Secondary return on the hot water?

[ARWadsworth]

Is it better to time control it (say 15 minutes every hour but only when the HW is ON ) or just have it operate every time the HW is calling for demand?

[Heliotrope Smith]

"ARWadsworth" wrote in news:jm9tnc$8gp$ [e-mail]:

Timed for when there is 'likely' to be a demand for hot water.

No good it not circulating on an off time when tap turned on.

--- Posted via news://freenews.netfront.net/ - Complaints to [e-mail]

[John Rumm]

The former (with well insulated pipes) I would think. HW demand might only be once in the morning before anyone is up to use a tap!

[ARWadsworth]

Only the wiring concerns me:-) It's a new build. Is it big? Well the master bedroom covers the same floor area as my house.

Deadlegs are the concern.

[ARWadsworth]

Tricky. I have no idea when the owners will use the HW.

Had I known about this on the first fix I would have installed PIRs in the ensuites to activate the pump. The kitchen and utility are close enough to the boiler/cylinder and so are not on the return.

I might still be able to do the PIRs (the place is not fully boarded) if you think it would be a better idea. How long does it take the pump to get the HW to the taps? It's a 15mm return.

[YAPH]

*Some* heat will escape anyway but insulation *reduces* the amount of heat lost. So if you don't insulate it you will lose more heat than if you do. You'd have to be using very little hot water and/or have a lot of uninsulated pipework for that to double the amount of energy (and therefore money) you use for water heating, though.

One reason for SHW circulation is to avoid the possibility of Legionella multiplying in standing lukewarm water by circulating *hot* water.

[sigh]

[Nospam]

I fitted a Grundfos UP15-14BU which has a built-in programmable timer. We experimented with timing for the first few months so I've no idea now what it's set to, but it works. Nearly instant hotwater is rather nice and even the kids (rather inappropriately) said it was "cool" ;-)

We have a megaflow cylinder so I guess the downside is that it's being churned-up rather then stratifying, but I don't know what the impact is on DHW heating demand - subjectively it doesn't seem excessive (whatever that means!)

[John Rumm]

About as long as running off the dead leg of water with the tap...

[NT]

The ideal control is a thermostat on the coldest bit of the pipe, ie next to the furthest tap. Then the pump just runs when needed to stay hot. Add a PIR near the taps and the system only keeps itself hot when someone enters a tap room.

Obviously insulation is necessary. The pipework isn't just hot when in use, its hot 24/7.

NT

[John Rumm]

I expect you need a combination of a 24hr timer, and a pipe stat. Set the timer to enable secondary circulation during typical waking hours. Then leave the pump to cycle on a pipe stat set in the return leg of pipework beyond the furthest draw off point.

[ARWadsworth]

Nice idea.

And another question. All the pipework is plastic apart from this secondary return. Any reason it was done in copper?

[Nospam]

Ref my other reply: use a (Grundfos) pump with a built-in timer. I wired mine via a pipe stat fixed on the return - the stat may call for heat but the pump will only run if the timer "aaproves". With timer and stat accessible the users can change them to suit their needs.

[John Rumm]

No, but then again a pipe stat will work better on copper...

[ARWadsworth]

The plumbing side of things is out of my hands!

And believe me. The owners of the house are unable to do much themselves other than eat money so I need something idiot proof.

[Tim]

You mean just like a conventional system when you turn off the hot tap leaving a long "dead leg" of water cooling?

Can't see why it would be much worse with a circulator.

Tim

[NT]

harry must be dribble

NT

[John Rumm]

It would actually be better, especially if you blended it down to final mix temperature at the point of use - since you would be periodically raising all the pipework to full temperature.

[charles]

and, having had it, I wouldn't wish it on anyone else.

[Onetap]

Did you? Do you know how you got it, did they trace the source? Did they have a reason to suspect legionella, had there been an outbreak? Or did they identify it by routine swab tests?

I'm just interested in how the hospitals and HSE work.

[Fredxx]

For sinks and the like, what's wrong with an undersink water heater. Probably less heat loss that lagged pipes and running a pump near 24/7.