Document 0qa4bL45bOw62vwRBRnjdge3b

HEATINC VENTILATING AIR CONDITIONING GUIDE 1944 The hot water supply may be distributed by either an up-feed or downfeed piping system. Three common methods of arranging the circulating lines are shown in Fig. 1. Although the diagrams apply to multi-story buildings the arrangements (a) and (b) are sometimes used in residential designs. A check valve should be provided in the run-out from each return riser to prevent temporary reversal of flow in the piping when a faucet is open. Proper air venting of a circulating system is extremely important, par ticularly if gravity circulation is employed. In Fig. 1 (a) and (b) this is accomplished by connecting the circulating line below the top fixture supply. . With this arrangement, air is eliminated from the system each time the top, fixture is opened. . ... .. ,-J . Where an overhead supply main is located above the highest .fixture as in Fig. 1 (c), an automatic float type air vent is installed at'the highest point of the system or a fixture branch is connected to the top of the main where air venting, is desired and then dropped .to the fixture outlet. . It is, sometimes necessary- to make an allowance for, pressure: drop through;the_:heater when sizing hot water lines.,; This is particularly true where instantaneous hot water heaters are used and. the available, pressure is low.. ; ... ", . . , rf. . ..... ' : STORAGE CAPACITY AND HEATING LOAD In:'estimating the size of hot water storage-tank required: and the heating capacity to be provided either from the boiler or from an inde pendent domestic hot water heater, it is necessary to know the total quantity of water to be heated per day, and the maximum amount which will be used in any one hour, as well as the duration of-the peak load. In cases where the requirements for hot water are reasonably uniform, as in'residences, apartment buildings, hotels, and the like, smaller storage 802 CHAPTER 46. HOT WTER SUPPLY capacity is required than in the case of factories, schools, office buildings, etc., where practically the entire day's usage of hot water occurs during a very short period. Correspondingly, the heating capacity must be pro portionately greater with uniform usage, of hot water than with, inter mittent usage where there may be several hours between peak demands during which the water in the storage tank can be brought up to tempera ture. As a general rule it is desirable to have a large storage capacity in order that the heating capacity and consequently the, size of the heater, or the load on the heating boiler, may be as small as possible. In estimating the hot water which can be drawn from a storage tank it should be borne in mind that only about 75 per cent of the volume of the tank is available, as by the time this quantity has been drawn off the incoming cold water has cooled the remainder down to a point where it can no longer be considered hot water. Where steam from the heating boiler is used to heat domestic hot water, the computed load on the boiler should be increased by 4 sq ft EDR (equivalent direct radiation) for every gallon of water per hour heated 1 flO Y S through a 100 F rise. The actual requirement is-----'-- = 3.48 sq ft , J4U per gallon of water heated 100 F. The value of 4 allows for transmission losses, etc. . There axe two ways in common use of estimating the hot water require ments of a building; first, by the number of people and second, by the number of plumbing fixtures installed. Where the number of people to be served is known or can be reasonably estimated, the data in Table 1 may be used. Example 1. From Table 1, a residence housing five people would have a daily requirement of 5 X 40 = 200 gal per day, and a maximum hourly demand of 200 X X Table 1. Estimated Hot Water Demand per Person for Various Types of Buildings Type of Building Res., apts., . hotels, etc: Hot Water Required at 140 F Max. Hourly Demand in Relation to Day's Use Duration of Peak Load Hours Storage Capacity in . Relation to Day's Use Heating Capacity in Relation to Day's Use 40 gal per person per day H 4 X X Office buildings 2 gal per person per day X 2 X X Factory buildings 5 gal per person per day X 1 X X Restaurants $0.50 meals $1.00 meals $1.50 meals 1.5 gal per meal 2.5 gal per meal 4.5 gal per meal Ho Ho Restaurants 3 meals per day Ho 8 X Ho Restaurants 1 meal per day X2 X X 803