Document Z49994NZ8k9JLOqQK48egQ88V

HEATING VENTILATING AIR CONDITIONING GUIDE 1941 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 Opacity 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 ah 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 Baths at 40 gal and 33 per cetot__________________ _______ ___ 270 gal . 20 Lavs, at 20 gal and 25 per cent----- ---- ---------------------- ----------------------------------------:.............. 100 gal 20 Sinks at 30 gal and 33 per cent................. ...................................................--1------------------------ 200 gal 20 Trays at 50 gal and 60 per cent........... ......................... .............------------------ ------------------ 600 gal Total.______________________________________________________________________________ _____ __ 1170 gal Probable peak use at one time..... ..........J___ _________________________________________;----------- 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 safe. 790 Chapter 46 TERMINOLOGY Glossary of Physical and Beating, Ventilating and Air Condi tioning Terms Used in the Text, Standard Abbreviations, Conversion Equations, Drafting Symbols, Specific Beat Table Absolute Humidity: See Humidity. Absolute Pressure: The pressure referred to that of a perfect vacuum. It is the sum of gage pressure and barometric pressure. Absolute Temperature: A reading on the absolute temperature scale. Absolute temperature is obtained by adding 459.70 degrees to the Fahrenheit temperature. Absolute Zero: The zero point on the absolute scale 459.70 F below the zero of the Fahrenheit scale. Acceleration: The rate of change of velocity. In the fps system this is expressed in units of one foot per second, a = V -ht. Acceleration Due to Gravity: The rate of gain in velocity of a freely falling body, the value of which varies with latitude and elevation. The international gravity standard has the value of 980.665 cm per second per second or 32.174 ft per second per second, which is the actual value of this acceleration at sea level and about 45 deg latitude. Adiabatic: An adjective descriptive of a process in which no heat is added to or extracted from the system executing the process. Air Cleaner: A device designed for the purpose of removing air-borne impurities such as dusts, fumes and smokes. (Air cleaners include air washers and air filters.) Air Conditioning: The simultaneous control of all or at least the first three of those factors affecting both the physical and chemical conditions of the atmosphere within any structure. These factors include temperature, humidity, motion, distribution, dust, bacteria, odors and toxic gases, most of which affect in greater or lesser degree human health or comfort. (See Comfort Air Conditioning.) Air Washer: An enclosure in which air is forced through a spray of water in order ' to cleanse, humidify, or dehumidify the air. Anemometer: An instrument for measuring the velocity of moving air. Atmospheric Pressure: The pressure indicated by a barometer. Standard atmospheric pressure is a pressure of 76 cm mercury (density 13.5951 grams per cubic centimeter, gravity 980.665 cm per second per second). It is equivalent to 14.6959 lb per square inch or 29.921 in. of mercury at 32 F. Baffle: A plate or wall for deflecting gases or fluids. Blast: This word was formerly used to denote forced air circulation, particularly in connection with central fan systems using steam or hot water as the heating medium. As applied in this sense, the word blast is now obsolete. Boiler: A closed vessel in which steam is generated or in which water is heated: ' Boiler Heating Surface: That portion of the surface of the heat-transfer apparatus in contact with the fluid being heated on one side and the gas or refractory being cooled on the other, in which the fluid being heated forms part of the circulating system; this surface shall be measured on the side receiving heat. This includes the boiler, water walls, water screens, and water floor. (A.S.M.E. Power Test Codes, Series 1929.) - Boiler Horsepower: The equivalent evaporation of 34.5 lb of water per hour from and at 212 F. This is equal to a heat output of 970.3 X 34.5 = 33,475. Btu per hour. British Thermal Unit: A unit of energy defined in terms of the international steam- table calorie through the convenient relation 1 Btu per pound per. degree Fahrenheit = 1 cal per gram per degree Centigrade. It is approximately the quantity of heat required to raise the temperature of 1 lb of liquid water from 63 to 64 F. i 791