Sizing of solar cooling systems

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A presentation from the SOLAIR project on sizing of solar air conditioners. their website has a lot of details information. For similar useful resources visit us on http://solarreference.com

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Sizing of solar cooling systems

  1. 1. Training course on solar cooling Chapter C : Predesign – system sizing funded by Speaker: XXXX YYYYY System sizing A) Building load characterisation needed Irradiance Internal load Convection Hygienic air Chapter C : Predesign – system sizing Source : TECSOL 2
  2. 2. System sizing Internal loads Chapter C : Predesign – system sizing 3 System sizing Chapter C : Predesign – system sizing 4
  3. 3. Solar collectors and thermally driven cooling A) Choice of technologies desiccant 1.0 adsorpti on CPC 0.9 1-effect absorpti on 0.8 2-effect absorpti on CPC ==stationary CPC stationary CPC CPC ηcoll 0.7 SAC ==solar air SAC solar air coll. coll. 0.6 SYC 0.5 0.4 FPC ==selectively FPC selectively coated flat plate coated flat plate EDF SAC 0.3 0.2 EHP ==evacuated EHP evacuated heat-pipe heat-pipe FPC 0.1 0.0 0.00 EDF ==evacuated, EDF evacuated, direct flow direct flow 0.05 0.10 0.15 EHP 0.20 0.25 0.30 0.35 2 ∆T/G [Km /W] SYC ==stationary SYC stationary concentrated, concentrated, Sydney-type Sydney-type Chapter C : Predesign – system sizing 5 Source : Fraunhofer ISE Solar production 0,9 1000 efficiency 0,6 0,5 0,4 0,3 0,2 Irradiation: 800 W /m ² direct norm al 200 W /m ² diffuse 0,1 0,0 0 25 50 75 FPC EFPC ETC CPC PTC Barcelona 800 energy yield [kW h/m²] 0,7 1000 900 700 800 600 500 400 300 200 100 100 125 150 175 T - T A MB [K] FPC EFPC ETC CPC PTC Huelva 900 energy yield [kW h/m²] flat-plate evac. tube evac. flat-plate CPC-collector parabolic trough 0,8 700 600 500 400 300 200 100 0 0 60 80 100 120 140 160 temperature [°C] 180 200 60 80 100 120 140 160 180 200 temperature [°C] FPC: flate plate collector EFPC: flate plate collector with concentrating parabolic compound (CPC) ETC: vaccum tube collectors CPC: vaccum tube collectors with concentrating parabolic compound (CPC) PTC: parabolic trough collector Chapter C : Predesign – system sizing Source : Aiguasol 6
  4. 4. Primary energy analysis Definitions Specific Primary Energy (PE) (KWh PE/KWh cold): PE spec Convencion al Energy Consumed Conversion Factor = Cold Produced Conversion factor: Electricity – 0.36; Fossil Fuel – 0.9 Conventional Compression Chiller: Qelec PEspec ,conv = ε elec Qcold = Qelec ε elec 1 1 Qelec 1 = = Qcold ε elec Qcold ε elecCOPconv Source : INETI Chapter C : Predesign – system sizing 7 Primary energy analysis Qbackup Definitions PE spec ,solar = ε fossil + PE spec ,cooling tower Qcold = Qbackup = Qdriving heat (1 - Fsol ) 1 + PEspec ,cooling tower Qcold ε fossil = Solar Thermal Driven Chiller: (1 - Fsol ) Qdriving heat + PEspec ,cooling tower Qcold ε fossil = With: COPthermal = 1 ε fossil Qcold (1 - Fsol ) + PE spec ,cooling tower ε fossil .COPthermal + PE spec ,cooling tower Qcold Qdriving heat Cooling tower: Ecoolingtower PEspec ,coolingtower = = ε elect Qcold = E spec,coolingtower Qheatrejected ε elect Espec,coolingtower ( Qdrivingheat + Qcold ) ε elect Qcold E  1 = spec,coolingtower 1 +  COP ε elect thermal  Chapter C : Predesign – system sizing 1 Qcold     Source : INETI 8
  5. 5. Primary energy analysis primary primary energy energy conversion conversion factor for factor for electricity: electricity: 0.36 0.36 2.5 COP = 0.6 COP = 0.8 COP = 1.0 COP = 1.2 Conv 2 Conv, 1 2.0 PEspec,sol , kWhPE/kWhcold heat source: heat source: solar collector solar collector + fossil fueled + fossil fueled backup backup 1.5 COPconv = 2.5 1.0 0.5 primary primary energy energy conversion conversion factor for factor for fossil fuels: 0.9 fossil fuels: 0.9 COPconv = 4.5 0.0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Solar Fraction for cooling Chapter C : Predesign – system sizing 9 Source : Fraunhofer ISE Comparison between absortion and compression Efficiency based on primary energy 2 specific primary energy per unit of cold 1.5 1 thermal system, low COP no primary energy saving 0.5 conventional system thermal system, high COP saves primary energy 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 solar fraction cooling Chapter C : Predesign – system sizing Source : Aiguasol 10
