what timer did you use for your secondary loop pump and what settings did you set it to?

[Adsibob]

The pump for my secondary loop plugs into a regular 13A socket. The electrician recommended I use a smart plug with it, so that I can set up a routine like 4 minutes on out of every 12 minutes for the hours that we are in the house and awake. Something like a TP Link Kasa plug would probably be able to do that, but I'm thinking it would be better to have something that doesn't rely on wifi, that way the secondary loop doesn't depend on Virgin Media, which are pretty unreliable. I have a basic rotary timer that I picked up in aldi for £4, but it can only do units of 15 minutes, which won't work. I think I need something much more intermitent than that, like 4min/12min or 5min/15min.

For those that have installed a a secondary loop, what timer did you use for your pump and what settings did you set it to?

[JohnMo]

My pump has a rotary timer already built in, I just run for a couple of hours in the morning and evening, but my secondary circulation only goes to our ensuite.

 

Not sure of the logic running for 4 mins every 12.  Not sure what you gain, your water will hot, warm, hot...  You may as well run all the times you are home and awake.

[Adsibob]

1 hour ago, JohnMo said:

My pump has a rotary timer already built in, I just run for a couple of hours in the morning and evening, but my secondary circulation only goes to our ensuite.

 

Not sure of the logic running for 4 mins every 12.  Not sure what you gain, your water will hot, warm, hot...  You may as well run all the times you are home and awake.

Based on what others on this forum have said (I think @PeterW or @Mr Punter, whereas I think @Bitpipe’s is activated by PIR) running it all day is unnecessarily wasteful of electricity for the pump AND heat loss from the pipe), whereas running it intermittently will keep energy costs down, whilst keeping the secondary loop pipe warm. My secondary loop is made from butyl and has some insulation on it (though not the best insulation, unfortunately)  so I’m hoping that by experimenting with different settings I can find a ratio of on/off per hour that keeps it warm without wasting too much energy.

[Nickfromwales]

4 hours ago, JohnMo said:

Not sure of the logic running for 4 mins every 12.  Not sure what you gain, your water will hot, warm, hot...  You may as well run all the times you are home and awake.

Praise be!!! Someone has finally said it. This haas been my advice to clients for a long time, even more so where the source of DHW is from PV or an ASHP.

[Adsibob]

1 hour ago, Nickfromwales said:

Praise be!!! Someone has finally said it. This haas been my advice to clients for a long time, even more so where the source of DHW is from PV or an ASHP.

Please explain. I have a system boiler with a Unvented HW Cylinder. I thought the secondary loop is basically like an extension to the cylinder, effectively bringing the source of HW closer to where it is needed, in my case most of the sinks/basins and the two bath tubs (not the showers). So pump runs fora minute or two and heats up the pipe. Pipe stays hot for a few minutes. So why would you need to run the pump all day long. As long as you run it long enough to keep the pipe warm, surely it is doing it’s job of giving you near instantaneous warm water at each outlet connected to it. If you want hot water, won’t the warm water run hotter very quickly because it is already warm to start with (other than dead legs, but I’ve tried to minimise those)???

[Adsibob]

I’ve found one that can do an infinite loop!!!

https://www.ebay.co.uk/p/22036966963?iid=384186148688
 

£5 cheaper on Amazon.

[JohnMo]

Your total heat loss has to be weighed against.

 

Average heat loss from pipe, (somewhere between the lower pipe temp and supply temp).  Plus the energy to reheat the system (pipes, pump, valves, insulation etc) after cool down.  Plus the huge number of start starts per year and wear and tear on pump and motor from frequently stopping and starting, so premature pump replacement is also possible.  Frequently injecting cool water into your cylinder that will mess with cylinder stratification, decreasing cylinder effective capacity.

 

My pump/stops 720 times per year. Your between 7 and 14000 at a guess.

[Adsibob]

53 minutes ago, JohnMo said:

Your total heat loss has to be weighed against.

 

Average heat loss from pipe, (somewhere between the lower pipe temp and supply temp).  Plus the energy to reheat the system (pipes, pump, valves, insulation etc) after cool down.  Plus the huge number of start starts per year and wear and tear on pump and motor from frequently stopping and starting, so premature pump replacement is also possible.  Frequently injecting cool water into your cylinder that will mess with cylinder stratification, decreasing cylinder effective capacity.

 

My pump/stops 720 times per year. Your between 7 and 14000 at a guess.

I’m not too worried about heat loss as the house is fairly well insulated now, and heat loss will just be lost into the house, which has MVHR which might help to spread it around a tiny bit. The volume of the cylinder is 300L, so I don’t think the loop (which probably doesn’t hold more than 10L at the very most) will contribute to that much heat loss).

