Rate my UFH design

[Shaun McD]

Learning as I go here having read lots of great content! Below is my first pass at a high level UFH layout for our new build. House is a single storey, and the area off the kitchen/dining to the south is covered flat roof, so will act as a brise soliel for the central living area. House will be on a kore insulated foundation, TF at 0.15 wall u value and looking around 4875w total heat loss at -10 based on @Jeremy Harris fantastic spreadsheet. Rough maths of around 18 W/m2 on hopefully a very very rare worst day.

 

My broad assumptions/reasonings on design;

• Due to size and orientation of house, two manifolds looks to be obvious, one central within each larger zone.
• Each of the two zones will have heat redistribution available within the zone to distribute solar gain around the slab - controls within HA
• I plan to have actuated loops to allow for heat limit - again controls within HA
• I am guessing I will need to use a buffer/llh but not got that deep into that understanding/calculations yet.
• Pipe spacing of 150mm (maybe less if negates need for buffer/llh) to allow for lower flow temps.
• ASHP will determine when there is heat demand based on temp of return - i.e. neither zone can call for heat independently. 
• Be aiming for a ASHP in the region of 6-8kw output (dependent on brand - assuming no issue as they can modulate), 300-500l DHW and around 5.5KW worth of south(ish) facing PV on the central living area pitched roof.

 

Hoping for input on;

1. A general keep me honest if design makes sense and has potential to be efficient and setup to allow low flow temps? What am I missing or not accounting for?
2. Does the zone proportions make sense, especially considering the redistribution of heat plan? I am conflicted if I should add kitchen area to zone 2 to better proportion the area of solar gain V low impact solar gain? Other option is to split the kitchen/living area and have half on each zone? 
3. Any issue with the distance between manifolds and if the system will have sufficient flow to satisfy both?
4. How best to go about decision on buffer/llh, 2 port, 4 port, coil in etc. My understanding is that in an ideal scenario, the best buffer/llh is NO buffer/llh but it seems to be the more cautious approach here to put one in and potentially sacrifice a very small COP hit to prevent any risk of under sizing of ASHP or promoting cycling & defrosting.  

 

 

Edited March 23, 2023 by Shaun McD

[nod]

Most of UFH companies will do you a design Free of charge 

[JohnMo]

Our house is a little smaller than your a similar W/m2.

 

Your floor buildup makes a big difference to how your floor performs, ours has a 100mm concrete screed and 300mm pipe centres, we have under 600m of pipe in nearly 200m2 area and a thermostat in each room was just a waste of money, as the reaction time is around 12 to 14 hrs.  Thermostat are still on the wall, but have no actuators installed now.

 

We now just use a single thermostat in the hall and have balanced flows to get the room temps we need.

 

Well insulated houses are very different from the normal housing.  Flow temps for UFH are very low, ours at -9 was 35 degrees and at around 8-10 degrees is 25. Floor surface temp is circa 21 to 22, so if you get solar gain, the floor no longer gives out heat as the room becomes warmer than the floor.

 

Your utility and halls does not need any loops, they will all get heated by the loops passing through them, just spread the pipes out.

 

I would do a single manifold, download a copy of loopcad, and use it to design a balanced system.  Go to a company they will get you to install several miles of pipe and about 10 to 12 zones. Which is a real waste of time and money in my opinion.

 

If you are doing zones do them by function, so bedrooms as one zone and living day space as another.

[Shaun McD]

46 minutes ago, JohnMo said:

Our house is a little smaller than your a similar W/m2.

 

Your floor buildup makes a big difference to how your floor performs, ours has a 100mm concrete screed and 300mm pipe centres, we have under 600m of pipe in nearly 200m2 area and a thermostat in each room was just a waste of money, as the reaction time is around 12 to 14 hrs.  Thermostat are still on the wall, but have no actuators installed now.

 

We now just use a single thermostat in the hall and have balanced flows to get the room temps we need.

 

Well insulated houses are very different from the normal housing.  Flow temps for UFH are very low, ours at -9 was 35 degrees and at around 8-10 degrees is 25. Floor surface temp is circa 21 to 22, so if you get solar gain, the floor no longer gives out heat as the room becomes warmer than the floor.

 

Your utility and halls does not need any loops, they will all get heated by the loops passing through them, just spread the pipes out.

 

I would do a single manifold, download a copy of loopcad, and use it to design a balanced system.  Go to a company they will get you to install several miles of pipe and about 10 to 12 zones. Which is a real waste of time and money in my opinion.

 

If you are doing zones do them by function, so bedrooms as one zone and living day space as another.

