95 (36) 110 (44)

13 (7) 13 (7)

108 (43) 123 (51)

12 (7) 12 (7)

120 (50) 135 (58)

tion cycle. For vapor compression systems, the driving energy to the compressor can be supplied by an electric motor or a prime mover. In a hermetically sealed electric-drive unit (motor contained in compressor housing), the heat of compression as well as motor heat losses are included in the condenser load. If, for example, a hermetic unit requires a driving energy input of 0.63 kW/ton (0.18 kW,/kWr), the total heat rejection in English units would be:

0.63 kW/ton x 3,413 Btu/kWh + 12,000 Btu/ton-h = 14,151 Btu/ton-h

In SI units, the heat rejection would be:

0.18 kWhe/kWhr + 1 kWhh/kWhe = 1.18 kWhh/kWhr where the full electric energy input, expressed in kWhe, is converted to rejected heat, expressed as kWhh.

In an open-drive unit, the heat associated with motor efficiency losses is dissipated to ambient air and is not rejected directly to the condenser. For example, if the motor efficiency is 93% (0.93), the total heat rejection in English units would be:

0.63 kW/ton x 0.93 x 3,413 Btu/kWh + 12,000 Btu/ton-h = 14,000 Btu/ton-h

In SI units, the heat rejection would be:

0.18 kWhJkWhr x 0.93 + 1 kWhh/kWhe = 1.17 kWhh/kWhr

In the case of a reciprocating engine-driven compressor, an additional heat rejection load may be present. When the heat that must be rejected from the engine cooling system cannot be used productively, it may be rejected by integrating it into the cooling tower loop or dissipating it separately through a dump radiator.

In the case of a condensing steam turbine, the cooling load required for steam condensation may also be passed to the refrigeration condenser water loop. Water-cooled surface condensers are the most commonly applied technology. Alternatives include direct contact condensers that spray cooling water directly into the steam flow, and air-cooled condensers, which may be applied when cooling water is not readily available or cooling tower operation is not acceptable.

In absorption chillers, the heat energy is input to the generator cycle in the form of direct-fired fuel, steam, hot water, or high-temperature exhaust gas. The full energy input minus the energy of exhausted combustion gas or condensate return must be removed from the tube bundle to the cooling tower or other heat sink. Total absorption heat rejection will vary widely, depending on the performance of the cycle. Typically, input energy ranges from 9,000 to 18,000 Btu/ton-h (0.75 to 1.50 kWhh/kWhr), bringing total heat rejection (condenser load) to between 21,000 and 30,000 Btu/ton-h (1.75 to 2.50 kWhh/kWhr).

If, for example, the total generator energy input to a direct-fired, double-effect absorption chiller is 12,000 Btu/ton-h (1.0 kWhh/kWhr) and the fuel combustion efficiency is 82%, total system heat rejection would be:

12,000 Btu/ton-h x 0.82 + 12,000 Btu/ton-h = 21,840 Btu/ton-h

In SI units, the heat rejection would be:

1.0 kWhh/kWh. = 1.82 kWhh/kWhr x 0.82 + 1 kWhh/kWhr

Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

Get My Free Ebook

Post a comment