In Leiden, like in most European cities, the heating of buildings can amount to as much as half of the total energy consumption. From creating centralized heating systems, installing solar panels to heat up water to improving the insulation of your house or cutting showers short a couple of minutes – there are many options to more effectively consume energy, save on heating costs and reduce your impact on the environment.
This is nothing new to you? But, have you ever wondered what happens to all the heat lost in industrial processes, or produced when heating your home, showering, cooking, and driving? There is still huge potential in using and recycling this excess heat.
Here are 5 new ideas on how to not lose the heat you produce, of which you might not have heard of until now:
- Don’t let your warm water go down the drain – By recycling heat from your warm water off your sinks, dishwasher, washing machine and shower you can already preheat the water for the next usage. Companies, such as Canadian-based Renewability, already apply this concept for residential housing as well as company buildings. The following video explains how Renewability’s system works: http://www.renewability.com/video.html
- Blow off some kitchen steam – Whenever you cook or bake or even simply when a refrigerator is running in your kitchen, vast amounts of excess heat are created that could be used to heat up your water or warm the dishwasher. An existing concept is South African’s Whirlpool’s eco kitchen, which redirects heat streams to where they are needed and is designed after natural ecosystem cycles. It can help create 70% more efficient kitchens than current the standard forms. 
- Suck that heat out of the pavement – Heat can be extracted almost everywhere, including sun-lit pavements. By building water pipelines beneath pavement surfaces, researchers are currently testing how excess heat can best be collected. But there is much more to streets than just the pavements. Heat from friction caused by traffic could in the future be used for energy creation, too. 
- Get more from your supermarket than just groceries – Supermarkets, and many other companies create heat through cooling processes or from industrial processes, which altogether equals millions of oil barrels wasted every year. New projects aim at connecting centralized city heating systems with industries to heat entire cities with waste heat. For instance Leiden, in cooperation with Heinken, will use waste heat from Rotterdam harbour’s industrial processes in the future. For a video of the process, click here: https://www.youtube.com/watch?v=vLHDx9dlWU4
Also, do you have a supermarket underneath your apartment or nearby your house? Local solutions might allow you to link your heating system to a supermarket’s cooling system generating a local supply of (up to now mostly unused) heat.
- Last but not least, use your body heat – The human body radiates about 100W of excess heat when resting and even more while rushing around. Imagine capturing the heat of hundreds of thousands of people to heat buildings. This is what is done in a 13-floor high office building next to Stockholm’s Central Station. The excess heat of 200.000 commuters is collected by ventilators and used to produce hot water with the help of heat exchangers. The host water is then transported to the office building. This system reduced energy costs of the office by 20%. Similar initiatives exist in Paris where body heat collected at metro stations is used to heat 17 nearby office buildings.  Surprisingly, using body heat for heating rooms has not yet been tested in fitness studios.
Unconventional ideas, such as the examples presented, might play a key role for efficient future management of energy usage. Do you have your own ideas or projects on how to recycle heat? Comment below and share your experience to help Leiden and other cities around the globe recycle heat and become sustainable.
Interested in the topic? Find out more by following these links:
Dawson et al. (2014) Energy Harvesting from Pavements. In: Gopalakrishnan et al. (eds.) Climate Change, Energy, Sustainability and Pavements. Heidelberg: Springer, 481-517.
 Fricke, Brian A. (2011) Final Report. Waste Heat Recapture from Supermarket Refrigeration Systems. http://info.ornl.gov/sites/publications/files/pub31294.pdf