Published September 19, 2006
Deep water cooling involves using naturally cold water as a heat sink in a heat exchange system, thereby eliminating the need for conventional air conditioning. We compare deep water cooling systems in Halifax, Nova Scotia and Toronto, Ontario, and find that this technology has significant ecological benefits and long-term economic benefits. This technology requires that a client with a large cooling need is situated near a deep, cold body of water, and payback times vary depending on the site. Diffusion is hindered by the low cost of energy. The City of Toronto's approach, in which many buildings are serviced at once while piggybacking onto existing water piping and pumping capacity, can deliver cost savings on a shorter time span. Other locations in which heavy air conditioning users are located next to deep, cold water bodies could use this technology to encourage sustainable building.
Sustainable Development Characteristics
In many areas of the world including North America, air conditioning imposes a significant load on local electrical systems. Air conditioning is required even in temperate areas, as technologies such as lighting and electronic equipment produce significant indoor waste heat that must be vented to the outdoors. Cooling can be particularly troublesome as it is thermodynamically more difficult than heating and demand is intermittent; air conditioning demand can trigger summer brownouts and voltage drops on hot summer afternoons. Air conditioning currently consumes 18 percent of US electrical output (Cox, 2006); any technologies that can considerably lower the energy demand of air conditioning will create a significant drop in electrical use and mitigate the associated environmental concerns of greenhouse gas emissions and local air pollution.
Conventional air conditioning functions by transferring heat from the air to a chilled medium, and then uses a compressor, motor, and refrigerant to transfer the heat from the chiller medium to the outdoors. If it is warmer outside than inside, heat must be pushed “uphill”, a very energy intensive operation. Significant energy savings can be realized if heat can instead be transferred to a mass of cooler material with a high capacity for absorbing heat, such as water, eliminating the need for a compressor-based cooling cycle. Water is not only a good heat sink, it also has an unusual relation between its density and its temperature. Like most substances, water becomes denser as it cools, but unlike most substances it reaches a maximum density at 3.9 degrees Celsius. As a result, in winter, cold water on the surfaces of oceans and lakes cools and sinks through the warmer water below. In summer, the warm surface layers float on top of the cooler water below, as it is less dense. A layer of perpetually cold water is created below a certain depth, known as the hypolimnion.
Over the years, there have been many suggestions on how to utilize this cold water; for an exploration of some of these suggestions, see (Lennard, 1995). One of the simplest applications, however, involves pumping hypolimnion water to the surface and using it as a heat sink. Hypolimnion water would be pumped from the water body and into a heat exchange unit where it comes into contact with a closed cooling loop. The heat exchanger takes the place of the traditional “chiller” or air conditioner.
Energy savings of up to 90% over conventional air conditioning can be achieved, depending on how the system operates. The system requires only the energy to run the pumps and the fans that blow air over the cooling loops. As conventional air conditioning units are no longer needed, the need for ozone harming chemicals such as CFCs would be eliminated.
Though the impact of deep water cooling is generally positive, some concerns have been raised that, if overused, the cold water source could experience “heat pollution”, which would negatively affect habitat and species composition. In the oceans, such effects might occur at the local level, but the amount of heat involved is too small to have a large scale effect. Lakes are another matter. A study of Lake Ontario estimated that up to 20,000m3/s of water could be withdrawn from the lake and used for cooling without changing its physical properties (Boyce et al, 1993). For the Great Lakes, the maximum draw amount is very large. The maximum amount will be lower for smaller lakes, however, and must be taken into account in discussions on the sustainability of deep water cooling using lake water. The projects discussed followed established procedure for construction in coastal area, but long-term effects might not yet be known.
The opportunities in Canada for expanding deep water cooling are quite large. Both Halifax and Toronto could greatly increase their use of this technology without creating a serious environmental hazard. Other cities that could take advantage of this technology include Victoria, Vancouver, Prince Rupert, Hamilton, Yellowknife, Kingston, and St. Johns. As well, there are hundreds of smaller centres located next to deep bodies of cold water that could utilize this form of cooling. One of the theoretical barriers to future expansion is what Gregory Unruh calls “carbon lock-in” (2000), as energy technologies have co-evolved to require carbon-based fuel and their return-on-investment increasingly favours large scale technologies and discourages the diffusion of non-carbon options, even if economically sound.
