ForTheDoers Blog

Clean your plate in industry too – by recovering waste heat

Heikki Keskiväli 20 March 2020, 15:07 EET

We teach our kids to clean their plates because food shouldn’t be wasted. The climate discussion has further emphasised the need to reduce consumption on all fronts. A cost-effective place to start is “clean your plate” also in industry by recovering waste heat.

With heat pumps, 1 = 5: one unit of renewable electricity can produce up to five units of clean heat

According to the Heat Roadmap Europe 2050 study funded by the European Union, industrial processes in Finland annually generate more than 20 TWh of waste heat, which is equivalent to the energy amount of the coal used in Finland.

In terms of heat production efficiency, heat pumps are in a class of their own. When using one unit of electricity, they can produce 3–5 units of heat – and, often, cooling at the same time. So it clearly goes without saying that heat pumps are an excellent way to reduce emissions in the heating sector, cost-efficiently. The industrial-scale heat pump plants connected to a district heating network are especially efficient.

However, it wasn’t too long ago when using electric heating was considered a fundamentally bad solution because electric energy was considered a more valuable energy than thermal energy. Unlike electricity, heat has an unfortunate way of dissipating. But utilising this waste heat has become easier, thanks to recent development in heat pumps.

By employing the properties of the refrigerants flowing in heat pumps, waste heat (e.g. at a temperature of 20–30 degrees) can be recovered and its temperature significantly increased (e.g. to 50–90 degrees). In order to do this successfully, heat pump needs a preferably steady heat source, like the heat from, say, warm shower water and toilet wastewater from households, the heat generated by computers in data centres, or the heat generated in industrial processes.

Heat pump in Suomenoja is an important part of carbon neutral district heat production in Espoo

Using waste heat from data centres and industrial areas can significantly reduce emissions

The most attractive sources of waste heat are the ever growing number of data centres around the world. At these data centres, thousands of computers process the data that drive social media, e-commerce, and business systems. Today, however, 99 percent of the waste heat generated at data centres goes to waste when it could be used in district heating networks as a replacement for fossil heat production.

Data centres built in the Nordic countries operate mainly with new-build wind power, so the energy they require is, in principle, emissions-free. However, even more than 80 per cent of the wind power electricity used by data centres could be fed cost-efficiently into the existing district heating network. This thermal energy can replace fossil fuels, such as coal. So renewable energy recovered from data centres can be called “carbon negative”.

The amount of waste heat from a big approx. 100-megawatt data centre could cover as much as 35 percent of the heat demand in Espoo’s district heating network in Finland. The potential emissions reduction is significant: heating in the Helsinki metropolitan area in 2018 generated more than two megatonnes of carbon emissions, i.e. more than three percent of all of Finland’s emissions.

Reducing the use of coal is also the aim of the Kilpilahti industrial area’s 700 – 1,000 million euro waste heat project in Porvoo, Finland. The amount of waste heat recovered in the industrial area could cover about one quarter of the heat demand in the entire district heating networks in the Helsinki metropolitan area, and there would still be enough heat for the cities of Kerava and Sipoo.

District heating networks enable a breakthrough for waste heat

However, it wouldn’t be possible to utilise the big sources of waste heat if the Helsinki area’s heating was generated only by building-specific heating solutions. The existing district heating network ensures the distribution of emissions-free waste heat also during freezing temperatures and without any significant extra investments in customer-specific equipment or in electricity distribution. At the same time, waste heat that reduces the use of fossil fuels is delivered to those who need it, when the network also serves a lot of consumers with constantly changing needs. Moreover, it’s a care-free solution: maintenance and heat supply are the responsibility of the district heating network operator and it isn’t as much dependent on the functionality of a single piece of equipment.

The era of irresponsible waste is over

It is important for our industry’s competitiveness and for the shared climate that all potential waste heat is recovered and fed into the common district heating network. Without a district heating network, wide-scale utilisation of waste heat is not possible. As renewable electricity becomes cheaper and heat pump technologies develop, the future of waste heat recovery looks very promising.

The era of irresponsible waste is over. So let’s clean our plates.