The 103-acre Ann's Choice, located in Warminster, Pa., is one of the developer's more recently built communities. Towson, Md.-based Kibart Inc., a mechanical-electrical-plumbing consulting engineering firm, handled construction phases at Ann's Choice.

The company installed Dry-O-Tron® make-up air units, said vice president Farshad Kassiri. The units use a reverse-cycle heat pump, modulating hot gas reheat, and variable heat pump capacity options to deliver additional energy savings to the ongoing project, according to manufacturer Dectron Inc., Roswell, Ga.

Long-Term Growth And Energy Savings

The equipment was specified for construction in the second phase of residential buildings and a second clubhouse. It also will provide heating and cooling for the total of 20 residential buildings, four clubhouses, and a chapel by the time the project is completed, which is scheduled for 2010.

"Both Erickson and their residents have a stake in the energy bills, so energy efficiency is a high priority," said Kassiri. "With the large amount of apartments they're dealing with, we've found through life-cycle analysis that a water-source heat pump system is the most efficient approach."

Separate heat pumps in 110 living spaces of each 125,000-square-foot, five-level residential building would have maintained temperature effectively, Kassiri said, but the technology isn't ideal for outside air ventilation requirements. Plus, each residential apartment's ductwork for outside air would reduce living space.

Kassiri used one Dry-O-Tron Series DK dehumidifying make-up air unit for each residential building. The top-floor unit supplies dehumidified, preconditioned air to each floor's common areas and corridor via a vertical trunk line located in a utility chase.

The corridor is slightly pressurized so that 100-percent outside make-up air infiltrates each unit from the corridor and exhausts through apartment bathroom vents. Make-up air is delivered at a 50 percent to 55 percent relative humidity (rh) at a supply temperature of 72 degrees to 74 degrees F year-round.

Kassiri said that the hot gas reheat option on each make-up air unit produces a better comfort level by helping maintain accurate set point temperature. "The make-up air strategy at Ann's Choice goes a step beyond with modulating hot gas reheat, which maintains a much more precise temperature and relative humidity inside the space while saving energy," he said.

The modulating reheat option also operates with the reverse-cycle heat pump option to provide more precise wintertime temperatures.

Saving Space

Earlier designs specified HVAC units for each floor, but Kibart has abandoned that idea to save approximately 800 square feet per residential building. When equated to local building costs of $125 per square foot, Kassiri's newest one-unit design saves Erickson approximately $100,000 per residential building in construction costs while adding revenue-producing living space.

"We used to put an HVAC unit on each residential floor, but have found that one large make-up air unit saves an enormous amount of space, which is then used for additional living area per building," Kassiri said. "Plus, now only one unit needs periodic maintenance, which also saves money."

The living spaces have recirculating heat pumps made by ClimateMaster Inc., Oklahoma City.

The common-area heat pumps and make-up air units are monitored and controlled by a building automation system from Novar Controls Corp., Copley, Ohio. The direct digital control (DDC) system was designed, installed, and will be serviced by Novar master distributor Yates Energy Management (YEM), Cockeysville, Md.

The factory-engineered dehumidifying make-up air units were compatible and interface with the Novar system, according to Gerald Atterbury, president of YEM.

Dectron's vertical make-up air Model DKV Series units will be applied in future planned buildings. The DKV Series is designed for service access from two sides instead of one, which enables it to be positioned in a corner, thus saving more floor space.

Each phase consists of five residential buildings and a clubhouse, which has its own independent central water-source loop.

Construction Phases

The project features two Baltimore Air Coil (Baltimore) cooling towers, two Tranter PHE Inc. (Wichita Falls, Texas) plate-and-frame heat exchangers, five Bell & Gossett (Morton Grove, Ill.) vertical split-case pumps for the cooling tower loop (two pumps), and condenser water closed loop (two pumps) with one pump as a standby.

In the Ann's Choice 55,000-square-foot clubhouse, Kassiri uses heat pumps in smaller spaces and two DKV Series HVAC units with dehumidification serving a large auditorium with high occupancy rates. The clubhouse also houses the central plant that accommodates four residential buildings and a chapel. The first clubhouse at Ann's Choice also uses a separate Dectron Dry-O-Tron dehumidifier custom designed for the high humidity loads of the facility's indoor swimming pool.

Based on their current success at Ann's Choice, Kibart and Erickson will continue to push the envelope for indoor comfort and energy efficiency. Kassiri's new designs will incorporate plug fans for more directional flexibility in ducting out of the make-up air unit, plus variable-frequency drives for additional energy savings.

"You can't always provide state-of-the-art designs to a client by using off-the-shelf equipment," said Kassiri. "In some cases, it really must be custom manufactured to the engineer's designs."

Publication date: 06/27/2005