1/74. Heat pumps. types parameters effectivity

Transcription

1 1/74 Heat pumps types parameters effectivity

2 Heat pumps 2/74 generally devices for: pumping the thermal energy from environment A at low (= nonutilisable) temperature (anergy) and transferring it to environment B at higher (=utilisable) temperature t 1 t 4 cooling heat extraction A HP B heating heat rejection t 2 t 3

3 Heat pumps 3/74 heat pumping: driving high-potential energy (work) W degrades and is transferred to environment B with the extracted (pumped) energy W (work) t 1 t 4 Q A extracted heat HP Q B = Q A + W rejected heat t 2 t 3

4 Devices 4/74 cooling machine, chiller uses primarily the cooling effect usable heat is extracted heat from environment A (lowering the temperature) heat rejected to environment B is not used (waste heat) A B

5 Devices 5/74 heat pump usable heat is the rejected heat to environment B B A difference is not in the principle, but in character of heat management both devices can t be simply mixed differences in practical construction

6 Energy performance 6/74 heat pumps (heat supply) coefficient of performance COP chillers (heat extraction) energy efficiency ratio EER COP = Q W B EER = Q W A

7 Carnot cycle 7/74 theoretical cycle reversible (ideal) most efficient thermal cycle can t be realised in reality isoentropic changes (s = const.) compression, expansion isothermal changes (T = const.) heat input (extraction) heat output (rejection)

8 Carnot cycle 8/74 specific energy q A = q 41 = T1 1 s ( s 4 ) q B q B = q 23 = T2 1 s ( s 4 ) [J/kg] w w = q B q A = ( T2 T1 ) ( s1 s4 ) q A COP C q T = B = 2 EER = A 1 C = = COPC 1 w T2 T w T2 T1 1 q T

9 Carnot cycle 9/74 unrealistic cycle not considering: finite surface area of heat exchangers thermophysical properties of working fluids (refrigerants) real efficiency of driving energy source heat losses auxilliary energy (pumps to overcome hydraulics losses) real coefficient of performance comparison with Carnot COP HP T2 T T =ηhp comparative efficiency η HP = 0,4 to 0,6 2 1 small capacity large capacity

10 Example 10/74 environment A 0 C environment B 30 C 50 C calculate Carnot cycle COP

11 Rankin vapour cycle 11/74

12 Heat pump 12/74 Q c sink side Q & = P + Q& c el e P el COP = Q& P c el Q & e = Q & c P el Q e source side Q& e = Q& 1 c 1 COP

13 COP dependent on temperatures 13/74 condensation temperature t c given by the rejection system space heating systems hot water preparation evaporation temperature t e given by temperature of heat source (cooled environment) ground, air, water, waste heat type of refrigerant type of compressor sizing of heat exchangers

14 COP dependent on temperatures 14/74 COP 12 t c t e t = t k - t v

15 Ground vertical boreholes 15/74 heat extraction by dry boreholes under 200 m usually under 100 m not space demanding 1 or 2 pipe circuits in borehole primary circuit tempratures: from -4 C to +4 C

16 Ground temperature 16/74 depth temperature

17 Borehole construction 17/74 injection pipe filling the borehole with bentonite reduction connection of circuits distance bar distance between pipes support bar U piece bottom of borehole anchor

18 Horizontal ground heat exchangers 18/74 heat extraction from subsurface layer (up to 2 m depth) possible influence of vegetation space demanding excavation large land need HX temperatures around 0 C

19 Construction of ground HX 19/74

20 Ground water 20/74 chemical quality of water sufficient quantity of water stable water temperature = average annual air temperature (9-10 C)

21 Ambient air 21/74 use of ambient heat heat power dependent on climate conditions winter: COP < 3 summer: COP > 4 mostly bivalent operation removal of condensate defrosting, removal of ice noise protection

22 Construction 22/74 indoor units outdoor units

23 Heat pump parameters 23/74 heat output, heat capacity Q c [kw] heat output from condenser coefficient of performance COP [-] at given boundary conditions t v1 and t k2 electric power P el [kw] evaporator input = source output Q e [kw]

