Refrigerant pipework for split units - basic practical info requested

[JamesPa]

In my long standing and extremely frustrating attempt to find a way through the minefield that I am presented with when it comes to finding a legal way to install an ASHP (see other posts for details - mad LPA being the latest) I'm now looking at the possibility of a split with the condenser located about 15 m from the house in the garden.

 

I know that the refrigerant piping has to be insulated with the correct type of insulation, what else do I need to know eg:

 

Can it be buried, if so are there any recommendations for how?

Is there a reason not to route the electric cable through the same trench?

Are there any restrictions on bends etc?

How much roughly am I going to have to pay the f-gas bod to connect it up?  Can he just turn up and do it then leave the rest to either a plumber or me?

 

Any info available would be appreciated

[JohnMo]

I would treat it the same as water pipe. Insulate and then encase on plastic duct. So something like 25mm wall thickness insulation, then a flex duct of some sort.  My 28mm is inside 110mm double wall convoluted duct. I pipe per duct. Yours will be smaller but you could fashion something similar.

 

No reason not to encase the cable on same duct, I would use armoured anyway, so it may be easier dropping in the trench.

 

F gas bod should be similar to a plumber.

[JamesPa]

18 minutes ago, JohnMo said:

I would treat it the same as water pipe. Insulate and then encase on plastic duct. So something like 25mm wall thickness insulation, then a flex duct of some sort.  My 28mm is inside 110mm double wall convoluted duct. I pipe per duct. Yours will be smaller but you could fashion something similar.

 

No reason not to encase the cable on same duct, I would use armoured anyway, so it may be easier dropping in the trench.

 

F gas bod should be similar to a plumber.

Thanks, so two ducts and armoured is the basic suggestion if I read you correctly.  Is the pipework flexible enough to pull through buried duct or must that be done first?  Also - just air surrounding the insulated pipe (presumably with duct sealed at each end with foam)?

[JohnMo]

Yes two duct and one cable. I used the duct I used because I had it as left overs from the build.

 

I sealed my duct ends with some stainless steel mesh and expanding foam.

 

I did my insertion first then buried.

[JamesPa]

1 hour ago, JohnMo said:

Yes two duct and one cable. I used the duct I used because I had it as left overs from the build.

 

I sealed my duct ends with some stainless steel mesh and expanding foam.

 

I did my insertion first then buried.

Thanks.  Stainless mesh is a good idea that had not occurred to me, keeps the rats out'

[NCXo82ike]

Hope this isn't hijacking the thread- related question I think.

I'm in a similar situation in a mid-terrace house. The water cylinder and "hub" of the heating setup will be under the stairs. The kitchen will be 10m behind this, and the heat pump will be at least another 8m into the garden. Ideally I'll push it right to the far end of the garden at 30m from the plumbing hub. The site is near-flat with ground level at the end of the garden 1m in ground level below that at the staircase.

 

 

Are there any stats for how much the distance effects the ASHP efficiency?

It'll be a trade-off between aesthestics vs installation cost and efficiency- but I don't know how much weight to put on the efficiency.

I've not been able to find this online. Vaillant Arotherm splits have a max distance of 25m, The Daikin Altherma can do 30m, and the Panasonic units quote 40m. 

 

 

Edited June 7, 2023 by NCXo82ike

[JamesPa]

I think it's possible to do the calculation for a monobloc at least.  The distance causes:

 

Heat to be lost - you can calculate how much given the u value of the insulated pipe.  I looked up upanor and they are around 0.2 W/mK

 

An increase in flow temp because of the heat lost, assume 2% penalty per degree.

 

A bit more pump power needed 

 

I did the calcs for a monobloc based on 20 m run of 32mm water filled pipe with insulation to 150mm dia, buried, and the first was about 400W.  This assumes the ground temp is zero, it will be better than this in practice.  However the second effect isn't insignificant, at 5kW delivered about 150W.

 

In terms of elec power input the first is reduced by the cop of say 3, so will cause an input penalty of about 140W.  Thus the total is about 300W penalty in my calculation.

 

I don't know how this would work out for a split, my gut feel says similar.  The refrigerant temp is higher but it might move faster through the the pipe.  However this is speculation not physics, whereas the calculation for a monobloc is physics.

 

Incidentally since posting this a couple of real heating engineers (not grant harvesters) have pointed out that a monobloc is possible also in this config which is why I calculated for a monobloc.

 

Edited June 7, 2023 by JamesPa

[markocosic]

Splits...

 

Try to ensure that duct stays dry. 90 mm plastic duct will be plenty for a small pair of refrigerant lines in closed cell lass "o" insulation.  Check the units for maximum line length. Cheaper ones might only be 15m. Spendier ones that can tolerate more receiver volume internally etc can often do longer (e.g. 30m) runs.

 

Fitting is a piece of pish. Pull lines. Flare ends PROPERLY. Attach ends. Vacuum down to remove air and boiler off moisture etc. Verify that it holes vacuum. Open up and you're away.

