Document O33RogxXLRVYxkmkEMJBR99b1

190 CHAPTER 14 1962 Guide And Data Boot equipment, thus reducing the labor required. Hie unitary type installation generally is less expensive, and maintenance is made easier and taster. Responsibility for the proper operation of the system is more easily fixed because the sys tem has been designed and assembled by the manufacturer with the components properly seed and balanced (see Chapter 35 of the 1961 Guide And Data Book). design considerations - The basic consideration in designing an air conditioning system for a supermarket is to obtain an economical, efficient system with as much amplification as practicable. Load Calculations Heating and cooling bads usually should be calculated using the methods given in Chapters 25 and 26 of the 1961 Guide And Data Boos. Data for calculating the loads from people, lights, motors, and special heat-producing equipment should be obtained from the store owner or manager. A minimum quantity of outdoor air (often established by local building code) is introduced through the air-conditioning unit, because the infiltration through tire entrance and delivery doors is often high enough to prevent pressurization of the building. Many supermarkets are unite of a large chain owned or operated by one company. Standardised construction, layout and equipment used in designing many similar stores ampli fies the load calculations. One large chain has developed load charts which show the heating and cooling requirements for any size of building (of their standard construction) in various areas of the coun try.* From experience, load factors have been determined based on the area of the entire store, includingand stock areas. The average cooling load for a store in the central part of the country would be 1 ton per 350 sq ft. In the southern sections, the area per ton would be 300, while in the northern section the value rises to 400 sq ft per ton. If the store is located in a shopping center with other types of stores adjoin ing, the area per ton requirements for cooling may be in creased. The heating load would also be decreased. Air Distribution With air-conditioning equipment located outside the sales area, a duct system is used to distribute the air to the sales space. If the units are located in back rooms, ducts are usually run along the ride walls to the frontof the store. No return air ducts are used, and air returns to the unit through the back room, thus cooling that area. If the units are on the roof, the duct system includes supply and return ducts, often using combination supply and return type diffusers installed in the ceiling over the sales, stock, and back room areas to be conditioned. Hie front section of a supermarket generally has the greatest load, due to large glare area, entrances, and customer concentration at the checkout stations. Many designers over come this concentrated load by discharging at least 50 percent of the total air supply into the front third of the sales area. Heating EQUIPMENT In most modern supermarkets the wrrw air handling equip ment and distribution system is used for both cooling and heating. Boilers may be used to supply hot water or steam to coils in the air handling unit, or direct-fired equipment such as duct heaters, blower-type unit heaters, or horizontal furnaces may be used. The direct-fired equipment is more commonly used bec&u^ of lower cost and reduced maintenance requirements. The entrance area of a supermarket is the most difficult section to heat. Many stores in the northern part of the United States are built with vestibules, which are provided with separate heating equipment to temper the cold air entering from outdoors. Auxiliary heat may also be provided at the checkout area which is usually, close to the front entrance. Other methods bring used to. heat entrance areas include: (1) air entrances, (2) infra-red radiant beating, using gas. firedorelectric heatere, and (3) the use of waste heat from the refrigeration condensers. Air-Cooled Condensers In recent years the use of air-cooled condensers has in. creased greatly. Most installations are made on the roof of the supermarket, although local codes or architectural design may prohibit such locations. If air-cooled condensers are located at ground level outside the store, protection must be provided against vandalism, as well as truck and customs traffic. Cooling Towers If water-cooled condensers are used on the air-conditioning equipment, and a cooling tower is required, provirion should be made to prevent freezing during winter operation. See Chapter 37 in the 1961 Guide And Data Book. Controls The control system should be as simple as practicable, so that store personnel are required only to change the position of a selector switch in order to start, stop, or change the sys tem from heating to cooling, or cooling to heating. A typical control system used byone large chain ts given in Reference 3. PART IV: DEPARTMENT STORES Department stores vary in size, type, and area of location so that the design of an ain-conditioning system requires &a individual solution for each store. However, the individual solution can be simplified when the designer is fully aware of the various factors to be considered, and their proper impor tance in the final analysis of store requirements. Special con sideration must be given to economic principles. Year-round air conditioning provides filtered air to the store, reducing stock spoilage and building maintenance costs. An ample minimum quantity of outdoor air reduces or eliminates odor problems. Essential features of the quality system include: (I) an automatic control system, properly designed to compensate for load fluctuations, (2) zoned air distribution to maintain uniform conditions under shifting loads, and (3) use of outdoor air for cooling during inter mediate seasons and peak season (Christmas and Easter) sales periods. Itis also desirable to adjust indoor temperatures for variations in outdoor temperatures. While the control of humidity to close tolerances is not necessary, the properly designed system should operate to maintain relative humidity of not over 50 percent with a corresponding dry-bulb tem perature of 78 F. The low humidity eliminates musty