Document Vjwo07zKxX3q7nRe33mvGRmGq

American Society of Heating and Ventilating Engineers Guide, 1936 If the hot-box or hbt-plate methods are used, tests are usually run under still air conditions, which means there is no wind movement over the surfaces of the wall during the test. In the hot-plate method of test the inside surface coefficient is eliminated by the plate's being in direct contact with the wall. In practice, some wind movement over the exterior surface of the wall should always be allowed for; hence, still-air coefficients cannot be used over the outside of the building during the heating season. Moreover, still-air transmission coefficients cannot be corrected to provide for moving-air conditions by applying a single constant factor. Computed coefficients of transmission for various types of construction are given in Chapter 5. EUPATHEOSCOPE The eupatheoscope affords a means of evaluating the combined effect of radiation and convection in a given environment in terms of a standard environment and in some terms related to human comfort. See Chapter 38. PROBLEMS Etf PRACTICE 1 9 What is the corrected barometric pressure of the atmosphere at 32 F when a mercurial barometer reading of 29.51 in. Hg, is determined in a room having a temperature of 91 F? Substitute in Equation 1. h = 29.51 [1 -- 0.000101 (91 -- 32)]. h = 29.33 in. Hg. 2 9 What advantages other than its sensitiveness, has the U-tube draft gage or manometer for measurement of low pressures? Inherent accuracy without calibration and low cost of the essential parts, which are glass tubing and an ordinary scale. 3 9 Are thermocouples as accurate as mercury thermometers? Within the range which can be measured with both instruments (below 1000 F) either one may be made as sensitive as the service requires. The accuracy of a thermocouple temperature measurement depends chiefly on: (1) an accurate calibration of the wire, (2) the sensitiveness of the electrical instrument, (3) accurate cold-junction control, and (4) proper placement of the sensitive junction. 4 9 When an anemometer is used for measuring- the air discharged from1 a grille or register, does it read the velocity through the gross face area or the velocity through the net free area? Neither. If either of these velocities is required, it should be calculated by means of Equation 2. 5 9 Do common errors made in humidity determination produce a result that is too high or too low? A higher relative humidity than the true value is likely to be found, either because there is insufficient velocity over the wet-bulb or because the reading is not taken at the right time. 6 9 What is the purpose of the carbon dioxide determination? It is an index of the adequacy of fresh air supply and also an indicator of air distribution. 770 Chapter 44 TERMINOLOGY Glossary of Physical and Heating and Ventilating Terms Used in the Text, Standard Abbreviations, Conversion Equations, Drafting Symbols, A.S.H.V.E. Codes Absolute Humidity: See Humidity. Absolute Pressure: The sum, at any particular time, of the gage pressure and the atmospheric pressure. Absolute Temperature: The temperature of a substance measured above absolute zero. Absolute Zero: The temperature ( -- 459.6 F) at which the molecular motion of a substance theoretically ceases. This is the temperature at which the substance theoretically contains no heat energy. Acceleration: The rate of change of velocity. In the fps system this is expressed in units of one foot per second per second. V Acceleration Due to Gravity: The rate of gain in velocity of a freely falling body. In the fps system this is 32.174 feet per second per second. Adiabatic: An adjective pertaining to or. designating variations in volume or pressure not accompanied by gain or loss of heat. When a substance undergoes adiabatic expansion, since it does not receive heat from without, the work which it does is at the expense of its internal energy,' and therefore its temperature falls; similarly, when it is adiabatically compressed its temperature rises. Adsorption: The adhesion- of the molecules of gases or dissolved sub stances to the surfaces of solid bodies, resulting in a concentration of the gas or solution at the place of contact. 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 tempera ture, humidity, motion, distribution, dust, bacteria, odors, toxic gases, and ionization, most of which affect in greater or lesser degree human health or comfort. . - Air Infiltration: The inleakage of air through cracks and crevices, and through doors, windows and other openings, caused by wind pressure or temperature difference. 771