Conservation Strategies

first steps to a high-performance building

1. Efficient Building Envelope

Trimming sprayed Icynene foam.

Heating, ventilation and air-conditioning (HVAC) account for about 39% of the energy load of the average office builiding. 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."

• Insulation and Offset-stud framing

• To deal with the related issues of insulation and air leakage, we chose to use the Icynene spray foam insulation system in the roof and exterior walls, 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.

Cross-section of offset-stud construction

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  Glazing

• 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% of its wall area devoted to windows, and a well-insulated building might expect up to 20% to 50% 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.

• Solar Heat Gain measures the percentage of solar heat gain through a window system compared to that through an unobstructed opening. R-values for these windows are more than double the values for double- and triple glazed clear glass units.

Motion detectors reduce unnecessary lighting loads.

2. Minimize Lighting, Plug & HVAC loads

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, we have replaced all incandescent lighting with fluorescents, exchanged 85% of our computer desktop systems for notebook computers using 10% of the power, and replaced the majority of our laser printers with inkjet printers. Motion detectors assure that lights are turned off when workers are gone or sleeping soundly. 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. We 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.

Daylighting is maximized.

3. Maximize Daylighting and Minimize Ventilation Energy Loss.

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, our 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, we have installed three enthalpy wheels, or Energy Recovery Units 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.

Outside air on an April day is preheated from 44.8 degrees F to 61.7 degrees F before supplying office ventilation.

©Woods Hole Research Center, 2007