Solar Cooling. Methods and Applications. Sargon Ishaya, PE, LEED AP

Transcription

1 Solar Cooling Methods and Applications Sargon Ishaya, PE, LEED AP

2 Objectives Describe two practical methods for solar cooling Give air conditioning engineers the confidence to offer customers a mechanical approach to solar power Review general concepts of engineering with green technologies Help engineers understand when and how to apply solar cooling systems

3 Presentation Agenda PART 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 Cooling PART TWO: Application of Solar Cooling (CST or PV) Green Technology Overview Constant and Transient Loads Maximizing Payback Correlating Load and Commodity Maximizing Payback Utilization Factor Application of Offsetting Loads with Green Technologies Where does solar power fit? (The Solar Multiple) Solar Cooling Nuances Utilization and the Solar Multiple Storage and the Solar Multiple Conclusions Questions

4 Solar Cooling with Photo Voltaic (PV) Panels Sunlight Photovoltaic Panels Electricity Comfortably Cool Building Vapor Compression Chiller

5 Solar Cooling with Photo Voltaic (PV) Panels Why use a chilled water system? What does vapor-compression mean? Heat Out Condensation Coefficient of Performance (COP) = Cooling Electricity Input 3.0 for air-cooled 5.0 for water-cooled Electricity Input Expansion High Pressure Side (Hot Refrigerant) Compression Low Pressure Side (Cold Refrigerant) Evaporation Heat In = Cooling

6 Solar Cooling with Solar Thermal Panels Evacuated Tubes Sunlight Solar Thermal Panels Hot Fluid Comfortably Cool Building Absorption Chiller

7 Solar Cooling with Solar Thermal Panels What does absorption mean? How hot is the driving heat source? Coefficient of Performance (COP) = Cooling Driving Heat Input 0.7 for single effect (180 F) 1.3 for double effect (350 F) Evacuated Tubes

8 Comparing Rooftop Solar Cooling Options Solar Cooling Efficiency (SCE) = Collection Efficiency * Cooling Efficiency Collection Efficiency = Available solar energy converted to electricity (PV) or heat (Thermal) Cooling Efficiency = Coefficient of Performance (COP) of the refrigeration process SCE PV = 15% Collection Efficiency * 5.0 VC = 75% Evacuated Tubes Removed from further SCE ST = 50% Collection Efficiency * 0.7 SE = 35% consideration SCE CST = 65% Collection Efficiency * 1.3 DE = 85% Fresnel Concentrator

9 Comparing Rooftop Solar Cooling Options Roof Area (not including service access clearances) Refers to actual solar panel area Roof footprint may be different, panels assumed to be on 25 angle Area PV = 66 square feet per ton (COP = 5, 170 Watts AC, GE panel) Fresnel Concentrator Area CST = 62 square feet per ton (COP = 1.3, Chromasun panel) Note for a cooling load of 400-square feet per ton that solar can cool at least two stories with ample roof area left over

10 Solar Cooling Cost Comparing Rooftop Solar Cooling Options 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 Cost PV = $5,000 per ton (COP = 5, $7/Watt) Fresnel Concentrator Incentives and Rebates Cost CST = $5,500 per ton (COP = 1.3, $2,400/Chromasun panel) Federal Investment Tax Credit (ITC) gives back 30% of the total system cost for a solar installation Most local utilities have programs in place to absorb even more money (about 25%) of costs

11 Comparing Rooftop Solar Cooling Options Energy 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 EPBT PV = 3 years to 7 years (7 years figure from: Blakers, Weber, The Energy Intensity of Photovoltaic Systems, October, 2000) EPBT CST = 0.7 years Fresnel Concentrator

12 Comparing Rooftop Solar Cooling Options Recyclability 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) Fresnel Concentrator CST panels have aluminum frames, steel pipe (receiver), and tempered glass covers. The unit is fully recyclable except for the sealing compound at the glass/metal interface, a small control board, and black receiver paint.

