unvented secondary return

[gil]

Oh, yes, I see. So is my original plan with a pump the best one then, or should I do both the Essex flange and the the pump, or should I go for the gravity feed with a timer on a valve?

 

[LegionellaSlave]

I'd tee it into the cold feed like others have said, and see if it circulates by gravity.

If it doesn't, fit a bronze pump (dont fit normal pump you'd find on a htg sysem or your hw will be brown)

 

[bill577]

A secondary return on unvented cylinder should be pumped with a bronze/ stainless pump

which is why I wrote "fit an essex flange on your new cylinder, it will save the the cost of an expensive bronze pump" as gils post was about doing the secondary return by gravity.

 

[fuzzy]

Thought at first it was a good idea, but I'm not too sure the more I think about it. It will only operate the pump on opening and shut off again when tap closed, could have a pump over run on it, but still means first draw off has to wait. Prefer a timer on the pump to operate at peak times.
Might need some more thought.

but the pump isnt there to provide power? its there to circulate the hot water so it is available at the outlet without drawing off lots of cold water. suggesting a float switch makes me think your looking at it as additional pressure

 

[SimonG]

but the pump isnt there to provide power? its there to circulate the hot water so it is available at the outlet without drawing off lots of cold water. suggesting a float switch makes me think your looking at it as additional pressure

Don't understand your response with regard to my post. I know how a secondary return pump works, but appreciate the need to reduce pump run time to increase thermal efficiency. A flow switch, although intriguing, or I thought so at first, isn't the way to go. Liked the PIR idea and is stored away for a situation that could utilise it, but the timer, for me, is the way to go.

 

[fuzzy]

Don't understand your response with regard to my post. I know how a secondary return pump works, but appreciate the need to reduce pump run time to increase thermal efficiency. A flow switch, although intriguing, or I thought so at first, isn't the way to go. Liked the PIR idea and is stored away for a situation that could utilise it, but the timer, for me, is the way to go.

oh ok, sorry thought you had it all wrong, not convinced the op understood though, or have i missed something?

how does slowing the pump help thermal efficiency?

 

[Gray0689]

oh ok, sorry thought you had it all wrong, not convinced the op understood though, or have i missed something?

how does slowing the pump help thermal efficiency?

Nothing to do with slowing pump he ment if the pump is not running ( ie only running when the timer calls for it not all the time)
It will not use as much hot water (less wastage of hot water) therfore more thermal efficent

 

[fuzzy]

so you meann it doesnt have to heat the water in the pipe? is that such a benefit?

 

[SimonG]

oh ok, sorry thought you had it all wrong

how does slowing the pump help thermal efficiency?

I see what you mean on re-reading it. From what the op was asking with regard to the flow switch I was thinking along the lines of a sika flow switch (paddle switch on oil combi) linked to the circulation pump. Open tap, flow switch detects and switches on circ pump, but still leaves you with cold draw off at first opening. That's what sprung to mind anyway.

Not on about slowing pump, but stopping it when not needed, thats what I mean about reducing pump run time. Seen too many secondary returns running 24hrs a day. Just don't like the pump running when not needed, drawing heat from cylinder, costs a lot to put the heat in there and I'm a big fan of keeping it in there.

I don't suppose you know if there's a 'smart' sec ret pump?, like the new htg pumps?

 

[Gray0689]

so you meann it doesnt have to heat the water in the pipe? is that such a benefit?

Em yes
Massive benefit
If the hot water is being moved around pipework your also cooling the cylinder as this is happening so if secondary pump running all time will need a lot more heating time !!!

 

[SimonG]

so you meann it doesnt have to heat the water in the pipe? is that such a benefit?

It was more around the pipe heat losses. Then again you have a timer that switches pump on and immediately pumps the cold water in the flow and return pipework back into the cylinder.

Probably needs an interesting calculation on maximising run times and heat losses and not after several beers. 🙂

 

[fuzzy]

I see what you mean on re-reading it. From what the op was asking with regard to the flow switch I was thinking along the lines of a sika flow switch (paddle switch on oil combi) linked to the circulation pump. Open tap, flow switch detects and switches on circ pump, but still leaves you with cold draw off at first opening. That's what sprung to mind anyway.

Not on about slowing pump, but stopping it when not needed, thats what I mean about reducing pump run time. Seen too many secondary returns running 24hrs a day. Just don't like the pump running when not needed, drawing heat from cylinder, costs a lot to put the heat in there and I'm a big fan of keeping it in there.