  6. 6. Consequences of primary energy performance ! High solar fraction for cooling necessary for solar thermally driven cooling equipment with low COP which use a fossil fueled backup ! A lower solar fraction is acceptable if thermally driven cooling equipment with a higher COP is employed ! An alternative is to use a conventional chiller as a backup (e.g. in case of a large overall cooling power) ! Primary energy savings are always achieved using a solar thermally autonomous systems but no guarantee for strictly keeping desired indoor comfort limits can be given ! In any case the use of the solar collector should be maximised by supplying heat also to other loads such as the heating system or hot water production Chapter C : Predesign – system sizing 11 Design Design with regard to solar-assisted air-conditioning mainly means ! Selection of the proper thermally driven cooling equipment for the selected air-conditioning system ! Selection of the proper type of solar collectors for the selected airconditioning system and thermally driven cooling equipment ! Sizing of the solar collector field and other components of the solar system with regard to energy and cost performance Chapter C : Predesign – system sizing 12
  7. 7. ‚Rules of thumb‘ Collector cost per heating capacity Cost of solar heat for given climate Load - gain - analysis for given climate and load Anual cost based on loadgain-analysis Computer design tool with predefined systems Open simulation platform Chapter C : Predesign – system sizing Required system information, effort for parametrization Accuracy, reliability of results, details of design information Design approaches Source : Fraunhofer ISE 13 Design point Acoll ⋅ Gcoll ⋅ ηcoll,design = == > Aspec = Example Pcold,design COP design 1 Gcoll ⋅ ηcoll,design ⋅ COP design Gcoll = 800 W/m2 hcoll,design = 0.5 ==> Aspec = 3.57 m2 per kW cooling power COPdesign = 0.7 Chapter C : Predesign – system sizing Source : Fraunhofer ISE 14
  8. 8. Advantages and disadvantages + Method allows a very quick assessment (guess) about the required collector area, if the efficiency of the collector and the COP of the thermally driven cooling equipment is known – Method neglects completely the influence of the variation of radiation on the collector during day and year – Any information on the specific site and load is neglected – Method neglects completely part load conditions of cooling load in thermally driven cooling equipment Chapter C : Predesign – system sizing 15 Sizing Average values of the specific collector area " for Absorption- and Adsorption chillers 3,0 to 3,5 m²/kW chilling capacity " for open technologies (DEC, liquid DEC): 8 to 10 m² per 1.000 m³/h rated air flowrate Source : EAW Chapter C : Predesign – system sizing 16
  9. 9. Collector first cost average fluid temperature η = k(Θ) ⋅ c0 − c1 ⋅ incident angle modifier optical efficiency & Quse = A ⋅ η ⋅ G⊥ ⇒ ambient air temperature (T − T )2 (Tav − Tamb) − c 2 ⋅ av amb G⊥ G⊥ linear heat loss coeff. A= & Quse η ⋅ G⊥ radiation on collector quadr. heat loss coeff. ⇒ Aspec = Costheat,power = Aspec ⋅ Costspec 1 kW η ⋅ G⊥ specific collector cost average fluid temperature = operating hot temperature of cooling system Chapter C : Predesign – system sizing Source : Fraunhofer ISE 17 collector first cost [€/kW] Collector cost versus specific required area 2000 Tav = 75°C Gcoll = 800 W/m2 1600 1200 800 400 0 1 2 3 4 5 6 required absorber area [m2/kW] evacuated tube Chapter C : Predesign – system sizing flat plate flat plate - integrated roof stationary CPC Source : Fraunhofer ISE 18
