Air Conditioning with Solar Energy

Transcription

1 SERVITEC Barcelona, October 3, 2000 Air Conditioning with Solar Energy Dr. Hans-Martin Henning Fraunhofer-Institut für ISE, Freiburg page 1

2 Contents 1 Fundamentals 1.1 Thermodynamics 1.2 Climatic conditions 1.3 Definition of air conditioning 2 Systems & Components 2.1 Chillers Absorption chillers Adsorption chillers 2.2 Open cycles - desiccant cooling 2.3 Solar collectors 3 Solar air conditioning systems 3.1 Comparative study of solar assisted systems Compared systems Required collector area Primary energy saving Pay back time 3.2 Autonomous systems 4 Built examples 5 Summary & outlook page 2

3 Solar cooling processes Fundamentals solar cooling processes electric systems thermal driven systems photovoltaicpeltier-system photovoltaikcompression system heat transformation systems thermomechanical processes open cycles closed cycles rankine-process/ compression Veulleumiercycle solid sorbents (rotary wheels, fix bed process) liquid sorbents liquid sorbents solid sorbents adsorption chemical reaction page 3

4 Fundamentals Solar thermal air conditioning systems chilled water heat Thermal driven cooling process conditioned air page 4

5 Thermodynamic process Fundamentals driving heat T heat driving heat T heat thermal driven cooling machine waste heat T waste heat engine mechanical power P vapour compression machine waste heat T waste cooling power T cold waste heat T waste cooling power T cold page 5

6 maximum COP of cooling machines COP (Coefficient of Performance) = produced cold required driving heat Fundamentals 5 4,5 4 3,5 3 2,5 2 1,5 reversible COP [-] 1 evaporator temperature 0,5 0 C 5 C 10 C 15 C driving temperature[ C] page 6

7 tpyical solar collector efficiency curves Fundamentals 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 1 collector efficiency [-] radiation fluid average temperature [ C] 200 W/m^2 400 W/m^2 600 W/m^2 800 W/m^ W/m^2 page 7

8 maximum COP of cooling machines COP sol = COP * η collector Fundamentals 1 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 collector efficiency, COPsol [-] COPsol collector efficiency driving temperature [ C] COP COP [-] 3 2,7 2,4 2,1 1,8 1,5 1,2 0,9 0,6 0,3 page 8

9 COP sol for different collector radiation values Fundamentals 0,7 COPsol [-] radiation 0,6 0,5 0,4 0,3 200 W/m^2 400 W/m^2 600 W/m^2 800 W/m^ W/m^2 0,2 0, fluid average temperature[ C] page 9

10 Fundamentals maximum COPsol and respective temperature as function of radiation on collector 0,7 COPsol [-] temperature [ C] 170 0, , , , ,2 95 0, radiation [W/m^2] page 10

11 definition of air conditioning solar loads return air conditioning of ventilation air supply air internal loads Fundamentals air conditioning: control of indoor air temperature and humidity according to comfort demands main loads are: conditioning of ventilation air (supply of fresh air) sensible internal loads: persons, equipment, artificial lighting latent internal loads: persons, plants, others (e.g. kitchen) solar loads (windows, glazings) conduction loads (walls, windows) page 11

12 requirements for conditioning of ventilation air at different sites specific cooling load of conditioning of ventilation air in kwh per m 3 /h per year supply air temperature: 18 C supply air humidity: 8 g/kg Fundamentals cooling load of ventilation air sensible latent total Copenhagen Freiburg Trapani Bangkok sensible 0,57 1,95 5,93 28,48 latent 1,43 2,88 17,59 69,33 total 2 4,84 23,52 97,81 page 12

13 Contents 1 Fundamentals 1.1 Thermodynamics 1.2 Climatic conditions 1.3 Definition of air conditioning 2 Systems & Components 2.1 Chillers Absorption chillers Adsorption chillers 2.2 Open cycles - desiccant cooling 2.3 Solar collectors 3 Solar air conditioning systems 3.1 Comparative study of solar assisted systems Compared systems Required collector area Primary energy saving Pay back time 3.2 Autonomous systems 4 Built examples 5 Summary & outlook page 13

