Document DGZ0yR7zOJ5go6jmD76aEmdQB

HEAT1NC VENTILATfNC AIR CONDITIONING GUIDE 1940 the temperature rise most commonly assumed and required. On this basis it will be seen that the various conditions cited in Example 5 will require additional boiler capacity as follows: Heating Capacity (Gph) 833 1200 1500 Additional Boiler Capacity (Sq Ft EDR) 3332 4800 6000 From this it is apparent that it is less costly to provide ample storage and to reduce boiler capacity than to diminish the storage and. supply a greatly increased boiler capacity to compensate. The boiler allowance value of 4 sq ft of equivalent steam radiation for each gallon of water heated through a temperature range of 100 F is based on an hourly heating rate. When reduced heating capacities are desired for economic reasons of boiler design and selection, engineers frequently recommend that the heating rate be extended over a period of two hours in which case the boiler allowance value would be reduced to 2 sq ft of equivalent steam radiation. Similarly, any other heating rate may be established and a corresponding value of boiler allowance deter mined. Reliable information based upon the installations of several heaters in existing heating systems indicates varying arbitrary values of boiler allowances to be used. When these values are selected for usage, a careful analysis of the varying factors involved in determining these values should be considered so that the proper heating allowances may be provided. ESTIMATING HOT WATER DEMAND BY FIXTURES In buildings where the occupancy is doubtful and only the number of plumbing fixtures can serve as a basis for determining the probable hot water demand, the problem is not so simple owing to the fact that a fixture gives no information as to how heavy a service may be demanded from the fixture and this amount of service is really-the governing factor in making an estimate of the probable hot water demand. Table 13 may prove of some value in this respect as it gives the maximum assumed quantity of hot water per hour which will be demanded of any fixture'and then gives a percentage of this amount which may be assumed as probable in different types of buildings. Table 14 gives approximate hot water re quirements in various types of buildings. Example 6. Let it be assumed that an apartment house with 20 apartments has 20 baths, 20 lavatories, 20 kitchen sinks and 20 laundry trays; what is the probable maxi mum hourly demand for hot water? 20 Batha at 40 gal and 33 per cent------------ ------- ---------- ---------------------------------------------- -- 270 gal 20 Lava, at 20 gal and 25 per cent----------..-------------- :------------------------------------------------------- 100 gal 20 Sinks at 30 gad and 33 per cent------------------------------------------------------------------------------------ 200 gal 20 Tray# at 60 gal and 60 per cent:-------------------------------------- --------------------------------------------- 600 gal Total___ _____...._____ _1170 gal Probable peak use at one time_____________________________________________ ______________ 35 per cent Probable actual peak demand.-,-- ------------------------ .---------------------------------------------409 gph If three persons are assumed to an apartment the total daily use of hot water should approximate 20 X 3 X 40 gal = 2400 gal and if the peak hour is 10 per cent of this amount, the peak hour by this method shows a probable demand of one-tenth of 2400 gal, which indicates that the values in Table 13 are safer 762 Chapter 45 TEST METHODS AND INSTRUMENTS Temperature Measurement, Pressure Measurement, Measure ment of Air Movement, Air Change Measurements, Meas urement of Relative Humidity, Dust Determination, Heat Transfer Through Building Materials, Measurement of Heat Exchange for Comfort Conditions, Combustion Analysis, Smoke Density Measurements, Carbon Monoxide Measure ments IN previous chapters, data from many tests and from much research on various divisions of heating, ventilating and air conditioning have been given. On pages 790 and 791 the test codes adopted by the Society for testing and rating of various types of apparatus are listed. This chapter presents a description of many test instruments, and discusses their use. TEMPERATURE MEASUREMENT Changes in the intensity of heat may be determined by several methods such as measuring the change in volume of a liquid, the change in internal pressure of a confined gas, the current set-up between dissimilar metals joined in a circuit, or the change in resistance of an electrical circuit. Thermometers The most common method used is the change in volume of a liquid such as mercury or alcohol enclosed in glass. Mercurial thermometers may be used for measuring temperatures from -- 40 F to approximately 1000 F. The lower limit is set by the freezing point of mercury. Since the boiling point of mercury is only about 675 F, the space above the mercury in thermometers designed for higher temperatures must be filled with an inert gas under pressure. Alcohol thermometers may be used for temperatures from --94 F to +248 F. The more accurate thermometers are individually calibrated and have divisions etched on the stem. The two most common reference points are the freezing and boiling points of water. On the Fahrenheit scale, which is most commonly used in engineering work, there are 180 divisions between these points. On the Centigrade scale which is used by chemists and physicists, there are 100 divisions in this range. The temperature in degrees Fahrenheit equals 9ft of the temperature in degrees Centi grade, plus 32. For permanent installations, glass thermometers are often protected by metal jackets and equipped with metal scales. Due to the heat 763