2 x indirect unvented cylinders, problems?

[RickyLee53]

I've posted another topic on this in the past, but it went a little off course.

I'll try to keep it brief.

Loft space (where the cylinder will go) is 1200mm max. This means i'll have to go horizontal cylinder or 2 smaller ones.

If I go 2 x 180l cylinders, its still cheaper than a horizontal 300l. Recovery time will also be much quicker.

I plan to have a double bath, and large shower. Bath capacity is 400l. Shower head 450mm square.

However I'm worried about balancing the flow from the 2 cylinders.

Also, if I store water at say 70 degree's. How much usable water do you get out of a 180l cylinder? I'm assume after 90l the water will be down to 50 degree's approx. So after 130l (260 total) the water temp would be too cold to shower.

I'm going to run a combi for the taps. So I could have the stored hot water temp at the very max.

I looked at the RM Stelflow brand. I'm going to call them tomorrow.

 

[Dan Robinson]

What kW are you going to have to heat these things?

Look at the twin coil versions. Link the coils together and have them on hot water priority so space heating is off. Easily done electrically.

Will let one of the maths wizards work out the usable capacity.

You might also think of using a buffer tank and plate heat exchangers. Not sure if you'll have the space though. For a house with a bath that bog you'd think you could find a better space for your plant.

Perhaps the expert in all things Joe90 can help you.

 

[Agile]

You are not meant to set the water temp above 60° C.

Its easy to balance by keeping all pipework equal and adding a couple of gate valves for fine tuning!

Joe will explain in detail!

Tony

 

[hazetimesfive]

I have no idea why you would want a combi in this situation. its just over complicating things, you are paying for stored HW so you may as well bloody use it.

 

[Agile]

I dont see any problem with a combi.

They are often cheaper than a heat only now.

Tony

 

[hazetimesfive]

i just cant fathom why you would pay for hw store and for instant hot water,

its like having food in the fridge and eating takeaway everynight

 

[Dan Robinson]

Its not a bad system actually as long as the combi is near the point of use i a big place.

 

[mickyg]

i just cant fathom why you would pay for hw store and for instant hot water,

its like having food in the fridge and eating takeaway everynight

yes i totally agree with this post. Added to that..a combi restricts the ability to size the boiler correctly for the demand as well as being more unreliable due to extra parts.

 

[Dan Robinson]

Possibly Micky - but a place that justifies that kind of bathroom and shower should be able to take the heating output of a combi. It is the Hot water reheat capacity that might be inadequate.

 

[mickyg]

Possibly Micky - but a place that justifies that kind of bathroom and shower should be able to take the heating output of a combi. It is the Hot water reheat capacity that might be inadequate.

maybe so, but still cant see the point of using one, with the added unreliability. If house is so big that hot water run is too far then it needs a secondary loop. As previous poster stated, why heat more water when you have already used gas to heat some elsewhere

 

[Dan Robinson]

Intergas HRE is nice and simple Can't remember if they do the 40 in a combi though

Combi would be cheaper than trailing a secondary loop around plus you don't need the timer, pump and stat .

 

[hazetimesfive]

priority hot water to taps would stop thermal store being regenerated.

 

[RickyLee53]

You are not meant to set the water temp above 60° C.

Its easy to balance by keeping all pipework equal and adding a couple of gate valves for fine tuning!

Joe will explain in detail!

Tony

I didn't know this. Are the rest of my assumptions correct? I.e. A 180l tank will only give say 140l of usable warm water?

I planned to keep the pipework equal, gate valves aren't a bad idea to tune. I was wondering if there was any kind of electronic control unit? That can detect temperature drop then switch to the other cylinder?

Thanks.

 

[RickyLee53]

i just cant fathom why you would pay for hw store and for instant hot water,

its like having food in the fridge and eating takeaway everynight

The cylinders only lose 1kw heat per day. We will all take a shower/bath etc.

The stored water is already heated yes, but it would/might have to be reheated if some is drawn.

The combi just heats the water you use. My main reasoning is the combi is going to be in the utility. The tanks in the loft. The tanks will have 30meters of pipes. The Utility is very close to the kitchen d/s toilet etc. My other reason was I could store the hot water hotter in the cylinders. And have the combi set to 50 degree's so the hot isn't scalding your hands.

I looked at the 2 cylinders and they require 15-16kw each. The combi I looked at was 38kw HW, but i'm guessing CH might be 24. So you are right, reheat, especially while heating the rads might suffer.

 

[Onetap]

I didn't know this. Are the rest of my assumptions correct? I.e. A 180l tank will only give say 140l of usable warm water?

More; the water should be stored at 60 degC, which is too hot for washing. most people will mix it to about 40 degC. Besides which, the cylinder will be reheating during the draw off, so more heat is added to the water.

Gate valves are carp for balancing, get some proper regulating valves, automatic flow restrictors or use equal length pipework (reverse return) if you want it balanced.

Will both cylinders be accessible for maintenance?

I'd put in one cylinder and leave blanked tees for another, if it proves necessary.