Try to contact Colin Furze, he has tons of experience in residential tunneling.

At the risk of not answering the question asked, what is the power output of the proposed heat pump, and how far is it between the external and internal unit? That will (somewhat) determine the diameter of flow and return pipes.

The Uponor pipes look rather bulky (and has a bend radius of 0.5m), with water pipe internal diameter of 25mm (or 26.2mm as it is unclear whether pipe 1 or pipe 2 is for water); that implies a power rating of 3.14*(2.5cm/2)^2 * 80 cm/s * 5 degrees C * 4.2 J/cm^3 = 8200W, or else 9050W assuming a delta-T of 5 degrees C and a desire to keep water speed to 0.8m/s.

I've been thinking about a split system as the best place to site a heat pump is about 15m away from the indoor unit, through a convoluted route. Have you considered a split system? I wonder if having refrigerant lines running through the house itself might be less obtrusive. For instance a 5kW Panasonic generation K bi-bloc heat pump requires 1/4" - 5/8" lines. An additional benefit of a split system is that you don't have to think about anti-freeze valves or (performance reducing) anti-freeze in the pipes.

Posted by: @chickenbig

↑

At the risk of not answering the question asked, what is the power output of the proposed heat pump, and how far is it between the external and internal unit? That will (somewhat) determine the diameter of flow and return pipes.

The Uponor pipes look rather bulky (and has a bend radius of 0.5m), with water pipe internal diameter of 25mm (or 26.2mm as it is unclear whether pipe 1 or pipe 2 is for water); that implies a power rating of 3.14*(2.5cm/2)^2 * 80 cm/s * 5 degrees C * 4.2 J/cm^3 = 8200W, or else 9050W assuming a delta-T of 5 degrees C and a desire to keep water speed to 0.8m/s.

Nominally, 6kW output. Linear distance would be around 4.5m outdoor, 7.5m under house not including bends up and down.

Viessmann branded quattro connection line (2x40x3.7-1x32x?.?-1x25x?.?/160): diameter 160mm; bend radius 600mn; core hole ?.
Uponor Ecoflex Thermo Twin HP (2x40x3,7-2x32x3,5/175): diameter 175mm; bend radius 700mm; core hole 250mm.
Uponor Ecoflex Thermo Twin HP (2x32x2,9-2x32x3,5/140): diameter 140mm; bend radius 500mm; core hole 200mm.

Posted by: @john-connett

↑

Viessmann branded quattro connection line (2x40x3.7-1x32x?.?-1x25x?.?/160): diameter 160mm; bend radius 600mn; core hole ?.
Uponor Ecoflex Thermo Twin HP (2x40x3,7-2x32x3,5/175): diameter 175mm; bend radius 700mm; core hole 250mm.
Uponor Ecoflex Thermo Twin HP (2x32x2,9-2x32x3,5/140): diameter 140mm; bend radius 500mm; core hole 200mm.

There is also:
Uponor Ecoflex Thermo Mini (32x2,9/68): diameter 68mm; bend radius 250mm; core hole 125mm.

Another possibility is to run the large pipe to the house wall then run two smaller pipes under the house. Smaller holes, tighter bend radius.

Using common sense alone,  I don't like the suggestion of using a core drill through a beam & block floor slab to take any of these pipe sizes. A standard block is 215mm wide. Even if the hole position just happened to be spanning evenly across two adjacent blocks, you're removing half of the material from each.
And in the worst case you actually end up drilling right across the width of a single block, thereby causing it to fall. It would no longer span between the two beams.

Consider also that the void beneath the beam/block layer must remain inaccessible to vermin.
Not only is that a requirement of Building Regs, but you can certain that any self-respecting rodent would first strip the insulation from around your pipes.

Posted by: @transparent

↑

Using common sense alone,  I don't like the suggestion of using a core drill through a beam & block floor slab to take any of these pipe sizes. A standard block is 215mm wide. Even if the hole position just happened to be spanning evenly across two adjacent blocks, you're removing half of the material from each.
And in the worst case you actually end up drilling right across the width of a single block, thereby causing it to fall. It would no longer span between the two beams.

