MCS requirements for whole home UFH

[cmdrawesome]

Ok, so in my 4 bed, 2-storey self build I'm having wet UFH installed at the bottom of the concrete slab, which sits on top of an isoquick passive slab. Walls are passive spec, roof is almost passive spec, ICF construction so airtightness will hopefully be <1. UFH and DHW all powered by an ASHP. Yay for acronyms!

 

I was planning to put aircon in the upstairs bedrooms, electric UFH / towel rads in the upstairs bathrooms, and leave it at that.

MCS are saying that in order to qualify for the £7500 grant the UFH needs to be in every room. Is this really the case? the aircon will be able to provide a small amount of top-up heating if required.

 

 

[JohnMo]

1 minute ago, cmdrawesome said:

UFH needs to be in every room

No. The house needs to be heated by the a heat pump, you can have radiators or UFH or fan coils. You can also over specify the ground floor heating as long as you/installer can demonstrate it provides enough heat to also heat the upper storey. This is a bit installer specific.  No sure the grant allow you take any credit for A2A just A2W heat pumps.

 

I would have UFH in bedrooms. 

 

Why not, UFH downstairs, fan coils upstairs (over size slightly). Then dump the Aircon altogether. Then run heat pump in cooling mode in the summer to UFH and fan coils. In winter run all in heat mode. Cool energy do some nice looking fan coils even ones for the bathroom.

[Gus Potter]

Ah philistine here.

 

Why on gods earth are we designing systems that are not passive in the UK to cool houses?

 

Why not design our doors / ground floor windows to provide purge ventilation and say put Velux windows in the roof to promote passive stack type convection with a bit of cross flow ventilation. You can achieve this even on a single story building. 

 

Again I'll come back to this. I've been designing UFH as a designer and as an SE for decades. So I kind of know what the long term costs are. And no one on BH has stepped up to this plate.. yet.. I'm alone in my view it seems.

 

But the thing is.. I'm pretty good at maths, have installed and designed UFH when most of you were in short pants, I know the economics! and to boot I'm an SE so know how you integrate UFH structurally. 

 

So get that up you and lets see some evidence about long term maintenance costs on UFH and the introduction of complex controls.. Oh and if you can make that basic argument then have a go at cooling.

 

If you want to make your arguement then explain how pipes in the floors work over the design life of the house first. Work up from there. Go  on and give it a go! I'm willing to learn. 

 

 

 

 

 

 

 

 

 

 

 

 

 

Edited yesterday at 01:10 by Gus Potter

[MikeSharp01]

5 hours ago, Gus Potter said:

Why not design our doors / ground floor windows to provide purge ventilation and say put Velux windows in the roof to promote passive stack type convection with a bit of cross flow ventilation. You can achieve this even on a single story building. 

 

Again I'll come back to this. I've been designing UFH as a designer and as an SE for decades. So I kind of know what the long term costs are. And no one on BH has stepped up to this plate.. yet.. I'm alone in my view it seems.

We have done this and I have found that it works but only up to a limit - once temps are at 30+ it is not able to make things comfortable, so after this summer I am fitting fan coil units in the bedrooms so I can cool them if I need to. 

[Dave Jones]

10 hours ago, cmdrawesome said:

Ok, so in my 4 bed, 2-storey self build I'm having wet UFH installed at the bottom of the concrete slab, which sits on top of an isoquick passive slab. Walls are passive spec, roof is almost passive spec, ICF construction so airtightness will hopefully be <1. UFH and DHW all powered by an ASHP. Yay for acronyms!

 

I was planning to put aircon in the upstairs bedrooms, electric UFH / towel rads in the upstairs bathrooms, and leave it at that.

MCS are saying that in order to qualify for the £7500 grant the UFH needs to be in every room. Is this really the case? the aircon will be able to provide a small amount of top-up heating if required.

 

 

 

yeah thats bollox.

 

I dont believe air con is allowed under MCS though.

 

You dont need it in any case as you already have an air con unit - the heat pump.

 

Like buying a tesla and then towing a trailer of batteries to charge it.

[JohnMo]

6 hours ago, Gus Potter said:

Why on gods earth are we designing systems that are not passive in the UK to cool houses?

Agreed the first priority, but if you have great views and have maximised glazing (it happens - me for example) solar gain can still be an issue, especially on a no wind day. So active cooling is great over and above that.

 

6 hours ago, Gus Potter said:

lets see some evidence about long term maintenance costs on UFH and the introduction of complex controls

First what complex controls - some do this but they are not needed. My heat pump for example runs as a single zone fully open system, all UFH in the house and a fan coil in an insulated summer house. Effectively one valve in the system a diverter to cylinder or heating system.

 

During winter it runs pure weather compensation all driven by ASHP controller with no external controls. Only thing to go wrong are the heat pump or diverter valve. 

