PIR sensor for secondary circulation

[Workerbee]

Hello! My shower is 17m away from where I'm getting a UVC installed. Because incoming pressure is only 2 bar, I've done the run in 22mm copper (the property will sometimes be let for holidays so I wanted a great shower experience). However, this will cause hot water delay.

 

My idea was to connect a secondary return to the UVC incoming cold feed, connect the pump to either a smart fused spur or Shelly, and trigger it with a PIR sensor in the bathroom.

 

There are some very tight gaps for the pipe runs so I planned to do the secondary loop in one run of 15mm plastic, uninsulated in tight areas. 

 

I could set the smart fused spur to run only long enough to clear the 22mm run of cold. The PIR could be set not to trigger again for eg 20 minutes after sensing movement. 

 

Has anyone tried something like this and could recommend products? And would I lose pressure if the PIR triggers while someone's in the shower? Any other issues I've overlooked?

 

Thank you.

[JohnMo]

22mm will take an age and half to get warm water - run in 15mm.  Add a secondary return if you want, at 15mm (assuming UVC) by the time your undressed you will have hot water anyway.  We are 20m and have no issue and have the water pressure, we have a set dynamic water pressure of 2 bar.  We have a hot secondary return system, but switched off a while ago as a trial and no-one (well the wife) hasn't noticed, may pop it back on for winter.

[Nickfromwales]

38 minutes ago, Workerbee said:

However, this will cause hot water delay.

I do continuous runs of 15mm Hep2o (every outlet as a dedicated radial supply, so nothing T'd off any feeds), and have done runs longer than 20m without more than 15-20 secs delay before warm water arrives, then becomes 'hot' soon after; without an HRC (hot return circulation) pump.

 

If you use a single run of 15mm pushfit then there will be zero elbows, and all bends will be long radii, reducing flow restriction etc, so the shower will be just fine. Very few people are expecting a jet wash, just a solid, consistent shower with at least 9/10lpm flow rate (which is plenty good enough if you have a rainfall shower head to stand under).

 

KISS, and take a chill pill . Less parts, less cost, zero maintenance, plenty good enough performance; caveat is, you must buy a good quality thermostatic shower mixer valve which has a full bore cartridge, not a cheap shower where you can't get a pencil in the inlets. 

[Workerbee]

Thanks so much @JohnMo and @Nickfromwales. Unfortunately I've already done the run in 22mm copper because I wanted to give people a great shower and 15mm would have produced 1.5 bar, which sounded a little weak. I've probably messed up, but I did my best with the research I'd done at the time.

 

I don't know if my 2 bar is static or dynamic; the water board came and measured it for me off the outside tap.

 

With the PIR idea, has anyone tried it and can recommend products? Or is it just a no-go? KISS would be best!

 

Thanks again

[Nickfromwales]

Just now, Workerbee said:

With the PIR idea, has anyone tried it and can recommend products? Or is it just a no-go? KISS would be best!

I did exactly this for @Wolfman310, so maybe he can report back as to its success (or lack of), with a PIR and a much more powerful pump (LINK) than would usually be installed (pumps like the ultra-low wattage Grundfos Comfort literally crawl the water along the pipe, so running the outlet actually gets the water there faster than the pump!!!), so beware as some pumps need to be on in advance of entering the room! Add to that the extra volume of dead leg (stagnant cold water sat in the 22mm pipe) and you'll see quickly that this needs more thought.

 

 

[Workerbee]

That's interesting - 0.5m3/HR Vs 3.2m3/HR! @Wolfman310 if you're able to give any info on how it's worked, that would be brilliant. What sensors and smart sockets did you use?

 

As a "cut my losses" option, could I run 15mm hep2o through the 22mm copper? And maybe not insulate the 22mm except in voids? I'm losing floor space in a small room because of a large service void behind the wall.

 

I'd have to remove the tees to the kitchen sink and find another way of doing those.

