Introduction
When considering the operational performance of pipework systems, the impact of pipe insulation is often overlooked. Frequently, insulation specifications will ask for “compliance with BS5422” (BS5422: 2023 (Thermal insulating materials for pipes, tanks, vessels, ductwork and equipment operating within the temperature range –40 °C to +700 °C. Method for specifying) without actually rationalising what that means.
Approved Document L: Conservation of fuel and power, Volume 2 Buildings other than dwellings, gives heat loss values which should not be exceeded, and directly signposts to BS5422 for compliance. BS5422 gives an effective “minimum” level of performance that should be achieved; found in Tables 15A, 16A, 17A, 18A and 19A.
Are the “minimum” Levels of Performance Sufficient?
It has been questioned by those in the building services industry if the “minimum” levels of performance are sufficient – for several reasons such as overheating, energy efficiency and operational costs. In 2013 the Carbon Trust updated the Energy Technology List (a government list of energy-efficient plant and machinery) to include a new thermal insulation standard. This standard called for an enhanced specification over and above the minimums of BS5422, and became the basis for the “Enhanced Capital Allowances” tax break scheme. The scheme offered tax benefits for investing in better operational performance. Although this tax scheme has since ceased to offer this benefit, this standard has now been included within the 2023 edition of BS5422 as “enhanced” tables (tables 15B, 16B, 17B, 18B, 19B) – to the extent that BS5422 states that unless otherwise specified the enhanced tables should be used.
The Effect on District Heating Systems
With the advent of district heating schemes which can service many hundreds or thousands of homes, there has also been a great deal of focus on the unnecessary heat loss between the point of generation and point of use, as there is no benefit to this heat loss and it creates unnecessary cost and performance issues across the entire network. The drive to improve operational performance has been enhanced by the release of CIBSE CP1 (Code of Practice for Heat Networks) which looks at increasingly enhanced levels of thermal insulation, as CP1 states (clause 3.9.5) it is important to understand the cost benefits of enhanced insulation due to the continuous nature of the system, and the CO2 emissions benefits of additional insulation.
The latest 2023 edition of BS5422 also recognises the necessity of maintaining performance of district heating systems, and includes a specific table (Table 19C) to address this (based on a low temperature of 55 °C as opposed to 75 °C assumed for other systems).
Operational Performance – Different Approaches
So when it comes to looking at the operational performance of pipework systems there are a number of different approaches that can be taken. The difference in performance can be seen in the graphs below.
Graph 1: Annual Heat Loss for Specified Insulation Standards.
Example based upon indicative pipe sizes of 100 metres of each 20 NB, 25 NB, 32 NB, 40 NB and 50 NB at 55 °C flow in 15 °C ambient with insulation thicknesses to meet the maximum permissible heat losses laid out in BS5422: 2023 Table 15A (Base) 15B (Enhanced), Table 19C (District Heating – NOTE only applicable for systems at 55 °C Flow) and CIBSE CP1 (50 mm thickness on all sizes) based upon continuous operation throughout the year.
This reduction in heat loss can then be directly translated into a reduction in the operational carbon and cost associated with this heat loss as shown in Graph 2 and Graph 3.
Graph 2: Reduction in Operational Carbon.
Note: Carbon emissions based on 0.0526 kg CO2eq-kWh.
Graph 3: Cost Associated with Heat Loss.
Note: Costs are based on £0.07 kWh, with graphs based on 1 year operation. Enhanced standards will have enhanced capital costs associated with them.
The Outcome
The graphs above show the following outcome:
- Increasing from the minimum standard to the enhanced table reduces annual heat loss, operational carbon and operation cost by around 12%.
- Increasing from the minimum standard to Table 19C reduces annual heat loss, operational carbon and operation cost by around 45%.
- Increasing from minimum standard to CP1 reduces annual heat loss, operational carbon and operation cost by around 45%.
The results above indicate that by using enhanced thicknesses of insulation, a significant reduction in heat loss and operational carbon can be achieved. However, the capital cost implication of doing so needs to be taken into account and understood in the context of the expected project length.
Capital Cost of Insulation and Payback
When taking the above example and comparing it with a custom thickness of 75 mm across all pipe sizes, which from a heat loss and operational carbon perspective will always be better, how long will it take for the capital cost of the enhanced insulation to pay back versus the use of CIBSE CP1 and BS5422: 2023?
Graphs 4, 5 and 6 show, as predicted, that the specified pipework insulated at a custom thickness of 75 mm, provides the lowest heat loss, embodied carbon and whole life cost. But how long does it take for that benefit of additional insulation to be realised?
Graph 7 shows that the payback period would be just over 18 years compared to a CP1 baseline. If the operating life of the system is less than 18 years, it would perhaps be more beneficial to specify using CIBSE CP1 or BS5422: 2023 table 19C.
For further information regarding carbon emissions associated with the heat lost from pipework systems over the systems lifetime, please email pipecarboncalculator@kingspan.com
