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29.8 2001 ASHRAE Fundamentals Handbook (SI) fan-cooled (TEFC) motors are slightly more efficient. For speeds The radiant heat gain from hooded cooking equipment can range lower or higher than those listed, efficiencies may be 1 to 3% from 15 to 45% of the actual appliance energy consumption (Talbert lower or higher, depending on the manufacturer. Should actual et al. 1973, Gordon et al. 1994, Smith et al. 1995). This ratio of heat voltages at motors be appreciably higher or lower than rated gain to appliance energy consumption may be expressed as a radia- nameplate voltage, efficiencies in either case will be lower. If tion factor. It is a function of both appliance type and fuel source. electric motor load is an appreciable portion of cooling load, the The radiation factor FR is applied to the average rate of appliance motor efficiency should be obtained from the manufacturer. Also, energy consumption, determined by applying usage factor FU to the depending on design, the maximum efficiency might occur any- nameplate or rated energy input. Marn (1962) found that radiant where between 75 to 110% of full load; if underloaded or over- heat temperature rise can be substantially reduced by shielding the loaded, the efficiency could vary from the manufacturer ’s listing. fronts of cooking appliances. Although this approach may not always be practical in a commercial kitchen, radiant gains can also Overloading or Underloading be reduced by adding side panels or partial enclosures that are inte- Heat output of a motor is generally proportional to the motor grated with the exhaust hood. load, within the overload limits. Because of typically high no-load Heat Gain from Meals. For each meal served, the heat trans- ferred to the dining space is approximately 15 W, of which 75% is motor current, fixed losses, and other reasons, FLM is generally assumed to be unity, and no adjustment should be made for under- sensible and 25% is latent. loading or overloading unless the situation is fixed, can be accu- Heat Gain for Electric and Steam Appliances. The average rately established, and the reduced load efficiency data can be rate of appliance energy consumption can be estimated from the obtained from the motor manufacturer. nameplate or rated energy input qinput by applying a duty cycle or usage factor FU. Thus, the sensible heat gain qsensible for generic Radiation and Convection types of electric, steam, and gas appliances installed under a hood can be estimated using one of the following equations: Unless the manufacturer ’s technical literature indicates other- wise, the heat gain normally should be equally divided between radi- qsensible = qinput FUFR (10) ant and convective components for the subsequent cooling load calculations. or q = q F (11) APPLIANCES sensible input L — where FL is defined as the ratio of sensible heat gain to the manu- In a cooling load estimate, heat gain from all appliances elec- ’ trical, gas, or steam —should be taken into account. Because of the facturer s rated energy input. variety of appliances, applications, schedules, use, and installations, Table 4 lists usage factors, radiation factors, and load factors estimates can be very subjective. Often, the only information avail- based on appliance energy consumption rate for typical electrical, able about heat gain from equipment is that on its nameplate. steam, and gas appliances under standby or idle conditions. Unhooded Equipment. For all cooking appliances not installed Cooking Appliances under an exhaust hood or directly vent-connected and located in the conditioned area, the heat gain may be estimated as 50% ( F = 0.50) These appliances include common heat-producing cooking U equipment found in conditioned commercial kitchens. Marn (1962) concluded that appliance surfaces contributed most of the heat to Table 4A Hooded Electric Appliance Usage Factors, commercial kitchens and that when applicances were installed Radiation Factors, and Load Factors under an effective hood, the cooling load was independent of the fuel or energy used for similar equipment performing the same Usage Radiation Load Factor F = F F operations. Factor Factor L U R Appliance F F Elec/Steam Gordon et al. (1994) and Smith et al. (1995) found that gas appli- U R ances may exhibit slightly higher heat gains than their electric coun- Griddle 0.16 0.45 0.07 terparts under wall-canopy hoods operated at typical ventilation Fryer 0.06 0.43 0.03 rates. This is due to the fact that the heat contained in the combus- Convection oven 0.42 0.17 0.07 tion products exhausted from a gas appliance may increase the tem- Charbroiler 0.83 0.29 0.24 peratures of the appliance and surrounding surfaces, as well as the Open-top range without oven 0.34 0.46 0.16 hood above the appliance, more than the heat produced by its elec- Hot-top range tric