Woods Hole Research Center

Heating, ventilation and air-conditioning (HVAC) account for about 39 percent of the energy load of the average office building. Consequently, the fundamental step in constructing a High Performance building is to establish a tight building envelope, preventing the uncontrolled exchange of heat from the inside to the outside of the structure. Insulation is an important part of this effort, but it is also important to control air leakage and to avoid the creation of structural thermal "bridges."

To deal with the related issues of insulation and air leakage, the Center chose to use the icynene spray foam insulation system in the roof and exterior walls of the Woodwell Building, providing an effective R-20 insulation (R-value of 3.6 per inch) that is both a thermal and an air barrier. Icynene is an open-cell, low density polyurethane with undetectable off-gassing of Volatile Organic Compounds (VOCs) a month after installation. Offset-stud framing complements the icynene application, eliminating the thermal bridge created by attaching interior and exterior walls to common studs.

Another common point of energy loss in any structure is through windows, which transmit energy into the building as solar gain, and out of the building through radiation from the glass, conductance from frame edges, convection within multiple glazed surfaces, and via simple leakage around movable window components. The average building has about 20 percent of its wall area devoted to windows, and a well-insulated building might expect up to 20 percent to 50 percent of its total energy loss to be related to its windows.

To minimize window energy loss, we selected two high performance window models from Loewen's Heat Smart™ Plus series which includes double- and triple-pane argon-filled glazing with Low Emissivity (Low-E) coatings to reduce radiative heat transfer. Additional conservation strategies employed in these advanced windows include enhanced seals and weather-stripping, and thermal breaks (airspace) between the outer metal cladding and the wood window frame.

With a building envelope designed to minimize waste in the heating and cooling cycles, the second strategy for reducing energy usage involves the specification of efficient lighting fixtures, office equipment (plug loads) and mechanical systems for heating and cooling the building. To this end, all incandescent lighting was replaced with fluorescents, 85 percent of our computer desktop systems were replaced with notebook computers (which use just 10 percent of the power), and laser printers were replaced with inkjet printers. Motion detectors assure that lights are turned off when staff are gone. Further gains are achieved by eliminating redundant equipment and adopting Energy Star appliances wherever possible.

The type of HVAC equipment used in heating and cooling the building is crucial for maximizing overall building energy performance. For the Woodwell Building, the Center elected to use a ground source heat pump for both heating and cooling the building (See figure, below). Large common areas are heated and cooled by a pair of water-to-air heat exchangers, while individual offices are heated and cooled by two water-to-water heat exchangers servicing ceiling-mounted "valence convectors" resembling over-sized hot water baseboards. The smaller size, and even further reduced heating and cooling loads of the Carriage house retrofit permit the use of recent advances in air-source heating and cooling.

After HVAC, lighting is the second largest energy load in a standard office building. Low-energy fluorescents and motion-detectors are an important part of reducing lighting loads, but another important strategy is the maximizing of natural daylighting. To this end, project architects strove to introduce natural lighting (and operable windows) to all areas of the building.

In a building that is tightly sealed, the introduction of fresh air is a necessity to avoid what has been termed "Sick Building Syndrome" or "Building Related Illness" for building occupants. Currently, ventilation standards provide for 20cfm (cubic feet/minute) for office occupants as established by ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers).

For a High Performance building, an unfortunate consequence of responsible ventilation is that a great deal of energy is heading out of the building in the exhaust air that has supplied the offices. To compensate for this, the Center installed three enthalpy wheels, or Energy Recovery Units, in the Woodwell Building to minimize the transfer of both sensible heat (temperature) and latent heat (moisture). During the winter months, the slowly rotating enthalpy wheel captures moisture and heat from the outgoing "return air" and passes this energy to the incoming outside air, effectively pre-heating and moisturizing what is to become supply air to building occupants. In the summer months, the process is reversed, with warm, moist incoming air being cooled and dried by the outgoing return air from the offices.