Page 117 - Designing for Zero Carbon - Case Studies of All-Electric Buildings

Heating Systems
It is the SFUSD’s policy to provide heating only, given the mild climate in San Francisco. Me- chanical heating is provided when needed by electric heat pump package units on the roofs of the north classroom wing and the gymnasium. The gymnasium system is a high-efficiency VAV heat pump5 serving the space immediately below the roof.
The classroom wings are provided with a variable refrigerant flow (VRF) heat pump package unit. This system uses refrigerant instead of air or water as the system’s heat transfer medium, increasing the heat pump’s overall efficiency. The classroom heat pumps are located at grade in order to maximize the roof area available for solar PV system. Each individual classroom is heated by a conventional vertical fan coil unit located in the room.
Domestic Hot Water
The toilet rooms are supplied by a conventional electric resistance water heater.
Master System Integration and Control Systems Integration
Because of the building’s size, its environmental management is largely controlled by individual system controls and manual operation rather than a centralized system.
Renewable On-Site Energy Supply
The principal issue for the solar PV system is the limitation on available roof area for the panels required by the agreement at the neighborhood group meetings. As noted, the modeling of the performance of the solar PV system located only on the roofs of the gymnasium and the north classroom wing predicted an annual production total of 82,530 kWh assuming a high output pan- el of 415 watts, or 13.4 kBtu/sq. ft. per year. This matched the total annual energy use modeled for the building, so the ZNE performance goal was shown to be achievable at least according to the assumptions of the energy modeling.
SFUSD did not install the solar PV system for funding reasons when the building opened in the fall of 2019. The plan currently is to enter into a PPA (solar power purchase agreement) with a supplier in 2022. The solar PV system will be installed on the planned roof areas and SFUSD will pay a low rate per kWh for the electricity generated.
5 Daikin Rebel package rooftop heat pump. https://www.daikinapplied.com/products/rooftop- systems/rebel
Designing for Zero Carbon: Volume 1
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SFUSD CLAIRE LILIENTHAL MIDDLE SCHOOL CASE STUDY NO. 5
(Opposite Page) Wall sections at south and north facades showing continuous insulation detail, sun shade (south) and large glazing areas. (Courtesy of Lionakis)