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Fit-for-purpose filter protection for heat pumps
With heat pumps now increasingly common in both new build and existing homes, it is important for installers to understand how to protect these systems correctly. Here, Mark Hall head of mechanical engineering & devices at Fernox looks at the role of system filters as part of a comprehensive best practice cleaning and protection approach
D
espite the clear differences between a traditional gas or oil boiler and a heat pump, there are also key similarities. Much
like a traditional heating system, a heat pump system contains water filled pipework, as well as radiators or underfloor heating that need protecting. Without the correct protection it is vulnerable to the formation of corrosion and scale as well as the effects of circulating debris. Whether it is an air-source or ground-source heat
pump, it is crucial to protect the components from damage to preserve the lifespan of the system and maintain its efficiency in the long term. In fact, due to the lower temperatures that heat pumps operate at, they are particularly affected by the losses in performance caused by sludge, scale, corrosion and other contaminants. In addition, it is important to remember that because underfloor heating is often used with heat pumps, any degradation of the pipework can be more challenging and costly to fix. As with traditional central heating systems, a
combination of effective water treatment and an in-line system filter, supported by regular servicing and testing of inhibitor levels, is essential. This is the approach outlined in BS 7593:2019, the British Standard for the installation, commissioning and maintenance of domestic heating systems, the requirements of which have formed part of the legal requirements of Part L of the Building Regulations in England since June 2022. This means that all new homes, or new heating installations in existing properties, must comply with this guidance. The reason that a filter is required alongside
water treatment is because they address different issues and operate together to protect the system. A high-performance inhibitor will prevent the formation of sludge and limescale build up by chemically protecting the metal surfaces within the system. Meanwhile, a filter will capture contaminants already in the system or those introduced accidentally, such as installation debris. When selecting an in-line filter, it is important
to look for one designed specifically for heat pump systems. It is often assumed that the same filters can be used for boiler and heat pump systems
DOMESTIC HEAT PUMPS
as the pipework is the same. However, there are key differences in the way they operate that mean a heat pump specific product should always be recommended. For example, heat pump systems typically have higher flow rates of up to 80 litres per minute. This can mean that some filters will not perform as expected. The selected filter should be capable of capturing, and crucially containing, all types of metallic and non-metallic debris, including magnetite, haematite and scale. Many of the filters on the market that claim to be suitable for heat pumps rely on magnets to capture the particles and therefore have limited effectiveness. This is because these filters are susceptible to wash-off or lost capture at higher flow rates, meaning contaminants are released back into the circulating system water. Filters intended for use with heat pumps and engineered for efficient capture at high flow rates, such as the Fernox Sigma HP Filter, should always be used. It is also important to look for a filter that has been designed to optimise the flow of water through it and minimise the pressure losses that can impact system performance as well as ensure the heat pump can maintain the required COP (Co-efficient of Performance) levels. As with all components in the heating system, it is important to select a high quality filter that is simple to install and service, eliminates the risk of leaks and has been comprehensively tested. For example, the
TF1 Sigma HP Filter has undergone rigorous testing throughout its design, development and production. This testing included long-term integrity testing that saw the filter repeatedly pressure cycled between 2 and 10 bar, and temperature cycled between 0°C and 90°C. There are also other important considerations
for the protection of heat pump systems. For example, due to the lower operational temperatures, typically between 35°C and 55°C, there is a risk of microbiological contamination. In this temperature range, microorganisms such as bacteria and fungi will thrive and multiply. This not only presents a potential health risk to homeowners or tenants but can also cause accelerated degradation of the system through Microbiologically Influenced Corrosion (MIC). There is also the risk of biofilms forming on surfaces within the system, leading to reductions in system performance. To prevent this, an effective biocide should be added to the heating system in the same way as inhibitor is dosed. The biocide will kill the microbes by altering the cell wall permeability and interfering with biological processes, destroying the cell as a result. Air- and ground-source heat pumps need to be
protected in the same way as a traditional heating system using both an effective inhibitor and inline filter. However, not all filters are alike, so it is important to choose one that is specifically designed for the application.
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