Page 68 - Zero Net Energy Case Study Buildings-Volume 3

CASE STUDY NO. 13
LA ESCUELITA EDUCATION CENTER
54
Zero Net Energy Case Study Buildings: Volume 3
Energy Design Analysis and Energy Performance:
Modeling versus Post-Occupancy Measurements
Energy Use — Modeling
Because of the uniqueness of the heating and cooling features developed for this project, conventional energy modeling software available at the time of the design could not effectively model their performance in any meaningful way. A labor-intensive, simple calculation using spreadsheets was instead used to calculate pressure drops under different conditions, then to apply conservative factors to the results. The engineers were confident that the results proved the concepts, albeit conservative in the amount of thermal mass and pressure relief louvers required. (Measured results showed that there was indeed a certain amount of over-sizing, but also verified that the basic concept was effective and the system performed extremely well.)
The engineers note for this case study that the energy modeling tool, IES Virtual Environment, now in extensive use in the U. S., includes a “bulk flow” Computational Fluid Dynamics (CFD) model that is accurate enough to model a unique system of air flow such as the one used.
The upshot is that there are no whole building energy modeling results for “The ZNE Group” to compare with the actual measured performance data. Given that the installation of solar PV panels would be sized to fill all available roof areas and would still likely not align with the energy load of the entire project, it would be pointless to match the size of system to just the energy demand of “The ZNE Group”. The District would still obtain good value for the entire project with the maximum build-out of solar PV system.
Still, to “check the box” for ZNE performance of “The ZNE Group”, it is useful to create some performance comparisons as a basis for making a statement that the project achieved its Zero Net Energy goal, albeit for a pre-established subset of the project. See the section, Energy Production versus Energy Use: Zero Net Energy, for the discussion.
Energy Use — Actual Measurement of Performance Results
In this section, the measurement of energy use of “The ZNE Group” is charted and discussed. The data was obtained primarily from the District’s dashboard system that was set up by Lucid, based on the metering system installed by the control systems contractor. However, the natural gas data was found to be obviously flawed due to reporting errors in the metering system, so the gas data reported in this case study is that recorded by the utility gas meter dedicated to the site boiler plant, which provides heating and the domestic hot water (DHW) to the entire site. The gas consumption data is then assigned to “The ZNE Group” based on the fraction of its gross floor area compared to the entire project’s gross floor area, namely 49%.
Even though this is an indirect way of establishing gas consumption data for the building under study, it is nevertheless a good measure of the heating and DHW energy use since the building envelope characteristics and general building use are uniform to a reasonable approximation. The total gas energy consumption numbers are certainly accurate since they are recorded by the utility meter, so the only inaccuracy would be the result of the assumption that heating energy use is the same on a floor area basis.
It is unfortunate that the metering system is not reliable for the gas consumption of each building in the complex, but the accurate utility meter can be used for total site consumption. The electric metering system was found to be functioning correctly and the data from the Lucid dashboard for electric energy use can be taken as accurate.