Insulation - It’s a wrap
Specification of the correct thermal insulation for pipes and ducts is essential to ensure heating and cooling systems perform effectively. Shaun Byrne of SIG explains some of the issues that need to be considered - and why it is wise to seek expert advice.
The insulation of vessels, pipework and ducting is essential to deliver a zero- carbon building. The requirement is both to minimise heating system heat losses and cooling system heat gains.
In England and Wales, Approved Document L (AD L)1 provides brief guidance on the minimum thickness of pipework insulation for low temperature hot water space heating applications and also for domestic hot water services, minimum heat losses and gains for ducts and hot water vessels. However, in almost all instances AD L recommends consulting BS 5422: Thermal insulating materials for pipes, tanks, vessels, ductwork and equipment operating within the temperature range –40 °C to +700 °C the method for specifying.
The Standard in turn refers to a calculation method for the required insulation thickness for particular installations: ISO 12241:2008 Thermal insulation for building equipment and industrial installations the calculation rules.
Alongside insulation thickness, there are several other factors that should be considered when selecting the most appropriate insulation for both piped and ducted mechanical services, not least the material itself.
The properties of the insulating material used can affect its effectiveness. The k-value (sometimes referred to as lambda-value) is a measure of the thermal conductivity of a material, or how easily heat passes across it.
K-values are determined through laboratory testing and can be used to easily compare the performance of different materials. Common pipe and duckwork insulating materials include mineral glass, mineral rock, phenolic and nitrile.
All of these materials will have different thermal conductivity characteristics and products from individual manufacturers may also vary in terms of their performance. The thickness of insulation required for any application therefore will be specific to individual products and individual manufacturers. It is dangerous to make assumptions based on one product or to trust generic specifications.
Alongside the temperature outside the pipe or duct, the temperature of the air or water inside a duct or pipe will need consideration. The bigger the temperature differential, the thicker the insulation requirement. This also means that a pipe located outside a building will generally require more insulation to cope with temperature fluctuations than one housed inside the building.
If chilled water is being transported, then preventing condensation between the pipe and the insulation should also be considered.
For pipework, the material from which the pipe is extruded and the outside diameter of the pipe will also affect the insulation thickness required. Copper is a good thermal conductor, so copper pipes typically require thicker insulation than, say, a PEX pipe. The surface emissivity of the pipework (and that of its insulation covering) will also vary depending on the material and the specific manufacturer.
Generally, the bigger a pipe's diameter, the bigger its surface area (and the more heat lost per metre) and so the thicker the insulation needed to prevent heat loss. However, when insulating for frost protection, the opposite is true. A smaller diameter pipe will carry a smaller volume of water which is more likely to freeze quickly and therefore requires thicker insulation. In either case, the space available for insulation around a pipe needs to be considered, particularly in refurbishment projects.
Capital cost is another issue when selecting the most appropriate insulation, although correctly calculated insulation should achieve payback in a very short space of time. And, depending on the project and application, the insulation's fire and acoustic performance may also be a project requirement.
Insulation providers such as SIG are ideally placed to help building services designers and installers select the optimum insulation system for their HVAC project. We supply a wide variety of insulation products and brands and are therefore well positioned to provide unbiased advice. Our technical insulation team includes experts in this area who will ensure the information provided is both technically accurate and based on the latest standards, including BS5422 and ISO 12241.
Shaun Byrne is Sales Directort at SIG