Top 5 technical questions

Meet our in-house technical expert, Darren Veal, who shares his answers to Kensa’s Top 5 most frequently asked technical questions, the first of a two-part technical blog series.

Meet our technical expert:

Kensa Darren VealDarren Veal, Commissioning Engineer

Darren is a time-served plumber having spent 30 years ‘on the tools’ and he commissions Kensa heat pump systems over the phone. Having also taught plumbing at Exeter College, Darren is responsible for training our network of installers.


How do ground source heat pumps work?

kensa-ground-source-heat-pumps246A ground source heat pump works in a similar way to a refrigerator; it extracts a high volume of low grade solar energy stored in the ground and water courses through energy absorbing pipes known as ground arrays, and converts this through the refrigeration process to a lower volume of higher temperature heat for use in a buildings heating distribution system.

This process is simply explained in this video.

Ground source heat pumps are extremely energy efficient and CO2 emissions are significantly lower than traditional fossil fuelled systems. Also, as the temperature of the ground and/or water source remains fairly constant all year round, this ensures that the system remains efficient despite colder weather conditions.

Can a ground source heat pump provide hot water?

Yes! All Kensa ground source heat pumps are capable of providing hot water with no need for additional heating. Achieving the maximum output water temperature of a heat pump depends upon many factors, including the hot water flow rate through the domestic hot water cylinder coil, the ground temperature and flow rate. Kensa supplies unvented cylinders specially designed for use with heat pumps including coils with the right amount of surface area. Remember that the immersion heater in the cylinder is used for legionella protection only.

Kensa also manufactures High Temperature heat pumps which have an output of 65°C.

What are slinkies? Are they better than straight pipe?

slinky 002There’s no real difference in efficiency and they both need the same amount of ground, but slinkies generally require less effort for ground work. Having said that, if you are digging your own trenches, then depending on what excavation equipment you use straight pipe can be easier because the trenches are narrower. If slinkies are spaced out correctly, they work really well and there’s no danger of over-extracting heat from the ground. Plus Kensa supply the slinkies pre-coiled so they are quite easy to install.

How can I ensure a successful commissioning?

Book your commissioning slot with Kensa in advance so that we have a dedicated time and try to make sure your slinkies are free of air before you call!

Run your purge pump for a good hour or so – this makes sure the antifreeze is well mixed into the system too. The time required depends on the size of the system, but the longer you can purge for, the better. I often find that installers don’t always run the circulating pumps on the heat pump before commissioning, so air gets trapped in the heat exchangers.  Cover up the electrics with a cloth, check that both circulating pumps are running (undo the pump screw and make sure), and then depress the schraeder valves on top of the heat exchangers to get rid of any air.

Make sure that all your controls are properly wired in before you call, or leave the link wire in place on the wiring terminals. Don’t switch the compressor on beforehand – there’s a sticker on the breaker to remind you not to – but do make sure you have a call for heat from those controls, as this signal causes the pumps to run.

Why do I need to oversize my emitters?


The lower the flow temperature around the heating circuit, the more efficiently the heat pump works and the better your customer’s RHI payments (this scheme has now closed – please visit this page to explore other funding) will be too. As a consequence, you have to make radiators larger so that they can meet the heating requirements of the room – or use underfloor heating instead. Many radiator manufacturers give outputs at the right delta T in their catalogues now, and your underfloor manufacturer should be quite happy to work with any given flow temperature. Bathrooms can be tricky as they often have a small area but a high heat loss. In this case, dual-element towel rails can be really useful to help reduce heat losses.

Always refer to the Heat Emitter Guide or SCOP calculator to help design a system capable of achieving the best efficiencies.

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