Motion sensor hot water recirculation
Northof60
| Posted in Energy Efficiency and Durability on
Hello everyone,
I am getting closer to starting the electrical on our new home build. I am wondering what solutions people have used for a motion activated hot water recirculation pump?
I would like to put motion sensors in 3 bathrooms. I have a dedicated return line from the farthest bathroom. I would like to use a sensor that is small, one that can be hidden as best as possible.
Your input is appreciated as always!
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Do you have plans for a home automation system? I'm personally a big fan of HomeAssistant because it is open-sourced and because I like to code in Python. That may determine what type of compatible sensor you want to go with.
Aeotec Multisensor 6 or something along those lines would be a good small, unobtrusive choice for Z-Wave compatible motion sensor (along with temp and RH, and other things like lumens). It is about 1.75" square and can sit recessed into the drywall.
In addition to the occupancy sensor, make sure your recirc pump has a built-in temperature sensor that will stop running once it detects hot water at the pump. That way it won't run needlessly if the line is already primed with hot water. So, in summary, two things must happen before pump is activate: 1) motion is detected in the room(s), and 2) the temperature at the pump is cold. I would use a Z-wave smart outlet for the pump.
The chain of events would be something like the following:
1) motion is detected in the room(s) and the Z-wave smart outlet is turned on, sending power to the Grundfos Alpha or similar constant-pressure pump
2) the pump uses it's built-in temperature sensor to determine if it should run or not, and it will only run until the sensor reaches its setpoint at which time it will turn off even if being sent power by the smart outlet.
I am thinking we will use some sort of home automation. We don’t have plans to go all out with automation, but it does make sense for some items. I am just beginning to learn more about it so I appreciate your recommendations.
I like the sequence you’ve used to prove if the pump should come on or not.
This is great information. I just installed home assistant and have been looking into doing this. I don't have a dedicated return line so i would have to use one of the ones that pumps hot water into the cold water line . I've been hesitant because they use a mechanical temp device that falls often.
If o could find one that would come on with a sensor and temperature sensor i would be on it!
Any ideas?
North,
When this came up a couple of years ago I did a day long experiment to see when we entered our bathrooms what proportion of those times we used the hot water. It wasn't very high. That behavour I'm sure varies wildly between households, but it might be worth looking at before deciding to put a sensor in.
Since they mentioned they have a dedicated return line from the furthest bathroom, I just assumed the output of the pump was plumbed back to the water heater inlet (would need check valve and expansion tank for this). If it's setup in this fashion, the energy usage is very minimal. You are not sending water down the drain, and the DC-powered ECM pump only runs long enough for it to detect warm water in the line. Other things that would help reduce cost would be short hot water line runs and good insulation on those lines, and also a heat pump water heater to reduce the cost to heat up the cold water you sent back to the tank.
Our longest hot water line is 20’ from the main trunk. You are correct that the plan is to put the recirc pump at the hot water tank with a check valve. The lines are insulated, and will actually be in a R20 insulated floor cavity.
I don’t think we plan to use a heat pump water heater as we are in a cold climate, the majority of our energy goes towards heating the living space.
20 feet is the longest run? Do you even need recirc? I understand the need in an old McMansion with a 200' run of 3/4" lines, but it might be adding extra cost and complexity for little real benefit.
It’s 20’ of 1/2” pex from the main trunk, which is 3/4” pex. The farthest fixture is probably 70’ away from the hot water tank.
Do you really want the pump to come on every time you happen to walk in a bathroom?
When I did the math, I think it costs 15 cents or so to heat my loop. I think I might start going in the bushes if it costs 15 cents to walk into the bathroom. LOL
How long will the wait be at the kitchen sink with no sensor?
My on-demand sensor operates of hot water flow. If I want hot water, I turn on any hot faucet for a second this starts the pump if the loop is below 90°F. Once the pump is started, I can turn off the water the pump will continue to run until the loop is hot or times out at 3 minutes.
Walta
Flow-based sensors are fine, but it's less convenient for guests since they won't know the routine.
The kitchen sink is directly behind the wall of the hot water tank, so let’s call it 10’
What are the details of your on-demand set up?
Use regular motion sensors. Make sure they have a neutral connection and realy not triac output. The triac ones don't work well with ECM pumps.
You can wire them all in parallel so any can trigger the pump. As a bonus, you can add something like a RIBU1C relay to the pump power and use it to trigger the boost function on your ERV.
Some manufacturers offer a thermal switch you can clip on the return line right at the end which will shut off the pump. You can also DIY your own, I use one of those Inkbird plug in thermostats for something similar.
The older I get, the less I like anything computer connected. With dumb controls, you wire once and never think about it again plus anybody down the road can fix it.
Funny you mention that, as that was my original plan. I’m a journeyman electrician so I also thought keeping it simple with something I understand might be the way to go.
Do you have a regular motion sensor that you prefer?
North,
"I also thought keeping it simple with something I understand might be the way to go."
Isn't that a pretty good rule of thumb in almost every building decision?
Setting this up via either Home Assistant or Hubitat seems like a great idea and will work as long as you live in the home. However, the hot water circulation seems like something that should simply work regardless of whether a smart home system is running.
I'd consider setting it up as follows:
1- In each bath, wire up the recirc pump to go on concurrent with when the tub/shower light is turned on.
