Architectural Products - May 2019

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on spec by John Mesenbrink Contributing Writer

Best Practices in HVAC ›› Heat Pumps, VRF

Pumping Up Carbon Control A couple of trends are coming to bear in downtown Bridgeport, Conn.—adaptive re-use and “electrification.” The former is self-explanatory, the latter is a trend surfacing in California, Colorado (Boulder) and New York City, where it’s become the desire of various governmental entities to ween their citizens and businesses off of fossil-fuel-based HVAC, to those electrically powered, which, theoretically, would be powered by some form of renewable energy. Last year at the AIA conference in New York, we addressed this issue in a special Net Zero Buildings’ panel, which was recapped in that magazine’s September issue. There, the focus was on VRF—variable refrigerated flow HVAC technology. But in the case of Bridgeport, its consultants went a different direction, and opted for heat pumps. Before briefly examining the differences, let’s take a look at the project. Spinnaker Real Estate redeveloped three vacant, but historic buildings in the city’s downtown, into a single property, now known as Harral Security Wheeler (HSW), adding retail and commercial space on the lower levels, and more than 70 residential units on the upper floors.

With limited exterior space, installing air conditioning wall units was impossible without damaging the buildings’ historic architectural elements. Working with consultants United Illuminating, the firm was able to retrofit the historic buildings with more modern lighting and heating equipment, saving them upwards of $50,000 in annual energy costs. The project was funded through a combination of historic rehabilitation tax credits, Brownfield programs, private equity and $26,235 in energy fund incentives. Using UI’s energy model, the upgrades could result in roughly $50,000 of annual energy savings. “The energy incentives allowed us to provide better and more efficient equipment in the building’s common areas, which are in use 24 hours a day, 365 days a year,” says Spinnaker Real Estate President Kim Morque. “The incentive shortened the payback period to justify the additional costs of the project. By their nature, Historic Tax Credit projects require subsidies to make projects feasible. The energy incentive helped lower construction and operating costs,” says Morque. With limited exterior space because of the large windows, installing air conditioning wall units was impossible without damaging the buildings’ historic

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Th ree vacant downtown historic buildings, now known as Harral Security Wheeler (HSW), have been repurposed into retail and commercial space on the lower levels and more than 70 residential units on the upper floors.

architectural elements. As a result, UI turned to heat pump units. According to UI’s Glen Eigo, the engineer on the project, as opposed to VRF. “A VRF requires a central condensing unit and a problem with that unit can cause problems to multiple tenants,” says Eigo. “Also individual heat pumps make it easier to have separate meters for each tenant without the need for sub-metering. This makes each tenant responsible for their own utilities and the developer does not get involved.” So, what’s the difference? According to Mike Smith, senior manager of marketing communications, Mitsubishi Electric Trane HVAC U.S.—the company is presently working with NYC and Boulder on electrification initiatives—heat pumps are designed to transfer thermal energy to and from interior spaces. At the most basic level, he says, a heatpump system consists of an outdoor unit connected to one or more indoor units via a pair of refrigerant piping. “During heating, the outdoor unit extracts ambient heat, and using refrigerant as the medium, transfers heat to interior spaces. During cooling, the indoor unit transfers heat from interior spaces to the outdoor unit where the heat is rejected,” says Smith. He adds split-ductless and variable-capacity ducted heat-pump systems are popular among

residential and light-commercial architects, as these systems reduce or eliminate bulky ductwork and are more compact than traditional systems. VRF, on the other hand, is more suitable for larger facilities. “VRF systems offer more connections to indoor units per outdoor unit, and provide greater capacities [tonnage] for heating and cooling compared to residential and light commercial systems,” says Smith, adding VRF systems can be ductless, ducted or a hybrid. “Heat pump systems are typically applied in moderate climates and in buildings with a single zone. In buildings with diverse requirements—such as a hotel, office or multifamily building—architects select heat-recovery VRF systems for simultaneous heating and cooling.” Ultimately, he says, VRF systems and residential heat pump systems enable architects to design comfort zones of various sizes and with consideration for how occupants will use a given zone. “Each zone is served by at least one indoor unit, which can be controlled individually to customize comfort. The variety of indoor units include ductless options such as ceiling cassettes, wall-mounted units and floormounted units as well as ducted options such as low-profile air handlers, multi-position air handlers and horizontal-ducted units.”

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