Up to the present time, residential heating and cooling equipment has primarily been controlled by temperature-sensing thermostats. In recent years, some manufacturers have incorporated humidity sensing in their controls. Humidity control has most often been accomplished through a "dehumidifying cycle" or through "humidity reset" (adjustment of the temperature setpoint) rather than through an integrated comfort control strategy. As attention in the HVAC industry becomes increasingly focused on providing greater comfort, the need for continuous control of humidity, as well as other environmental parameters (such as relative air velocity, mean radiant temperature, CO.sub.2 concentration and air contaminants) becomes more critical.
The advent of AC inverter technology has made relatively low-cost variable-speed compressors, fans and blowers possible in residential heat pumps and air conditioners. In addition to heat pumps and air conditioners, variable-capacity operation is becoming possible with conventional heating-only systems. Variable-capacity operation allows greater flexibility as to, how the equipment is controlled. The goal therefore becomes that of not only maintaining adequate comfort, but also doing so in the most energy efficient manner.
Not only is it desirable to control the thermal parameters described above, but due to the increased emphasis placed on controlling indoor air quality, it becomes necessary to also control air contaminants such as CO.sub.2, Volatile Organic Compounds VOC's and particulates. Conventional, single-variable control strategies are not appropriate for this more advanced level of control. Therefore a more sophisticated approach is required.