According to the U.S. Department of Energy, buildings represent 39% of the energy used in the U.S., and they consume about 70% of the nation’s electricity. One of our goals with the new building was to create a highly efficient building using the latest in energy efficiency technology. Through the use of renewable energy, a super-insulated structure, energy efficient windows, lighting and equipment, and a climate control system that optimizes energy performance, our green building uses one-fourth the energy that conventional buildings use.
Our building is powered primarily by a 78.5-kilowatt solar photovoltaic (PV) system, a 10-kilowatt wind turbine and uses another renewable resource—wood pellets made from lumber milling waste—for heating. This solar installation is the largest in Vermont. Upon entering our site, visitors are greeted by 15 solar trackers that move and follow the sun to capture its energy. Each 2.2 kilowatt tracker uses a unique non-electric “thermal motor” to track the sun and improves the collection of solar energy by about 30% compared to fixed solar panels. Each tracker has its own inverter and its own meter to record how much electricity is produced.
To complete our solar installation, the building features 45.5 kilowatts of building-mounted PV panels. On the south-facing roof, sheets of dark purplish black silicon PVs are adhered directly to the standing seam metal roofing. On the building’s south wall, there is an awning of high efficiency crystalline silicon PV panels. Roof-mounted solar collectors use the sun’s energy to heat the building’s main domestic hot water tank. We plan to purchase green tags for our remaining power needs not met by the solar PV system and wind turbine. By making a substantial investment in renewable energy, we are not only helping the environment by avoiding emissions and reducing our reliance on fossil fuels, we have essentially prepaid our energy bill. We won’t have to worry about rising energy costs in the future.
Two wood pellet boilers provide the primary heat for our building.
A highly efficient radiant heating and cooling system provides optimal comfort and climate control in the building. Water circulates through eight miles of tubing in the building’s concrete floors. In the winter, warm water is circulated through the tubing. In the summer, cool water is circulated. Five high efficiency heat pumps provide chilled water to the radiant floors and the ventilation system for cooling. The heat pumps reject heat from the building through two miles of tubing in the bottom of the pond located in front of our building. Radiant heating has been used extensively in this country, while radiant cooling is more unusual and has been used mostly in Europe. Wood waste from lumber milling and other sources is transformed into pellets to provide heating for the building. Two home-sized wood pellet-fired boilers provide primary heating for the building’s radiant heating system. A 90+% efficient propane-fired boiler provides back-up heating. Wood pellets are 30% cheaper than oil and half the cost of propane. A wood pellet silo located in our warehouse holds 30 tons of pellets—enough for one year’s worth of heating. The pellets are gravity fed into the boilers located on the floor below. A networked control system orchestrates the building’s heating, cooling and fresh air ventilation systems. The system is programmed to provide the best comfort at the lowest energy consumption. It also tracks energy use in the building to maximize energy efficiency. Office spaces include operable windows so employees can have fresh air and natural cooling. Green and red indicators on “nurse’s station lights” let employees know when windows may be opened or closed as desired. The ventilation system provides fresh air to all the office working spaces, while removing stale air at the same time to provide superior indoor air quality. With its large open space and ample windows, the warehouse uses natural ventilation for its fresh air needs. During the summer, the nights are often cool enough to pre-cool the building for the next day, avoiding the use of air conditioning and saving a significant amount of energy. Several automatically operated windows open when conditions are right. Two large “barn fans” in the warehouse area supplement this natural air flow when needed. An “energy recovery wheel” recovers 75% of the energy required to heat the fresh air in winter and 75% of the energy required to cool the fresh air in summer. The boilers add more heat in the winter when it is needed and the heat pumps further cool and dehumidify the air in the summer. The fresh air system operates all year during working hours.
With a large solar PV installation, a super-insulated steel structure, energy efficient windows, lighting and equipment, our building is a model in energy efficiency, using just 1/4 the energy of conventional buildings. The building’s walls and roof are air-tight and “super-insulated.” Two layers of foam insulation on the roof form a special air barrier to reduce air leakage. The roof’s overhang is specially designed to avoid “thermal bridges” caused when steel, passing from inside to outside insulation, carries heat out during cold weather. The warehouse walls consist of 4” thick foam, steel-skinned panels. The office walls have 3” of sprayed-on foam, forming a tightly insulated wall system. The windows have an R-value of 5, more than twice that of windows designed to meet current energy code. Triple glass layers, filled with the insulating argon gas, slow heat flow to the outside in winter and reduce heat gain in summer. The edge spacers between the glass act as insulators and the frames are made of insulated fiberglass. We researched every motor to minimize our building’s power usage and heat gain from equipment. Our employees use laptops, which consume only 27 watts, compared with 100 to 150 watts required for a typical desktop computer. Our kitchen and other areas feature Energy Star-rated equipment and appliances to further reduce our energy consumption. Roll-down window shades in our workspaces reduce the sunlight’s glare and also help prevent heat build-up. A networked control system orchestrates building operations to maximize energy efficiency. The system also tracks building operations so we can ensure our heating, cooling and ventilation systems are operating properly.
Our building is all about lighting – the more natural light we could bring in, the better. The building’s southern orientation and numerous windows and skylights bathe the warehouse and office areas with natural light. The building’s open floor plan and high panels of glass within the work areas bring the light deep into the building and further reduce our electric lighting needs. Skylights in the second-floor offices supplement and balance the light coming from the windows on the south. The direct sun from the skylights strikes the white walls, where the light is diffused and re-distributed throughout the spaces. High-efficiency fluorescent general lighting in the offices directs most of the light toward the ceiling to mix the electric light with the daylighting coming in through the windows. Automatic dimming ballasts dim or brighten the lights as sunlight increases or decreases. Occupancy sensors throughout the building turn lights off when they are not needed. A high strip of south-facing windows in the offices are equipped with special “light guiding” blinds to redirect sunlight up onto the ceiling and diffuse the light for general illumination. In the warehouse, skylights and large windows practically eliminate the need for artificial lighting on sunny days. Triple-glazed skylights use special plastic layers that diffuse the light for more even lighting over the work areas.