  10. 10. Advantages and disadvantages + Method allows a rough comparison of different solar collectors, if the collector parameters and the operation temperature of the thermally driven cooling equipment are known – Method neglects completely the influence of the variation of radiation on the collector during day and year – Any information on the specific site and load is neglected – Method neglects completely part load of cooling load and thermally driven cooling equipment Chapter C : Predesign – system sizing 19 Solar heat cost Costannual = Costspec ⋅ fannuity annual collector cost solar heat cost (€/kWh of heat) spedific collector cost (€/m2) Costheat = Costannual Qgross annuity factor collector gross heat production Qgross = annual collector heat productionat a given site and a given operationtemperatur . e Typically calculatedu sing hourly values of the dominating meteorological data. Chapter C : Predesign – system sizing Source : Fraunhofer ISE 20
  11. 11. Solar heat cost heat cost [€-cent/kWh] 20 etc fpc irc Palermo, Tav = 75°C cpc 16 12 8 4 0 0 200 400 600 800 1000 1200 1400 2 annual gross heat production [kWh/m ] Source : Fraunhofer ISE Chapter C : Predesign – system sizing 21 Solar heat cost heat cost [€-cent/kWh] 20 etc fpc irc Palermo, Tav = 95°C cpc 16 12 8 4 0 0 200 400 600 800 1000 1200 1400 annual gross heat production [kWh/m2] Chapter C : Predesign – system sizing Source : Fraunhofer ISE 22
  12. 12. Simple software tool SHC (NEGST project) Only needs monthly cooling (heating) load Free download in: http://www.swt-technologie.de/html/publicdeliverables3.html Compares monthly loads (heating and coling) with monthly solar energy gains. It is based on PHIBARFCHART Method - The results are primary energy savings for colector area installed. Chapter C : Predesign – system sizing 23 Advantages and disadvantages + Method allows a good comparison of different solar collectors using their parameters and the radiation data of a specific site + The maximum possible heat production of a specific solar collector for a given site (annual meteorological data file) and a given constant operation temperature is determined – Any information about the load profile is neglected – Method neglects completely part load of cooling load and thermally driven cooling equipment Chapter C : Predesign – system sizing 24
  13. 13. Correlation of loads and gains ! Global efficiency factors for transformation of heat in cooling (heating) are used to describe the technical equipment ! Calculation of hourly collector gains using different operation temperatures for cooling and heating Chapter C : Predesign – system sizing meteo data building model collector model 250 heating cooling 1 0.5 0.25 0.1 200 COP, ε heat load ! For each hour of the year the required heat for cooling (heating) is computed, e.g. using building simulation 150 100 50 0 0 100 200 300 400 500 600 700 800 solar gains solar fractions for heating and cooling Source : Fraunhofer ISE 25 Software tools needed to determine hourly cooling (heating) loads of a building TRNSYS – Commercially available (www.sel.me.wisc.edu/trnsys/) Energy plus – Download free (www.eere.energy.gov/buildings/energyplus/ ) ESP-r – Download free (http://www.esru.strath.ac.uk/Programs/ESP-r.htm ) A list of other software tools can be found : (http://www.eere.energy.gov/buildings/tools_directory/) Chapter C : Predesign – system sizing 26
  14. 14. Simple software tools using hourly cooling (heating) load SACE Cooling evaluation light tool – available in http://www.solair-project.eu/218.0.html Results using this software tool while be shown latter Chapter C : Predesign – system sizing 27 Simple software tools using hourly cooling (heating) load SolAC – available in: http://www.iea-shc-task25.org/english/hps6/index.html Four different units are considered in this software: • Solar system • Cooling device • Air handling unit • Cooling and heating components in the room The input data for the programme is: • weather data including solar radiation (hourly data) • load files including heating and cooling loads (hourly data) Chapter C : Predesign – system sizing 28