24 Brine-water heat pump (ground source) 24/74 conden.output temperature heating capacity [kw] evaporator input = source temperature

25 Air-water heat pump characteristics 25/74 electric power, heating capacity [kw] conden.output temperature evaporator input = ambient air temperature

26 Air-water heat pump characteristics 26/74 COP [-] evaporator input = ambient air temperature

27 Testing of heat pumps 27/74 EN Air conditioners, liquid chilling packages and heat pumps with electrically driven compressors for space heating and cooling. EN : dtto - Terms and definitions EN : dtto - Test conditions EN : dtto Test methods EN : dtto - Requirements nominal conditions: nominal heating capacity, nominal COP brine-water water-water air-water B0 / W35 W10 / W35 A2 / W35

28 Example 28/74 ground source heat pump parameters for B0/W35 heating capacity = 10 kw coefficient of performance = 4.2 calculate power input cooling power heat pump comparative efficiency = COP / COPcarnot

29 Declared COP of heat pump 29/74 producer of has tested the heat pumps for given nominal conditions brine-water B0 / W35 COP = 4.3 water-water W10 / W35 COP = 5.1 air-water A2 / W35 COP = 3.1 is it a REAL coefficient of performance for the heat pump operation? how about climate conditions? e.g. for air-water HP how about different heating system operation conditions? heating water temperature (low temperature x high temperature systems) required hot water temperature (hygienic requirements) 29/26

30 Operation 30/74 declared COP x real COP COP is changing with operation conditions variable temperature of heat source (air, surface water) variable heating water temperature (equithermal control)! hot water preparation heating at C significant decrease of performance

31 Seasonal performance factor 31/74 hot water space heating back-up SPF Q SH,HW heat pump COP Q HP COP = Q E HP HP SPF = Q SH,HW E tot E HP E aux E tot E bu

32 32/74 Are the heat pumps renewables? consume electric energy! do heat pumps save primary energy?

33 Total energy balance 33/74 primary fuel 100% power plant, η e = 35% electricity 35 % losses -5 % 90 % 90 % electricity 30 % gas boiler, η = 90% heat pump, SPF = 3

34 European RES directive 34/74 requirement on heat pump systems electricity is produced mainly from fossil fuels (primary nonrenewable energy source) therefore minimum seasonal performance factor should be SPF 1 > 1,15 η e η e electricity production efficiency European average 45.5 % SPF > 2,5 otherwise it is better to use direct combustion of fuels...

35 EN Annex C (informative) 35/74

36 Annual balance of heat pump 36/74 target real electricity consumption of heat pump real electricity consumption of back-up heater evaluation of SPF evaluation of primary energy needs, CO 2 emission savings simple calculation method simple calculation with Excel climatic parameters (temperature frequency histogram for given location)

37 Why detailed balance? 37/74 unstable power output during year winter insufficient heat output autumn sufficient heat output

38 Why detailed balance? 38/74 unstable COP during year winter low COP autumn high COP

39 Energy balance for heat pump 39/74 monthly method is not possible (!) average monthly temperatures are rarely under balance point Prague Budweis Hradec Brno I -1,5-2 -2,1-2 II 0-0,9-1 -0,6 III 3,2 3 2,7 3,7 IV 8,8 7,4 7,4 8,7 V 13,6 12,7 12,8 14,1 VI 17,3 15,7 15,6 16,9 VII 19,2 17,5 17,4 18,8 VIII 18,6 16,6 16,8 17,8 IX 14,9 12,9 13,5 14 X 9,4 7,7 8,3 8,7 XI 3,2 2,8 3,1 3,6 XII -0,2-0,4-0,4-0,2 Q [kw] C t e [ C]

40 Energy balance for heat pump 40/74 bin method, method of temperature bins (intervals) standardized method in EN using the temperature histogram for heating season or whole year resolution of bins 1 K each temperature bin is characterized by: mean ambient temperature t e,j duration of ambient temperature (hours) τ j

