2 x indirect unvented cylinders, problems?

[RickyLee53]

They cylinders will be accessible, its just height thats an issue.

I think the easiest way would be to have the water through both cylinders. It would save having to balance the cylinders.

So it would be, cold feed to first cylinder, hot to cold feed of second, then out. Obviously one cylinder will have more work to do than the other. But this should give good hot water till I get near the end of the tank. The reheat is true, but it will only take 10 minutes to draw off all of the water. So it won't reheat all that much I wouldn't think.

 

[hazetimesfive]

I dont think thats the right approach mate

 

[Dan Robinson]

Parallel is the way to go.

 

[doitall]

Only way you'll get 2 or more cylinder to work is with a reverse return secondary circuit.

You'll also need a reverse return primary circuit.

 

[RickyLee53]

Hello,

Thanks again for the replies.

Is there any reasoning why to go parallel over series. To me series made more sense.

Doitall, What is a reverse return primary circuit?

 

[doitall]

The primary pipes are from the boilers to heat the cylinders.

The reverse return is the same meaning in both cases.

Number the cylinders 1 and 2, make 1 the first flow and 2 the first return, so it goes out to the left and returns from the right (example) That way you get a blend through both cylinders and no balancing required.

 

[Onetap]

Doitall, What is a reverse return primary circuit?

Untitled

• Onetap
• 25 Jan 2013
• 1

ROHRS REVERSE RETURN PIPEWORK

Reverse return is a pipework arrangement intended to have an equal length of pipework and number of fittings on the circuits to/from each cylinder/boiler. Have a search on Google for more information.

The intention is that each cylinder/boiler circuit has equal hydraulic resistance and so receives equal flow.

Is there any reasoning why to go parallel over series. To me series made more sense.

Each unvented cylinder must be set up with the control valve assembley (strainer/ Pressure Reducing Valve/Pressure release valve) on cold feed. If the DHW is in series (one cylinder, then the other) you'd have to ensure the heated water entered the second cylinder after the valve assembley, or that the valve assembley could tolerate the temperature and entrained limescale particles in the hot water (probably not). I'd go parallel.

I still think you're going at it the wrong way but the customer is always right.

 

[rpevans]

Just an observation that may help. If you want to fill a bath with 400litres of water at 45C then you need 280litres of water at 60C and 120litres of water at 10C. Also, consider if the bath and shower are likely to be used at the same time.
Richard

 

[doitall]

Perfect drawing Onetap

 

[RickyLee53]

Doitall, What is a reverse return primary circuit?

Untitled

• Onetap
• 25 Jan 2013
• 1

ROHRS REVERSE RETURN PIPEWORK

Reverse return is a pipework arrangement intended to have an equal length of pipework and number of fittings on the circuits to/from each cylinder/boiler. Have a search on Google for more information.

The intention is that each cylinder/boiler circuit has equal hydraulic resistance and so receives equal flow.

Is there any reasoning why to go parallel over series. To me series made more sense.

Each unvented cylinder must be set up with the control valve assembley (strainer/ Pressure Reducing Valve/Pressure release valve) on cold feed. If the DHW is in series (one cylinder, then the other) you'd have to ensure the heated water entered the second cylinder after the valve assembley, or that the valve assembley could tolerate the temperature and entrained limescale particles in the hot water (probably not). I'd go parallel.

I still think you're going at it the wrong way but the customer is always right.

What way would you say is better?

Would I need the second pressure reducing valve? I was actually thinking about setting the first cylinder at a slightly lower temp to the second.

If I was running parallel I would try to keep the length, and more importantly bends equal. I planned on running just a short equal length to a T piece anyway. However I still don't think you would get a perfectly balanced system.

 

[doitall]

I agree you'll never in a million years get a perfect balance so don't try.

The reverse return ends the need too.

And yes you need the second PRV, MV etc

 

[Onetap]

Perfect drawing Onetap

Copied from the internet; sorry if I disillusion you about my many talents.