UA Analysis

Unlike most modeling tools, the UA model, an excel spreadsheet-based tool, was very easy for all members of the team to use. The tool helped the team prioritize energy retrofit strategies.

Using the existing conditions as a starting point, several parametric analyses were completed to examine the impacts of different enclosure strategies. The tool helped answer questions. For example, does it make more sense to use more insulation in the walls or use higher R-value windows?

The UA tool incorporates current enclosure and ventilation loads into its calculations and then derives energy savings from various energy efficiency measures. It also includes a feature to evaluate savings per dollar spent on a given measure, to ensure that the most cost effective measures are followed.

More details….

Gas-Related Savings Calculations Building Science Corporation conducted an analysis of the current enclosure conductance and infiltration loads on the buildings at Castle Square.  In addition to the enclosure loads, ventilation was also included due to it being a significant portion of the space conditioning load on the buildings.  Using the existing conditions as a starting point, several parametric analyses were completed to examine the impacts of different enclosure and ventilation strategies.

In this analysis, the area of enclosure components and estimated conductance of the components were used to estimate the heating load under winter design heating conditions for the midrise building.  The cooling load analysis added peak solar radiation and window solar heat gain coefficients to these factors to project the cooling load under summer design conditions.

Elton + Hampton Architects supplied building and component area take-offs as well as assembly descriptions for use in this analysis.  Existing building conductance performance was based on reported construction assemblies and estimated U-Values from ASHRAE Fundamentals 2005 Chapter 25 Table 1 and Table 4.  Windows currently installed in the building are aluminum framed double glazed slider type windows.  The assumed U-Values and Solar Heat Gain Coefficients (SHGC) are based off ASHRAE Fundamentals 2005 Chapter 31 Table 4 and Table 13.  Air infiltration estimates used in the analysis are derived from air infiltration testing performed by BSC on April 16, and April 17, 2009.  With contribution from Petersen Engineering, once the heating load and hot water calculations were performed to estimate annual energy use for the existing and proposed building conditions, the calculated equipment-based efficiency percentages was then applied to gas consumption data to provide an estimate for predicted gas savings.

Electrical-Related Savings Calculations Refrigerator savings were calculated utilizing the Energy Star program’s refrigerator savings calculator, updated with actual product specifications. Cooling-attributed electrical savings were calculated by Petersen Engineering utilizing cooling loads derived from the analysis described above, with equipment electrical efficiencies derived by comparing the average Castle Square air conditioner today to the specified air conditioner. Run times were based on Energy Star recommendations for Massachusetts.