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

Heat, Ventilation and Damper Control Trendsvalve opens, steam flows through the humidifier in the supply airstreamand raises the relative humidity.Dehumidification methods involve the use of desiccants, surfacecooling and indirect cooling coils. Indirect cooling coils are used withsprayed coil dehumidification.Dehumidification may take place with sensible (dry bulb) coolingusing surface dehumidification on the cooling coils. Dehumidification inlow dew point process systems is usually done in a separate dehumidificationunit.Air leaving the cooling coil from surface dehumidification is usuallynear a saturated condition. If cooling is controlled from the relativehumidity in order to remove water vapor, the supply air will often becooled more than is required for sensible or dry cooling. The space maythen require some reheating to prevent overcooling.HVAC IntelligenceMost improvements to HVAC systems involve increasing theirintelligence. Setback thermostats, which are also known as clock or electronicthermostats, automatically raise or lower indoor temperatures tomeet the building’s schedule. Indoor temperatures can setback to lowerthan average comfort levels while the building is unoccupied, then theyare automatically brought back up to the comfort level before it is fullyoccupied. Other smaller setbacks might start at mid-morning when theoutside temperature starts to warm.Without any sacrifices in comfort, a 10 to 20% savings on annualheating bills are feasible. In the summertime the setback feature is usedto save on air conditioning costs. Some clock thermostats use 7-dayprograms with a different schedule for each day of the week. Anotherschedule is the 5 + 1 + 1 weekly program, which uses a Mondaythrough-Fridaytimetable and separate timetables for Saturday and Sunday.There are also 5 + 2 schedules which use two programs, one for thefive workdays and another for the weekend.Programmable units have evolved into flexible electronic unitswith displays and buttons from the earlier electromechanical modelsthat used small levers or pins to mark the setback times. Manual overridesare used to override the current temperature setpoint without reprogrammingthe thermostat. Newer models automatically return to the©2001 by The Fairmont Press, Inc. All rights reserved.