Pumps and pipes for heat networks

One of the largest capital costs in setting up a heat network is installation and insulation of the heat delivering pipework. This piping can last for up to 50 years and opportunity to retrofit once pipes are already in the ground is almost zero, so consideration needs to be made to get it right. Oversized pipes lead to increased pumping costs, but pipes that are undersized can exclude future expansion opportunities for the network.

Pre-insulated plastic duo piping

A common pipework solution is pre-insulated plastic duo piping. Although plastic piping typically requires more pressure than metal piping, it tends to be cheaper and is less prone to erosion. Duo pipes have both the flow and return pipe within the same insulation casing. The benefit of duo piping to single piping is that it is much easier to install and requires less space, meaning it is cheaper. Table 1 outlines indicative pipe diameters, volume flow, pressure, and costs for plastic duo pipes with differing flow and return temperature differences.

Variable Speed Drive

Pumps should be fitted with a Variable Speed Drive, which adjusts the electricity supply to the pump to enable the motor to slow down or speed up, to meet system demands. These have the benefit of electricity saving, as well as allowing for smaller and, therefore, cheaper pipe sizing. A rule of thumb for pressure losses in pipework should be around 100 Pa/m for main lines and 250 Pa/m for network branches, which gives a good balance between heat loss and pumping costs. Since pumps are an essential part of delivering heat across the network, backup capacity is almost always installed.

Table 1: Indicative pipe sizing, volume flow, pressure, and costs for 15⁰C and 30⁰C flow and return temperature differentials.