Solar space cooling

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Contents

Introduction

There are many benefits to Solar Cooling systems. For one the sun is a clean energy resource that we should be using more often. It also produces no emissions and is replenished naturally, it reduces greenhouse gases, it saves the release of 1.6 lbs. of carbon dioxide (CO2) for each kilowatt-hour (kWh) produced, it saves the use of one-half gallon of water for each kWh of solar energy produced, it saves the release of other emissions that result from the burning of fossil fuels such as nitrogen oxides, sulfur dioxide or mercury and it provides customers with options to reduce their electric bills. But up to this point Solar Cooling systems are not widely used at all. Why?

  • There are a couple of reasons: Stand alone units are way too expensive, at $4000 to $8000 per ton. They may become more competitive if paired with solar heating systems. Not only are the costs high but in order to work efficiently theses solar systems need plenty of sunlight therefore will not be effective in some areas. But could easily be the future of places like Africa, Australia and the Southwestern United States. In addition, most solar cooling systems are only provide 40 to 70% of the buildings cooling needs. So if paired with a traditional air conditioning unit energy will be saved, but the solar cooling unit can not stand on it's own as the sole cooling unit of a building yet. But technologies are continuously being developed so that in the future we can use the sun's energy to cool our homes and office buildings.

Solar Absorption Technology

Needs:high temperatures, evacuated-tube solar collectors, fans

  • The advanced absorption technology may be the futures air conditioning using solar power. Absorption cooling is essentially an air conditioning system driven not by electricity but by a heat source, in this case the sun. Evacuated-tube solar collectors and solar panels absorb the sun's heat which is then used to heat up a 1200 gallon insulated hot water storage tank until the water reaches 180 degrees Fahrenheit. The hot water is then pumped into a generator then into a chiller. The chiller contains an absorbent, usually lithium bromide salt. This absorbent yields the refrigerant, which condenses and produces chilled water. The air from inside the building is pushed, by a fan, over the the coil units containing the chilled water. The, now cool, air is circulated back into the building.
  • There are single-effect and double-effect absorption systems. Double-effect systems use the heat twice in the series and are twice as efficient but require nearly twice as much heat.

Solar Desiccant Technology

Needs: solar collectors, desiccants

  • The desiccant is on a wheel that rotates into the air stream going into the room. A desiccant is mostly a solid, like silica gel or calcium sulfate, used for absorbing the humidity of the air, therefore lowers the air temperature. Solar collectors are used to dry off the desiccant of the absorbed water so it can continue to absorb humidity.

Passive Solar Cooling

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The goal of passive cooling is to cool the home or building without using air conditioning and instead using shading, natural ventilation and adequate construction materials.

  • Shading:
    • Trees: Use deciduous trees on the sunniest side of the structure (for the Northern Hemisphere that's the south side and for the Southern Hemisphere the north side) and also on the east and west for the the maximum shade.
    • Overhangs: If properly built and dimensioned overhangs can block out most of the sum in the summer when the sun is at its highest.
  • Low Thermal Materials: Materials like wood and metal have low thermal mass meaning they are hard to heat up and cool down quickly. This is ideal in materials for a passive cooling building. Wood frames with a metal roof are used often.
  • Reflective Exterior Surfaces: Large amount of the sun's heat can be reflected away with the right surfaces. Shiny or smooth surfaces and the color white work the best. By making roofs reflect the sunlight instead of absorbing it can really cut down on our energy consumption and therefore lessen our CO2 output. The National Lab came out with a study that revealed “that retrofitting 80 percent of air-conditioned buildings in the United States with white roofs would save $735 million annually in reduced energy bills while achieving an emissions reduction equivalent to removing 1.2 million cars from the road.”

References

House Energy.com alternativeenergybase.com williams.edu uesaz.com [1] greenblog