Measurements of heat losses from an insulated domestic hot water cylinder

Abstract

The paper provides data for heat losses from exposed pipes, plugs, thermostat cap and base of an insulated domestic hot water cylinder (capacity 120 litres), and examines their influence, and the effect of air movement, on standing heat loss performance as prescribed by standard methods such as BS699. Results show that under 'still air' conditions heat losses from exposed areas are 17% of the total loss. This figure is likely to increase for higher levels of insulation, and decrease for larger cylinder sizes. The experimental data compare favourably with standard theoretical models and data given in the CIBSE Guide. The standing heat loss is sensitive to changes in air velocity, increasing by almost 7% in the range 0.1 to 0.3 m s^-1, in reasonable agreement with predictions. The pipework is responsible for the majority of the heat losses from the cylinder appendages, and is shown to be particularly sensitive to air movement.