Document RjX143mn0RZr6pQybqB6M2rKB

472 CHAPTER 46 1960 Guide graphical location, since areas requiring fewer hours of op eration on the cooling cycle will require more hours of opera tion during the heating cycle. LOCATION OF COOUNG EQUIPMB'JT In general, both cooling and heating equipment should be located as far from the sleeping quarters as other circum stances permit. In many existing residences, the location of the evaporator coil (or coils) is governed by the present fur nace and duct arrangements. The location of cooling and heating equipment near bed rooms can be made acceptable through the use of suitable noise prevention and sound absorbing barriers as discussed in the next section Operating Sound Level. In the split system, the cooling coil is located over the fur nace, but the location of the water- or air-cooled condensing unit is quite flexible. The water-cooled condensing units are usually located near the furnace unless space availability or other considerations favor another location. The remote air cooled condensing units (or air-cooled condensers) are usually located outdoors adjacent to the residence. Proximity to neighboring houses is to be avoided. Locations at the front or rear of the residence are usually preferred. Proximity to areas that are likely to be used when the house is being conditioned should be avoided. This applies to porch and patio areas. Preferences of the family and their habits of living must be given consideration so as to keep all space as useful as possi ble and still locate the equipment in such a place that it ran do its intended job and be accessible. OPERATING SOUND LEVEL One of the prime problems with residential air-conditioning installations is the operating noise level. Almost any degree of quietness in an installation can be had for a price. How ever, the numerical standards for describing sound levels have little meaning for the average person. It is difficult to ascertain from the prospective user in advance of installation just what sound levels will be acceptable and to describe what sound levels will result from any particular arrangement. Motors and motor drives, compressor, blower, pumps if any, and flowing air and liquids are potential sources of noise and vibration. The first, and frequently the least expensive and most effective measure in noise reduction, is to put dis tance between the noise and the listener. Installations of cool ing equipment in basements, crawl spaces, utility rooms or attached garages are preferable to those in alcoves, closets, or attics adjacent to bedrooms and living rooms. Mounting of units on concrete floors is preferred. Further steps which may be taken to achieve an acceptable low noise level are as fol lows: 1. Minimize the production of noise and vibration. Use only true, concentric pulleys with smooth belts at the proper tension and use properly balanced blower wheels and other rotating parts, operated at the minimum practical speed. Provide an adequate duct system which promotes smooth air flow at reasonable velocity and is sufficiently rigid in construction so that it does not vibrate unduly. 2. Prevent the transmission of noise and vibration to the bouse structure and to ducts and piping. Use properly loaded isolation mounts for compressors, even when on concrete floors, and provide vibration isolators on blowers and refrigerant lines and vibration loops in the refrigerant system. Install flexible connections between the cooling unit and the ductwork. Double stud walls with sound isolation blanket between the two free standing walls have been successfully used between utility rooms and bedrooms to provide improved sound isolation. 3. Control' airborne noise with sound-absorbing material or other acoustical treatment. Install sound-absorbing material within ductwork and, where practicable, use one or more elbows between the equipment and the registers or grilles. In locating components outdoors, careful consideration should be given so that the sound level and air discharges trill'not be come an aggravation to neighboring property owners. Compo nents should be located far enough away from the structure so that sound reverberations will not occur. Particular care is re quired when the adjoining property does not consist of an airconditioned structure and where the owner depends on open windows to provide an acceptable level of'comfort. Hot air should not be discharged into neighboring property, shrubs or open windows. AIR DISTRIBUTION METHODS Systems should be designed and installed in accordance with authoritative information such as given in the design manuals of the National Warm Air Heating and Air Conditioning Association.1 2The sizes of the ducts of year-round air-condi tioning systems are usually larger than those of equivalent winter heating systems since air is supplied for cooling pur poses between 15 and 25 F deg below room temperature. Several manufacturers have developed reliable methods of duct design. Such methods should be used when recom mended, since they take into account the specific air-flow and static pressure characteristics of the systems to which they apply. They should, however, be applied with caution to sys tems and equipment other than those for which they were developed. Under any circumstance, careful consideration must be given to the type of supply outlets selected and their locations in order to effect satisfactory room air dis tribution. For new construction, it is customary to give careful con sideration to combining the heating and cooling functions in the same air circulating system. This works out very well for the usual single story and ranch type homes. The usual prac tice is to estimate both the cooling and heating requirements and to supply cooling and heating elements of adequate size, with an air distribution system designed for the larger air quantity required. In the case of one or two-story homes, the heating and cooling loads will not be proportionately the same for all rooms. Generally, the design concept is to make separate pre liminary calculations for the heating and cooling- air distribu tion requirements and then to make the necessary adjust ments to achieve a compromise solution. For example, it may be necessary to have additional cooling supply outlets in one or more of the upstairs bedrooms or in other rooms which have large glass areas facing south or west, or which have unusually high internal beat loads such as in kitchens. It is important to consider certain technical and economic aspects of residential air conditioning. An elaborately zoned air distribution system rarely can be justified economically. However, since.the diurnal load variation is primarily in fluenced by external weather effects, the cooling