|Photo taken after I had bailed out quite|
a lot of the water
The manifold manhole is a watertight concrete box, and unfortunately, there is a slight tendency in the tarmac at the surface to run water towards the lid, and the lid is not water proof. I never inspected it until recently, and found it damp but not swimming in water. The weather was dry. I now understand why the insulation in there was so soggy and deteriorated. We have now had a month of rainy weather (always happens after a hosepipe ban), and the manhole is half full of rainwater.
If the pipes are immersed in water, all the effort of solar charging is wasted - the conductivity of water is so good that it will average the temperatures of up and the down flows very effectively, especially if running at slow pump speed. My earlier efforts to insulate these pipes against losses to the air are nothing compared with the rate of loss to standing water.
I seem to have three choices here, and I could use all, or two of these.
- Get a core drill and make a drainage hole in the base, although I am worried that with the dense soil that the house is built on, the effect of a soak away will be pretty poor.
- Protect the lid from accepting water by sealing the edge of the lid somehow - rubber strip, sealant, clay puddling etc. The tarmac contours around the lid are apparent while bailing, so that much of the water thrown out tries to drift back.
- Install a hand pump, so that the manifold can be inspected monthly, and bailed out with a suction pump. I can't install an automatic pump, as there is no way to lead wiring into the manhole.