UFH Design for extension, UVC? TS?

[Tin Soldier]

Hi there,

I've been posting sporadically as my thoughts move from one topic to another. I've had such a fantastic response so thank you.

Next up is heating. I'm struggling to get a hold of any local plumbers who know anything/are willing to come and discuss/ quote on ufh design, uvc or thermal stores.

 

I've attached a picture of my extension, I've tried to remove as many layers of detail (so its easier to read) as I can which is why there is some weird colouring etc.

its all on one level

 

currently the plan is simplistic. UVC and Oil Boiler in the utility room top left connected to radiators in the old house, and ufh in the new house. It was going to be in screed UFH, but based on some research and discussion with you guys yesterday I've asked to change this to in slab pipework.

 

my next area of concern is.

 

1. location of UFH Manifold and length of runs. - Looking at the heating during the planning stage it was simple UFH manifold in utility room connected to boiler, no probs. however when I look at the length or runs when I am trying to figure out layout, locating the manifold in there will mean there are some excessively long runs. could anyone recommend a better location for the manifold? can it be at a distance from the Boiler - ie located in the middle somewhere?

 

2. Should I be looking at a thermal store in place of an UVC. can I Heat my UFH and radiators and DHW separately from this, would it be a more efficient store to a UVC? I keep seeing snippets on 'short cycling' which is putting the fear into me.

 

as I try and get someone local to discuss with, any pointers  would be much appreciated

 

cheers

 

Scott

[le-cerveau]

You want to put your manifold centrally, make a small cupboard on an appropriate wall or cupboard, one by bed 2 or in the dressing area (take out a small area).  You then put an insulated run from your heat source to the manifold.  As you have an oil boiler you need a long burn time to be efficient.  If you are running the radiators directly from the boiler then you need a buffer of some sort for the UFH.

You could run the whole system of a large TS, UFH tapping low down, radiator tapping middle/top and DHW from the store.  The boiler would then be heating the TS direct.  It would also allow you to add solar (not our favorite) or an ASHP later.  This is the advantage of a TS.  However the experts here will tell you that an UVC gives better DHW performance, so what is your overall requirement.  How many bathrooms/showers, what is your DHW requirement and recovery time?  What is the heat load of your house? What is teh power of your boiler?.....

[Tin Soldier]

1 bathroom, 3 showerroom overall, family of 5

 

DHW, it would be great to be able to run two showers at once

I guess recovery time in the evening is important (If I'm understanding recovery time right) as theres a lot going on, three young kids to bath etc. and likewise in the mornings when they are a little older.

 

boiler will be purchased new to replace current, so power is non currently limited.

 

currently we have no hot water tank of any sort and a struggling combi oil boiler.

What type of boiler is suitable to heat a thermal store, a system boiler?

[le-cerveau]

You don't need a combi.  A regular boiler will require pump and controls, a system boiler will have it all in and usually there isn't much difference.  All your boiler does is heat up the TS when there is a demand.  The UFH, Rads just take out heat as required, same as the DHW.  One of the biggest issues is heat loss, even the best TS's are at best C/B rated and loose more heat than that (see @JSHarris blog on his heat loss issues).

Are you considering an ASHP? make it more complex but possible savings compared to oil prices.

With just an Oil Boiler then a simple TS with a large DHW coil will suffice, you want it large enough to provide your DHW requirement, this is a combined function of TS size vs boiler power, bigger boiler means smaller tank (within limits).

If you add an ASHP, then you need a stratified TS or a separate buffer (and DHW preheat) and TS/UVC.  A large stratified TS is the simplest option, though possibly not the most efficient (someone else do the maths) and there are plenty of companies doing them AKVATERM (Finnish) have a range with separator plates between low grade and high grade heat (GEO range).

 

In doing your calculations, size of bath/ capacity of showers all needs to be factored in, it takes some time and you will end up making some compromises.

 

There are numerous options and no simple answer.

[Nickfromwales]

@Tin Soldier

Go with a TS, mainly because of the mix of space heating types you have means you don't really have much option as your on oil. 

