The rate of radiation from an object may be determined by use of the Stefan- Boltzmann law of radiation. This law states that the amount of energy radiated from a perfect radiator, or a blackbody, is proportional to the fourth power of the absolute temperature of the body. Because most materials are not perfect radiators or absorbers, a proportionality constant called the hemispherical emittance factor is used with this law. Methods for calculating and estimating radiation transfer rates can be found in the ASHRAE HandbookFundamentals. The quantity of energy transferred by radiation depends on the individual temperatures of the radiating bodies. These temperatures are usually combined into a mean radiant temperature for use in heating and cooling calculations. The mean radiant temperature is the uniform temperature of a block enclosure with which a solid body (or occupant) would exchange the same amount of radiant heat as in the actual nonuniform environment. 13.3.10 Thermal Criteria for Building Interiors There are three very important conditions to be controlled in buildings for human comfort. These important criteria are dry-bulb temperature, relative humidity, and velocity or rate of air movement in the space. Measurements of these conditions should be made where average conditions exist in the building, room, or zone and at the breathing line, 3 to 5 ft above the floor. The measurements should be taken where they would not be affected by unusually high heat sources or heat losses. Minor variations or limits from the design conditions, however, are usually acceptable. The occupied zone of a conditioned space does not encompass the total room volume. Rather, this occupied zone is generally taken as that volume bounded by levels 3 in above the floor and 6 ft above the floor and by vertical planes 2 ft from

Rubber Hose. Nearly all rubber hose is laminated and composed of layers of rubber combined with reinforcing materials like cotton duck, textile cords, and metal wire. Typical hose consists of an inner rubber lining, a number of intermediate layers consisting of braided cord or cotton duck impregnated with rubber, and outside that, several more layers of fabric, spirally wound cord, spirally wound metal, or in some cases, spirally wound flat steel ribbon. Outside of all this is another layer of rubber to provide resistance to abrasion. Hose for transporting oil, water, wet concrete under pressure, and for dredging purposes is made of heavyduty laminated rubber. Vibration Insulators. These usually consist of a layer of soft rubber bonded between two layers of metal. Another type of insulated consists of a rubber tube or cylinder vulcanized to two concentric metal tubes, the rubber being deflected in shear. A variant of this consists of a cylinder of soft rubber vulcanized to a tubular or solid steel core and a steel outer shell, the entire combination being placed in torsion to act as a spring. Heavy-duty mounts of this type are employed on trucks, buses, and other applications calling for rugged construction. American Concrete Institute, Polymer Modified Concrete, SP-99; Polymers in Concrete, ACI 548; and Guide for the Use of Polymers in Concrete, ACI 548.1. American Society of Civil Engineers, Structural Plastics Design Manual, and Structural Plastics Selection Manual. Modern Plastics Encyclopedia, Plastics Catalog Corp., New York. A. G. H. Dietz, Plastics for Architects and Engineers, M.I.T. Press, Cambridge,

However, if the water towers and evaporative condensers are designed for 75
F WB, then at a wet-bulb temperature above 75, the equipment capacity would be decreased and the compressor head pressure would build up too high, overload the motor, and kick out on the overload relays. So we use 78
F WB for the design of heat rejection equipment. Now, on a 78
F WB day, the compressor head pressure would be at design pressure, the equipment will be in operation, although maintaining room conditions a little less comfortable than desired. At 80
F WB, the compressor head pressure will build up above design pressure and the motor will be drawing more than the design current but usually less than the overload rating of the safety contact heaters. Water condensers are sized for 104
F refrigerant temperature and 95
F water leaving. The amount of water in gallons per minute required for condensers is subject to the type of heat rejection equipment used and manufacturers data should be used. A rule of thumb is 3 gpm/ton per 10
F water-temperature rise. When choosing a condenser for water-tower use, we must determine the water temperature available from the cooling tower with 95
F water to the tower. Check the tower manufacturer for the capacity required at the design WB, and 95
F water to the sprays, and the appropriate wet-bulb approach. (Wet-bulb approach is equal to the number of degrees the temperature of the water leaving the tower is above the wet-bulb temperature. This should be for an economic arrangement about 7
F.) Thus, for 78
F, the water leaving the tower would be 85
F, and the condenser would be designed for a 10
F water-temperature rise, i.e., for water at 95
F to the tower and 85
F leaving the tower. Evaporative condensers should be picked for the required capacity at a design wet-bulb temperature for the area in which they are to be installed. Manufacturers ratings should be checked before the equipment is ordered. For small- and medium-size cooling systems, air-cooled condensers are available for outdoor installation with propeller fans or for indoor installation usually with centrifugal blowers for forcing outdoor air through ducts to and from the condensers. Compressor capacity decreases with increase in head pressure (or temperature) and fall in suction pressure (or temperature). Therefore, in choosing a compressor-motor unit, one must first determine design conditions for which this unit is to operate;