 

In summer exactly the same almost, but now it runs in Weather Compensation mode but at a fixed temperature, no more controls in the system. Heat pump just senses return water and reacts when it sees return water getting above a preset temperature. It works well, it's not Aircon, but let's the house recover from solar gains quickly and more importantly limits the ultimate temp the house reaches, so it remains comfortable.

 

Only control in the system outside of the heat pump, is to switch from cool to heat, I used a light switch to give heat pump volt free contacts an open or closed signal.

 

Pipe life. During heating the pipes may see 36 degrees water and during cooling the target flow temp is 14, during a compressor cycle this temp can dip to nearer 12 degs. So neither temperature is going to shorten the expected life span of the pipes or valve. Similar the pipes out of the floor, a mix of copper and Hep2O are all in the normal and expected range of operation and a mile away from the max and min allowed. Do not expect any issues there either.

 

The system as configured with no zone valves on the manifold or in the system, which makes it more reliable than a normal system, as there are no pins to stick on the manifold from valves being in a closed position over the summer. Or pumps or mixer valves locked for the same reason - as I don't have any of those either.

 

So for clarity system is

ASHP 

Diverter valve controlled by ASHP 

DHW Cylinder 

UFH manifold 

UFH pipes 

Fan coil teed into main system flow and return.

A 50L volumiser on the return piping to extend cycle time of compressor.

A zero volt switch to select heat or cool.

 

[saveasteading]

Aircon is bad. Design the house to avoid it.

There are options.

Minimising S facing glazing OR fit external roller blinds.

Purge fans as required.*

Curtains in theory don't help but in reality do.

 

It doesn't cost much to extend your ashp heating upstairs, to radiators or even ufh. I'm working on options for that atm.

 

* we have decided against heat recovery ventilation ( £12k or so is not justified)  and will retrofit fans to remove excess heat  if necessary.

 

There is a risk but I am generally "lucky" with such decisions. That's according to rhe people who failed to sell me the latest 'must-have'.

 

You don't need to heat stairs and corridors. Bedrooms are debatable.

 

Design for the ashp heating everywhere and you get the grant.

[Bonner]

6 minutes ago, saveasteading said:

we have decided against heat recovery ventilation ( £12k or so is not justified)

I agree with your comments about passive cooling. MVHR doesn’t help much with cooling but has so many other benefits and it is not necessary to spend £12k. I self installed this unit and spent another £1k on rigid plastic ducting and other materials. Of course you can spec something more sophisticated but this works very well and I wouldn’t want to live in a house without MVHR and I don’t want people to be put off by these quotes.
https://www.ventilationland.co.uk/en_GB/p/itho-daalderop-mvhr-hru-350-eco-unit-lr-rft-low-rise-350m3-h/9945/?gad_source=1&gad_campaignid=22563121607&gbraid=0AAAAAB0qKPDJ-kmgBYRAOrw1rwDPtmlOW&gclid=Cj0KCQiAiKzIBhCOARIsAKpKLAOKcw9T7CHFnPu-qqBlrN6gM85GPOdAMbqVvfGZpXWti5CANHf1dMwaAjWTEALw_wcB

[JohnMo]

9 minutes ago, saveasteading said:

ashp heating everywhere and you get the grant

Or don't bother with the grant a do what ever you want.

 

Was looking at Hisense ASHPs the other day, great modulation, Hitachi compressor and other parts £2k.

[saveasteading]

3 minutes ago, Bonner said:

spent another £1k on rigid plastic ducting and other materials

We have looked at the sundries costs of getting ducts invisibly through ceilings and beams, and it's a lot. It's a big house.

 

It's a holistic decision though. Our plan is great insulation and airtightness,  ashp and ufh. Solar and batteries. Thus the cost of generated heat is low, and the value of recovered heat is also low.

 

Ventilation? High ceilings, possibly old fashioned vents in the windows, a few extractors perhaps added later if necessary.

Over decades I have found that  the non radical, holistic design tends to work better than the latest fashion.

[Bonner]

I also tend to avoid the latest fads. My first house had open fire places in every room and leaky sash windows, plenty of fresh air without any fans. Now though, with modern standards of air tightness and more concerns about VOCs, CO2 levels etc. active ventilation is essential for most new houses.

[JohnMo]

23 minutes ago, saveasteading said:

We have looked at the sundries costs of getting ducts invisibly through ceilings and beams, and it's a lot. It's a big house.

 

Most of that can be deleted with a simple cascade MVHR system, you will still extract points in wet rooms, but not in dry rooms.

 

But a well thought out dMEV system can be nearly as good, no noisy fans that come every time you switch on light. Add some humidity activated trickle vents, you have a system that looks looks after itself, while minimising ventilation losses etc.

