CAN WE PUT A/C IN THE DOG HOUSE, TOO? Nations around the world including the USA are interested in solar air conditioning. The U.S. Energy Independence and Security Act of 2007 created a program that funded solar air conditioning research and development with the idea that this technology might play an increasing role in zero-energy and energy-plus building design. This can be done through passive solar, solar thermal energy conversion, and photovoltaic conversion.
BASIC PV: Simply put, PV can provide the power for any type of electrically powered cooling be it conventional compressor-based or adsorption/absorption-based, though the most common implementation is with compressors. For small residential and small commercial cooling PV-powered cooling has been the most frequently implemented solar cooling technology.
For example, a 100,000 BTU U.S. Energy Star rated air conditioner with a high seasonal energy efficiency ratio of 14 requires around 7 kW of electric power for full cooling output on a hot day; thus, taking the full output of a 7 kW solar photovoltaic electricity generation system at optimal climatic conditions. Due to the advent of net metering allowed by utility companies, a photovoltaic system can produce enough energy in the course of the year to completely offset the cost of the electricity used to run air conditioning, depending on the amount of electric costs one wishes to offset. A more efficient air conditioning system would require a smaller, less-expensive photovoltaic system. A 100,000 BTU SEER 20 air conditioner would require less than 5 kW while operating. Newer and lower power technology including reverse inverter DC heat pumps can achieve SEER ratings up to 26.
SOLAR POWERED ABSORPTION CHILLERS: These chillers are powered by hot water which is supplied through evacuated tube collectors. The solar collectors collect thermal energy from the sun and transfer it using a glycol-water solution (or some other combination) along with a system of pipes, pumps and controllers. Here, the solar energy is gained through the collector, and is accumulated in the storage tank. Then, the hot water in the storage tank is supplied to the generator to boil off water vapor from the chemical solution and water. The water vapor is cooled down in the condenser and then passed to the evaporator where it again is evaporated at low pressure, thereby providing cooling to the required space. Not so hard to understand was it?
THE FUTURE FOR SOLAR AIR CONDITIONING: There are new non-compressor-based electrical air conditioning systems with a SEER above 20 coming on the market. New versions of phase-change indirect evaporative coolers use nothing but a fan and a supply of water to cool buildings without adding extra interior humidity. In fact, a 100,000 BTU indirect evaporative cooler would only need enough photovoltaic power for the circulation fan (plus a water supply).
A less-expensive partial-power photovoltaic system can reduce the monthly amount of electricity purchased from the power grid for air conditioning. And it is fairly simple to reduce the heating-and-cooling requirement for new construction by one half. This can often be done at no additional net cost, since there are cost savings for smaller air conditioning systems and other benefits.
See You Next Time! Dr. Stripling