From Nuisance to Nurture: Using Residual Heat for Low-Temperature Local Heating Systems in Cities

According to the Paris Agreement, cities need to be carbon neutral by 2050. This entails a dramatic transition from a fossil fuel based built environment to one entirely running on renewable energy. In many European cities this means moving away from natural gas as prime source. At present, three options are generally considered as alternatives to a fossil energy system: (1) all-electric, using solar or wind power and solar heat or heat pump systems, (2) district heating, using high-temperature industrial waste heat or geothermal heat, (3) green gas, which can be biogas or synthetic gases as green hydrogen or synthetic methane. In addition, hybrid solutions are also an option.

Which of the sustainable alternatives is most suited strongly depends on the urban plan, building typology and technology used so far. Districts with a great extent of repetition can be easier renovated to a net zero-energy plan than an area with a great variety of building types. High-density districts are suited for relatively expensive district heating. Districts that are neither are usually designated for a green gas-based system. The problem however is that few cities can produce sufficient biogas or do not have a renewable power over-production to generate synthetic gases. This in particular applies to historic city centres.

The 17th-century inner city of Amsterdam is facing a similar problem. The municipality decided to keep this part of the Dutch capital connected to the gas grid, but under the condition that the demand for gas would be reduced by 70%, as to enable usage of locally produced green gas. However, with a great share of listed buildings – a large part of the inner city of Amsterdam is Unesco World Heritage – such a reduction in heat demand is virtually impossible. Or is it?

From various studies it is known that the old city centre has considerable sources of renewable heat, among which residual heat from cooling processes and exhaust air. This heat is now released into the air, disturbing the temperature in the city and getting lost for other purposed. In the research project presented, sources of renewable heat and residual heat were investigated, quantified and proposed as feed-in for a low-temperature heat (and cold) network, including seasonal storage. The full paper will discuss this study relevant to many cities across the continent.