 

28 minutes ago, saveasteading said:

great insulation and airtightness.... few extractors perhaps added later if necessary

 

Sounds like an invite to black mould and unhealthy living to me. Airtightness is great, but you you still need controlled ventilation

[Kelvin]

There’s no particular reason for UFH pipes to fail under normal use. Every house I’ve lived in with rads have had leaks. Other than the obvious benefits an often overlooked benefit of UFH is the practicality of no rads on the walls so it makes room layout better. I’ve also simplified our heating system so there’s nothing overly complex about it. 

 

We’ve done the wall of South facing full height glass, big West facing picture window, and big full height picture window in a small bedroom. There’s no doubt it has some impact in the hot summer days and on cold dull days (especially the bedroom) and less glass would have been better from a performance point of view. But houses are a compromise between aesthetics, performance, and how they make you feel and I’d rather have the view and live with the minor downsides. That said the heating has only really started to come on in the last week. Had we built the house with a performance at any cost perspective we’d barely need heating at all. Interestingly, despite us running the house relatively cool,  all our friends, who live in old cold stone buildings, find it too hot. 

[saveasteading]

26 minutes ago, JohnMo said:

controlled ventilation

 

27 minutes ago, JohnMo said:

an invite to black mould

My hunch is that this hyped by the mvhr industry. If there is knowledge on mould in newbuilds then of course uI want to know.

 

Black mould is commonest in old houses with dampness and poor insulation... ie condensation on cold surfaces.

 

So we may have trickle vents, will have the usual wet room extractors, which draw loads of air in from adjacent rooms and of course will have opening windows and people moving around.

dMEV, is an acronym I only discovered on BH last week.

I've looked briefly into dMEV and am astonished at the variety and range available. 

I guess when things are simple and economical they aren't so much publicised.

Seems ideal to me, especially when it's your own house in design and construction.

[JohnMo]

17 minutes ago, saveasteading said:

dMEV

Look at Greenwood CV2 or CV3. Totally silent in normal operation, have a smart humidity control, so looks for a rising humidity over time not a general rise because rainy. Just needs power cable, no switched power needed. Electrically take a couple Watts to run them, so pennies a year.

[Mr Punter]

24 minutes ago, JohnMo said:

Look at Greenwood CV2 or CV3.

 

I have had these fitted in some flats.  They are quite clever.  If you wire in a switched live they also look at how long the light is on to work out the overrun needed.  Cheap too.

[cmdrawesome]

Ok, I'll respond to some points:

- The Ground floor UFH is at the bottom of 250mm of concrete, which is sat on top of 225mm of insulation. I expect it to be a strong stabilising influence on the internal temperature of the house, but have huge latency. It could easily take 24h to react to any changes in ASHP activity.

- Aircon is non-negotiable for me. It can react to changes in temperature demand very quickly, and provide substantial cooling and heating. Mrs Awesome is at the stage of life where her demands for temperature changes can be unpredictable and volatile. It's expensive to install and operate (coincidentally, Mrs Awesome...), but the UFH should keep things stable so it isn't needed frequently. MVHR does not have the circulation rates to provide decent levels of cooling. I'm very dubious about switching the UFH ASHP into cooling mode as I still want hot water in a heatwave.

- Yes, I have a big glazed gable but I will also be fitting external louvres and shutters to mitigate solar gain.

- I'm going big on solar PV / battery, and also will be fitting a basic but decent MVHR. My system is coming in around 5k for a 4 bed house, 12k seems a bit excessive.

My question is all about the MCS grant - if the UFH is providing heat to all rooms from the bottom of the slab, is that enough to obtain a grant or do I actually need to have wet pipes in all the rooms?
 

[JohnMo]

15 minutes ago, cmdrawesome said:

Mrs Awesome is at the stage of life where her demands for temperature changes can be unpredictable and volatile.

A thermostat connected to nothing is good for that. But if you go aircon but well. A very good one goes unnoticed others can be drafty and blow and bug the you. They can also make the air really dry, good ones will manage that.

 

18 minutes ago, cmdrawesome said:

I'm very dubious about switching the UFH ASHP into cooling mode as I still want hot water in a heatwave.

You can have both the ASHP just switched mode.

 

19 minutes ago, cmdrawesome said:

if the UFH is providing heat to all rooms from the bottom of the slab, is that enough to obtain a grant or do I actually need to have wet pipes in all the rooms?

Depends on installers take on things, some will be fine others not, depends on their experience really. Just don't speak Aircon while doing the grant stuff.

[Bonner]

As above, depends on the MCS installer’s calculations … which depend on assumptions made. You certainly don’t need UFH upstairs but the calcs may show the need for some heating in the bedrooms. I went for (wet) towel rads in the bathrooms and radiators in bedrooms, were quite cheap to install but rarely needed.