Missed chance for hot water recirculating design
Hello everyone, I wasn’t sure how to post this since it’s more of a pondering/discussion than me asking for help.
Just for fun I’ve been looking at digital temperature controls for showers since I thought it would be a convenient all in one device. Because you’re specifically setting a “desired” temperature, it would include plumbing re-circulation until that temperature is reached as the valve.
I haven’t had looked at much other than https://www.us.kohler.com/us/DTV-Prompt-Digital-Showering-System/article/CNT121000008.htm from Kohler, but in reaching out to their customer service it seems they did not design their product this way. All it does is turn on the fixture and runs water down the drain for you until the temperature is reached. They have all the pieces there to add in re-circulation functionality that would waste zero water while still providing the set temperature functionality.
I’m only posting this to ask if this disappoints anyone else as much as it disappointed me? Maybe there are digital shower controls that do include this, which in that case any links would be of interest.
Thanks!
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Hot water recirculation to make hot water at the fixture hot quickly isn’t a function of the fixture, it’s something you need to implement in the plumbing system supplying the fixture(s). Normally for large systems this means making a loop of hot water line to supply all the fixtures (each fixture is tapped off of a main line), then at the end of the main line a return line loops back to the source. You need your hot water heater in the loop too so that you’re circulating heated water and not just running water around and around a loop of pipe. The return line can be small since it only takes a small amount of flow to keep things hot. Normally a small pump provides the circulation, similar to a hydronic heating system.
If your hot water heater is in the basement, you might be able to use a “thermosiphon” to avoid having a pump. In this type of system, the normal convection currents provide the necessary water circulation. There is no pump to break, and no electricity needed to run it. I have such a system in my house, and it’s one of my favorite upgrades I’ve done.
If you implement such a system, make sure to insulate ALL of the hot water loop piping. Without the insulation you’ve just built a long radiator and you’re wasting energy in the form of heat from your water heater. That’s the trade off for these systems from a green perspective: waste heat, or waste water.
It’s possible to implement a recirculating loop with instant water heaters too, but you usually need a small tank in the loop and you can’t use the thermosiphon system — only a pump will work in this case.
Bill
On-demand recirculation allows you to circulate hot water only when you require it, so you avoid the standby losses of having hot water in the pipes all the time. It still requires a third water pipe for the return and a pump. With demand recirculation, the pump turns off when it senses the temperature rise, so there is very little pumping energy cost.
This would work fine with the Kohler system and it would significantly reduce the amount of water thrown down the drain, as is its intent. Kohler can't really build in that functionality because they just sell fixtures. I suppose it would be possible for them to include a pump that sends the not-yet-hot water back down the cold water pipe (one alternative to the return pipe), and I expect the smart people at Kohler know about this technique as well, but the (equally smart?) marketing people haven't seen the demand for it just yet.
In areas where water efficiency is starting to become critical, recirculation might start gaining ground, as water rates inch up. Maybe then some of the major manufacturers will start figuring out how to add that functionality to their fixtures.
I guess marketing could be a reason for this to be missing. If you follow the link below, you can see that you need to use their thermostatic valve with the system I included in my original post. It just seems like it would be trivial to also have a pump accessory that would do the demand re-circulation when the system starts (replacing their dump-down-the-drain warm up procedure).
https://www.us.kohler.com/us/DTV-digital-two-port-thermostatic-valve,-landscape-setting/productDetail/showering-digital-valves-controls/428394.htm?skuId=410384&brandId=785778