Heating, District. A large, central heating facility that provides heat from steam or hot water to a large number of buildings often under different ownership. Heating, Radiant. Heating by ceiling or wall panels, or both, with surface temperatures higher than that of the human body in such a manner that the heat loss from occupants of the space by radiation is controlled. Heating, Warm-Air. A heating system that uses warm air, rather than steam or hot water, as the heating medium. Heating Surface. Actual surface used for transferring heat in a boiler, furnace, or heat exchanger. Heating System, Automatic. A complete heating system with automatic controls to permit operation without manual controls or human attention. Heating System, Hot-Water. A heating system that utilizes water at temperatures of about 200
F. Humidity. Water vapor mixed with dry air. Humidity, Absolute. Weight of water vapor per unit volume of a vapor-air mixture. It is usually expressed in grains / ft3 or lb / ft3. Humidity, Percent. Ratio of humidity in a volume of air to the maximum amount of water vapor that the air can hold at a given temperature, expressed as a percentage. Humidity, Relative (RH). Ratio of the vapor pressure in a mixture of air and water vapor to the vapor pressure of the air when saturated at the same temperature. Humidity, Specific (Humidity Ratio). Ratio of the weight of water vapor, grains, or pounds, per pound of dry air, at a specific temperature. Hygrometer. A mechanical device used to measure the moisture content of air. Hygroscopic. Denoting any material that readily absorbs moisture and retains it. Hygrostat. A mechanical device that is sensitive to changes in humidity and used to actuate other mechanical devices when predetermined limits of humidity are

The amount of efflorescence that occurs is related to the amount of water in the bricks, and their drying time. The more water in the bricks, and the longer it is there, the more chance salts will have to dissolve and be brought to the surface as the bricks dry out. Efflorescence on new brickwork may be unsightly, but it will not cause damage unless it persists for a long time. Persistent efflorescence should be taken as a warning that water is entering the wall through faulty copings, damp-proof courses or pipes. If allowed to continue unchecked, the salts carried to the face of the wall may eventually attack the bricks and cause deterioration. Remedy: Laying dry bricks and providing good ventilation to speed up the drying process after the bricks have been laid can minimise efflorescence. Forced ventilation and heating of the premises may be necessary to ensure drying during cold winter months. The best removal method is simply to brush off the deposit with a stiff dry bristle brush after the wall has dried out.

Task and worker characteristics Weight W Workers ages Under 40 1 40 to 55 0 Over 55 1 Importance of speed or accuracy Not important 1 Important (errors costly) 0 Critical (errors unsafe) 1 Reflectance of task background Greater than 70% 1 30 to 70% 0 Less than 30% 1 * Based on data in Selection of Illuminance Values for Interior Lighting Design, RP-15A, Illuminating Engineering Society of North America. Calculate W by adding the weighting factors W for the specific environment or required performance and determine the corresponding visual condition from Table 15.7. Use W
0 for environment categories A to C. TABLE 15.6 Visual Condition Number for Determining Recommended Illuminances Category AtoC 4 4 3 2 2 DtoI 4 4 3 3 3 2 2 *W
sum of weighting factors given in Table 15.5 for a specific environment or required performance. building. Consequently, for task lighting, illumination should be kept to the minimum necessary for maintenance of adequate quantity and quality of lighting. For many years, single values for minimum illuminance, or level of illumination, fc, developed by the Illuminating Engineering Society of North America (IES) and listed in tables in the IES Lighting Handbook, have been widely used in the United States. In 1979, however, the IES revised its criteria to a recommended range of target illuminances. These recommended values take into account many of the factors listed above. Following is an example and abbreviated tables to illustrate the use of the tables in the IES handbook. To determine the target illuminance, start by ascertaining the type of activity, or illuminance category, for the space to be illuminated. (The IES Lighting Handbook contains a detailed table correlating specific areas or activities with categories labeled A to I. For some of these categories, the effects of veiling reflections should be evaluated, for which purpose equivalent-sphere-illumination, ESI, calculations may be used, as indicated in Art. 15.10.5.) The first column of Table 15.7, which TABLE 15.7 Recommended Illuminances for Interior Lighting, fca Category of environment or required performance