UFH and heat loss calcs show insufficient heat

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rangorgubbins

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Have started renovating our house.
We will be removing our LPG gas tank and ancient boiler to be replaced with an Air Source Heat Pump.
As part of the renovations we'll be adding insulation in the roof, floors, walls, and doubling glazing windows.
The company installing the ASHP have run a heat loss calculation using the MCS Heat Pump Calculator v1.1.
We were hoping to put UFH in on the ground floor and first floor, but the HLC shows that on the first floor the rooms will struggle to reach required watt output, with the bedrooms being short of 160 Watts. See image.
My question is, is that going to mean very cold rooms or will the 160 W shortfall be ok as the heat from light bulbs, computers, people, etc provide enough extra heat?
 

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It'll mean cold rooms, and maybe more importantly will mean you don't qualify for RHI payments I think. It'd be interesting to know what outside temperature they've based their calculations on as well - often it's -1°C, so if we got another cold Winter like we've just had your shortfall would be greater than 160W.

I'd suggest that your property isn't suitable for this system, unless you can do more to improve the insulation
 
Thanks guys. Not what i was hoping to hear, but helpful.
The calculations are based on outside temp of -1.8.

Not sure where else we can improve the insulation. The roof is being insulated to 0.18 U value and the windows double glazed to 1.4 U. The walls are currently solid brick walls and I'm planning on adding 50mm of insulating render (Bauwer Light) which would give the walls a U value of 0.9. All of this is already factored into the Heat Loss Calculation.
 
Perhaps it's time to take advantage of some passivhaus features? Larger windows on the south side, tiny windows on the northside. Air tight everything for no draughts.

Nozzle
 
Thanks. I guess that might help a bit but 2 of the bedrooms don't have any south facing walls. We already have quite large windows on the south side and we'll be blocking up drafty holes during the renovations.
 
I'm not sure how a heat loss calculation works but is 20c warm enough for a living area? At night I like to sit in my pj shorts and top, I know I'd be chilly at 20c
 
rangorgubbins said:
Thanks guys. Not what i was hoping to hear, but helpful.
The calculations are based on outside temp of -1.8.

Not sure where else we can improve the insulation. The roof is being insulated to 0.18 U value and the windows double glazed to 1.4 U. The walls are currently solid brick walls and I'm planning on adding 50mm of insulating render (Bauwer Light) which would give the walls a U value of 0.9. All of this is already factored into the Heat Loss Calculation.
Click to expand...

what happens if you fit triple glazed windows with a u value of say 0.8 for the bedrooms.

is that a typo: walls 0.9?
 
rangorgubbins said:
Thanks guys. Not what i was hoping to hear, but helpful.
The calculations are based on outside temp of -1.8.

Not sure where else we can improve the insulation. The roof is being insulated to 0.18 U value and the windows double glazed to 1.4 U. The walls are currently solid brick walls and I'm planning on adding 50mm of insulating render (Bauwer Light) which would give the walls a U value of 0.9. All of this is already factored into the Heat Loss Calculation.
Click to expand...

That means that any temperatures lower than -1.8 outside will really show up your shortfall. ASHP's lose efficiency quite considerably in very cold weather as well, so you may well end up sitting in your house in the middle of Winter with three jumpers on watching your electric meter spinning like a top as it tries to keep up with demand. The UK hit -15 in parts this last Winter.

Triple glazing should get your windows down to around the 0.9/1.1 mark, which would help. Can you get more than 50mm external insulation on there? I still wonder if ultimately this isn't the right heating solution for you though
 
Just out of interest, what's your motivation for having ASHP? If it's that you have money burning a hole in your pocket and want to make your house eco-friendly then great. If it's that you think it's going to save you money then I think you'll be disappointed
 
Notch7 said:
what happens if you fit triple glazed windows with a u value of say 0.8 for the bedrooms.

is that a typo: walls 0.9?
Click to expand...
Thanks, I'll look into the cost of triple glazed windows.

0.9 for the walls is not a typo. The U value for solid brick walls is apparently 2.15 and upwards. Adding 50mm of insulating render on the internal face of the walls (we are not adding anything to the external) gives the walls a U value of 0.9 . I could perhaps get it down to 0.6 if i used insulated plasterboards but I'd prefer the render - the bricks on the inside are old and a bit crumbly in places so the render should stabilise it.


muggles said:
That means that any temperatures lower than -1.8 outside will really show up your shortfall. ASHP's lose efficiency quite considerably in very cold weather as well, so you may well end up sitting in your house in the middle of Winter with three jumpers on watching your electric meter spinning like a top as it tries to keep up with demand. The UK hit -15 in parts this last Winter.

Triple glazing should get your windows down to around the 0.9/1.1 mark, which would help. Can you get more than 50mm external insulation on there? I still wonder if ultimately this isn't the right heating solution for you though
Click to expand...
-15 not likely where we live (Kent), -5 maybe occasionally.
The insulation has got to go on the interior side of the walls and 50 mm is the max, otherwise we're losing too much room space.
As for watching the electricity meter spinning in the depths of winter, we already experience that but with the LPG tank AND the electricity meter (electric heaters supplementing the CH).

muggles said:
Just out of interest, what's your motivation for having ASHP? If it's that you have money burning a hole in your pocket and want to make your house eco-friendly then great. If it's that you think it's going to save you money then I think you'll be disappointed
Click to expand...
The ASHP works out relatively cheap, certainly cheaper than a new LPG boiler + buying LPG. ASHP RHI payments would cover 99% of the installation cost, and we can get rid of the LPG tank. We've spoken with quite a few people who have had it installed and they say its worked out great for them.
 
Picture the scene. Multimillion pound detached houses in a leafy private road in Surrey. You have had a bespoke house built on three stories all with underfloor heating. Your neighbour happens to be the managing director of Daiken U.k who has sold you on the idea of ASHP. When you suggested the idea of a small 12kw gas boiler as backup he poo pooed the idea. Well guess what its -5 outside the ASHP is frozen solid.. There is no latent heat in frozen air. You can see your breath inside the house. You paw over the manual..troubleshooting..backup electrical heater...You look inside the casing off the ASHP there is just a empty void where the heater should be!!.
You go round to your neighbour...mr Daiken...he says " well you have to expect to wear thick jumpers with this type if heating"

And that is a true story !!!

Great when they work a bugger when they stop.

Had various problems with ASHP over the years just shutting down and going to error.

For example they dont like under floor heating pumps and bypass loops have to be massive.
 
Not planning on installing a Daiken, but "great when they work, a bugger when they stop" is true for anything. A knackered gas boiler is just as rubbish as a knackered ASHP.
modern ASHP can extract energy from air down to -20 *C. The one we've been looking at is still relatively efficient at -15, heating water to 45*C (CoP of 2), and highly efficient at 2*C outside heating water to 45*C (CoP of 3).

Never knew hybrids were an option. Sounds like a good development, but only if you've got mains gas. we're trying to get rid of the gas tank in the drive!
 
Back to my original post....
The heat loss calculation shows that for UFH will struggle to get enough heat into the bedrooms. I've run the same calculation but using radiators (oversized for low flow temps), and there's no problem at all with getting enough warmth into the house.
I'm wondering if its worth going for UFH but leave a couple of spare valves on the manifold so that we could plumb in radiators should we need to in the future? Can't be too costly/difficult to leave a few pipe tails in the wall in each bedroom for adding rads in the future if we need it.
 
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