Shipping Delivery Order tracking Returns. Asnrae standard is also available to be included in Standards Subscriptions. Applies to electrically driven mechanical-compression unitary air conditioners and heat pumps consisting ashrse one or more assemblies that include an indoor air coil sa compressor sand an outdoor coil s. Test conditions and procedures in general Your Alert Profile lists the documents that will be monitored.
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One of the methods for non residential buildings discussed in Chapter 18 may be used to calculate the block load. These values can provide guidance for hand estimates, and illustrate the need for achieving low duct leakage. To the extent conditions differ from those shown, specific calculations should be made using a method cited previously.
Note also that Table 6 cooling factors represent sensible gain only; duct leakage also introduces significant latent gain. Opaque Surfaces Heat gain through walls, floors, ceilings, and doors is caused by 1 the air temperature difference across such surfaces and 2 solar gains incident on the surfaces. The heat capacity of typical construction moderates and delays building heat gain.
This effect is modeled in detail in the computerized RHB method, resulting in accurate simultaneous load estimates. The latent portion of the cooling load is evaluated separately. Although the entire structure may be considered a single zone, equipment selection and system design should be based on room-by-room calculations. For proper design of the distribution system, the conditioned airflow required by each room must be known. Peak Load Computation To select a properly sized cooling unit, the peak or maximum load block load for each zone must be computed.
The block load for a single-family detached house with one central system is the sum of all the room loads. If the house has a separate system for each zone, each zone block load is required.
When a house is zoned with one central cooling system, the system size is based on the entire house block load, whereas zone components, such as distribution ducts, are sized using zone block loads. In multifamily structures, each living unit has a zone load that equals the sum of the room loads. OFt values less than 1 capture the buffering effect of attics and crawlspaces, OF b represents incident solar gain, and OFr captures heat storage effects by reducing the effective tem perature difference.
As shown in Table 7, roof solar absorptance has a significant effect on ceiling cooling load contribution. Table 8 shows typical values for solar absorptance of residential roofing materials. Note that low absorptance cannot be achieved with asphalt shingles. Although solar gain occurs throughout the day, RP regression studies Barnaby et al. Steeper, nonvertical slopes are not supported by the RLF method.
Exterior Attachments. Common window coverings can significantly reduce fenestration solar gain. Table 11 shows transmission values for typical attachments. Permanent Shading. The shaded fraction F shd can be taken as 1 for any fenestration shaded by adjacent structures during peak Therefore, in all but special circumstances, interior shading should be assumed when calculating cooling loads.
Residential values from that chapter are consolidated in Table In some cases, it is reasonable to assume that a shade is partially open. For example, drapes are often partially open to admit daylight. Table 12 shows SLFs for July 21 averaged over the hours of greatest solar intensity on each exposure.
More complex shading situations should be analyzed with the RHB method. Fenestration Solar Load Factors. Fenestration solar load factors FF s depend on fenestration exposure and are found in Table The values represent the fraction of transmitted solar gain that contributes to peak cooling load.
It is thus understandable that morning east values are lower than afternoon west values. Higher values are included for multifamily buildings with limited exposure.
Interior Shading. Interior shading significantly reduces solar gain and is ubiquitous in residential buildings. Predicted gains are typical for U.
Further allowances should be considered when unusual lighting intensities or other equipment are in continuous use during peak cooling hours. In critical situations where intermittent high occupant density or other internal gains are expected, a parallel cooling system should be considered.
For room-by-room calculations, qig,s should be evaluated for the entire conditioned area, and allocated to kitchen and living spaces. These may be estimated and included. Lstiburek and Carmody provide data for household moisture sources; however, again note that Equation 31 adequately accounts for normal gains. Because air conditioning systems are usually controlled by a thermostat, latent cooling is a side effect of equipment operation. During periods of significant latent gain but mild temperatures, there is little cooling operation, resulting in unacceptable indoor humidity.
Summary of RLF Cooling Load Equations Table 15 contains a brief list o f equations used in the cooling load calculation procedure described in this chapter. HEATING LOAD Calculating a residential heating load involves estimating the maximum heat loss of each room or space to be heated and the simultaneous maximum block heat loss for the building, while maintaining a selected indoor air temperature during periods of design outdoor weather conditions.
As discussed in the section on Calculation Approach, heating calculations use conservative assumptions, ignoring solar and internal gains, and building heat storage. This leaves a simple steady-state heat loss calculation, with the only significant difficulty being surfaces adjacent to grade. The effect of attic radiant barriers can be neglected.
In cases where the ceiling or wall is not well insulated, the adjacent buffer space procedure see the section on Surfaces Adjacent to Buffer Space can be used.
Below-Grade and On-Grade Surfaces The Heating Load Calculations section of Chapter 18 includes simplified procedures for estimating heat loss through below-grade walls and below- and on-grade floors. Those procedures are applicable to residential buildings. In more detailed work, Bahnfleth and Pedersen show a significant effect of the area-to-perimeter ratio.
Generally, simple approximations are sufficient except where the partition surface is poorly insulated. Crawlspaces and basements are cases where the partition the house floor is often poorly insulated; they also involve heat transfer to the ground. Most codes require crawlspaces to be adequately vented year round. However, work highlighting problems with venting crawlspaces DeWitt has led to application of sealed crawlspaces with insulated perimeter walls. Equation 5 may be applied to basements and crawlspace by including appropriate ground-related terms in the heat balance formulation.
