Westhills Recreation Centre, Langford, B.C. Photo: Accent Refrigeration.
From the August-September 2015 print and digital editions, page 24
The 75,000 sq.ft. Westhills Recreation Centre in Langford on Vancouver Island, B.C. includes an NHL size indoor ice rink that operates 11 months of the year, an outdoor ice rink, and a skating trail joining the two together. It also has a 20-lane bowling alley, a restaurant and lounge, party rooms and 930-sq.m of leased office space. The outdoor ice rink is designed with embedded refrigeration piping for winter ice, and water fixtures to convert it into a children’s splash park in summer.
Accent Refrigeration Systems designed and installed the mechanical systems at the centre, which opened in 2012. In 2014, we were awarded the first place ASHRAE Technology Award for New Public Facilities for the project.
The mechanical systems for the three ice surfaces are integrated into the building HVAC system to the extent that no fossil fuels are used other than in the kitchen. Even though the complex uses an extensive amount of energy, it requires only 40% of the waste energy that is harvested. The remaining 60% is pumped 365 metres to the growing Westhills housing development as an energy source for their household heat pumps.
The project turned a typical ice arena sub-floor heating system (traditionally used for preventing frost heaves) into an enhanced geothermal field. The centre is the first in North America to use new ultra high-efficient reciprocating compressors, and the first total integration between an ice facility and an entire community. The centre is also the first in North America to use ammonia heat pumps to heat a housing community and one of only a few with ammonia-based air-conditioning systems.
Eliminating natural gas
Vancouver Island has among the highest natural gas prices in North America, so the objective of the project was to eliminate the centre’s natural gas consumption for all heating, hot water and dehumidification loads, while minimizing its electrical consumption year round. The source of all thermal energy used within the facility is warm glycol, which is harvested from the ice rink refrigeration system via an energy recovery condenser.
In order to ensure that there would be no energy gaps between refrigeration run cycles, two approaches where taken. The refrigeration compressors and brine pumps were equipped with variable speed drives. The computer controlled speed drives operate the compressors and all associated pumps at their lowest permissible speed, while precisely maintaining the ice temperature set point. This results in the compressors always operating at their maximum COP due to the low compression ratios, while the pumps benefit from the Pump Affinity Law resulting in reduced electrical consumption. The main objective of perpetuating the heating cycle is also met as the compressor run cycles are much longer throughout the day.
A very cost-effective solution to provide thermal storage between compressor run cycles was to install a modified ice rink sub-floor heating system. The system consists of 6” of R-5 insulation board between the ice pad and the heating floor, which enabled us to increase the temperature of the subfloor to 75°F from the typical 40°F, resulting in an uninterrupted energy source for the heat pumps. These operate with COP’s ranging from 4.99 to 7.6.
The outdoor ice rink, which operates from November to January, offered an interesting energy balance opportunity by providing additional waste heat during the peak heating season, just when it is needed most.
The warm glycol directly provides radiant heating throughout 19,000 sq. ft. of public space during the shoulder seasons. In mid-winter, an energy recovery heat pump boosts the glycol temperature as required to maintain comfort in all areas.
There are 15 HVAC units and two HRVs equipped with close-approach coils designed to provide heating with 95°F glycol and cooling with 50°F glycol. In very cold months, the heating glycol temperatures will automatically reset to provide sufficient heat.
The domestic hot water for the facility is provided through two stages. The first stage is free heat from the ammonia de-superheating system and ranges from 100°F to 120°F. The water is then brought up to 140°F using another energy recovery heat pump.
A custom designed ice rink desiccant dehumidifier uses a low temperature desiccant rotor that can be regenerated at 125°F, versus the traditional gas fired rotors that require 275°F. The system uses two coils in series to regenerate the desiccant wheel. The first coil is circuited for the 82°F glycol that is directly harvested from the energy recovery condenser. The second coil obtains its heat from an energy recovery heat pump.
As a result of the combined initiatives, no fossil fuels have been used in the facility other than in the kitchen since the complex was commissioned in 2012.
Air-conditioning and electrical energy efficiency
Ultra-high efficient VFD-driven ammonia compressors were installed that handle both the ice rink duty in winter and the air conditioning duty in summer. The compressors have a cooling COP of 4.62 during the ice season and a summertime air conditioning COP of 15.1. The uneven parallel configuration provides a capacity range of 15 to 120 tons, allowing them to exactly track the refrigeration load year round. With 100% of the energy being recovered, the compressors have a combined heat/cool COP of 10.2 in winter. All of the facility fans, pumps and compressors have VFDs to minimize energy consumption.
During summer months the hot water heat pumps extract heat from the 19,000 sq.ft. of radiant floors, taking advantage of both sides of the heat pump cycle. The Zamboni removes 8,000 pounds of snow per day during normal ice maintenance. When melted, this quantity of snow provides 96 ton-hours of useful cooling that helps shave the peak off the air-conditioning requirement. An enhanced surface coil in the snow melt pit has the ability to deliver 325,000 BTUs per hour of glycol to the air-conditioning system at 45°F for several hours per day, further reducing the air-conditioning load.
The pie chart shows where the harvested heat was used within the arena during a single 24-hour period in October 2012. This is a snapshot in time with the dynamic heating requirements for each load changing day to day with the various user groups, outdoor ambient temperature and humidity.
Approximately 40% of the waste energy is required within the complex and the remaining 60% is pumped 365 metres to the housing development. Once the on-site geothermal field is satisfied and all of the zones are within their programmed range, the excess heat is then transferred via a VFD driven pump to the development.
The energy transfer program is designed to maintain the ice rink energy loop at 82°F. All of the recreation centre’s excess waste heat is used by the community, which simplifies the control strategy. The average value of the energy sent to the housing development if it was natural gas would be $41,470. Two 180-ton VFD-driven ammonia geothermal heat pumps make up the balance of the energy source for the housing development. The ammonia heat pumps operate at COPs up to 15, providing a constant 60°F to the household heat pumps.
During most of the year the evaporative condenser is not used which results in an annual water reduction of approximately 750,000 gallons per year. The payback for the extra incremental cost of all the high efficient features was 2.81 years. cce
Art Sutherland, is president of Accent Refrigeration Systems, Victoria, B.C. E-mail email@example.com.