Cooling pond Advantages and Disadvantages

Deep water source cooling is very energy efficient, requiring only 1/10 the average energy required by conventional cooling systems.Therefore, its running cost is also expected to be greatly reduced.The energy is very localized and fully renewable, provided that the water and heat discharged into the environment (usually the same lake or a nearby river) does not interfere with natural cycles.It does not use any ozone-depleting refrigerants.Depending on the cooling needs of the building and the local weather, deep water source cooling can often meet the entire cooling needs of the building, eliminating the building's reliance on mechanical cooling provided by chillers.Not only does this reduce the building's electricity requirements (or steam requirements for applications using absorption refrigeration), it also reduces reliance on evaporative cooling towers, which often harbor the deadly Legionella pneumophila bacteria.However, building operators must follow and implement proper sanitation procedures before restarting any cooling towers that remain dormant on cooler days when deep water source cooling is able to meet the cooling needs of the building..

Depending on needs and water temperature, coupled heating and cooling can be considered.For example, heat can first be extracted from water (making it cold); second, the same water can be circulated to a refrigeration unit for more efficient cold production.

Disadvantages

Deep water source cooling requires a lot of deep water around.To obtain water in the range of 3 to 6 °C (37 to 43 °F), a depth of 50 m (160 ft) to 70 m (230 ft) is typically required, depending on local conditions.The system is expensive and labor intensive to set up.The system also requires a lot of source material to build and place.Although deep water source cooling is referred to as "free cooling" in some literature, it takes a lot of energy (usually electrical) to run a pump with enough head to overcome friction and tiny losses in the distribution piping and any heat exchangers.

First major system in the United States

Cornell University's Lake Source Cooling System uses Cayuga Lake as a radiator to run its campus' central chilled water system and provide cooling for the Ithaca City School District.The system has been in operation since the summer of 2000 and cost $550-60 million to build.It cools a load of 14,500 tons (51 MW).The system has an inlet pipe length of 3,200 m (10,498 ft) with a pipe diameter of 1,600 mm (63 in), installed at a depth of 229 m (750 ft), allowing ingress at 3-5 degrees Celsius (37-41 F).Water passes through 1,200 mm (47 in) long 780 m (2,560 ft) drain back into the lake. The pipe chosen for this project was Sclairpipe, made of high-density polypropylene (HDPE).The estimated savings is an 80% reduction in the fossil fuel previously required to run a conventional electric cooling system.

First system

Deep lake water cooling system

Enwave Energy Corporation in Toronto,Ontario has operated a deep lake water cooling system since August 2004.It pumps water from Lake Ontario through a pipeline extending 5 kilometers (3.1 miles) into the lake, to a depth of 83 meters (272 ft), where the water temperature is maintained at a constant 4°C, and its temperature is protected by a layer of water covering it above, called the thermocline.The Deep Lake Water Cooling System is part of an integrated district cooling system covering Toronto's financial district and has a cooling capacity of 59,000 tons (207 MW). The system currently has enough capacity to cool 40,000,000 square feet (3,700,000 square meters) of office space.The installed deep lake cooling water inlet line has a diameter of 1,600 mm (63 in), a length of 15,000 m (49,213 ft), and an installation depth of 85 m (278 ft), allowing the use of 3-5 degrees Celsius (37 -41 F).The pipe of choice is Sclairpipe, made of high-density polyethylene (HDPE) resin.

Water drawn from the depths of Lake Ontario is not circulated directly through terminal air conditioning units within the building. Instead, the lake water is circulated through a bank of closed-loop heat exchangers to allow a net transfer of thermal energy from the heat transfer fluid returning from the building to the lake water.Chilled water in buildings is part of a closed loop district cooling system and is pumped back into the building from a centralized location where heat exchangers are installed, where it can absorb heat from installed fan coil units to provide potential and perceived space cooling.The cold water that the Enwave system draws from the depths of Lake Ontario passes through a heat exchange system and does not return directly to the lake. Instead, the water is pumped to the city's water filtration plant for treatment and distribution to residential and commercial users.

The potential of deep water source cooling

The potential to integrate lakes into district cooling (and heating) systems is firstly limited by the availability of lakes.However, other factors such as the spatial distribution of cooling demand or installation and operating costs determine the techno-economic potential of lake source district heating and cooling.