Yes please feel free to share the info, its just an idea thats seems to work quite well when you have the flexibility of designing from scratch.

Thank you for a very detailed reply, the idea of having say 3 loops in a room instead of 2 makes sense if there is a smart controller fitted that can isolate part rooms. I presume you recommend loops at 150mm spacing.

I think about my own system and incorporating your examples would have added more flexibility, my controls are relatively simple, using the heat pumps WC, the problem comes with variable weather conditions. Every temperature has 2 values, take +3° on a calm dry day, the pump efficiency is at its best, the same temperature on a windy wet day the efficiency is at its worst, this is because the airflow through the pump is not as regular when its windy, the same wind draws more heat from the house, and the damp air means the pump goes into defrost more often. Because we are in a barn conversion bungalow we have a long thin design giving a large wall to total floor area ratio, the different heat requirements listed above are at least 10% and maybe more.

When my friends they get to the stage of talking to heating engineers would you be ok with me sharing your comments? i would not share your details.

Cheers Mike

While you have the chance you can lay additional loops for the UFH for much better control allowing you to have open loop but a % of control in main rooms, this is not additional pipe laid but additional control, if the room needs 330m of UFH pipe you are just splitting it into 3No 110m loops, the UFH manufacturer will help with this. Auxiliary such as hallways and landings areas can just be open loop as they tend to be background heating or transit areas. Control loops should be away from the external walls where possible.

For example:

Living room 900w 3 loops (2loops open and 1 loop controlled by UFH room stat) Try to make the loop down the middle of the room the control loop as the heat loss will be higher along the longer edges until there is solar gain.

Kitchen 800w 2 loop (1 loop open and 1 loop controlled by UFH stat) make the loop away from the external wall the control loop 

WC 60w 1 loop (Open loop no UFH control)

Hallway 260w 1 loop (Open loop no UFH control)

Landing 160w 1 loop (Open loop no UFH control) 

Bedroom 1 320w 2 loop (1 loop open and 1 loop controlled by UFH stat)

Bedroom 2 420w 2 loop (1 loop open and 1 loop controlled by UFH stat)

Bedroom 3 220w 2 loop (1 loop open and 1 loop controlled by UFH stat)

No blending or interface control form the UFH to the heat pump just pipework straight connected to the UFH rail then on your rail connect the actuators for loops that will be controlled and the other leave off, your ASHP commissioning engineer will understand this.

Now set the ASHP to run on its own internal interactive smart stat with a compensation curve around 40@-3 and 20@20 to start or at 0.6 subject to which manufacturer you are using (this can be set correctly once you have the full heat loss, your ASHP engineer will be an expert in the manufacturers controls options) 

What the above does is covers every eventuality including solar gain over heating in the winter period, take the living room for example if the heat loss is the full calculated 900w but its a February sunny morning and the solar is offsetting 200w then the rest of the building heats on the curve and the living room UFH stat will gently close the 3rd loop reducing the capacity flow from 900 w to between 600-900 by adjusting the flow on the 3rd loop. The HP sees it DT return rise and either can divert the unused energy back into the building to other rooms or reduce its output.

The control set up above is to set the UFH control stats connected to one loop as an over heat stat, so your ASHP interactive smart stat is set for 21, this controls the whole house and the ASHP, the UFH rooms stats set for 22 in main rooms and say 17 in a bedroom and will nicely hold off that extra heat not wanted, adjust the rooms stat to 20 and the bedroom will heat up to its maximum design. (assumes the bedroom design is 20 where other rooms are 21 and 22) all of this can be designed by your fully qualified low temp heating design engineer, just make sure you find a good one.

UFH designs work perfectly well without the extra loops once balanced perfectly but people do not, I have had it where customers once agreed to a design of 20 or 21 want it 22 in the main rooms sometimes but 16 in the bedroom even though they decided 18 on the bedroom design, this system above adds a small amount of flexibility so like a deluxe design, this is my thought the second I hear someone is building from scratch.

We have been and are still experimenting with multi control and simple control, on retro fit and standard heating, open loop and steady balanced control works very well and is the go to optimal design, on new build its the same but with added single loop control makes it that little bit more control that we are all used to with stats in rooms. This method also prevents the customer setting the HP to run full power but a large proportion of loops closed, this is a big cause of low flow. 

Avoid a buffer at all costs as you can design it out on anew build.

I hope this gives you options for your friends. 

I agree that they should look at MVHR, but will need to get their builder onside, some builders don't think air-tightness matters, so they look for the quickest option, not the best option. The more airtight the house is the more successful the MVHR will be.

The belligerent part of me says they don’t need to get the builder onside at all; they just need to tell the builder that’s what they expect, since they’re paying for it. I realise the real world is more nuanced than that and that the builder may well have other qualities that your friends wiuldn’t want to jeopardise, but it’s still worth rememvering that if you say what you want that’s what the tradesperson should be delivering.

