Variables for Retrofitting with VRF

The 15-story, 170,000-square-foot Towson City Center was completed in 1967. Alleged ventilation problems and a reputation as a sick building led to the facility’s closing in 2002. It remained unoccupied for more than 10 years until new owners undertook a giant renovation project, which included mechanical and electrical systems and curtainwall.
For Steve Wagner, director of engineering for design/build mechanical firm MEC2, the gutted tower had limited space for new ductwork. The floor-to-floor height on 12 of the building’s floors is only 10 feet, 6 inches. To earn LEED certification, energy efficiency was also a top priority for the new HVAC.

The choice of a Mitsubishi Electric VRF system met those requirements. “We knew that if we went the VRF route, the sheet metal could be kept to a minimum,” says Wagner. The low, 9 7/8-inch profile of the indoor fan coil units also saved space.

On the building’s penthouse mechanical level there was more space to be saved. With no need for the cooling tower and boiler of the previous central system, this equipment was removed. The small footprint of the VRF system’s 15 outdoor units (one for each floor) freed up 12,000 square feet of the penthouse for storage or other uses. A dedicated outside air system with energy and desiccant recovery wheels was installed on the steel grillage of the former cooling tower. The rentable square feet on each floor was increased due to the reduction in vertical shaft space needed for ventilation.

Uncommon Flexibility and Efficiency

Listed on the National Register of Historic Places, the former Imperial Hotel in Atlanta was built in 1910. Gutted and converted into subsidized residential housing units, the building is now known as the Commons at Imperial Hotel. The renovated building has more than 90 housing units, which made it a good fit for a VRF solution.
The building needed individual HVAC controls for each apartment but the rooftop area was too small to accommodate so many split-system condensing units. However, the VRF system from LG Electronics required only one outdoor unit for each of the eight floors and the basement, resulting in nine rooftop units.
According to Robert Barfield, vice president of construction services for the developer, Columbia Residential, the VRF system also increased the area of the housing units by eliminating many vertical ventilation shafts. Indoor fan coil units for the VRF system were installed above the ceilings in the apartments.
The VRF system’s heat recovery capability was also important for efficiency. Barfield explains that the north and south facades of the building had large expanses of historic metal bay windows but the east and west facades had much less window area. As a result, indoor temperatures on different sides of the building were often unbalanced. The VRF system allows heat from warm zones to be transferred to cooler zones instead of rejected to the outside. Residents also have a high degree of control over heat and cooling within their units.
The building’s renovation was designed to achieve LEED Gold certification.

 

GSA Applies VRF to Diverse Buildings

GSA has implemented VRF technology in 10 projects, according to Kevin Kampschroer, director of GSA’s Office of Federal High-Performance Green Buildings. BUILDINGS content director Chris Olson spoke with Kampschroer about three retrofit projects: the Wayne Aspinall Federal Building and U.S. Courthouse in Grand Junction, CO; the Bishop Henry Whipple Federal Building in Fort Snelling, MN; and the Byron Rogers Federal Building in Denver.

What has been GSA’s experience with VRF retrofits?
I’ll mention three projects because each is interesting in its own way.

The smallest is the Aspinall building, which is the first building on the National Register of Historic Places to achieve net zero. It uses a combination of VRF, ground source heat pumps, rooftop solar, efficient windows, and extraordinary attention to increasing the envelope insulation from the inside as the historic exterior can’t be tampered with.

This is a particularly good facility for the application of variable refrigerant flow because of its location in what is essentially a high desert. For half of the year there is a large temperature differential between the east and west facades. As the sun heats up the east side of the building, it requires cooling while the west side calls for heat. Variable refrigerant flow allows you to move heat from one side of the building to the other, making everyone more comfortable.

The building’s heat pumps make a great combination with VRF. Geothermal wells and VRF are like a marriage made in heaven.

Has GSA used this VRF/geothermal combination on other facilities?
Yes, the Whipple building in Fort Snelling, MN. It’s a much bigger building – 618,000 square feet – but it also needed replacement of the entire HVAC system. It is one of the largest buildings in our inventory with geothermal wells and VRF.

For Whipple, the east-west orientation was not such a big factor. Much of the savings from the VRF involves the ventilation. The energy it takes to push air around a building typically makes ventilation the largest single energy cost in maintaining building temperature. Pumping refrigerant in the VRF system is more efficient than using fans to move air. You can vary the pump speed and the pump pressure, which saves on energy distribution.

The renovated facility is 72% more energy-efficient, in part due to the VRF system. The efficiency makes it a beautiful building!

Does your third example also use geothermal wells?
The third example is not ground source. It’s the Byron Rogers Federal Building in Denver, which was built in 1964. At 620,000 square feet, it’s about the same size as Whipple but it’s tall. Because of its downtown location, ground source heat pumps were not an option.

From an energy perspective, the Denver building’s orientation could not be worse – long facades on the east and west and short facades on the north and south. Through the day we need to move heat from the east side of the building to the west or back in the other direction. By switching over to VRF, we save space because we’re not moving as much air. Instead, we’re moving chilled water through beams for cooling.

The condensing units are installed within the existing boiler room. They serve VRF fan coils on each floor, which are the equivalent of a radiator that heats and cools. And the separation of heating and cooling from the ventilating system enables us to concentrate on high-quality, super-filtered outside air.

The retrofit saved a lot of area on every floor by eliminating ductwork running up and down the building. On the top mechanical level, it was the equivalent of adding a new floor. If you imagine an 8 ½ by 11 sheet of paper as the cross section of a duct, you need a pipe about the diameter of a nickel to move the same amount of heat. That gives you an idea of the space that you’re saving.


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