The primary benefit of the removable EPROM control program is the ability to easily implement different control strategies (by software changes) without changing hardware. Multiple input sensors (temperature and humidity) could be used to detect the current state of the system, and required output actions can be determined. Different environmental requirements can be handled by simple software changes. For example, with a mild air-heating demand and simultaneous water-heating requirement, the microprocessor control system could set the compressor speed to medium and the hot water pump speed to medium, the indoor fan speed to low, and the loop pump speed to high. This would maximize the heat transfer to the hot water system while meeting air-heating load with high part-load efficiency. These motor and fan speeds may satisfy a northern climate, but a simple EPROM reprogramming can change the system to meet ideal conditions for another climate.

Variable-speed water heating or a combination of variable-speed water and air operation is also possible. The obvious process of using all waste heat during cooling to produce hot water is one mode of operation, but dedicated water heating and producing hot water while air heating are also control problems to be addressed.

Since any water heated with a COP over 1.0 is more efficient than electric element heating, all water-heating opportunities should be utilized. To accomplish this, variable-speed pump control could play a significant role. One possibility is to increase the desuperheater flow rate during heating rather than decreasing the compressor speed...