Common sense is a good starting point but not a full solution. I suspect that a lightweight concrete floor block may lack the structural strength to maintain a core hole and an expanding ring seal. A possible approach would be to replace a floor block with something of sufficient structural strength that was consistent with the floor beam point loading limits. Using 2 x 68mm pipes rather that a 140mm pipe might give more design flexibility. There is also the question of how the pipe(s) would be anchored. Would an expanding ring seal give sufficient support? Pipe expansion would also need to be considered. There are questions that probably need answers from a beam and block expert and someone with experience working with these pipes.

Posted by: @transparent

↑

Consider also that the void beneath the beam/block layer must remain inaccessible to vermin.
Not only is that a requirement of Building Regs, but you can certain that any self-respecting rodent would first strip the insulation from around your pipes.

According to What size hole can a rat get through? an adult rat will need 12mm in a horizontal gap and a round hole of 25mm diameter and young rats will bring those measurements down to 8mm and 20mm diameter. Any practical solution to this challenge is likely to be rodent resistant. Pipe seals will be designed with this in mind. My house is fairly airtight and any thermal bridging should be kept to a minimum.

Any solution would need to comply with Building Regulations.

Thanks for your comments.

Posted by: @chickenbig

↑

At the risk of not answering the question asked, what is the power output of the proposed heat pump, and how far is it between the external and internal unit? That will (somewhat) determine the diameter of flow and return pipes.

The Uponor pipes look rather bulky (and has a bend radius of 0.5m), with water pipe internal diameter of 25mm (or 26.2mm as it is unclear whether pipe 1 or pipe 2 is for water); that implies a power rating of 3.14*(2.5cm/2)^2 * 80 cm/s * 5 degrees C * 4.2 J/cm^3 = 8200W, or else 9050W assuming a delta-T of 5 degrees C and a desire to keep water speed to 0.8m/s.

The Viessmann  branded pipe is 2x40x3.7 with an internal diameter of 32.6mm which is suggested for all of the Vitocal 200-A range (six models from 2.3 to 11.8kW (EN 14511 A2/W35, spread 5K)). Using your calculation gives a power rating of 14022W. The largest of the range claims a maximum output of 14.3kW (EN 14511 A7/W35, spread 5K) which seems appropriate.

Looks like the Ecoflex 2x32x2,9 would be adequate for the 5.7kW model.

Where does the 80 cm/s come from? I think I understand the rest of the calculation.

Thanks for the comment.

Yes, I like the idea of replacing a block in the sub-floor to provide a more robust entry point into the house.

Sleeving the pipe(s) with corrugated PVC/PE conduit and pouring a barrow-load of concrete around the entry point would suffice,
but it's not 'elegant'.

I wasn't concerned about rodents entering the house, but rather having access to the 7.5m length below the block & beam layer.
You wouldn't be able to see what damage they did to the pipe insulation below the house.

There needs to be a rodent-resistant zone around the point where the pipes enter that under-house void.
A barrow of sharp chippings would do it if you can somehow ensure that it provides sufficient depth of material that a mouse/vole/shrew would give up before penetrating the stone.

Posted by: @john-connett

↑

Where does the 80 cm/s come from?

It is a rule of thumb to keep water flow within reasonable limits (not making too much noise or eroding the pipe). I am struggling to find references on the internet;  https://www.heatweb.co.uk/w/index.php?title=Pipework_Calculations recommends a peak speed at design load greater than about 0.75 m/s (to move debris around) but less than 1.5 m/s. That page collates somewhat conflicting advice.

I second chickenbig.  When I did the research for my system, I found a lot of information suggesting that, when the connection between the outdoor unit and inside is long and/or complicated, that is a pointer towards a split system design - refrigerant pipes can be longer + thinner, doesn't need such enormous insulation, to achieve the same performance. 

There's a presentation (on this forum) here https://renewableheatinghub.co.uk/what-is-the-difference-between-a-split-and-a-monobloc-heat-pump   

might be worth you looking at some split system specs?

Posted by: @chickenbig

↑

a peak speed at design load greater than about 0.75 m/s (to move debris around) but less than 1.5 m/s.

A second reference, https://www.h2xengineering.com/heat-pump-ebook-lp/ page 29, recommends a maximum speed of 1 m/s. Graham Hendra's book "50 things heating professionals need to know about Heatpumps" section 67 states "The problem is if you push too fast the pipes become noisy. So, the rule is to never let the water move at more than 1.5 meres per second"