1. Solar CoolingMethods andApplications Sargon Ishaya, PE, LEED AP Pragmatic PE, Incorporated 408-813-2970

2. ObjectivesHelp engineers understanding when andhow to apply solar cooling systemsDescribe two practical methods for solarcoolingGive air conditioning engineers theconfidence to offer customers amechanical approach to solar power 3. Presentation AgendaIntroduction Load Calculation Significance and Methods Overview on Applying Green TechnologiesPART ONE: Introduction to Solar Cooling (CST vs PV) Photo-voltaic systems Solar thermal systems Efficiencies of solar cooling systems Compare and contrast PV to CST in Solar CoolingPART TWO: Application of Solar Cooling (CST or PV) Where does solar power fit? (The Solar Multiple) Solar Cooling Nuances Utilization and the Solar Multiple Storage and the Solar MultipleConclusionsQuestions 4. Load Calculation Methods What are the steps to sizing an air conditioning system for abuilding? Obtain architectural plans Write or review Basis of Design and Owner Project Requirements Enter space diagnostics into a computer program Find peak loads for cooling and heating from computer program Size equipment to satisfy the peak loads Is the process different when applying technologies for a greenbuilding? The answer is a big YES, but why? Lets look at rainwater harvesting in Los Angeles as an example. 5. Load Calculation Methods Given information for Rainwater Harvesting Example: Building is in Los Angeles with monthly precipitation as shown below City water is available, but owner would like to be green and harvest rain Load is constant and equivalent to 150-mm precipitation on capture surface Goal is to minimize cost and complexity of rainwater harvesting It should also be said that this graph is suspect, but will suffice for our exampleChart copied from http://www.weather-and-climate.com/average-monthly-precipitation-Rainfall,Los-Angeles,United-States-of-America 6. Load Calculation Methods Question: What capacity should the rainwater harvest system havein terms of mm precipitation per month? Peak: The July value so it can be stored during summer for use in winter. This is analogous to how an HVAC system would be sized. 150-mm: The capacity needs to match the load. Minimum: The January value and use city water for the remaining. Answer: It depends on cost, but the minimum (January value) willmost likely be the correct answer.Chart copied from http://www.weather-and-climate.com/average-monthly-precipitation-Rainfall,Los-Angeles,United-States-of-America 7. Load Calculation Methods Lesson: Load calculations regarding green technologies depend ontime of use; therefore, calculations need to be run that way. In almost all building and green technology applications the timestep needs to be hourly. Example for a wind turbine application in Decatur, Illinois: Go to http://rredc.nrel.gov/solar/old_data/nsrdb/1991- 2005/tmy3/by_state_and_city.html and scroll down to Decatur Download the file and open it in Excel Note the fields at the top and the dates down the side For a full explanation of all the fields and how to use the data, download the manual from http://www.nrel.gov/docs/fy08osti/43156.pdf Go to column AU and note that wind speed is given for every hour of the year 8. Load Calculation Methods Choose a sample wind turbine. The one I have chosen has thefollowing characteristics Cuts in at 3.5-m/s wind speed Is rated at 13-m/s wind speed Cuts out at 25-m/s wind speed Looking at the Power Output vs. Wind Speed curve of the turbine Isurmise that Im not going to count a usable hour of wind turbineoutput until the wind speed is 7-m/s 9. Load Calculation Methods Now go to the spreadsheet and create a toggle column to countthe hours of usable wind per year in Decatur On a real job the curve below would be input so the actual power output would get calculated by the spreadsheet The time of day energy use would also be input so that the value of the power offset by the turbine would be accurately calculated After the toggle formula is created, count the hours per year thatthe turbine provides usable power Answer: 1,375 hours/year When do these hours occur? 