Instead of a centralized rooftop makeup air system with vertical chases, each floor has its own customized heat pump makeup air units that use the building’s water-source heat pump hydronic loop to heat, cool, and dehumidify the air. The configuration saved the building developer $2 million in HVAC retrofit costs.

DALLAS - Mechanical contractor H&G Systems LP, Garland, Texas, is a mechanical contractor whose work is made up of office buildings, data-processing centers, and natatoriums (swimming pool spaces). The company’s specialty market, however, is the conversion of existing office buildings to multistory residential spaces, or lofts.

“A small group of contractors have experience in that,” said Kirk Fitzgerald, president of H&G Systems. The contractor performed all of the equipment placement, piping, and sheet metal work for the project.


Think of a typical office space. Each floor may have two more restrooms, kitchens, and interior spaces divided into cubicle and office areas, with windows on the outer walls; the HVAC system is controlled by zones from a common system. Compare it to an apartment building which has a single kitchen and bathroom for each living space, and individual HVAC control for each apartment.

Add to the situation, “There’s a limited amount of space to accommodate the required plumbing, air conditioning, and ductwork,” said Fitzgerald.

HVAC makeup air is typically ducted vertically in high-rise buildings. However, an unconventional horizontal design contributed significantly toward a $2 million savings in retrofit costs at the Republic Bank project. “It was value engineering that actually added value,” said Fitzgerald.

The converted Gables Republic Tower is a 400,000-square-foot, 56-year-old historic landmark. Its total conversion costs were pared down $8 million ($2 million in mechanical savings) as a result of value engineering team members’ creative solutions.

Condenser water is connected laterally to the heat pump makeup air unit that heats, cools, and dehumidifies during Dallas’ typically humid weather.


“Sometimes the term ‘value engineering’ in the vernacular means to cheapen the building,” he said.

“But sometimes you can do value engineering that lowers the cost and makes the building’s goals more achievable.

“In the case of Republic, we had vertical chases that went up and down the building. They were using a large portion of the floor space,” said Fitzgerald.

“On a new building, maybe three large makeup air units on the roof are more practical,” he said.

“But rigging three 25,000-pound makeup air units into the 35th floor below the roof of an existing high rise appeared nearly impossible, and would have cost at least $100,000 with special heavy-duty helicopters, plus another $150,000 in structural work, not to mention a myriad of other costs associated with that option.”

The project’s team (Bill Deniger, project manager for building owner-developer Gables Residential, Dallas; general contractor Andres Construction, Dallas; Fitzgerald of H&G Systems LP; and manufacturer’s representative McMillan Choate Associates LLP, Irving, Texas) came up with the idea of handling makeup air horizontally on individual floors.

“In this instance, installing 27 units was considerably cheaper than installing three central units,” he said. Each apartment has a water-source heat pump (Dectron Inc., Roswell, Ga.) and a supply of outside air. You have clothes dryer and toilet exhaust vents taking air out of the building. We have to heat the outside air, cool it, and dehumidify it to provide neutral air to the building.”

The vent pipe feeds makeup air from the corridor’s makeup air plenum, to the HVAC return air closet.


According to the team, three key elements made the $2 million in mechanical savings possible:

1. The discovery that vertical bathroom exhausts could be rerouted horizontally to an existing plenum slot in each floor’s curtain wall.

2. A stairway with existing outside air louvers on each floor provided a location and outdoor air access for a makeup air system on each of the 25 residential floors.

3. The ability to get customized heat pump makeup air units that used the building’s water-source heat pump hydronic loop to heat, cool, and dehumidify makeup air. A condenser water preheating coil preheats the air, allowing for heat pump mode heating during ambient conditions as low as 10°F.

“With anything that doesn’t follow convention, you’re always skeptical,” said Deniger. “We knew the design we wanted, and then we sought a custom manufacturer to make it. Dectron made a prototype per our specification, then verified the design in their performance testing laboratory.”


Each 10,000-square-foot floor’s 1,000-cfm makeup air dehumidifier has a plenum that draws 100 percent outdoor air through the building’s existing louver on each floor. After conditioning the makeup air by dehumidifying it (if needed), heating, or cooling, it’s supplied to a corridor ceiling plenum via a 20-foot-long metal connecting duct.

“Aside from the connecting duct, there were minimal ductwork costs because the corridor ceiling also serves a drywall plenum supplying makeup air to each unit,” said Deniger. “In this instance, we just used the space between the concrete and the drywall.”

The corridor plenum supplies outdoor air to the common areas and each residential unit on the floor. A secondary fan at the end of the plenum supplements the primary fan and pulls air through for even, 10 percent outside air distribution to each residence’s heat pump. The Trane (Tyler, Texas) units range from 1.5 to 5 tons.

Each outside air makeup air dehumidifier has a reverse-cycle heat pump, so any surplus heat is rejected to the heat pump loop. That loop is cooled by three Marley Cooling Technologies (Overland Park, Kan.) 700-ton fluid coolers. Other equipment on the project included three 40-hp vertical condenser loop pumps by Armstrong International (Three Rivers, Mich.) and 2 million-Btuh copper tube boilers from Lochinvar Corp. (Lebanon, Tenn.).

Additional savings were realized by eliminating pipe chases with existing makeup air shafts within them, plus 13 of 17 elevator shafts to increase leasable area on each floor by an average of 7.1 percent.

Without all the changes, “We would have had to take out a vertical wall and pull some kind of Houdini trick to get it in there,” said Fitzgerald.

“Putting horizontal units in each floor got rid of the necessity for vertical chases,” he said. It saved costs, helicopter rental, structural changes, and vertical chase spaces. They got a product that had the same outcome, they were able to save a lot of rentable space, and they could avoid a lot of other expenses.”


Contractor H&G Systems’ niche in office building conversions is in a potentially lucrative market. According to the Building Owners and Managers Association (BOMA), office space conversions offer a growing opportunity in the commercial market.

In its 2005 “State of the Industry” report, the association cited “office building conversions; loft rentals, student housing, and ethnic apartments; lifestyle shopping centers; ethnic retail, housing, and recreation; second homes or resorts; green buildings; and Brownfield sites” - under-used industrial and commercial facilities “where redevelopment is complicated by real or perceived environmental contaminations” (Wikipedia).

“The combination of worsening traffic congestion and changing lifestyles, matching our changing demographics, are compelling more mixed-use town center developments, [and] urban mixed-use projects,” according to BOMA.

Fitzgerald said one of his company’s most recent projects, the conversion of the 35-story Republic National Bank Building into lofts, has created rentable apartments out of “the old, original Republic Bank building.”

The developers built the apartments to lease, offering a variety of amenities “to reach a broad section of the marketplace,” he said.

Some restoration funds were provided to the owner through Dallas Tax Increment Financing (TIF). The financing and development tool can be used to encourage urban renewal projects.

Publication date:04/16/2007