Document y1wMw3ONRp8LNqbV75MGLpY2

668 CHAPTER 45 1960 Guide where the distance from the guard to the fan is more than 4 in., they shall not permit the passage of a cylindrical rod K in. in diameter. Motor Speed Classifications A Constantspeed motor is one in which the speed remains practically constant with changes in load; eg., a d-c shuntwound motor or a-c squirrel-cage motor with low slip. A Varying-speed motor is one in which the speed varies with the load, usually decreasing when the load increases;- eg., a d-c series motor or an induction motor (with large slip. An Adjustable-varymg-speed motor is one in which the speed can be adjusted gradually, but when once adjusted for a given load will vary in considerable degree with change in load; eg., a shunt-wound d-c motor adjusted by armature resistance con* trol. An Adjustable-speed motor is one in which the speed can be varied gradually over a considerable range, but when once ad justed remains practically unaffected by the load; egn a d-c shunt motor with field-resistance control. The standard ratings for open-type, adjustable-speed motors, having a speed range of 3 to 1 and greater are in accordance with the following: (1) A standard continuous horsepower rating at 150 percent of minimum speed with a temperature rise of 40 C. (2) The next higher standard continuous horsepower rating at 3 times minimum speed with a temperature rise of 40 C. (3) Between 150 percent of minimum .speed and 3 times minimum speed, the standard continuous horsepower rating with a temperature rise of 40 C will vary with the speed along a straight line connecting these two horsepower ratings. No further increase in horsepower is recognized above 3 times minimum speed. (4) Below 150 percent of minimum speed the lower continuous horsepower rating (see preceding item 1) will apply with a temperature rise of 50 C. Example: 20/25 hp, 400 to 1600 rpm. This motor may be rated 20 hp, 40 C at 600 rpm and 25 bp, 40 C from 1200 to 1600 rpm. Between 600 and 1200 rpm the rated horsepower increases directly with speed from 3) to 25 hp. (5) Motors may also be rated 1 hour with temperature rise of 50 C with the higher horsepower rating (see proceding item 2) throughout the entire speed range. Example: 20/25 hp, 400 to 1600 rpm. This motor may be rated 25 hp, 60 C 400/1600 rpm; 1 hour. Mechanical Modifications Vertical Mounting* are available for such applications as pumps and agitators. This type of application may require a special umbrella-type hood to protect against dripping liquids. Flanged Mountings are available for use where' motors are built in as part of machines. Motors may also be supplied with flush plate mountings, suitable for close coupled pump and similar applications. i t h < 1 \ 1 i I - " CHAPTER 46 RESIDENTIAL SUMMER AIR CONDITIONING Consumer Requirements, Equipment Capacity Selection, Types of Equipment, Types of Systems, Gos Year-round Air Conditioners, Heat Pump Year-round Air Conditioners, location of Cooling Equipment, Operating Sound Level, Air Distribution Methods, Operating. Costs, Effects on Future House Design SUMMER air conditioning of residences has become a tion Guide/ Published procedures of reliable manufacturers, major factor in the air-conditioning industry. It is re when used in conjunction with their equipment, are also ade ceiving increasing support from home owners, builders and quate. architects. Although residential air conditioning began at the AH of the industry methods mentioned employ cooling same time as comfort applications in theaters and depart load factors for the various components of the load that are ment stores, it received its initial impetus when equipment averaged over a peak period of several hours and thereby for use with warm air furnaces was introduced in the late make allowance for thermal storage effects. They avoid the 1930's. possibility of pyramiding non-concurrent, instantaneous peak > CONSUMER REQUIREMENTS loads. With most methods it is possible to select the desired de Present practice is to design residential summer air condi sign indoor temperature, and the commonly used outdoor tioning on the basis of an 80 F indoor temperature. In using temperature for the area as listed in Chapter 13. this basis it is assumed that the home owner will operate the The use of any capacity selection procedure based on a rule system continuously with a thermostat setting of 75 or 76 F of thumb such as 10 average wmdmre or doors per ton or and thereby take advantage of the thermal storage in the 600 sq ft of floor area per ton should be avoided. Insulation, house and household furnishings to reduce the peak tempera glass areas, shading effects, and solar orientation must be tures. The preference of the individual home owner must, given careful consideration by using an engineering procedure however, be considered in selecting the design indoor tem for estimating the load. perature and may require that a temperature lower than 80 F be selected, particularly in existing bomes and"higher TYPES OF EQUIPMENT cost custom-built homes. Analog computed studies and field investigations1 have apparently demonstrated the adequacy of the 80 F indoor temperature as a basis for equipment se lection procedure for lower cost homes. To assure comfort, it is essential that the proposed opera tion and performance of the system be explained to the user in advance. Usually the greatest degree of comfort can be obtained by keeping the house closed and operating with a fixed thermostat setting throughout the cooling season. In some climates the opening of the house to utilize night-air cooling creates humidity difficulties that take several hours to overcome during the following day. The use of night-air cool ing may lead to unsatisfactory conditions-when the equip ment is not turned on again sufficiently early the next day. It will also allow unfiltered air to enter the house thus reduc ing the cleanliness advantage of air conditioning. Hermetic, semi-hermetic and split systems are available for the mechanical refrigerating portion of residential air conditioning systems. The hermetic units are of the factorysealed refrigerant charge type which require cutting into the system for either the addition of charge or replacement of any part of the refrigerant cycle. The semi-hermetic types'are factory assembled (and may be shipped with a refrigerant charge), but have readily accessible arrangements for adding refrigerant or changing parts. The split systems are generally separate low-side (evaporator coil) and high-side (compres sor and condenser) assemblies. Each of these types has advantages and features which make it suitable for various applications. For example, the hermetic type of system can be made with simpler parts and is less subject to leaks, but the cooling system must be de signed to route the air through the fixed arrangement of the EQUIPMENT CAPACITY SaECTlON cooling coil- The field-assembled components of a split sys- y tern can more readily meet the requirements of existing homes Considerable study and research relating to the problems of already heated with warm air systems. load calculations -for residential air conditioning have con All three types of systems have been made with water- vinced engineers and researchers that the load calculation cooled or air-cooled condensers. Where water for condensing methods used for commercial and industrial air conditioning purposes is readily available and of low cost, it is usually the are not directly applicable to residential air conditioning. preferred medium of heat disposal. The air-cooled condensing There are three industry-sponsored methods of calculating method has been rapidly gaining in popularity, although cool residential air conditioning loads: ARI Standard 610-56, Ap ing towers and evaporative condensers also have been used plication Engineering Standard for Year-Round Residential for residential applications. Air Conditioning]*NWAH <fe ACA Manual 11, Summer Air Cooling towers in home installations may present unac Conditioning ;* and 1=B=R No. C-30, Cooling Load Calcula ceptable complications, such as the necessity of using water 669 JS