Book - School of Science and Technology

Chapter 5Electrical storage heatingDirect in the sense that energy is consumed within the space to be heated but, conversely,indirect in the sense that consumption is remote (albeit only in time) from occupation ofthat space, any storage heating system must be considered as a hybrid.The concept of storing heat energy may, of course, be applied in a variety of ways andto any type of fuel supply. For example, steam stored in an accumulator may be usedin industrial plants to supply demands which are cyclic, or which fluctuate predictably,in order to provide a more constant load on boiler plant with consequent improvedefficiency. Similarly, where a combination of circumstances precludes extension to ahot-water boiler plant, operation of that existing plant over the full 24 hours may allowan increased daytime demand to be met, in part directly and in part from water heatedovernight and stored. In each of these instances, it should be noted, the unit cost of thefuel purchased would not vary.Uniquely, and for the good reasons discussed in Chapter 11, it is the policy of electricalsupply companies in England and Wales to offer differential tariffs whereby currentconsumed during the seven hours after midnight is sold for approximately half the priceof that consumed during the remaining 17 hours. In Scotland the tariff is arranged slightlydifferently but a similar principle applies. The availability of such a reduction to consumersin general transforms the economics of electrical heating, provided that thevarious forms of storage equipment are applied to take maximum advantage of theirdistinctive characteristics.Methods of storageThe methods commonly used for storage of heat taken during the hours of reduced-pricesupply, for use during the following day, may for convenience be grouped as being eitherroom stores or central stores, thus:Room storesStorage radiators where heat is retained in a solid material contained within an insulatedcasing and emitted continuously with no more than marginal control of output.Storage fan heaters where heat is retained similarly but where the addition of a fan,switched by a room thermostat, provides that a significant proportion of the heat fromthe store will be emitted only when required.