By Stan Sauerwein
The coincidence of being located adjacent to the waste treatment plant serving a small city has given Okanagan University College (OUC) in the interior of British Columbia, Canada, a chance to institute a world first.
The campus, located in Kelowna at the southern end of the province, will use about 10% of the treatment plant's daily 6.6-million gallon (30-million liter) clear water discharge to realize heating savings of £44,000 ($100,000 CAD) annually.
Integrating the option with an existing system, through the use of leading-edge heat pump technology, makes the Okanagan's £668,000 ($1.5-million CAD) energy saving initiative unique.
The campus heating system currently has 3 x 10,461 MBH Cleaver Brooks boilers in service with a sum total input capacity of 31,383 MBH. At 40 years old, the boilers are reaching the end of their life expectancy. All three boilers are dual-fuel operating. Hot water is generated at about 200-250oF (93-121oC) by the central boiler plant and distributed in three supply loops of 6-8 inches (15-20 cm). Branch mains of 2.5-4 inches (6-10 cm) run to the buildings in each loop. Inside each building, the hot water serves the secondary heating zones, where it is distributed to the heating coils in the air handling units, radiation panels, wall fin elements, convector radiation, unit heaters and force flow units.
Aidan Kiernan P.Eng., the Associate Vice President of Campus Development and Facilities Management, initiated an investigation of ways to use the clear water discharge as a heat source to meet part of the campus heating requirements through a heat pump plant application.
Temperature of the discharge ranges from 53oF (12oC) in winter to 72oF(22oC) during the extremely hot summers in this semi-desert region of Canada's western-most province. The treatment plant's effluent flow averages 5,250 GPM.
Rather than just replace existing boilers, Kiernan suggested combining a heat pump and high efficiency boiler plant to a heating system upgrade. His concept was to supply and install new heat pump chillers tied into the existing heating water distribution to act as a base load heat source. The new heat pump units would transfer heat from the discharge near the property boundary and two high efficiency Camus Hydronics DynaFlame boilers could supplement the heating requirements when the heat pumps were not able to maintain the load. One of the existing boilers could than be retained as additional back up system.
In February 2003, Kiernan approached several manufacturers who were asked to provide equipment that could provide 120oF (49oC) condenser water using 55-65oF (12-18oC) evaporator water with approximate flows around 500 GPM. It was determined that a positive displacement chiller was the only option due to the requirement of a large refrigeration lift and high condenser water temperature. This eliminated centrifugal chillers as an option. A Trane screw chiller was eliminated due to the unwillingness of Trane Canada to replace the R22 refrigerant with a more environmentally friendly refrigerant. A York screw chiller was eliminated due to a 5% de-rating of efficiency when using an environmentally friendly refrigerant and because it could only achieve a maximum temperature of 128oF (53oC).
As a result a Multistack heat recovery chiller (scroll chiller) was selected. Using R407C refrigerant, an environmentally friendly refrigerant that nullifies the need to have refrigeration detection equipment in the system, it could achieve the highest condenser temperature at 140oF (60oC).
A heat pump chiller plant building will be erected to house two chillers, each having 3,450 MBH capacities.
Originally, the campus staff had requested tapping into the clear water gravity fed discharge line from the city's 95 year-old water treatment facility. The Kelowna City Waste Water Manager, Bill Berry P.Eng. nixed that notion.
"We've got 30 million liters a day traveling out that pipe discharging into Okanagan Lake and there's no plug for it. It's going through one way or the other and there was no chance that we could take a risk that something could go wrong," he says.
"I thought the idea however was good. If they could gain the benefit of using the heat and put the effluent back colder than when it came out, that's also good from a fisheries perspective."
The city engineers have allowed the campus to tie in a new pipe from the plant's discharge chamber and return it to the discharge line after use. A set of monitors to constantly test for temperature and contaminants will be required to meet the terms of their federal environmental permits however.
Kiernan had previously been involved in two alternative heating projects at Memorial University in Newfoundland. One involved using a ground water source for a heat pump system and the other employed seawater. His experience with those projects led him to believe innovations in heat pump and chiller technology could make the treatment plant's discharge a viable base source for a similar heating system in Kelowna.
"We couldn't have done this five years ago. We couldn't have gotten the heat," he says. Traditionally, heat pumps have been able to raise water temperature to 110o F (43o C), but that was not high enough to be workable considering the existing heating system at OUC.
"We had to get 130o F (43oC)." Kiernan estimates a pay back on energy savings of eight years or less.
Other savings are being realized through various additional energy efficiencies such as an electric meters amalgamation will reduce heating cost by another $111,000.
"We're having to do a lot of technological innovation to make sure we can get the heat out of the water. Because we can't re-pipe the whole building, we're running the heating water out through the heating coils and the cooling coils during the heating season. That gives us more surface area just like bigger pipes."
A typical heating plant can handle 90% of its heating requirements with 60% of its full capacity. The new heat pump plant at OUC is expected to handle 43% of the heating load, when outside air temperature is 35oF (2oC), and a combination new heat pump and high efficiency boilers will handle the approximately 54% of the heating load when outside temperature is between 10oF (-12oC) and 35oF. Below that, the existing Cleaver Brooks boiler will hand the remaining 4% heating load.
Direct Energy Business Services of Toronto, will function as the project manager. Stantec Consulting Ltd. of Kelowna, has been selected for the engineering contract, and tendering on construction phases will begin immediately. The first contract to be let involves installation of PVC to tie-in the treatment plant and boiler system. That is scheduled for completion in December.
Kiernan targets October 2004 for completion of the entire system installation.
"The stacking chillers we'll likely be using get really high efficiency. They are very much prototype and the manufacturer has asked to use this as a demonstration site."
The project also has direct environmental benefits as well, he says. Savings in energy correspond to the elimination of 313 tonnes of green house gas emissions annually. That is the same as planting 160 acres of trees.
"It's a tremendous application because it's totally renewable." Temperature of the wastewater used will be reduced to about 7o C, so the clear water discharge going into Okanagan Lake will also be a lower temperature.
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