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Equipment In IW SolarThermal System

Parabolic trough solar collector

The parabolic trough solar collectors installed have been provided by Broad Air Conditioning of China.  Each module is 6 m long with a 2.3 m aperture, as shown in Figure 1.  It comprises a parabolic trough reflector mirror, a surface treated absorber pipe at its focal line surrounded by an evacuated transparent tube, a supporting structure, and a tracking mechanism. This module of the Broad PTSC receiver weighs 200 kg.  It is designed to withstand a 31 m/sec wind load. The 13.34 m2 aperture area and 0.68 m2 absorber tube area correspond to a 19.6 concentrate ratio.  The reflector mirror has a 0.8 typical reflectance.


Figure 1.  The Parabolic Trough Solar Collector 

The absorber pipe is coated with selective blackened nickel. This coating has high absorptivity for short length solar radiation and low emissivity for long length heat radiation. The absorber pipe is contained within an evacuated glass tube to minimize convection and radiation losses. The Broad PTSC tracking drive is a compact, accurate combination of a large semi circular gear, engaged with a small gear and a 24 V powered servo motor. PTSC's typically have a higher efficiency than plate solar collectors or an evacuated tube collectors, when the solar field is operated at the high temperatures required by a double effect absorption chillers.

Double effect absorption chiller

Broad Air Conditioning especially designed and fabricated the 16 kW double effect absorption chiller shown in Figure 2  for the IW solar thermal system. This chiller has a regenerator driven either by a hot fluid or by natural gas firing.  This dual capability reduces the cost of solar thermal system by eliminating the need for an auxiliary heater to be used when solar radiation is inadequate. The absorption chiller uses lithium bromide as the sorbent and water as the refrigerant.  In the cooling cycle, the water vapor is absorbed into concentrated LiBr solution in the absorber.  A solution pump then pumps up the dilute LiBr solution to the regenerator that operates at a higher pressure and a higher temperature to vaporize water from the solution making use of thermal energy from the solar collectors or from the natural gas burner.  The water vapor is condensed by rejecting heat to cooling water in the condenser. Next, the condensed water is passed through an expansion nozzle into the evaporator. The water is vaporized there at a low pressure, absorbing heat transferred from chilled water flow. The installed double effect absorption chiller in the IW has a coefficient of performance of 1.2 when operated in cooling mode.  A single valve can be opened to switch the chiller from the cooling to heating mode.  In the heating mode, the water vapor boiled off LiBr solution in the regenerator, directly flows into the evaporator.  The evaporator now acts as a condenser and heats a second water stream that is used for heating the IW.
Figure 2.  The absorption chiller