14 process overview Systems & Components method closed cycle open cycle refrigerant cycle closed refrigerant cycle refrigerant (water) is in contact to the atmosphere principle chilled water dehumidification of air and evaporative cooling phase of sorbent solid liquid solid liquid 1) typical material pairs water - silica gel, ammonia - salt 1) water - water/ lithiumbromide, ammonia/water water - silica gel, water - lithiumchloride water - calcium chloride, water - lithium chloride market available adsorption chiller absorption chiller desiccant cooling - technology typical cooling adsorption chiller: absorption chiller: 20 kw kw - capacity [kw cold] kw 20 kw - 5 MW (per Module) typical COP (single effect)) 0.5->1 >1 driving temperature C C C C solar collectors vacuum tubes, flat plate collectors vacuum tubes flat plate collectors, solar air collectors 1) still under development flat plate collectors, solar air collectors page 14

15 system overview Systems & Components heat supply system chilled water buffer storage backup heater chiller supply air heat recovery wheel desiccant wheel ambient air building/room return air conditioned air exhaust air page 15

16 single-effect absorption cycle (e.g. water - lithiumbromide) Systems & Components.. Q Q C G liquid refrigerant high concentration low concentration. Q Ev. Q A page 16

17 status of absorption chillers Systems & Components absorption chillers are market available components, mainly employed in combined heatpower-cold systems chilled water can be used for conditioning of air (dehumidification, temperature decrease) or for cold supply in the rooms (fan coils, chilled ceilings,...) many products available in the high capacity range (tpyically > 200 kw); only few products with small capacities driving temperature of single effect machines at > 85 C with COP of driving temperature of double-effect machines at > 150 C with COP of 1.2 page 17

18 adsorption chiller cycle Systems & Components condenser phase 1 adsorber 1 adsorber 2 phase 4 phase 2 condenser evaporator condenser adsorber 1 adsorber 2 adsorber 1 adsorber 2 evaporator condenser phase 3 evaporator adsorber 1 adsorber 2 evaporator page 18

19 status of adsorption chillers Systems & Components adsorption chillers are market available from to Japanese companies chilled water can be used for conditioning of air (dehumidification, temperature decrease) or for cold supply in the rooms (fan coils, chilled ceilings,...) cooling capacity range 70 kw kw driving temperature starting at 55 C COP at design conditions 0.65 page 19

20 principles of open cooling cycles (desiccant cooling cycles) Systems & Components open cooling cycles use the effect of evaporative cooling production of conditioned air (no chilled water) potential for application of evaporative cooling is increased by dehumidification of fresh air thermal energy required for regeneration of the sorbent (desiccant) separation of cooling and conditioning of ventilation air page 20

21 status of desiccant cooling systems Systems & Components system components and complete systems market available and employed since many years about 5 producers of wheels worldwide (Japan, US, Sweden, Germany) driving temperatures for regeneration usable down to about 45 C technology raised attention due to CFCproblem during past 10 years adiabatic dehumidification process page 21

22 standard desiccant cooling cycle bypass Systems & Components temperature [ C] humidity ratio [g/kg] % 20 % 30 % 40 % 50 % 70 % 100 % 10 heat heat exhaust air humidifiers return air 7 fresh air dehumidifier heat recovery supply air page 22

23 desiccant cooling cycle for humid climates exhaust air bypass heat Systems & Components 8 humidifier temperature [ C] return humidity ratio [g/kg] air % 1 20 % 30 % 40 % 50 % 70 % 100 % fresh air dehumidifier heat recovery supply air chilled water chilled water page 23

