Boiler efficiency and gas consumption: Effects of cycling and pump speed

Abstract

This brief note sets down some results on the effects of decoupling the room thermostat and cylinder thermostat from the pump and boiler in a 'wet' domestic gas-fired central heating system. Decoupling means that the boiler and pump operate continuously, as opposed to coupled control in which the control thermostats switch off the pump and boiler when no heat is required. The results showed that, for decoupled control, the boiler cycling rates were increased by 62%, the mean boiler efficiency was reduced from 68% to 62% and the gas consumption was increased by about 3% across the 1990/91 winter season. In mild weather the deterioration was much worse and it is important that the controls be properly coupled in these conditions. Lower pump speeds also increase boiler cycling and slow down the heating-up rates for space and hot water heating.