By employing a natural refrigerant with a zero GWP and superior thermodynamic properties, ammonia-based refrigeration systems are intrinsically good for the environment. But the environmental benefits of such a system don’t have to stop there.
Dufferin Arena, in Stratford, Ontario, Canada, not only uses an ammonia chiller to maintain its ice rink, but also leverages the waste heat from the system (1,200MBH at full-load capacity) to drastically reduce its reliance on natural gas. In addition, the arena makes use of an “ice battery” during the winter to reduce its use of the electrical grid, and employs variable-speed drives (VFDs) for Bitzer compressors and cooling-tower fans. The building also features a “green” roof garden, polymer glass for daylighting, and lighting upgrades; solar panels are in the plans for 2021.
Originally the site of an outdoor rink, the Dufferin Arena was built in 1971 and remodeled with its current refrigeration system – the Eco Chill low-charge (130lbs) ammonia chiller from Canadian manufacturer/contractor Cimco, with a capacity of 80TR (281kW) – in 2010; the remodel expanded the facility from 20,000ft2to 30,000ft2. It was recently the subject of a webinar hosted by Cimco.
“The existing facility when I came in 2009 was horribly inefficient and needed upgrades to bring it to modern standards; it was a real energy pig,” said Jim Bryson, manager of community facilities for the city of Stratford, during the webinar. He also oversees three other ice rinks in Stratford as well as an art gallery, swimming pool and other facilities.
The upgraded refrigeration technology, along with other efficiency measures, has cut Dufferin Arena’s annual electricity bill by about CA$53,000 (US$38,463) – more than 50% – compared to another comparably sized, single-rink arena in Stratford.
In terms of natural gas, the use of heat from the refrigeration system cuts annual natural gas costs by about CA$6,000 (US$4,355), approximately two-thirds, compared to the other arena.
In its use of heat reclaim, the Dufferin facility is staking out relatively new ground among ice rinks “Typical arena refrigeration systems do not have heat recovery, and are wasting all of that free heat and dumping it out of the condenser,” said Brad Wilkins, Cimco’s U.S. Recreation Project Team Lead, during the webinar.
The Dufferin Arena’s energy upgrades represent one step in Stratford’s goal to generate net-zero emissions by 2035. “That’s a very aggressive target, and it may be affected by what we’re doing today with COVID-19,” said Bryson. “However, it’s achievable, and comes down to retrofitting a lot of buildings.”
Heat reclaim plus ice battery
The Dufferin arena uses three Alfa Laval plate-and-frame heat exchangers to execute heat reclaim. (Another is utilized for chilling the glycol via ammonia evaporation.) The first heat exchanger receives hot ammonia gas from the compressors, which sheds the heat to glycol returning from the ice rink. The hot glycol is then used to heat the dressing room and hallway area, to melt snow and ice gathered by the Zamboni in the snow-melting pit, and to warm a concrete path used by the Zamboni.
The hot glycol is also channeled to a second heat exchanger where it pre-heats potable boiler make-up water. Finally, the hot glycol is sent to a third heat exchanger where excess heat is rejected to water, which is directed to a rooftop Evapco water tower.
To reduce the energy consumption of the compressors, the facility maintains a Cimco ice battery – a large insulated container filled with ice – on the roof. During the winter, when temperatures in Ontario drop below -15°F (-26°C), glycol can be chilled in the ice battery rather than through the chiller system, and channeled to the ice rink. “Only if [the rink] doesn’t capture the desired temperature will the compressors kick on,” said Bryson.
However, since the ice battery system doesn’t generate waste heat, a small back-up boiler using natural gas steps in.
The rehabilitation of the Dufferin Arena cost CA$4 million (US42.9 million), half of it coming through the Canadian federal government’s Recreational Infrastructure Canada (RinC) energy-efficiency program. The refrigeration system itself, including heat reclaim, cost about CA$930,000 (US$675,000).
In obtaining the other half from the city government, Bryson presented a year-by-year breakdown in the operational cost savings of the project over 75 years, compared to that of the existing facility. He applied RETScreen clean energy management software to do the calculations. “Where a lot of project managers fail is they just talk about the [initial] capital cost, not what it’s going to cost over 75 years,” he said. “When you show why this is cheaper, then the politicians start to understand.”
Bryson encourages municipal managers and other not to give up on ambitious projects. “You’re going to be challenged by people who don’t have your vision,” he said. “But when you are told no, try and try again.”
“Where a lot of project managers fail is they just talk about the [initial] capital cost, not what it’s going to cost over 75 years.”Jim Bryson, city of Stratford, Ontario, Canada