Document 108p2gxVZdb4q3ZKxBGgpq4oa

HEATINC VENTILATINC AIR CONDITIONING CUIDE 1941 the non-heating, season with the operation of the fuel burning device controlled by the water heater thermostat. (See Chapter 33.) During the heating season the water heater temperature control functions as a low limit control. When an indirect water heater is applied to a gravity hot water system, it is necessary to provide a valve in the supply to the heating system to prevent the flow of hot water from the boiler when heat is not required in the house. This valve may be controlled from a room thermostat and the automatic fuel-burning device controlled from the water heater thermostat. To prevent circulation in a forced hot water heating system flow control valves may be installed in the flow and return lines which act merely as check valves when the circulating pump is not operating. In' this arrangement the pump is controlled by the room thermostat and the automatic fuel-burning device is controlled from the water heater thermostat. STORAGE CAPACITY AND BOILER ALLOWANCES The amount of storage provided in the hot water tank or heater is somewhat a matter of choice but is usually made ample to carry over the peak shortage which is likely to occur and is based on the assumption that only 75 per cent of the storage capacity will be available, as it has1 been found that if more than this amount is withdrawn from storage, the tank is so cooled down as to make the balance useless. The general rule may be cited that the less the heating capacity the greater must be the storage, and the greater the storage the less may be the heating capacity down to a point where the heating capacity will fail to be sufficient to heat up the tank storage during the periods of small load. . Example 6. A heater to supply 500 persons will have an average daily use of about 500 X 40 gal = 20,000 gal and this is an average of ^ = 833 gph but the peak hour will require Ho of 20,000 = 2000 gal and the shortage during the peak hour, if the heating capacity is made to suit the average hourly use of 833 gal, will be 2000 -- 833 = 1167 gal so that the storage capacity, based on 75 per cent being available from this 1167 capacity without cooling the tank excessively, will be = 1556 gal. Should it be desired to reduce the size of storage tanks and to use a greater heating capacity, it is only necessary to increase the heating capacity to 1200 gph which then gives 2000 -- 1200 = 800 gal as the shortage during the peak hour, and the necessary storage will be --80^0 eal = 1067 gal; or the heating capacity can be increased to 1500 gal, leaving a shortage of 2000 -- 1500 = 500 gal. Good design requires that the heating capacity be made as small as possible without introducing undesirable amounts of storage, as the heating capacity directly determines the load on the source of heat. As indicated in Example 5, the heating load is proportional to the heating capacity and the boiler capacity must be increased for higher heating capacities and may be reduced for smaller heating capacities with greater storage. It may be assumed that a boiler capacity of about 4 sq ft of equivalent steam heating surface2 (radiation) must be provided for every gallon of water heated 100 F or from 50 F to 150 F, which is 100 X 8 33 f JAc4ial requirement for 100 deg temperature difference = -----240~-- ~ 3.48 sq ft per gallon ot water heated. 788 CHAPTER 45. WATER SUPPLY PIPING AND WATER HEATINC Table 13. Ordinary Maximum Hourly Demand for Hot Water for Various Fixtures in Gallons and Probable Percentage of Usage Tips o .Building Lavatories Private -PubEe Baths Showers Slop Sines Kitchen Pantbt Sinks Sines Foot Baths Wash Tbats Avc. Max. Use* Maximum Probable GPH 20 ' 20 40 300 30 30 20 20 50 Probable Usage in Per Cent of Maximum Ordinary Use Apt. house Club Gymnasium Hospital Hotel Industrial Laundries Office building Baths Residences Schools Y. M. C. A. 25 50 33 67 67 33 50 25 60 .35 25 75 50 67 25 100 100 100 67 67 100 . 25 100 _8_0 60 80 25 75 50 33 67 67 100 25 . 80 45 25 25 25 25 25 25 100 50 33 100 150 100 100 ___ _1_00 67 33 75 50 150 __ 150 50 100 33 50 50 67 6_7 33 _10_0 __ 25 _10_0 80 _10_0 _ 70 90 100 20 100 50 50 60 50 25 75 100 67 33 100 50 25 25 100 100 100 67 67 100 100 80 75 Percentage of fixtures likely to be demanding maximum probable usage at any one time. Table 14. Hot Water Consumption in Various Types of Buildings for Different Purposes Ttps op Building Conditions Gallons Hotels Buildings Industrial Buildings Restaurants Room with basin only Room with bath (Transient) (Men) (Mixed) (Women) Two-room suite and bath Three-room suite and bath 10 (per day) 40 (per day) 40 (per day) '60 (per day) 80 (per day) SO (per day) 100 (per day) Public bath or lavatory 150 (per day per fixture) Public shower 200 (per day per fixture) Public lavatory with attendant 200 (per day per fixture) Per office employee Per factory employee Cleaning floors 2 (per day) 5 (per day) 3 (per 1000 sq ft per day) 80.50 Meals $1.00 Meals $1.50 Meals 0.5 (per customer with hand washing) 1.0 (per customer with machine washing) 1.0 (per customer with hand washing) 2.0 (per customer with machine washing) 1.5 (per customer with hand washing) 4.0 (per--customer with machine washing) 789