UFH - validate my thinking plus some questions

[Bigdeadbadger]

Evening All,

 

Was looking for collective thoughts on my ideas for my UFH.

Yes, I have quotes from most of the major players, just wanted some second opinions.

 

About the house first:  380m2 in total, 210m2 on the ground floor.

Planning UFH on ground floor only with only towel rads in the 4 upstairs en-suites.

House is 220mm SIPS panels throughout including roof.  Triple glazed.  Aiming for < 2 AH (I know not super fantastic, but trying to be realistic based on time I've had).  House will have MVHR.

Foundation is an insulated raft 250mm concrete + 65mm screen on top.  Raft has 250mm EPS and external Insulated upstand.

Heat will be via Gas Boiler (its available right outside my house and building warrant was done in 2023).

Location - central Scotland

I'm happy that I didn't attach the pipe to the slab during pour as there is no way the cowboys that put up my kit would not have blasted nails through it.

 

Main system points are:  looking at minimum of  14 ports, some places up to 15 to accommodate the number of loops and volume of pipework.

Would be 16mm pipe on 150mm spacing

Because of the number of ports, it's looking like 2 manifolds.  And therefore 2x pumps.  Any things I should be aware of there? does it make balancing the system horrendous? or just more time?

With what will be 1200m or so of pipework, is there any benefit to fitting a buffer tank.

 

Am I missing anything? or creating future headaches?

 

I'm clear that warm up / cool down time will be long.  Trying to just run the house at a steady temp.

 

Edited 3 hours ago by Bigdeadbadger

[JohnMo]

2 hours ago, Bigdeadbadger said:

Heat will be via Gas Boiler

Our new build was completed with gas boiler, soon after moving in solar gains were painful. Bought a cheap ASHP to allow cooling via UFH. A year later the gas was disconnected, and ASHP used for heat and cool. Was cheaper then gas, no gas standing charges for one, using a time of use tariff, some solar and battery, makes ASHP as cheap as chips to use.

 

I would drop down to 200mm centres and run from a single manifold (our floor area is 192m2 and we have 7 loops on 300mm centres).  Run direct from a good boiler, so no pumps or mixers.

 

UFH design, you need it room balanced by design, as far as possible, so room loops need to output room heat loss and each room receive its heat loss via the UFH. This makes balancing easy, I have all loops fully open at the flow meters and let the ASHP decide the flow it wants or needs.

 

So operation can be two ways, WC or simply a fixed flow temp and a thermostat to limit, a single thermostat will do or a few, but don't bother with manifold actuators, so one thermostat needs heat all loops come on. Get an under floor wiring centres with some bells and whistles, so the room thermostats are actually temperature sensors and the can doo heat and cool, for when you install the heat pump.

 

Boiler get a system boiler, not heat only one.  Run PDHW (priority domestic hot water), this drive two temperatures from the boiler, one for heating the other for DHW heating. Get a heat pump cylinder, nothing else. Reheat times super quick and best boiler efficiency.

Edited 1 hour ago by Nickfromwales
Typo fixed :)

[Bigdeadbadger]

Thanks @JohnMo
 

some more questions - see you’re in NE Scotland and still had solar gain issues - that’s a bit concerning for me - was there something specific about your amount of glass? 
 

I have ~26m2 south/southwest facing glass. Although I do have an overhang 
 

 

[JohnMo]

We have a 6m overhang, but its the westerly afternoon sun in spring and autumn that gets in, can get really hot.  Today sun all day solar gain from a low sun, so a benefit.

 

So a cylinder with 3m2 coil as used by heat pumps, used with a gas boiler are great, either low flow temp or super fast reheat. Or you could do a cylinder heated by a heat pump, as in an all in one unit

Edited 1 hour ago by Nickfromwales

[Nickfromwales]

59 minutes ago, JohnMo said:

I would drop down to 200mm centres and run from a single manifold (our floor area is 192m2 and we have 7 loops on 300mm centres)

315mm of 'slab' to heat......

