From Servers to Swimming Pools: Reusing Waste Heat

As we push towards a low-carbon future, the way we think about energy must evolve. It’s no longer enough to focus solely on generating clean power, we must also get smarter about using the energy we already have. One underutilised opportunity lies in capturing and reusing waste heat, particularly from unconventional sources like data centres and crematoria.

These facilities generate significant amounts of heat as a by-product of their operations. Rather than venting this heat to the atmosphere, we can redirect it to heat buildings or even swimming pools, helping reduce fossil fuel use and cut carbon emissions. This isn’t just theoretical, it’s happening right now in forward-thinking projects across Europe.

Understanding the Waste Heat Opportunity

Data centres house rows of computer servers that consume large amounts of electricity and convert much of it into heat. This heat must be removed to maintain safe operating temperatures, typically using air- or water-based cooling systems. Likewise, crematoria operate at extremely high temperatures, and their exhaust gases can contain valuable heat that would otherwise be wasted.

By capturing this waste heat and delivering it via heat exchangers into a local district heating loop, we can redirect it to buildings or facilities that require heating, such as nearby residential developments, leisure centres, or public swimming pools.

How It Works: Technical Overview

1. Heat Capture

• Data Centres: Hot air or water from server racks is routed through heat exchangers. These transfer heat into a secondary water loop that is safely isolated from the data centre’s own cooling system.
• Crematoria: Exhaust gases pass through a flue heat exchanger that recovers thermal energy before it is released through the stack.

2. Heat Transfer

The recovered waste heat is transferred to a thermal loop, a closed water circuit that delivers hot water to the end user, typically between 40°C and 70°C.

3. Integration with Heating Systems

At the destination (e.g. a swimming pool or housing block), the heat is used either:

• Directly, via underfloor heating or heat exchangers in a swimming pool,
• Or indirectly, by pre-heating water that is then topped up by traditional boilers or heat pumps.

4. Control and Efficiency

Smart controls ensure the system responds to demand and manages the temperature, while variable-speed pumps and flow control valves optimise energy transfer and avoid waste.

Backup Heating and Resilience Planning

One of the key design considerations in these systems is continuity of supply. Waste heat sources are valuable but not guaranteed. Downtime may occur due to:

• Routine or emergency maintenance,
• Reduced output (e.g. a shift to low-power server technology),
• Complete closure of the heat source facility.

Therefore, any building or district heating system relying on waste heat must include robust backup systems. These typically include:

1. Supplementary Heat Pumps – Electric heat pumps can raise the temperature of water when waste heat is too low or absent, using grid electricity (preferably during periods of low carbon intensity).
2. Gas or Biomass Boilers – These act as final backups and can take over fully during planned maintenance or permanent outages of the heat source.
3. Thermal Storage – Large insulated water tanks can store surplus heat generated during off-peak hours or periods of excess availability. This buffer helps smooth supply fluctuations.
4. Modular Heating Plants – A combination of smaller systems (e.g. solar thermal, air source heat pumps) can provide long-term resilience and mitigate reliance on any one source.

A Future-Proof Strategy

Waste heat reuse is an excellent example of the circular economy in action, making the most of existing energy flows before generating more. But it requires careful integration into a hybrid heating system that prioritises local, low-carbon sources while maintaining resilience.

With thoughtful engineering and backup planning, a swimming pool heated by a crematorium, or a housing block warmed by a data centre, can be both environmentally smart and operationally secure.

As businesses and local authorities seek to reduce emissions, embrace Net Zero goals, and deliver cost-effective heat, turning waste into warmth is a compelling solution worth exploring.

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