Geothermal Heat Pumps

Geothermal Heat Pumps Add to Natatorium’s Efficiency

Quebec Aquatic Centre Boasts LEED Benefits through Green Technologies

November 4, 2013
Trans

The city of Côte Saint Luc’s new $18 million Aquatic and Community Centre could easily qualify as a Leadership in Energy and Environmental Design (LEED®)-certified silver project. The facility’s HVAC strategy, for example, far surpasses many national energy-efficiency code requirements and equates to tens of LEED credits. The 45,000-square-foot facility employs a 500-foot-deep geothermal field, exhaust-air heat recovery for preheating outside air, dehumidifier compressor heat recovery for efficient pool water heating, and is recognized as one of Canada’s first natatoriums to use a cutting-edge reduced refrigerant HVAC dehumidifier strategy.

The state-of-the-art technology is a residual of design ideas from a LEED-certification goal the city withdrew early in the planning process. While state-of-the-art green technology typically carries a higher upfront price tag, the city will achieve a quick four-year payback, saving millions of dollars in energy costs over the lifespan of the facility.

“The city realized there could be unprecedented savings in operational costs by using the original LEED-inspired designs,” said Stéphane Maccabée, P.Eng., project manager, Kolostat®, Laval, Quebec, Canada, a design installation and service mechanical contractor. Maccabée led a Kolostat design/build team with Michel St. Pierre, P.T., LEED AP, estimator/designer; and Daniel Robert, P.Eng., vice president-engineering.

Kolostat’s design was also coordinated with a joint-architect venture between Rubin & Rotman Associates, Montreal, and Martin Marcotte/Beinhaker Architects, Mon-
treal; general contractor, Pomerleau, St. Georges, Quebec; and The Master Group, Boucherville, Quebec, a manufacturer’s representative for natatorium dehumidifier manufacturer, Seresco Technologies Inc., Ottawa, Ontario, Canada.

The HVAC technology leading the project’s environmental stewardship is the energy recovery dehumidifiers from the new Protocol NP-Series by Seresco. Named for the 1997 Kyoto Protocol environmental treaty, the NP-Series delivers an annualized operating cost reduction of 5-7 percent. Instead of an all-refrigerant design, the dehumidifiers use heat exchangers and environmentally friendly glycol for heat rejection to the water-source loop.

Using glycol eliminates the liabilities of perpetually rising refrigerant and maintenance costs associated with systems holding large refrigerant charges.

Pool water heating is supplied by a coaxial-type heat exchanger using recovered waste heat from the two Seresco dehumidifiers’ refrigeration circuits, which are required for dehumidifying the space to a comfortable 55 percent relative humidity (rh). If pool water heating is satisfied, the remaining heat is rejected to the geothermal water-source loop or into supply air for reheat. On subzero days, when pool water heating isn’t 100 percent satisfied by heat recovery, the 96 percent efficient backup condensing boilers by Camus Hydronics Unlimited, Mississauga, Ontario, Canada, are activated.

Throughout the summer months, heat rejected to the water-source loop is stored in the six-well, 500-foot-deep geothermal field for use later in the heating season. The water-source loop, which averages temperatures over 80°F in the summer and provides almost all the heating for domestic hot water and locker room showers, also uses two rooftop evaporative cooling towers by Baltimore Aircoil Co., Jessup, Md., to reject any excess heat not required within the complex.

The geothermal loop’s operational and redundant 20-hp pumps by Taco Inc., Cranston, R.I., use Danfoss VLT, Milwaukee, variable-frequency drives (VFD) to operate at only the needed flows. For example, when the heat pumps or dehumidifiers are not requiring cooling or heating, the VFDs ramp down the pumps’ water flow for further energy savings.

The Kolostat design uses an option provided by the dehumidifier manufacturer for exhaust air energy recovery. This recovered energy is then used for pretreating the code-required outdoor air. Most codes adopt ASHRAE Standard 62 to ensure adequate outdoor air for the facility and IAQ for the patrons. Cold outdoor air is expensive to condition most of the year, therefore the payback on the option is typically less than a year. The energy recovered from the warm energy-rich 85° pool exhaust air is used to preheat colder incoming outdoor air as high as 40° warmer than the ambient, via a unit-mounted heat exchanger.