 

Thanks @JohnMo, I will look at loopcad over weekend and see how it goes. For sure caught between playing it safe with pipe centers and zones V larger spaced open loops. I would have thought I would struggle with loop length on a single manifold but maybe will look about having it in a kitchen unit if I can make the lengths work

[JohnMo]

Longest reach loop would be master bedroom, but there will not be that much pipe in the floor, you are allowed about 100m run, so that should be ok.  Dressing room and ensuite do as another loop, both want to be warmer than the bedroom. So you can increase compared to master bedroom to more heat out of the floor at same flow temp and or run at closer spacing for UFH pipes.

 

Kitchen living will have possibly 3 loops, then possibly another 4 loops for the other side of the house. So a single 9 or 10 loop manifold.  The rest of the house will just borrow the heat from the heated areas as it's fairly open.

 

Here is my UFH plan.

 

Only change I made, was to meander the kitchen loop around the hall a little near the doorway into the house.

 

My bathroom and kitchen are on the same loop. Works fine.

 

The store is actually an office now, it is fine without UFH as the door stays open and it gets its heat from the hall, which itself is not directly heated.

 

Things I would change are

Closer spacing on ensuite and dressing room loops, say 200mm instead of 300mm.

 

 

 

[Shaun McD]

3 hours ago, nod said:

Most of UFH companies will do you a design Free of charge 

 

I am finding that most companies want a deposit before they will design

[JohnMo]

Forgot to mention, with free loopcad I couldn't get the insulation down far enough so the heat losses are slightly higher on the drawing are slightly higher than reality.  I also operate on a 4 deg delta T so flow temps are lower and floor temps are more even.

[Shaun McD]

5 minutes ago, JohnMo said:

Longest reach loop would be master bedroom, but there will not be that much pipe in the floor, you are allowed about 100m run, so that should be ok.  Dressing room and ensuite do as another loop, both want to be warmer than the bedroom. So you can increase compared to master bedroom to more heat out of the floor at same flow temp and or run at closer spacing for UFH pipes.

 

Kitchen living will have possibly 3 loops, then possibly another 4 loops for the other side of the house. So a single 9 or 10 loop manifold.  The rest of the house will just borrow the heat from the heated areas as it's fairly open.

 

Here is my UFH plan.

 

Only change I made, was to meander the kitchen loop around the hall a little near the doorway into the house.

 

My bathroom and kitchen are on the same loop. Works fine.

 

The store is actually an office now, it is fine without UFH as the door stays open and it gets its heat from the hall, which itself is not directly heated.

 

Things I would change are

Closer spacing on ensuite and dressing room loops, say 200mm instead of 300mm.

 

 

 

 

Thanks for this, would you mind sharing what your wall, floor and ceiling U values are? And what sort of temps are you at in each room? My better half must have been an eskimo in a previous life as she has current house at 22-23 in living area, and is happy to sleep in bedroom at 21

[JohnMo]

Floor 0.09

Walls 0.14

Roof 0.13.

Glazing 0.6 to 1.

 

Rooms at 19 to 20, bedrooms at 17 to 18.

 

Our house is approx 3 to 4 degs cooler than the last one (single glazed 1830s house) and more comfortable, there are no drafts, triple glazing doesn't suck the heat from your body like single glazing did, the warm floor is always radiating heat at you.  So room air temp can be misleading.

[Shaun McD]

23 minutes ago, JohnMo said:

Floor 0.09

Walls 0.14

Roof 0.13.

Glazing 0.6 to 1.

 

Rooms at 19 to 20, bedrooms at 17 to 18.

 

Our house is approx 3 to 4 degs cooler than the last one (single glazed 1830s house) and more comfortable, there are no drafts, triple glazing doesn't suck the heat from your body like single glazing did, the warm floor is always radiating heat at you.  So room air temp can be misleading.

 

Ok good to know. For the pipe spacing, whats the cons (outside of cost to install) of having them closer to allow for lower flow temps? Does the principle of having more water in the floor allowing for more heat/cooling not fully translate?

[JohnMo]

Use this to make your own informed decision. I made the assumption the outside temp average is more likely to 4 or 5 degs in the heating season instead of the odd day in the -5 or below. So more likely to be heating at 10 to 15W/m2 than 20 W/m2. Which is well below the chart for flow temps.

 

 

[JohnMo]

What I noticed is the more normal house with heat demands in the 50W/m2 + spacing makes a big difference to flow temp, low energy house a very small difference.

[Shaun McD]

57 minutes ago, JohnMo said:

What I noticed is the more normal house with heat demands in the 50W/m2 + spacing makes a big difference to flow temp, low energy house a very small difference.

 

Yeah fair point. In terms of working this back to ASHP sizing, is there big negative to having a much larger machine than needed? Assuming for heat loss at the average temp range is naturally a chunk smaller, so adding 125% to this number will be a chunk smaller than the -10 worst case heat loss * 125%.

And how would I normally go about adding the energy needed for DHW into the overall heat loss? 

Also on buffer v no buffer - how did that look for you? 

