Book - School of Science and Technology

124 Electrical storage heatingR 3 ˆ YZR 1whereY ˆ factor from Table 5:3Storage fan heatersHere, a new quantity has to be considered, the active store (R 4 ), which is a function ofheater design but seems to be quantified in the publications of only a minority ofmanufacturers. This is the storage capacity remaining after the night-time static loss hasbeen deducted from the total input, thus:R 4 ˆ XZR 1whereX ˆ an empirical factor (approximately 0:85)Floor warmingIn the heyday of electrical underfloor warming during the late 1950s and early 1960s,many authorities were offering a cheap off-peak supply not only for current used overnightbut also, critically, for a 3 hour midday or afternoon boost. The success of thistariff was such that a temporary system peak arose during those daytime hours in 1969and, as a result, it was not long before the facility for the low cost boost was withdrawn.This new situation had a very substantial effect upon the feasibility of providingadequate service to domestic premises from an electrical underfloor storage system. InAGround floorBIntermediatefloorScreed with elementThermal insulationFloor slabSound insulationFigure 5.1 Alternative positions for heating elements in floors