Book - School of Science and Technology

example. Recovery periods to be two hours for service and one hour for catering. Thedemands are to be met by two separate plants.CloakroomsFrom Table 20.5Storage requiredˆ 1:1 litre/personBoiler rating ˆ 1:1 0:032 ˆ 0:035 kW/personThusStorage ˆ 1:1 500 ˆ 550 litreWith margin for mixing ˆ 1:25 550 ˆ 687 litreBoiler rating ˆ 0:035 500[(55 10)/(65 10)] ˆ 14:3kWCateringFrom Table 20.5Storage requiredˆ 1:6 litre/mealBoiler rating ˆ 1:6 0:064 ˆ 0:10 kW/mealThusRequirements for storage capacity and boiler power 589Storage ˆ 1:6 400 ˆ 640 litreWith margin for mixing ˆ 1:25 640 ˆ 800 litreBoiler rating ˆ 0:10 400 ˆ 40 kW. An office has a staff of 120 and requires water for cloakrooms at 55 C for a 10 hourworkingday. Energy supply is to be electrical with 80% of the annual total supplytaken off-peak. Recovery period for daytime use to be 2 hours. The heat losses areestimated to be 0.8 kW.From Table 20.5Storage required above upper elementˆ 1:2 litre/personUpper element rating ˆ 1:2 0:032 ˆ 0:04 kW/personFrom Table 20.6Storage required between elements (i:e: lower)ˆ 3:0 litre/personThusUpper storage ˆ 1:2 120 ˆ 144 litreUpper element ˆ (0:04 120)[(55 10)/(65 10)] ˆ 3:93 kWTotal, includingheat loss ˆ 3:93 ‡ 0:8 ˆ 4:73 kWLower storage ˆ 3:0 120 ˆ 360 litreStored volume equivalent to heat lossˆ (3600 0:8 10 0:8)/[4:2 (55 10)] ˆ 122 litreTotal storage ˆ 144 ‡ 360 ‡ 122 ˆ 626 litreWith margin for mixing ˆ 1:25 626 ˆ 782 litreLower element ˆ 0:01 626 ˆ 6:26 kW