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

HVAC Control in the New Millenniumoriginal program after the override period is complete. Electronic thermostatsalso use a key or switch that allows you to change from a heatingseason program to cooling, or back again without reprogramming.Some models will make the changeover automatically.Heating-only and cooling-only systems have two or three wires,and combined heating-cooling systems typically have four or five wires.Heat pumps use eight or nine wires.Electronic thermostats use batteries to maintain the program incase of a power failure. Most units use a 24-volt power source, but thereare also 120-volt or millivolt systems. Some use batteries as their onlysource of power. This type of battery-only thermostat should have alow-battery indicator to warn of impending problems.A key improvement in the future is to equip systems with moreand better sensors so that the controller has the proper feedback it needsto make smarter adjustments. These sensors will monitor not only theindoor and outdoor air temperature, but relative humidity and windconditions may be monitored as well.More extensive climate control will be used that defines heatingand cooling needs using current weather information along with forecastinformation in some cases.The concept of zoning will also grow as a cost effective techniqueand control systems will use more thermostats and/or remote sensorsthroughout the building.Pressure ControlIf a forced-air system is not in pressure balance, some areas will bepressurized while others are depressurized. The depressured areas willbe subject to intrusion by cool, dry air from outside. Ductwork leaksallow the depressurization effects and dryness to become worse. Whenthe ductwork is used for air conditioning, depressurization can allowhot, humid air to enter. When a furnace draws its combustion air fromoutdoors, this can also cause depressurization.One way to reduce the dryness and fuel consumption is to raise therelative humidity inside. Another technique is to add new supply orreturn air ducts to supply a better balance or regulate the system byopening and closing air outlets. Air outlet and duct control in the futurewill be based on a continuation of existing trends includes increased©2001 by The Fairmont Press, Inc. All rights reserved.