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Topic Title: Secondary pump ?
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Created On: 21 December 2012 06:13 PM
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 21 December 2012 06:13 PM
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goldenboy1818

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Hi doing a job today, and the plumber told me there will need to be a secondary pump to do the hot water. The heating is done separate through underfloor heating. I haven't encountered a secondary pump before he was also talking of putting in on a programmer too ?? But unsure
 21 December 2012 06:36 PM
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impvan

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The sec return pump only serves to pull hot water past the taps to either 1) compensate for long pipe runs, or 2) provide the convenience of instant hot at the tap.

If the pipe runs are well lagged the SR pump might only need to run for a few minutes twice an hour. Some grundfos models have a timeclock built-in to the body of the pump. You could also use pipestats on the return(s) to tell the pump to switch off - A site I look after has 6 sec returns to the calorifier, the sec return pump runs every hour for a minimum of five minutes, then switches off when all six stats are satisfied.

One thing to watch out for - you're circulating warm water, so need to think about legionella. A weekly 1-hour pump run at over 60deg ought to sort that.
 21 December 2012 09:11 PM
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leckie

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Well that's a bit complicated! If his is a domestic property, the chances are it merely is to stop having to run 5 gallons of water before the hot water arrives at the tap. The secondary pump, a bronze pump, is designed to run continuously. But it can be run via a time clock to turn it off during periods water draw off is not required, eg at night. It can also be connected via a cylinder or pipe stat so that it does not run if the water is not up to the required temperature. This might be if you were on holiday and had shut the system down. Then you would wire the cylinder stat to the pump via the normally close terminals, so that the stat opened when the water was below a given temperature
 22 December 2012 10:01 AM
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SKElectrical

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hi lads, can we clarify when the sec return pump should be on then? I programmed one last night to run 6am - 11.59pm, for a domestic property, is this way too much? All pipes are insulated. timer has option of 4 programmes.
 22 December 2012 10:58 AM
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leckie

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Well the secondary pump is used to achieve a quick draw off of HOT water. So it needs to run when the water is hot and when the water is needed by the occupants. The thermostat ensures the pump only operates when the water is up to a minimum temperature. The time clock needs setting to come on as required. Incidently, the cylinder stat wants to be fitted on the top third of the water tank because the top gets hot quicker than the bottom.

Edited: 23 December 2012 at 10:26 AM by leckie
 23 December 2012 10:12 AM
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potential

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Originally posted by: goldenboy1818

Hi doing a job today, and the plumber told me there will need to be a secondary pump to do the hot water. The heating is done separate through underfloor heating. I haven't encountered a secondary pump before he was also talking of putting in on a programmer too ?? But unsure


I'd be unsure too.
I'd clarify what is needed rather than making a guess.
I have known some installs that had a pump fed hot water cylinder (between boiler and cylinder) to speed up the heat transfer.
 23 December 2012 10:49 AM
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Fm

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As these systems tend to have a programmer for the hot water, we tend to borrow a sw and n torun the bronze pump, if they call for heat the pump cicrculates.

It can also be to prevent legionella in systems, as you need to draw of min 50 deg water within a time period, long runs will stop this from happening.
 23 December 2012 10:18 PM
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leckie

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Well let's get the op to confirm what's required. A secondary pump usually refers to a ring of pipe for the hot water supply with a pump to circulate the water around the pipe. When a tap is opened the hot water is "on demand". The pump is required when the water in the cylinder is up to temperature. All explained in previous posts. It does not go on and off with the hot water on signal from the programmer. It's on when the water is hot and there are people wanting to use it.
 23 December 2012 10:45 PM
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Fm

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Sorry forgot to mention all my experience are in commercial environments where staff enter and leave at a certain time so hot water is timed accordingly. Not in domestic environs.
 23 December 2012 11:25 PM
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Fm

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 02 January 2013 08:00 PM
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goldenboy1818

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So it's best to wire the secondary pump via the normally closed contact on cylinder stay so it will only run if the water is hot enough ?
 02 January 2013 10:25 PM
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leckie

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That how I would do it. Stat up on the tank and set to a fairly low temperature. If the water is warm you may want to use it. You could also fit a time clock to turn it off when not required. That's what I think others may disagree
 02 January 2013 11:19 PM
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goldenboy1818

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Yea a programmer would do, ppl say best to have it run a few times a day
 03 January 2013 07:39 AM
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Fm

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From a non domestic point of view and for L8 compliance
Assuming its not point of use heaters
You want to be heating water to 60 deg
You want hot water at each hot tap within 60 seconds at a min of 50 deg
You want to mix the water in the tank when it reaches 60 deg for an hour at a time when there will be no draw off.
Lots of fun
 03 January 2013 07:50 AM
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Fm

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From a non domestic point of view and for L8 compliance
Assuming its not point of use heaters
You want to be heating water to 60 deg
You want hot water at each hot tap within 60 seconds at a min of 50 deg
You want to mix the water in the tank when it reaches 60 deg for an hour at a time when there will be no draw off.
Lots of fun
 03 January 2013 09:21 AM
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goldenboy1818

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Sorry I didn't mention earlier guys it Is in a domestic property
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