©2019 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 61, no. 3, March 2019.
About the Authors
Morgan Heater, P.E., is a mechanical engineer and Stephanie Baker is an architect and analyst at Ecotope Inc., in Seattle.
The Westside school project converted and expanded a 1970’s era Presbyterian Church into a kindergarten thru eighth grade elementary school with a measured operating Energy Use Intensity (EUI) of 14.3 kBtu/ft2·yr (162 405 kJ/(m2·yr).
The school is 52,826 ft2 (4908 m2) with a conditioned area of 49,904 ft2 (4636 m2) It includes an auditorium, library, classrooms, gymnasium, lobby gathering space, and administrative offices.
The architects sought an energy-efficient HVAC system that would not upstage or disrupt the church architecture they were preserving. The mechanical engineers proposed a design flexible enough for retrofits, and well suited to multi-zone buildings. The building is equipped with a variable refrigerant flow (VRF) system and a dedicated outdoor air system (DOAS) with upgrades to the building envelope to improve its performance. The building maximizes energy savings by embedding the existing structure in an efficient envelope, and supplying heating, cooling and ventilation tailored to each space.
Energy Efficiency
Westside School is the most energy-efficient school in the Northwest region, designed around a small HVAC budget by concentrating on introducing energy efficiency where it would count the most. The HVAC design realized greater comfort than conventional school HVAC systems, at a very competitive cost. Small dedicated outside air systems (DOAS) serve each occupied space, along with zonal ductless inverter driven heat pumps for heating and cooling. Low-flow water fixtures, daylighting and LED fixtures reduce the building base load, and an external perimeter of modern efficient envelope reduces the conditioning load of the building. The school uses just 30% of the energy of the school’s former building.
The following Figures 1 and 2 detail the performance of the new school versus the old one (a former city of Seattle school), and in comparison to benchmark data and a baseline model.
Modeled savings were predicted to be 17% over the C407 Seattle Energy Code Baseline. Seattle City Light bills show savings over the baseline model predictions of 39%. Real world savings compared to Seattle Office of Sustainability 2015 Seattle Public Schools energy performance benchmark data are 68%.
Indoor Environmental Quality
Outside air quantities are provided per ANSI/ASHRAE Standard 62.1-2012 during all occupied hours. HVAC equipment in regularly occupied spaces is controlled via occupancy sensors to shut off during periods of vacancy and to provide full ventilation whenever occupied. In intermittent high occupancy spaces (the theatre, gym, and rehearsal room), ventilation rates are controlled with CO2 sensors. All air is filtered to MERV 8 levels. The majority of the rooms in the building include operable windows for fresh air in good weather. Ceiling fans help evenly distribute the fresh air in classrooms and provide air movement for improved thermal comfort.
Innovation
Innovative features of the building include the application of a small zonal dedicated outside air systems in a retrofit and a school, as opposed to larger central systems. Smaller ERVs and smaller ducts reduce headspace loss in the ceilings while meeting the energy use targets on a tight budget.
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