* Geekery warning * Apparently, this post is heavy on technical detail and somewhat light on comedic anecdotes. (Personally, I’m ok with that.)
After the assembly work described in part 1 was complete it was time to get to work on the plumbing. This system uses a single submersible pump that’s permanently running 24 x 7. As it’s on all the time, power consumption was obviously a key factor and I was pleased to find this one – Jebao Jecod super low wattage XOR-5000 garden pond pump – on Amazon for just under £60. This has a flow rate of 5,000 litres/hour and uses a mere 22w.
This is the process I went through to size the pump:
- Assume the grow bed volume is around 300 litres (third of an IBC), but half of the volume is the growing media. So there’s about 150 litres in each grow bed.
- If this grow bed floods and drains every 15 minutes then that’s 600 litres per hour.
- There are two grow beds so that’s 1,200 litres an hour.
- Allow a 50% expansion factor (for vertical growing or an additional bed) which makes the total grow bed water supply at 1,800 litres per hour.
- The fish tank is 1,000 litres and the general recommendation is that all of this should be cycled once an hour.
So that makes a total of 2,800 litres per hour.
Driven by the need to over-engineer, the 5,000 litres / hour pump was the natural choice. The pump raises the sump water to a valve assembly where the flow to the grow beds and fish tank can be regulated. The pipework was 1.5″ PVC pressure pipe (from koilogic.co.uk) – this is expensive but a joy to work with.
