Document ExgZp252Q3VdYK025wmKDDbD0

650 CHAPTER 45 1959 Guide where the from the guard to the fan is more than 4 in, they shall not permit the passage of a cylindrical rod Y* in. in ' diameter. Motor Speed Qossifications A Constant-speed motor is one in which the speed remains practically constant with changes in load; eg., a d-c shunt- wound motor or a-c squirrel-cage motor with low slip. A Varymg-epeed 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-varying-epeed 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; eg., 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 ISO 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 recognised 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 1000 rpm. This motor may be rated 20 hp, 40 C at 600 rpm and 25 hp, 40 C from 1200 to 1600 rpm. Between 600 and 1200 rpm the rated horsepower increases directly with speed from 20 to 25 hp. (5) Motors may also be rated 1. hour with temperature rise of 50 C with the higher horsepower rating (see pre ceding item 2) throughout the entire speed range. Example: 20/25 hp, 400 to 1600 rpm. This motor may be rated 25 hp, 50 C 400/1600 rpm; 1 hour. Mechanical Modifications Vertical Mountings 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 fiush plate mountings, suitable for close coupled pump and wimUftf applications. CHAPTER 46 RESIDENTIAL SUMMER AIR CONDITIONING Consumer Requirements, Equipment Capacity Selection, Types of Equipment, Types of Systems, Gas Year-round Air Conditioners, Location of Coo/ing Equipment, Noise, Air Distribution Methods, Operating Costs, Effects on Future House Design UMMER air conditioning in residences has become a tial Air-Conditioning published by the Air Conditioning and S major factor in the air-conditioning field and has created Refrigeration Institute. Published procedures of reliable a heavy interest among home-owners, builders, architects manufacturers when used in conjunction with their equip and business men. Residential cooling, particularly for the ment are also adequate. small home, received its initial impetus when equipment spe Both of the industry methods mentioned employ cooling cifically designed for such purposes became available in the load factors for the various components of the load that are 1930's. averaged over a peak period of several hours and thereby The first installations were made by using commercial and make allowance for thermal storage effects. They avoid the industrial methods as the estimating basis and did not prove possibility of pyramiding non-concurrent, instantaneous peak as satisfactory as the installer or designer desired. Actually, loads. the difference between estimating the residential summer air- With most methods it is possible to select the desired de conditioning and commercial summer air-conditioning loads sign indoor-outdoor temperature difference, using 80 F or is in the design temperature differences used, the type of in the user's preference for the indoor temperature, and the ternal load in the conditioned area, and the .method of cal commonly used outdoor temperature for the area as listed in culating equipment size. Chapter 13. CONSUMER REQUIREMENTS Design methods which average load conditions for a period in excess of 12 hr have not been accepted by the industry Present practice is to design residential summer air condi tioning on the basis of an 80 F indoor temperature. In-using this basis it is assumed that the home owner will operate the system continuously with a thermostat setting of 75 or 76 F and thereby take advantage of the thermal storage in the house and household furnishings to reduce the peak tempera tures. The preference of the individual home owner must, however, be considered in selecting the design indoor tem perature and may require that a temperature lower than 80 F be selected. Analog computed studies and field investi gations1 have apparently demonstrated the adequacy of the SO F indoor temperature as a Haris for equipment selection procedure. To ensure 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 coding 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 committees. Such methods require the introduction of fac tors that are not at present considered to be adequately sub stantiated by mathematical analysis or to be justified by the thermal storage effects of a typical residence. The contractor should avoid any capacity selection pro cedure based on a rule of thumb such as 10 average windows or doors per ton or 500 sq ft of floor area per ton. Insulation, glass areas, shading effects, and solar orientation must be given careful consideration by using an accurate, step-by-step procedure for estimating the load. In residences, peak lighting loads will not usually occur during the period of greatest load from outdoor temperature and solar conditions. Unlike summer air conditioning in com mercial or industrial establishments where internal heat pro ducing sources may be a major portion of the load, internal loads in residences may generally be neglected except under the most unusual circumstances. The heat and moisture introduced by a clothes dryer or wa ter heater should be vented to outdoors. Heat introduced by the kitchen range should be discharged through an exhaust fan. These are major internal loads that must be taken into account if adequate venting is not to be provided. The load calculation method presented in Chapter 13 is not recommended for residences where it has been found* to ing the cleanliness advantage of air conditioning. result in oversizing because internal loads that are generally a EQUIPMENT CAPACITY SaECTION prime consideration in commercial applications are not gen erally significant in residences. Furthermore the method out There are two industry-accepted methods of calculating lined in Chapter 13 gives an instantaneous peak load without residential cooling loads. These are as given in Manual 11, consideration of residential usage and heat storage effects Summer Air Conditioning, of the National Warm Air Heat applied in the ARI and NWAH A ACA load calculation pro ing and Air Conditioning Association and Standard 610-56, cedure. Oversizing is objectionable from at least two view Application Engineering Standard for Year-Round Residen points: (1) it increases the capacity and consequently the 651