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Button-activated recirculation system questions

doughpat
doughpat Member Posts: 35
edited April 2020 in Domestic Hot Water
I've got the walls open on new construction. I ran a dedicated 1/2" PEX return line from the farthest faucet back to near the combiboiler (currently its not hooked up....just thought I'd get the pipe ran while the walls/floors are open). I also ran a cat5e cable back alongside it, just in case the pump ends up being located down by the combiboiler.

So a few questions:

- One pump can be activated by two buttons, correct? (i.e. if I did one button at the bathroom, and one button at the kitchen) If so, would I wire them in parallel to the pump activation wires?
- It seems there are many options out there for recirculation systems. I like the idea of the button-push system, as it seems like it'd be the most efficient as well as reduce the number of cycles that the combi-boiler has to complete. Most of the systems I am seeing use the cold water line as the return line, but since I have a return line, does that change the system I should select?
- I'd like to try and minimize the cycling of the combi-boiler. Is there a configuration of a buffer tank, or a sensor/timer, or something else I don't even know about, that would help reduce on/off cycles? What I don't want is for someone to push the button, causing the pump to turn on (and therefore the combiboiler to fire up), then as soon as the hot water reaches the pump (maybe 60 seconds later), its sensor sees warm water and turns off the pump. This would then stop the combiboiler until the user actually opened the faucet, at which point the combi would kick back on. This would effectively add a cycle every time someone used the button! Is there any way around this?

By the way, this is a Lochinvar Noble 110K. The pipe runs are quite short -- maybe 15 feet to the kitchen and 40 feet to the bathroom. I'm not even sure this is recirc is at all necessary, but I was hoping there might be a configuration/use-pattern in which a recirc loop could somehow reduce cycling of the boiler.

Comments

  • Larry Weingarten
    Larry Weingarten Member Posts: 2,129
    Hello, A few thoughts. Metlund, www.gothotwater.com was the first to have demand pumping for DHW. To them, it doesn't matter if you have a dedicated recirc line or use the cold piping. Note that there have heard complaints about the cold water being warm with systems like this, when hooked up to the cold piping. They also have wireless remote buttons that can operate the system. It's common to have multiple buttons in these systems and yes, I think they get wired in parallel. Push-button systems use about 90% less energy to do recirc than conventional methods.

    Have you considered installing an indirect tank? It seems to me that would eliminate the concerns of boiler cycling.

    Last, unless the recirc line is quite short, I'd consider putting in a 3/4" line so you get good flow without having to install a huge pump. Unlike a standad recirc, that's only there to compensate for piping heat loss, demand pumping needs to move the water quickly, as you're waiting for it!

    Yours, Larry
  • doughpat
    doughpat Member Posts: 35
    Hi Larry -

    Thanks for the comments. I'll look into gothotwater.com. I'll hopefully be able to hardwire the buttons (I'm always a fan of hardwiring where possible!) since I"ve already got some Cat5 cable run from the locations where the buttons will be mounted.

    How would an indirect tank be used in this system? Would the DHW side of the combi-boiler feed its hot water through the indirect tank, which would act as a heat exchanger? Then the actual hot DHW would be drawn from the indirect tank?
  • rick in Alaska
    rick in Alaska Member Posts: 1,178
    I have done a few of the push button recirc systems, and they work well. Yes, the push buttons are wired in parallel. In the ones I have done, I wire them up to a timer that I have set for 2 minutes, and then shuts back off. That timing seems to be good for most of the situations I have had to deal with, and gives the on demand heater, in my cases, time to fire up and get the heat to the fixtures ok. This should help with your cycling, as the water is being used, and the boiler is running, before the timer shuts off, and will keep running as long as the fixture is open.
    Rick
  • doughpat
    doughpat Member Posts: 35
    Hi Rick - could you give a specific setup (button, timer, pump) that has worked well? I like the 2 minute timer.
  • rick in Alaska
    rick in Alaska Member Posts: 1,178
    The first one I installed at my mother in laws house, I used an ICM253 timer, with a 24 volt mechanical relay, a doorbell button,and hooked up to a stainless Grundfos pump. This was just what I had available at the time, so I would probably use an RIB relay instead of the big noisy mechanical one.
    https://www.icmcontrols.com/documents/ig_LII274-3.pdf
    Rick
  • retiredguy
    retiredguy Member Posts: 386
    This is what I did with my recirc, lines from 3 bathrooms in my house. I ran 1/2" copper tubing, with a swing check in the lines, from each bathroom to a common 3/4" manifold and from there to the smallest bronze pump available . I used a 1/2" B&G pump rated at 39 watts powered by a cheap plug in wall timer that cycles the pump during the day and turns off at night. There is no button to push or fancy expensive control system. This has worked great for 20+ years and my wife is happy. (another plus) .you married guys get the picture. We have almost instant hot water any time of the day.

    my 2 cents
  • GroundUp
    GroundUp Member Posts: 1,170
    With only a 40ft run to the furthest point, what would the purpose of a recirc on a button be? With 1/2" pex that's only 3 pints of water down the drain, with hot water still arriving faster than with the recirc.
  • JUGHNE
    JUGHNE Member Posts: 8,263
    My master bath is about 50-60' of pipe from the WH.
    I added a 1/2" OD line from the farther hot pipe back to the WH.
    There is a swing check and throttling ball valve connected to the bottom inlet of the WH tank. Ball valve almost closed.
    Hot water right now 3-5 seconds.
    I suppose an energy wasting continuous loop. But is insulated.
    No pump....no timer or aquastat.....no electricity.
    No pump or controls to replace in the future.
    Compare the heat loss to ROI investment of hardware costs......???.....but I consider it a luxury in life that I am willing to pay for such as AC.....which is not a necessity for life IMO.

    I have 120 gallon storage tank with separate tube in shell HEX. This continuous micro flow keeps the tank closer to even temp and prevents top of tank stratification.
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