Critical Success Factors
Success in both of the study cases hinged upon the private-public partnership model. This model provided the means to overcome the high up-front costs associated with this technology.
In the City of Toronto case study, what really pushed the project forward was the pairing of deep water cooling and deeper water intakes for the drinking water supply. In effect, two major projects were combined into one, a good use of holistic planning processes that differed quite a bit from more traditional planning processes where different infrastructure needs are considered separately. Enwave’s Kevin Loughborough reported that this is the first such combination of uses with this technology. Toronto’s success was also supported by the establishment of Enwave as a “middleman”. Individual developers didn’t have to install the infrastructure, they just had to make the choice to hook into the cooling network. The Toronto project succeeded as it had support from individuals in government and in business. The Purdy’s Wharf project went forward because the developer was willing to take a risk on fairly new technology. The projects' “champions” worked together to move their projects over various hurdles.
Community Contact Information
Enwave can be contacted through their press office at http://www.enwave.com/contact_us.php; the corporation is interested in developing other deep water cooling projects. Purdy’s Wharf is a private development.
Each project achieved its goal to significantly lower energy use. Economies of scale seem to be applicable here as well; larger projects might be more practical as a bigger cooling load can be displaced with a similar initial infrastructure layout. Each building that hooks onto the Enwave system lowers the cost per displaced kWh. The larger and newer project in Toronto, which continues to expand, has attracted more attention partly due to its location in a city experiencing significant smog problems and electricity shortages. The Purdy’s Wharf project, however, demonstrates that, in certain situations, deep water cooling technology can also work successfully on a smaller scale.
What Didn’t Work?
The Purdy’s Wharf project did not create a widespread adoption of the technology even though it is considered a successful project. This probably was due to the low cost of energy at the time of the project, a lack of comparable projects, and as it was one of the first in the world. Also, a developer wanting to mimic the Purdy’s Wharf project would have to start from scratch as the infrastructure has capacity for only the one development. One could say that deep water cooling has now hit a “critical mass” of sorts with several large projects in the planning phase, including projects in Hawaii and the Persian Gulf. Kevin Loughborough says the main factor in a successful deep water cooling project is geography. Key ingredients for successful projects are a high density cooling cluster located near a renewable cooling resource.” (Loughborough, per. comm.)
Financial Costs and Funding Sources
The Purdy’s Wharf project was funded jointly as a demonstration project by the development company, JW Lindsay Enterprises Limited, and the federal government. Reports of the costs vary, but there is a general agreement that the cooling system paid for itself in a little over two years. Currently, the cooling system saves the complex over $100,000 in energy costs and maintenance costs. The largest expense is the pumping cost, plus the minor expense of copper anodes.
Toronto Deep Lake Water Cooling
The Toronto deep lake water cooling project was a major project with initial expenditures near the $200 million range (Canadian Press, 2003). Capital costs continue as the urban pipeline network expands. The project was a public-private partnership: $33 million was funded by the City of Toronto’s pipe repair fund (Moloney, 2004), the federal government provided low-interest loans, and Toronto Hydro provided incentives to companies to hook their buildings up to the system in order to overcome the high initial capital cost. Kevin Loughburough of Enwave commented on the up-front costs:
“The pay back on the project requires a patient investor. It can be compared to a hydroelectric dam project in that it is capital intensive at the front end, but costs very little to operate over the long-term. The return on the project is competitive with other investments.” (Loughborough, per. comm.)
This case study involved interviews and a literature search. It reveals that deep water cooling projects deliver impressive energy savings, but that initial investment is high and serves as a barrier to development. The case studies suggest that large-scale installations of this technology are better positioned to overcome the inertia of the high start-up cost and high payback time. An intermediate agency that bears the infrastructure costs and the initial risk can be useful in encouraging developers to use the technology. Sites with year-round access to deep water cooling might be preferable, and support for start-up costs is a major factor in the success of these projects.
Detailed Background Case Description
This case study involved a background literature search and the investigation of two deep water cooling projects in Canada. The first project is the Purdy’s Wharf project on the waterfront of Halifax, Nova Scotia, which was constructed in 1986 and expanded in 1989. The second project is the Enwave Corporation’s Toronto Deep Lake Water Cooling Project, which began to provide cooling to buildings in 2004 and continues to expand.
The two projects are both public-private partnerships, but represent vastly different scales of application of the technology. The cooling media is also different. Purdy’s Wharf draws upon seawater and Toronto’s project uses fresh water.
