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Quebec City Transit Garage's HVAC Retrofit Features Solar, Heat Recovery

Five-phase project plans to provide 492,000-sq-ft facility 35% annual energy savings vs. typical gas-fired heating.

When a Quebec City public transportation maintenance garage required HVAC replacement, engineers designed a retrofit employing solar hot air, heat recovery and other energy-saving methods.

Engineers from the consulting engineering firm Genivar Inc.; solar manufacturer Enerconcept Technologies; general contractor TBC Construction; and the municipality combined talents to design an outdoor-air heating system and other HVAC components that will save the city 35% energy annually with a six-year global energy-savings payback when all five retrofit phases are completed. The savings and payback include a $3 (CAD)/m3 of natural gas rebate from the Energy Efficiency Fund of natural gas utility Gaz Metro, in addition to incentives from Natural Resources Canada.

The 492,000-sq-ft facility of Réseau des Transports de la Capitale, most of which is used for maintenance and storage of up to 600 buses, was previously using nearly $1 million (CAD) in energy annually with conventional gas-fired equipment that had exceeded its lifecycles. The majority of energy use was dedicated to heating outdoor air for the dozens of employees' indoor air comfort and for the facility’s IAQ requirements of up to four air changes per hour.

According to an energy audit by Genivar's building unit, led by the Project Coordinator Dany Hammond, T.A., LEED AP, the facility’s HVAC systems were previously using 650,000 m3 of natural gas and 11.5-million kWh of electric power annually of which 7.5–8 million kWh were attributed to heating costs. Existing equipment included two gas-fired, 400-hp boilers; one gas-fired, 250-hp boiler; and one 600-kW electric boiler supplying a variety of ceiling-hung fan-coil units combined with 30 rooftop 100% outdoor-air systems for IAQ requirements.

“This project is part of Quebec City’s green mission where conventional HVAC equipment at the end of its lifecycle is evaluated for alternative and energy efficient retrofits,” said Hammond. "A solar design, as long as it has a cost-effective payback, was encouraged by the city because it projects a green image."

Phase one
Phase one’s emphasis was utilizing wall-mounted metal Unitair and glazing Luba GL roof-mounted solar hot-air collectors, both manufactured by Enerconcept Technologies. Wall-mounted solar was preferred because of its efficiency and cost advantages over rooftop solar, therefore Hammond's design team chose 1,280 sq ft of Unitair on the 25-ft-high metal building's south wall to supply solar-heated outdoor air to one Trane 100% make-up air HVAC rooftop system. The Unitair is a corrugated metal collector with the capability of heating 12,000 cfm of air to 23°F (13°C) above the ambient temperature.

Other make-up air units located too far from the south wall would have required spiral metal duct runs too long for cost-effectiveness, therefore Genivar specified and located 3,900 sq ft of Luba GL rooftop systems near the units. There are 144 solar collectors in 22 rows with a southern azimuth and a 70-degree inclination. The Luba GL boasts a performance factor rating of 1.10, according to the Canadian Standards Association. Each Luba GL supplies 300 cfm, provides heated-air capacity of 21°F (12°C) above ambient temperatures and generates a 2.5-kW capacity on optimum solar days.

A design consideration for rooftop solar collectors is roof loading, especially with potential for causing snow accumulations in a significant snow zone such as Quebec City. However, the 111-in. x 36-in. x 8-in. (2,840-mm x 916-mm x 205-mm) Luba GL has a light weight of 93 lb (42 kg). Its patented perforated back-panel design with a felt-covered absorber increases efficiency and negates the need, cost and weight of insulation in conventional collectors. The collector also has a 36-in. (914-mm) clearance above the roof surface that does not attract snow drifting. The high profile and the absence of insulation combined with a roof structural study, commissioned beforehand by Genivar, eliminated snow and equipment load concerns, according to Hammond. Additionally, the flatness of the expansive roof and the area’s inherent high winds discourage snow accumulations, even though Quebec City is known for large snowfalls.

TBC, a multi-discipline mechanical contractor specializing in refrigeration, heating, ventilation, electrical, plumbing and medical gases, installed the collectors as well as 40-in.-diameter spiral metal ducts that supply the solar-heated air to the HVAC rooftop systems. The rooftop collectors have 20-in.-diameter branches that connect each row to the 40-in.-diameter trunk lines. All ducts are painted black to negate the need and expense of insulation. Also installed were actuators by Belimo Aircontrols USA and bypass dampers manufactured by T.A. Morrison Co.

Additional incentives for energy savings came from Hydro Quebec for lighting retrofits; kitchen exhaust and the paint room intelligent-control exhaust systems outfitted with VFDs; energy recovery of chiller heat rejection; and displacement-ventilation air distribution. Hydro Quebec provides financial aid from $0.07–$0.10 (CAD) of kWh saved.

All variable-speed equipment, dampers for the solar systems, the number of hourly air changes and general HVAC operation are controlled by the facility's building automation systems by Delta Controls and Reliable Controls. Integrating the new retrofit controls into the BAS systems was performed by Delta dealer, Regulvar; and Reliable dealer, A.C. Controles. The BAS also maintains temperature setpoints of 60°F (15°C), 65°F (18°C) and 72°F (22°C) in the bus storage, maintenance and office areas, respectively.

The free solar heat is an advantage for a facility that moves hundreds of buses through large open doorways and suffers large heat losses that are inherent to the process. Additionally, Genivar's energy study recommended replacements of older or less-efficient air curtains over bus entry doors to retain as much heat as possible.

The heat-recovery portion of Phase one used ThermoGain heat pipe, air-to-air heat-exchange technology from Innergy Tech Inc. Phase one also retrofitted exhaust-hood fan motors in the paint shop with VFD controlled by switches on paint applicators with a back-up VOC sensor.

Upcoming phases
The next three phases include another 1,280 sq ft of Unitair that will add 12,000 cfm and also 80 Luba GL units that will add 24,000 cfm for additional capacity of free outdoor-air heating. Both systems will be integrated into four more rooftop 100% outdoor-air systems. The solar equipment will also be combined with reverse-flow exhaust heat recovery technology by BKM Energy & Environmental Products.

Phase five will convert fire-tube gas-fired boilers to six 2,000-MBtu condensing boilers. Other refinements include the closed-loop existing heating system conversion to low 131°F (55°C) temperature instead of high 179°F (82°C) temperature. Additionally, 80 Luba GL rooftop solar collectors and 1,280 sq ft of Unitair wall-mounted solar will also be added to another rooftop 100% make-up air system.

The addition of solar to the retrofit gives the project an invaluable sustainable energy appeal as well as a cost-effective heating solution with a relatively short payback for the taxpayers, according to Hammond, who has previously designed several buildings with both wall-mounted and rooftop solar hot air collectors.

The Genivar team reviewed other solar alternatives, such as solar hot water, which conceivably could have the dual purpose of providing hot water to fan coils and cutting water-heating costs of bus washing. However, solar hot water would not deliver an acceptable payback.

"Compared to solar electric (photovoltaic) and solar hot water, solar hot air is definitely better value and we now review its feasibility for every outdoor-air heating project we specify," Hammond said.

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