13 Comparing Rooftop Solar Cooling Options Ulterior Benefits of a PV system PV is more common than CST and has industry inertia behind it (easier to permit and get competitive rates)

14 Objectives Summary Describe two practical methods for solar cooling Photo-voltaic (PV) Concentrating Solar Thermal (CST) Give air conditioning engineers the confidence to offer 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 market Help engineers understanding when and how to apply solar cooling systems

15 Presentation Agenda PART 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 Cooling PART TWO: Application of Solar Cooling (CST or PV) Green Technology Overview Constant and Transient Loads Maximizing Payback Correlating Load and Commodity Maximizing Payback Utilization Factor Application of Offsetting Loads with Green Technologies Where does solar power fit? (The Solar Multiple) Solar Cooling Nuances Utilization and the Solar Multiple Storage and the Solar Multiple Conclusions Questions

16 Applying Green Technology Base and Transient Loads Constant (base) loads are building loads that are not a function of the time of day nor seasons of the year Lobby and corridor lighting within a hotel is one example of a hotels constant load components Do you know of any other examples of constant loads in a building or facility? Transient loads are building loads that are a function of the time of day or seasons of the year A fancy restaurant within a hotel is one example of a hotel s transient load components Can you think of any other examples of transient loads in a building or facility? Transient Load Total area under the curve represents kw-hr per day Constant (Base) Load Chart copied from

17 Applying Green Technology Correlation and Payback Payback (or higher Net Present Value) of a green technology is optimized when the green commodity s availability and it s consumption are correlated (directly proportional to each other) Daylighting an elementary school classroom (only open during school 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? 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 green technologies versus loads

18 Applying Green Technology Utilization and Payback Payback (or higher Net Present Value) of a green technology is optimized when the most expensive components of the system are operating 100% of the time Obvious 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 mile 1 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? Not so Obvious Example: The solar arrays in solar-thermal power plants The steam-to-electricity generation system is much, much more expensive than the solar array 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 Ramification: Sizing a green system often depends on costs instead of 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

19 Examples of Offsetting Base and Transient Loads with 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 it s availability? From a correlation/utilization standpoint, are fuel cells best for constant loads or transient loads? Fuel cell in Nebraska Total area under the curve represents kw-hr per day Constant (Base) Load Wind Turbines (non-utility) Residential or community wind turbine plants 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 applying green technologies

20 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 and availability? Rainwater Harvesting System Storage Tank Electric/Hybrid Automobile Battery Conclusion: Understanding the application and the characteristics of a specific green technology are very important NOW LET S LOOK AT SOLAR COOLING

21 Harnessing the Sun as a Green Technology for a Building Is the sun s 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?

22 Can the Environment Satisfy All Cooling Loads? (Yes!) When outside air is cold enough to satisfy cooling load use airside economizers When air is not cold enough but sun is out satisfy load with solar cooling Elevating supply air setpoint achieves sustainable cooling with some free heating

23 The Solar Multiple Should the Environment Satisfy All Cooling Loads? Recall Utilization: Economics of a green technology are optimized when the most expensive components operate 100% of the time Solar panels (CST or PV) are by far the most expensive components of a solar cooling system Solar cooling should possibly be sized for less than the total load to maximize utilization (Solar Multiple < 1) Solar Multiple = Maximum Cooling Output of Solar Panel Array Design Cooling Load of Building Correlation Sizing Strategy: Size the solar cooling system to satisfy only the solar-dependent components of the building s cooling load This sizing strategy maximizes correlation and utilization

24 CST or PV Solar Cooling: Utilization and the Solar Multiple If Cooling SAT > 62 F it favors full-load free-cooling (Solar Multiple 1) Solar Multiple < 1 in all other systems to optimize economics

25 PV Solar Cooling: Storage and the Solar Multiple Benefits 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

26 CST Solar Cooling: Storage and the Solar Multiple Benefits 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

27 Conclusions What to Remember Applying a green technology where consumption and availability of the green commodity are closely correlated has superior economics Sunlight and solar-dependent heat gains are closely correlated Applying a green technology where the most expensive system component(s) are utilized as much as possible has superior economics Solar cooling panel utilization is always high when sized for the solar component of the cooling load (Solar Multiple < 1) Coupling solar cooling and airside economizers gives the potential for 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 a job thereby increasing profits for air conditioning companies Questions?