[JohnMo]

Currently still on a gas boiler, with a big buffer.  But getting closer to getting the ASHP hooked up, that will be run on two zones, 1. house and 2. summer house. Summer house will not be allowed to call for heat, just switch off heat.  House will have over temp thermostat and generally run 24/7.

 

I wouldn't size for a few hours or days in a year, the norm is to size for -2 to 3. Most of its life it will be above 5 degs.

 

Then you are looking at what the output of the ASHP is at that temp.  Mine basically does 6kW down to -15.  But it's rated at 6kW at 15 degs also.  What's more important is turndown so when it's 10 degs outside and you only need 1kW it works with out short cycling. You need about 60l system capacity open to the heat pump for that.

 

You have a limited choices of ASHP available, too big you need a buffer, too many zones you need a buffer.

[nod]

4 hours ago, Shaun McD said:

 

I am finding that most companies want a deposit before they will design

Cadman 

Manchester They have been in business over a hundred years 

 

[Susie]

8 hours ago, JohnMo said:

Longest reach loop would be master bedroom, but there will not be that much pipe in the floor, you are allowed about 100m run, so that should be ok.  Dressing room and ensuite do as another loop, both want to be warmer than the bedroom. So you can increase compared to master bedroom to more heat out of the floor at same flow temp and or run at closer spacing for UFH pipes.

 

Kitchen living will have possibly 3 loops, then possibly another 4 loops for the other side of the house. So a single 9 or 10 loop manifold.  The rest of the house will just borrow the heat from the heated areas as it's fairly open.

 

Here is my UFH plan.

 

Only change I made, was to meander the kitchen loop around the hall a little near the doorway into the house.

 

My bathroom and kitchen are on the same loop. Works fine.

 

The store is actually an office now, it is fine without UFH as the door stays open and it gets its heat from the hall, which itself is not directly heated.

 

Things I would change are

Closer spacing on ensuite and dressing room loops, say 200mm instead of 300mm.

 

 

 

Did you not put any loops under the beds. I’ve had two drawings done both have loops under the bed. For one room I definitely will as it may be an office the other two rooms I’m not sure, what if the bed is in the place for the next owner or even me when older with a walking frame. 

😂
 

[Mike]

25 minutes ago, Susie said:

I’ve had two drawings done both have loops under the bed.

Personally I put loops everywhere (for maximum flexibility), and at no more than 150mm centres (to allow for the possibility of using it for cooling in the future).

[IanR]

1 hour ago, Susie said:

 I’ve had two drawings done both have loops under the bed.

 

I'd only avoid the areas under fixed furniture, ie. kitchens, bathrooms. built in cupboards etc. to keep flexibility. I was happy to go up to 200mm centres for cooling and it works well. In the bigger picture, pipe is relatively cheap.

 

There's not a single solution that suits all houses. I'm glad for the zoning that I have since with the benefit of solar gain, on the cold days where there's only intermittent sunshine, there's enough gain to heat the rooms that get the gain directly, so those zones will switch off, but the rooms on the North-East side will continue to be heated.

[JohnMo]

9 hours ago, Mike said:

150mm centres (to allow for the possibility of using it for cooling in the future)

Fully intend to run cooling this year in 300mm loops.

 

10 hours ago, Susie said:

Did you not put any loops under the beds. I’ve had two drawings done both have loops under the bed. For one room I definitely will as it may be an office the other two rooms I’m not sure, what if the bed is in the place for the next owner or even me when older with a walking frame

Hot enough already in bed, without a heater under the bed as well, putting the beds anywhere else in the room, would look away from the Loch view so you wouldn't move them. All room are large enough to move around with a walking frame and even have wheelchair access to the front decking.

[Mike]

On 25/03/2023 at 09:07, JohnMo said:

On 24/03/2023 at 23:11, Mike said:

150mm centres (to allow for the possibility of using it for cooling in the future)

Fully intend to run cooling this year in 300mm loops.

I was involved with a commercial development a few years back where overheating was a problem and suggested using the 300mm-spaced UFCH pipes for cooling. I don't have their calculations, but the consulting engineers concluded that 150mm spacing would be required for it to make a worthwhile difference. Of course that's a specific case, but I've opted from 150mm maximum spacing since then. It will be interesting to see how you find it @ 300mm.

[JohnMo]

18 minutes ago, Mike said:

will be interesting to see how you find it @ 300mm

Agreed. I intend pumping circa 18 deg water around 

 

Found last summer doing some modifications, that mid summer the water in the UFH pipes was at 25 deg, sitting static.  So thatcwould equate to the floor being a similar temperature.  So 18 degs should make difference 

[Dave Jones]

100mm spacing max for low flow temp.

 

put the loops everywhere, excluding chunks of the slab just reduces the overall efficiency by making the surrounding loops work herder.