41 heating season data Hours Average (A) Warmer (W) Colder (C) Climatic data Average Strasbourg(-10 C) Warmer Athens(+2 C) Colder Helsinki(-22 C) 41/ Ambient temperature [ C]

42 Prague: temperature histogram 42/74 heating season summer

43 Prague: temperature histogram 43/74

44 Energy balance 44/74 for each temperature bin is determined (for given mean temperature of the bin) heat demand for the building heat output from HP / energy from HP available heat delivered by HP to cover heat demand electricity demanded by compressor heat delivered by back-up heater (electricity) operation time of HP consumption of auxilliary energy (pumps)

45 Bin method: inputs 45/74 space heating demand distribution to bins simplified method, based on degree-hours DH j in the bin calculation based on: total space heating demand Q SH ~ DH in the given period Q SH, j = Q SH DH j DH = Q SH ( t t ) i j e, j DH τ j j

46 46/74 Bin method: inputs heat pump characteristics Φ HP = f (t v1, t k2 ), COP = f (t v1, t k2 ) utilization of linear or quadratic interpolation and extrapolation of the heat pump characteristics for other operation conditions k v k v k v HP t t F t E t D t C t B A = Φ k v k v k v t t f t e t d t c t b a COP =

47 Bin method: inputs 47/74 heat source temperature = temperature at the input to evaporator t v1 air: t v1 = t e water: t v1 = 10 C ground: t v1 = 0 C

48 Bin method: inputs 48/74 flow temperature of heating water 55 flow temperature [ C] C t w1 = t w1, des flow t w1 return t w2 ( t t ) w1, des w1,min t t e i t t e, des e, des ambient temperature t e [ C]

49 Energy balance 49/74 for each temperature bin is calculated (for given mean temperature of the bin) heat demand for the building heat output from HP / energy from HP available heat supplied by HP (heat demand coverage) electricity consumed by compressor heat supplied by back-up operation time of HP consumption of auxilliary energy (pumps)

50 Bin method: outputs 50/74 available energy from HP [kwh] Q HP,avail,j = ΦHP, j τ j heat supplied by HP to cover demand [kwh] Q = HP, del,j min( QHP,avail; QSH,HW) j electricity consumed by heat pump [kwh] E = HP,j Q HP,del,j COP j heat supplied by back-up heater electricity use of electroboiler [kwh] E bu, j = Q SH,HW,j Q HP,del,j

51 Bin method: outputs 51/74 operation time of heat pump τ HP,j = Q Φ HP,del,j HP,j auxilliary energy consumption (pumps, valves, etc) E aux, j =P aux τ HP,j

52 Bin method: annual results 52/74 total delivered energy by heat pump Q HP,del = j Q HP,del, j total electricity for heat pump E HP = j E HP, j total electricity for back up heater E bu = j E bu, j total electricity for auxiliaries E aux = j E aux, j total operation time of heat pump τ HP = τ HP,j j

53 Bin method: annual results 53/74 seasonal performance factor SPF = E Q HP HP,del + E bu + Q + E bu aux = Q SH + Q E tot HW

54 Example: family house 54/74 space heating heat loss 30 kw (-18 C) space heating demand kwh/a climate defined by table, d = 235, t e,m = 3,0 C heating system 50/40 C hot water 6 persons, 60 l/per.day, heat losses 30 % hot water temperature 55 C, cold water temperature 10 C hot water heat demand = cca kwh/a

55 Example: heat demand 55/74

56 Example: heat pump 56/74 ground source heat pump WPF 20 nominal heat output Q HP = 21,9 kw COP = 4,8 B0/W35

57 Example 57/74 Φ HP = 25,9 + 0,569*t v1-0,103*t k2 35 C 50 C 60 C

58 Example 58/74 COP = 8,6 + 0,091*t v1-0,104*t k2 35 C 50 C 60 C

59 Example: boreholes 59/74 ground source input to evaporator t v1,j = 0 C space heating regime (radiators) nominal temperatures flow / return t w1,des = 50 t w2,des = 40 C design ambient temperature t e,des = -18 C t w1, j = t w1, des ( t t ) w1, des w1,min = t i t e, j t i t t e, des e, des

