Ashrae Journal - November 2008 - 40

use. Oriented southerly toward the view of the kettle pond, major windows are protected from otherwise large summer solar heat gains by large overhangs, sun screens, and adjustable interior shades. Fenestration is minimal on the other elevations, further limiting solar exposure. Clear, low-e, high performance, argon gas-filled insulated glazing was selected for maximizing energy performance without disrupting views. The roof and walls are also well insulated. The ventilation unit is equipped with “free” heating and cooling coils that precondition ventilation air using the groundwater. The large multipurpose room unit is similarly equipped with a “free” heating coil. The “free” heating and cooling coils work in unison with variable speed heat recovery wheels. Building exhaust/relief air is ducted through the wheels and energy otherwise exhausted to the outside is recovered. Between the “free” heating and cooling coils and energy recovery wheels, the building ventilation air is almost entirely preconditioned without having to use mechanical heating or cooling. An additional cooling coil provides dehumidification capabilities on rare occasions that the free cooling coil does not remove enough moisture from the ventilation air. By using energy recovery and the well water systems for “free” heating and cooling, the loads imposed on the heat pumps www.info.hotims.com/16019-48 were significantly reduced and the heating and cooling equipment downsized. The “free” heating and cooling coils allowed heat pump downsizing by 5 tons (18 kW) of cooling and 100 MBH (29 kW) of heating. Similarly, the energy recovery wheels reduced the required capacity by 15 tons (53 kW) of cooling and 250 MBH of heating. Compared to the calculated cooling ventilation loads, the calculated heating ventilation loads were proportionally larger to the building’s total. A proportionally larger capacity savings was obtained from the energy recovery equipment on the heating side versus the cooling side. This coincidentally allowed the heat pumps’ respective heating and cooling capacities to match the calculated heating and cooling loads. Without the energy recovery wheels and coils, the heat pumps would require selection to meet the calculated 715 MBH (210 kW) total heating demand and 65 ton (229 kW) cooling demand. Heat pumps with a 715 MBH capacity would have a corresponding cooling capacity of about 80 tons to 15 tons ( 281 kW to 53 kW) or 25% greater than needed. Without the additional coils and energy recovery wheels, the required groundwater flow would have been significantly greater than the 50 gpm (3.2 L/s) minimum needed for the kettle pond and wetlands. Not only does the well water provide free heating and cooling for the ventilation unit, the heating coil also provides frost protection for the energy recovery wheel. With cold outside temperatures, energy recovery wheels can develop frost on their media. This will initially affect performance and can eventually block airflow. Traditional frost control measures include stopping or slowing down the wheel or bypassing the wheel entirely. However, these control schemes reduce the wheel’s overall efficiency and capacity. In addition to providing “free” heat, the ventilation unit heating coil preheats the outdoor air up to a temperature where frost control is not needed. Full heat wheel efficiency and capacity is obtained even with cold outside air temperatures when heat recovery is needed the most. Using the groundwater and energy recovery wheels to reduce building demand also increases the system efficiencies and reduces energy costs. Since the groundwater is nearly always 50°F to 55°F (10°C to 13°C), the heat pump cooling is very efficient (EERs greater than 20). The heating mode is kept efficient by selecting heating equipment capable of providing heating with relatively low temperature (120°F [49°C]) hot water. Multirow hot water coils were provided where single row coils would otherwise be sufficient. Ventilation airflow rates and subsequent energy use are kept to a minimum November 2008 40 ASHRAE Journal

Ashrae Journal - November 2008

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