How much space required for this plant room?

[doitall]

With diversity you can lower the spec considerably for domestic, and anyone that listens to a builder or other non tradesman is an idiot.

Note; I already said the OP wouldn't need massive hot water storage, on the other hand I would expect someone that installs 2 or more cylinders to know how to plumb them up, including the primary and secondary circuits.

What the chances of 2 baths and 3-4 showers being used at the same time I have no idea, that information should come out in the planning stages.

So Alec to add your two penny's worth, what would you throw in the hat as best practice.

 

[ALEC1]

hot water priority with a CYLINDER SENSOR (not a thermostat) direct from the boiler, a suitably sized cylinder with the right sized coil and a proper conversation with the client to manage his/her expectations...

 

[doitall]

hot water priority with a CYLINDER SENSOR (not a thermostat) direct from the boiler, a suitably sized cylinder with the right sized coil and a proper conversation with the client to manage his/her expectations...

yep, sounds about what I was saying, sitting down with the client (OP) is something we all agree on.

Wouldn't take hot water priority straight from the boiler though, keeping in mind there's should be two boilers, and not one 60Kw Atag with a brain.

 

[ALEC1]

I am not clear why a second boiler...and I doubt you can "properly" cascade two 30cdis...
If he really wants a second boiler, the rinnai is the route to go...

 

[gaswizzard]

Hot water storage being dependant on recovery time I tend to agree with MM regards the 500 litre/70 kw coil rating.

46 minute reheat time. (90% efficiency)

600 litre @ 50 kw coil rating = 77 minutes. (90% efficiency)

300 litre won't cut it when utilising two 10l/m shower heads. (20 minutes max)

Take yer pick.

 

[ALEC1]

thats not quite correct a 70kw boiler with the right sized coil will give about 25l/m continuosly..with a temperature rise of about 35c, enough for 2 showers at 12.5 l/m

 

[gaswizzard]

thats not quite correct a 70kw boiler with the right sized coil will give about 25l/m continuosly..with a temperature rise of about 35c, enough for 2 showers at 12.5 l/m

Can you do the maths for me please Alec? (storage reheat times)

 

[ALEC1]

24kw heats 9.8 l/m with a delta t of 35c, we know that from combis...dont we.

assuming everything else is equal, ie the coil really can dissipate heat, then the maths is pretty basic...

 

[ALEC1]

reheat times are a pretty silly guide...as the boiler kicks in when the stat detects a drop...complete cylinders rarely reheat from incoming temps throughout the whole cylinder...



with low flows ie one shower at 10l/m a 70kw boiler reheating through a 70 kw coil would cycle...

 

[SimonH2]

4.2kW will heat 1kg of water 1˚C per second.

So if you've (say) 100l to heat, through 40˚C, and you've 30kW available, then your formula is :
t = 100 * 40 * 4.2/30 = 560s or 9 to 10 minutes.

It's a bit more complicated as (for example) the performance of the coil will reduce with reducing difference in temperature between primary and tank contents.

 

[doitall]

reheat times are a pretty silly guide...as the boiler kicks in when the stat detects a drop...complete cylinders rarely reheat from incoming temps throughout the whole cylinder...



with low flows ie one shower at 10l/m a 70kw boiler reheating through a 70 kw coil would cycle...

Not if it had two smaller boilers it wouldn't.

And a 70Kw boiler is plain crazy, the only time you'll need half of that is if/when 3-4 showers are used at the same time, complete overkill.

 

[gaswizzard]

24kw heats 9.8 l/m with a delta t of 35c, we know that from combis...dont we.

assuming everything else is equal, ie the coil really can dissipate heat, then the maths is pretty basic...

How does this relate to recovery rates for HW tanks? , who's talking about combis Alec? , sorry but you're way off the mark.

 

[ALEC1]

how come?

 

[ALEC1]

ALEC1 wrote:
reheat times are a pretty silly guide...as the boiler kicks in when the stat detects a drop...complete cylinders rarely reheat from incoming temps throughout the whole cylinder...



with low flows ie one shower at 10l/m a 70kw boiler reheating through a 70 kw coil would cycle...


Not if it had two smaller boilers it wouldn't.

And a 70Kw boiler is plain crazy, the only time you'll need half of that is if/when 3-4 showers are used at the same time,

I agree, but you need a compensation controller that handles boilers under35 kws

 

[gaswizzard]

Size of boiler would depend on recovery rate , considering the OP wants two 10 litre showers running at the same time along with a bath and washing up to run consecutively then 70 kw wouldn't be overkill.

We can only give answers based on the info given.