The term "economies of scale" often pops up in discussions about energy. Which raises the following question: what is cheaper and less polluting?

• Two hundred small boilers in two hundred different homes, with two hundred chances of breaking down, two hundred bills to pay and two hundred services to be carried out?
• Or just one large boiler for everyone? Admittedly, the large boiler will be more expensive, but the cost can be split between two hundred households...

In short, it is worth calculating. And the specialists do not always agree.

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.

Weak points

• The main weak point of district heating is the insulation of the underground pipes. If defective, the system may leak the heat into the ground, so it will not be economically viable.
  By comparison, in traditional central heating, it does not matter if heat is lost via the heating pipes connecting the radiators as it remains in the home. At least, if the pipes pass through the living rooms. The other pipes need to be insulated (cellars, crawl spaces, etc.). On the other hand, losing heat through the distribution pipes in district heating is a pure waste of heat and money.

• Another weak point: the homes cannot be too scattered or too far away, and there is a considerable initial investment.

Strong points

District heating has many benefits.

• The first is better energy efficiency, i.e. less pollution for the same service rendered. A single heating installation for fifteen, two hundred or one thousand households ultimately consumes less resources and costs less than fifteen, two hundred or one thousand individual installations. But the output is about the same in both cases: 86% to 87% on average.
• The second benefit is the degree of ease involved: the occupants have their heat delivered to their homes just like water, gas, electricity, telephone and pizzas! And no more worries over servicing or repairs: you just pay for what you consume.
• Lastly, the system can operate in conjunction with heat sources that cannot be used individually, for example thermal sources or basement volcanic heat. Or wood chips, which small individual boilers cannot use. The system can also recover the heat generated by industry which would otherwise be lost.

In Iceland, 89% of residents have their homes connected to a district heating network, fuelled by heat sources at 150°C maximum.

Brussels: the perfect situation for district heating

The Bervoets sustainable quarter in Forest in Brussels has 239 housing units and twelve workshops and shops connected to a district heating system. There are also other opportunities in the capital, where housing is dense and there are many sources of free heat (incinerators, industry, etc.).