Abstract: A refrigerant system adjusts, in a coordinated prioritized manner, the variable capacities of a compressor, evaporator fan and a condenser fan to minimize the system's overall power consumption while maintaining a comfort zone within a target comfort range. The target comfort range is defined by desired temperature and humidity limits. When the comfort zone is within the target comfort range, the system periodically attempts to reduce the compressor capacity. If the attempt succeeds, the evaporator fan capacity is then minimized. The condenser fan capacity can also be minimized provided the refrigerant system can maintain at least a minimum saturated suction temperature of the refrigerant flowing from the condenser to the compressor.

Abstract: A refrigerant system adjusts, in a coordinated prioritized manner, the variable capacities of a compressor, evaporator fan and a condenser fan to minimize the system's overall power consumption while maintaining a comfort zone within a target comfort range. The target comfort range is defined by desired temperature and humidity limits. When the comfort zone is within the target comfort range, the system periodically attempts to reduce the compressor capacity. If the attempt succeeds, the evaporator fan capacity is then minimized. The condenser fan capacity can also be minimized provided the refrigerant system can maintain at least a minimum saturated suction temperature of the refrigerant flowing from the condenser to the compressor.

Abstract: A flue gas/combustion air heat exchanger for a furnace. The furnace includes a combustion chamber that burns a mixture of fuel and combustion air to produce heat for a comfort zone. The resulting products of combustion, along with any waste heat not transferred to the zone, pass through a flue duct before venting to atmosphere. Incoming combustion air is discharged across the relatively hot flue duct before it enters the combustion chamber. In passing across the hot flue duct, the incoming air is preheated by waste heat of the combustion products. The heat exchange relation between the incoming combustion air and the combustion products within the flue duct enables the furnace to recover waste heat that would otherwise be lost if the combustion products were free to discharge to atmosphere before giving up a portion of their waste heat to the incoming combustion air.