Document MwZ5vX3XBNzGGLg5G9gJxG9V

2 CHAPTER 1 1951 Guide Blast Heater: A set of heat transfer coils or sections used to heat air which is drawn or forced through it by a fan. Blow (throw): In air distribution, the distance an air stream travels from an outlet to a position at which air motion along the axis reduces to a velocity of 50 fpm. For unit heaters, the distance an air stream travels from a heater without a per ceptible rise due to temperature difference and loss of velocity. 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. (AJS.M.E. Power Test Codes, Series 1929.) Direct Heating Surface is generally understood to be the boiler heating surface subject to direct radiation from the surface of the grate, or from the surfaces of oil or gas burners. Indirect Heating Surface is the boiler heating surface within the flues. Boiler Horsepower: The equivalent evaporation of 34.5 lb of water per hr from and at 212 F. This is equal to a heat output of 970.3 X 34.5 =.33,475 Btu per hr. British Thermal Unit: Classically, the Btu is defined as the quantity .of beat required to raise the temperature of 1 lb of water 1 Fahrenheit degree. By this definition the exact value depends upon the initial temperature of the water. Several values of the Btu are in more or less common use, each differing from the others by a slight amount. One of the more common of these is the mean Btu which is defined as 1/180 of the heat required to raise the temperature of 1 lb of water from 32 F to 212 F at a constant atmospheric pressure of 14.696 lb per sq in. absolute. For most accurate work the International Table (I.T.) Btu is usually used. This is defined by the relation: 1 (I.T.) Btu per (pound) (Fahrenheit degree) = 1 (I.T.) calorie per (gram) (Centigrade degree). This value corresponds to the amount of . heat required to raise the temperature of 1 lb of water 1 Fahrenheit degree at 58 F and also at 149 F. The mean Btu corresponds to 1.0008 (I.T.) Btu. By-Pass: A pipe or duct, usually controlled by valve or damper, for conveying a fluid around an element of a system. Calorie (Gram Calorie): Classically the calorie is defined as the quantity of heat required to raise the temperature of 1 gram of water 1 Centigrade aegree. By this definition the exact value depends upon the initial temperature of the water. Several values of the calorie are in more or less common use, each differing from the others by a slight amount. Among these are the 15 C calorie and the 17\ C calorie. The mean calorie, i.e., 1/100 the quantity of heat required to raise the temperature of 1 gram of water from 0 C to 100 C, is also extensively used. For the most accurate work the International Table (I.T.) calorie, defined in terms of the international electrical units, is usually used: 1 (I.T.) calorie = 1/860 inter national watt-hour = 3,600/860 international watt-seconds or international joules. The kilocalorie = 1,000 cal. Central Fan System: A mechanical indirect system of heating, ventilating, or air conditioning, in which the air is treated or handled by equipment located outside the rooms served, usually at a central location, and is conveyed to and from the rooms by ' means of a fan and a system of distributing ducts. (See Chapter 29.) Chimney Effect: The tendency of air or gas.in a duct or other vertical passage to rise when heated due to its lower density compared with that of the surrounding air or gas. In buildings, the tendency toward displacement (caused by the difference in temperature) of internal heated air by unheated outside air due to the difference in density of outside and inside air. Comfort Air-Conditioning: The process by which simultaneously the temperature, moisture content, movement and quality of the air in enclosed spaces intended for human occupancy may be maintained within required limits. (See Air Condi Honing.) Comfort Line: A line on the comfort chart showing relation between the effective temperature and the percentage of adults feeling comfortable. Comfort Zone {Average): The range of effective temperatures over which the ma jority (50 percent or more) of adults feel comfortable. (See Chapter 6.) Condensate: The liquid formed by condensation of a vapor. In steam heating, . water condensed from steam: in air conditioning, water extracted frojn air, as by con densation on the cooling coil of a refrigeration machine. 1 >1 -5 Terminology * Condensation: The process-of changing a vapor into liquid by the extraction of heat. Condensation of steam or water vapor is effected in either steam condensers or in dehumidifying coils and the resulting water is called condensate. Conductance* Surface {Unit): The amount of heat transferred by radiation, con duction and convection from unit area of a surface to the air or other fluid in contact with it 'or vice versa, in unit time for a unit difference in temperature between'the surface*and the fluid. The common unit is: Btu per (hour) (square foot) (Fahrenheit degree). Symbol/. The temperature of the fluid should be taken in a plane suffi ciently far from the surface that it will not be affected by the temperature of the surface. Conductance, Thermal: The time rate of heat flow through unit area of a body, of. given size and shape, per unit temperature difference. Common unit is: Btu per (hour) (square foot) (Fahrenheit degree).. Symbol C. Conduction, Thermal: The process of heat transfer through a material medium in which kinetic energy is transmitted by the particles of the material from particle to particle without gross displacement of the particles. Conductivity, Thermal: The time rate of heat flow through unit area of a homo geneous substance under the influence of a unit temperature gradient. Common units are: Btu per (hour) (square foot) (Fahrenheit degree per inch). Symbol!;. Conductor, Thermal: A material which readily transmits heat by means of- conduction. Convection: The motion resulting in a fluid from the differences in density and the action of gravity. In heat transmission this meaning has been extended to include both forced and natural motion or circulation. Convective Heat Transfer: The transmission of heat by either natural or forced motion of a fluid (liquid or gas). Convector: An agency of convection. In heat transfer, a surface designed to ' transfer its heat to a surrounding fluid largely or wholly by convection. The heated fluid may be removed mechanically or by gravity (Gravity Convector). Such a surface may or may not be enclosed or concealed. When concealed and enclosed the resulting device is sometimes referred to as a concealed radiator. (See also definition of Radiator.) (See also Chapter 22.) Decibel: A unit used to express the relation between two amounts of power. By definition the difference in decibels between two powers Pi and P*, P*. being the larger, is: db difference = 10 logioP*/Pi. In acoustics the threshold of hearing at 1,000 cycles per sec has been standardized at 10rw watts per sq cm. If Pi is the power in watts per square centimeter of a measured sound, then 10 logio Pi/10~u is the db difference above the threshold and is known as the intensity level. This is a definite recognized way of describing the intensity of a sound. Declination of Sun: The angle above or below equatorial plane. It is plus if north of the plane, and minus if below. Celestral objects are located by declination. Degree-Day: A unit, based upon temperature difference and time, used in estimat ing fuel consumption and specifying nominal heating load of a building in winter. For any one day, when the mean temperature is less than 65 F, there exists as many degree-days as there are Fahrenheit degrees difference in temperature between the mean temperature for the day and 65 F. Dehumidlfy: To reduce by any process, the quantity of water vapor within a given space. Dehydrate: To remove water in all forms from matter. Liquid water, hygroscopic water, and water of crystallization or water of hydration are included. Density: The ratio of the mass of a specimen of a substance to the volume of the specimen. The mass of a unit volume of a substance. When weight can be used without confusion, as synonymous with mass, density is the weight per unit volume. Dew-Point: See Temperature, Dew-Point. Direct-Indirect Heating Unit: A heating unit located in the room or space to be heated and partially enclosed, the enclosed portion being used to heat air which enters from outside the room. Direct-Return System {Hot Water): A hot water system in which the water, after it has passed through a heating unit is returned to the boiler along a direct path so that the total distance traveled by the water is the shortest feasible, and so that there are considerable differences in the lengths of the several circuits composing the system. - Down-Feed One-Pipe Riser {Steam): A pipe which carries .steam downward to the beating units and into which the condensate from the heating units drains.