All systems are monitored and controlled by a BACnet-based building automation system by Automated Logic, Kennesaw, Ga., that was supplied, installed, and programmed by Kolostat. Single-compressor/dual-stage heat pumps by ClimateMaster Inc., Oklahoma City, also efficiently provide conditioned air, based on occupancy.

Two Pools, One Room, Many Windows

A primary HVAC challenge was designing a two-pool community natatorium where seniors, families, and competitive swimmers could congregate, but also experience comfortable individual water and air temperatures in the same room.

The 6,800-square-foot, 25-meter competition pool and 3,133-square-foot recreation pool have their own dedicated 30-ton dehumidifiers that provide set point water temperatures of 80° and 86°, respectively. Both the 25,000- and 13,000-cfm dehumidifiers are programmed to supply 85° air temperatures. While ASHRAE natatorium standards recommend a 2° air and water temperature differential to minimize pool surface evaporation, the design concept can be problematic when both pools are in the same space.

The ventilation system consists of several royal blue fabric ductwork systems manufactured by NAD Klima, Sherbrooke, Quebec, Canada. The competition and recreation pools have their own respective dedicated perimeter systems even though they share the same space. Duct sizes vary between 24-36 inches in diameter. The competition and family pool areas have 400 and 160 linear feet of perimeter ductwork that’s 25- and 18-feet high, respectively.

Kolostat, which won an honorable mention in the 2012 ASHRAE Technology awards for a Bell Canada office building energy design, worked closely with the architects to ensure synergy between the architecture and mechanical systems. For example, a 150-foot-long, 20-foot-high wall of windows was challenging because glass is difficult to keep dry and condensation free in Montreal’s ASHRAE winter design condition of -11° with extremes reaching -30°. Kolostat, which has designed many pool facilities, requested exterior window mullions so as not to block airflow critical for keeping the windows condensate-free. Fabric ductwork positioned closely to the windows include strategically placed linear diffusers that bathe the glass and deck surfaces with warm dry air. “We have designed many natatoriums that all have had under-the-floor air distribution, so we were initially concerned when the construction design team opted for overhead air distribution,” said Robert. However, the client has reported no problems with condensation or fogging on the windows after one full winter season.

Besides energy efficiency, Kolostat also delivered on the city’s request for quiet indoor and outdoor operation, because of the facility’s tranquil residential neighborhood setting. Only the evaporative coolers are outdoors on the roof. All heat pumps are indoors and the large 30-ton dehumidifiers were painstakingly rigged into an indoor mechanical room after the building structure was completed.

As part of the contract, Kolostat will guarantee the performance of the equipment it specified as well as monitor and maintain it over a five-year period. The “pay now” strategy city officials built into the facility ranks it as one of the most energy-efficient natatoriums in Quebec and will reap long-term benefits over the building’s expected 70-year lifecycle, said Robert.

SIDEBAR: Advantages of Glycol

The refrigerant circuit of a dehumidifier that uses glycol as a heat-rejection transfer fluid is compact, factory-charged, and sealed, which eliminates onsite refrigeration work by EPA-certified technicians. In multiple compressor units, the fluid-cooled circuits are combined into a single manifold set of PVC pipes to the fluid cooler (dry cooler).

Glycol is often less expensive than refrigerants. With refrigerant prices and management costs perpetually rising, a system with hundreds of pounds of refrigerant carries considerably more risk management liability than a glycol-based system.

Glycol systems can be piped to nearly infinite lengths and height levels that are only dependent on proper pump horsepower sizing and hydraulic design considerations. Conversely, onsite placement of a conventional DX system’s condenser and dehumidifier may be limited before refrigerant and oil management issues are encountered.

Glycol system installation labor and material costs are considerably less, since the required copper line sets needed for each DX circuit can be substituted with a single PVC or CPVC piping set on glycol systems.

Glycol is an environmentally preferred heat transfer liquid that can add to Leadership in Environmental and Energy Design (LEED) credits in applications where freeze protection of the thermal fluid is required.

Eliminating exterior copper minimizes exposure to the recent trend of copper theft.

Article courtesy of John Parris Frantz; an account executive for Seresco Technologies Inc. Contact him at John@jpfcomm.com.

Publication date: 11/4/2013 

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