Keep me honest - UFH and MVHR

[wardie9025]

Hi all,

 

We are about to push the go button on a big extension/retrofit and I want to make sure my ducks are in a row.  Final advice being taken on heat source (probably ASHP) sizing as well as a few other bits but want to make sure the bits that need to be finalised for the main build are correct.  I've uploaded a PDF to show 1) where we are disturbing anyway (most of the house!) and 2) what my thoughts are around heating.  1969 house in Southampton with some existing extensions to be largely demolished and remodeled with the opportunity for significant changes to optimise the fabric and heating emitters whilst we move out. 

 

Please test me on the main points and assumptions to date:

 

 1) floor is concrete slab throughout; we assume there is no insulation underneath and as the back of the house is to be removed, we have the opportunity to smash the slab up and and re-lay it to keep the heating consistent in the kitchen/dining/sitting area (see plans). If we do this, only the lounge remains so we may as well smash this up and relay as well.

 

2) aim is for very low temp heating system (targeting 35degC max at -2 external);

 

3) insulation under the slab with with pipes either cast into the slab or clipped onto the slab for high thermal mass.  Pipes at 100mm centers throughout with no allowance for kitchen units/toilets etc (e.g. pipes everywhere).  This sorts downstairs heating.

 

4) upstairs heating - either via fan coil rads or warm air?  Have also had a suggestion that with an MVHR unit extracting from downstairs and supplying upstairs would mean that heating actually not required upstairs.

 

Be gentle, but not too gentle!

 

Cheers!  Gaz

20230603-Heating and Plumbing (excl UFH pipe) -v1.0.pdf

[Dave Jones]

im doing pretty much same as you, albeit its new build. Im adding a chiller unit to the MVHR and provision to reverse the ASHP to chill the slab and provide a cold feed to the fan coils.

 

Are you maxing out solar ?

 

You sure a single cylinder is enough hot water for a 5 bed ? Our family of 5 need a min of 2 of the large ones and im leaving room to add more in case they needed. 

 

What U values for walls, floor and roof are you designing for ?

Edited June 3, 2023 by Dave Jones

[Dan F]

1 hour ago, wardie9025 said:

Have also had a suggestion that with an MVHR unit extracting from downstairs and supplying upstairs would mean that heating actually not required upstairs.

 

MVHR will recirculate, but air from downstairs isn't enough to heat upstairs given you'll have heat loss via the roof, windows and walls on the first floor.  If you think about it, the air supplied via MVHR on the coldest days of the year will be approx 17.5C (assuming -2C outside 85% efficient MVHR).

 

If the house is insulated to a passive standard throughout and airtight (a bit harder to do with a retrofit), some people do skip the first-floor heating relying on UFH/towel rails in the bathrooms only.  This can work well but only if you are happy for the first floor to be a few degrees colder than the ground floor on the coldest days of the year.  Some people are fine with this, others aren't, while others use supplementary heating for just a couple of weeks a year.  If the final spec won't be passive level though, I'd definitely be panning for UFH, radiators or potentially fan-coils on the first floor.

Edited June 3, 2023 by Dan F

[Dan F]

1 hour ago, Dave Jones said:

Im adding a chiller unit to the MVHR and provision to reverse the ASHP to chill the slab and provide a cold feed to the fan coils.

 

When you say MVHR chiller do you mean one of those units that uses a brine loop to cool incoming air using ground temperature?

 

1 hour ago, Dave Jones said:

You sure a single cylinder is enough hot water for a 5 bed ? Our family of 5 need a min of 2 of the large ones and im leaving room to add more in case they needed. 

 

Depends on how big the cylinder is, what temp you have it at, how long you shower for and if you use WWHRS.   We find that a 300L@55C with WWHRS works well for the 4 of us.  We heat it at 2 am every night on a cheap tariff and it lasts all day.   A 12 min shower @ 12L/min uses around 20% of the tank.

[Dave Jones]

3 hours ago, Dan F said:

 

When you say MVHR chiller do you mean one of those units that uses a brine loop to cool incoming air using ground temperature?

 

 

Depends on how big the cylinder is, what temp you have it at, how long you shower for and if you use WWHRS.   We find that a 300L@55C with WWHRS works well for the 4 of us.  We heat it at 2 am every night on a cheap tariff and it lasts all day.   A 12 min shower @ 12L/min uses around 20% of the tank.

 

ASHP supplies cold feed to the MVHR. No way a 300L cylinder would be enough for us without rationing which isnt an option. Planning for double/treble that.