 

2 hours ago, Bigdeadbadger said:

Heat will be via Gas Boiler (its available right outside my house and building warrant was done in 2023).

I think you should reconsider this, as cooling via your slab wold be quite a nice thing for the summer months.

 

Is it a Heb home? Or independant?

[Bigdeadbadger]

Thanks too @Nickfromwales

 

independent - all on my own some.

 

reluctance to go ASHP is upfront cost and pain of dealing with change to my building warrant - my local council have been a source of much pain. 
 

 

[marshian]

9 minutes ago, Bigdeadbadger said:

Thanks too @Nickfromwales

 

independent - all on my own some.

 

reluctance to go ASHP is upfront cost and pain of dealing with change to my building warrant - my local council have been a source of much pain. 
 

 

 

Can always "upgrade" to ASHP later??

 

What do you think your heat loss will be at design temp because that's going to determine what min boiler output you need and the HW cyl size and HW demand is going to determine the maximum boiler output? (unless HW is lower than the heat loss)

 

 

[Nickfromwales]

16 minutes ago, Bigdeadbadger said:

reluctance to go ASHP is upfront cost and pain of dealing with change to my building warrant - my local council have been a source of much pain. 

Fit it and say feck all. I doubt anyone other than the next door neighbour, if you've pissed them off, would ever pull you up over it.

 

If they do, just go for a retrospective amendment to get it approved. This country is an ass!!!!

[Nickfromwales]

17 minutes ago, Bigdeadbadger said:

independent - all on my own some.

Good man.

 

Have you considered AeroBarrier to get you to <0.6ACH? One we just had done started out at 1.2 ACH and a few hours later was sub 0.2.

[Bigdeadbadger]

If i can read my SAP calcs correctly 

 

fabric heat loss = 194 W/K

 

Averaging for seasonality, energy for water heating is ~200KW/H per month 

 

5 bed house, 3 kids - all be it boys 😬. So was thinking 400l HW cyl

does that help? @marshian

 

[Bigdeadbadger]

19 minutes ago, Nickfromwales said:

Good man.

 

Have you considered AeroBarrier to get you to <0.6ACH? One we just had done started out at 1.2 ACH and a few hours later was sub 0.2.

No - had not - although it looks interesting. Sounds like radweld for cars 😊

 

also budget is under a lot of strain, and still almost all internals to get done. 

 

closest I have (appreciate it’s not as comprehensive as what you’ve just shared) is using the spray on airtightness paint from pro clima for some tricky junctions. 

Edited 47 minutes ago by Bigdeadbadger

[Nickfromwales]

24 minutes ago, Bigdeadbadger said:

closest I have (appreciate it’s not as comprehensive as what you’ve just shared) is using the spray on airtightness paint from pro clima for some tricky junctions. 

Won't scratch the surface of all the places you don't even know you have air leaking out of.

 

25 minutes ago, Bigdeadbadger said:

also budget is under a lot of strain

Use the force.

[marshian]

23 minutes ago, Bigdeadbadger said:

If i can read my SAP calcs correctly 

 

fabric heat loss = 194 W/K

 

Averaging for seasonality, energy for water heating is ~200KW/H per month 

 

5 bed house, 3 kids - all be it boys 😬. So was thinking 400l HW cyl

does that help? @marshian

 

 

If my mental maths is right I'd say your water heating is going to need more poke than your space heating so get a boiler which will go as low as possible for space heating (Viessmann 200 will go down to 2kWh)

 

Then size the boiler to to recharge a 400 litre cylinder with a heat pump coil in the shortest time possible (so 400 litres from 20 to 55 needs 17 kWh of energy) to do that in ~30 mins would need a boiler capable of throwing 32 kW at it)

[Nickfromwales]

17 minutes ago, marshian said:

so 400 litres from 20

If it gets to that low a recovery temp, the cylinder stat is on the floor and the cylinder is sat on it?