  15. 15. Dynamic simulation software tools using hourly cooling (heating) load - System orientated TNSYS - www.sel.me.wisc.edu/trnsys/ ColSim - www.colsim.de Insel - http://www.inseldi.com/index.php?id=21&L=1 - Building Orientated Energy plus - www.eere.energy.gov/buildings/energyplus/ Software Solar Components AC Components New Components TRNSYS ColSim Yes Yes Yes Yes Energy Plus INSEL Yes Yes Yes, but no clear list was possible to obtain. Yes Free Open downlaod source code No Yes Not clear Yes Yes Yes Not clear Yes Yes Yes NO NO Chapter C : Predesign – system sizing 29 Identification of HVAC components available which are most interesting for CTSS TRNSYS 16. Type 107 – Absorption Chiller (hot water fired, single effect) Type 51 – Cooling Towers. TESS Libraries Type 680 – Single-effect hot water-fired absorption chiller (Equivalent to type 107 of TRNSYS 16) Type 679 – Single-effect steam-fired absorption chiller Type 677 – Double-effect hot water-fired absorption chiller Type 676 – Double-effect steam-fired absorption chiller Type 683 – Rotary desiccant dehumidifier – models a rotary dessicant dehumidifier containing nominal silica gel. Chapter C : Predesign – system sizing 30
  16. 16. Calculation methods : Estimated calculation with energy balances Solar thermal energy availability • Simulation tool for the solar systems • “Infinite” consumption with high return temperature (chilled water) • 100% use of produced solar energy Energy load determination, per year and per month: cold, heat, and DHW • Calculation tool for the building energy load • DHW energy load determination Use factor determination • Depends on the relation availability / load • Depends on the heat storage solar absorció gas caldera elect bomba calor calefacció refrigeració Definition of energy flows between subsystems • -> Definition of a control strategy Chapter C : Predesign – system sizing Chapter C : Predesign – system sizing Source : Aiguasol Source : Fraunhofer ISE 31 32
  17. 17. Guidelines for design, control & operation of solar assisted adsorption chillers COPsol = COPsol = Radiation on Radiation on 2 collector: 800 W/m 2 collector: 800 W/m 0.6 COP, COPsol, etacoll COP * ηcoll COP * ηcoll 90 80 0.5 70 0.4 60 0.3 50 0.2 40 etacoll COP COPsol 0.1 COP-maximum at about 70°C cooling power cooling power, kW 0.7 30 0 20 60 65 70 75 80 85 90 95 temperature, °C Chapter C : Predesign – system sizing 33 Source : Fraunhofer ISE Efficiency of solar thermal cooling systems 0.60 Irradiation W/m2 0.50 500 600 700 800 900 1000 COPsolar 0.40 0.30 0.20 0.10 ==> optimal working temperature depends on the irradiation level 0.00 Chapter C : Predesign – system sizing 60 80 100 120 140 160 180 200 Working temperature [°C] Source : Fraunhofer ISE 34
  18. 18. Evaluation parameter: Costs of saved primary energy ! Combined Energy-costs-Performance ! enables comparison of different system designs Costs of primary energy saved ∆total annual costs ==annual supplementary costs of the solar ∆total annual costs annual supplementary costs of the solar = driven system compared to aa driven system compared to conventional reference system conventional reference system ∆ Total annual costs ∆ Primary energy ∆primary energy ∆primary energy ==annual primary energy saving of annual primary energy saving of the solar driven system compared to aa the solar driven system compared to conventional reference system conventional reference system Source : Fraunhofer ISE Chapter C : Predesign – system sizing 35 Example: primary energy savings Growing collector surface ! Office buildings ! Flat plate ( in % of the reference system) ! Madrid Primary energy saved 60% 50% 40% 30% ! Backup: Gas boiler ! Absorption Collector surface, m2 20% collector 160 180 200 220 240 260 280 10% 55 65 75 85 95 105 115 125 135 2 Storage volume, l/m chiller Chapter C : Predesign – system sizing Source : Fraunhofer ISE 36
