ASHP - choices, choices. Feel like I’m back at square one

[Great_scot_selfbuild]

Where to start. I'll try to set this out logically. I thought I'd landed on a plan for how to go about the ASHP (and by close association, UFH), but as we're now going for a smart home using KNX, the ASHP we were looking at doesn't have native KNX integration and so I'm taking a fresh look at this.

 

Many of my issues chime with that of ___ in this thread - https://forum.buildhub.org.uk/topic/46547-how-can-i-roughly-calculate-ufh-output-at-given-flow-temps/

 

Bottom-line:

1. We need an ASHP, 300L DHW cylinder and UFH design.
2. Passive-level of insulation & air tightness (MVHR planned - DIY, Zehnder Q600). Ground floor height = 3m, First floor is into the roof space (steep pitch) - ceiling = 4m. Open void at the entrance to a double-height space.
3. UFH - 111sqm ground floor only, single zone, spiral pattern, multiple circuits. Upstairs will have electric towel rails and UFH mats in bathrooms just for the ‘warm floor’ feeling rather than to heat upstairs. I’d like to vary the spacing so that the single zone system heats the rooms at a different emitting rate (bear with me) - the thermostat will only be set in one location, whilst there are 5 separate areas (living room - no opening window), study (small, has an opening window), hall (massive tbh), WC (tiny), Utility room (clothes hanging to dry), Kitchen/diner (massive and huge sliding doors). I’m suspecting that I may struggle to get this ‘done the way I imagine it could be’ as all the companies just roll out a default - same spacing everywhere plan.
4. AC - detailed modelling shows we don’t need cooling, but we’ll install power to the locations where an AC unit could be installed, but we plan to live in the house without it. Shade is ‘not a problem’ we have plenty.
5. Smart home integration - we’ve managed to get a KNX designer on board at a manageable cost and so want to ensure we can integrate the heating into it as the KNX controller could negate the need to duplicate having an ASHP controller separately. KNX is a protocol rather than proprietary system and so is widely compatible, but I’m looking to choose one that is directly compatible rather than via a 3rd party controller; I understand Vaillant and Panasonic are just 2 examples that are compatible.
6. ASHP - I’m no plumber and lots of threads (here and elsewhere) refer to ASHP only being any good if they’re set up well, and getting someone who knows the specific make will know how to get the most out of it etc, etc. I’d love to learn this stuff, but I don’t have much time and this feels like something we should be getting done by an ‘expert’. The plumber (via our builder) doing the rest of the house is not familiar with ASHP and just needs a flow and return to connect up our UFH, but his only experience is system that have a buffer and when I started describing having a simple / optimised system with no buffer, it wasn’t clear to him. He’s clearly practical at all other aspects of the plumbing, but not one for designing a system.
7. We’re approaching the point of laying floor insulation and being ready for UFH will be straight behind that. I’ve got UFH quotes for design and supply, but I’d prefer to  need a plan, and the relationship between the UFH. 

 

Options (there are undoubtedly more that I can’t think of - it’s late…):

1. Contract one company for ASHP design, supply & install, with UFH design & supply (some of the MCS quotes have insisted on having upstairs emitters as the calcs won’t work otherwise (apparently - I’ve got no way of knowing if this is correct).
2. Rely on my heat loss spreadsheet calcs, purchase ASHP direct from a supplier (not sure how to install - is it as hard to set up as I’m led to believe?, do they come with instructions), get a company to design & supply UFH, lay the pipework myself and get our plumber to help connect it up, if we need.
3. Something else?…

 

Grateful for your collective advice on ASHP options that will be KNX compatible, and how to go about our design/install.

 

 

 

Our journey so-far:

 

Pre-buildhub days:

NSBRC, Architect recommendations… approach ‘Renewables company x,y,z’ Single ‘do it all’ coherent blah, blah, (all sounds great until the crazy quote eventually arrives).

Oh, how little we knew then!

 

Local self-builder:

Sheer luck, came across a local self-builder whose build was almost the same SQM, very similar passive-level performance, UFH downstairs only and only needs a 5.5kW ASHP (Samsung). This gave me a yardstick for what we would be expecting.