10. Load Calculation Methods Applying solar thermal technologies is not different than therainwater harvesting or wind turbine examples Load calculations need to be done on an hourly basis to determine if the application is even worthwhile The analysis must optimize the size of the system based on hourly usage and not peak loads Equipment limitations must be taken into account; for example, hot water tanks cannot store water at temperature overnight Spreadsheets are an excellent tool for these analyses and allow forrepeatability and speed Money talks so put this dimension into the engineering calculations 11. Applying Green Technology Base and Transient LoadsConstant (base) loads are building loads that are not a function ofthe time of day nor seasons of the year Lobby and corridor lighting within a hotel is one example of a hotels constant load components What are other examples of constant HVAC loads in a building or facility? Transient LoadTotal area under the curverepresents kW-hr per dayConstant (Base) LoadChart copied from http://www.esource.com/files/esource/images/CEA-06_2F.gif 12. Applying Green Technology Base and Transient LoadsTransient loads are building loads that are a function of the time ofday or seasons of the year A fancy restaurant within a hotel is one example of a hotels transient load components Can you think of any other examples of transient loads in a building or facility? Transient LoadTotal area under the curverepresents kW-hr per dayConstant (Base) LoadChart copied from http://www.esource.com/files/esource/images/CEA-06_2F.gif 13. Applying Green Technology Base and Transient Loads Is it possible to engineer transient loads so that they become baseloads? How?Transient Load Total area under the curve represents kW-hr per day Constant (Base) Load Chart copied from http://www.esource.com/files/esource/images/CEA-06_2F.gif 14. Applying Green Technology Base and Transient LoadsSometimes it is advantageous to flatten out transient loads so thatthey act like base loads (fuel cell applications are like this)Going back to the example of a hotel, look at the hot water loadsand note that they are mostly transient: Showers and lavatory use Pool and/or hot tub heating Kitchen and Dining Facility - human consumption Kitchen and Dining Facility - cleaning Laundry Space heating Is it possible to flatten out these transient loads? 15. Applying Green Technology Base and Transient Loads Using Storage and Time-of-Use Scheduling can make transientloads base loads, but the operators must complyMorning Time12:00 AM 1:00 AM 2:00 AM 3:00 AM 4:00 AM 5:00 AM 6:00 AM 7:00 AM 8:00 AM 9:00 AM 10:00 AM 11:00 AMShowers/LavatoryStorage Storage Storage StoragePool/Hot TubBoilerBoilerBoiler Dining/DrinkingBoilerBoilerBoilerBoilerBoiler Kitchen CleaningBoiler BoilerBoiler Boiler Laundry Boiler Boiler BoilerSpace HeatingBoiler Boiler Boiler Boiler Boiler BoilerBoilerBoiler Boiler Afternoon Time 12:00 PM 1:00 PM 2:00 PM 3:00 PM 4:00 PM 5:00 PM 6:00 PM 7:00 PM 8:00 PM 9:00 PM 10:00 PM 11:00 PMShowers/LavatoryStorage Storage StoragePool/Hot Tub BoilerBoilerBoiler BoilerBoiler Dining/Drinking Boiler BoilerBoilerBoilerBoilerBoilerBoilerBoiler Boiler Kitchen CleaningBoiler Boiler Boiler LaundrySpace Heating BoilerBoilerBoilerBoilerBoilerBoiler Boiler 16. Applying Green Technology Correlation and PaybackPayback (or higher Net Present Value) of a green technology isoptimized when the green commoditys availability and itsconsumption are correlated (directly proportional to each other) Example: Daylighting by which windows and skylights are used inplace of electrical lightingDaylighting an elementary school classroom (only open duringschool hours) Commodity = sunlight Consumption = lighting requirement for the room Are consumption (occupied room) and availability (sunlight) correlated? Does the electrical infrastructure to fully light the room at night need to be installed? 17. Applying Green Technology Correlation and PaybackPayback (or higher Net Present Value) of a green technology isoptimized when the green commoditys availability and itsconsumption are correlated (directly proportional to each other)Daylighting a movie theater Are consumption (lighting theater between movies) and availability (sunlight) correlated? Does the electrical infrastructure to fully light the room at night need to be installed?Sharing examples of correlated and uncorrelated greentechnologies versus loads Many well-engineered daylighting systems dont show substantialsavings. Why do you think this happens? In my calculations I dont factor in the human component ofignoring the design constraints. 