Losses from piping or ducting should be included as additional buffer space heat gain. Determining the ventilation or infiltration rate for crawlspaces and basements is difficult. Latta and Boileau estimated the air exchange rate for an uninsulated basement at 0. Field measurements of eight ventilated crawlspaces summarized in Palmiter and Francisco yielded a median flow rate of 4.
Clearly, crawlspace infiltration rates vary widely, depending on vent configuration and operation. The energy required to raise the temperature of outdoor infiltrating air to indoor air temperature is the sensible component; energy associated with net loss of moisture from the space is the latent component. Determining the volumetric flow Q of outdoor air entering the building is discussed in the Common Data and Procedures section and in Chapter Humidification In many climates, humidification is required to maintain comfortable indoor relative humidity under heating conditions.
The latent ventilation and infiltration load calculated, assuming desired indoor humidity conditions, equals the sensible heat needed to evaporate water at a rate sufficient to balance moisture losses from air leakage. Self-contained humidifiers provide this heat from internal sources.
If the heat of evaporation is taken from occupied space or the distribution system, the heating capacity should be increased accordingly. Because the design outdoor temperature is generally much lower than typical winter temperatures, under most conditions excess heating capacity is available for pickup. Therefore, many engineers make no pickup allowance except for demanding situations. If pickup capacity is justified, the following guidance can be used to estimate the requirement.
Relatively little rigorous information on pickup load exists. Building simulation programs can predict recovery times and required equipment capacities, but a detailed simulation study is rarely practical. Armstrong et al. Nelson and MacArthur studied the relationship between thermostat setback, furnace capacity, and recovery time.
Hedrick et al. The designer should be aware that there are tradeoffs between energy savings from thermostat setback and energy penalties incurred by oversizing equipment. The preceding guidance applies to residential buildings with fuel-fired furnaces. Additional considerations may be important for other types of heating systems. For air-source heat pumps with electric resistance auxiliary heat, thermostat setback may be undesirable Bullock Thermostats with optimum-start algorithms, designed to allow both energy savings and timely recovery to the daytime set point, are becoming routinely available and should be considered in all cases.
Summary of Heating Load Procedures Table 16 lists equations used in the heating load calculation procedures described in this chapter. Construction characteristics are documented in Table Using the RLF method, find the block whole-house design cooling and heating loads.
Solution Design Conditions. Table 18 summarizes design conditions. Typical indoor conditions are assumed. Outdoor conditions are determined from Chapter Component Quantities. Areas and lengths required for load calculations are derived from plan dimensions Figure 1. Table 19 summarizes these quantities. Opaque Surface Factors. Heating and cooling factors are derived for each component condition. Table 20 shows the resulting factors and their sources.
Window Factors. Deriving cooling factors for windows requires identifying all unique glazing configurations in the house. Equation 25 input items indicate that the variations for this case are exposure, window height with overhang shading , and frame type which determines U-factor, SHGC, and the presence of insect screen.
CF derivation for all configurations is summarized in Table Overhang depth Doh is 2 ft and the window-overhang distance X oh is 0 ft. Allow for typical interior shading, half closed. Envelope Loads. Given the load factors and component quantities, heating and cooling loads are calculated for each envelope element, as shown in Table Infiltration and Ventilation.
From Table 3, Aul for this house is 0. Using Table 5, estimate heating and cooling IDF to be 1. Table 23 summarizes the sensible load components. Distribution loss factors F dl are estimated from Table 6 at 0.
Latent Load. Load calculation for residential winter and summer air conditioning—Manual J , 7th ed. Manual J residential load calculations, 8th ed. Armstrong, P. Hancock, and J. Commercial building temperature recovery—Part 1: Design procedure based on a step response model RP Commercial building temperature recovery—Part 2: Experiments to verify step response model RP Thermal environmental conditions for human occupancy.
Ventilation and acceptable indoor air quality in low-rise residential buildings. Air leakage performance of detached single-family residential buildings. Method of test for determining the design and seasonal efficiencies of residential thermal distribution systems. Standard terminology of building constructions. Standard Ea e1. Bahnfleth, W.
Pedersen A three-dimensional numerical study of slab-on-grade heat transfer. Development of the residential load factor method for heating and cooling load calculat ions. Barnaby, C. Spitler, and D. The residential heat balance method for heating and cooling load calculations RP Beausoleil-Morrison, I. Building America. Building America research benchmark definition v. Bullock, C. Energy savings through thermostat setback with residential heat pumps.
Determining the required capacity of residential space heating and cooling appliances. Canadian Standards Association, Toronto. DeWitt, C. Crawlspace myths. Franciso, P. Ecotope, Inc. Hedrick, R. Witte, N. Leslie, and W. Furnace sizing criteria for energy-efficient setback strategies. Houghten, F. Taimuty, C. Gutberlet, and C. Heat loss through basement walls and floors. Residential heat loss and gain calculations: Student reference guide. Mississauga, ON.
James, P. Cummings, J. Sonne, R. Vieira, and J. The effect of residential equipment capacity on energy use, demand, and runtime. Koenig, K. Gas furnace sizing requirements for residential heating using thermostat night setback. Krarti, M. Choi Simplified method for foundation heat loss calculation. Latta, J. Heat losses from house basements.
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