 

F-Gas bod won't like vacuuming down lines installed by A N Other unless they know that the ends were crimped shut (extra length left) and there are no kinks in the lines. 1/4" and 3/8" lines are easy to bend. If you can run 15 mm Hep20 without kinking it you can probably run those. 1/2" and 5/8" lines require more care. 

 

Have you ever run copper brake lines on an old car? Very similar.

[JohnMo]

On 07/06/2023 at 11:51, JamesPa said:

did the calcs for a monobloc based on 20 m run of 32mm water filled pipe with insulation to 150mm dia, buried, and the first was about 400W

If the losses are that high would you be better installing 22mm pipe, have high velocity and install a return pump to overcome the pressure loss.  The return pump would pull about 33W - set to fixed speed so the heat pump variable speed pump can do its own thing.

[JamesPa]

Indeed, that had occurred to me.  My calculation assumes insulated pipe in a cold atmosphere, I haven't yet factored into the calculation the insulating properties of wet soil, which will help.  I'm yet to find an accessible formula for this.

[sharpener]

1 hour ago, JamesPa said:

Indeed, that had occurred to me.  My calculation assumes insulated pipe in a cold atmosphere, I haven't yet factored into the calculation the insulating properties of wet soil, which will help.  I'm yet to find an accessible formula for this.

 

If reasonably deep you can assume a mean temperature of 10C not 0 which will improve the result somewhat. Also the additonal pumping losses serve to heat the water so are not completely wasted.

 

Start collecting surplus packaging materials, polystyrene squiggles, bubble wrap, bags filled with air, that kind of thing to use when backfilling the trench if it isn't in a heavily trafficked area, or put it down the path under the slabs.

 

Edited June 11, 2023 by sharpener

[SteamyTea]

6 hours ago, sharpener said:

Start collecting surplus packaging materials, polystyrene squiggles, bubble wrap, bags filled with air, that kind of thing to use when backfilling the trench if it isn't in a heavily trafficked area, or put it down the path under the slabs

A few cans of expanding foam.

If it is wrapped in thick polythene, it will last for decades.

[JamesPa]

Any idea what the gwp of a can of expanding foam is?

[SteamyTea]

24 minutes ago, JamesPa said:

Any idea what the gwp of a can of expanding foam is?

All depends on how you calculate it.

They generally use hydrofluoroolefin which has a GWP of 4.

Zero ozone depletion. Quite a stable molecule, so will hang around for at least 100 years.

The drive to the shop to buy it will do more damage as I think there is only a few grams in a can.

[NCXo82ike]

Thanks all, genuinely appreciate the thoughts.

 

Anyone ever seen a data sheet for the split units?

 

Edit: I've just sent an enquiry to Vaillant to see if they have this data for their Arotherm split units.

Edited July 4, 2023 by NCXo82ike

[NCXo82ike]

So Vaillant have basically told me that at a distances between 3 and 25m, the distance between the indoor and outdoor units doesn't affect sCOP:

___________

Enquiry:

Please can you help with some technical data for the Arotherm split air source heat pump series.

 

I want to install one in my garden as far as possible from the house.

 

Can you send me some data for efficiency losses and performance relative to the distance between the indoor and outdoor units i.e. based on the length of the refrigerant pipework?

_______________

From Vaillant: 

The units performance and efficiency is related to many variables, but important one to take on board are the length runs of refrigerant between outdoor & indoor units.

Please adhere to below suggestions for normal efficiency and performance.

 

Please also refer to section 5 Hydraulics unit, page 68 with two tables indicating outdoor unit above the indoor unit and indoor unit above outdoor unit.

 

The unit does come pre-charged with enough refrigerant for a 15m pipe run.

 

If the pipe run is greater than 15m, up to 25m, an extra 30g is added per meter for the small units (VWL 35/5 & VWL 55/5) or 70g is added per meter for the larger units (VWL 75/5, VWL 105/5 & VWL 125/5).

 

For anything above 25m, and extra 47g is added (per meter), for the VWL 35/5 & VWL 55/5, 107g (per meter) for the VWL 75/5 & 83g (per meter) for the VWL 105/5 and VWL 125/5.

 

_____________

From me:

Hi, thanks for your reply. I had read section 5 of the installer manual and I'm afraid it still doesn't answer my question.

 

https://www.vaillant.co.uk/downloads/aproducts/renewables-1/arotherm-split-1/vaillant-arotherm-split-1-0-lr-1454128.pdf <page 5 Can you tell me if the technical datasheet above quotes sCOP measured with a particular distance between the units?

Has this been measured at the distance of 25m and can Vaillant estimate the change to the sCOP? For example for the 7kw model.

______

From Vaillant:

Thank you for your email.

 

As specified on the table:

Measured at water temperature 35 deg, and distance between 3 to 25 meters for the Arotherm Plus 7kW unit the sCOP is 4.56.

 

If you adhere to suggestions in my previous email then sCOP should not be affected.

 

If you require any further assistance please reply directly to this E-Mail or call our Aftersales team on 0330 102 8570 for Commercial enquires or

0330 100 3540 for Renewables enquiries.

 

Kind Regards,