ASHP - choices, choices. Feel like I’m back at square one

[-rick-]

2 hours ago, Great_scot_selfbuild said:

I’m not doing the loop design myself (I’m drawing the line at buying a windows laptop just to use LoopCAD), and although the suppliers don’t share their designs before we commit to using them, we’ve had some say their design has 7 circuits and others say they have designed for 11 circuits. Are you advising that we make sure we ask for more than one circuit per room for the redundancy (just to make sure they factor it into their design)?

 

Gus and I have debated this before. My position is you should design the loops to output the heat you need at very low temps. Within reason more shorter loops vs fewer longer ones makes sense. Less than 100m but close to it is about the ideal loop length IIRC. But I wouldn't deliberately add extra loops if it throws off your heat output calcs, etc. In the event of a loop failure, firstly you want to find it and fix it before the concrete gets really hard and in the event that isn't possible then because you have designed the system for very low temperatures, you should be able to compensate for the loss by running temps a bit higher and adjusting flow rates.

Edited yesterday at 10:18 by -rick-

[Iceverge]

Don't forget physics. 

 

Meaningful energy transfer will only occur when there's enough  temperature difference. A slab at 24⁰ will impart very little heat into a room at 22⁰ but a lot into a room at 15⁰. 

 

Given identical pipe spacing, on a single zone, the room with big windows or a leaky external door will extract far more energy from the UFH all by itself than the small internal room. 

 

Its not the case that a pantry will end up at 30⁰ and the hallway at 15⁰. 

 

The pantry will probably get to 22⁰ and the hallway to 20.5⁰. 

 

In a passive class house it'll all end up at 21⁰. Regardless of pipe spacing or omitting rooms or forgetting UFH and ASHP and just plugging in a cheap oil filled rad. 

[Nickfromwales]

23 hours ago, Iceverge said:

Don't forget physics. 

 

Meaningful energy transfer will only occur when there's enough  temperature difference. A slab at 24⁰ will impart very little heat into a room at 22⁰ but a lot into a room at 15⁰. 

 

Given identical pipe spacing, on a single zone, the room with big windows or a leaky external door will extract far more energy from the UFH all by itself than the small internal room. 

 

Its not the case that a pantry will end up at 30⁰ and the hallway at 15⁰. 

 

The pantry will probably get to 22⁰ and the hallway to 20.5⁰. 

 

In a passive class house it'll all end up at 21⁰. Regardless of pipe spacing or omitting rooms or forgetting UFH and ASHP and just plugging in a cheap oil filled rad. 

Amen. 🙏 

[Iceverge]

Ok.....

 

Having a brainwave here .......it's hurting......there's blood coming out my ears..............

 

Take a well insulated house with an ASHP. Lay UFH at 200mm centres  Don't bother with room by room patterns. Just slap it down in a big up and down pattern or whatever.

 

Pour 150mm of concrete over the top and then ensure no one drills more than 75mm into the concrete. And after than go to town with room layout etc. 

 

"Trim" heat the bathrooms with direct electric to make warmer if needed.

 

Any reason this wouldn't work? 

 

 

 

 

 

 

 

 

 

Edited 3 hours ago by Iceverge

[JohnMo]

1 minute ago, Iceverge said:

Ok.....

 

Having a brainwave here .......it's hurting......there's blood coming out my ears..............

 

Take a well insulated house with an ASHP. Lay UFH at 200mm centres  Don't bother with room by room patterns. Just slap it down in a big up and down pattern or whatever.

 

Pour 150mm of concrete over the top and then ensure no one drills more than 75mm into the concrete. And after than go to town with room layout etc. 

 

"Trim" heat the bathrooms with direct electric to make warmer if needed.

 

Any reason this wouldn't work? 

I did similar but at 300mm centres, just didn't pipe under internal walls, kitchen units or beds and only did 100mm concrete.

[Iceverge]

I'm thinking idiot resistant ( not idiot proof, that's impossible).

 

Simple pattern to lay. Single zone. Run at a low flow temp.

 

Would it actually make any difference to the feel of the house avoiding walls beds, kitchen cabinets etc etc. 

 

 

[-rick-]

4 minutes ago, Iceverge said:

Would it actually make any difference to the feel of the house avoiding walls beds, kitchen cabinets etc etc. 

 

In a low temp system I'd guess not. My planning around this is to aim to not worry about kitchen cabinets etc. Seems like extra effort to try and route around things and in the event the layout is changed in future might you end up with an area of floor that is a touch cooler than others (I can't see it affecting room temp but might be noticable with feet on the floor).

[BadgerBodger]

I know I’ll probably be told this is wrong but I pneumatic tested mine and left pressurised while pouring. 
 

And then beyond. 
 

I forgot and knicked the pipe which was flush up to the edge of the concrete in a rebate o left so I could screed the shower to falls and boy did I get a surprise. 
 

 

[-rick-]

55 minutes ago, BadgerBodger said:

I know I’ll probably be told this is wrong but I pneumatic tested mine and left pressurised while pouring. 

 

Thats the right thing to do.

 

55 minutes ago, BadgerBodger said:

I forgot and knicked the pipe which was flush up to the edge of the concrete in a rebate o left so I could screed the shower to falls and boy did I get a surprise. 

 

Worked as intended then! Good to know of the problem straight away. Though if it really made an impression on you maybe you had the pressure a bit too high