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254 CHAPTER 15 1948 Guide Table 1. Typical Commercial Design Room Conditions for Summer Average Peak Load in Comfort Air Conditioning*1 Type of Installation Deluxe Application. Normal Application It) to 4U min Uccupancv Dry-Bulb Temp 78 80 82 Wet-Bulb TEMPb 65 67 68 Relative' Humidity Per Cent 50 51 49 Grains Per LBb 72 7 78 5 . 80.0 Effective Temp* 7? ? 74 0 75.3 Values in TabJe 1 are for peak load conditions. It is general practice to operate a system at approxi mately 76. F and 50 per cent relative humidity at other than peak load. bPsychrometric data for standard barometric pressure. *Fig. 10, Chapter 12, air movement 15 to 25 fpm. These factors will be discussed in turn. The material presented leads to an illustrative procedure for a cooling-load calculation, and a numerical example is given to demonstrate the calculations involved. Indoor Conditions DESIGN CONDITIONS Indoor air conditions for human health and comfort have been and continue to be the subject of much discussion and research. The effective temperature index, explained in Chapter 12 is probably the best available source of design criteria for comfort air conditioning systems for buildings or enclosures in which the air and inside surface temperatures.remain substantially equal; a condition that can safely be assumed for most ordinary comfort air conditioning installations. Other sources of design specifications are to be found in the requirements of codes and ordinances, and in the varied long-term experiences of manu facturers, contractors, and engineering specialists. Past experience, cumulative over many years, indicates that indoor design conditions for which summer air-conditioning equipment is selected, should not exceed a temperature of 80 F or a.relative humidity: of 50 per cent for the average job in the United States.. If these conditions are exceeded, complaints of discomfort may be expected, especially with continuous occupancy. For very brief occupancy only, a slightly higher peak-load design temperature may be employed. In regard to the lower limit of humidity, complaints are not encountered for store installations operated down to 35 per cent relative humidity or, for office jobs, some what lower. These observations apply to normal commercial practice in this country only; for extremes such as tropical or very hot regions it is regarded, as more practicable to design for a peak-load outdoor-indoor temperature difference of about 15 to 20 F. Table 1 offers typical design conditions for average requirements encountered. The deluxe figures would also apply in general for localities having a summer outdoor design temperature of 90 F or less; and the 15 to 40 min occupancy values or even somewhat higher dry-bulb tem peratures would indicate acceptable conditions for very hot localities. Table 1 is to be used with good judgment, for there is no universal rule which may be applied to indoor design conditions. Guarantees of conditions to be maintained for summer operation are based upon a definite set of load conditions. At other than the guarantee load, the conditions produced by a system are determined by the balance , of imposed load and equipment capacity and by the method adopted for Cooling Hoad 255 Table 2. Illustrative Temperatures and Relative Humidities Applicable to Industrial Air Conditioning* Classification Materials, Location or Process Temperature F Employe Efficiency Offices......................-................... --.............. ......... Storage. Prior to Manufacturing' Ceramic Materials-- ......................... ........... Sugar----- ---------------------------------------- ----- ------- Hardened Aluminum Alloys.....-...................... Manufacturing Process ----------------- s------------ Instrument Calibration...................................... Match Manufacturing-----------------................... Research and Development 78-80 78-80 78-80 80 60-80 70-80 80 75-80 60-80 60-75 60-75 60 0 to -30 70-90 75-80 80 60-80 65-80. 78 68 72-74 60-80 70 -100 to +170 78 70-75 78-80 -80 to +150 Relative Humidity % 50 50 50 50 50 30-35 35 35 35-50 55-65 40-50 30-45 40-55 60 35-50 40-50 <50 . 50-55 . 50 55-65 65 50 50-65 45-50 Taken from the article. "Indoor Climate and Refrigeration for Post-War Industry," by E. K. Heglin. Cleveland Engineering, Vol. 40, No. 27, July 3, 1947. p. 5. regulating- the system operation. Complete specifications of indoor design conditions would include part-load and overload-operation, particularly from the viewpoint of economy. ; In the field of industrial air conditioning, indoor design conditions are established by the requirements of goods and processes, in addition to the comfort and efficiency of the workers. No generally-applicable speci fications are possible, as each job. has its own special requirements. Table 2 offers illustrative general information.............. The indoor design conditions suggested have had reference to con ditions to be maintained at the level of occupancy. For extremely high ceilings in public or industrial buildings, only the zone from 10 to 15 ft above the floor may be cooled to the full.extent. The air temperature at the ceihng would be much higher, and this should be kept in mind, when calculating the convective portion of the roof heat gain. A reduction of outdoor-to-indoor air temperature differential may be assumed in such instances; radiation from the inner roof surface is not diminished. Outdoor Conditions Summer climatic conditions and suggested design wet-bulb and drybulb temperatures are given in Table 3 for various locations in the United States. The highest temperature ever recorded is for the period of record shown. In some cases it should be noted that this period of record is comparatively short and higher temperatures may be expected. In making comparisons for other localities than those shown in Table 3 due consideration must be given to elevation. Column 6 of Table 3 indicates the design dry-bulb temperature sug gested by the A.S.H.V.E. Technical Advisory Committee on Weather