counterpart. These higher temperature surfaces radiate heat to without oven 0.79 0.47 0.37 the kitchen, adding moderately to the radiant gain directly associ- with oven 0.59 0.48 0.28 ated with the appliance cooking surface. Steam cooker 0.13 0.30 0.04 Marn (1962) confirmed that where the appliances are installed Sources : Alereza and Breen (1984), Fisher (1998). under an effective hood, only radiant gain adds to the cooling load; convected and latent heat from the cooking process and combustion products are exhausted and do not enter the kitchen. Gordon et al. Table 4B Hooded Gas Appliance Usage Factors, (1994) and Smith et al. (1995) substantiated these findings. Radiation Factors, and Load Factors Sensible Heat Gain for Hooded Cooking Appliances. To Usage Factor Radiation Factor Load Factor establish a heat gain value, nameplate energy input ratings may be Appliance FU FR FL = F UFR Gas used with appropriate usage and radiation factors. Where specific Griddle 0.25 0.25 0.06 rating data are not available (nameplate missing, equipment not yet Fryer 0.07 0.35 0.02 purchased, etc.) or as an alternative approach, recommended heat Convection oven 0.42 0.20 0.08 gains listed in Table 5 for a wide variety of commonly encountered Charbroiler 0.62 0.18 0.11 equipment items may be used. In estimating the appliance load, Open-top range probabilities of simultaneous use and operation for different appli- without oven 0.34 0.17 0.06 ances located in the same space must be considered. Sources : Alereza and Breen (1984), Fisher (1998). Nonresidential Cooling and Heating Load Calculation Procedures 29.9 or the rated hourly input, regardless of the type of energy or fuel actual ratio of total heat gain to nameplate ranged from 25% to 50%, used. On average, 34% of the heat may be assumed to be latent and but when all tested equipment is considered, the range is broader. the remaining 66% sensible. Note that cooking appliances venti- Generally, if the nameplate value is the only information known and lated by “ductless ” hoods should be treated as unhooded appliances no actual heat gain data are available for similar equipment, it would from the perspective of estimating heat gain. In other words, all be conservative to use 50% of nameplate as heat gain and more energy consumed by the appliance and all moisture produced by the nearly correct if 25% of nameplate were used. Much better results cooking process is introduced to the kitchen as a sensible or latent can be obtained, however, by considering the heat gain as being pre- cooling load. dictable based on the type of equipment. Recommended Heat Gain Values. As an alternative proce- Office equipment is grouped into categories such as computers, dure, Table 5 lists recommended rates of heat gain from typical monitors, printers, facsimile machines, and copiers, with heat gain commercial cooking appliances. The data in the “with hood ” col- results within each group analyzed to establish patterns. umns assume installation under a properly designed exhaust hood Computers. Based on tests by Hosni et al. (1999) and Wilkins connected to a mechanical fan exhaust system. and McGaffin (1994), nameplate values on computers should be ignored when performing cooling load calculations. Table 8 pre- Hospital and Laboratory Equipment sents typical heat gain values for computers with varying degrees of Hospital and laboratory equipment items are major sources of safety factor. heat gain in conditioned spaces. Care must be taken in evaluating Monitors. Based on monitors tested by Hosni et al. (1999), heat the probability and duration of simultaneous usage when many gain correlates approximately with screen size as components are concentrated in one area, such as a laboratory, an – qmon = 0.2 S 20 (12) operating room, etc. Commonly, heat gain from equipment in a laboratory ranges from 50 to 220 W/m 2 or, in laboratories with where outdoor exposure, as much as four times the heat gain from all qmon = heat gain from monitor, W other sources combined. S = nominal screen size, mm Medical Equipment. It is more difficult to provide generalized Wilkins and McGaffin tested ten monitors (330 to 480 mm), heat gain recommendations for medical equipment than for general finding the average heat gain value to be 60 W. This testing was office equipment because medical equipment is much more varied done in 1992 when DOS was prevalent and the Windows™ operat- in type and in application. Some heat gain testing has been done and ing system was just being introduced. Monitors displaying Win- can be presented, but the equipment included represents only a dows consumed more power than those displaying DOS. Table 8 small sample of the type of equipment that may be encountered. tabulates typical values. The data presented for medical equipment in Table 6 are relevant Laser Printers.

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