[wardie9025]

Thanks all for input so far.  Long response....here goes..

 

@Dave Jones

 

6 hours ago, Dave Jones said:

im doing pretty much same as you, albeit its new build. I'm adding a chiller unit to the MVHR and provision to reverse the ASHP to chill the slab and provide a cold feed to the fan coils.

Good to know.  I had considered adding a "trimmer battery" i.e heating/cooling coil to the MVHR outlet and if MVHR alone wont be enough to keep upstairs warm/cool then this is how I was thinking we could do warm heating/cooling upstairs. @Dave Jones, a couple of follow up questions:

1.  What heat pump are you using?

2.  How do you intend to activate cooling mode if OEM doesn't support cooling in the UK?  I've seen you can buy a cooling mode resistor to activate it on the control board of some heat pumps and DIY install?  I had thought I'd also like to be able to cool.

3. How do you intend to control water flow to the coil?

 

6 hours ago, Dave Jones said:

Are you maxing out solar ?

Solar not planned at the moment as its very budget dependent.  Intend to fit "for but not with" i.e. space in the dist board and run the cables etc and then fit at the end if money left.  Thinking we need immersion heater in the tank, solar diverter and batteries if budget allows (have seen a great DIY example on here somewhere).  Anything else???

 

6 hours ago, Dave Jones said:

You sure a single cylinder is enough hot water for a 5 bed ? Our family of 5 need a min of 2 of the large ones and im leaving room to add more in case they needed. 

Not done the sums yet but I don't think we'll need that much.  We have 3 kids (but only one daughter!) - oldest is 9 so not at major hot water usage yet but we do want to plan for the future.  If you don't mind me asking, what's your hot water usage - both volume and profile through the day?

 

6 hours ago, Dave Jones said:

What U values for walls, floor and roof are you designing for ?

  - walls - 0.6 - allowed for 75mm cavity for extra partial or full fill insulation in the extension.  Existing walls are cavity wall insulation of unknown quality; possibility of suck out and re-install later?

 - floor - 0.18 - 100mm insulation under the slab.

 -  roof - 0.15 - insulation is currently rubbish.  Need to upgrade but I'll DIY this for the existing house.

 

Sound reasonable???

 

@Dan F - excellent point.  We will get as tight as reasonably possible but wont be looking to get to anything like passiveso yes, need to plan to include heating on the first floor.  I guess this is where the coil on the MVHR outlet could come in as an easy win to get the heat in.

 

Cheers!  

 

Gaz

 

[Dan F]

4 hours ago, wardie9025 said:

@Dan F - excellent point.  We will get as tight as reasonably possible but wont be looking to get to anything like passiveso yes, need to plan to include heating on the first floor.  I guess this is where the coil on the MVHR outlet could come in as an easy win to get the heat in.

MVHR post heater won't be enough on its own, air flow is too slow.   Fancoils would work through, as would ufh or good old radiators. Not sure why @Dave Jones is using both post-heater and fancoils..

 

Out hot water usage is 2-4 15min showers a day. 300L is enough given WWHRS and heating it to 55C, but wouldn't be otherwise.  That's because we only heat it on cheap/night tariff though. If we were happy to reheat it during the day would be plenty, unless maybe if everyone decided to shower at same time.

 

900L of water at 55C with no WWHRS gets you 5 x 15min showers a day at 18l/min with no reheating.  Is this is your calculation @Dave Jones, do you plan to only heat at night? Also have you considered WWHRS to avoid need for 3rd tank?

[Dan F]

4 hours ago, wardie9025 said:

. How do you intend to control water flow to the coil?

You set it up as a zone as part of heating installation.  You'd do the same if using fancoils, they ideally be a zone on same install using same ashp.  Unless you were using separate A2W unit for fancoils like they often do europe, but that's not typically justified, at least for typical house in UK.

[Dave Jones]

9 hours ago, Dan F said:

MVHR post heater won't be enough on its own, air flow is too slow.   Fancoils would work through, as would ufh or good old radiators. Not sure why @Dave Jones is using both post-heater and fancoils..

 

Out hot water usage is 2-4 15min showers a day. 300L is enough given WWHRS and heating it to 55C, but wouldn't be otherwise.  That's because we only heat it on cheap/night tariff though. If we were happy to reheat it during the day would be plenty, unless maybe if everyone decided to shower at same time.

