Document 37zmkEvJvV0Rmxbxb5Lm7kwQa

258 CHAPTER 12 1952 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 Commebcial Design Room Conditions fob Summer Average Peak Load in Comfort Air Conditioning* Type of Installation Deluxe Application_____ Normal Application____ 15 to 40 min Occupancy-- Dry-Bulb Temp 78 80 82 Wet-Bulb Temj* 65 67 63 Relative Humidity Per Cent 50 51 49 Grains Per Lb* 72.7 78.5 80.0 Effective Temp* 72.2 74.0 75.3 values Ul A auic A mv >ui >vuw vu**<A*~w*~< .. __ 0______________ . mately 76 F and 50 percent relative humidity at other than peak load. " k Psychrometric data for standard barometric pressure. 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 IS to 40 min occupancy values, or even somewhat higher dry-bulb tem- Cooling Load 259 peratures, would indicate acceptable'conditions for very hot localities/' Table 1 is 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 :loy 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 from the'viewpoint of economy. In the field of industrial air conditioning, indpor design conditions are. established by the requirements of goods and processes, in addition to .the Table 2. Illustrative Temperatures and Relative Humidities Applicable to Industrial Air Conditioning* Classification Matbbialb, Location ob Process Employee Efficiency Drafting Rsvmxi Offices'....................... Temperature F. - 78-80 . 78-80 78-80 Relative - Humidity % .50 50- Storage Prior to Manufacturing Manufacturing Process Sugar................................... ... Paper..................................... Electrical Goods ............ Flour .... Rubber.................................... ` Grains................................. Hardened Aluminum Allnvn Machine Tool Oil Cooling Precision Parts Honing tt*u*hin*rv Ceramic WoMimr Manufacturing of Electrical Wiring.'___ Gage Rooms................................. Instrument Calibration Match Manufacturing Research and Development Textile. Testing I A.hnrA.tiTvrv Special Process Temperature Boxes Chemical Laboratories..................... Fibres and Plastics Drafting..-....... .............. Temperature Shock Tests;............ ... 70-80 80 60-80 - 60 " r 0 to -30 70-00 75-80 ` 60-80 78 .72-74- . 60-80 70 -100 to +170 - .78 70-75 78-80 -80 to +150 50 15-35 ; > 30-45 40-55 35-50 40-50 50 55-65 . 65 for Post-War I-durtry." by E. K. Heglin. comfort and efficiency of the workers. No generally-applicable specifica tions 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 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. . Outdoor Conditions Summer climatic conditions and suggested design wet-bulb and drybulb temperatures are given in Table 3 for various locations in the United