They are already looking at the cabling, i used the same electrician and he was very pro active in this .

That’s good. Network cabling is a bit of an art in itself and so not all sparkies understand all that’s necessary (like the need to ensure unshielded cat 6 is kept separate from electrical wiring), but if the person you’ve used before knows what he’s doing then getting structured cabling and electrical wiring done at the same time is an excellent idea.

The definition of an Expert, a Ex is a has been, a Spurt is a drip under pressure.

That's a great one for the Uxbridge English dictionary (I'm Sorry I Haven't a Clue - Radio 4)

Sounds a perfect fit, I am in a 200m2 Bungalow, unfortunately i didn't know about this site so allowed the heat loss calculations to dictate the size of the pump. I have a 10kw which is way over-sized, the records, over 3 years, show the most we have ever needed was 6kw,  and this was only for 5 days over 3 winters, a 5kw would have been fine. I will try to get my friends to challenge their designers if they start saying that they need anything bigger than a 5-6kw. Thanks to everybody here, now i can suggest the questions that they need to ask, rather than take an "experts" view as gospel.

The definition of an Expert, a Ex is a has been, a Spurt is a drip under pressure.

Cheers

The house is extremely well insulated with U values as follows, walls=0.15, roof=0.1, floor=0.1, windows and doors=1.0

We have MVHR with about 0.3 ACH.

We have a very heavy floorslab downstairs with UFH heated by a 5 KW Vaillant heat pump.

The pump more-or-less never cycles and generally only runs at night on an E7 tariff. If we have very cold winter weather then we might run the ASHP during the day using free solar electricity

There is no heating upstairs but heat rises via the open(ish) hallway.

If the downstairs is around 21C then the upstairs landing is around 20C, the family bathroom is also about 20C as the air extraction pulls warm air in, the bedrooms are around 19C, if you leave the bedroom doors closed then they settle at about 18-18.5C

If we were building another house then we would do the same again.

They will see what the plumber is suggesting when he gets back the projected heat loss, Maybe with a fancoil on the landing, the design temperature can be 35 or less

cheers  

A single design temp of 35 or less really would be the way to go.  If it were my newbuild I would be insisting on it unless I had concrete proof (not just plumber BS) that it was not practical. 

Bear in mind that the domestic heating industry, for the most part, hasn't got a scooby about heating design (ie they just don't understand it).  The same seems to go for 'M&E consultants' often employed by architects to design heating systems.  Unfortunately the industry has got used to decades of the lazy approach of showing in a (grossly oversized) 30kW+ condensing gas boiler set to a flow temp of 75C (with the result that it doesn't condense), putting oversized rads and TRVs everywhere and letting the system 'sort itself out'. 

With dirt cheap North Sea gas and a population that knew no better, it could get away with this, even though the result was a lower standard of comfort and higher bills than a properly designed system.  The chickens are now coming home to roost but the industry is slow to change.  Thus anything you/they are told should be considered suspect unless backed up by a coherent explanation that can be related directly back to the underlying physics or a properly explained mechanism for the alleged phenomenon.  Im sorry to be so critical of the heating industry and there are of course some very good guys, of which the plumber in question may be one, but its abundantly evident from what we see here and what I have personally experienced that it is, at least in large measure, this bad.

They will see what the plumber is suggesting when he gets back the projected heat loss, Maybe with a fancoil on the landing, the design temperature can be 35 or less

cheers  

A little bit of thinking out loud, if the plumber says they must have radiators upstairs to cover all eventuality's, on my heat pump(Viessmann) its easy to push up the WC, to a maximum flow of 40°. The pump would cycle a lot from the UFH but flow upstairs may help to keep it running. The COP would fall substantially when run like this, but it may only be for a couple of weeks each year, thoughts anybody?

Im not sure what your thought process is here.  Are you suggesting running with a max FT of 40 rather than the max of (say) 35 that the UFH is likely designed for.  If so how will you stop the downstairs overheating?  And what will happen at moderate OATs - the requirement to heat the upstairs, if there is one, doesn't magically vanish!

If the amount of heat needed for the upstairs is small, once you take into account transfer from downstairs, then maybe you can design for rads at 35!  If not put a fancoil on the landing and in any upstairs rooms where you dont sleep, or even in ones where you do but then turn the fan off at night.

Fundamentally you want, I think, to design for the same max flow temperature throughout and make that as low as possible having accounted for heat transfer from down to up.  That shouldn't be impossible at all because its early enough in the process and you are aiming for low loss.  The numbers (loss accounting for heat transfer) are key to this; once those are available the answer should emerge.