Underfloor, condensing, thermal store and weather comp

[Dan Robinson]

But if you are heating a cylinder for a family of 4 twice a day.... to 60 degrees? Your boiler is going to need to hit 70+ to do it. 80 if it to be done in any reasonable time.


You are not totally wrong - hence my looking into greater separation of TS stores. And as I have pretty much concluded, it is not financially viable to bring WC into play for most people.

However, You ignore the fact that they do everything else very well indeed. When done correctly. And certainly are no less efficient than an Unvented and S-Plan.

 

[ALEC1]

coil size is significant, with a big coil you wont want high temperatures as the hot water will exceed target value by a big margin..

storing water at 82c must loose more heat than storing it at 65 so a TS must be more wasteful....

thats just plain old thermodynamics...

 

[Dan Robinson]

But your big coil is going to be heating a large volume of tap water?

Your big coil is also going to keep on chugging along - most probably with cycling of the burner until the stat is satisfied....

A TS has no coil. You set the stat to whatever you want the return temp of the boiler to be. The amount of standing losses is determined by the correct sizing of the store in the first place.

 

[ALEC1]

correctly commissioned by matching the KW rating to the coil size, and working around the dhw temperature with a sensor decent boilers do not cycle at all...so both a viessmann 200 and all vaillants using the cylinder sensor will replenish in one long burn...just like your thermal store...

 

[Dan Robinson]

But they would still need to be bigger than required otherwise to make up for the longer reheat times if you are running at lower boiler temp.

And as the other thread on Vaillant controls has shown - not every can work them out - even when they aren't there

 

[SimonH2]

storing water at 82c must loose more heat than storing it at 65 so a TS must be more wasteful....

thats just plain old thermodynamics...

Correction, a cylinder at 82˚C will lose (note spelling) more heat than the same cylinder at 65˚C.

A different cylinder at 82˚C may or may not lose heat faster than the cylinder at 65˚C - it depends on other factors, such as degree of insulation, and also the definition of "lose" since heat "lost" inside the heated space is not in fact lost.

However, I would question why heating the cylinder to 82˚. With a "firking great PHE" there shouldn't be the need to go that high - in fact if it's working then it should cope with the store at little more than the required DHW temp. When I was looking into it, the heat banks I investigated all had a minimum of a 100kW rated PHE.

I think part of the problem is that some thermal stores are "over sold" in terms of DHW output. Raising the store temperature is an easy way of hiding the fact that the coil could have done with a bit more surface area. A heat bank is better in that respect in that the PHE can easily have a higher transfer area for little marginal area - though they do have other downsides compared to a thermal store.

EDIT: Another area where perhaps "poor design and selection" could be an accusation. A slightly larger store, with a bigger coil would allow significantly lower store temperatures for the same DHW draw off.

yeah its the 82c that is only needed presumably for the PHE that wastes the energy

Err, a PHE doesn't waste heat - are you suggesting that it somehow defies the laws of physics and less energy comes out than went in ?

there wouldn't be any standing loss if the heating was off as the boiler would be off

Only true of a combi - something which I wouldn't allow in the house unless there was no other reasonable option. Any other reasonable option (ie one that gives a decent flow of adequately hot water) requires the storage of hot water - and so standing losses without the boiler being on.
Turning that around, now I have the TS in the flat, the boiler actually runs a lot less when the heating is on. Before, it would be short-cycling all the time, now it fires up and runs hard for a couple of minutes to recharge the store before turning off again. There is no boiler I know of which can range from 30+kW (minimum for decent DHW from a combi) down to a few hundred watts - hence no mater what you put in, for most of the heating season it will be short cycling all the time the heating is on. What does that do for efficiency ?
Add to that, the return would be barely cooler than the flow for much of the time (because of the need for a bypass to keep the boiler flow rate up), so unless you run that rads "quite cool" the boiler will rarely condense while heating.

As an exercise, I compared the standing losses between the TS installation and the combi in the house when they were both empty last time. TS about 80W, combi about 160W equivalent - unless you put it in eco mode and then wait up to a minute (with tepid water running down the drain) whenever you want hot water.

 

[DeltaT2]

yeah its the 82c that is only needed presumably for the PHE that wastes the energy...

Using sensors in lieu of numpty on off thermostats means a boiler in a properly desugned system never needs to go over 70c with out the exagerated standing losses...

Aye, there great these boilers, they defy the laws of physics; You can get your sludge bucket up to 80 ° C with your boiler set at 70 ° C!!! Amazing!!!

 

[DeltaT2]

Thermal Stores & Heatbanks are sludge buckets!!

It's so amusing to watch playground arguments But if you are going to claim the high ground, then you really ought to at least try and hide your own hypocrisy - you slag off <someone else> for having set opinions on certain topics, but give the impression that you cannot conceive of any valid use case for certain things you dislike. See if you can think of a well known phrase involved pot, kettle and the colour black. <someone else> may well be trolling something you don't like, but you aren't much better when it comes to being open minded.

