Five-phase project plans to save 492,000-square-foot Quebec City facility upwards of 35 percent of energy vs. typical gas-fired heating.
When a Quebec City public transportation maintenance garage required HVAC replacement, engineers designed a state-of-the-art retrofit employing solar hot air, heat recovery and other energy-saving methods.
Engineers from the Quebec office of consulting engineering firm Genivar Inc.; solar collector manufacturer Enerconcept Technologies, Magog, Quebec; general contractor, TBC, Quebec; and the municipality combined talents to design an outdoor air heating system combined with other HVAC components that will save the city 35-percent energy annually with a six-year global energy saving payback when all five retrofit phases are completed. The savings and payback include a $3/m3 of natural gas rebate from the Energy Efficiency Fund (EEF) of natural gas utility, Gaz Metro, in addition to incentives from Natural Resources Canada (NRC).
The 492,000-square-foot facility of Réseau des Transports de la Capitale (RTC), most of which is used for maintenance and storage of up to 600 buses, was previously using nearly $1 million 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 indoor air quality (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 to 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-percent 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’s emphasis was utilizing wall-mounted metal Unitair and
Luba GL roof-mounted solar hot air collectors both manufactured by Enerconcept Technologies. Wall-mounted solar is preferred because of its efficiency and cost advantages over rooftop solar, therefore Hammond’s design team chose 1,280-square-feet of Unitair on the 25-foot-high metal building’s south wall to supply solar-heated outdoor air to a 100-percent make-up air HVAC rooftop system manufactured by Trane, Picataway, N.J. The Unitair is a corrugated metal collector with the capability of heating 12,000-cfm of air to 13°C (23°F) 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-square feet 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 an industry-leading performance factor rating of 1.10, according to the Canadian Standards Association (CSA-International). Each Luba GL supplies 300 cfm, provides heated air capacity of 12°C (21°F) 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 2,840 x 916 x 205-mm (111 x 36 x 8-inches) Luba GL has a light weight of 42-kilogram (93-lbs). 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 914-milimeters-high (36-inches) clearance above the roof surface that doesn’t 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 Construction, Quebec City, a multi-discipline mechanical contractor specializing in refrigeration, heating, ventilation, electrical, plumbing and medical gases, installed the collectors as well as 40-inch-diameter spiral metal ducts that supply the solar heated air to the HVAC rooftop systems. The rooftop collectors have 20-inch-diameter branches that connect each row to the 40-inch-diameter trunk lines. All ducts are painted black to negate the need and expense of insulation. Also installed were actuators by Belimo Aircontrols USA, Danbury, Conn., and bypass dampers manufactured by T. A. Morrison Co. (TAMCO), Stittsville, Ontario.
Additional incentives for energy savings came from Hydro Quebec for lighting retrofits, kitchen exhaust and the paint room intelligent control exhaust systems outfitted with variable frequency drives (VFD), energy recovery of chiller heat rejection, and displacement ventilation air distribution. Hydro Quebec provides financial aid from 7 to 10-cents 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 (BAS) by Delta Controls, Surrey, British Columbia; and Reliable Controls, Victoria, British Columbia. Integrating the new retrofit controls into the BAS systems was performed by Delta dealer, R?gulvar, Quebec City; and Reliable dealer, A.C. Controles, Quebec City. The BAS also maintains temperature set points of 15°C (60°F), 18°C (65°F) and 22°C (72°F) 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., Drummondville, Quebec. 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.
The next three phases include another 1,280-square feet 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-percent outdoor air systems. The solar equipment will also be combined with reverse flow exhaust heat recovery technology by BKM Energy & Environmental Products, Hartford, Conn.,
Phase Five will convert fire tube gas-fired boilers to six 2,000-MBtu condensing boilers among other refinements, such as the closed loop existing heating system and convert to low 55°C (131°F) temperature instead of high 82°C (179°F) temperature. Additionally, 80 Luba GL rooftop solar collectors and 1,280-square-feet of Unitair wall-mounted solar will also be added to another rooftop 100-percent 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 wouldn’t 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.