The Purdy’s Wharf office complex sits on the waterfront of Halifax, and buildings extend out over the harbour on pilings. Cold seawater is drawn from the bottom of the harbour through a pipe to a titanium heat exchanger in the basement of the complex where the closed loop of water, cooled by the sea water, is then pumped to each floor of the building where fans blow air over the cooling pipes to cool the air. The seawater is returned to the harbour floor. The project was jointly funded by the Government of Canada and the building’s developer, and was intended to serve as a demonstration of the technology. The project was constructed from 1983 to 1989 and consists of an 18-story tower, a 22-story tower, and a four-story retail centre. The total area cooled by the system is 65,000 sq. meters.
The Purdy's Wharf Deep Water Chiller
Purdy’s Wharf required innovative technologies in order to mitigate the corrosive power of seawater. Piping is corrosion-resistant polyvinyl and polystyrene. The pumps are made of stainless steel. One of the challenges to this project was to control marine growth. Initially, chlorine was used to prevent marine growth in the system, but this was both costly and potentially environmentally damaging. The chlorine system was replaced by cathodic protection provided by copper plates.
To provide proper cooling, the water temperature must be below ten degrees Celsius. The intake for the pumping system is located less than two hundred meters offshore at a depth of 18 meters where conditions are appropriate for cooling for ten and a half months a year. Purdy’s Wharf operates conventional chillers in the late summer when harbour temperatures are too high. Mapping of the harbour water temperature column was provided by the Bedford Institute of Oceanography and the Fisheries and Oceans Research Lab.
Toronto Deep Lake Water Cooling
The Enwave Corporation’s deep lake water cooling project is a much larger project than the Purdy’s Wharf initiative. Pipes extend five kilometers into Lake Ontario and draw water from a depth of 83 meters to the John Street pumping station where heat exchangers cool Enwave’s closed cooling loop that snakes through downtown Toronto. Lake water, slightly warmed, then goes on to supply Toronto with drinking water. This sharing of drinking and cooling water saves pumping water out of the lake twice, and the new deeper water intake solved the problem of algae blooms tainting Toronto’s water in the summer. The idea of providing cooling to Toronto using lake water had been considered at various times, but the project began in earnest in 2002 (Deverell, 2002). As of June 2006, 46 buildings were signed onto the system of which 27 were already connected (City of Toronto, 2006). As the system nears capacity, energy savings will be 85 million kWh, for a CO2 reduction of 79,000 tonnes annually, or the equivalent of 15,800 cars. The total cooling load will be 3,200,000 square meters, or fifty times the area of the Purdy’s Wharf complex. 61% of this capacity has been sold. (City of Toronto, 2006). There is some discussion to expand the system once capacity is reached. Energy savings are about 90%, and as the required cold water is available year-round, the need for supplementary chilling is eliminated. The Toronto project is jointly-owned: 57% by the municipal pension fund and 43% by the City of Toronto, and is thus an example of a public-private partnership.
Does the outfall of warm water cause ecological damage in a Halifax-style project?
What mechanisms could best encourage this sort of project? An end to energy subsidies, a carbon tax, grants, or further public-private partnerships?
- Would more demonstrations projects help to speed the diffusion of innovative infrastructure choices?
Resources and References
Boyce, F, Hamblin, P, Harvey, L, Scherzer, W, & R. McCrimmon. 1993. 'Response of the Thermal Structure of Lake Ontario to Deep Cooling Water Withdrawals and to Global Warming.' Journal of Great Lakes Research 19(3) 603-616.
Candian Press, 2003. “Lake Water to Cool Downtown” Toronto Star. Feb 28, E11.
City of Toronto “Deep Lake Water Cooling and the City”
Cox, Stan 2006. Air Conditioning: Our Cross to Bear. AlterNet.
Deverell, J. 2002. “Enwave Launches Deep-Lake Cooling Project” Toronto Star. June 20, B02.
Lennard, D. 1995. 'The Viability and Best Locations for Ocean Thermal Energy Conversion Systems Around the World.' Renewable Energy 6(3) 359-365.
Molony, P. 2004. “Pipe Funds Diverted” Toronto Star, May 24, B02.
Unruh, G. 2000. 'Understanding Carbon Lock-in.' Energy Policy 28, 817-830.