Document Dv36e4x3XMJKyYwa7m2nw15ya

258 CHAPTER 12 1951 Guide sky radiation and from outdoor-indoor temperature differential for glass areas and exterior, walls and roofs, modified by periodic heat flow or lag factors depending on the type of structure; (2) load due to heat gain through interior partitions, ceilings and floors; (3) load due to ventilation, either natural or mechanical; (4) load due to heat sources within the conditioned space such as people, lights, power equipment, and appliances; (5) load due to moisture transfer through permeable building materials; (6) miscellaneous heat sources. C. Determination of Air Quantity and Apparatus Dew-Point. 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. DESIGN CONDITIONS Indoor Conditions Indoor air conditions for human health and comfort have been and con tinue to be the subject of much discussion and research. The effective temperature index, explained in Chapter 6 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 Table 1. Typical Commercial Design Room Conditions fob Summer Avehaqe Peak Load in Compost Air Conditioning* Type of Installation Dry-Bulb Temp Deluxe Application_____ ___ Normal Application___ .___ 15 to 40 min Occupancy____ 78 80 82 Wet-Bulb Temp<>. 65 67 68 Relative Humidity Per Cent 50 51 49 Grains Per L-Qfi 72.7 78.5 80.0 Effective Tempo 72.2 74.0 75.3 * Values in Table 1 are for peak load conditions. It is genera! practice to operate a system at approximately 76 F and 60 percent relative humidity at other than peak load. b Psyehrometrio data for standard barometric prcae us. Fig. 10, Chapter 6, air movement 15 to 25 fpm. 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 manufacturers, contractors, and engineering specialists. Past experience, cumulative over many years, indicates that indoor de sign 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 continu ous 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 oper ated down to 35 percent relative humidity or, for office jobs, somewhat 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 en countered. 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- 259 Cooling Load peratures, would indicate acceptable conditions for veiy hot localities. Table Its to be used with goodjudgment, 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 regulating the system operation. Complete specifications of indoor design conditions would include part-load and overload operation, particularly froImn tthhee vfiieelwdpoofinint douf setcroianloamiyr. conditioning, indoor design,conditions are established by the requirements of goods and processes, in addition to the Table 2. Temperatures and Relative Humidities Applicable Illustrative^^DgTBIAL Ajr Conditioning* CLASSIFICATION Employe , Efficiency General Machine Shop Work.. Drafting Booms.. Offices.. Prior to jtanulftcturing Bough Castings. Ceramic Materials. pharmaceutical Powders.. Sugar.................................. Paper.. : Electrical Goods. Flour...... Rubber.. Hardened Aluminum Alloya.. Manufacturing Machine Too! Oil Cooling................. Precision Parts Honing Machinery... Ceramio Molding................................. Manufacturing of Electrical Wiring.'. 70-90 75-80 60 60-80 65-80 Assembly Line.. Gage Rooms.... . * * Instrument Calibration. Match Manufacturing-. 78 68 72-74 and Development 60-80 Paper Testing laboratory............. 70 Textile Testing Laboratory............. Special Process Temperature Boxes -100 to + 170 78 Chemical Laboratories...................... 70-75 Fibres and Plastics 78-80 Drafting.................. -80 to +150 Temperature Shock Tests. and Refrigeration for Post-War Industry, Clee*eTfaankdeEnnfgroinmtetrhineQa,rVticolle. ,4`"0x'I,nnNadooo.oo'x2r7Cv,.laJiam*u*lay.tve3s. ,--19-4--7-;--p--._5. 55-65 65 50 50-65 45-50 by E. K. Heglin. No generally-applicable specifica comfort and efficienci yeaocfhthjoebwhoarskeitrss.owrn*uspecial requ~rirze-m---e-nts. Table 2 tions are possible, as offTerhseilinludsotroartdiveesiggnenceornadl itiniofnosrmsuagtigoens.ted have had reference to conditions 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 ceiling 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-toindoor air temperature differential may be assumed in such instances; radiation from the inner roof surface is not diminished. OuStduomomr eCr ocnlidmitiaotnics conditions and suggested design wet-bulb and dryn,~u1~ v f'"- various locations in the United