A review of data from the Energy Information Administration (DOE 2001) shows that there is rarely any site electricity generation in a 1990s vintage house. This is a reflection of the low market penetration of site electricity systems. Therefore, all electricity is purchased from the local utility in the Benchmark. As costs for photovoltaic systems and other site electricity systems continue to decline, they are expected to begin to make a significant contribution toward meeting residential energy needs by the year 2020. Therefore, site electricity generation must be included in the whole-house energy performance analysis of the Prototype.
Modeling the Prototype
The Prototype is modeled either as-designed or as-built, depending on the status of the project. All parameters for the Prototype model shall be based on final design specifications or measured data, with the following exceptions and clarifications:
Any house characteristics that are unknown and are not part of the package of energy efficiency improvements shall be the same as the Benchmark.
The ELA for the Prototype shall be calculated based on blower door testing conducted in accordance with ASTM E779. Guarded blower door tests shall be conducted in attached and multi-family housing to disaggregate leakage to the outside from leakage to adjacent units (see SWA 1995 for guidance on this technique). If the whole-house simulation tool cannot calculate hourly infiltration based on effective leakage area, an annual average natural infiltration rate may be used based on the guidelines in ASHRAE Standard 119 (ASHRAE 1988), Section 5, and ASHRAE Standard 136 (ASHRAE 1993), Section 4. It is recommended that blower door measurements be supplemented with tracer gas testing when possible.
If the Prototype does not have a cooling system, but there is a non-zero cooling load, then the Prototype shall be modeled assuming a standard 10 SEER air conditioner connected to the heating ducts. If the Prototype does not have a duct system for heating, the air conditioner shall be modeled as a ductless 10 SEER room air conditioner.
Mechanical ventilation shall be combined with natural infiltration in accordance with Section 4.4 of ASHRAE Standard 136 to determine an approximate combined infiltration rate.
The openable window area shall be 33% unless specific provisions have been taken to increase this percentage, for example by installing hinged casement windows.
If the actual EER for the Prototype is not readily available, Equation 16 may be used to make an approximate conversion from SEER to EER (Wassmer 2003):
EER = –0.02 × SEER2 + 1.12 × SEER
If the Prototype has a hot water distribution system different from the Benchmark (see Table 13), the equations in Table 18 of the 2009 Benchmark Definition (Hendron 2008) shall be used to determine the change in daily hot water volume, the internal heat gain, the change in recovery load on the water heater, and any special pump energy. These calculations are automated in the BA Analysis Spreadsheet. For any distribution system type not listed, other than centralized DHW in multi-family housing, the Benchmark distribution system shall be applied to both houses, unless the analyst has performed a detailed energy analysis of the distribution system