  19. 19. Example: annual costs ansteigende Growing collector Kollektorfläche surface ! Madrid ! Bürogebäude Office ! ! ! ! ! ! buildings Flachkollektor Flat plate Backup: collector Gaskessel Backup: AbsorptionsGas boiler kältemaschine Absorption chiller Jahreskosten, % Referenz Annual costs, % reference 180% 175% 170% 165% 160% 155% 150% 145% 160 Collector surface, Kollektorfläche, m2 m2 180 200 220 240 260 280 140% 55 65 75 85 95 105 115 125 135 Speichervolumen, l/m2 Storage volume l/m2 Source : Fraunhofer ISE Chapter C : Predesign – system sizing 37 ! Madrid ! Bürogebäude Office buildings ! Flachkollektor ! Flat plate ! Backup: collector Gaskessel ! Backup: ! AbsorptionsGas boiler kältemaschine ! Absorption chiller Kosten eingesparte PE, €/kWh Costs of primary energy saved, €/kWh Example: Costs of primary energy savings 0.28 160 0.26 180 Collector surface, Kollektorfläche, m2 200 220 240 260 280 Minimu m 0.24 0.22 0.2 0.18 0.16 0.14 0.12 55 65 75 85 95 105 115 125 135 2 Speichervolumen, l/m Storage volume l/m2 Source : Fraunhofer ISE Chapter C : Predesign – system sizing 38
  20. 20. System sizing Dynamic modelling with TRNSYS… necessary Chapter C : Predesign – system sizing 39 Transient simulation – TRNSYS TRNSYS features – Numerical calculation methods – Continuous yearly simulation of the thermal behaviour of the installation, analysing the transitory phenomenon of the heat flows – Variability of climatology (temperature, irradiation) is taken into account – Enables analysis of the different factors which determine the energetic behaviour of the system # parametric study# optimisation Chapter C : Predesign – system sizing 40
  21. 21. Transient simulation – TRNSYS TRNSYS Workspace Chapter C : Predesign – system sizing 41 Transient simulation – TRNSYS Results obtained with TRNSYS Chapter C : Predesign – system sizing 42
  22. 22. Transient simulation – TRNSYS 35 30 Analysis of the results 25 20 Tamb Tair 15 7000 Monthly heating demand in kWh Total demand in kWh 6000 10 5 Solar contribution in kWh 0 5000 1 14 27 40 53 66 79 92 105 118 131 144 157 kWh 4000 3000 2000 1000 0 Gener Febrer Març Abril Maig Juny Juliol Agost Setembre Octubre NovembreDesembre Chapter C : Predesign – system sizing 43 Transient simulation – TRNSYS Calculation options with dynamic simulation tools Separated calculation of building and cooling system – Step 1: Simulation of the building demand (heating, cooling) – Cooling system model= ideal system with infinite power. – Intermediate result: hourly data of heating and cooling demand. – Step 2: Simulation of the cooling system – Result: energy contribution of the real cooling system Coupled calculation of the building and the cooling system – Simulation of the building (demand) and of the cooling system in the same software – Cooling system model = real system – Results: • Energy contribution of the real cooling system • Degree of fulfilment of the comfort criteria Chapter C : Predesign – system sizing 44
  23. 23. Which questions have to be answered? 1. Which is the basic sizing of the main equipments? • Collector field : type and size in m2 • Absorption machine: kWf 2. What is the solar contribution to the cooling, heating and global demand? 3. Which is the basic sizing of the back-up system? • type (boiler, heat pump, air conditioner...); • size kW 4. Which are the energy savings? 5. What are the additional costs compared to a conventional installation? 6. What is the pay-back time? Chapter C : Predesign – system sizing 45 Chapter C : Predesign – system sizing 46