24 WINDOWS design tool Systems & Components page 24

25 Teststand für Solare Sorptionsgestützte Klimatisierung (SSGK) 20 m 2 Flachkollektoren (GreenOneTec/Sonnenkraft) 20 m 2 Solarluftkollektoren (Grammer) 2,0 m 3 Pufferspeicher (Solvis) Vermessung von Sorptionsrädern vielfältige Verschaltungsvarianten Entwicklung & Optimierung von Regelungsstrategien begleitende Systemsimulationen page 25

26 Systems & Components modelling of sorption dehumidifier measured dehumidification [g/kg] 1980 m3/h 2790 m3/h 3670 m3/h manufacturer calculated dehumidification [g/kg] page 26

27 Systems & Components solar collectors for thermal driven cooling 1 collector efficiency [-] flat plate collector 0,8 adsorption evacuated tube collector solar air collector 0,6 0,4 desiccant cooling single effect absorption double effect absorption ambient temperature 25 C 0,2 collector radiation 800 W/m fluid average temperature [ C] page 27

28 Contents 1 Fundamentals 1.1 Thermodynamics 1.2 Climatic conditions 1.3 Definition of air conditioning 2 Systems & Components 2.1 Chillers Absorption chillers Adsorption chillers 2.2 Open cycles - desiccant cooling 2.3 Solar collectors 3 Solar air conditioning systems 3.1 Comparative study of solar assisted systems Compared systems Required collector area Primary energy saving Pay back time 3.2 Autonomous systems 4 Built examples 5 Summary & outlook page 28

29 Solar air conditioning systems Air conditioning with solar energy solar assisted systems solar autonomous systems solar collector system covers a certain fraction of regeneration heat obtainable indoor air conditions not limited by solar gains system design: solar fraction solar collector system delivers regenaration heat completely obtainable indoor air conditions limited by available solar energy system design: probability function of indoor air temperature and humidity page 29

30 study on solar assisted air conditioning Solar air conditioning systems building data meteorological data energy balance, costs Building Simulation (TRNSYS) simulation of AC system (CONVCOOL, SGKCOOL) simulation of solar system (SOLCOOL) economic analysis (EXCEL) cooling / heating load time series driving energy time series solar fraction for cooling/ heating page 30

31 climatic and load data Solar air conditioning systems parameter Copenhagen Freiburg Trapani latitude [ north] annual average temperature [ C] annual average rel. humidity [%] annual average humidity ratio [g/kg] annual radiation sum on collector [kwh/m 2 ] annual average cooling load [W/m 2 ] cooling load [kwh/m^2] Copenhagen Freiburg Trapani Jan Feb Mar Apr May Jun Jul Aug Sept Okt Nov Dec page 31

32 assumptions for the comparative study Solar air conditioning systems building indoor conditions investion costs energy costs climatic data reference office building with south oriented glazed facades (glazing fraction about 60 %), floor area 400 m 2 according to german standard DIN 1946/II 10 % of investion costs according to values on german market (1998) (electricity: 0.08 US$/kWh, 171 US$/kW peak gas: US$/kWh, 4.5 US$/kW peak ) Copenhagen/Denmark, Freiburg/Germany, Trapani/Sicila page 32

33 reference system with adiabatic cooling in return air CCh HT warm, humid cooling loads cold, dry heat recovery CCh = compression chiller HT = heater (gas burner) page 33

34 system with thermal driven chillers aux. heater CT = cooling tower AbCh = abs. chiller AdCh = ads. chiller HF = humidifier CT AbCh AdCh HF warm, humid cooling loads cold, dry heat recovery page 34

35 Solar air conditioning systems solar assisted desiccant cooling system (Copenhagen, Freiburg) auxiliary heater warm,humid humidifiers cooling loads cool,dry dehumidifier heat recovery page 35

36 solar assisted desiccant cooling system (Trapani) Solar air conditioning systems auxiliary heat humidifiers warm, humid cold, dry cooling loads desiccant wheel heat recovery CT VPC VPC = vapour compr. chiller CT = cooling tower page 36