2. For powder room simply wire up for recirc to go on when PR light is turned on.
3. In the laundry room wire up so recirc pump goes on when laundry room light is turned on.
4. In kitchenn, consider a toe kick switch - momentary contact. Wire up so that kicking the switch turns on the recirc pump.
5. Set up recirc pump so it goes on and runs for x time (a duration such as 1,2 or 3 minutes that you can physically adjust via a knob at the pump)
This has the benefit of only going on when the particular shower light is turned on, so when you go into the bathroom in the middle of the night, the recirc does not start up. It also has the benefit of a particular action, so if someone wants hot water at a sink to wash their face, they know to turn on the light at the shower. It also only turns on the recirc once, which is all you need. A motion sensor would forver be triggering it - multiple times when you get in and leave the shower, when you go in to brush your teeth, get something out of a drawer, etc. You only want to recirc the hot water when you actually need the hot water...
Thanks for the reply.
One issue I see with that specific setup is a very location specific problem. Because I live in The Yukon Territory, which is next to Alaska, we will often go months without turning a single light on in the summer. In mid to late June we receive 18hrs of direct sunlight! In the winter… well we don’t talk about that..
Also, if I used a pump with a built in aquastat, the pump would only come on with motion, and if the water temperature was low. The pipes will be surrounded by R20 insulation, so I’m guessing they will retain heat for a decent amount of time.
User...022,
Everyone has a different take on how resilient they want their house to be and the level of advanced technology it is defendant on. To me making the provision of hot water dependent on that many sensors and a central tech hub isn’t something I’d consider. These types of complex controls have become pervasive in appliances, and have lead to them basically becoming disposable, as the logistics and cost of getting them fixed exceeds the price of the unit. That’s fine for something you can replace at a box box store, but when it is integrated into the house it's just one more thing to go wrong you can’t repair yourself.
Luddite rant over.
Well it’s not really dependent on it, it’s just a recirc system which is arguably just a convenience. Also if we adhered to this we would still be cooking with wood… I don’t think the answer is to just be a Luddite, it’s to design advanced systems that are repairable. Advanced control systems typically make things more efficient, at least that should be their goal.
freyr_design,
I'm not advocating for an end to technical innovation, more that the method by which anything is added to the house should take unto account whether it's a necessary improvement, the possibility of it failing, and it's inevitable obsolescence.
I'm currently resisting replacing my 2008 Ford Ranger because it is both easy to repair, and contains very few parts of suspect longevity. There is no way you will get 16 years out of a 2024 Maverick with the technology it has been laden with.
It just seems like home automation overcomes the obsolescence aspect with ease of replacement (not to say I think it will become more obsolescent than say a system that is wired to lights that does not actually achieve what you want, ie I don’t turn the light on every time I need hot water).
I think the fear of unreliability comes from people buying cheap stuff from unreliable manufacturers. For instance I have had Leviton smart switches for almost ten years with no issues ever. The same goes for a number of smart devices in my house. It’s the same as someone buying cheap knock off plumbing fixtures that look the same as expensive ones and being surprised when they fail in a year.
For automated control I think smart homes are the way to go as all the accessories are extremely easy to replace should they go out and much more modifiable than wired systems. I can’t count the number of houses that have terrible switches locations that could be fixed with a movable remote switch, as one example.
Complexity should not be a deterrent to improvement. I have no idea how to repair a cpu, but no one is suggesting we get rid of computers.
Also just out of curiosity what technology on the new ford ranger would make it last less than 16 years? Even if many of the convenient features fail, will that make the vehicle non functional? And conversely, are those systems not repairable? And lastly, if an advanced safety feature stops you from smashing into someone, does it matter if it doesn’t last 16 years?
Malcom - Agree and that is my point exactly - which is why I recommended AGAINST advanced tech and sensors and a central tech hub, and advocate a good old fashioned switching - turn the pump on when the light is turned on...
and to put this in context, I run a smart house, with a Hubitat, and MANY automated things (lights go on when you walk in a room and the lux level is under x, etc) but I would solely rely upon automation for heat, cooling, dehumidification and plumbing
I use tp link motion sensors and smart plugs. The motion sensors I have are now obsolete, but there are now some new tp Link smart switches with built in motion sensor. If i were to set my system up now I may use that switch https://a.co/d/gYfg3oW
I have two separate recirc return lines with two separate recirc pumps. One for kitchen. One for upstairs bathrooms. The kitchen runs for 1 min activated by motion. Totals 35 minutes of run time per day. The upstairs motion activation runs pump for 2 mins, and totals about 30 minutes per day.
It's also fairly straightforward to pair the smart plug activation to a smart light switch in the bathroom.
You are in cold enough climate that efficient control of recirc doesn't matter. The heat lost from the recirc pipes stays in the house to heat it so it is not lost. About the only reason to use fancy recirc is if you have a tankless or heat pump water heater that will wear out if used with continuous recirc. Some basic controls that gets you good enough operation is all you need.
Thick insulation on the pipes is also not really needed. A bit doesn't hurt but I would not go overboard.
Important part is you end up with a system where if you open a tap, you get hot water right away. At the end of the day, that is the main reason for it.
Thanks Akos,
It’s more by chance that the pipes will be surrounded by r20 insulation. I’m insulating the ceiling of the main floor to slow down noise transfer between floors.
I agree that the main goal is to have hot water quickly when I turn the taps on. I’m really just trying to work through the best solution for that to happen.
I’m also still tossing around the idea of a heat pump water heater, but being in a cold climate I’m not sure how that math works out.