How does district heating work?

What if we could recover the heat produced by a factory, household waste incineration or even the computer servers of a local business to heat homes and other buildings in the neighbourhood? This is the principle behind district heating, a system that works a bit like central heating but on the scale of an entire city or neighbourhood.

Economies of scale

In practical terms, a central boiler heats water, which is then transported to each home through a network of insulated underground pipes. The energy used comes primarily from local sources:

• heat recovered from industrial processes, offices, waste incineration, wastewater, etc.
• heat contained in the ground (geothermal energy)
• solar power
• gas or coal-fired power stations

What does district heating include?

• A high-powered central boiler fuelled by oil, gas, wood chips, etc.
• A network of well-insulated pipes buried underneath the streets. This network carries the hot heating water (or steam) into each home.
• A heat exchanger where the network enters each home. It captures the heat from the network and transfers it to the network inside the home (radiators and domestic hot water production systems for baths, showers, etc.)
• An additional system (solar power, heat pump, boiler, etc.) in each home to produce domestic hot water individually when the district heating is out of service in the summer.

Strong points

• Economies of scale: a single heating system for 1,000 homes consumes fewer resources and costs less overall than 1,000 individual systems. But the efficiency is roughly the same in both cases: 86 to 87% on average.
• Convenience: residents have heat delivered to their homes just like water, gas, electricity, telephone service and... pizzas! And no more maintenance and repair worries: you only pay for what you consume.
• Collective use of heat sources that could not be used individually because they cannot be exploited by small boilers (thermal springs, volcanic heat, wood chips, etc.) or would be lost (heat produced by an industrial process).

Weak points

• Risk of heat loss: if the insulation of underground pipes is defective, heat is lost into the ground. This is not the case with conventional central heating: if heat escapes from the heating pipes, it remains in the home.
• Only possible for closely spaced homes: if homes are too scattered and far apart, the system cannot function.
• Significant initial investment.