How much space required for this plant room?

[gaswizzard]

Seems recovery times and hot water usage is way off the mark here.

The following is a slight correction towards a previous post.............................

12 l/m @ 65c would use 6 l/m of hot water when mixed with incoming mains @ 10c.

(6 x 65) + (6 x 10) / 6 + 6 = 37.5c mixed temp @ shower head. (perfect)

6 litres x 20 min = 120 litres.

4 showers at 20 min = 480 litres.

Two 210 litre tanks with a coil rating of 20kw would take around 40 minutes to recover.

 

[doitall]

Excluding my poor additions Gaswizzard.

The Op is talking 2 x 20 minute showers, which as you rightly say is 240Ltrs hot water. or roughly half the 2 x 210cylinders.

By the time the 240ltrs is taken out the remaining water would be around 45-50c without going into working it out, with no recovery.

Now lets assume we want to boost the cylinder back to 65c or a Δ t of say 20c. According to your numbers 2 x 210Ltr cylinders would take 40mins to recover 480ltr which would be nearer 20c.

Now lets assume the boilers are working well whilst you are in the showers, after 20mins when you get out, the water in the cylinders would be what. Shall we say 60C for the sake of an argument.

 

[indus]

Gaswizard

I'm a little confused.

1) are you saying that the recovery time is 40 mins after two showers or after four?

If it's after 4 doesn't that mean (assuming cylinders are used sequentially) that after the fourth shower the first cylinder has already been recovered?


2) Is the recovery time limited by the coil rating despite what the boiler is capable of? If so what is the maximal coil rating you can get in a cylinder?

Thanks

 

[doitall]

The cylinder would be linked with a common cold feed, a reverse return secondary and primary circuits.

The coil rating varies with manufacturer, but most fast recovery are around 28Kw.

Completely ott but the MHS range of calorifiers will heat faster than you can draw off.

 

[ALEC1]

British manufacturers have not really caught on to "hot water performance" in a big way..and coils are still woefully small even those categorised as Part L compliant...this is why I nearly always specify twin coils and connect them in series...


Decent hot water performance comes with certain cylinders, none made in the UK......

 

[doitall]

If this was the only choice Alec

I mentioned 70kW as the heat transfer rate of each coil in a Viessmann Vitocell 300-B twin coil 500 litre cylinder

i wouldn't even bother with a cylinder or two.

An MHS plate would be a far better.

http://www.mhsboilers.com/site/81/21.html

 

[ALEC1]

Agreed, I mentioned the Rinnai...

How does a plate HEX cope with small demands... surely some sort of storage is necesary for these...

 

[indus]

British manufacturers have not really caught on to "hot water performance" in a big way..and coils are still woefully small even those categorised as Part L compliant...this is why I nearly always specify twin coils and connect them in series...


Decent hot water performance comes with certain cylinders, none made in the UK......

Hi Alec

Am I missing something with the twin coil cylinders? Both you and mysteryman are suggesting them yet when I internet search them it always seems to suggest the second coil is heated by solar or heat pumps.

Since I don't have either of these two sources of energy what is the relevance of a twin coil cylinder to me?

Thanks for your input

 

[Dan Robinson]

They are sold to be heated via solar or heat pumps, but they can be linked easily to get he cylinder to reheat a little bit faster.

 

[doitall]

2 x 210 cylinders have twin coils. one in each.

I'm getting bored and starting to repeat myself, time to step back and watch.

 

[Norcon]

You lot are wasting your time. This one's on a winder...

18 pages here....
//www.diynot.com/forums/plumbing/mega-flo-vs-thermal-store.291880/

Another 4 here...
//www.diynot.com/forums/plumbing/help-speccing-a-new-heating-dhw-system.297149/

And another 7 here.....
//www.diynot.com/forums/plumbing/how-much-space-required-for-this-plant-room.319865/

Even Drwaterjonasbigburnerdrivels has been involved to no avail.

 

[ALEC1]

thats what they say, but it does not mean you cannot connect the two in series...so 2 28kws means that 56kws can be absorbed..you get a quicker reheat time...

 

[gaswizzard]

Excluding my poor additions Gaswizzard.

The Op is talking 2 x 20 minute showers, which as you rightly say is 240Ltrs hot water. or roughly half the 2 x 210cylinders.

By the time the 240ltrs is taken out the remaining water would be around 45-50c without going into working it out, with no recovery.

Now lets assume we want to boost the cylinder back to 65c or a Δ t of say 20c. According to your numbers 2 x 210Ltr cylinders would take 40mins to recover 480ltr which would be nearer 20c.

Now lets assume the boilers are working well whilst you are in the showers, after 20mins when you get out, the water in the cylinders would be what. Shall we say 60C for the sake of an argument.

My head hurts John.

 

[doitall]

My head hurts John.

And mine.

Abbreviated I said.

Two 30Kw boilers feeding two 210 cylinders, will have a far greater output, than two showers using 12ltrs/min between them.

And if you consider a same size combi chucking out 12 ltrs min, therefore there's no reason not to believe the two boilers couldn't replace 24 ltrs/min from 4 showers as it was being used.

 

[gaswizzard]

And if you consider a same size combi chucking out 12 ltrs min, therefore there's no reason not to believe the two boilers couldn't replace 24 ltrs/min from 4 showers as it was being used.

24 l/m @ 55 dt would require 92.5 kw.

92.5 x 60 / 4.2 x 55 = 24 l/min.

This is the deal considering were talking mixed temps , anything less just aint gonna keep up.

Recovery rate for two 30 kw boilers would be around 15 litres minute.

Temperature rise of 27.5 (10c cold main temp) will require a boiler output of 46.5 kw , two showers @ 10 l/m would use 400 litres (out of tank/no mixing) over 20 minutes.