Page 118 - Zero Net Energy Case Study Homes-Volume 1

CASE STUDY NO. 5
COLONIAL HOUSE MULTI-FAMILY HOUSING
It is possible to do a ZNE performance analysis using the total energy use of all units versus the energy production recorded for the entire array. This analysis is shown in the two charts on the opposite page The cumulative net energy performance of the project as a whole shows that the housing did not achieve ZNE performance in 2015, as expected due to the reduction in solar PV panels in the rooftop arrays. The performance bears out the results of energy modeling analysis.
However, it is possible to look at net energy performance of the individual units, as opposed to simple averages, by considering the individually metered results for the energy use and the basis for the utility allowance in kWh. The HERS Rater’s site inspection carried out such and analysis in September 2017, which showed that over a period of 2-1/2 years, seven individual units had performed at net positive energy, with two more within a few percent of ZNE performance, out of the total 44 units of housing. With the exception of the 4BR units, these ZNE-performing units are representative of all unit types in terms of the fraction that are performing at ZNE.
Post Occupancy: Observations and Conclusions
The Colonial House multifamily housing project is primarily a design based on the requirements of affordable housing as prescribed by federal and state agencies, but in this case including de- sign features corresponding to the special sustainability and energy performance goals set in the developer’s brief in its funding application. These goals were met to some degree as described in the preceding sections.
Post Occupancy: Solar PV System
As noted above, initially the design of the solar PV system called for 670 panels of a SunPower module (Type E) with an output of 240 watts (DC) each for a total installation of 160.8 kW. De- spite the energy modeling result that showed that ZNE performance would require a 147 kW system, the decision was made to install the smaller system of 100 kW. As expected, according to the data collected in 2015, the result was that the project as a whole fell short of ZNE perfor- mance.
However, several individual units were found to be achieving ZNE performance that year based on the allocation of their share of the solar PV system output and the average energy consump- tion of all the units. The HERS Rater’s site inspection in 2017 verified that seven individual units had performed at better than ZNE (net positive), with two more within a few percent of ZNE per- formance. The project’s ZNE performance was therefore achieved for some of the project units.
Post Occupancy: User Behavior
In the informal post-occupancy interviews, the tenants’ observations about the project’s design concerned those aspects unrelated to the energy goals. Since the cost of energy is included in the rent calculation by formula, unless their energy use is particularly high to cause an increase in the individual utility cost, there is little incentive to modify behavior based on energy use. There was some awareness of the home energy monitoring system, which is standard in every unit and gives visual cues to the occupants about possible excessive energy use, but the wall-mounted indicators in the units visited during the interviews were not operational.
Locating the laundry facilities in a central building was actually a design strategy to lower energy use. In general, laundry dryers are used only half as often when located in a central shared facil- ity than when located within the individual unit, primarily for user-behavior reasons. Since the effect on marketability was not considered large in this case, the central location was chosen7.
7 S. Armstrong, M. Winkler, “The Impact of a Home Laundry on Energy Consumption”, (2012) https://www.redwoodenergy.tech/publications/
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Zero Net Energy Case Study Homes: Volume 1