Go for 300- 350L and you'll be able to sustain nigh on constant instant high flow ( ~20Lpm ) DHW to the house. Size the boiler ~26kw and that will suffice. I recently did a Grant 21/26 with a 500L TS and that would run the bath and a shower simultaneously with ease, plus enough DHW capacity to get a reasonable flow from the kitchen hot tap too. That install was fortified with a cold mains accumulator ( 300L ) so you do need a good cold mains to get good DHW flow, so bear that in mind. 

The interconnecting pipework all needs insulating well and all the different flows need a motorised valve to arrest nuisance convection circulation which otherwise leads to a huge amount of heat loss. 

Put the TS where the waste heat is useful, eg airing cupboard, rather than an utility room if possible, and go for an external oil boiler. You'll save the space and avoid smell / grot when access is required for servicing. ?

If you have pv then great as that'll help offset and losses and will contribute to the heating / hot water when generating. 

[Tin Soldier]

is bigger, better in terms of ts and boiler power?

 

Funny you should mention an outdoor boiler. I've been looking at GRANT outdoor boilers as there is a local installer.

 

any recommendations on boiler type/thermal store?

[Nickfromwales]

8 minutes ago, Tin Soldier said:

is bigger, better in terms of ts and boiler power?

 

Funny you should mention an outdoor boiler. I've been looking at GRANT outdoor boilers as there is a local installer.

 

any recommendations on boiler type/thermal store?

Deffo a system boiler as it's all in one box   

For a TS you will get a great price off Trevor@ cylinders2go. Just mention the forum and my username and he will quote you happy. 07939 996940. 

To proceed with an order you'll need to know tank size ( capacity in L ), DHW coil size 22mm or 28mm ( bigger is better ), number of tappings and what they're for, number and size of immersion heaters ( e.g. 2 x 3kw etc ) and number of thermostat pockets ( usually only one for the cylinder thermostat if a system boiler ), so get your ducks in a row here first . 

You don't need to go any bigger with the TS as circa 300-350l will give you a decent buffer size for DHW sustain, have enough volume to heat transfer linear to two showers being run or a bath + 1 shower etc without a drop in DHW performance, ( subject to the boiler heating the TS on demand via the cyl stat ), and be big enough to get long solid burns from the oil boiler. That will allow you to set it up to maximise on efficiency and get flow temp into the optimum condensing range. Oil like to burn long and hard, and they don't modulate like gas does, hence the red flag about short-cycling. 

[le-cerveau]

23 minutes ago, Tin Soldier said:

is bigger, better in terms of ts and boiler power?

@Nickfromwales can better answer but it is a compromise, Bigger is better buts costs more and takes up more space!  A Bigger TS enables you to use a smaller boiler (within reason) and not run out of hot water.  A bigger boiler allows you to run a smaller TS (quicker re-heat) but again there is a size not to be dropped below.

Crossed replies with Nick.

[Nickfromwales]

Just now, le-cerveau said:

@Nickfromwales can better answer but it is a compromise, Bigger is better buts costs more and takes up more space!  A Bigger TS enables you to use a smaller boiler (within reason) and not run out of hot water.  A bigger boiler allows you to run a smaller TS (quicker re-heat) but again there is a size not to be dropped below.

Crossed replies with Nick.

+1

As it's a year round heat battery, eg you need it hot all summer just for DHW, it stays hot 24/7/365 for DHW + space heating. Storing at lower set temp means lower standing losses but that can only be achieved by going bigger in capacity.

@Tin Soldier

Is pv in or out of the equation? 

[le-cerveau]

For recommendations, I can't really comment as I am fitting a custom SunAmp Stack with 2 different temperature PCM sets (v-expensive), but before I finalised on that the best I could find were the Akvaterm range of TS's as they come out a B/C efficiency (heat loss is an issue in a Passive type House).  Their standard ones (just the one DHW coil are 300 & 500L (or bigger).

 

If you are considering an ASHP then there are other versions (GEO) with stratification (option I was looking at) but as Nick says it is then getting more complex.

