Page 28 - Climate Control News Magazine August 2019

Heating Systems
Subway tunnels generate a lot of heat that is currently being wasted.
Researchers calculate subway heat transfer
Councils lead adoption of district heating networks
THE GLOBAL DISTRICT heating and cooling market is set to reach $AUD 46 billion by 2025.
Countries around the globe are looking at district heating systems to reduce carbon foot- prints, according to Adroit Market Research.
And while district heating has been adopted extensively in Europe it has had a relatively slow start in Australia. Overseas it is local councils that are driving the adoption of dis- trict heating systems.
For example, Växjö, a city in southern Swe- den, has been able to achieve a 17 per cent re- duction in emissions in just one year.
The city has a local district heating system that makes up 90 per cent of the city's energy. It was the local council that introduced the system, which is similar to another project that has just begun in Manchester in the United Kingdom.
Known as the Civic Quarter Heat Network (CQHN), it will generate low-carbon power, heat and hot water for the city, helping Manchester reach its carbon-neutral and zero waste goal by 2038.
Initially, the network will serve six council buildings, including the Town Hall, and save more than 3,100 tonnes of carbon emissions in its first five years of operation.
The energy centre for the network, features five flues forming a sculptural ‘Tower of Light’ which contains a 3.3MWe combined heat and power (CHP) engine and two 12MW gas boilers.
The centre will generate electricity, and harness the recovered heat from this process for distribu- tion via a 2km district heating network, which will supply heat and hot water for the buildings.
Work has just begun on the project which will be completed by the end of 2020. ✺
Manchester Town Hall will be part of the heating network which has a 3.3MWe CHP engine and two 12MW gas boilers.
SUBWAY TUNNELS GENERATE a lot of heat which is why researchers at the EPFL university in Switzerland have crunched the numbers on heat transfer in the air of train tunnels, and out- lined a geothermal heat recovery system that could potentially supply heating and cooling to thousands of nearby homes.
Accurately calculating the amount of heat in the air of train tunnels has been a difficult task, but now researchers at EPFL's Soil Mechanics Laboratory (LMS) claim to have cracked it.
The team has developed a model that al- lows them to precisely calculate the convec- tion heat transfer coefficient of a given tunnel environment.
That formula could be applied to develop sys- tems that harness the extra energy and pump it back up to the surface, where it can be used as heating (or cooling) for nearby apartments.
The concept of the technology works a bit like a giant fridge. Plastic pipes are built into the walls of the tunnel, and filled with a heat-transfer fluid – or failing that, just plain old water. Cold liquid is pumped through the pipes, where it's warmed by the air in the tunnel and emerges at the surface as a hot liquid.
In summer, the system can be reversed to act as air-conditioning. Heat can be ferried away from homes and dispersed into the ground, which tends to naturally stabilize its own temperature.
The team said the system would be rela- tively cheap and energy-efficient to install, and have an expected lifespan up to a century although the heat pumps would need to be replaced every 25 years.
The researchers applied the model to a metro line currently in-development in the city of Laus- anne, Switzerland, and calculated the potential benefits to the city.
"Our research shows that fitting the heat-re- covery system along 50 to 60 per cent of the planned route – or 60,000 sq m (645,000 sq ft) of tunnel surface area – would cover the heating needs of 1,500 standard 80 m2 (860 sq ft) apart- ments, or as many as 4,000 Minergie-certified energy-efficient units," according to lead re- searcher, Margaux Peltier.
"Switching from gas-fired heating would cut the city's CO2 emissions by two million tonnes per year." - This research was first published in the jour-
nal of Applied Thermal Engineering
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