37 definitions Solar air conditioning systems solar fraction for cooling (SFC) fraction of the total heat required for cooling (air conditioning) which is supplied by the solar system specific collector area (m 2 /m 2 ) collector (absorber) area per floor area of conditioned space page 37

38 compared systems Solar air conditioning systems ABV ADV ADF DCF DCSA absorption chiller system with evacuated tube collector adsorption chiller system with evacuated tube collector adsorption chiller system with selective flat plate collector desiccant cooling system with selective flat plate collector desiccant cooling system with solar air collector page 38

39 required collector area specific collector area = collector area per floor area of conditioned space Solar air conditioning systems 0,6 0,5 0,4 0,3 0,2 specific required collector area solar fraction cooling 0,3 0,5 0,7 0,85 FREIBURG 0,1 0,5 0,45 0,4 0,35 0,3 0,25 0,2 0,15 0,1 0,05 0 specific required collector area solar fraction cooling 0,3 0,5 0,7 0,85 COPENHAGEN ABV ADV ADF DCF DCSA 0,6 0 ABV ADV ADF DCF DCSA specific required collector area TRAPANI SFC 0,5 0,3 0,5 0,4 0,7 0,85 0,3 0,2 0,1 0 ABV ADV ADF DCF DCSA page 39

40 primary energy balance Solar air conditioning systems normalized primary energy demand [%] FREIBURG solar fraction cooling 0 0,3 0,5 0,7 0, reference normalized primary energy demand [%] COPENHAGEN solar fraction cooling 0 0,3 0,5 0,7 0, ABV ADV ADF DCF DCSA normalized primary energy demand [%] TRAPANI solar fraction cooling 0 0,3 0,5 0,7 0, reference reference ABV ADV ADF DCF DCSA 0 ABV ADV ADF DCF DCSA page 40

41 electric peak load due to air conditioning Solar air conditioning systems normalized maximum electric power [%] Copenhagen Freiburg Trapani 100 % = reference system absorption/adsorption desiccant cooling page 41

42 simple pay back time Solar air conditioning systems 80 simple payback time [a] TRAPANI solar fraction cooling ,3 0,5 0,7 0, simple payback time [a] solar fraction cooling 0 0,3 0,5 0,7 0,85 COPENHAGEN ABV ADV ADF DCF DCSA simple payback time [a] FREIBURG solar fraction cooling 0 0,3 0,5 0,7 0, ABV ADV ADF DCF DCSA 0 ABV ADV ADF DCF DCSA page 42

43 Solar air conditioning systems Solar autonomous desiccant cooling systems employing solar air collectors humidifier warm, humid cooling loads cold, dry humidifier warm, humid cold, dry cooling loads desiccant wheel heat recovery wheel desiccant wheel heat recovery wheel system integrated collector regeneration with ambient air page 43

44 Solar air conditioning systems results for a lecture room in Freiburg operative room temperature room air temperature DIN 1946 part Temperatur [ C ] T_operativ T_luft DIN 1946 T2 j = 0,3 j = 0,4 j = 0,5 j = 0,6 j = 0,7 j = 1,0 Temperatur [ C ] T_operativ T_luft DIN 1946 T2 j = 0,3 j = 0,4 j = 0,5 j = 0,6 j = 0,7 j = 1, ,005 0,01 0,015 0,02 0,025 Feuchtegehalt X [ kg/kg ] 0 0 0,005 0,01 0,015 0,02 0,025 Feuchtegehalt X [ kg/kg ] specific collector area 0.22 m 2 per m 2 of room area page 44

45 Contents 1 Fundamentals 1.1 Thermodynamics 1.2 Climatic conditions 1.3 Definition of air conditioning 2 Systems & Components 2.1 Chillers Absorption chillers Adsorption chillers 2.2 Open cycles - desiccant cooling 2.3 Solar collectors 3 Solar air conditioning systems 3.1 Comparative study of solar assisted systems Compared systems Required collector area Primary energy saving Pay back time 3.2 Autonomous systems 4 Built examples 5 Summary & outlook page 45

