Document GMQaxvYK4G2vxxLJEQbeaQaV

216 CHAPTER 9 1957 Guide Heat Loss Studies in Four Identical BuildingB to Determine the Effect of Insulation, by D. B. Anderson (A.S.H.V.E. Transactions, Vol. 48, 1942, p. 471). Effect of Ceiling Insulation upon Summer Comfort, by T. D. Phillips (National Bureau of Standards Report JJMS52, July 1, 1940). Thermal Insulation Made of Wood-Base Materials, Its Application and Use in Houses, by L.V. Teesdale (U. S. Forest Products Laboratory Report No. R1740, October 1949). Heat Transmission Through Building Materials, by F. B. Rowley and A. B. Algren {University of Minne sota, Engineering Experiment Station Bulletin No. 8). * Building Insulation, by Paul D. Close (American Technical Society, Chicago, 4th Edition, 1951). CHAPTER 10 MOISTURE IN tfuILmNLr CONSTRUCTION Properties of Water in Air; Water in Building Materials; Movement of Moisture in Materials; Vapor Transmission; Permeance and Testing; Visible Condensation; Concealed Condensation in Heated Buildings; Control of Concealed Condensation; Condensation in Cooled Structures THE behavior of moisture is too often overlooked or given scant at tention in the design and construction of buildings. It is present as a vapor in all air and as adsorbed moisture in most building materials. It may be present also at times in th& free liquid state or ,as ice, in the solid state, within the range of temperatures encountered in many buildings. Problems involving moisture may arise from changes in: moisture content, from the presence of excessive moisture, or from effects associated with its changes in state, ; Of particular interest here is the change from the vapor to the liquid or solid state, known;as condensation. This may be associated with a re duction of temperature with time, or may occur as a result of migration of water vapor to regions of lower temperature. Moisture problems involv ing condensation are therefore most likely to occur in' buildings in any climate in which there is a source of water vapor at temperatures above normal, or in cooled structures, and in buildings in cold: climates. Moisture problems in residences occur in winter and become increasingly important as homes are built smaller and tighter. Water vapor originates from such necessary living requirements as cooldng, .laundering, bathing, and the breathing and. perspiration of people. In. a typical family of four, the average daily production of water vapor from these sources may be as much as 25 lb, and may be much greater where such appliances as humidifiers, automatic washers, and dryers are used.1 Another large source of water vapor is sometimes the bare earth in a crawl space or base ment. All this water vapor must escape from the dwelling. PROPERTIES OF WATER VAPOR IN AIR Water vapor in air is a gas which occupies all the space, along with the mr present. In many ways, the water vapor can act independently of the mr, since in general its properties do not depend on the presence of the "r- It exerts its own vapor pressure, and can move about through air in space, or move through materials under differences in its own vapor, independently of the air. However, when the .air is moved aff r *s Seated or cooled, the water vapor present is similarly ~iected,.80 that it is usually necessary to consider it as a part of ah airVaPr mixture. The properties of mixtures of air and water vapor are relatively well in tlT* TM are (?ea*t with fully in Chapter 3, Thermodynamics. Changes the A6 ProPert'es with heating and cooling can be followed readily with met of a psychrometric chart, shown in outline in Fig. 1; The satura- 217 .