Why Indirect Evaporative Cooling

INDIRECT evaporative coolers employ a heat exchange process. The heat exchanger has a dry-side air passage (sensible cooling with no moisture addition) and a wet-side air passage (secondary air to force evaporation at the heat exchanger). As opposed to DIRECT evaporate coolers, INDIRECT units will remove sensible heat without increasing latent heat. INDIRECT units are used as pre-coolers with some very distinct advantages:

1. To provide sensible cooling at a high energy efficiency ratio. Compared to conventional refrigerated units the cooling output, per watt of input, can be increased ten or more times significantly decreasing operation costs.
2. To pre-cool the air to cooling coils. This will reduce the sensible cooling load resulting in a reduction in sizing of the coil, refrigeration unit, and heat rejection unit. The connected electrical load is reduced. First cost of electrical wiring as well as operating costs are reduced.
3. Extend the operation of the system economizer cycle to a much higher dry-bulb temperature range, reducing the running time of the refrigeration system and providing better ventilation standards and reduced operating costs.
4. Reduce KW consumption when the utility company demand charges are being set, resulting in across-the-board savings for all electricity used. Substantial cost reduction is achieved. The savings are even more significant when ratchated demand charges apply.
5. Sensibly pre-cool the air to DIRECT evaporative units to increase their effectiveness. This is the two stage system concept.

System Benefits:

• Reduce the refrigerated system size or eliminate it entirely.
• Provide the majority or all of the required annual cooling requirements at a very high energy efficiency ratio, thus reducing operating costs.
• Reduce kilowatt consumption during demand periods thus reducing demand charges and affecting across-the-board costs.
• Provide excellent ventilation standards. The return side cooling load (heat gain), by system design, is exhausted reducing the applied system load.
• Provide wintertime humidity control as a by-product of the system.

The VARI-COOL unit provided a first by making possible the use of evaporative cooling (adiabatic saturation) to accomplish all or part of the air conditioning system load. The evaporative cooling incorporates a heat exchange to accomplish TOTAL SENSIBLE cooling with no offsetting latent heat increase.

The use of VARI-COOL to pre-cool the air entering a conventional cooling coil will reduce the coil load significantly (as well as the refrigeration required) and reduce operating costs.

A substantial enthalpy change (BTU/lb. of dry air) of the dry-side air is achieved. This is in contrast to typical evaporative coolers which achieve no change in enthalpy, because they increase the latent heat in proportion to the sensible heat removed and provide no net cooling.

The energy required to obtain the sensible cooling effect with the VARI-COOL indirect evaporative cooler consists of the wattage requirements to run a small water pump and the wet-side fans. No additional energy is required.

Water is the coolant. The evaporation of water is a nondepleting energy source.

Indirect evaporative pre-cooling can have an significant impact in reducing air conditioning energy consumption.

The VARI-COOL dry air evaporative utilizes two well-known engineering principles to provide sensible cooling with extremely low energy consumption. These two principles are evaporative cooling and heat transfer.

The VARI-COOL unit is designed with two air passages, a dry one through the interior of the heat exchange tubes and a wet one around the exterior of the heat exchange tubes. Water is circulated over the exterior of these heat exchange tubes while air is moved over them, creating an evaporative cooling effect that reduces the temperature of the tubes. At the same time, air is moved through the dry air passage in the interior of the cooled tubes, thus releasing its heat to the cooled tube surfaces, creating cold air that has not had moisture added to it. This is the cooled dry-side air.

	Screened air intake. Omit on recirculated air system.
	VARI-COOL indirect evaporative unit.
	Dry side, air moving device. May be part of the building air conditioning system.
	Duct to convey cooled or heat reclaimed air to the conditioned space.
	Wet side, air moving device. May be part of the building exhaust system. Wet air discharge may be ducted to the inlet of the air conditioning system condenser to increase condenser efficiency.