Installing heatpump pipes under the slab?

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mattwnz

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#229007 2-Feb-2018 23:52

We are looking at installing the connection wiring and pipes between the exterior and interior boxes, under the slab. This is due to distance and going in any other diretion, such as up the wall into the roof space, then down, due to it being a double height space, would exceed the maximum distance the piping can go. Has anyone else done this? We have been told by one installer to make sure the builder puts in a 100mm PVC pipe under the slab between the units, and they will then be able to push the pipework through. However another installer appears to suggest wrapping the pipework up and installing it into the actual concrete slab before they pour it. I think option B sounds a bit risky, as any movement of the slab from earthquakes etc, could damage the pipe. Also It isn't future proof, so if something goes wrong with the heatpump and it needs replacing, you can't easily install new pipework. Whereas a PVC conduit pipe allows you to pull new pipework through in the future. Anyone have any suggestions? Would the heatpump pipework between the exterior and interior units, be able to work with a new heatpump in the future if it even needs replacing, or would they need new pipework? I have found installer have given such conflicting information, even on the actual sizes that the heat pumps based on the room volumes need to be!

Aredwood

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#1950979 3-Feb-2018 00:06

Can the 100mm PVC be installed as a straight length? Or will you need to put bends in it where it enters and leaves the slab? You might need to put reasonably sized pits at each end of the pipe.

As for using the same pipes with different heatpumps, that partly depends on what refrigerant they use. R404 by my understanding has a much higher operating pressure. So it cant be used in pipe systems designed for R12/R134A.

There is also a really new refrigerant called HFO-1234yf which is a replacement for R134a. I don't know what it's operating pressures are like, or if it will only get used for automotive aircon. Vs also getting used in home heatpumps.

Bottom line, I would want the ability to replace the heatpump pipes at a later date.

mattwnz

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#1950983 3-Feb-2018 00:30

Aredwood:

Can the 100mm PVC be installed as a straight length? Or will you need to put bends in it where it enters and leaves the slab? You might need to put reasonably sized pits at each end of the pipe.

As for using the same pipes with different heatpumps, that partly depends on what refrigerant they use. R404 by my understanding has a much higher operating pressure. So it cant be used in pipe systems designed for R12/R134A.

There is also a really new refrigerant called HFO-1234yf which is a replacement for R134a. I don't know what it's operating pressures are like, or if it will only get used for automotive aircon. Vs also getting used in home heatpumps.

Bottom line, I would want the ability to replace the heatpump pipes at a later date.

Thanks for your reply. The pipes will be straight lengths, but I am guessing the part that goes up into the internal wall will need a bend, and I am guessing it could be a problem pulling a stiff refrigerant pipe up though that, or whether they will use an elbow connection. I can see how having a pit would make it easier to pull it in and then bend it up, but they didn't say they needed that, and it would be a bit messy for the builder to have to deal having to then in the pit with another concrete pour. The outside connection will just go out through the side of the footing of the slab, to where the the pump is located, so that end shouldn't be a problem. I would also want the ability to replace the pipework at a later date, which is why I think having it in a PVC tube is preferable, because once something is in a slab, it is vertically impossible to do any work on it, unlike a timber wall which can be cut into relatively easily.

Aredwood

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#1950988 3-Feb-2018 01:16

The reason I suggested a pit, I was meaning never fill the pit with concrete. Just have a removable lid on top of it. Can you locate the pit inside a wardrobe or cupboard? Note that elbow fittings in heatpump pipes are normally brazed elbows. If an elbow can't be created by just bending the pipe.

Also some new generation refrigerants are actually flammable. Heatpumps using such refrigerants have restrictions on min room size and pipe length. So if all of the gas leaks out into a sealed room, in theory the gas won't be concentrated enough for it to be able to burn. There might be restrictions on installing such heatpump pipes in small spaces, where a gas leak could create higher gas concentrations.

mattwnz

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#1950989 3-Feb-2018 01:21

Thanks. I will discuss the pit option with them, as that would give them more room to work with, and luckily there is a wardrobe behind the indoor unit location.

mdf

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#1951051 3-Feb-2018 10:44

This is a new build? Another option might be a ground source heat pump. Don't need the outside unit at all then (they are spendy, so are only really justifiable as part of a central heating system. But very efficient - at least 400% from what I gather).

