How District Heating Works in Lerwick

District Heating, also known as Community Heating, is a system where heat is generated in a central location and distributed to residential and commercial buildings for space heating and process systems. In the case of Lerwick, heat is generated through the Energy Recovery Plant (ERP), which burns municipal refuse, including waste from the neighbouring Orkney Islands. The heat generated is then converted into hot water and pumped through a network of underground pipes that stretch across the town.

Here’s how the process works:

1. Heat Generation at the Energy Recovery Plant (ERP)

The ERP burns municipal waste, including refuse from Orkney, to generate heat. This heat is transferred to water, creating a continuous supply of hot water.

2. Distribution Network

This hot water is circulated through a network of 40 km of pre-insulated pipes buried throughout Lerwick. These pipes carry the heated water to over 1,200 customers. The pipes are made up of a steel core, surrounded by polyurethane foam for insulation, and an HDPE outer layer for protection. Each joint is welded meticulously to maintain the integrity of the network.

3. Customer Interface

Each customer’s property is connected to the network through a Flow and Return main line with connection supply pipes that lead to an internally mounted heat exchanger. The heat exchanger interfaces with the customer's internal heating system, eliminating the need for conventional oil boilers, solid fuel fires, or electric storage heaters.

4. Backup with Peak Load Boiler Station

To ensure there is always enough heat, especially during periods of high demand (like early mornings and evenings), the scheme also operates an oil-fired Peak Load Boiler Station. This station helps provide extra heat during peak times and during maintenance periods when the ERP is offline. It features three oil-fired boilers with a backup capacity of 14.5 MW, ensuring there is no interruption in supply during ERP downtimes, which are limited to 40 days per year, split across two main shutdowns in the spring and autumn.

5. Environmental and Efficiency Benefits

District Heating systems, like the one in Lerwick, offer higher efficiencies and better pollution control than individual, local heating systems like boilers. The scheme is an excellent example of visionary, sustainable technology that not only helps reduce carbon emissions but also avoids costly oil alternatives, especially in winter.

This approach to heating is innovative and environmentally friendly, making it a model for other communities and local authorities looking to adopt similar systems.

If you'd like to dive deeper into the technology and history of the Lerwick District Heating Scheme, you can explore the paper written by Neville Martin (former SHEAP General Manager) and William Spence (former SIC Environmental Services Team Leader) for the Institute of Civil Engineers. You can download the paper for more insights.