18. Applying Green Technology Utilization and PaybackPayback (or higher Net Present Value) of a green technology isoptimized when the most expensive components of the system areoperating 100% of the timeObvious Example: Company electric vehicles Vehicles and charging stations are the most expensive components (as opposed to parking spaces, maintenance, and management) Electric vehicles save about $0.065 per mile1 If an outside sales engineer drives an average of 100-miles per week and an inside sales engineer drives 50-miles per week, then who should get the electric vehicle? 19. Applying Green Technology Utilization and PaybackPayback (or higher Net Present Value) of a green technology isoptimized when the most expensive components of the system areoperating 100% of the timeNot so Obvious Example: The solar arrays in solar-thermal powerplants The steam-to-electricity generation system is much, much more expensive than the solar array (parabolic troughs) These plants may have a solar array capable of 2-MW when the steam/electrical infrastructure only handles 1-MW because it makes economic cents/sense 20. Applying Green Technology Utilization and PaybackPayback (or higher Net Present Value) of a green technology isoptimized when the most expensive components of the system areoperating 100% of the timeRamification: Sizing a green system often depends on costs insteadof loads Typically air conditioning systems are sized to handle the maximum load, but they operate at about 60% of capacity on average (60% utilization) A green technology system should not be sized this way; rather, it should be sized so that 100% of the expensive components are utilized while the system operates This is similar to the rainwater harvesting example spoken about earlier This is why spreadsheets with hourly calculations and integratedcosts are so important when engineering green technologies like solarcooling 21. Examples of Offsetting Base and Transient Loadswith Green Technologies Fuel Cells Typically use natural gas in an emission-free, non combustion process to produce electricity and high grade waste heat that can be used for heating or cooling Initial cost of fuel cell is very high compared to other components What is the green commodity and what is its availability? From a correlation/utilization standpoint, are fuel cells best for constant loads or transient loads? Fuel cell inNebraska 22. Examples of Offsetting Base and Transient Loads with Green TechnologiesWind Turbines (non-utility) Residential or community wind turbine plants typically generate more electricity in the evenings Given this information, what kind of building load would wind turbines be best suited for?Note how loads are targeted when applyinggreen technologies 23. What Happens if Correlation is not possible?Do commodity availability and consumption have to be correlated?What can be added to a system to account for uncorrelated consumption andavailability? RainwaterHarvesting SystemStorage Tank Electric/Hybrid Automobile BatteryConclusion: Understanding the application and the characteristics of a specificgreen technology are very important NOW LETS LOOK AT SOLAR COOLING 24. ObjectivesHelp engineers understanding when andhow to apply solar cooling systemsDescribe two practical methods for solarcoolingGive air conditioning engineers theconfidence to offer customers amechanical approach to solar power 25. Presentation AgendaIntroduction Load Calculation Significance and Methods Overview on Applying Green TechnologiesPART ONE: Introduction to Solar Cooling (CST vs PV) Photo-voltaic systems Solar thermal systems Efficiencies of solar cooling systems Compare and contrast PV to CST in Solar CoolingPART TWO: Application of Solar Cooling (CST or PV) Where does solar power fit? (The Solar Multiple) Solar Cooling Nuances Utilization and the Solar Multiple Storage and the Solar MultipleConclusionsQuestions 26. Solar Cooling with Photo Voltaic (PV) PanelsSunlight Photovoltaic Panels ElectricityComfortablyCool BuildingVapor Compression Chiller 27. Solar Cooling with Photo Voltaic (PV) Panels Coefficient of Performance (COP) Heat Out = Cooling Electricity Input 3.0 for