[Nickfromwales]

Just rang Grant and they no longer do a true heat-store combi. Ones of yesteryear had a TS inside the boiler with a DHW coil and had fantastic DHW flow rates, but now they use an integral TS to collect heat for a DHW plate heat exchanger, BUT if not used to its max output it still suffers from short cycling, ( made even worse if you specify the largest 36kw model and only run a basin hot tap for eg ), plus you'd still need a buffer for the UFH. 

System boiler and TS seems the way forward. You could still consider a stand alone buffer for the UFH, so only heated seasonally, and a separate UVC for DHW. No reason you couldn't do that, and decrease your summer nuisance heat loss / cost. If the wife likes a nice warm airing cupboard then the TS will provide that year-round. 

[Tin Soldier]

Hi guys, this is some fantastic feedback, genuinely amazed that you take the time to put in so much detail

 

Nick, I think Solar PV is out of the equation just now, as is ASHP and GSH,

I simply don't have the fund to commit to it, I've tried to get the shell of the house right.

 

I'm liking the sound of a good sized thermal store and a reliable system boiler. plenty of room to put it in, at least there is in the utility room,

no upstairs room to even contemplate it unfortunately.

 

oh if only I could hook up my ground floor woodburner to the TS, I couldn't, could I?

[le-cerveau]

1 minute ago, Tin Soldier said:

oh if only I could hook up my ground floor woodburner to the TS, I couldn't, could I?

 

Yes, that is what a TS does!  You need to run the pipes and have a wood burner with the backboiler (heat take off) functionality!  You also have to put in some specific safety features but it is all doable.  The question is is your wood burner compatible and can you easily run the large bore pipework to the TS?

[Nickfromwales]

You can add a "flue boiler" to an existing wood burner ( if it isn't already a wood burning stove with back boiler ). 

Random internet grab for example only

A TS is exactly the kind of medium that would be required when integrating multiple heat sources, so yes, you could. The question is can I afford to do it and would it be both practical and economical to do so . It's a twat of a job to retrofit this, but you can get a WBS with a BB off the shelf that can have a pumped flow and return on a sealed circuit ( so can be pumped left / right / up / down without gravity constraints ), plus has no need for open header tanks and all that faff as they are cooled by a cold mains 'sprinkler' which cools them down accordingly if they boil or overheat etc. 

@djvasey, David, any feedback on yours?

 

Oh and for the UFH manifold......

Are the runs way over 100m in length if you don't put the manifold in the middle? 

If centralising the manifold is easier then by all means do it, but running insulated flow and return pipework between the TS and the manifold is in no way problematic.  

 

[dpmiller]

I'll put a vote in for a Turkington boiler as I've been well impressed with ours (and they don't use a Riello burner, I hate them) and I see they have a system variant now:

 

http://www.turco.co.uk/countrymanpros---outdoor-system-boiler

[Tin Soldier]

Now I’m super interested

 

the plan was to buy a wood burner anyway to supplement the other wood burner in the older part of the house that we run half the year

 

10 tonnes of wood in my barn and a wood at the end of my garden ready to be cut split and set on fire

 

i assumed no gravity no hookup.

 

so far my plan is to centralise the manifold and run a connection in the middle layer of the insulation under the slab to the boiler, 

 

coukd i I do the same with a connection to the thermal store? And have a pump in the same location as the manifold?

[Nickfromwales]

22 minutes ago, Tin Soldier said:

 

coukd i I do the same with a connection to the thermal store? And have a pump in the same location as the manifold?

Yes. The UFH manifold must have a pump to circulate the water through the TMV and back into the loops. No need for a pump to get from the TS to the manifold as it'll pull through by itself, unless it's the most adverse run in history. 

 

24 minutes ago, Tin Soldier said:

i assumed no gravity no hookup.

In most cases yes, but a lot here from our days at Ebuild 

http://www.ebuild.co.uk/topic/14379-thermal-store-advice-comments/page__fromsearch__1

 

Worth a read. 

 

[Nickfromwales]

4 hours ago, Tin Soldier said:

Nick, I think Solar PV is out of the equation just now

After re-reading, I'd seriously reconsider this TBH, and try to at least fit a non-MCS system now, maybe just 2kw, so your cabled out and can upgrade in the future with more panels and MCS sign off if necessary. 