I don't suppose you know if there's a 'smart' sec ret pump?, like the new htg pumps?

sorry for the confusion, im with you now.

Im sure there are some smart pumps that will reduce speed at least based upon the resistance. On reflection, isnt a straight forward timer helpful? run at peak demand?

I fitted them mainly on commercial like hotels, the pump noise was never an issue in a plant room, and the water was used 24/7. I presume the additional water content was calculated into the heat up time, so cylinder + pipe = total water requiring heating.

I see little advanage domestically to such a set up, happy to be proved wrong though

 

[fuzzy]

It was more around the pipe heat losses. Then again you have a timer that switches pump on and immediately pumps the cold water in the flow and return pipework back into the cylinder.

Probably needs an interesting calculation on maximising run times and heat losses and not after several beers. 🙂

and gray,, again commercially this will be calculated and heavily lagged so im not convinced the issue is as big as you suggest, the advantage will out do the disadvantage, unless a unlagged domestic house with few people living there, then id just waste the cold water

 

[SimonG]

sorry for the confusion, im with you now.

Im sure there are some smart pumps that will reduce speed at least based upon the resistance. On reflection, isnt a straight forward timer helpful? run at peak demand?

I fitted them mainly on commercial like hotels, the pump noise was never an issue in a plant room, and the water was used 24/7. I presume the additional water content was calculated into the heat up time, so cylinder + pipe = total water requiring heating.

I see little advanage domestically to such a set up, happy to be proved wrong though

Hospitals where the big users that I saw.

The timer is what I like to see, couple of hours on a morning and same again on an evening. Preferably don't like a secondary return and a lot of the time they could have been avoided by better cylinder positioning. Domestically seen them in 'big' houses where generally cust has more money than sense.

 

[Gray0689]

I guess you never seen it done then
On a domestic system it will be the larger property mainly that has a secondary return and it will cool the cylinder down quite a lot if pump running 24/7
Ps wastage of water is not a good thing as even this costs money
It's all About efficiency

 

[fuzzy]

every large commercial installation i have fitted has had a secondary return, dont see how it cools cylinder down as much as you say if the insulation is as much on the pipe as it is the cylinder, in fact some jobs ive done the lagging seems thicker on the pipe. if the water content is calculated as the total amount required heating there is no additional water or heat loss. the only additional efficiency cost is the running of the pump which is outweighed by reduction in loss of expensive water on long runs. I think they are good and many designers agree

 

[Gray0689]

We are talking about domestic here not commercial I've done lots on domestic but can't comment on commercial
But on domestic it's bad practice to have a secondary return pump on all the time it does cool cylinder quite a bit IMHO

 

[fuzzy]

We are talking about domestic here not commercial I've done lots on domestic but can't comment on commercial
But on domestic it's bad practice to have a secondary return pump on all the time it does cool cylinder quite a bit IMHO

which i why i posted that i dont see any real advantage in a domestic property. I didnt realise the conversation was limited t domestic only, the op title is unvented secondary return

 

[Gray0689]

which i why i posted that i dont see any real advantage in a domestic property. I didnt realise the conversation was limited t domestic only, the op title is unvented secondary return

It's not as I said can't comment on commercial I don't do it that's all

 

[SimonG]

Don't know if it's just me but the commercial stuff I did as an apprentice wasn't unvented, hence the swimming pool sized sectional water tanks. I think the cylinders came from IMI Rycroft, but that was a long, long, long time ago.

 

[tamz]

As far as i'm concerned, a secondary return on a domestic is a total waste of energy especially in these energy efficient green times.
From my experience, most who ask about it carefully seperate their rubbish, burn condensing boilers and energy saving light bulbs, and generally do their bit for the planet but they can't wait 10 seconds or so to step into a shower.Save the planet my rse!

 

[Megaflo-Experts]

There are benefits of a secondary return in certain domestic properties. Quite often large bungalows with long pipe runs in 22mm pipe - that's potentially a lot of water to draw off before getting hot water. Also remember the hot water left in the pipe will cool down and need to be drawn off when the next person uses the hot water; that's wasting water and heat! The return pipework should be in 15mm (or even smaller!) and I normally wire the pump to come on when the hot water is on, which generally works for the customer. However, it will be more efficient if the pump had some sort of temperature sensor (if such thing exists) to determine if it needs to come on or not.

