Help me understand heat loss calc and UFH

[Susie]

I have used Jeremy's heat loss calc inputing all my U-values, area dimensions and OAT (Cornwall).

Background

The Build will be ICF, 144m2 internal, ground bearing slab with Celotex on top but no wet screed I'm looking at the fast to heat up dry board UFH systems.

Solar PV will heat the DHW ,immersion thermal store, which will heat UFH.  And economy 7 or willis heater are options.

No air source heat pump, combination of the build being near my listed building and own choice that I don't want one.

Wood burner stove for very cold winter months when PV struggles, own grown trees already cut and drying in storage more still growing.

I'm home all day most days and quite happy to wear a jumper when a little cold.  

The quick to warm up systems advertise they can be at desired floor temp in 3 hours and room temp in another 2 hours can any body confirm this for a similar build?

Example from one manufacturer is flow temp of 40deg, 50.8 W/m2 and floor temp of 24.9deg.

Back to Jeremy's calc I how do I match my W and kWh to the best UFH

 

 

 

 

 

[Conor]

Put 50mm liquid screed down and do the job right. Ours heats up in an hour and house goes from 18c-20c in about 4hrs with a 34c flow temp.

[Andehh]

Yes the low profile UFH do heat up faster, yours times are about right vs our low profile retrofit system, but for such a well Insulated house I don't really see the value on that vs just Ufh in screed and setting the temp to 18 degrees and leaving as is. 

[Susie]

It could come down to cost on something we might not use @Conorand @Andehh were in the country so distance and narrow roads go against the cost of £5000 for screed or £3000 for DIY low profile UFH the extra can go towards better insulation/windows etc and so even less likely to need the UFH.  

I presume its also less digging out and less time.   We probably won't fit the manifold till we know we need the UFH, Im from up north so Cornwall is already warmer.

 

 

 

Edited November 5, 2022 by Susie

[JohnMo]

So your max heat demand in w/m2 is

 

1541/144=say 11w/m2

 

Using the attached you get the flow temp you need, but the chart needs extending downwards, mean flow temps are low/mid 20s.  That is to balance heat loss with heat input.  If you want to blast heat and use a thermostat just add a couple of extra degrees.

 

[Susie]

Thanks @JohnMo that's a low temp so I need to know this when looking at the thermal stores it might make the Willis system better its just a basic immersion on the UFH.

 

[Susie]

 @Nickfromwales you said back in 2019 you installed Ivar mixing pumps, is it this one and do you still rate them,

 

https://underfloorparts.co.uk/product/ivar-uni-mix-underfloor-heating-ufh-pump-mixing-kit-underfloor-heating-manifold-control-unimix/

 

Thanks

 

Edited November 5, 2022 by Susie

[JohnMo]

This where I bought most of my parts

 

Seem quite good prices and was good service. They do Iver mixers and manifolds

[Nickfromwales]

2 hours ago, Susie said:

 @Nickfromwales you said back in 2019 you installed Ivar mixing pumps, is it this one and do you still rate them,

 

https://underfloorparts.co.uk/product/ivar-uni-mix-underfloor-heating-ufh-pump-mixing-kit-underfloor-heating-manifold-control-unimix/

 

Thanks

 

Yup and yup. 
Always used this supplier and great service every single time. Got 5 of their setups to order in the next few weeks for 3 new full passive builds I’ve got on atm.

Very happy with them, supplier and product, and prices are good enough for me to not look elsewhere. 

[SteamyTea]

17 hours ago, Susie said:

Back to Jeremy's calc I how do I match my W and kWh to the best UFH

The W [watt] is the power, kWh [mega joules] is the energy required.

If the W is 'on' for 1000 hours, then that is 1 kWh of energy [kWh or MJ] is just power multiplied by time (the k just means multiplied by 1000).

 

 

Edited November 6, 2022 by SteamyTea

[Susie]

Thanks for all the help,  I also found this thread useful, (Floor heat loss and UFH calculator) and I will be looking into loop cad at a later date.

So far I have required underfloor heating power 10.5 W/m2 and required floor temperature 21.2 deg

Thanks to everyone.