air-cooled 5.0 for water-cooled Condensation Electricity High Pressure Side Input(Hot Refrigerant) Expansion Low Pressure SideCompression(Cold Refrigerant)Evaporation Heat In = Cooling 28. Solar Cooling with Photo Voltaic (PV) PanelsWhy are we using a water-cooled chiller system in the PV panelanalysis?The answer is the same as why the first step in putting PV panels ona home is to make the appliances more efficient The cost of the PV system is much more expensive than the cost ofupgrading appliances (in a home) or installing a very efficient coolingsystem (in a building) so it makes economic sense to minimize the PVpanel quantity 29. Solar Cooling with Solar Thermal Panels Evacuated TubesSunlightSolar Thermal PanelsHot FluidComfortablyCool BuildingAbsorption Chiller 30. Solar Cooling with Solar Thermal Panels Single Effect Absorption Cycle Uses Ammonia or Lithium Bromide as a sorbent Ammonia is an atmospheric pressure cycle, LiBr is under a vacuum There are very common in applications where there is waste (free) heat like in hospitals and power plants 31. Solar Cooling with Solar Thermal Panels Double EffectAbsorption CycleUses Ammoniaor LithiumBromide as asorbent There are otherways to achievedouble effect,drawing shown isonly oneapplication 32. Solar Cooling with Solar Thermal Panels Coefficient of Performance (COP)= Cooling Driving Heat Input 0.7 for single effect (180F) 1.3 for double effect (350F)Evacuated Tubes 33. Comparing Rooftop Solar Cooling OptionsSolar Cooling Efficiency (SCE) = Collection Efficiency * Cooling EfficiencyCollection Efficiency = Available solar energy converted to electricity (PV) or heat (Thermal)Cooling Efficiency = Coefficient of Performance (COP) of the refrigeration process SCEPV = 15% Collection Efficiency * 5.0VC = 75% Removed from further SCEST = 50% Collection Efficiency * 0.7SE = 35% considerationEvacuated Tubes SCECST = 65% Collection Efficiency * 1.3DE = 85%Fresnel Concentrator 34. Comparing Rooftop Solar Cooling OptionsRoof Area (not including service access clearances) Refers to actual solar panel area Roof footprint may be different, panels assumed to be on 25 angle AreaPV = 66 square feet per ton(COP = 5, 170 Watts AC, GE panel) AreaCST = 62 square feet per ton(COP = 1.3, Chromasun panel) Fresnel ConcentratorNote for a cooling load of 400-square feet per ton that solar cancool at least two stories with ample roof area left over 35. Comparing Rooftop Solar Cooling Options September 2009 ASHRAE article compared several methods of harnessing solar power and concluded that solar-thermal beat photo-voltaic in Abu Dhabi 36. Comparing Rooftop Solar Cooling OptionsSolar Cooling Cost Refers to new installations first-costs Maintenance cost differences between PV and CST are insignificant Balance-of-Plant cost differences between PV and CST are insignificant CostPV = $5,000 per ton (COP = 5, $7/Watt) CostCST = $5,500 per ton (COP = 1.3, $2,400/Chromasun panel)Fresnel ConcentratorIncentives and Rebates Federal Investment Tax Credit (ITC) gives back 30% of the total system cost for a solar installation Many local utilities have programs in place to absorb even more money (about 25%) of costs 37. Comparing Rooftop Solar Cooling OptionsEnergy Payback Time (EPBT) = Energy to Manufacture Annual Output Energy to Manufacture = Requirement to manufacture solar collector Annual Output = Useful energy output from the collector over a one year period EPBTPV = 3 years to 7 years (7 years figure from: Blakers, Weber, The Energy Intensity of Photovoltaic Systems, October, 2000) EPBTCST = 0.7 years Fresnel Concentrator 38. Comparing Rooftop Solar Cooling OptionsRecyclability at the end of panel life The most widely used solar PV panels...have the potential to create a huge new wave of electronic waste (e-waste) at the end of their useful lives...new solar PV technologies are increasing cell efficiency and lowering costs, but many of these use extremely toxic materials or materials with unknown health and environmental risks. - Toward a Just and Sustainable Solar Energy Industry, Silicon Valley Toxics Coalition (1/14/09) CST panels have aluminum frames, steel pipe (receiver), and tempered glass covers. The unit is fully recyclable except for the sealing compound atFresnel Concentrator the glass/metal interface, a small control board, and black receiver paint. 