I don't think a flow switch will work as the the user will still need to draw off the cold water before getting hot water!

 

[fuzzy]

if plumbed in correctly with sufficient lagging etc the only disadvantage i see is power to the pump and noise. If its in a cupboard or separate room the noise issue can be reduced. What is the amount of power the pump uses? if you want it based on temp would a pipe stat work ?

 

[quality]

if you want it based on temp would a pipe stat work ?

I have used this method before nice and simple and works a treat

 

[quality]

if you want it based on temp would a pipe stat work ?

<br>I have used this method before nice and simple and works a treat although I used a capillary stat

Stange edit ??????

 

[SimonG]

Would you use the pipe stat in conjunction with a timer? and would you use the pipe stat to turn the pump on or turn it off?

 

[quality]

Depends on demand for hot water

 

[stevetheplumber]

As far as i'm concerned, a secondary return on a domestic is a total waste of energy especially in these energy efficient green times.
From my experience, most who ask about it carefully seperate their rubbish, burn condensing boilers and energy saving light bulbs, and generally do their bit for the planet but they can't wait 10 seconds or so to step into a shower.Save the planet my rse!

everytime you open a hot tap on a lengthy draw of your wasting water that has been heated so secondary is saving in that sense
one house i look after is six floors high and cylinder is in base ment

 

[mike_s]

As the original poster I'm really happy with the discussion here, cheers.
It has got me thinking, especially the cooling effect on the hot water store with the pump running from morning til night like they plan to but they actually havn't been using the secondary return pump as they wern't sure about having it on all day.
It is a large 5 bedroom property and they say you can go for a *** before the hot water comes through so the wait is an issue as it is more like minutes rather than seconds at times.

A pipe stat certainly sounds more useful, combined with the timer. Their secondary return pipework is actually all in 22mm I think and lagged most of the way, I mentioned that 15mm would've been more efficient. The cylinder and pump is in a loft room that could become a bedroom, I tried it out and the noise wasn't a major issue after all.

I would like to find out more on the cooling effects of having the pump running all day which they may try out, I see if the pipe is 15mm or less and lagged properly it shouldn't be majorly inefficient.

Seeing as they are coping without the secondary return pump running and if the heat losses from it are that great then probably not worth installing in most domestic situations.

 

[quality]

On / in / with any system that is not the normal 3 bed semi, most systems require a bit of trial and error.
Equipment has to be installed correctly to start with and that goes without saying. But the user is one of the biggest factors which determine how a system should be controlled.

I have had some nightmares, but to combat those I have had plenty of sweet dreams

Let them run for four weeks and then decide what needs to be done thats what I normaly do

 

[fuzzy]

As the original poster I'm really happy with the discussion here, cheers.
It has got me thinking, especially the cooling effect on the hot water store with the pump running from morning til night like they plan to but they actually havn't been using the secondary return pump as they wern't sure about having it on all day.
It is a large 5 bedroom property and they say you can go for a *** before the hot water comes through so the wait is an issue as it is more like minutes rather than seconds at times.

A pipe stat certainly sounds more useful, combined with the timer. Their secondary return pipework is actually all in 22mm I think and lagged most of the way, I mentioned that 15mm would've been more efficient. The cylinder and pump is in a loft room that could become a bedroom, I tried it out and the noise wasn't a major issue after all.

I would like to find out more on the cooling effects of having the pump running all day which they may try out, I see if the pipe is 15mm or less and lagged properly it shouldn't be majorly inefficient.

Seeing as they are coping without the secondary return pump running and if the heat losses from it are that great then probably not worth installing in most domestic situations.

no cooling affect if lagged as much as the cylinder

 

[Gray0689]

Yes it will cool if pump running all time won't be lagged like cylinder
As said before fuzzy this is domestic won't be lagged like commercial

 

[fuzzy]

Yes it will cool if pump running all time

if the lagging is at least the same as the cylinder how does it cool anymore than it would in the cylinder?

 

[Gray0689]

if the lagging is at least the same as the cylinder how does it cool anymore than it would in the cylinder?

Because it won't be lagged the same as the cylinder the cylinder will be 50mm lagging

 

[SimonG]

Scientifically speaking............It will cool, even the cylinders have a heat loss of about 2.5 kw in 24hr period (approx) with the 2" foam they have applied. Doesn't matter how well insulated the flow and return are on the hot water side you will have heat loss of some description.