Document pmjrqQEKkL17g1wV8w6ap8KD6

Heating Ventilating Air Conditioning Guide 1938 the resulting device is'sometimes referred to as a concealed radiator. (See also definition of Radiator. See also Chapter 14.) Corrosive: Having the power to wear away or gradually change the texture or substance of a material. Decibel: The standard unit for noise or sound intensity. One decibel is equal to ten times the logarithm to the base e of the ratio of the sound intensities. Degree-Day: A unit, based upon temperature difference and time, used in specifying the nominal heating load in winter. For any one day there exists as many degree-days as there are degrees Fahrenheit dif ference in temperature between the average outside air temperature, taken over a 24-hour period, and a temperature of 65 F. Dehumidify: To remove water vapor from the atmosphere; to remove water vapor or moisture from any material. Density: The weight of a unit volume, expressed in pounds per cubic W foot, d = -y- Dew-Point Temperature: The temperature corresponding to satura tion (100 per cent relative humidity) for a given moisture content. Diffuser: A vaned device placed at an air supply opening to direct the air flow. " 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 Radiator: Same as Radiator. . 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 heating units and into which the condensation from the heating units drain. Down-Feed System (Steam): A steam heating system in which the supply mains are above the level of the heating units which they serve. Draft Head (Side Outlet Enclosure): The height of a gravity convector between the bottom of the heating unit and the bottom of the air outlet opening. Draft Head (Top Outlet Enclosure): The height of a gravity convectorbetween the bottom of the heating unit and the top of the enclosure. Drip: A pipe, or a steam trap and a pipe, considered as ai unit, which conducts condensation from the steam side of a piping system to the water or return side of the system. Dry Air: Air with which no water vapor is mixed. This term is used comparatively, since.in nature there is always some water vapor included in air, and such water vapor, being a gas, is dry. 822 Chapter 45. Terminology Dry-Bulb Temperature: The temperature of the air indicated by any type of thermometer not affected by the water vapor content or relative humidity of the air. Dry Return: A return pipe in a steam heating system, which carries both water of condensation and air. -The dry return is above the level of the water line in the boiler in a gravity system. See Wet Return. Dust: Solid material in a finely divided state, the particles of which are large and heavy enough to fall with increasing velocity; due to gravity in still air. For instance, particles of fine sand or grit, the average diameter of which is approximately 0.01 centimeter, such as are blown on a windy day, may be called.dust. Dynamic Head or Pressure: The total or impact pressure. This is the sum of the radial pressure and the velocity pressure at the point of measurement. Effective Temperature: An arbitrary index of the degree of warmth or cold felt by the human body in response to temperature, humidity, and movement of the air. Effective temperature is a composite index which combines the readings of temperature, humidity, and air motion into a single value. The numerical value of the effective temperature scale has been fixed by the temperature of saturated air which induces an identical sensation of warmth. Enthalpy: Total heat or thermal potential. Entropy: A ratio, evaluated for practical purposes by dividing the heat content of a unit weight of a substance, by its absolute temperature. Useful in examining changes during a heat cycle. Entropy is constant during a reversible adiabatic change of state. Equivalent Evaporation: The amount of water a boiler would evaporate, in pounds per hour, if it received feed water at 212 F arid vaporized it at the same temperature and atmospheric pressure. Estimated Design Load: The load, stated in Btu per hour or equiv alent direct radiation, as estimated by the purchaser for the conditions of inside and outside temperature for which the amount of installed radiation was determined. It is the sum of the heat emission of the radiation to be actually.Jnstalled plus the allowance for the heat loss of the connecting piping plus the heat requirement for any apparatus requiring heat con nected with the system. (A.S.H.V.E. Standard Code for Rating Steam Heating Solid Fuel Hand-Fired Boilers--edition of April 1932.) Estimated Maximum Load: Construed to mean the load stated in Btu per hour or equivalent direct radiation that has been estimated by the purchaser to be the greatest or iriaximum load that the boiler will be called upon to carry. (A.S.H.V.E. Standard Code for Rating Steam Heating Solid Fuel Hand-Fired Boilers--edition of April 1932.) Extended Heating Surface: See Heating Surface. Extended Surface Heating Unit : A heating unit having a relatively large amount of extended surface which may be integral with the core containing the heating medium or assembled over such a core, making good thermal contact by pressure or by being soldered to the core or by both pressure and soldering. An extended surface heating unit is usually placed within an enclosure and therefore functions as a convector. 823