Book - School of Science and Technology

62 The building in winterfollowing extensive examination of a number of buildings of various types. Figure 2.15provides a summary which illustrates the order of saving in fuel consumption which maybe achieved as a result of intermittent operation.Preheat capacityWhen a heating system is operated intermittently, the temperature within the building willfall during the period of system shut-down and, in order to restore this to the proper levelby the time the occupants arrive, a preheating period is necessary. Since the outsidetemperature varies during the winter nights, so will the time required for preheat increaseor decrease and control equipment which provides means for dealing with this variation isdescribed in Chapter 22 (p. 639).OccupancyInternal temperature °C6800 4 8 12 16 20 24Time hBoostperiodOccupancyHeat input percent load100Boostlevel00 4 8 12 16 20 24Time hFigure 2.16 Profiles of temperature and load for intermittent heating