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Building America Research - page 53 / 66





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Operating Conditions

The following operating conditions and other assumptions shall apply to both the Prototype house and the Benchmark. The operating conditions are based on the cumulative experience of the authors through their work on Building America, HERS, Codes and Standards, and other residential energy efficiency programs.

Thermostat set points based on the optimum seasonal temperature for human comfort as defined in ASHRAE Standard 55-1992 (ASHRAE 1992).

  • Set point for cooling: 76°F with no setup period

  • Set point for heating: 71°F with no setback period

  • Set point for dehumidification (if controlled): 60% relative humidity

  • The natural ventilation schedule shall be set to reflect windows being opened occasionally. In situations where it is a Monday, Wednesday, or Friday and there is a cooling load, windows will be opened if the cooling capacity of outdoor air flow can maintain the cooling set point and the outdoor humidity ratio is below the indoor humidity ratio. The natural ventilation rate shall be calculated using the Sherman- Grimsrud model. Twenty percent of the maximum openable area for windows on each facade and on each floor shall be open. Windows are assumed to be closed once the indoor temperature drops below 73°F or if the air change rate exceeds 20 air changes per hour. If there are local circumstances that would tend to discourage window operation (pollution, high humidity, security, community standards, etc.), then it is acceptable to use a more appropriate schedule, as long as the same natural ventilation schedule is applied to both the Benchmark and the Prototype. Mechanical ventilation fans shall be turned off when natural ventilation is being used.

  • Interior shading multiplier = 0.7 when the cooling system is operating, and 0.85 at all other times.

  • Internal heat gains from lighting, hot water fixtures and distribution systems, appliances, and MELs were discussed in previous sections. These loads are not necessarily the same for the Prototype and the Benchmark; therefore, they are not considered operating conditions for the purposes of Building America performance analysis.

  • Annual cycles for clothes washers, dryers, and dishwashers calculated using the Building America Analysis Spreadsheet posted on the Building America Web site.

The occupancy schedule is defined with the same level of detail as other internal load profiles. For typical Building America houses, the number of occupants for single-family and multi- family dwellings shall be estimated based on the number of bedrooms using Equations 20 and 21, respectively.

Equation 20:

Number of occupants = 0.59 × Nbr + 0.87


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