The Drive reappears

Well the pressure test was OK and infilling has started - stopped by the need for more sand to cover the pipes!

Things will probably speed up from Tuesday, with more gravel we hope coming Wednesday (from beds near Peterborough). There will need to be rather a large manhole covering the manifolds because they have ended up at right angles (see the previous post), and the cover will thus need to be a steel one fabricated to order. We should be able to lightly cover it with gravel like the other one.

The builder thinks the infilled trenches will drop a bit and may need topping up in 6m or so.

Pressure testing

Hum

Well it looks the same but it has taken a couple of re-runs to get the whole complex pipework to hold pressure fully. The initial installation changed from 4 to 1 bar in a couple of days, but after some joint re-making and two pipe replacements (the seals are rubber o-rings onto the pipes, so a scratch on the pipe can cause leakage) we seem to be holding >3 bar for 24 hours. The Ice Energy book well describes the test procedures but does not quite give criteria for a 'pass'! Since the final circuit is not significantly pressurised I think we are now OK.

However I fear that we have now lost our builders to another job for a while - I wonder who is paying for the hired machinery?

Pipes in

Well that is all the ground loop pipes in. Pressure testing still seems to show some decline (5 bar to 4 in an hour or so) so we shall see.

The missing valve came in OK.

The actual heat pump delivery is now scheduled for 3 weeks time or thereabouts.

It will be good to get the drive back!

It is interesting to see that the soil/clay/rock in the drive bed is quite layered and varies with position. I suppose the area has been a yard for centuries and must have seen a good deal of change.

Plumber Day 1

Well much of the connecting is done - should be finished tomorrow. We did have to call to get them to come (about midday in the end) and we seem inexplicably short of one manifold valve (IceEnergy will ship another) but apart from that all seems well.

Ready for the plumber

Well we now have a fine dig in the drive and a big spoil heap elsewhere (to the left of shot). The work looks good and we can still, just, get round to the garden.

All the trenches

Well that is all the trenches dug - and dampened by the rain.

More trenches

Well there are a good many more trenches, now sanded, and space for spoil is getting tight. And we have drains we did not know about and the drains we did know about run in different places we did not know about (probably!).

The plumber thinks he needs wider trenches to work more easily but this generates far too much spoil so most of them will be narrower. The builder tells me plumbers are like that. Because all the connecting pipes are to be insulated we can at least run them beside each other, or we would need to take the whole drive away....!

Predictably much more disruptive than the hole boring; and now we really realize the problem with having 8 rather than 4 holes. Let us hope that things are back to normal in a couple of weeks!

Trenching Starts

Well there is some progress, but it is limited by the unavailability of the expected digger, delayed by the failure of the transport for it.

But work has started on the manual-dig bits, essentially into the washroom where the heat pump will be located under its wall. The terrace tiles are mostly damaged and will need replacement - and the original makers no longer do them but know a man that does....

The plumber is fairly satisfied that he has what he needs except for the considerable amount of insulation needed (for all the connecting pipework - otherwise it would need to be very deep and all go and return pipes would need to be 1m separated). The Ice Energy book is usefully specific.

Heat v depth

I note FTR that geothermal heating (ie mostly radioactively-generated heat from the hot core of the earth) should be about 1 degree at 39m (of course this does not mean that geothermal is a significant contributor to the heat pump - it is very small - about 40W for the house and pump area compared with 15kW peak for the pump). The temperature change due to heat pump heat extraction over a year might be similar.

But the daily temperature fluctuations reach down a few cm, annual fluctuations 2-3m and on the same basis at 39m we are talking 400 years or so! (quadratic with depth). Though groundwater movements might reduce this a good deal I imagine.

Trenchers

Are now expected Monday - the office 'was supposed to have called and told me that things were slow on the previous job' - I suppose builders are like that...

8 holes!

Well that is the full set of 8 holes done, all at 37-38m or so, and they all hit 'voids' (meaning abrupt loss of return water) at 32-39m. In all cases they hit harder rock-like material first, which returned fragments of what looked like creamy-white limestone. After this the drillers went on a few metres using a fire hydrant as a water supply to allow for no returning water! For these last few metres drilling was mostly clay-like in terms of resistance to drill, with intermittent rock-like resistance. The void holes if any were not so apparent except insofar as the drilling water flowed away at a considerable rate.

Anyway we have enough pipe in the ground and they have 'grouted' it with some sort of sloppy 'bentonite' material that apparently semi-hardens.

The drillers (Geocore) were as good as their word in terms of leaving the site clean and tidy - the plastic sheet is very effective at containing the mess. And they were polite and sensible always.

Slight glitches (apart from the voids!) were the eventual need for 3 skips (some extra cost), partly to clear the drive for the intermediate weekend and partly because the 2nd skip got full of unwanted pump water. This caused some fun for the skip driver when he later stopped quickly and covered his lorry in clayey water!

But basically OK so far. The picture is a fisheye, and boards cover pipes cut off a bit lower to allow drive usage. We expect the builder late next week to start cutting trenches and connecting the ground loop up, using a new manhole. The pipes and bits (but not the insulation needed) were supplied by the heat pump supplier and seem all here.

4 holes

Well after a busy Monday we now have 4 holes, which is more promising, though all 37-39m deep. So the definite plan is to go for 8 holes and we have the requisite extra pipework coming tomorrow.

My geologist Professor friend signs up to the 150M yr old blue-grey lias clays OK but the underlying creamy limestone containing the voids is not really what the UK geological map says. Next hole we will get him a sample!

They now hope to be away late Thursday if all goes well.

The big family party went well - we got 3 cars in the other drive section (with some care) and the other 9 or so cars used the road. Perfect weather anyway!

2.1 holes

Well we do have some holes - but they are 36-38m deep only so there may be a 'void' everywhere around here! My geologist brother-in-law will be consulted this weekend! Anyway we now need 8 holes, and there has been some tree-trimming to accommodate this.

The existing holes have plastic pipes in - with blue end caps - and are both in the grass at left. The machine is starting on hole 3.

Note that 'voids' may well be full of water rather than air, but the drilling fluid still flows away. There are granular materials that are put down in the fluid that can block small cracks - but they did not work here so we may have a more fractured-rock (limestone) environment. They used to use compressed air instead of water - much messier but you do not run out of it if you hit a void! We will now be OKish provided that the remaining holes run to 37.5m or thereabouts (the existing ones are 38 & 36). The current 3rd hole is unlikely to get to this depth today anyway (they stop drilling at lunchtime).

The drillers blocked off the hole base with grout as they put the pipes in - and the hole then fills with water from a gravel/sand layer that is quite close to the surface.

The top picture is of the actual drill bit.