Carrier Solutions for District Cooling Systems
The thermal energy required for heating and cooling purposes is produced by systems that require the combustion of fossil fuels. Foes associated with thermal energy production, include among others, oxides of sulphur, nitrogen and carbon. Such emissions contribute both locally and globally, to the background level concentrations that result from all the air emission sources, and together result in negative environmental impacts such as global warming, acid rain and poor local air quality. In addition, chilled or cooling water production systems, in most applications to date use electrically driven compressor chilled water production systems that require refrigerants such as chlorofluorocarbons (CFCs). These chemicals are thought to be the primary contributor to ozone layer depletion in the upper atmosphere.
With heating and/or cooling systems, much electric power is required to operate fans, pumps, cooling system compressors, and in some cases, heating coils. Such power is typically generated by hydro, nuclear, fossil fuel fired power generating plants, or a combination of all three. In the case of the fossil fuel fired power plants, the combustion process results in harmful emissions and impacts as described previously.
In the case of nuclear power plants, disposal of radioactive wastes and releases of radioactive material to the air and water systems during process upsets are a major source of concern. Even hydro-electric power plants are being identified as possible sources of pollution problems, and negative environmental impacts, that result from the loss of agricultural, wildlife habitat, and forest lands and flooding and impacts that result from the build-up of the concentration of mercury in the environment upstream of hydro dams.
Thermal power generation plants (nuclear and fossil fuel fired) also discharge large quantities of waste heat to the environment (via air and/or water) from the steam turbine condensing system portion of the plant. With the above, it is apparent that heating and cooling systems that minimize the quantity of fuel and electrical power required to meet the users needs will result in reduced negative impacts on the environment.
It should be noted that the combustion process and CFC refrigerant based thermal energy systems represent the most prevalent systems used throughout the industrial world, from the household level up to major power production plants. While DHC plants are not immune to the production of pollution causing emissions, the nature of operation of these plants is such that significant reductions in the pollutants emitted can be realized, compared to the other widely utilized alternatives.
District cooling is the most sustainable solution. A district cooling system can offer significant benefits to property/building owners, the municipality, and society at large. That’s because the refrigerant (chilled water) for conditioning systems is supplied directly, whilst the building is free of its own cooling centre and attendant infrastructure. A district cooling system allows the building owner to eliminate on-site chiller operation and maintenance.
By doing this, the building owner no longer needs to purchase utilities. For future buildings that are constructed or existing structures under restoration, especially multifunctional, the overall capital costs are reduced, when the cost of the chiller room is eliminated; or the space allocated to the building chiller may be converted to revenue generating space. The structures look more attractive, because, for example, there’s no longer need for erection of cooling towers on roofs or within stylobates. Maintenance and staff costs also decrease.
The developers enjoy the benefits of less extensive power utility network. Chill production for conditioning system is paid by the owner of district cooling system, as well as construction works and routine maintenance. There’s no need to pay for upgrading of energy transfer station, if more cooling efficiency is required. Overall, the reliability provided by a properly designed and constructed district cooling system is greater than most buildings can achieve individually.
District cooling is a system in which chilled water is distributed in pipes from a central cooling plant to buildings for space cooling and process cooling. A district cooling system contains three major elements: the cooling source, a distribution system (piping and collectors), and customer installations (fan coils, cooling heat exchangers of central conditioners, cooling beams etc.), which also referred to as energy transfer stations (ETS).
District cooling systems can be subdivided into three groups based on supply temperatures:
• Conventional chilled water temperatures1: 4oC (39°F) to 7°C (45°F)
• Ice water systems: +1°C (34°F)
• Ice slurry systems: –1°C (30°F)
This report focuses on the conventional and ice water based chilled water systems, which are generally designed for a maximum pressure of 1030 kPa (150 psig). A brief general discussion on ice slurry system technology is also included.
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ext by Michael Terekhov, Cand. of Tech. Sciences, key appraisal engineer at AHI Carrier Moscow