Hot water recirculating pump: Run on demand for set duration

[TanerH]

Hello!

 

I've read a few posts and How-To's regarding automation of a whole-home hot water recirculation pump (see end of post for one reference), but none quite fulfill my needs. Here's the rundown:

 

* I'd want to run the pump for (for example) 30 min on single-tap or 60 min on double-tap (or perhaps other lengths of time, based on which remote was triggered).

* There are 5-6 locations where I'd want a remote keypad/control for this.

* Possibly: Each remote trigger would "reset" the run time to the greater of current_remaining_runtime or runtime_proposed_by_this_switch. (So that an already-counting-down timer will not get shortened if a shorter runtime were to be requested by a different remote)

 

 

I was planning to set this up in this fashion:

 

* Install OutletLinc Relay @ the pump location

* Have multiple "remote" switches around the house -- What should I use for these?

* Programming:

1) Master program that is essentially (this is pseudo-code!):

        IF $pump_run_time > 0
       THEN
          turn pump outlet on
          decrement $pump_run_time
          wait 1 min
        ELSE
          turn pump outlet off

2) Each remote will run a program that assigns a value to $pump_run_time based on if it received an "ON" or a "FAST ON". (Or perhaps simply based on which remote was used). A simple conditional could be added to ensure the greater of ($pump_run_time) and (NewTime) is used, so that a 60min timer that is counting down and is already at 45 min will not get suddenly shortened to 30min.

3) Set up one controller/remote to be able to signal an OFF (don't want "Off" control from each location)

 

My main questions are:

 

1) Does that program make sense? To have a control variable that can be adjusted (set) by each remote, and just decrement it a minute at a time? Am I doing what I want in the proper manner (is that the right way to decrement the counter once a minute?)

 

2) What sort of devices should I have to control the ON signals?

- Should I be using SwitchLincs (On/Off, not dimmer)? There is power in the walls at each location.

- Should I use MiniRemotes? (These do not seem to come in Ivory, so that is a bit saddening, and thus I'd prefer not to use them)

- Should I use KeypadLincs? Seems like overkill, but might work for one of the locations where I might have need for other control buttons, and isn't really all that much more expensive.

 

3) What sort of status/feedback will each switch show? Can I make them reflect the state of the OutletLic?

 

I've officially caught the home automation virus, I think

 

Thanks so much!

 

For reference, this post inspired me a bit: viewtopic.php?f=26&t=1800

 

-Taner

[arw01]

Oh no, the bug would be predictive modeling of the movement in the house to turn on the pump when you think someone will be calling for hot water.

 

How long does it take without the recirculation pump going?

 

Do you have small tanks below the sinks to buffer the flow?

 

Why run an hour at all? Why not just a few minutes at most? What about stirring the water occasionally? E.g. how long does it take to cool to a point you would even notice?

 

I assume you still need a couple seconds run time before it is hot even with the recirculation pump running.

[LeeG]

1) Does that program make sense? To have a control variable that can be adjusted (set) by each remote, and just decrement it a minute at a time? Am I doing what I want in the proper manner (is that the right way to decrement the counter once a minute?)

 

Not as coded. The Wait 1 minute at the end of the Then clause has nothing after it so the Wait is effectively a no-op.

 

2) What sort of devices should I have to control the ON signals?

- Should I be using SwitchLincs (On/Off, not dimmer)? There is power in the walls at each location.

- Should I use MiniRemotes? (These do not seem to come in Ivory, so that is a bit saddening, and thus I'd prefer not to use them)

- Should I use KeypadLincs? Seems like overkill, but might work for one of the locations where I might have need for other control buttons, and isn't really all that much more expensive.

 

I think this totally personal preference. Any Insteon device that can send On command (which is just about all of them) can drive the Program (not the one posted).

 

3) What sort of status/feedback will each switch show? Can I make them reflect the state of the OutletLic?

 

I think this is the overriding question as it may well dictate the answer to number 2 as well.

 

What kind of feedback do you want?

 

Some newer devices have a Beep function that is not very loud but will be heard when at the device. It could beep for each time increment (10 minutes for example) that remains. A SwitchLinc Dimmer (not connected to any actual load) could be turned On to various % On Levels which is represented by the status LEDs to the left of the paddle. There are 8 or so LEDs that represent the % On Level of the SwitchLinc. With sufficient programming the status LEDs could show the amount of time remaining with an On button press incrementing and Off button decrementing the status LEDs and pump time remaining. The status LEDs may move to full On or full Off when the paddle is pressed but would be corrected by ISY programming. Something similar could be implemented with an 8 button KeypadLinc with each KPL button representing an increasing amount of pump run time.

 

Decide on what if any feedback/control you want first. That should provide the answers to 2 and 3.

 

You might also give some thought to the idea that too much thought is being put into this. Once the pump has moved hot water to the location there is no longer any need to have the pump running. A simple turn pump On for 5 minutes or 10 minutes may be all that is needed.

[apostolakisl]

First off, you need to add the "run program line" to keep this program looping until the clock runs out

IF $pump_run_time > 0

THEN
          turn pump outlet on
          decrement $pump_run_time
          wait 1 min
          Run Program (this one) if clause

ELSE
          turn pump outlet off

 

But I am confused as to why you want the pump to run for 30 minutes or 60 minutes after it is triggered by someone pushing the button. Isn't the point of an on demand pump to run just long enough to get water to the faucet and then shut off? I would think it should take only a few seconds depending on pump size and distance.