 

900L of water at 55C with no WWHRS gets you 5 x 15min showers a day at 18l/min with no reheating.  Is this is your calculation @Dave Jones, do you plan to only heat at night? Also have you considered WWHRS to avoid need for 3rd tank?

 

not using a post heater no sure where you got that idea. fancoils for 1st floor supplementary heating/cooling if required.

 

a 300L tank is nowhere near enough for 5 showers @ 18/l thats 1350L even diluting with cold. 

 

Also plan for pressure unless you will only shower 1 at a time, not have the washing machine, dish washer, sink etc as well.

 

yes to wwhrs, using the column. not factoring it into usage though it will just be an energy bonus.

 

[Dave Jones]

14 hours ago, wardie9025 said:

Thanks all for input so far.  Long response....here goes..

 

@Dave Jones

 

Good to know.  I had considered adding a "trimmer battery" i.e heating/cooling coil to the MVHR outlet and if MVHR alone wont be enough to keep upstairs warm/cool then this is how I was thinking we could do warm heating/cooling upstairs. @Dave Jones, a couple of follow up questions:

1.  What heat pump are you using?

2.  How do you intend to activate cooling mode if OEM doesn't support cooling in the UK?  I've seen you can buy a cooling mode resistor to activate it on the control board of some heat pumps and DIY install?  I had thought I'd also like to be able to cool.

3. How do you intend to control water flow to the coil?

 

Solar not planned at the moment as its very budget dependent.  Intend to fit "for but not with" i.e. space in the dist board and run the cables etc and then fit at the end if money left.  Thinking we need immersion heater in the tank, solar diverter and batteries if budget allows (have seen a great DIY example on here somewhere).  Anything else???

 

Not done the sums yet but I don't think we'll need that much.  We have 3 kids (but only one daughter!) - oldest is 9 so not at major hot water usage yet but we do want to plan for the future.  If you don't mind me asking, what's your hot water usage - both volume and profile through the day?

 

  - walls - 0.6 - allowed for 75mm cavity for extra partial or full fill insulation in the extension.  Existing walls are cavity wall insulation of unknown quality; possibility of suck out and re-install later?

 - floor - 0.18 - 100mm insulation under the slab.

 -  roof - 0.15 - insulation is currently rubbish.  Need to upgrade but I'll DIY this for the existing house.

 

Sound reasonable???

 

@Dan F - excellent point.  We will get as tight as reasonably possible but wont be looking to get to anything like passiveso yes, need to plan to include heating on the first floor.  I guess this is where the coil on the MVHR outlet could come in as an easy win to get the heat in.

 

Cheers!  

 

Gaz

 

 

heat pump - not decided yet but it will have to support cooling out of the box. Wont be MCS scam install either.

control/flow/valves will leave to the plumber. 

Your missing a trick on solar. It's cheap and has immediate payback.

75mm cavity (0.6 is a typo I would guess?) may just scrape past regs but its very very  poor U value even using expensive insulation. Insulated plasterboard as well unless you can make the cav wider.

for showers im allowing 5 simultaneous @ 19L/min and the washing machine, dishwasher etc. basically worst case. accumulator to maintain flow and starting of with 2 x 300L with space for 2 more. see how we get on. I'll keep adding them until running out of hot isn't  an issue. Poverty mode for hot water isnt an option. 

 

[jfb]

15 hours ago, wardie9025 said:

floor - 0.18 - 100mm insulation under the slab.

If you are going for ripping up existing floor why wouldn’t you go for 200mm? Extra cost upfront but if you really want low temp Ufh then I would go for it. No brainer in any new build sections. Isn’t the minimum floor value for new build floor 0.13 anyway?

 

[jfb]

22 hours ago, wardie9025 said:

Have also had a suggestion that with an MVHR unit extracting from downstairs and supplying upstairs would mean that heating actually not required upstairs

Pretty sure the volumes moved by MVHR aren’t any way near enough to redistribute heat in the way you are hoping.

[Dan F]

1 hour ago, Dave Jones said:

not using a post heater no sure where you got that idea.

Sorry, my bad. What is the chiller unit that uses cold feed from ASHP then?

 

(We have a Comofopost after our MVHR using an ASHP feed and while it cool as well, I've heard them called post heaters). My experience is that they are only sufficient to stop MVHR heating house when very hot outside, but not really effective for any active cooling.

[Dave Jones]

chiller unit is a cooler yes not a heater.

 

Your right they wont cool enough on their own hence using the fancoils as well as the ufh to provide cooling.