You can still export to the grid, but you need to contact the DNO for that arrangement / it's feasibility. 

Offsetting the losses from the TS and covering your background electricity consumption would be a wise choice if this property will be your snuff-box. 

 

[Tin Soldier]

Ok Nick I'll listen to your suggesting and look into it, thought I don't know what MCS means?

 

things getting pretty complicated now but  reading through that old ebuild post the guy had a woodburner with a cold water cooling coil to quench the back boiler in the event of it overheating.

 

setting aside financials for the moment could something like this work for having a wbs connected to to thermal store on the same level?

 

 a quick google has come up with https://www.modernstoves.co.uk/wood-burning-stoves-with-back-boiler/apollo-multi-fuel-wood-burning-stove-with-back-boiler.html

which has an optional thermal safety flush valve for connecting the water, and recommend a pumping station to be connected up too

 

could that work?

 

we use a wbs a lot at the moment, and have a practically unlimited wood supply so its worth me investigating now if I can utilize it to warm the thermal store.

 

cheers

 

Scott

[Nickfromwales]

MCS ?

[Nickfromwales]

38 minutes ago, Tin Soldier said:

Ok Nick I'll listen to your suggesting and look into it, thought I don't know what MCS means?

 

things getting pretty complicated now but  reading through that old ebuild post the guy had a woodburner with a cold water cooling coil to quench the back boiler in the event of it overheating.

 

setting aside financials for the moment could something like this work for having a wbs connected to to thermal store on the same level?

 

 a quick google has come up with https://www.modernstoves.co.uk/wood-burning-stoves-with-back-boiler/apollo-multi-fuel-wood-burning-stove-with-back-boiler.html

which has an optional thermal safety flush valve for connecting the water, and recommend a pumping station to be connected up too

 

could that work?

 

we use a wbs a lot at the moment, and have a practically unlimited wood supply so its worth me investigating now if I can utilize it to warm the thermal store.

 

cheers

 

Scott

Yup. With a quench system it's ( the WBS/BB ) seen as a sealed and pressurised arrangement which you can fully pump eg any pipe run should be feasible as long as normal disciplines are observed, like air release valves at the highest points etc. 

If you have such a plentiful supply of dry seasoned wood available, and routinely burn regardless, then I'd 100% get a WBS/BB fitted and go for a bigger TS. 

Your summer standing losses will increase slightly as you'll be storing more water, but you can lower the boiler flow temp a little to help there, plus, as I've said, I'd really think of pv to offset these latent losses. 

Youll have to manage the burns to suit your storage, e.g. no point in having a roaring fire heating water that can't be stored anywhere, plus you may want to fit a huge K2 ( double ) radiator in the garage or outhouse for heat dump, pumped from the TS controlled by a dedicated high limit stat. That should stop your quench system doing overtime as you should design now to limit that functions requirement, other than it operating as a terminal / failsafe. 

Doesn't matter if it means a super long pipe run to the heat loss rad, but fitting one is imo a very good idea. You could put a clothes airer above it on the garage for drying towels etc in the winter so it's functional too.  

[Nickfromwales]

1 hour ago, Tin Soldier said:

Ok Nick I'll listen to your suggesting and look into it

Sun will remain in the sky, but oil prices are only going to go up and up. . 

[Tin Soldier]

surely if we burn enough oil we can block out the sun?

[Nickfromwales]

12 minutes ago, Tin Soldier said:

surely if we burn enough oil we can block out the sun?

?. Second thoughts.......leave the pv ?

[Tin Soldier]

so...

 

I've been thinking about the return and flow connections to ufh Manifold to be laid within my eps insulation, under slab,

 

What type and size of pipe is best, and how best to lay it? individual pipes, or some form of conduit?

at the moment there will be a 50mm layer of eps insulation, sandwiched between two 100mm Layers, which I thought would be a prime candidate to channel out and lay the pipes in.

 

The reason I ask about a conduit is that I would need the ends of the pipes to be exposed by about 8 meters at the edge of the new slab, to allow me to channel out an insulated route through the existing slab, once we break through.

 

Thoughts appreciated

 

thanks

 

Scott