load in each room changes from hour to hour during the operation of the system. In order to obtain ultimate conditions of.comfort, these factors make it almost mandatory that the.owner per form seasonal or even more frequent adjustments to the air distribution system. Such adjustments may involve the open ing of additional outlets in the upstairs bedrooms during the cooling cycle and the throttling or doting of heating outlets in some rooms during the winter. On deluxe applications some additional refinements may be economically justified. One such refinement could be the installation of a heating and cooling system based primarily on beating requirements, with additional independent cooling ducts or self-contained units Residential Summer Air Conditioning 673 serving some or all of the second floor rooms. Another solu tion would be the inclusion of zone controls for rooms which have unusual load variations or high internal heat gains dur ing the summer cooling season. When considering zoning, how ever, careful consideration must be given to the operating characteristics of both the heating and cooling equipment. For example, a reduction in the air quantity to one or more rooms may result in reducing the air flow across the evapo rator to such a degree that it may freeze. A reduced air vol ume to a given room could reduce the velocity of air from the supply outlet ranging an unsatisfactory air distribution pat tern in the room. In split level houses, both the heating and cooling processes are complicated by the internal gravity circulation that takes place through the large openings between the various levels. In many split level houses, the upper bedrooms tend to over heat in the winter. Double sets of outlets, both at the upper levels and the lower levels, have been used with some success with the owner opening some and doting others from season to season. National Warm Air Heating and Air Conditioning Manual 9 recommends operation with returns located high in each room while keeping doors dosed. In existing homes, the amount of cooling that can be added is limited by the air handling capacity of the existing furnace and duct system. While this is frequently satisfactory for normal occupancy, it is usually less than the owner would like to have in the higher cost home where large party enter tainment could be a usual occurrence. In all cases where cool ing is added to existing homes, the supply-air outlets must be checked for acceptable cooling air distribution. If the outr lets are not already arranged for upward distribution of air, new upward deflection grilles should be installed if excessive cooling stratification is to be avoided. The importance of ar ranging for an upward throw at an effective velocity cannot be overstressed in converting existing heating systems with floor or baseboard outlets to do a combined heating and-cool ing function. It is not necessary to change the deflection from summer to winter for registers located at the perimeter of a a residence.' Registers located at the inside walls of rooms have also been found to operate satisfactorily without change of deflection from summer to winter. In some cases, the owners of residential air conditioning systems prefer the minimum of perceptible air motion. Ceiling outlets having multi-directional vanes, and perimeter base board outlets having multiple slots or orifices, have been found effective in meeting these requirements. CONTROLS Control devices and systems and their application in resi dential air conditioning are discussed in Chapter 43, Auto matic Control. OPERATING COSTS The operating cost of residential cooling equipment during a particular summer depends on variables such as the amounts of sunshine and run, the number of abnormally hot or cool days, the efficiency of the equipment, and the local power rate. It is also influenced by human factors such as operation of equipment only during the hottest weather, opening windows at night,* and difference in preferred indoor temperatures' Nevertheless, it is important that landing agencies and prospective buyers of equipment be given a rea sonably accurate estimate of the operating cost during nor mal summer weather and under- usual operating conditions. Adjustments can then be made for any special conditions Table 1 .... Approximate kw Input per 12,000 Btuh Cooling Capacity Typs of Hgci fiajoefion* Wafer Cooled Condenser Item of Power Load city Water Atmos pheric Cooling Tower Mechani Aircal Draft Cooled Cootfng Con- Tower Refrigeration Compressor........ Blower for Air Conditioner. .. Blower for Rejection Air......... Pump, Cooling Water............... 1.00 0.10 -- -- 1.00 0.10 -- 0.15 1.00 0.10 0.15 0.15 1.15 0.10 0.15 -- Total kw per 12,000 Btuh 1.10 1.25 1.40 1.40 * Other bent rejection neeas include well*, spny ponds, evnpotntire con- vnter tf*'* la tt* ground, wiser is lir, etc. anticipated. The approximate electrical power inputs for the various motorized components in mechanical cycle air condi tioners are shown in Table 1. Power cost per hour can be estimated by multiplying the estimated power per ton, the cooling capacity in tons and the C06t per kilowatt-hour. Thus the estimated cost per hour for a 3-ton air conditioner with an air-cooled condenser will be 1.4 kw X 3 tons X the power rate. It is essential to use the cor rect step of the utility residential rate structure to get a good estimate. The basis of the method used* requires the use of a table of the estimated annual hours of operation for properly sized equipment in typical cities. See Table 2. The values in Table 2 have been substantiated by utility records of actual performance in several major cities when the average indoor temperature is maintained at 80 F. Low indoor temperatures increase operating cost as do weather conditions above normal. Water usage is another important factor with water-cooled equipment. Various manufacturers have published water us age data for their equipment at varying summer water tem peratures. Representative water consumption values are given in Table 3. For a given application the power rate and water rate may be obtained from the local utilities. Since the average power requirement depends on the particular equipment used and the condensing' method, values obtained from the manu facturer should be used in preference to those in Table 1. If the evaporator fan cycles with the compressor, the power requirement as found from Table 1 also represents the total power requirement for air-cooled condenser applications. For Table 2 .... Estimated Annual Hours of Operation for Properly Sized Equi >ment in Typical Cities x' during Norma Cooling Season City Hoar* City Hoon 750 400 450 Fresno, Calif................. 900 Waahmgton, D. C......... 800