 

Either that or you run the pump continuously during the times when it might be used. Like at your typical wake up time and your go to bed time. That way there is no need to do anything to trigger the pump, the hot water will be there during those times regardless of use. Or maybe some combo of both.

[TanerH]

Hello, all -- thanks for all of the responses!

 

I'll address the questions by starting with some more background, and then addressing questions in a slightly random order (not on purpose, heh)...

 

I currently have the recirc pump come on at about 6:30am, and turn off at about 1:30pm, since that is when we would want instant hot water the majority of the time. If the pump is OFF, it takes 3+ minutes (of wasting water) to get hot water to a faucet that is not right next to the tankless water heaters (which happens to be the majority of the faucets that are in use, daily).

 

Our schedules are erratic, however, and sometimes we'd want to shower at ~7am, and sometimes not until 11am or even later (sometimes it ends up as early afternoon)... this is why there is a long run time already.

 

The recirc pump pulls about 175+W (as per my kill-a-watt), and (realistically) we'd really only need the pump running for maybe 1.5-2 hours of the day, tops -- instead of the 7+ hours it runs today. Being able to take a shower in the evening without waiting 5min for the water to heat up would also be nice

 

Once the pump turns on, it takes about ~30 sec for hot water to reach the farthest location in the house (compared to the 3+min without it... and a recirc pump is at least not wasting the water).

 

There are no tanks at any sinks for flow buffering.

 

But I am confused as to why you want the pump to run for 30 minutes or 60 minutes after it is triggered by someone pushing the button. Isn't the point of an on demand pump to run just long enough to get water to the faucet and then shut off? I would think it should take only a few seconds depending on pump size and distance.

Sometimes if we happen to take a cooler shower, the hot water flow is not enough to convince the tankless heaters to stay on, and so they will turn off briefly, and then fire back up 30 sec later -- meanwhile I get blasted by super-cold water for a short time. :-/

 

This is why I'd rather just run the recirc pump while showering.

 

I've considered simply hooking the light switch for the shower to a trigger that also starts the pump -- but that only works for the bathrooms that have a separate light for the shower or tub area.

 

I have also considered doing a partial on/off sort of deal (on for 5 min, off for 3, etc) but stopping/starting a motor generally shortens its lifespan more than just leaving it on for a longer period of time.... and I'm still left with the situation where I come home late at night and want to shower.

 

It's very good to hear that I could use a SwitchLinc Dimmer and have it (essentially) show how much time is left on the pump run cycle -- I think that would be a neat way to display status! I had just assumed I'd get an "it's on" or "it's off" (LED) sort of feedback, but the gradient display is much better

 

 

Honestly, I also sort of want to just do this to see it work... I mean, the "tinkering" side of me

 

 

Also, thanks for the pointers on the program code... I didn't realize you'd have to make it (essentially) recursive like that. Is that the normal way to do that sort of "loop"?

 

I guess a more fundamental question: How often (and under what circumstances) are the IF conditions checked to see if a given program should run?

 

Oh, one last thing:

Oh no, the bug would be predictive modeling of the movement in the house to turn on the pump when you think someone will be calling for hot water.

...is it sad/scary that I actually DID think about doing it that way, too? Well, at least, with motion detectors or somesuch hahah

 

Thanks, again!!

 

-Taner

[apostolakisl]

I have to wonder about your tankless heaters if they will shut off during a shower. Ours turns on for even small amounts of water, washing your hands for example even with the flow rate on low.

 

I might suggest taking a drill and opening up the flow restrictor on your shower heads. It probably would be cheaper than running the recirc pump and make for much nicer shower experience.

 

Also, recirc pumps void the warranty on many if not most tankless hot water heaters. Once the hot water makes the full loop a couple tmes the returning water barely needs to be heated which results in lots of cycling of the burners.

[oberkc]

One thing that may also help with the water heater cycling during shower is to turn the water temperature DOWN. Doing so might allow a higher ratio (thus quantity) of heated water.

[arw01]

I think the recirculation pump is the culprit to the cold shower. My Takagi used for the floor heat in my shop, cuts way back on the heat being applied when the water coming back in is warmer. I think your pump is causing warmer water to recirc through the unit and you get these "pulses" as it takes time to fire back up to full heat capacity since the water was just hot enough to cut back a few moments ago.

 

It almost seems counter intuitive, but may be worth a try.

[apostolakisl]

One thing that may also help with the water heater cycling during shower is to turn the water temperature DOWN. Doing so might allow a higher ratio (thus quantity) of heated water.

 

Agreed. I have mine set to 120 which results in about a 90% hot to cold mix. Also is less risky for the kids.

 

I have seen some of the tankless units allow recirc pumps and still warranty the device, but only if you added a holding tank. Kind of defeats the purpose though.

[oberkc]

Agreed. I have mine set to 120 which results in about a 90% hot to cold mix. Also is less risky for the kids.

 

I agree. For showers, a temperature of (even as low as) 110F could work. One has to balance that against other needs for hot water, such as dish washing and sanitation. I am not sure what the accepted temperature for these purposes is, but I suspect it is 140+. I choose to use shower temperatures as my driving requirement.