Secondary return

[ACOperson]

Hi all,

Have got a full system to do over the next few weeks which requires a DHW secondary return. Couple of questions relating to this:

1. Do the yellow pumps used for this secondary return have any kind of timer integrated in them, or are they wired to an external timer , or do they spin constantly?

2. The water pipework will be 22mm up to the various branches for bathrooms, shower rooms, kitchen etc which are all 15mm. Should the secondary return follow this sizing, and therefore returning to the cylinder in 22mm, or can it be run in 15mm to the cylinder then up to 22mm just before the point of re-entry.

Cheers

 

[Dan Robinson]

I think they do have an integrated timer version, if not an LP111 would be fine.

I would do the pipe in 22mm.

 

[Biggles..]

Grundfos make a pump for secondaries with a timer on the top of it. cant remember number and cant find the spare one in the garage now either.

 

[Balenza]

15mm is fine for a secondary return on most domestic installs.

 

[namsag]

Haven`t had much to do with secondary returns . What is the rule as in how far a hot outlet is away from cylinder before a return must be fitted. And would you have the pump running all day or a set period every hour .

 

[Gasman1015]

Its more a case of if you want the system or not, the pumps are generally timed for the periods of bathing or hot water usage, the system can include towel rails and the pumps are temperature controlled as well as timed.

 

[htgeng]

I did one with a PIR in the kitchen. Works good as the pump only ever powers up when somone is traipsing around. Have seen one where it was powered up 24/7 and they were on lpg only.

Pipe can be very small as you don't want any significant amount of hot water actually on the return pipe...

 

[Nige F]

"flow pipe of sec circuit is also hot distributing pipe and should be sized accordingly".....so is 22 big enough for the load of 2 or more bathrooms?....."the return pipe should be sized so the temp. drop on the circuit is not less than 8deg. C and not more than 22.deg.Cdependant on the temp @ the draw off points".....quoted from my ancient IOP design guide then there`s legionella protection..and mixers @ point of use ...Hope it helps some, good luck.

 

[nigelengineer]

the return pump should run 24-7 the hole point of a return is there is hot water within seconds this elevates the problem of Legionella, the water is always above 60deg C. as for the return pipe if you run 22 supply 9 out of 10 times will be 15mm there is a calculation you can do but it will end up as a size of pipe they don't make. have fun if you want the calculation let me know.

 

[doitall]

the return pump should run 24-7 the hole point of a return is there is hot water within seconds this elevates the problem of Legionella, the water is always above 60deg C. as for the return pipe if you run 22 supply 9 out of 10 times will be 15mm there is a calculation you can do but it will end up as a size of pipe they don't make. have fun if you want the calculation let me know.

Hi Nigelengineer welcome to DiyNot

Sorry to disagree with your first post, but you are wrong on several points.

The pump on a secondary circuit is best time controlled to save energy.

A secondary circuit does not prevent Legionalla, storing water above 55c does that.

With any secondary circuit, the norm is to reduce the return by one size.

The post is a year old.