The ANSI/ASHRAE/IES Standard 100-2015 Energy Efficiency in Existing Buildings provides comprehensive procedures to improve the energy efficiency of buildings. Although Standard 100 provides direction for residential and non-residential buildings, the purpose of this article is to describe the application of Standard 100 to residential buildings.
The Energy-Use Intensity (EUI) of a building is calculated as the annual net energy use divided by the gross floor area (expressed either as MJ/m2 or BTU/ft2). When calculating the EUI, building energy-use data for twelve consecutive months within the last 18 months must be considered. The energy targets for a building depends on the climate zone in which the building is located. Table 1 shows the climate zone number for major cities in Canada together with the Energy Targets for single-family detached residential buildings. Buildings that meet their energy targets are not required to perform an energy audit.
Table 1 - Energy Target for Single-Family Detached Homes in Major Canadian Cities
Performing an Energy Audit
In accordance with Standard 100, buildings that do not meet their energy targets are required to undergo an energy audit. As part of the audit, the historical energy use is allocated to end uses such as HVAC, lighting, domestic hot water, and electrical plug loads. Once the energy audit has been completed, the energy efficiency measures (EEMs) to be implemented are selected and the estimated energy savings for the EEMs is calculated. An adjusted EUI is calculated that considers what the EUI would be with the EEMs implemented. Once the adjusted EUI meets the energy target, then the EEMs are implemented.
The energy savings is expressed in both cost units as well as energy units. The cost of implementing each EEM is included together with the simple payback for each EEM or the recommended package of EEMs. Once the EEMs have been implemented, the building's EUI is monitored until twelve consecutive months of data demonstrate that the energy target has been achieved.
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