Book - School of Science and Technology

Hours-run meters 227Figure 8.26 Evaporative proportioning meter for radiatorsApportioning metersFor radiator systems, the type of device shown in Figure 8.26, one of which must beclamped to each radiator, was used in Europe for many years. It consisted of a housingbearing a scale, to the rear of which was a replaceable open phial containing a volatileliquid. The amount of liquid evaporated by the heat from the radiator was a broadlyapproximate measure of usage and this was read from the scale each season or otherperiod. This type of device was subject to vandalism and has now been superseded by arelatively simple and secure electronic counter which integrates time and temperature andprovides a numerical LED display. As before, readings are taken and totalled for thewhole system and used as a basis to apportion the overall running cost to individualradiators or groups of radiators. The more obvious disadvantages include the necessity toprovide access for a meter reader to each radiator, not always achieved easily in domesticpremises. It is understood, however, that the manufacturers continue to offer an all-inmeter reading and accounting service in given circumstances.Water flow metersAn alternative method, for radiator systems, uses a simple rotary water meter, as forcondensate measurement, associated with a temperature limiting controller. This device,when fitted to the return pipe of the circuit being metered, acts to maintain a constantoutlet temperature and, by doing so, adjusts water flow in proportion to heat demand.Hours-run metersFor any part of a system which requires a power supply to an individual fan or circulatingpump, it is possible to arrange for a cyclometer type hours-run meter to be wired in paralleltherewith and sited so that it may be read from outside the premises. The products of the