Energy conserving water heater control system

Abstract

Water temperature sensors in the form of thermisters are in physical thermal contact with the inlet and outlet pipes of a water heater and may be surrounded by insulating material to make them more insensitive to the ambient air temperature and more sensitive to the temperature of the respective water pipes and the water contained therein. These two thermisters are connected in a bridge circuit connected to an operational amplifier whose output will be of a given polarity only if the measured temperature difference exceeds a predetermined value. The operational amplifier's output is then used to adjust the effective thermostatic setting of the hot water heater in a two-valued control arrangement. Alternatively, each of the two water temperature sensors may assume a purely mechanical form, such as an enclosed volume of fluid or plastic material operating a bellows or piston arrangement, so that at higher temperatures the volume increases and the bellows or piston moves in one direction while at lower temperatures, the volume decreases, and the bellows or piston moves in an opposite direction. If two such mechanical sensor arrangements are connected to work in opposition to one another through appropriate spring linkages, the resultant mechanical movement is proportional to the difference in sensor temperatures and adjusts the thermostat setting of the heater in a proportional form of control.