But you make a good point about the potential for premature pump failure: if it was intermittently going on every 10 minutes for 2 min, that is 5 on off cycles per hour. for 2hr in the morning and 6hr in the evening, that’s 40 a day, or 280 a week.  So almost 15,000 a year. I think my plumber has fitted a fairly quiet Grunfos pump, but don’t have the model to hand. How often do you think I would need to replace it? 

[JohnMo]

If you search grunfos for the model, they may an expect start stop life on their datasheet

[Adsibob]

On 08/05/2022 at 01:31, Nickfromwales said:

Praise be!!! Someone has finally said it. This haas been my advice to clients for a long time, even more so where the source of DHW is from PV or an ASHP.

Just refreshing this in case @Nickfromwales (or somebody else) has time to respond to this:

 

On 08/05/2022 at 02:45, Adsibob said:

Please explain. I have a system boiler with a Unvented HW Cylinder. I thought the secondary loop is basically like an extension to the cylinder, effectively bringing the source of HW closer to where it is needed, in my case most of the sinks/basins and the two bath tubs (not the showers). So pump runs fora minute or two and heats up the pipe. Pipe stays hot for a few minutes. So why would you need to run the pump all day long. As long as you run it long enough to keep the pipe warm, surely it is doing it’s job of giving you near instantaneous warm water at each outlet connected to it. If you want hot water, won’t the warm water run hotter very quickly because it is already warm to start with (other than dead legs, but I’ve tried to minimise those)???

 

[Nickfromwales]

1 hour ago, Adsibob said:

Just refreshing this in case @Nickfromwales (or somebody else) has time to respond to this:

Time is a bloody precious commodity atm! 

 

The Grundfos Comfort HRC pump seems to be the KISS companion for a fit & forget solution tbh, with models / options for steady flow ( modulated pump activity to suit the required temp ) or constant flow. Both can be timed / otherwise activated, but pulsing the HRC pump on - off - on - off - on is just utterly pointless imho.

 

When you open a tap, say the kitchen sink, do you want warm then hot water, or hot water? Waiting for water to go from warm / tepid to hot would piss me off even more than not having an HRC at all.

 

Why fit all the pipework and components, plus wiring and controls, and then turn the bloody thing off?!?!

[Adsibob]

7 hours ago, Nickfromwales said:

Why fit all the pipework and components, plus wiring and controls, and then turn the bloody thing off?!?!

Because I don’t want to waste heat by having the pump circulate hot water all the time. Are you saying that if I were to have it on continuously 2h in the morning and 4h in the eveningthe heat loss will be minimal.
 

As for waiting for warm water to get hotter, surely with thermostatic tap mixers, this wouldn’t be noticeable other than a slow increase in flow.

[JohnMo]

The models Nick recommended or a Lowara Ecocirc Pro - same as I have.

 

Inbuilt timer and thermostat.

 

Set it to time periods you want hot water, i.e. when you get up until you go to work, when you get home until when you go to bed.  It automatically circulates enough to get loop to the temp you set it at then maintains that temp.

 

You're trying to invent a wheel that already made and available off the shelf.

 

 

[Adsibob]

22 minutes ago, JohnMo said:

It automatically circulates enough to get loop to the temp you set it at then maintains that temp.

I disagree. All the pump will do is circulate the water that is in HW cylinder around the secondary loop, thereby increasing the ratio of surface area enclosing the hot water to volume of hot water in the system as a whole, thereby increasing heat loss of the system as a whole. So whilst the secondary loop will be nice and hot, this comes at the expense of the hot water in the tank retaining heat for as long as possible. Now it may well be the case that this is only a theoretical concern because the volume of the secondary loop is so small compared to the volume of the tank. The loop is made of 22mm buteline. This has an internal diameter of 17.6mm so a radius of 0.88cm, which works out as one litre of water for every 4.11m of pipe. I think my secondary loop is approximately 20m long, so we are talking about c. 5L out of the full tank capacity of 300K, so 1.67%. I figured out that of the three speed settings on my pump, the lowest is more than adequate to keep the secondary loop hot. Not sure what that speed is though, but maybe my concerns about heat loss in this case are overblown.

[JohnMo]

You know what you want do, just do it.

[Adsibob]

don’t get me wrong, I’m not trying to be contrarian or stubborn. I just want to understand why this is the case, particularly with a gas boiler:

On 08/05/2022 at 01:31, Nickfromwales said:

On 07/05/2022 at 20:49, JohnMo said:

Not sure of the logic running for 4 mins every 12.  Not sure what you gain, your water will hot, warm, hot...  You may as well run all the times you are home and awake.

Praise be!!! Someone has finally said it. This haas been my advice to clients for a long time, even more so where the source of DHW is from PV or an ASHP.

and what heat losses I would sustain if I were to run it constantly for the hours we use hot water. 

 

 

 

 

 

 

 

[JohnMo]

You can always do a trial, a couple of days of lots of one-off and a couple of days on for two set periods and compare, the running cost and how long you wait for hot water