Voltage In—Voltages for input to the control
Voltage Out—Output voltage and options
Power Out—Given in amps or hp, and specified by the manufacturer; tells what size pump or other equipment can be powered directly by the controller. Larger pumps will require added, higher-capacity relays.
Unit Power Consumption—What the control uses in power; both standby and energized are noted
Sensor Ohms—Sensor resistance at 77°F
On-Differential—Difference in temperature when the control turns the pump on
Off-Differential—Difference in temperature when the control turns the pump off
High Limit—Tank temperature that turns the pump off. Some controllers do not have this option.
Low Limit—Low tank temperature that turns the pump off
Recirculation—A freeze-protection feature that will turn on the pump and circulate storage tank water through the collector to keep it from freezing
Overtemperature Protection (a.k.a. “vacation mode”)—A feature that activates the circulator pump at night to circulate cooler water from the collectors to lower the storage tank temperature. Some controllers feature a diversion load for overtemperature protection.
Number of Differentials—Most controllers have a single differential, but some have more than one to control two pumps at different times. For example, one differential would control a collector loop pump heating a tank; another differential would control a pump heating the domestic hot water, if the large tank was hot enough.
Digital Display—Any option for digital display of temperature
Data-Logging Capability—Capability of the control to be connected to a computer and/or data logger to record performance
Remote Monitor—A feature to add a remote digital display for ease of monitoring operation
Warranty—Full or limited; length of warranty
Street Price—Estimated retail price