Book - School of Science and Technology

60 The building in winterTemperature controlAlthough this subject is dealt with in some detail in Chapter 22, it is apposite here toemphasise that the ideal system is one where separate automatic control of temperature isavailable in each room or space. With such a system, heat emitting elements having thecapacity to bring the room up to temperature may be provided and then, as heat fromoccupants, lighting, machines and the sun begins to have effect, the output of the system isreduced to prevent overheating and save unnecessary fuel consumption. The availabilitytoday of inexpensive thermostatic radiator control valves has made room-by-roomresponse an economic possibility.Continuous versus intermittent operationA building occupied for 24 hours each day, such as a hospital, a police station or a threeshiftfactory, will require that a continuous supply of heat is available. Most buildings,however, are occupied for a limited number of hours each day and, moreover, not for alldays of the week: offices, schools and churches are examples of very different patterns ofuse. It is, in consequence, a matter of considerable importance as far as energy consumptionis concerned to establish whether a pattern of intermittent operation will providesatisfactory comfort conditions for the whole of the occupied period. The manner inwhich proportions of total energy consumption vary with different operational regimes isshown in Table 2.16.The thermal response or time lag of a building vis aÁ vis a heat supply is perhaps bestvisualised initially by considering two extreme cases, the first being a lightly constructedbuilding, insulated but overglazed, which will have minimal thermal capacity and hencea relatively short time lag. At the other extreme, a medieval or similar building with thickmasonry walls, negligible window areas and massive construction throughout willrespond very slowly to a change in external conditions, have a considerable thermalcapacity and thus have an extended time lag taking as much as a week or more of heatinput to recover from breakdown.Table 2.16 Per cent annual fuel consumption for various operational regimesInternal temperatures maintained20 C for 24 h 20 C for 10 h15 C for 14 h20 C for 10 h10 C for 14 hPeriod Day Night Day Night Day NightJanuary 51 49 60 40 72 28February 50 50 60 40 73 27March 49 51 60 40 76 24April 48 52 61 39 86 14May 44 56 65 35 99 1September 43 57 78 22 100 0October 47 53 66 34 100 0November 50 50 62 38 80 20December 51 49 60 40 73 27Average over season 48 52 64 36 84 16