Book - School of Science and Technology

134 Electrical storage heatingFinishScreed andelementsDamp proofcourseInsulationFigure 5.6 Insulation, etc., for heated floorcontroller is a manually set rotary switch having a scale representing the charging level.An intermediate setting delays the start of the charge period, thus varying its durationwhile avoiding post-charge losses. Automated versions of this arrangement, relative tonight-time outside temperature, are available.Heat output control of storage radiators is possible only when they are of a type whichincorporates means to admit and regulate air flow over the core. The level of regulationavailable may be improved in the case of storage fan heaters, the power-assisted componentof output then being controlled very easily via a room thermostat and the fanmotor. A facility for multi-speed fan operation may exist in addition to provide `low',`normal' and `boost' outputs.Control of floor warming output, subsequent to the charging period, is not possiblebut, perhaps fortuitously, some inherent adjustment exists. For example, taking a meanfloor surface temperature of 25 C, as previously noted, and an environmental temperaturein the heated space of, say 18 C, the difference is then 7 K. If the room temperaturewere to rise by 2 C, then the notional temperature difference would be only 5 K andoutput from the floor would have fallen (theoretically) by approaching 30%. It is adifficult task nevertheless to explain this situation in an office which is overheated byunseasonable solar radiation in January and yet retains a `hot' floor!Equipment for central storesAs was noted for room store units, there has been a number of significant advances inequipment development. Warm air as a heating medium in the domestic field no longerhas the appeal it once enjoyed but some commercial interests have appreciated that it mayhave marginal advantages in application to spaces where occupation is either intermittentor transient.In 1979, for domestic use, two quite different types of storage unit, aimed at provisionof an indirect supply of hot water to piping and radiators were being developed. Bothwere noted as being of interest although, rather confusingly, they shared the single`Centralec' name. One was a dry core unit based upon an adaptation of a large fan storeand the other a prototype of the `Economy 7 boiler'.