Page 87 - Zero Net Energy Case Study Buildings-Volume 1

Energy Use – Actual Measurement and Comparison to Modeling Results
A summary of the energy use measurements of the building, metered and recorded in 2010- 2011, is shown on the facing page. This measurement data indicates significant differences between the modeling and actual building use in some categories of energy use. There was also missing data for the building plug loads because of inadequate programming of the BMS to record and communicate that important measurement information. The latter appears to be a persistent issue with post-occupancy monitoring of low-energy buildings, as noted in the prior case studies in this monograph, and needs attention by both design teams and building owners.
The heating energy used was much lower in this first year than predicted by the energy model, which may be explained by the very clear skies during the heating season of the year of mea- surement and the passive heating effect of the predominantly southern exposure of a long, thin building. Domestic hot water use was also significantly less than that predicted by the model, which may simply be the result of unexpected use patterns by the occupants at this facility.
On the other hand, the lighting energy used was nearly double that assumed in the model, no doubt due to unexpected use patterns. The higher lighting energy use may also partially explain the reduced heating load since this extra energy from the warm lamps would ultimately reside in the space as heat. The cooling energy used, almost entirely in the laboratory wing of the build- ing, was 60% higher than modeled; again, the likely cause is simply use patterns and hours of operation different from the modeling assumptions.
Ideally, these differences between measured and modeled energy use would be reported to the facility manager, commissioning agent and design engineers so that appropriate actions could be taken, including involvement of the building users. The building designers and managers for the Watsonville WRC are beginning to address this issue.
Because of this problem of the missing plug load data, the modeled total for plug load is used in place of the absent measured total for plug load for the purposes of presenting the measured results in all other categories of energy use. Therefore, the quantities shown in the charts on the facing page are actual measured data for the first year of occupancy, with the exception of the plug load, for which the modeling assumption is used. With this one caveat, the building’s actual energy use in the first year of post-occucpancy measurements totaled 241 MWhr and an EUI = 51.4 kBtu/sq. ft. per year.
Zero Net Energy Case Study Buildings: Volume 1
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WATSONVILLE WATER RESOURCES CENTER
CASE STUDY NO. 4