60 Example calculation 60/74 t e,j = -14,5 C τ j = 14 h f SH = 483 / t e,j = 2,5 C τ j = 433 h f SH = 7578 / Q SH = 305 kwh Q SH = 4785 kwh

61 Example calculation 61/74 t v1 = 0,0 C t v1 = 0,0 C t k2 = t w1 47,2 C t k2 = t w1 33,8 C Φ HP = 21,0 kw Φ HP = 22,4 kw COP = 3,7 COP = 5.1

62 Example calculation 62/74 τ HP = 14 h τ HP = 433 h Q HP,avail = 294 kwh Q HP,avail = 9707 kwh Q HP,del = 294 kwh Q HP,del = 4785 kwh E HP = 80 kwh E HP = 941 kwh τ HP = 14 h τ HP = 213 h Q bu = 10 kwh Q bu = 0 kwh

63 Annual results 63/74 SPF HW = 2,60 SPF SH = 4,61 SPF = 4,17

64 Standard house 64/74 space heating 160 m 2 heat loss 10 kw (-12 C) SH heat demand kwh/a (135 kwh/m 2.a), typical meteorological year in Prague heating system 50/40 C 35/30 C hot water 4 persons, 45 l/per.day, heat losses 15 % hot water temperature 55 C, cold water temperature 15 C hot water heat demand kwh/a (14 % from total demand)

65 Standard house 65/74 září listopad prosinec říjen srpen teplá voda hot water heating vytápění červenec únor březen duben květen červen leden kwh

66 Heat pump air-water 66/74 heat ouput 8,1 kw and COP = 3,4 at A2/W SPF /40 35/30 SPF HW SPF VSH SPF sys

67 Heat pump ground-water 67/74 heat output 9,9 kw and COP = 4,5 at B0/W SPF /40 35/30 SPF HW SPF SH SPF sys

68 Standard house 68/74 recommendations for SPF from EN can be met high space heating demand compared to hot water preparation low temperature heating system high coverage of heat demand by heat pump (requirement for monovalent solutions) well designed low-potential heat source usual concept of heat pumps

69 Passive house 69/74 space heating 160 m 2 heat loss 2.7 kw (-12 C) SH heat demand kwh/a (20 kwh/m 2.a), typical meteorological year in Prague heating system 35/30 C hot water 4 persons, 45 l/per.day, heat losses 15 % hot water temperature 55 C, cold water temperature 15 C hot water heat demand kwh/a (52 % from total demand)

70 Passive house 70/74 září říjen listopad prosinec srpen hot water teplá voda heating vytápění červenec únor březen duben květen červen leden kwh

71 Heat pump air-water 71/74 heat output 6,7 kw and COP = 3,2 at A2/W , ,0 kwh 300 back-up doplňkový zdroj auxilliary pomocná energie hot water příprava TV 2,5 SPF 200 space heating vytápění 2,0 SPF 100 SPF SH = 2,94 1,5 0 SPF HW = 2,40 1,0 leden únor březen duben květen červen SPF = 2,63 červenec srpen září říjen listopad prosinec

72 Heat pump ground-water 72/ heat output 5,8 kw and COP = 4,3 at B0/W35 back-up doplňkový zdroj auxilliary pomocná energie hot water příprava TV space heating vytápění SPF SPF 3,5 3,0 2,5 kwh SPF 200 2,0 100 SPF SH = 4,15 1,5 0 SPF HW = 2,12 1,0 leden únor březen duben květen červen SPF = 2,76 červenec srpen září říjen listopad prosinec

73 Passive house 73/74 recommendation for SPF from EN cannot be met despite low temperature system monovalent solution well designed low potential heat source but at usual concept of heat pump high hot water heat demand when compared to space heating (high temperature) gas boiler + solar system = 20 to 30 % lower primary energy consumption

74 74/74 Tomáš Matuška Dept. of Environmental Engineering Faculty of Mechanical Engineering, CTU in Prague Technická 4, Prague 6 tomas.matuska@fs.cvut.cz