Discontinuous temperature control

1.6 million homes were solely electrically heated in the United States in 1963; by 1980, the predicted number is 19 million. In most of these residences temperature is controlled by a 2-position line-voltage thermostat in each room. Suitable continuous and quasicontinuous temperature-control systems have been developed, but the price trend of the semiconductor devices they employ indicates that they will not successfully compete with line-voltage thermostats in the next decade. The 2-position line-voltage methods currently available in the United States have economic and discomfort disadvantages. Facile graphical displays of the extra heating costs caused by cycle time and droop have been derived from a basic electrical-network analogue for the electric space-heating process. Test results illustrate the cold-air currents caused by long cycle times. 2-position controlled skirting-board heaters are prone to deposit dirt on walls; this tendency increases with cycle time. The performance of a discontinuously controlled electric space-heating process is conveniently characterised by portraying the cycle time, manipulated variable and droop in a cycling-characteristic display. The current problems of 2-position line-voltage-controlled electric space heating could be remedied if two performance requirements were set. Recommended values for these are suggested; these can be met if simple design criteria are observed, as is shown using a sample thermostat constructed from standard components.