Vancity Goes Green With HVAC
By Ted Barker
When Vancouver City Savings Credit Union (Vancity) was looking to replace the aging 70 per cent efficient HVAC system at its head office, it brought in SES Consulting and a team of industry suppliers to find a way update and optimize the efficiency of the boiler plant.
The 12-storey, 115,000 sq. ft. office tower in downtown Vancouver houses the credit union’s management, administration and support staff, as well as a large data centre that has a need for year-round cooling.
Looking for novel solutions, Scott Sinclair, president and CEO of SES, proposed installing a heat recovery chiller that would be used to capture the waste process heat load from the third-floor data centre to heat the entire building.
SES used a year-long BC Hydro-sponsored continuous optimization study and applied those insights to first drop the base operating temperature of the heating system by a minimum of 30°C, or 37.5 per cent. Next, SES produced a feasibility study detailing the potential energy savings of a heat reclamation system.
That helped secure $85,000 in funding toward the project from Fortis BC.
The Vancity Centre
: Retrofit update of space & water heating system
: Vancouver, BC.
: 12 storey, 115,000 sq. ft. office tower built in 1995.
: The Vancouver City Savings Credit Union
At the core of the retrofit is an 80-ton helical rotary heat reclaim chiller that features only two rotating parts. It uses a low-speed direct drive compressor, and manages a heat recovery efficiency rating in the range of 4.2 COP at 60°C.
When the heat recovery chiller was being installed, a pair of one horsepower constant volume pumps was also installed, to circulate the water from the existing hydronic loops to the new heat recovery chiller.
”One serves the condenser side of the chiller, and one serves the evaporator side,” explains Chris Goodchild of SES.
Vancity opted to replace the original 2,500,000 BTUH boilers with smaller 720,000 BTUH boilers in a second phase of retrofitting. Thanks to the success of the reclaim system, the company found there was no need to stay with such large boilers, since they are now rarely used, and are essentially employed as a backup heating system.
”And even then, the boilers are only used to top up the waste heat recovered from the data centre,” adds Goodchild.
Thanks to the energy efficiency improvements with the new system, all costs are expected to be recouped in as little as 4.5 years.
IDENTIFYING THE POTENTIAL
Although heat reclaim systems are becoming more common in new buildings, many over-specified older buildings with higher temperature systems or available waste heat may be able to incorporate heat reclamation technologies into their planned system improvements.
According to SES Consulting, there is a simple way to assess whether a building has a waste heat problem. When you observe flue gas exiting a chimney while simultaneously noting water evaporation in the cooling tower, it is time to seek out some professional advice.
For a heat reclaim chiller to be a good option, Doug Robertson of Trane Canada advises that simultaneous heating and cooling loads are required. In this building, the data centre was a heat source that could be farmed, since it generated residual heat that would otherwise be vented into the atmosphere or offset by a cooling system.
”Sometimes people assume there is not simultaneous heating and cooling if the chiller is not running. For example, if the building is ‘free cooling’ with a waterside economizer or with air-side economizers,” he explains. ”In both cases, heat is being rejected from the building, either though the cooling tower or though exhaust air. In these cases, capturing that heat with a heat recovery machine makes sense. A data centre in the building is a great source of waste heat.”
Vancity was designed with separate cooling and high-temperature heating systems, which helped to make this project feasible because the waste heat was accessible.
”Each project is unique,” says Robertson. ”Some projects are more difficult to install, for many reasons, so the threshold of available heat might be higher on those projects. Other factors come into play, such as: How long do the simultaneous cooling and heating loads persist? Does the heating load exist in the summer? How large is the cooling load in the winter?
”Another big factor is the temperature of the heating and cooling loops. Hotter water temperatures may reduce the COP, which can negatively impact paybacks.”
HOW IT WORKS
The heat recovery chiller at Vancity boosts the low-grade waste heat that is generated by the data centre, taking it from 20°C to a useful optimal system temperature of 50°C, before sending it back into the building where it can be used where it is needed.
This has the effect of reducing cooling tower fan and pump usage, which offsets much of the energy required to operate the chiller while also significantly reducing water consumption.