[Nickfromwales]

1 hour ago, Workerbee said:

That's interesting - 0.5m3/HR Vs 3.2m3/HR! @Wolfman310 if you're able to give any info on how it's worked, that would be brilliant. What sensors and smart sockets did you use?

 

As a "cut my losses" option, could I run 15mm hep2o through the 22mm copper? And maybe not insulate the 22mm except in voids? I'm losing floor space in a small room because of a large service void behind the wall.

 

I'd have to remove the tees to the kitchen sink and find another way of doing those.

Don’t run the pushfit inside the copper unless you can flare the ends, as you need to be 1000% sure the pipe won’t get damaged. 
 

Rotary pipe cutters leave a very sharp turned in edge, which will cut into the plastic pipe; it’ll move when heating / cooling.

[Workerbee]

Thanks @Nickfromwales - okay, I'll avoid that. I'll add a hep2o 15mm line for secondary circulation, and if I find it's a nightmare then I could swap the pipes around and use it as the hot feed to the shower instead. It would mean the hot being in 15mm and the cold in 22mm, but still. 

 

The Wilo SB 30 has a good flow rate and decent price, so I might try that.

 

Which PIR sensors and smart plugs etc did you use, please?

[Nickfromwales]

23 minutes ago, Workerbee said:

Thanks @Nickfromwales - okay, I'll avoid that. I'll add a hep2o 15mm line for secondary circulation, and if I find it's a nightmare then I could swap the pipes around and use it as the hot feed to the shower instead. It would mean the hot being in 15mm and the cold in 22mm, but still. 

 

The Wilo SB 30 has a good flow rate and decent price, so I might try that.

 

Which PIR sensors and smart plugs etc did you use, please?

If you swap, then the 22mm cold will be good enough to have things T’d off it.

 

Run the 15mm pipe, test the flow rate, reassess if you need to go an inch further.

 

PIR (aka “occupancy switch”) was just Screwfix jobby. Set to lowest setting for time (30 or 60 secs iirc).

 

You can blind one half of the lens of the sensor so it can only ‘see’ the doorway, so once in the room you don’t keep triggering the pump.

 

Seriously doubt you need all this faff, but you seem committed. I strongly suggest you do the 15mm hot run and test it first, then you may get the bit out from between your teeth lol. 

[Workerbee]

😂It's not so much that I'm keen to have the faff, but that I've already put the 22mm copper in, so I feel a bit stuck. The thought of taking out the pipework after spending so much time (that I couldn't really afford) getting it through difficult gaps is heartbreaking. Such is the life of house renovation, I guess...

 

I will follow your sound advice: I'll try squeezing a 15mm hep2o line through the tight wall cavities and test the flow, and I'll report back if that's okay. Thanks again.

[-rick-]

1 minute ago, Workerbee said:

😂It's not so much that I'm keen to have the faff, but that I've already put the 22mm copper in, so I feel a bit stuck. The thought of taking out the pipework after spending so much time (that I couldn't really afford) getting it through difficult gaps is heartbreaking. Such is the life of house renovation, I guess...

 

I'm not sure I would bother if it's an issue. Just get the pump and the PIR but also add some kind of timer/automation (shelly can likely do it) to run the pump if some combination of the following happens*:

1. PIR in bathroom

2. PIR in bedroom (if ensuite - and on first trigger)

3. Certain times of day when showers are likely

4. Whenever the DHW water heating cycle is on

5. Whenever the pipe temp at the bathroom is lower than x (maybe 30-35C, ie, not full temp but high enough that when the bathroom PIR kicks on it doesn't take long to raise the temp)

6. Whatever else

 

Basically, suck up that the energy efficiency will be a bit lower than you hoped and move on. Think now about what you would change later if the above doesn't work.

 

Even simpler is a timer for when you are living in the property (you can plan your shower times) and just run the pump frequently when you have paying guests.

 

* This is not a prescriptive list just ideas of ways to mitigate the situation. A shelly device (not connected to anything else) can do 1-3 with some planning 4-6 might require more.