46 built examples solar assisted desiccant cooling system in Sintra / Portugal air conditioning of the office from company ATECNIC desiccant system from robatherm solar collector from SETSOL/Portugal commissioned Dec. 99 funded by the EU (THERMIE-program) coordination and scientific evaluation: Fraunhofer ISE INETI / Lissabon page 46

47 built examples desiccant cooling machine in Sintra / Portugal (manufacturer: robatherm) page 47

48 built examples technical data of the system in Sintra / Portugal DEC system: variable volume flow system with nozzle type air humidifiers in supply and return air, heat recovery wheel and desiccant wheel (silica gel), bypass along desiccant wheel in supply air stream and bypass along regeneration air heat exchanger and desiccant wheel maximaum air volume flow 9600 m 3 /h maximum cooling power 75 kw maximum electric load COP at design conditions (cooling capacity/regeneration heat) 15 kw 0.78 solar collector system: CPC-collector with low optical concentration ratio (CPC = compound parabolic concentrator) filled with anti-freezing fluid; connected to buffer storage (water) with plate heat exchanger buffer storage volume 3 m 3 collector area 72 m 2 expected solar fraction for cooling (regeneration heat) 70 % expected solar fraction for heating 70 % page 48

49 built examples solar assisted air conditioning of a laboratory building in Freiburg (university hospital) with adsorption cooling technology page 49

50 schematic of the system in Freiburg built examples page 50

51 Contents 1 Fundamentals 1.1 Thermodynamics 1.2 Climatic conditions 1.3 Definition of air conditioning 2 Systems & Components 2.1 Chillers Absorption chillers Adsorption chillers 2.2 Open cycles - desiccant cooling 2.3 Solar collectors 3 Solar air conditioning systems 3.1 Comparative study of solar assisted systems Compared systems Required collector area Primary energy saving Pay back time 3.2 Autonomous systems 4 Built examples 5 Summary & outlook page 51

52 general results summary & outlook typcial value of required collector area (office) required solar fraction with solar assisted systems solar autonomous systems system design m 2 per m 2 of floor area of conditioned spac for a solar fraction of % % required in order to achieve relevant primary energy saving possible if the user does not request strict indoor air conditions (solar comfort improvement) system design required which takes specific climatic conditions into consideration page 52

53 general results (continued) summary & outlook collector technology evacuated tube collectors for absorptions systems and adsorption systems flat plat collectors for desiccant cooling systems and eventually adsorption solar air collectors for desiccant cooling (e.g. autonomous systems) economic feasibility payback time depends on technology and climate lowest pay back time found for desiccant cooling in Trapani (with conventional chiller backup) (less than 10 years) payback time in general in the same range as for solar domestic hot water systems or below page 53

54 summary & outlook lessons learned from pilot systems control issues system design operation experiences solar heat source is not constant (time dependance of power and temperature) system control is more complex than for systems with standard heating system (gas or oil burner) optimized control has a strong influence on system performance no standardized system design guidelines or tools available important to control operation in order to identify mistakes in control and/or design page 54

55 summary & outlook needs for an integrad approach To employ solar active equipment makes only sense if potentials of energy saving and reduction of cooling loads have been exploited Building reduction of internal loads (equipm., lighting) advanced shading & daylighting concepts reduction of conduction loads reduction of leakages A/C system separation of ventilation (handling of latent loads) and cooling (handling of sensible loads) employing heat (or enthalpy) recovery systems employing high efficiency chillers page 55

56 outlook summary & outlook solar thermal energy has a strong potential to be used for air conditioning in combination with centralized A/C plants no technical solution for substitution of small split type units available (if, then PV driven compression) research, development & demonstration required in order to gain experience in design, control and operation international collaborative work in the framework of the Solar Heating & Cooling Programme of the International Energy Agency (IEA): 11 countries particpate in Task 25 Solar Assisted Air Conditioning of Buildings page 56