Apart from the cost, there are many things in favour of a thermal store or heatbank. For one thing, it means you can completely eliminate the inherent incompatibility between a decent sized boiler and a moderate sized heating system (which is made worse when grossly oversized combi boilers are fitted to supply hot water).

If properly setup you should be able to get a thermal store or heatbank system such that :
The boiler is always condensing, and never runs in short cycles - though this is made harder to achieve by p**s poor design on the part of the boiler manufacturers.
The heating system can run quietly with variable flow rate (fully modulating pump is great for this).
Running multiple heating systems (eg rads and UFH in different areas) is trivial without cross interaction.
Hot water is available on demand, at decent flow rates* and at mains pressure*.
You can have an electric backup for hot water and heating for when your new and horribly complicated boiler breaks down.


* Yes, that's subject to mains capacity - but that's the same with a combi which seems to be very popular.

Simon, you are using multiple threads to have a go at me, as I said in the other thread, if you have a problem with me then please send me a PM.
How can someone like you that has fitted one sludge bucket have infinite knowledge of all Plumbing & Central Heating systems?? Where's your 35 years of trade experience?? You're a Google monkey with too much time on your hands.

 

[DeltaT2]

They also help make TPi controllers super efficient when hooked up to a TS - something I know gets a bee up several poster's backsides .


Bit like a certain someone slagging off the CC, but then bleating on about wanting to get back in

A TS is a nice way to mix underfloor heating and rads, and condensing boilers. Granted the condenser has to work harder to top up the hot water section, but it certainly condenses the whole time.

How do I know....? 'cos I have one.

Still trying to find the time to jam a camera inside to see all the wonderful sludge from my microbore heating system , but the longer I leave it, the more there is to build up I suppose .

The only thing I will add though - make sure you lag the pipes and tappings, otherwise the standing losses can be a bit annoying.

Oh Dan you b.tch!!!....................

Have you got the details of your own system on your Web Site Dan?? I'd love to know more about it.

 

[SimonH2]

Simon, you are using multiple threads to have a go at me ...

No, I'm merely commenting on your deliberately emotive terms used to disparage something you clearly don't like. The fact that you do so in multiple threads isn't down to me.

You're a Google monkey with too much time on your hands

If only I did have too much time on my hands. Nor do I claim infinite knowledge of plumbing systems - but thanks for the compliment

 

[Dan Robinson]

For those that are interested...

I have a 350 litre Excel store from the recently demised, now Specflue Dedicated pressure systems.

It is unvented due to my choice of boiler. Which was - A Coopra N30C. Which actually thinks it is an N40B, although they don't technically exist. A recent Gas Safe Inspector put it down as a "work in progress". The C boiler was a 2 pipe heat only, the B is a 4 pipe system boiler. Mine does't have the diverter valve but is operating off the cylinder terminals, via a Honeywell EvoHome set up with wireless TRV's and an Alpha pump for heating.

Deeeeeeeep Breath.

6 bar mains pressure, through a (correcting myself form earlier) 100kW Plate and blending valve.

I was looking to utilising the OpenTherm Bridge available for the EvoHome and converting the boiler to a true 4 pipe variant and seeing how well it worked with no separating baffle; but now I can have underfloor heating in my house I don't think I'll bother. Thinking of taking it out and converting it to a small twin coil unvented so i can play with other things - NOT for any sludge related issues.

The heating system is/was a dirty microbore system that is actually plumbed with the returns backfeeding through a 15mm section of pipe that was on the cylinder... it was a lash up from when I moved in and we had to take out the old boiler at short notice and didn't have time to rip up floors.

So, the boiler is running in native "heat the cylinder quick" mode which effectively runs the burner flat out until the cylinder sensor reports satisfied. In my case the EvoHome is looking for 52 degrees. This is leaves the bottom third of the cylinder at around 40 degrees, or slight higher - where the heating return feeds back in just under the boiler return connection. The idea was to feed the 4-pipe heating flow in there that would be WC'd; but I would still have to do something clever as the boiler would be expecting it's internal pump (variable speed) to be pushing the rads/UFH. I have spare boards with secondary pump ports - but I think they get powered in Hotwater demand too, which would mean a 2 port valve/added complication .

There are a few snaps of my store somewhere in my profile Dicky. It looks a but like Frankenstein's monster at the moment as I have added sensor tappings to the spare ports on the side of the cylinder. In fact there is a little album complete with some charts showing temperature changes in use.

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[doitall]

Is that Magnaclean big enough for a 500Ltr sludge bucket

 

[mickyg]

using the term "sludge bucket" to describe all TS shows a distinct lack of knowledge of thermal stores. Its obviously based on the likes of BM2s and BM2000s which indeed were sludge buckets due to their design.
Have a look at the design of a Boilermate BP however, and explain to me where the sludge comes from and where it ends up?

 

[Dan Robinson]

Is that Magnaclean big enough for a 500Ltr sludge bucket

Cheeky git... I there isn't enough sludge in there - I could get one of those new Micro Magnaclean jobbies

 

[gaswizzard]

using the term "sludge bucket" to describe all TS shows a distinct lack of knowledge