[Dan F]

2 hours ago, Dave Jones said:

chiller unit is a cooler yes not a heater.

Got it.  I used it for both heating and cooling.  It's not very effective though.  Fan coils make a lot of sense, I was just wondering why you are using the "chiller unit" if you'll have fan coils, given the relative effectiveness of the "chiller unit" is significantly lower than both UFH and fan coils.

 

4 hours ago, Dave Jones said:

a 300L tank is nowhere near enough for 5 showers @ 18/l thats 1350L even diluting with cold. 

I know.  Are you assuming that you don't heat UVC(s) during the day, or is it simply that you want to plan for the 5 showers to be in parallel of close succussion and therefore reheating isn't an option?

 

1350L is a lot, even at 18L/min and ignoring WWHRS.   What UVC temp are you assuming? What shower length?

 

4 hours ago, Dave Jones said:

yes to wwhrs, using the column. not factoring it into usage though it will just be an energy bonus.

Right. It is worth considering though, that it will in practice, will mean that a 15min 18L/min shower may only need around 125L hot water instead of 190L (assuming 55C UVC). 

 

 

[JohnMo]

5 hours ago, Dave Jones said:

showers im allowing 5 simultaneous @ 19L/min and the washing machine, dishwasher etc. basically worst case. accumulator to maintain flow and starting of with 2 x 300L with space for 2 more

Assume you will have a separate heat source for all this hot water, as it will be busy most of the day, either reheating water or making up for the heat loss. Plus may be, if well insulated you may not need much other heat in the house, if you can distribute the heat coming off the cylinders and interconnected pipes. But plenty of cooling in the summer required.

 

Quick calc makes about £10 per day on DHW alone, assuming CoP of about 2 to 2.5.  £3.5k a year - you must have deeper pockets than most.

 

Have you looked at something like this, which may offer more flexibility.

 

https://originaltwist.com/2016/06/23/eco-heating-system-for-heat-pumps/

[Dave Jones]

13 minutes ago, JohnMo said:

Assume you will have a separate heat source for all this hot water, as it will be busy most of the day, either reheating water or making up for the heat loss. Plus may be, if well insulated you may not need much other heat in the house, if you can distribute the heat coming off the cylinders and interconnected pipes. But plenty of cooling in the summer required.

 

Quick calc makes about £10 per day on DHW alone, assuming CoP of about 2 to 2.5.  £3.5k a year - you must have deeper pockets than most.

 

Have you looked at something like this, which may offer more flexibility.

 

https://originaltwist.com/2016/06/23/eco-heating-system-for-heat-pumps/

 

planning for worst case, reality should be half of spec mostly. dhw free for summer and most of shoulder months (10kw solar) cheap rate in winter.

 

will have a read of link thanks.

[Ewan]

On 03/06/2023 at 22:51, Dan F said:

You set it up as a zone as part of heating installation.  You'd do the same if using fancoils, they ideally be a zone on same install using same ashp.  Unless you were using separate A2W unit for fancoils like they often do europe, but that's not typically justified, at least for typical house in UK.

 

Curious about this as currently back to brick and want to future proof in this ability to cool with FCUs later.

It's a circuit for the ASHP to any FCUs, separate from any UFH and raditor circuits? Would you do it in copper or plastic, and I am assuming it's insulated?

BTW what FCUs do you think are good?

[wardie9025]

Hi all,

 

Thanks for the responses and very interesting conversation and sorry for the radio silence - its been manic whilst we finalise our build!  Have now manage to design the system in loopcad and putting it up here for people to throw rocks at.

 

Assumptions:

1. Assumed 50w/m2 heat loss throughout based on advice and looking at the heatgeek table and choosing a reasonably conservative estimate- not used loop cad for the calcs but that does spit out just under 9kW so figure that size would be fine on the basis that it would allow for some over capcity where I've been conservative.
2. Pipes sized at 20mm throughout to minimise pressure drop.  Plan to throttle down on flow rate if needed
3. Pipes going into 100mm thick screed (couldn't persuade builder last minute to drop the screed and go insulation under slab...long story and I've probably compromised a bit much but hey ho) so high thermal mass.
4. Assumed, 35degC flow temp and a dT 2degC for the design but can increase to dT5 if needed depending on what flow rates the HP needs.
5. Planning for a Panasonic Aquarea 9kW - for high COP; self install - BUS not worth it as they just add the 5k on to take it off again.

Hit me!!

20230808-41NFR UFH Piping-v1.0.PDF