I haven't used one myself - I saw one on Grand Designs many years ago and promptly lost the next two days down an internet rabbit hole. Have followed developments in the area since. Geek.

sparkz25

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#1951110 3-Feb-2018 14:01

defanately straight lengths, if you cant use a pit inside i would go to your local electrical wholesaler and get some electrical ducting bends as they are a nice sweeping bend and not a sharp 90

you could even bring them up in the wall and no one would know.

and then in future if you did need to replace a pipe or something it wouldn't be that hard to replace as it would be a nice sweeping bend and you could pretty much push the paircoil through.

how long is the run going to be?

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mattwnz

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#1951225 3-Feb-2018 18:56

sparkz25:

defanately straight lengths, if you cant use a pit inside i would go to your local electrical wholesaler and get some electrical ducting bends as they are a nice sweeping bend and not a sharp 90

you could even bring them up in the wall and no one would know.

and then in future if you did need to replace a pipe or something it wouldn't be that hard to replace as it would be a nice sweeping bend and you could pretty much push the paircoil through.

how long is the run going to be?

That is a good alternative to a pit. What sort of radius and diameter of pipe should a bend be for that sort of thing? I am not sure what diameter the paircoil is and ow much it can be bent,as that isn't listed on the mitsubishi website, but guessing it does have a reasonable amount of flex in it

The run is about 20 metres from memory. But it is within the max limit as it was checked by the installer. It is for a new build, but the installer says they can't make it to the site to check where the builder is putting it in properly due to high workload over summer. So are looking at using another installer, because we don't want to take the risk of it not being put in correctly. Once slab is poured it makes things very difficult if they haven't installed it right.

webwat

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#1952685 6-Feb-2018 22:51

Aredwood:

Can the 100mm PVC be installed as a straight length? Or will you need to put bends in it where it enters and leaves the slab? You might need to put reasonably sized pits at each end of the pipe.

As for using the same pipes with different heatpumps, that partly depends on what refrigerant they use. R404 by my understanding has a much higher operating pressure. So it cant be used in pipe systems designed for R12/R134A.

There is also a really new refrigerant called HFO-1234yf which is a replacement for R134a. I don't know what it's operating pressures are like, or if it will only get used for automotive aircon. Vs also getting used in home heatpumps.

Bottom line, I would want the ability to replace the heatpump pipes at a later date.

Yup, you cant be sure what pipes are suitable for the next heatpump until the guys that supply it tell you what pipes it needs. I'm suprised that the maximum length would be exceeded simply by the height of the building, would have assumed this can be compensated for by bigger pipes.

Bottom line is whether the pipes can be accessed for replacement/repair, you don't want to bolt something down onto the concrete and find the pipe lifted a bit when the concrete was poured so you've drilled through a pipe thats impossible to repair.

Time to find a new industry!

mattwnz

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#1952705 7-Feb-2018 00:17

webwat:

Bottom line is whether the pipes can be accessed for replacement/repair, you don't want to bolt something down onto the concrete and find the pipe lifted a bit when the concrete was poured so you've drilled through a pipe thats impossible to repair.

That is a good point. They are now putting them in conduits under the slab, it is really about making sure they are in a straight run and end up in the right locations, and have a decent radius on the pipe as it goes vertical out of the slab. I found the install instructions on the Australian website, as the technical stuff on the New Zealand website is locked down for installers only. That mentions that you can only have up to 8 bends in the paircoil, and the maximum bend radius is 100mm. So that does provide a bit more knowledge for me.

wellygary

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#1952810 7-Feb-2018 10:05

mattwnz:

That mentions that you can only have up to 8 bends in the paircoil, and the maximum bend radius is 100mm. So that does provide a bit more knowledge for me.

I'm assuming you mean minimum bend radius?