September 20, 2019
District cooling is a method for providing chilled water for indoor cooling purposes to buildings through a closed loop pipe network. In its functionality and technology, it is similar to district heating.
Chilled water is circulated via underground insulated pipes to buildings within a district and is then fed into each individual buildings’ own cooling systems through a heat exchanger. Units in these buildings then use this water to lower the temperature of air passing through the building’s air conditioning system.
Typically, a District Cooling System (DCS) comprises of a central chiller plant, a distribution network and an interface with each building’s own air-conditioning circuits.
The chilled water is usually generated at the central chiller plant through the use of compressor driven chillers, absorption chillers or sources such as ambient cooling or free cooling sourced from lakes, rivers, aquifers or the sea.
Groups of water-cooled chillers are typically installed in a central chiller plant in order to take advantage of economies of scale as well as the diversity in demand between different buildings within its district.
The chilled water is distributed to the user stations through a network of supply pipes and is returned having extracted heat from the building’s secondary chilled water system. Pumps are then used to distribute the chilled water through the creation of a pressure differential between the supply and return lines.
The user station is the interface between the district cooling system and the building cooling system and usually comprises of an air handling unit, heat exchanger and chilled water piping in the building. A user station is needed in each of the user’s building in order to connect the DCS distributed chilled water pipe to the building. Within the user station, heat exchangers transfer heat between the chilled water supply of DCS and the air-conditioning system of the building. It is possible to design the user station for either direct or indirect connection to the cooling distribution system. In the case of direct connection, the cooling water is distributed within the building directly to terminal equipment, for example, air handling and fan coil units and induction units. On the other hand, indirect connection uses either one or multiple heat exchangers in between the DCS and the building’s system.
When the water has cooled the building, it returns to the cooling plant at a higher temperature where it is chilled again and redistributed in a closed loop.
District cooling is becoming increasingly relevant as the need for clean cooling increases across the planet.
Forty percent of commercial and institutional buildings in Europe have cooling systems and that demand is growing, especially as CO2 reduction is being placed high on the political agenda. As it combines renewable and surplus energies, district cooling emits far less CO2 than conventional cooling systems and does not emits hazardous refrigerants.
The EU has placed district cooling systems high on its list of priorities and are requiring of the industry that they create even more efficiency, make better use of intelligence systems and provide a cheaper package for customers. It states that it is important to develop and deploy systems which take advantage of smart metering and control solutions together with exploiting multiple energy resources.
One of the largest District Cooling Systems in Europe is in Stockholm which can be generated by different fuel sources and techniques to generate district cooling with minimal levels of energy consumption and a low impact on the environment, in comparison to cooling through building specific facilities. The cooling generation plant is run more efficiently, based mainly on sustainable energy sources, providing free cooling. In Stockholm, the piping infrastructure measures 250 km for the district cooling network. Stockholm’s district cooling is not only an efficient way to cool buildings and industrial facilities but is also a vital part of the city’s environmental ambition to be a sustainable city, and fossil fuel free by 2040.
Around the world, District Cooling Systems are making a big difference to a number of countries’ carbon footprint. For example, a UN Report on Sustainable Development 2018, stated that district cooling systems and technologies being used in the UAE are helping to reduce the amount of energy used for cooling by around 50%.
Closer to home, the Southampton District Energy Scheme has operated in tandem with Southampton City Council for over 25yrs. It is a project that has led the way in the delivery of sustainable chilled water in the UK. The scheme, which incorporates a district cooling system, currently saves around 10,000 tonnes of CO2 emissions per annum and supports TV studios, a hospital, a university, a shopping centre, a civic centre, residential buildings and a hotel together with public and private-sector residential developments.
Many towns are based around rivers, which can be a key resource that can used to purge heat from a District Cooling Network. Furthermore, many of the world’s largest cities are located next to the sea and therefore have an infinite capacity for heat exchange with the sea water.
There are many benefits to District Cooling systems and perhaps greatest amongst these is the fact that they are five to ten times more energy efficient than conventional cooling systems. District cooling is able to reduce cooling energy consumption by anything up to fifty percent through its better energy utilization.
Furthermore, a network including electric chillers for cold storage helps to reduce peak electricity demand for cooling in urban areas by shifting production to those periods of the day and night when demand on the electrical network is low. The use of heat exchange with cold groundwater is also significantly less expensive than roof mounted chillers, which struggle to waste heat into hot air.
District cooling systems save space compared to conventional cooling systems freeing up space for other purposes. Also, district cooling with groundwater is discreet and silent when compared to air exchange chillers.
Finally, the system will last for approximately twice the length of a conventional cooling systems, which ranges from 13 to 15 years.
There is little doubt that a district cooling system using renewable resources and smart meter technology provides a significant step towards reducing the carbon footprint of air cooling.
At a time when temperatures appear to be rising generally and countries are increasingly vulnerable to periods of intense heat, it is important to have systems in place that don’t exacerbate the problem.
District cooling systems are proving effective across the globe, from Sweden to the UEA, and now with the support and encouragement of institutions such as the EU and the UN they are likely to expand rapidly, working in tandem with district heating solutions.
To learn more about district cooling and heating, simply get in touch with our expert team here at Therma-Mech.