 

Initial research:

ASHP theory, all quite straightforward (in principle - reverse fridge etc…).

Find a local ASHP firm that had a good sales pitch, MCS registered, quote didn’t take the ****, but scratch the surface and they really didn’t know the maths and understand WC curves and flow rate details. Seemed to very much be a UK office where ‘technical’ was more on the practical installation rather than actually calculating how the setup should be done.

 

Buildhub reading began in ernest:

Jeremy’s heat loss spreadsheet - https://forum.buildhub.org.uk/topic/439-fabric-and-ventilation-heat-loss-calculator/#comment-4407 (everyone seems to find their way to this eventually; I put this off for a while tbh, I deal with too many spreadsheets at work, I wasn’t actively searching for more). Measured everything up, ran the numbers, ~4.5kW before factoring in DHW.

 

Quotes:

Throughout this journey we’ve had blips of focus at trying to ‘commit’. We’ve had quotes proposing 14kW (WTF!), lots of default ‘buffer + pre-plumbed cylinders, no questions about UFH’ and the list goes on.

 

Who to trust:

I really struggle with working out which company actually has the competence to *design* the ASHP & DHW cylinder installation optimised for our build.

 

DIY vs MCS:

As I’ve learned from threads on here, the cost of parts can completely negate any benefit that the MCS grant suggests. There have been 2 quotes that have actually brought the cost down to zero/near zero through an MCS umbrella company, but I seem to recall there was another reason they put me off (will have to dig through the quotes & emails…). I would much prefer to have a system that we have someone to go back to if we have a problem (plus I don’t know if our building warranty will want some guarantee behind the install - just remembered as I type that I need to check this).

Landing towards entrance void.JPG Hall towards plant.JPG Kitchen-Dining.JPG Living.JPG

[Great_scot_selfbuild]

5 hours ago, Great_scot_selfbuild said:

Many of my issues chime with that of ___ in this thread - https://forum.buildhub.org.uk/topic/46547-how-can-i-roughly-calculate-ufh-output-at-given-flow-temps/

Missed off @jimseng from here. 
 

How do people learn about calculating the heat output from UFH for a given room size and heat loss? Any recommended books/reference material/youtube accounts/online courses?

 

I’ve been wondering how the downstairs heating might perform if we had wider spacing in the living room compared to the other areas, and where to put the thermostat as the whole of the GF will be single zone 🤔🧐. Even just as an exercise, I’d like to be able to work through the calculation as an exercise.

 

Has anyone done this before?

[Big Jimbo]

I have not had a chance to work out, how to pair heat requirements of individual areas, into a simple system for my ground floor yet. So i am at the same stage as you, with perhaps a little more time on my side. My ,thick bloke ,understanding  so far suggests that if you can get each individual area to have an emitter that matches the heat requirement as near as damn it. Which would be for the coldest day you have designed for,  means the system works as a whole. I think this is preferable to all the different areas, shouting all at once. Heat...enough heat...heat...etc.

On an underfloor heating system, I have seen where the manifold has been used to balance the system using various flow rates to each loop. Again my, dont know what im talking about suggests that the flow to an area might be dialed up or down a bit. When done well, all the valves on the manifold are taken off.

the way my small brain thinks of it is...and lets go back to Rads... you have four bedrooms. each has a radiator with a TRV. You have the boiler set to come on at 6am till 8am. Bed 1 and 2 get the room up to your desired temp. Bed 3 gets up to temp very quickly, and the TRV closes that rad. Bedroom 4 however has the TRV fully open, and never gets up to temp. That says to me that the design of those 4 rads is a bit rubbish. The rad in bed 4 is too small, the rad in bed 3 is to big. To try and balance this out you would try and use the lockshield valves and trv's. I believe that it would be better to size the bloody rads correctly in the first place..

Sorry, none of this is helping you. I just dont have the heart to delete it, now i have typed it all. The Welsh Wizard, and others will be along shortly to tell me to shut up.

[Big Jimbo]

Right, as @Nickfromwales has given me a like.... Now im on a roll.

