Give heat pumps the special treatment

Sentinel Commercial, heat pump, space heating, water treatment, renewable energy

The performance of heat pumps can decline rapidly if the heat-transfer fluid is not properly treated. Ian Barnes of Sentinel Commercial, explains why cleaning and protecting systems at the commissioning stage is key to maximising the long-term performance, energy and cost efficiency of heat-pump systems.

For the past few years, the commercial heat pump market hasn’t quite enjoyed the flood of sales expected of this renewable-energy technology, with growth being described as either slow or even flat-lining. However, the tables could soon be turning for heat pumps as support for this exciting technology steps up.

Any day now, the Government is due to publish plans for expanding the non-domestic Renewable Heat Incentive scheme (RHI) — including proposals for new or alternative support for air-source heat pumps — alongside the outcome of the 2013 non-domestic tariff review.

The existing tariff for ground-source heat pumps (GSHP), having failed to bring forward the anticipated number of installations, is also under review.

What’s more, it’s expected that the Department of Energy & Climate Change’s recent announcement of tariffs for heat-pump technologies within the domestic RHI will have a positive knock-on effect in the commercial market, especially as an increasing number of installers train and qualify in heat pump technology.

The cost of treating heat pump systems at the commissioning stage is fractional compared to the cost of recovering degraded glycol.

With things looking hopeful for the heat-pump market, it’s prudent to focus attention on installation practices. Unfortunately, some systems have failed to deliver the specified performance levels, but rather than being a reflection of the technology — which is proven and highly reliable — it is widely thought that poor quality installations are often to blame. A heat-pump field trial by the Energy Saving Trust also came to the conclusion that performance is heavily dependent on the quality of the installation and commissioning process. While there are many factors to be considered in sizing and temperature capability alone — with the advice being, as always, to seek help from professional system designers and to follow the manufacturer’s guidance and recommendations — one of the most crucial, yet commonly poorly executed steps is system cleaning and protection.

Just like traditional boilers, the heat transfer fluid in a heat pump system must be treated in order to deliver on carbon and performance promises. Of course, unlike conventional systems that use water to capture and transport the available heat, air and ground-source heat pumps often use a glycol-based heat transfer fluid. Unfortunately some ‘standard’ glycol mixes used within these systems are not designed for purpose (some are even toxic), and have been shown to prematurely degrade, sometimes within months of installation.

Glycols break down due to the chemical action of thermal stress or oxygen ingress, and can also degrade by the action of bacteria, which use the glycol as a food source.

Anyone who has observed the installation and commissioning of GSHP systems will be aware that there are many opportunities for the system ground loop to be contaminated with bacteria from soil, insects, vermin and contaminated flush water. Locked within a system containing a massive food source, the bacteria multiply rapidly.

Despite containing much smaller quantities of glycol thermal fluid, air-source heat pumps can also be prone to such bacterial growth problems, as they tend to operate at ideal growth temperatures.

Degraded glycol becomes progressively discoloured and more viscous — taking on the appearance of a thick, unhealthy-looking wallpaper-type paste.

Degraded glycol, whether broken down by chemical or biological action, becomes progressively discoloured and more viscous — taking on the appearance of a thick, unhealthy-looking wallpaper-type paste. In order to circulate the ‘paste’, pumps have to work harder, severely compromising the energy efficiency of the system. The freezing point of the fluid also rises as it degrades, resulting in a progressive loss of frost protection for the system.

As well as increasing operating costs, systems with degraded glycol can also be expensive to put right. A good example is a 9 kW GSHP which was recently treated, having shown no heat output after just two years in operation, all because of premature glycol degradation. The process of recovering the system involved specialist cleaning fluids, biocide and sanitiser, degraded glycol disposal, two days’ labour, and replacement thermal fluid — all at a cost of over £1500. In comparison, getting the glycol right at commissioning stage would have cost around £30.

The good news is that it is quick and relatively inexpensive to ensure the long-term efficient, reliable and cost-effective operation of heat pump systems — if they are safeguarded at an early stage. Key to this is selecting system cleaning and non-toxic protection products which are technology-specific (ASHP products are different to GSHP products), and sourcing them from industry-leading commercial heating system treatment brands. OEMs will usually offer a recommendation, but it’s also worth doing your own homework and seeking out a company that can demonstrate its experience through existing case studies.

Despite the commercial heat-pump market still being relatively small, there are plenty of products on the market that meet this criteria, including robust, long-lasting and non-toxic thermal fluids; flushing liquids to help remove old degraded glycol and debris from existing systems; sanitisers and biocides that address bacterial growth, and test kits to check the system.

Thanks to improved support, the murky waters are clearing for the commercial heat-pump market, and sales look set to take off. With the correct treatment, we can ensure that this technology delivers the promised carbon, energy and cost savings long into the future.

Ian Barnes is head of Sentinel Commercial.

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