Page 264 - Alternative Energy Systems in Building Design

240 PASSIVE SOLAR HEATING TECHNOLOGIES

unit. A ton of cooling energy is 12,000 Btu/h, which, as defined in the past, is the energy
required to remove heat from a space through melting a ton of ice. One ton, or
12,000 Btu, is equal to 3413 W of electric power.
Based on the preceding definitions, the COP of an air-conditioning unit that requires
1500 W of electric power per ton is equal to 12,000 Btu/h (1 kW = 3413 Btu).
Therefore, 1.5 kW × 3414 = 5121 Btu of supplied energy, which means that COP =
12,000 Btu cooling energy/5121 Btu supplied energy = 2.343. A lower electric-energy
requirement will increase the COP rating, which brings us to the conclusion that the
lower the amount of energy input, the better is the efficiency.

HYBRID ABSORPTION CHILLERS

The combined use of passive solar and natural gas–fired media evaporation has given
rise to a generation of hybrid absorption chillers that can produce a large tonnage of
cooling energy by the use of solar- or geothermal-heated water. A class of absorption that
commonly uses LiBr has been available commercially for some time, with solar power
as the main source of energy. A 1000-ton absorption chiller can reduce electric energy
consumption by an average of 1 MW, or 1 million W, which will have a very significant
impact on reducing electric-power consumption and resulting environmental pollution,
as described in earlier chapters.

DESICCANT EVAPORATORS
Another solar power cooling technology makes use of solar desiccant-evaporator air-
conditioning, which reduces outside air humidity and passes it through an ultraefficient
evaporative cooling system. This cooling process, which uses an indirect evaporative
process, minimizes air humidity, making the use of this technology quite effective in
coastal and humid areas.

Direct Solar Power Generation

This section discusses a project, undertaken by Solargenix Energy, that makes use of
special parabolic reflectors that concentrate solar energy into circular pipes located at
the focal center of the parabola. The concentrated reflection of energy elevates the tem-
perature of the circulating liquid mineral oil within the pipes, raising the temperature to
such levels that considerable steam generation via special heat exchangers drives power
turbines. The following newspaper article discusses this viable electric-power genera-
tion in Arizona.

RED ROCK, ARIZ.—APS today broke ground on Arizona’s first commercial solar trough
power plant and the first such facility constructed in the United States since 1990.
Located at the company’s Saguaro Power Plant in Red Rock, about 30 miles north of Tucson,
the APS Saguaro Solar Trough Generating Station will have a one-megawatt (MW) generating
capacity, enough to provide for the energy needs of approximately 200 average-size homes. APS