39. Comparing Rooftop Solar Cooling OptionsUlterior Benefits of a PV systemPV is more common than CST and has industry inertiabehind it (easier to permit and get competitive rates) 40. Objectives SummaryDescribe two practical methods for solar cooling Photo-voltaic (PV) Concentrating Solar Thermal (CST)Give air conditioning engineers the confidence tooffer customers a mechanical approach to solar power CST slightly beats PV in efficiency CST wins over PV in cost and moves solar power monies to the mechanical scope CST obviates PV when considering environmental impact PV is much more popular than CST in the current marketHelp engineers understanding when and how toapply solar cooling systems 41. Presentation AgendaIntroduction Load Calculation Significance and Methods Overview on Applying Green TechnologiesPART ONE: Introduction to Solar Cooling (CST vs PV) Photo-voltaic systems Solar thermal systems Efficiencies of solar cooling systems Compare and contrast PV to CST in Solar CoolingPART TWO: Application of Solar Cooling (CST or PV) Where does solar power fit? (The Solar Multiple) Solar Cooling Nuances Utilization and the Solar Multiple Storage and the Solar MultipleConclusionsQuestions 42. Harnessing the Sun as a Green Technology for a BuildingIs the suns energy best-suited for offsetting base loads or transient loads?What kind of building load correlates well with sunlight?Can the transient sun satisfy the entire cooling load of a building?A better question is can the environment satisfy the entire cooling load? 43. Can the Environment Satisfy All Cooling Loads? (Yes!)When outside air is cold enough to satisfy cooling load use airside economizersWhen air is not cold enough but sun is out satisfy load with solar coolingElevating supply air setpoint achieves sustainable cooling with some free heating 44. The Solar MultipleShould the Environment Satisfy All Cooling Loads?Recall Utilization: Economics of a green technology are optimizedwhen the most expensive components operate 100% of the timeSolar panels (CST or PV) are by far the most expensive componentsof a solar cooling systemSolar cooling should possibly be sized for less than the total load tomaximize utilization (Solar Multiple < 1) Solar Multiple =Maximum Cooling Output of Solar Panel Array Design Cooling Load of BuildingCorrelation Sizing Strategy: Size the solar cooling system to satisfyonly the solar-dependent components of the buildings cooling loadThis sizing strategy maximizes correlation and utilization 45. CST or PV Solar Cooling: Utilization and the Solar MultipleIf Cooling SAT > 62F it favors full-load free-cooling (Solar Multiple 1)Solar Multiple < 1 in all other systems to optimize economics 46. PV Solar Cooling: Storage and the Solar MultipleBenefits of a PV system with Solar Multiple > 1 The grid is a readily available and free storage system Systems can be sized to make annual energy bills zero out (100% utilization) A potentially less-expensive approach might be a hybrid CST and PV system 47. CST Solar Cooling: Storage and the Solar MultipleBenefits of over-sizing a CST system (Solar Multiple > 1) Building or campus loops are readily available and free storage systems When CST output > building cooling load, the extra is still used in-house 48. Solar Collectors - Flat PlatesSunlightEvacuated TubesSolar Thermal PanelsHot Fluid 49. Standard Flat Plate Collector 50. Flat Plate Collector Types 51. Flat Plate Collectors Pros and ConsSunlight Evacuated TubesSolar Thermal Panels Hot FluidAdvantages DisadvantagesComparatively very inexpensive method forHeat of the fluid generated is not high gradeharnessing solar resource(only domestic hot water or pool heating)Very common in the industry, competitive Large receiver surface area means highproducts and installers are easy to find losses on cold, sunny daysLow energy payback time and almost fully Evacuated tubes usually lose their chargerecyclable after about 7-yearsQualify more easily for solar-thermalNo way to turn panel off controlsrebatesnecessary to prevent overheating 52. Photo-Voltaic Collectors Pros and Cons SunlightElectricity Photovoltaic Panels AdvantagesDisadvantagesLast longer than flat plates (20-25 years) Expensive method for harnessing solar resource compared to flat platesVery common