› 60 m uncompacted material – expensive tubing for GSHP 

41 





x4 

x4 

GK Norway 

HP1 

HP2 

Secondary circuit – anti-freeze fluid 

Reversible A/W heat pump units x 2 

Condenser heat from 

water chiller, computers 

Electro boiler 

Heating or cooling to 

heating/cooling batteries 

42 




Example 4 – B/W HP in Low-Energy School 

› The building (2008) 

› 6600 m 2 – school and kindergarten 

› Solid wood construction, low-energy bldg. (74 kWh/m 2 y) 

› The heat pump system – bedrock as heat source 

› Heating and cooling 

› Space heating – radiators (60/40 °C) and floor heating 

› Heating of ventilation air (40/25 °C) 

› Preheating of hot water 

› Cooling of ventilation air (10/16 °C) – free cooling 

› Unit – standard R134a water chiller 

› Nominal heating power 132 kW 

› 4 scroll compressors, on/off operation 

› To separate refrigerant circuits 

› 14 energy wells á 200 metres 

› Peak load – district heating 

43 




Example 4 – B/W HP in Low-Energy School 

VVS Norplan AS 

› The entire cooling demand is covered by free cooling from the energy wells 

44 




B/W HP for Heating/Cooling – Full Flexibility 

Geir Eggen, COWI AS 

› Heat pump for peak load cooling – excess heat utilized for thermal charging 

45 




Example 5 – A/W HP in District Heating Syst. 

› District heating system (2012) 

› Heat source 

› Ambient air 

› DOT -9 °C – average air temperature 4.2 °C 

› Heat pump plant – heating only 

› Refrigerant – ammonia (R717, NH₃) 

› Total heating capacity 920 kW at -1 °C and 68/55 °C 

› Single-stage plant 

› 2 identical compressor/condenser units – in parallel 

› 75 (60) bar mono-screw compressors – slide valve and v i control 

› Huge oil separator 

› Evaporator – 4 separate air coolers, hot gas defrosting 

› Condenser – plate heat exchanger 

› Oil cooler – shell-and-tube HX for heat recovery to district heating network 

› Max. 75 °C outlet water temperature from the condenser at -6°C 

46 





Evaporator 

Evaporator 

Ambient air 

Ambient air 

Liquid 

separator 

Hot gas defrosting 

Compressor 

OS 

Condenser 

Compressor 

OS 

Condenser 

Oil cooler 

Oil cooler 

Supply 

District heating system 

Return 

OS = Oil Separator 

Norsk Kulde 

47 





Norsk Kulde 

› The air coolers are parallel to the main wind direction – reduces fan work 

› The hatches are closed during defrosting in order to minimize heat loss 

48 





Liquid separator 

Compressor 

Oil separator 

Condenser 

Oil cooler 

Norsk Kulde 

49 




Air-to-Water HPs – Comments 

› Air-to-water vs. brine-to-water heat pumps 

› Less energy saving due to lower SPF and lower energy coverage 

› Shorter lifetime due to large temperature variations 

› Lower outlet water temperature for same ”technologcial level” 

› Technolocial development for air-to-water HP systems 

› Two-stage system design 

› Economizer compressor design 

› Cascade system design 

› Scroll compressors witl EVI (Economized Vapour Injection) 

› Mono screw compressors – variable speed drive, v i control 

› Improved demand controlled defrosting systems 

› Optimized evaporator design – larger fin distance etc. 

› Surface treatment of evaporators ("blue/gold coating") 

› Improved control systems etc. 

50 




Water/Brine-to-Water HPs – Comments 

› Water/Brine-to-water vs. air-to-water heat pumps 

› Higher energy saving due to higher SPF and higher energy coverage 

› Longer lifetime due to more stabile heat source temperature 

› Higher outlet water temperature for the ”same technological level” 

› Technological development for brine-to-water HP systems 

› Single-stage design +high-pressure compressors, 60-65 °C water temp. 

› Two-stage design + high-pressure compressors, 80-90 °C water temp. 

› Twin-screw compressors – variable speed drive, v i control 

› Mono-screw compressors – variable speed drive, v i control 

› Evaporators with micro porous surface coating (nano technology) 

› Propane (R290) og ammonia (R717) units for smaller capacities 

› Turbulence collectors for GSHPs 

› New heat exchanger types, e.g. bundle collector systems 

› Class A variable speed pumps 

51 



Thank you for your attention! 

HEAT PUMP 

52

Air-Source vs. Water/Ground-Source Heat Pump Systems ...

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