odors and retards perspiration, particularly in fitting rooms, which should receive special consideration. DESIGN CONSIDERATIONS Before making load calculations, the designer should exam ine the store arrangement to determine the various items which will affect the load, as well as the system design. Store Air Conditioning por briefing buildings, a survey can be made of actual con junction, floor arrangement and load sources. For new build- examination of the drawings and discuaion with the jrchitect or owner, or both, will be required. ftte survey should include consideration of location for jlfivators, escalators, service areas, fitting rooms, specialty &>ps, and other areas or enclosures which may require special tRfttment Location of columns and ceiling beams should be poted with regard to duct arrangement and possible location of equipment. If central station or unitary equipment a to be jocated on the roof or suspended from ceilings, the resulting sectoral or architectural problems should be considered. Service areas should be checked for possible location of duct tad pipe risers. Larger stores usually have beauty parlors, restaurants, counters, and auditoriums. These special areas may operate during all the time the store is open. Where the load fom one of these areas is small in proportion to the total, this load may be included in the portion of the air-condition ing system serving the same floor. If, for any reason, present or future operation of the plant may be compromised by such a method, a separate air-conditioning system could serve this space, with refrigeration supplied by the main plant or a Separate system. A separate air distribution system should be provided for the beauty parlor, due to the concen trated load in this area. The restaurant, because of the required service facilities, is seldom relocated to another part of the store. However, it is generally used only during the noon hours. For these reasons, and also for control of odors, a separate air handling system and sometimes a separate refrigeration system should be considered. In some dining areas, it is advisable to provide a forced exhaust equivalent to the supply in the restaurantarea, because of the possibility of odor leakage. An important item which should not be overlooked daring the building survey is the determination of future plans for the store by direct consultation with the architect and owner. This factor can have a great effect on the final decision of the type of air-conditioning system to be employed. LOAD DETERMINATION The load calculations should be made in accordance with the methods described in Chapters 25 and 26 of the 1961 Guide And Data Book. Indoor Conditions Because the occupancy (except for store personnel) is transient, indoor conditions are commonly established not to exceed 78 F dry-bulb and 50 percent relative humidity at maximum outdoor summer design conditions, and .73 F drybuib at minimum outdoor winter conditions. Winter humidifi cation is seldom employed in store air conditioning, due to the problem-of moisture condensation on windows. Indoor sum mer conditions of 78 F dry-bulb and not over 50 percent relative humidity are used for high quality installations. Internal Loads Estimates should be obtained from the store management of the number of customers and store personnel normally found on each floor being conditioned. Particular attention dradd be paid to specialty departments or other areas which Ray have greater than average concentrations of occupants. electric lights should be checked for wattage and type (fluorescent, cold cathode or incandescent). Table 2 gives approximate values for lighting in various areas, while Table 3 Erees approximate occupancies. ^ere the collected data shows a wide divergence from the 191 Table 2 .... Approximate lighting Loads for Department Stores Upper Floors, Women's Wear..................................... Upper Floors, House Furnishings.............................. WottiSv s** 3-5 4-7 3-5 Table 3 .... Approximate Occupancy for Department Stores Aren Sqft par Penan 15 20-40 20-25 25-50 50-75 100 or more approximate check values of Tables 2 and 3, the differences should be reconciled with the store management to insure complete understanding between designer and owner. Other sources of load, such as motors, beauty parlor and restaurant equipment* and any special display or merchan dising equipment, should be determined. Ventilation In general, the use of artificial light is increasing, with the result that the internal sensible load is substantially inde pendent of outdoor temperature. The minimum requirement is one air change per hour to overcome infiltration by pro ducing a slight positive pressure within the structure. The minimum ventilation standard is 5 cfm per person, but 7J$ cfm per person is preferred. However, the air change rate must not be less than one per hour. These standards have been found generally acceptable and adequate for removing odora and keeping the building atmosphere fresh. However, local ventilation ordinances may require greater quantities of outdoor air. Faint shops, alteration rooms, rest rooms, eating places and locker rooms should be provided with positive exhaust ventilation, and their requirements must be checked *g*tngfr minimum outdoorsir. SYSTEM DESIGN Air-conditioning systems are generally of the unitary, or central station type. The unitary systems may range from completely self-contained equipment to factory-assembled air-conditioning units with separate air-cooled condensing units. For further information on unitary equipment, see Chapter 57 of the 1961 Guide And Data Book. Central sta tion systems are discussed in Chapter 1 of this volume. A central station, system may be provided for a particular store area, such as an entire floor, or it may provide condi tioned air to booster units-which are field-assembled units containing a fan and drive, dehumidified air and bypass damp ers, filters, and sometimes a heating coil. Heat pumps, either water- or air-source, are also used in department store air conditioning, where favorable electric rates are available, and where a suitable location can be found for the equipment. The selection of the system type should be based on an