Land required: real world examples

[eandg]

How much land did any GSHPers require to lay their slinkies in? 

[Jeremy Harris]

14 minutes ago, eandg said:

How much land did any GSHPers require to lay their slinkies in? 

 

 

Depends almost entirely on the heat output that's needed, together with the type of soil, and, to some degree, the acceptable soil recharge time (which is location dependent).  It's not hard to calculate, but without at least some basic data it's impossible to guess, I'm afraid.

[ProDave]

We have a 1/3 acre plot.  Some of that is "cut off" by a burn.  So on the house side of the plot we have about 1/4 acre.

 

I was originally going to use a GSHP until I realised it would need almost all the garden.  I had my own digger at the time so it would just have been my time, but it would have been a lot of work.

 

Then I realised the cost of the slinky pipe, manifolds and antifreeze to go in it, would far exceed the cost of the actual GSHP unit.

 

It was at that point I decided the huge extra costs would never be paid for by the slightly higher efficiency, so I decided on an Air Source Heat Pump instead.

[Jeremy Harris]

The very rough rule of thumb for good, wet, soil, that doesn't have big rocks in it,  is that a trench about 1.2m wide, 10m long and 1.2m deep, with a slinky laid horizontally in the bottom and covered with sand, will yield about 1 kW of heat.  So for a 10 kW output GSHP you need very roughly 100m of trench 1.2m wide and 1.2m deep.  If that folds back on itself then it has to be spaced so that the centres of any parallel slinky trenches are not closer than 5m.  Collector trenches can be no closer than about 2.5m to the house foundations or the boundary.

 

For example, a 10 kW collector run as four folded trenches, would need an area roughly 25m long by 25m wide.  The amount of soil excavated, not allowing for the trenches for the pipes to and from the collector, would be about 144m², or around 250 tonnes.

[dpmiller]

thought about it, had enough land for it, but having seen how much solid rock we have within a couple of foot of the ground, I'm glad I discounted it...

[eandg]

Thanks and apologies the initial info was so scant. I reckon we've only about 400m2 we could use which would be on the cusp if at all possible in the best of circumstances so given your responses it's perhaps not worth the time investigating further. 

[ProDave]

One of the things that put me off was the sheer volume of earth to move, and the logistics (which on our site would have been tight) of where to put the excavated soil while you lay the pipes before you put it back.

 

And then, much of that land was where services, drain pipes etc would then be laid, so you would be trying to lay other services over soil that had been disturbed, hoping it had been compacted properly and would not settle more.

[scottishjohn]

saw something somewhere that said you need  at least 10times the sqm of floor area for slinkies  -minimum as a rough guide