By Kevin Provencher, PDA Associates, Inc.
Located on a beautiful cleared and gently sloping hilltop site overlooking a wildlife management area atĀ the edge of the former Lyman School campus, the two story building responds to the horizon with theĀ long side oriented on the east-west axis for maximum solar exposure. The sloping shed roof is coveredĀ by an impressive 300 kW photovoltaic panel array. A deep overhang on the south facing faƧade providesĀ shading for interior spaces from high angle sun in the summer months, reducing solar heat gain duringĀ the cooling season, but allows low angle winter sun to penetrate the interior to offset the heat loadĀ during the heating season. North facing clerestory windows allow daylight to penetrate the interior,Ā reducing the energy required for artificial illumination through daylight sensors and controls, whichĀ regulate interior lighting levels based on the available daylight. Ā Vacancy sensors were chosen for daylitĀ spaces to avoid turning lights on unnecessarily. Unlike an occupancy sensor, a vacancy sensor requiresĀ the room occupant to turn the lighting on manually when entering the space, then turns the lights offĀ automatically after the occupant leaves. When adequate daylight is available, the occupant is less likelyĀ to turn the lights on.Ā
The exterior walls and roof are constructed of structural insulated panels (SIPs), a layer of foam plasticĀ insulation with oriented strand board bonded to both sides. When compared to framed wall and roofĀ assemblies, SIPs allow for continuous insulation uninterrupted by framing members, maximizing theĀ insulating value in a minimum depth. A continuous air and weather barrier was applied over the SIPsĀ behind open joint rain screen panels. Maintaining the continuity of the air barrier is critically importantĀ to the thermal performance of the building envelope. Whole building blower door testing confirmed theĀ building's air barrier performed at an average leakage rate of .062 cfm/ftĀ² at 75 Pa, far exceeding theĀ minimum energy code performance value for building tested assemblies (0.40 cfm/ftĀ²). The open jointĀ rain screen design allows for bulk water to penetrate the cladding and drain down the face of theĀ weather barrier in the air cavity behind. Ventilating the cavity promotes air circulation and drying whichĀ increases the overall resilience of the wall assembly.
In addition to passive design measures, the project utilizes highly efficient environmental systems toĀ drive down the Energy Use Intensity (EUI) which is a measure of the energy consumed annually perĀ square foot at the site. The design and engineering team targeted a low EUI (26.3KBtu/ftĀ²/yr) whichĀ could be offset by the renewable energy production available from the photovoltaic array, resulting in aĀ balance of energy consumed with energy produced on site. The building's primary systems are allĀ 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 coolingĀ systems from ventilation air through the use of a dedicated outdoor air system (DOAS) and lowĀ temperature hydronic radiant floor and ceiling panels. Compared to air delivery systems, a lowĀ temperature differential between heating and cooling modes is possible when radiant energy is utilizedĀ to maintain thermal comfort. Further, the pump energy required for hydronic systems is significantlyĀ less than the fan power required for air systems to deliver heating and cooling. Hydronic systemsĀ become more increasingly more efficient than air systems as the size of the building increases. The lowĀ temperature differential is supported by a ground source heat pump system with 20 closed loop wellsĀ by transferring the thermal energy of the ground beneath the site, which is at near constantĀ temperature year round, to the building's heating and cooling systems. 'Free cooling' is available duringĀ the swing seasons via bypassing the heat pump compression cycle and running the cooling tower.
Thank you to Conor, Dan and the staff at the Division of Fisheries & Wildlife for leading the in-depthĀ discussion and tour of this skillfully designed, engineered and constructed net zero energy facility.