CIBSE/ADE Heat Networks Code of Practice 1 (2020) outlines Acceptance Testing as a crucial part of the heat network commissioning process that provides performance verification of all end points and the energy centre. FairHeat provided input into the development of the updated document as part of the steering group, which included the introduction of Section 5.7 “To carry out on-site acceptance tests to deliver an efficient and reliable service”. FairHeat’s Acceptance Testing process provided the basis for the minimum requirements and best practices outlined within this objective.

In addition to its inclusion within the new Heat Networks Code of Practice, the government are currently writing legislation in order to develop a heat network market framework which will officially regulate heat networks as a utility within the UK. This new regulation will come into effect by the end of 2022, therefore will be live by the time that many current designs become a reality.

As part of this regulation, two key protections are likely to be introduced, customer protection and technical standards (via a certification scheme(s)). This heat network certification will include Acceptance Testing as a minimum so it should be seriously taken into account as a process that needs to be developed and accepted by all heat network developers.
We have seen over the years that this process has many benefits, not just for one particular party, but for all major stakeholders, developers, designers, contractors and ultimately the end users, the residents. 
As a result of poor installation and commissioning across heat networks, there is often a substantial performance gap between design intent and observed performance. Poor commissioning and performance of end points (such as heat interface units or fan coil units) is often associated with elevated flow rates and return temperatures, with only a few poorly performing units having a large detrimental effect on the heat network’s performance and efficiency. Similarly, poor commissioning and performance of the energy centre is often associated with unstable flow temperatures.

Acceptance Testing is a rigorous testing process that seeks to address these issues.

The Acceptance Testing process highlights issues for contractors to rectify, preventing issues and faults emerging during the early years of operation, where their rectification would be more expensive and intrusive. However, it is not a procedure which can just be undertaken with little preparation. In order to carry out Acceptance Testing successfully and achieve heat networks which perform well, this needs to be built into the development process from day one.

This process is one which FairHeat have been developing over the last five years and is tried and tested with both private and social housing to ensure that results can be achieved. Getting early buy-in from all parties involved is a necessity, as this then facilitates collaboration at all stages, from the initial system design, to installation, system commissioning, and finally the Acceptance Testing procedure and associated remedials. Early buy in and a collaborative, transparent process from the off can mitigate the risk of costly reworks and issue rectification further down the line.

The introduction of Acceptance Testing to the new build process provides performance verification of all end points. An independent heat network specialist follows a rigorous testing process which involves inspecting installation quality and analysing end point performance through all operational modes with subsequent feedback provided to contractors for rectification. This process ensures installation, commissioning and operation are all as per design and performance specification.
Under the new minimum requirements detailed within Section 5.7 of CP1 (2020), dwelling Acceptance Testing must be carried out in two main phases.

The first, an initial set of tests on a small number of dwellings (section 5.7.5 of CP1 2020). It is strongly advised that this initial round of Acceptance Testing is carried out with the commissioning engineers present in order for commissioning to be demonstrated and the testing to be introduced to each party. This initial testing often highlights endemic issues which can be rectified and learned from to prevent their proliferation through commissioning the rest of the dwellings.

The second phase of Acceptance Testing is the full rollout. Section 5.7.6 of CP1 2020 states that Acceptance Testing must be carried out on at least 20 % of dwellings (first 10 % commissioned, then a randomised 10 % sample of the remainder), with best practice dictating that all dwellings must undergo this process. Therefore, it is imperative that developers are aware of the Acceptance Testing procedure and plan for its implementation as soon as possible so that it can be factored into the project delivery plan with suitable time for issue rectification and retesting.

To ensure complete transparency amongst all parties a clear set of commissioning parameters and installation benchmarks (called the Acceptance Testing Criteria) is developed which the commissioning engineers can work to. These parameters and benchmarks will have been developed from the system design, Building Regulations and industry best practice, focussing on a system which performs well in four areas:

The criteria and benchmarks will also have clear indications as to what constitutes a failed test or not, to provide utmost clarity on Acceptance Testing results and therefore, an easy to do list for contractor rectification.
In practice, Acceptance Testing highlights issues such as HIU bypasses, poor insulation quality, unsafe hot water temperatures, cold radiators, re-occurring minor issues and many more.
Its effect can be seen from the following two graphs of return temperatures from two phases of a London development. Figure 1 shows the return temperature from an existing phase which had already been built and was showing poor performance. Figure 2 shows a similarly sized phase on the same development where dwelling Acceptance Testing was carried out prior to occupation.

At a building level, Acceptance Testing provides performance verification of the energy centre under minimum, varying, and peak load, proving operation for phased and whole developments.

Once all plant room equipment is commissioned separately and enough end points are connected to the network to provide elevated loads, the load test can be undertaken. Load is induced gradually on the system, building up to design peak load, with focus on key plant operation modes. This particular focus on sequencing and changeovers ensures that heat delivery is not compromised in these periods of changing load, return temperatures remain low and as per design and pump differential pressure is maintained.

Heat meter data becomes incredibly useful at this stage as flow and demand can be monitored at all points in the system as well as temp and pressure data from the Building Management System (BMS).

In practice, energy centre Acceptance Testing highlights issues such as poor temperature stability, cycling of equipment, network bypasses or thermal storage not being optimised. Figure 3 and 4 below shows two iterative tests over two days on the secondary side of a district heating plate heat exchanger. In the load test, once load was induced, the secondary flow temperature dropped drastically, then once load was removed, the plate control caused several fluctuations.

Once the changes were made, this fluctuation was eradicated, and the secondary flow temperature remained relatively stable. This was rectified on the day to ensure that risk of heat delivery at elevated demand was drastically reduced. This dynamic and iterative testing ensures that these operational issues are rectified pre-occupation.

FairHeat have developed and championed this process over the last five years and are delighted and proud that it has been included as a minimum requirement within CP1 2020 as it has been proven to achieve excellent results. So if you want to get the best out of your heat network, do connect with us directly or on LinkedIn and we can help.

For further information and to learn what benefits Acceptance Testing provides for contractors and developers, please do take a look at a presentation we delivered about Acceptance Testing at our Anniversary Event; as well as a previously published blog about plant room controls and testing.

acceptance testing, CP1 2020, dwelling, energy centre, heat networks, performance testing, regulation