By Kevin Provencher, PDA Associates, Inc.
On Tuesday February 23rd, the USGBC MA Chapter hosted an in depth discussion and tour of the LEED Platinum, Commonwealth of Massachusetts Division of Fisheries & Wildlife Headquarters located in Westboro, Massachusetts, winner of the Chapter's 2015 Innovation in Green Design Award. Designed for net zero energy performance with direction from the Division of Capital Asset Management and completed in early 2015, the facility is on-track to meet and perhaps exceed its performance goal in 2016, according to Conor McGuire, Director of Sustainability at Columbia Construction Company. The project was designed to be the first publicly owned net zero energy building in the Commonwealth. Conor was joined by Dan Arons, Principal Architect for Architerra, Inc. who was responsible for design of the project. They report the facility was 94% efficient in first year of operation. Record breaking snow accumulation and cold temperatures in February of 2015 reduced the energy output of the rooftop photovoltaic array to below expected levels; however the overall annual performance suggests the facility may even be net positive in 2016.
Located on a beautiful cleared and gently sloping hilltop site overlooking a wildlife management area at the edge of the former Lyman School campus, the two story building responds to the horizon with the long side oriented on the east-west axis for maximum solar exposure. The sloping shed roof is covered by an impressive 300 kW photovoltaic panel array. A deep overhang on the south facing façade provides shading for interior spaces from high angle sun in the summer months, reducing solar heat gain during the cooling season, but allows low angle winter sun to penetrate the interior to offset the heat load during the heating season. North facing clerestory windows allow daylight to penetrate the interior, reducing the energy required for artificial illumination through daylight sensors and controls, which regulate interior lighting levels based on the available daylight. Vacancy sensors were chosen for daylit spaces to avoid turning lights on unnecessarily. Unlike an occupancy sensor, a vacancy sensor requires the room occupant to turn the lighting on manually when entering the space, then turns the lights off automatically after the occupant leaves. When adequate daylight is available, the occupant is less likely to turn the lights on.
The exterior walls and roof are constructed of structural insulated panels (SIPs), a layer of foam plastic insulation with oriented strand board bonded to both sides. When compared to framed wall and roof assemblies, SIPs allow for continuous insulation uninterrupted by framing members, maximizing the insulating value in a minimum depth. A continuous air and weather barrier was applied over the SIPs behind open joint rain screen panels. Maintaining the continuity of the air barrier is critically important to the thermal performance of the building envelope. Whole building blower door testing confirmed the building's air barrier performed at an average leakage rate of .062 cfm/ft² at 75 Pa, far exceeding the minimum energy code performance value for building tested assemblies (0.40 cfm/ft²). The open joint rain screen design allows for bulk water to penetrate the cladding and drain down the face of the weather barrier in the air cavity behind. Ventilating the cavity promotes air circulation and drying which increases the overall resilience of the wall assembly.
In addition to passive design measures, the project utilizes highly efficient environmental systems to drive down the Energy Use Intensity (EUI) which is a measure of the energy consumed annually per square foot at the site. The design and engineering team targeted a low EUI (26.3KBtu/ft²/yr) which could be offset by the renewable energy production available from the photovoltaic array, resulting in a balance of energy consumed with energy produced on site. The building's primary systems are all electric, which eliminates on-site combustion of fossil fuels and carbon emissions.
The key strategy employed by the team for reducing the EUI includes separating the heating and cooling systems from ventilation air through the use of a dedicated outdoor air system (DOAS) and low temperature hydronic radiant floor and ceiling panels. Compared to air delivery systems, a low temperature differential between heating and cooling modes is possible when radiant energy is utilized to maintain thermal comfort. Further, the pump energy required for hydronic systems is significantly less than the fan power required for air systems to deliver heating and cooling. Hydronic systems become more increasingly more efficient than air systems as the size of the building increases. The low temperature differential is supported by a ground source heat pump system with 20 closed loop wells by transferring the thermal energy of the ground beneath the site, which is at near constant temperature year round, to the building's heating and cooling systems. 'Free cooling' is available during the swing seasons via bypassing the heat pump compression cycle and running the cooling tower.
The energy required to meet the ASHRAE 62.1 ventilation standard required for LEED certification is offset by the dedicated outdoor air system. Latent load, which is the energy required to remove moisture from air without change in temperature, is decoupled from the sensible load, which is the energy required to raise or lower the air temperature, by dehumidifying the ventilation air. The thermal energy of the air returned from the interior spaces is exchanged with the incoming ventilation air by an energy recovery ventilator (ERV). The entire latent load and a portion of the sensible load are taken by the DOAS, while the hydronic radiant system handles the balance of the sensible load. The overall result of running the two systems in parallel is a highly energy efficient solution that provides superior thermal comfort for the occupants.
Thank you to Conor, Dan and the staff at the Division of Fisheries & Wildlife for leading the in-depth discussion and tour of this skillfully designed, engineered and constructed net zero energy facility.