Insufficient depth of pipes to the ground probes?

  • Erstellt am 2023-08-06 14:03:18

grericht

2023-08-06 14:03:18
  • #1
Hello,

short: From the house both pipes go out of the basement at about 1.5m depth to the probe distributor and then about 5m again at only about 50cm depth to the 99m deep boreholes.

long: we have now successfully gotten through the first two winters in the new single-family house. The annual performance factor of the ground source heat pump is overall just above 4. Not record-worthy (neither in the underfloor heating nor in the dimensioning of the heating was much planned beforehand) but I think it's OK. For 2 years I have been thinking again and again whether I am losing some efficiency because maybe the pipes to the two 99m probes lie very shallow in the ground. I haven’t measured it to the centimeter but they lie no deeper than 60cm. Since we want to remove some soil over one of the pipes, it could be only 50cm there.
So this is not even really in the frost-safe zone. I mean, the pipe is regularly "flushed" especially in winter. And it does not freeze at 0 degrees either. But I just have the feeling that it can't be very good to lead probe water at about 9 degrees out of the house, probably cool it again over the first 5m to then warm 2*99m and then cool it down again over the last 5 meters before it goes to the heating.

Question: does this shallow installation probably affect the annual performance factor or even the lifespan of the system?

if yes: are there possibilities/recommendations to insulate the pipes over the first 5m or possibly insulate them in the ground above with e.g. aerated concrete blocks? Or do I have to try to expose them again and lay them deeper?
 

Allthewayup

2023-08-07 21:18:27
  • #2
I will take the floor. Normally, the manufacturer of your heat pump should be able to make statements about the necessary depth of the pipe laying. Have you asked there politely? Is it possible to rule out that the pipes were not already insulated when they were laid? At a depth of only 50cm, that should be the logical consequence. Are there any photos from the time the pipes were installed?
 

Harakiri

2023-08-08 09:39:10
  • #3
Not optimal - deeper (>1 m) uninsulated pipes would even be advantageous, you can take a bit along with you. The impact on the annual performance factor is minimal though.

Insulating the pipes afterwards is also possible, but a bit fiddly - you can quite easily insulate the pipes themselves with Armaflex or similar (make sure it is approved for contact with soil) afterwards: there are slitted versions that can be pushed over the pipe (depending on how close your pipes are laid to each other). However, you must not place any weight directly on the insulation, because the effect is partially lost through compression. Therefore, insulated pipes are usually laid in KG pipes to decouple them. That will be rather difficult for you - but there is also a fairly simple solution for that - you can build a kind of protective cover/shaft in a U-shape from XPS boards around the pipes, then you can pour earth on top.

But I would only do that if you have to do any other earthworks there anyway.
 

grericht

2023-08-18 10:12:20
  • #4
What does the heat pump manufacturer have to do with how deep the pipes to the probe distributor go? There must be standards for that?! The manufacturer only recommends the temperature difference between WQin and WQout – how/whether that is achieved is the heating installer’s business. He told my excavator operator how to bury the pipes to the probe drillings. Probably he just told him to bury them, and that’s why they aren’t very deep. I’ve attached a picture. Why is it advantageous from 1m already? It’s still not 10 degrees there in winter, is it? Technically speaking, it should be favorable to insulate the pipes to a depth from which the ground temperature is warmer than the temperature of the fluid, right? Anyway... it’s never 1m. I hope/think it’s more than 50cm. But definitely not more than 70. Those are great tips! I could imagine that longitudinally halved KG pipe laid over would also quite well bear the weight above, wouldn’t it?! But we’ll see. I recently had an excavator here for a cistern, but that wasn’t included. I think I’ll probably still endure it for a while until something is really changed structurally there.
 

guckuck2

2023-08-18 11:43:35
  • #5
I wouldn’t worry about freezing. On the one hand because of the constant circulation, especially in winter, and on the other hand, the probes are filled with brine, i.e., the freezing point is not at 0°C. I would rather be concerned about the superstructure of the pipes and how to protect the pipes. We have a terrace above ... everything’s fine.

At 1.5m, I also wouldn’t worry about heat loss. Yes, you’re basically right about that, but I think those are peanuts with about 200m probe length.

Chapeau for the probe depth, 2x99m for a single-family house is pretty extreme. Is the extraction performance that poor on your side and/or is the house that big?
You can also save drilling meters (=money) by drilling deeper than 99m and only running one probe, but well, it is what it is now.
 

grericht

2023-08-18 14:40:25
  • #6
1.5m? Both pipes run about 6m each to the probes and only about 0.6m deep in my case. I don't worry about freezing at all. Even if it only kicks in once a day or is off for two weeks, -10 degrees for the brine solution won't be reached so quickly. I think that's fine. For me, it's purely about the seasonal performance factor. If I knew the heating would only work 2% better if the pipes were insulated or 30cm deeper, I would probably spend a little extra money on that. They are located where nothing is above them. At some point, it will be paved there. The new build was so spontaneous that we hardly had time to properly inform ourselves about many things. Here, the heating engineer simply decided. We have 220 sqm of heated area. The uninhabited basement is also heated and livable. Five people live here on about 150 sqm. Actually, he wanted to install an 11kW heating system and drill 2x99m. Fortunately, we managed to talk him down to an 8kW heater due to the official switch from KfW 70 to 55. And frankly, I am always a fan of doing two deep drillings now rather than later realizing the seasonal performance factor is worse. Whether the extra cost was worth it I can't and don't want to calculate anymore.
 

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