Abstract: A domestic combined heat and power (dchp) unit includes a Stirling engine 1 to provide heat for a domestic dwelling along with a source of electrical power. Under normal operation, the dchp is supplied with power from the national grid. When there is an interruption in the mains power from the grid, the dchp switches into a grid independent mode wherein power is generated by the dchp and is supplied to a controller 26 and to a water pump so as to maintain integrity of heat supply to the dwelling; the remaining power after that is supplied to selected domestic electrically powered equipment such as lights or television sets. The invention also discloses methods for black start of the dchp during a mains power loss, and also modification of the operating voltage on start up of electrical equipment during a power loss, to prevent the Stirling engine stalling.

Abstract: A meter to measure the volumetric flow rate of a liquid, for example water, is formed with a pipe forming a liquid flow path containing a low power electrical heater. A first temperature sensor measures the temperature T of the liquid adjacent to an upstream end of the heater and a second temperature sensor measures the temperature T.sub.2 of the liquid adjacent to a downstream end of the heater. The heater adds heat power of a value P to the liquid. A control arrangement comprising a computer means calculates the flow rate Q using the expression ##EQU1## where ST.sub.1 and DT.sub.1 are respectively the specific heat capacity of the liquid and the density of the liquid at the temperature T.sub.1 measured by the first sensor.

Abstract: A heat meter for measuring the amount of heat consumed in a region. A heat exchanger is supplied with heated fluid through an inlet pipe which carries temperature sensors for sending signals to a control. The control also receives signals from a temperature sensor in an outlet pipe carrying fluid away from the region. A low power electric heater is mounted between the sensors to add a known amount of heat to the fluid. The control calculates the heat power consumed in the region based on the temperature difference across the regions and the temperature difference across the region and the temperature difference across the heater.