What we need to know is how much heat our length of pipe buried in the floor can emit, if we put hot water through it at 30 degrees. If we find this out, and lets say it is 100watts at 4 litres per minute, at 30 degrees, over 10 meters of buried pipe. our room/area, needs 500watts. therefore we need,  5x 10 meters of pipe in that area, 50meters to give us the heat output we need. All the areas need to be calculated in same way, in order to give us our loop sizes. ????

I was going to start talking in K/ws, but i always get the kw's mixed up, and @SteamyTea then tells me off.

 

[Nickfromwales]

36 minutes ago, Great_scot_selfbuild said:

Missed off @jimseng from here. 
 

How do people learn about calculating the heat output from UFH for a given room size and heat loss? Any recommended books/reference material/youtube accounts/online courses?

 

I’ve been wondering how the downstairs heating might perform if we had wider spacing in the living room compared to the other areas, and where to put the thermostat as the whole of the GF will be single zone 🤔🧐. Even just as an exercise, I’d like to be able to work through the calculation as an exercise.

 

Has anyone done this before?

The thing I’d say is, when you’ve PH levels of fabric, then setting (or attempting to set) different temps for different spaces just doesn’t really work that well in practice. The house seems to achieve one general ambient, and cooler spaces steal heat from warmer ones, ergo none are ever that different. 
 

A few people have commented to that effect, so it’s not a misconception, one of the advantages here is folk being good enough to offer feedback after moving in. Doing this all on paper, even for the great Jeremy Harris, didn’t work out well in practice.

 

Basic heat loss calcs, to decide the size of the heat source, plus DHW, then UFH spaced uniformly accordingly (avoiding any spaces you simply don’t want to specifically heat such as pantry) and that’s you pretty much done afaic.

 

Having digital control of the input temp and a good thermostat or WC will allow you quite a lot of accurate control over what that ambient will be. The mix becomes more of a thing when you ttt to balance the heat over upper and lower floors, but some will omit FF heating, and some won’t.

 

Finding the sweet spot is just about tweaking up or down on the flow temps (for heat source efficiency) and thus altering the room temps to suit. How much more control you actually need after this basic commission is the real question. 
 

MVHR is introduced and you’re off to the scientific calculator to attempt to factor that in.

 

PHPP is slightly helpful, largely for identifying overheat risk %, but tbh common sense and basic practice will get you most of the way here.

 

Self builders can focus on this until they get dizzy and self destruct, but the mainstream heating people just rock up and fit a bunch of boxes, almost always a buffer (they need an insurance policy against client interference, or the manufacturer does so mandates it in their installation instructions) and a stat gets slapped on the wall, zoned per floor.

 

Why we fight this so is a question I am finding myself asking, as, once it’s set up and you’re happy, you just leave it alone to do its thing. Most of my clients are happy with a box on the wall that gives them control to the nearest 0.1-0.2°C (plenty good enough hysteresis for PH) and they can walk away from that as happy as Larry.

 

The one great thing about these types of dwellings is the way they hold an ambient temp so well (effectively) and you can just set these systems up to ‘just get on with it’, minus human intervention.

 

One system we did in Leicester had zones, AHU, heat & cool, a room thermostat centrally mounted, and a buffer and ESBE mixing, etc, etc, and had an SCOP of 5.3. It’s a Stiebel Eltron setup and the company who supported dialled in to it to show me live data. So this is a fact.

 

Performing incredibly well, running extremely efficiently, and has been doing so for a couple of years now.

 

I'm beginning to accept the two different types of client (all self builders); there are those who want to know / understand / fiddle etc, and those who simply don’t.

[Big Jimbo]

It is defo more complicated than just bunging in as much pipe as you can, to each area. Then it all gets even more complicated. The room at the front gets a fair bit of solar gain, and the one at the back gets none, and faces north. But only sometimes... You have One thermostat on the ground floor, and stick it in the wrong area. All the other areas either overheat, or are bloody cold.   As i said, i think it is complicated. However, perhaps my teachers were right, and I am just a bit thick.

[JohnMo]

UFH design get a a free trial version of loopcad, do your own design. Design by room heat loss and balance system out of the box by loop design.

