What size of pre-insulated pipe do I need?

Pre-insulated pipe is typically used to form either district heating networks or connect a building to a remote heat source in smaller A-to-B projects. This type of product is specially designed to maintain the water temperature (for hot water and /or heating water) when in transit between the heat source and the buildings on the site. We can supply a wide range of pre-insulated pipe products from leading manufacturers like Rehau, Microflex or our own Mibec DHP Pipe to suit your application.

At Mibec, we offer a full free of charge specification service covering the whole of the UK, designed to support architects, specifiers or contractors, helping you to select the optimum underground piping solution to meet your project needs. When carrying out the initial design of the project our customers will often want us to get involved in advising on their plant size, thermal storage and network layout requirements. An important decision in the design stage is what type and size of pre-insulated pipe to use for the application in question. In this short article we look at what factors need to be taken into consideration when selecting suitable pipe sizes (especially for larger projects). The Mibec technical team are more than happy to talk through this process with you for your next project, give us a call on 01948 661639.

It is important that the pre-insulated pipe sizes are optimised in terms of energy efficiency and cost. The network also needs to be able to meet the peak capacity and potentially allow for future expansion on the site. The 2015 CIBSE guide ‘Heat Networks: Code of Practice for the UK’ contains some very useful information on this topic including the following key design considerations:

  1. Heat loads

An important factor is to determine what the peak heat loads will be for each building in the scheme as accurately as possible. This will influence not only the pipe diameters but also the size of the main heat source and ancillary components such as pumps, etc.

  1. Pressure loss

The CIBSE guide gives a couple of different methods of sizing pipe (in section 2.5). Firstly published flow velocity tables can be used and the guide itself contains information on plastic pipes. An alternative method is to size pipes using pressure losses (these will normally be no more than 250 Pa/m).

  1. Diversity factors

With large district heating networks it is important to consider the impact of diversity in demand. Again the CIBSE guide includes a good explanation of this (in section 3.2) – a basic explanation is that when there are a large number of buildings with a wide mix of customers in the project not all are likely to be at maximum heat loads at the same time giving a smoothing effect. In very large projects the diversity factor can be 70% which would enable pipe sizes near to the supply point and peak heat source capacities to be reduced accordingly (therefore reducing project costs). However on smaller systems it is advisable to assume a 100% diversity factor because the overall project demand is less predictable.

To answer the original question ‘what size pipe do I need?’ as can be seen there are a number of factors that go into this decision if you want to achieve an optimised, efficient and future-proof pipe network. Our highly knowledgeable technical team can help advise you on these and other requirements to make the process of network design and sizing as straight-forward as possible. Please feel free to email or call our Mibec support department on 01948 661639 where we will be more than happy to help you with your next project.