Combi and domestic HW buffer vessel (domestic)

[looneyfitter]

Has anyone got a link or schematic to the above? I have a couple of diagrams for industrial commercial installtions i have carried out but feel they are a little over kill for domestic.

Any ideas?

 

[looneyfitter]

Anyone? surely someone on here has some knowledge of domestic practice?

 

[mysteryman]

What do you want to do, and why?

 

[looneyfitter]

Basically i have picked up a new 35kw 200w very cheap. However my house is fairly big and we have a 210l megaflow fitted indirectly at the moment.

My plan is to use the cylinder as a HW buffer and use the coil for a solar installation next summer. I have done the same plenty of times for hotels/schools etc but was just wondering if there was a basic domestic layout?

JUst wondering what other engineers thoughts are and if they had any design layouts?

Pro's/ cons? What are your thoughts matey|?.

 

[looneyfitter]

we have a 35mm mdpe cold main matey so all is good.

Sorry what i am implying is to load the cylinder (now a buffer) with hot water from the combi via a bronze pump giving 210l of permanant hot water. (should also stop the boiler cycling as wont be heating indirectly) It has high and low temp switches and a few other componants,

I have heard of it being done domesticaly but never seen it.

Im not even sure what im getting out the taps at the moment

As i said i have done many installs in commercial property. I have a schematic somewhere ill post it tomorrow if you like.

Works wonderfully commercialy as to how efficient it is im not sure? I see it would heat the buffer in approx 10 mins as opposed to the 30 mins it take snow

 

[mysteryman]

210 litres @ 14 litres/min would be about 15 mins from stone cold and raised through 35 deg, longer for a bigger temp increase. By all means try it, and let us know how you get on. You would need a very small bronze pump, controlled by a cyl 'stat plus whatever timer. I would keep the flow rate down to about 14 litres/min, and try to minimise mixing inside the cyl.

 

[looneyfitter]

Hello mate, basically on a comm installation, the hot is pumped put of the combi, through a double reg, into and teed to a blender from the top of the cylinder then returned to the cold inlet of the combi from the cylinder cold main in. Its a bit more complex but thats just a simplified version for ease of writting.

The theory is that there is a stat on the CWS back to the combi and a second half way up the buffer. What happens is when the middle stat drops below 35 deg, it turns the pump on and forces the water back round the buffer. when the CWS reaches 60-65 it then turns the pump off.

It will cycle like this whilst no HW taps are calling so there is no need for a timer (you could if you like but much cheaper to leave it on i found) Also aids hw heating time as in general the cws is already at 30-35 deg.

I designed and fitted a 2 boiler system for a 30 bed hotel and never had a single complaint. In fact we turned 1 boiler off and the system still recovered with no probs

Simples.

 

[Biggles..]

If you've done it commercially then why not do the same domestically.
A crane 931 is only £150,a stainless pump next to nought. You see the point.

The theory is just the same as say adding a buffer to an Andrews or rinnai.
Rinnai show a good version of just this thing in there tech guide when using one of their heaters with a buffer and solar.

 

[looneyfitter]

I dont suppose you have a link to a schematic do you?>

 

[Biggles..]

http://www.rinnaiuk.com/5_Downloads...2_Commercial_Hot_Water_Solutions_Brochure.pdf

page 8, swap water heater for combi,jobs a fish.

just make sure combi is suitable for accepting preheated water as not all domestic products are.Not a viesmann man so couldnt tell you.

 

[looneyfitter]

Good man thanks, wouldnt open with that link tho said was damaged.

Hadnt even considered it not accepting pre-heated. I cant think what probs it would cause either tho? Have you had eperiance with it before? What are the likely faults mate?

Thanks for the input.

Gareth

 

[looneyfitter]

Managed to get it on mate. NO not like the one on page 8 page 7 is very very similar

Here

Gareth

 

[Biggles..]

Not done it myself domestically as I don't see the need.

Most manufacturers won't allow water above 35 to enter the boiler.not that it won't work just it invalidates warranties.you have to remember domestic boilers are full of plastic crap.

My thoughts seem confirmed by the boilers that use the zenex, have their preheat fed through a blender to limit it's temp.

 

[looneyfitter]

To be honest mate your theory is beginning to make sense. Im going to phone viessmann Tomorrow see what they think. As said, could always blend the CWS feed to the boiler. 14l a min will more than likely be fine for my house but i want to be able to use the coil for solar You see

Dont suppose you know what the flow rate of a 15mm blender is do you? Say one you would use for a doc m?

 

[Biggles..]

Sorry looked at page 7 but didn't fully check my hot/cold/return flows on page 8.

A decent 15mm blender will easily pass 25lpm,obviously the better the quality the better the operation.

So they'll be a difference between say a Saracen valve at £30 and a Horne valve at £130.

I'd toted with the idea myself having took out a 2 month old gledhill unvented and the thought of putting preheat into my atag did cross my mind.