HVAC Control in the New Millennium.pdf - HVAC.Amickracing

Heat, Ventilation and Damper Control TrendsFilteringAir filters include those that can be mechanically cleaned as well asreplaceable and electronic units. The air filter is usually operated yearround. There are times when the cooling and humidifying functions arenot needed, but the filter is one part of the system that may be kept incontinuous operation.Air WashersAn air washer is a unit that brings the air into contact with wateror a wet surface. The principal functions of the air washer are to cool theair passed through the spray chamber and control the humidity.In some cases, the air may be passed over the wet surface. Moreintimate contact is possible when the water is divided into a fine sprayand the air passed through the spray chamber.Some of the finer water particles will be carried along with the aircurrent and a series of curved plates called eliminators may be used tochange the direction of air flow and throw off some of the water particles.The water is generally circulated with a pump. Warm water ispassed over refrigerating coils to cool it before being passed to the spraychamber.In some cases, the water is cool enough to use as it is drawn fromthe ground. In other cases, the water is not cool enough and must becooled by refrigeration.Indoor Design ConditionsThe indoor conditions to be maintained in a building are the drybulbtemperature and relative humidity of the air at a breathing line 3to 5 feet above the floor. The area should indicate average conditionsand not be affected by abnormal or unusual heat gains or losses from theinterior or exterior.Since it is difficult to maintain the mean radiant temperature at thedry-bulb temperature in actual practice, the effect of warmer walls normallyencountered during the cooling season requires a lower design©2001 by The Fairmont Press, Inc. All rights reserved.