in the industry, competitive Very high energy payback time, at end ofproducts and installers are easy to find life they become electronic wasteQualify for electrical rebates, can takeComparatively very low efficiencies versusadvantage of the coefficient of performance flat plates and concentrator panelsThe grid is free storage Do not qualify for thermal rebates (unless heat recovery is accepted) 53. Concentrating Solar Thermal CollectorsSunlightSolar Thermal Concentrating PanelsHot Fluid 54. Concentrating Collector Types Parabolic Troughs and Compound Parabolic Concentrators Parabolic Troughs Compound Parabolic Concentrators (CPC)Tracking necessaryNo tracking necessary! 55. Concentrating Collector Types Linear Fresnel ConcentratorsAdvantages over other ConcentratorsLowest heat loss of all concentratorsFlat Panel shape for easy roof-mounting(troughs are ground-mounted)Easily stowed by moving mirrors (dissipatersnot required as opposed to CPC) Fresnel Mirror Arrays 56. Concentrating Solar Thermal Pros and ConsSunlight Solar ThermalConcentrating PanelsHot Fluid Advantages DisadvantagesFresnel and Troughs: Last as long as PV panels Expensive method for harnessing solar(20-25 years), internally controlled to loseresource compared to flat platesthe sun instead of overheating (CPC not so)High grade heat (solar cooling and hydronicNot common in the industry, competitiveheating are easily viable) products and installers are hard to findQualify for thermal rebates, take advantage of Require storage tank for uncorrelated loadsheat pump coefficients of performanceHighest efficiency for harnessing solar energy 57. Flat Plate Collector Applications Coefficient of Performance (COP)= 1.0 for heating SunlightSolar ThermalEvacuated TubesPanelsSwimmingPool Hot Fluid 130F Heating Domestic Hot Water Heating 58. Solar Thermal Temperatures Solar Collector Performance Curves 100%Ambient Temperature 20CSolar Radiation 800 W/m2 90% 80% 70%Collector Efficiency [%] 60% Chromasun HT MCT 50% Evacuated Tube Flat Plate 130F Line 40% CPC 30% 20% 10%0%0 204060 80 100120140 160 180200 Temperature Difference (Tm-Ta) [C] 59. Solar Heating with Photo Voltaic (PV) PanelsCoefficient of Performance = Cooling Electricity Input 2 for air-source heatingSunlightPhotovoltaic PanelsElectricity ComfortablyWarm Building Air-CooledHeat Pump 60. Solar Cooling with Photo Voltaic (PV) PanelsCoefficient of Performance = Cooling Electricity Input 3.0 for air-cooled 5.0 for water-cooledSunlightPhotovoltaic Panels Electricity Water-CooledChillerComfortablyCool Building OR Air-Cooled Heat Pump 61. Solar Heat Recovery with Photo Voltaic (PV) Panels Coefficient of Performance 3.0 for cooling 2.2 for heating Every Watt of sunlight becomes 5.2 Watts of useful thermal energy! Sunlight Photovoltaic CoolPanelsBuildingElectricityDomestic HeatHotRecovery WaterChiller 62. Solar Heating with Rooftop Concentrators SolarCoefficient of Performance (COP) Thermal Direct Heating = 1.0Panels 1.6 Absorption Heat Pump SunlightHot Fluid 365F Domestic WaterHeating ORHydronicAbsorption WaterHeat Pump Heating 63. Solar Cooling with Rooftop Concentrators Coefficient of Performance (COP) 1.3 Double Effect AbsorptionSunlight Solar Thermal PanelsHot FluidComfortablyCool Building Absorption Chiller 64. Solar Heat Recovery with Rooftop Concentrators Solar Coefficient of Performance (COP) Thermal Every Watt of sunlight becomes 2.2Panels Watts of useful thermal energy!Sunlight CoolCOP 0.6 Hot FluidBuildingDomestic COP 1.6AbsorptionHot Heat Pump Water 65. Conclusions What to RememberApplying a green technology where consumption and availability ofthe green commodity are closely correlated has superior economicsSunlight and solar-dependent heat gains are closely correlatedApplying a green technology where the most expensive systemcomponent(s) are utilized as much as possible has superior economicsSolar cooling panel utilization is always high when sized for the solarcomponent of the cooling load (Solar Multiple < 1)Coupling solar cooling and airside economizers gives the potentialfor free cooling 24/7 in buildings with elevated supply air set points(laboratories, data centers, classrooms, DOAS, UFAD)Solar cooling adds substantial scope to the mechanical portion of ajob thereby increasing profits for air conditioning companiesQuestions?