  24. 24. Rules of Thumb – pre-design rules of solar cooling systems Sizing of the absorption machine Demand peak < maximal total power (absorption + auxiliaries) + cold storage Operating with solar energy: minimal power required to absorb the solar heat produced and convert it into cold. # 3 m2/kWf – Criteria 1: the absorption machine is able to use the maximal solar production. Solar peak production approx. 0.5 kW/m2 (1000 W/m² x 50 % efficiency) kWf kW kW kW m2 0.65 × 0.5 solar ×1 gen = 0.32 2f = 3 kWgen m2 kWsolar m kWf – Criteria 2: the solar energy produced during the day of maximal irradiation can be totally used by the absorption machine, assuming that the required heat storage is available – Maximal power to guarantee a minimal solar contribution (typically > 60...70 %) and/or an reasonable number of operating hours (> 1000 h/year). Chapter C : Predesign – system sizing 47 Rules of Thumb – pre-design rules of solar cooling systems Sizing of the heat/cold storage Cold storage – Cover demand peaks (smaller machines, larger number of operating hours) – Avoid part-load or intermittent operation Heat storage – Gap between cooling demand and solar heat availability – Guarantee continuous operation of the machine during days of intermittent irradiation – Typical size: 25 .. 50 litres / m2 of collector Chapter C : Predesign – system sizing 48
  25. 25. Rules of Thumb – pre-design rules of solar cooling systems Control strategy Starting priority (cold production) according to the energy efficiency – Cold production with heat-pump in case of simultaneous heat demand. Solar contribution for space heating. – Cold production with absorption through solar heat – Cold production with heat-pump (without heat recovery) – Cold production with absorption through gas boiler Chapter C : Predesign – system sizing 49 System sizing 127 kW 85 kW 700W/m² 75 – 95°C 75 – 95°C 200 m² 25 - 35°C 77 kW 7 – 12 °C Chapter C : Predesign – system sizing 50 kWf Source : TECSOL 50
  26. 26. System sizing 1 Cooling load : 50 kWc ! 2 Inlet generator : 50 / 0.65 = 77 kW ! 3 Cooling tower : 77 + 50 = 127 kW ! 4 Primary loop efficiency : 0.9 ! 5 Heat load on collector side : 85 kW ! 6 Average irradiance : 700 W/m² ! 7 Collector efficiency : 0.6 ! 8 Collector area : 85/0.7/0.6 = 200 m² ! 9 Optimal tilt : 30° (France South) ! 10 Groung space necessary > 300 m² ! Chapter C : Predesign – system sizing 51 Check list concept : example Industry 3 3 3 2 2 Space for technical premices 3 2 1 Adapted distribution network 3 3 2 Adapted existing material (or planned) for back up 3 3 3 Daily adequation production <-> load 3 3 1 Yearly adequation production <-> load 3 2 2 Yearly heating and DHW needs 3 2 2 Passives actions decrease potential 3 3 3 Possible undersizement of solar system thanks to back up TECHNICAL FEASIBILITY Hotel 3 Important area for solar collection Building Public building Climate 3 3 2 Load Chapter C : Predesign – system sizing Source : TECSOL 52
  27. 27. Check list concept : example Industry 3 3 2 2 3 3 1 Building owner motivation 3 3 3 Importance in term of marketing impact 3 2 3 Environmental action politics 3 3 3 National & international supports eligibility 1 3 2 Financial stability of building owner 3 3 1 Skilled internal technical staff 3 2 2 Regulat operation action possibilities FEASIBILITY 3 High investment capacity ECONOMICAL Hotel 1 Low water cost Cost of energy Public building High cost of saved energy 3 2 2 Presence of a long term financed monitoring 2 3 2 58 55 45 Building owner ORGANISAT. O&M FEASIBILITY Monitoring TOTAL SCORE (on 63) : Source : TECSOL Chapter C : Predesign – system sizing 53 Disclaimer This training has been developed in the context of SOLAIR. SOLAIR is a European cooperation project for increasing the market implementation of solar-air-conditioning systems for small and medium applications in residential and commercial buildings. For further information on the project or on products of the project see: www.solairproject.eu The project SOLAIR is supported by the Intelligent Energy – Europe (IEE) programme of the European Union promoting energy efficiency and renewables. More details on the IEE programme can be found on: http://ec.europa.eu/energy/intelligent/index_en.html The sole responsibility for the content of this training lies with the authors. It does not represent the opinion of the European Communities. The European Commission is not responsible for any use that may be made of the information contained therein. Chapter C : Predesign – system sizing 54

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