 

Keep everything simple. If you only want heating downstairs you need to design heat output to meet whole house heat loss. Some are ok with that, some hate it. If you have a big hall upstairs stick a big radiator or two and run at UFH temps, if room are a little cool you just open the doors and let some heat in. If you like warm bedrooms you may need heat in every room. But everything needs to sized correctly.

 

Smart homes crap and heat pump is a utter waste of money and effort. Not needed will not help anything. Sorry to be blunt and to the point.

 

Either run WC or a simple centrally located thermostat to drive heat pump on and off (if you do this you also need to run a hotter flow temp so get slightly worse CoP/running costs).

 

Pre plumbed cylinder is an utter waste of money - as 90% of the equipment on a pre plumbed cylinder isn't really needed.

 

 

[Big Jimbo]

@Nickfromwales I'm defo in the want to understand camp. Up to a point. But then just want the bloody thing to run. On its own, with no intervention from me. Oh, i forgot, i want to keep me at 21 degrees (southern softy) provide me with ample hot water, and cost me pence per week to run.

[Nickfromwales]

6 minutes ago, Big Jimbo said:

It is defo more complicated than just bunging in as much pipe as you can, to each area

That’s what I do, to get the volume, and nobody’s called me to say one end of the room is hotter / cooler than the other. These just seem to blend into each other, from my direct experience(s).

 

If doing this on paper then you’ll get number-drunk, just so many variables to try to balance out, but doing it in real life, in real homes, for real clients gives me an eye into the world of ‘did it, it was fine’ and then on to the next one.

[Big Jimbo]

@Nickfromwales So i shouldn't get so hung up on loop sizes, and trying to get it right for each area ?

[Nickfromwales]

Just now, Big Jimbo said:

@Nickfromwales I'm defo in the want to understand camp. Up to a point. But then just want the bloody thing to run. On its own, with no intervention from me. Oh, i forgot, i want to keep me at 21 degrees (southern softy) provide me with ample hot water, and cost me pence per week to run.

Same remit as the last lot of clients, for the latter part.

 

Some lap up the design and complication, and others just stare straight through me. I’m fine with either option as they’re employing me to gauge their needs and expectations, and meet or exceed them. So far so good I guess. 

[JohnMo]

2 minutes ago, Big Jimbo said:

, i forgot, i want to keep me at 21 degrees (southern softy) provide me with ample hot water, and cost me pence per week to run.

We all want that - in our dreams, you can 1 or 2 of your choices - never all 3. Unless you move to another country (not inside the UK)

[Big Jimbo]

@JohnMo You have just dashed my dreams Sir.

[Nickfromwales]

1 minute ago, Big Jimbo said:

@JohnMo You have just dashed my dreams Sir.

Relax, I’ve got you covered . 

19 minutes ago, Nickfromwales said:

One system we did in Leicester had zones, AHU, heat & cool, a room thermostat centrally mounted, and a buffer and ESBE mixing, etc, etc, and had an SCOP of 5.3. It’s a Stiebel Eltron setup and the company who supported dialled in to it to show me live data. So this is a fact.

This.

 

These clients have all 3, so you can go to the ball, Cinders   

[Big Jimbo]

Am i correct in thinking that a snail layout is better than an up and down ? In my head it is, as the heat is more evenly distributed.

[Nickfromwales]

1 minute ago, Big Jimbo said:

Am i correct in thinking that a snail layout is better than an up and down ? In my head it is, as the heat is more evenly distributed.

Yes and no. If the flow goes to the ‘coldest end’ of the room first so the heat lessens as it comes into the centre of the room then pretty moot in these circumstances tbf.

 

The time you lose the choice is when the cc of the pipes are less than the minimum bending radius of the pipe, eg at 150mm cc you will seriously struggle to perform a U -turn at the end of every serpentine loop.

 

If you lay ‘snail’ or inverted loop then you are only performing 2 U-turns per loop, with all others just a 90° turn (if the space is a perfect square or rectangle eg).

 

At 100mm cc as per this…

 

 

…you’d have zero chance of going serpentine.

 

TBH, unless it’s a job with 200mm cc, I’d just go to snail layout as default. Just a better job imho.

 

This was at 150mm cc iirc…

 

 

…still note just the 2 U-turns at the centre of each loop. Much easier.