Welcome to the Ground Arrays module.
As we have seen in the Heat Pump Basics module, the ground arrays are the part of a heat pump system that harvest low-grade heat from the ground (or from water).
In this section we will examine the different types of ground array, and consider the pros and cons of each type so that you can select the right kind for your project.
We'll go over sizing arrays in order to get the best performance and to comply with MCS guidelines.
We will look at how the arrays are installed in the ground, and illustrate a few important points to remember.
Slinkies are simply straight pipe coiled up!
Kensa sell slinkies that are made with 32mm pipe, cut into 3 different sizes. We make a 30m, 40, and 50m slinky. A slinky that is 30 metres long actually contains 200m of pipe, coiled up. A 40m slinky is 250m of pipe, and a 50m slinky is 300m.
Slinkies are installed into trenches similar to straight pipe - at the same depth (1.2m). But because the slinkies are physically wider, the trenches now have to be 1.2m wide, and at 5m spacings (centre to centre). This means that metre for metre, you need the same amount of space for slinkies as you do for straight pipe. MIS3005 stipulates 3 metre spacings - Kensa have had thousands of slinky installations though, and to guard against over extraction, we stick to 5m. We've never once had an issue with frozen ground because of this extra caution.
Why bother? Well, slinkies can make life easier.
Because you have a bigger space between trenches, you have space to dump the spoil from the trench; you can just leave it alongside. When you are digging for straight pipe and only leaving a metre gap, you won't have anywhere to put that spoil - you have to dump it elsewhere and then move it again to backfill. If you are doing your own groundworks, this isn't generally an issue, but if you are paying groundworkers to do it for you, then time is money!
Over the few years that ground source heat pumps have started to gain popularity in the UK, slinkies seem to have attracted an unfair amount of criticism. Historically this was because often they were installed without enough spacing. MIS3005 actually specifies 3 metres; it's Kensa that stipulate 5 metre centres. In the thousands of slinky jobs we've sold, we haven't had any issues with over-extraction.
Like any ground array, when installed correctly, they work.