Book - School of Science and Technology

Period of use 669Table 23.7 Factors relating structural mass to mode of plant operation and system typeContinuousplant operation(24 hours)Slow response systemIntermittent plant operation aFast response systemBuildingstructure7-day week 5-day a week 7-day week 5-day b week 7-day week 5-day b weekHeavy 1.0 0.85 0.95 0.81 0.85 0.71Medium 1.0 0.80 0.85 0.68 0.70 0.56Light 1.0 0.75 0.70 0.53 0.55 0.41a With night-time shutdown. b With weekend shutdown.Table 23.8 Factors relating structural mass to period of occupationBuildingstructurePeriod of actual occupation4 hours 8 hours 12 hours 16 hoursHeavy 0.96 1.0 1.03 1.05Medium 0.82 1.0 1.13 1.23Light 0.68 1.0 1.23 1.40occupation during a 12 hour day. The inside and outside design temperatures are 20 Cand 3 C, respectively, and thus:Degree-days (Table 23.4) ˆ 1895Temperature increment (Table 23.5)ˆ 3 CFactor for building type, use and temperatures (Table 23.6) ˆ 1:22Factor for intermittent use over 5 days of a slow response systemin a heavy building (Table 23.7) ˆ 0:81Factor for occupation over 12 hours in a heavy building (Table 23.8) ˆ 1:03Hence,Equivalent full load operationˆ 1895 1:22 0:81 1:03ˆ 1929 hours/annumIt is a simple step from this point to calculate the net annual heat requirement, i.e. for aheat loss of 500 kW:Annual load ˆ (1929 500)/1000 ˆ 965 MWhorˆ 965 3:6ˆ 3474 GJAnnual fuel or energy consumptionIn order to determine annual fuel consumption, and hence cost, it is necessary in each caseto take account of both the properties of the fuel and the seasonal heat conversionefficiency. The latter, which includes allowance for plant operation at less than full load,may be read from that part of Table 23.9 appropriate to the plant under consideration. In