The ground source heat pump system at Vaillant’s Derbyshire headquarters was sanitised by Sentinel Commercial
In the pursuit of visible sustainability, the rudimentary is often overlooked in favour of the advanced
blockage, degradation of boiler efficiency or system effectiveness and, ultimately, loss of system integrity. A study commissioned by Sentinel Performance Solutions, a leading water treatment specialist, showed that contaminants can cause a reduction in efficiency by up to 15% on some heat emitters (radiators, for example), which translates into an overall system loss of 3%. In commercial buildings, where five- and six-figure fuel bills can be commonplace, 3% represents a significant expense. The size of commercial systems also means they are more vulnerable to scale build- up. The investment in cleaning, flushing
Case study
Vaillant Group’s £3.5m redevelopment of its headquarters in Belper, Derbyshire, fulfilled an ambition to create a zero-carbon building, incorporating the group’s portfolio of renewable energy products, including a ground source heat pump, air-to-water heat pumps, air-to-air heat pumps, solar thermal and photovoltaic systems. Sentinel Commercial, supplier of commercial heating and renewable system cleaners and inhibitors was brought in at the commissioning stage of the 30kW geoTHERM ground source heat pump (GSHP) system in order to ensure efficiency was maximised through optimum system cleanliness and glycol heat transfer performance. The process began by pressure flushing the entire GSHP system to perform an initial cleanse. Once filled with mains water, initial tests found that bacteria levels were above the ideal level for system performance – unsurprisingly, since the installation environment cannot be completely sterile. One gram of soil can contain more than 100 million bacteria. To remove the bacteria, R700 Sanitiser was
58 CIBSE Journal February 2013
added in the correct proportion to the volume within each loop, and this fluid was then pumped through each subsequent loop, using the isolating valves in each section. Bacteria levels were tested once again, using dip slides (for a general aerobic bacteria count) and ATP bio assay techniques (to measure general micro-biological activity and kill rates during the sanitisation process while on site), while the active level of R700 was measured using a product-specific dip test kit.
Results showed that the GSHP system had been completely sanitised, and the recirculating water was visually clean and contained no physical debris. Following sanitisation, the ground loop was then filled with R500C, a glycol-based thermal fluid specifically designed for use as a highly efficient heat transfer fluid, which was diluted to the correct concentration using mains water. Safeguarding against corrosion, microbiological fouling, scale deposits and glycol degradation, this product also provides excellent frost protection down to temperatures of -22˚C.
and periodical treatments can therefore be recouped with comparative ease. Sentinel’s study made use of a purpose-
built replica of a simple domestic installation, where the hydraulic load was accurately balanced, with the flow and return temperatures set at 65 o
C and 47o
C
respectively. Starting with a clear system, the thermal efficiency was measured to provide a benchmark, before the system was fouled with sludge. Measurements were then taken to determine the effect of this on the system’s thermal performance. A new boiler was then fitted and the measurements taken again to provide an analysis equivalent to retrofitting a new boiler without first power flushing the system. Finally, the system was power flushed and the tests repeated once again. The results were startling. Perhaps most
notable was the insight that sludge deposits can cause a reduction in the effectiveness of the system as a whole by as much as 3%, and that adding a new, clean boiler to a dirty system can achieve very little in terms of efficiency gains. The presence of sludge has an effect
on both the flow and distribution of water within the system. Reduced system flow was associated with a reduction in boiler output, which reduced heat output to the point where the system was no longer capable of transferring the required heat to the building. This needed to be countered by turning up the pump or opening the valves, resulting in the return water temperature increasing. The loss of heat transfer surface meant
the boiler flow temperature had to be raised, lowering boiler efficiency still further. More significantly, however, this in turn raised return temperatures, causing further loss of efficiency.
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