hot water return

[MP plumb]

i am installing a secondary hot water circuit and have a few questions.

i have been reading bits on the web and some sites suggest the return pipe needs to be smaller than the primary. Other sites dont mention sizing at all.

is it important to use a smaller pipe?

i have run the whole lot in 22mm, and it will be lagged.

the bronze pump will be in 22mm anyway so does it matter?

where would you place the pump? as soon as it comes off the cylinder or is there a certain distance away?

thanks

 

[Cds]

Typically the secondary return will be a size (or more) downform the hot water pipework. This is to reduce cost as much as anything. Theactual flow required is low as with insulated pipework the heatloss that isbeing made up is only small.

The fact that you have used 22 mm will not be a problem.

 

[markfxy]

Depends what system its for if its commercial it may need 22mm if its domestic its way over size 12 mm is more than enough for most houses youre only providing circulation it doesn't need a high flow rate

 

[MP plumb]

the flow rate will be at 3.5 bar, as i have 3 accumulators installed

 

[dancinplumba]

the flow rate will be at 3.5 bar, as i have 3 accumulators installed

thats the pressure, i believe flow rate will set at pump

 

[MP plumb]

thats the pressure the pressure reducing valves will be set at on the accumulators and just before the cold to the cylinder

 

[SimonJohns]

You could run a return in 10mm of you wanted to. It all depends on the amount of outlets
Duty of outlets
Scenario of installation

If its a domestic house it is usually 15mm

I would also put a gate valve by every out let on the return pipe for balancing. This would only be applicable in a larger property and be undertaken by someone who has done their home work

Can you give plans or an overview of what your doing so that best advice can be given?


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[diamondgas]

If I may offer my penithworth .. Don't forget the none return valve on the return before the cylinder! Had a few complaints of cold water coming out of the hot taps... Water takes the easiest path and if the cylinder is cold or there's a high demand you'll know!

IMHO

 

[MP plumb]

ok, but if the pump is on constant, which this installation will be, there wont be a chance of the cold water coming back on itself?
all my drawings are on site, but i think i may have over done it using 22. do you think it will be a problem? the scondary return is only going up 3 floors. the cylinder is on the 3/4th floor and it needs to circulate down to the basement, and back up again.

any one have advice on how far away the pump needs to be?

also, i have 5 seperate returns going to the boiler. i will be connecting them as close to the boiler as i can. would you recommend non return valves on the returns to stop wastage of the heating water flowing through the pipes instead of going back to the boiler?

 

[markfxy]

you wont need it on constantly you should have a timeclock and pipestat to avoid the pump running constantly

Just re read the last post this has got to be a wind up why would you take hws returns back to the boiler

 

[Cds]

What do you mean 5 separate returns going to the boiler? Thesecondary return can only go back to the cylinder.

A sketch of what you have installed would help.

 

[MP plumb]

oh sorry! i wrote a confusing post then! when talking about the comment about the returns at the bottom of the post, i mean heating returns. i have 5 heating returns going back to the boiler.

i am having it on constant because i have talked to my electrician and he has suggested that even on a time clock, if they get up in the night and want to wash their hands, the water will be cold and will end up complaining to us about it.

 

[Cds]

It’s usual to have a time clock and limit the running to thetimes that hot water is actually required. If you use a Grundfos Comfort secondary return pump this can have an integratedtime clock as well as none return valve and thermostat.

If there is more than one branch to the secondary returnconsider using thermal balancing valves rather than gate valves as these willprovide a better system.

 

[Dannypipe]

oh sorry! i wrote a confusing post then! when talking about the comment about the returns at the bottom of the post, i mean heating returns. i have 5 heating returns going back to the boiler.

i am having it on constant because i have talked to my electrician and he has suggested that even on a time clock, if they get up in the night and want to wash their hands, the water will be cold and will end up complaining to us about it.

Unlikely they will complain if it takes a while to supply hot water at 3am!? It'll only take the length of time if takes to run off the dead leg, not forever.

I like the idea mentioned above about the pipe stat. Never done that myself. Makes sense.

 

[chris watkins]

It’s usual to have a time clock and limit the running to thetimes that hot water is actually required. If you use a Grundfos Comfort secondary return pump this can have an integratedtime clock as well as none return valve and thermostat.

If there is more than one branch to the secondary returnconsider using thermal balancing valves rather than gate valves as these willprovide a better system.

Have any of you lot seen (or fitted) the new Comfort Auto Adapt, very clever. A client pestered Grundfos at Ecobuild into giving him one to try, so we install it for him. It has a sensor & lead that comes out of the pump head & it attaches to the HW flow (pump on the return), it uses the sensor to detect whenever hot water is drawn off through to the taps, it logs these times over the next 20 days & uses this to set its own timing as to when it should be on or off. Lots of other clever things such speed control to keep the right temp on the return etc. It's a brave new (energy saving) world out there !!!!

 

[jase158]

where does the return go to? the cold feed to cylinder? or the cylinder itself?

 

[SimonJohns]

where does the return go to? the cold feed to cylinder? or the cylinder itself?

You can have many options

First is a dedicated Hws recerc connection

In cold feed. With cv on cold, just incase

Using Surrey flange

Few other ideas too. But they are the most comman

 

[Gray0689]

If you have it running constantly it will cost a lot more as hot water will be cooling constantly( even if lagged well)
And running in 22mm not only costing you a lot more it will cost client as your using to much volume of water will cost a fortune to run in long term