In London, Ont., Brescia University College’s new residence hall and dining complex has a sustainable HVAC system providing air comfort while also helping the project earn an environmental rating of five Green Globes under the online green building rating program.
Facility managers for the women’s university worked with the design team to specify variable refrigerant flow (VRF), which makes the $31-million facility one of Ontario’s first major commercial projects featuring the technology as both its primary heating and cooling source. The facility’s VRF strategy saves an estimated 25 per cent in operating costs versus conventional HVAC equipment. This played an important part of the total energy performance, which was 60 per cent lower than Canada’s Model National Energy Code for Buildings (MNECB).
VRF had additional benefits for the 11,610-m2 (125,000-sf) Clare Hall, the 300-bed student residence, and Mercato, a dining pavilion.
“It offered the quietest and most energy-efficient HVAC system option for the resident rooms at reasonable equipment and maintenance costs,” said Derek Vakaras, P.Eng., LEED AP, principal at Chorley+Bisset, the project’s consulting engineer.
Rooftop VRF esthetics
A major VRF system concern among engineers and architects is the fact conventional lineset foam insulation prematurely deteriorates due to weather conditions. In some cases, birds are known to bite foam pieces for nest materials. The result can cause thermal transfer degradation copper piping leaks from formicary and pitting corrosion.
The corrosion- and scratch-resistant zinc/aluminum/magnesium (ZAM)-coated metal duct preserves lineset insulation and its thermal transfer functions. It is also a critical factor in presenting a clean, professional appearance, especially since there are rooftop sightlines from nearby campus buildings.
“The appearance factor doesn’t always take precedence in all projects’ rooftop HVAC systems, but it should,” explained Eric Shaw, Baymar Supply’s refrigeration engineering technician.
The protection duct comes with a full line of fittings, adaptors, and couplings with foam gaskets—such as the 90-degree elbows and 45-degree offsets specified to raise the 304-mm (12-in.) high lineset run for rooftop service chase penetration. Moisture infiltration prevention included the caulking of connections with a moisture-preventing caulking sealant.
Adding to the rooftop esthetics, the 34 VRF condensers were mounted on equipment mounts. The 3.6 x 3.6-m (12 x 12-ft) tubular, hot-dipped galvanized steel frames are modular and feature adjustable legs and anti-vibration nylon feet.
The mounts elevate the equipment 508-mm (20-in.) above the roof to facilitate proper drainage, comply with snow clearance codes, and function as an aesthetic alternative to concrete slabs, railroad ties, or steel I-beams. Co-ordinated H-stand roof supports for the lineset ducting were also included. In the future, when the building is re-roofed it can be replaced underneath one leg at a time while the units and piping stay connected and functional, according to Shaw.
The condensers supply 350 evaporators—most of which are floor-mounted and concealed. Two 3539-L/s (7500-cfm), 100 per cent outdoor air systems supply the common areas with fresh air, which is drawn into living quarters through bathroom exhaust fans. A third unit provides cooling and make-up air for the dining pavilion. Common area heating and cooling is handled by a combination of ducted and ductless equipment.
Critical VRF grouping and configuration
In terms of refrigerant charge volume concerns in small occupied spaces, the project’s most difficult HVAC design challenge was fitting evaporator grouping configurations to the condensing units, while not exceeding the requirements of Canadian Standards Association (CSA) B52, Mechanical Refrigeration Code, according to Shaw. Nearly $400,000 in VRF equipment costs were saved by specifying single-mode heat pumps versus models that heat or cool simultaneously, which made grouping configurations generate optimal performance and energy savings. The engineer also innovatively grouped systems together that supplied spaces with similar solar loads and exterior exposure.
“We limited the number of evaporators per system to minimize the total refrigerant charge, which further emphasizes the importance of concealing the additional piping arrays with protection duct and properly mounting the rooftop equipment for esthetics,” explained Shaw.
Other HVAC specifications included domestic hot water and snow melting handled by a trio of 2 million-Mbtu condensing boilers. Each occupant room has a backup 500-W electric baseboard heater controlled by the VRF system’s central controller, which provides web-based data and is separate from the building’s campus-wide building automation system. The three boilers also handle other campus applications.
Further adding to the facility’s sustainability was the architect’s specification of triple-glazed glass and urethane insulation.
Shaw said VRF is one of Canada’s fastest-emerging HVAC technologies, and rooftop presentation has become equally important as performance function.
“As a result of a dedicated design team that paid as much attention to esthetics as function, the rooftop HVAC condensers, equipment mounts, and lineset protection ducting are some of the project’s highlights,” said Shaw.
Alex Frean is the international sales manager at RectorSeal Corp., a manufacturer of HVAC, electrical, firestop, and plumbing materials. Before joining the company in 2011, Frean was an export sales manager for a major mini-split and room air-conditioner manufacturer for 13 years. He can be reached at firstname.lastname@example.org.