Question about hot water recirculation system...

edsut

Hi,
I am about to install a hot-water recirculation pump that uses the cold water line as the return half of the loop. I see these kits from WATTS (https://www.amazon.com/Watts-500800-Instant-Recirculating-Install/dp/B000E78XHG) and I've been youtubing for a few hours, so of course now I'm an expert (hopefully there's some obvious sarcasm noted there)...

Anyway, as I understand it, the sensor-bypass-valve under the sink (that connects the hot back to the cold) opens when the water is cold to allow that water to feed back to the water heater. When it gets hot enough, the bypass valve closes and the hot water is now immediately available to the faucet above. That makes sense. The part that confuses me is when the sensor has the bypass valve closed and the faucet is also closed...

What prevents the pump from being on, but the sensor-bypass-valve being closed AND the hot water faucet closed? Does the pump sense the back pressure and automatically shut off?
Thanks in advance...
Ed

STEVEusaPA

Doesn't programming the timer control the pump? If it were me I'd plug it in for constant power and run that power in series thru a flow switch, then the sensor. Then when water is flowing and is cold, the circ runs, when the sensor detects heat or flow stops, the circulator would stop.

edsut

Doesn't programming the timer control the pump?
Yes (AFAIK)
If it were me I'd plug it in for constant power and run that power in series thru a flow switch, then the sensor. Then when water is flowing and is cold, the circ runs, when the sensor detects heat or flow stops, the circulator would stop.
Yea, I get what you mean, but the kit doesn't include any flow switch, so it shouldn't really need that.... Or should it? Everything I've seen (i.e. youtube) implies that it just works as is.

edsut

I've been doing more reading and everything I see seems to say that the pump just keeps pumping even if all faucets are off and the bypass is closed. That seems inefficient at best; and wouldn't that put more load on the pump?

Thinking more about STEVEusaPA's flow-switch idea, that only works to turn the pump off (I think). Something needs to trigger the pump to go back on when the sensor changes state and opens the valve.

Seems like the ideal control would be for the sensor valve to also control the pump (wirelessly maybe?).
Am I just overcomplicating this?

edsut

Ok, I found a slightly different version of the pump that mounts under the sink..
https://www.hvacquick.com/products/residential/Instant-Hot-Water/Hot-Water-Recirculation-Pumps-NON-TANKLESS/Laing-AutoCirc-Hot-Water-Recirculation-Pumps
For this system, the pump and the sensor are in the same unit, so the sensor now controls the pump.
This makes more sense to me; however, I'd still like to understand my original question...

kcopp

https://www.tacocomfort.com/product/smartplus-e-ecm-high-efficiency-instant-hot-water-system/

I recommend running a separate return loop for the hot water. That way you wont have hot water in your cold water piping.

Condoman

I looked at these a few years back and found them a little expensive. I ended up building my own as shown here: condoman.us/CoolMountainStreams.pdf

I use a temperature sensor with a timer to insure the pump will shut off. It has had no issues for 8 plus years now.

edsut

@kcopp: Yea,... Running the separate return path does eliminate the issue of pumping with all valves closed because there's no sensor valve so the loop is always open. Plus, as you say, it eliminates the "hot-water-in-cold-faucet" problem. Bad news is that I would have to run a lot of pipe to make that return path. Gotta think about this...

edsut

@condoman: Very nice! I assume this is for a full loop (vs using cold-water return) configuration right?

JUGHNE

I have posted several times about hot water recir systems.
I have the insulated return line run to the bottom of the tank, constant trickle flow.
Instant hot water water. No pumps or controls. Only moving part is a check valve.

Yes, I know I have a tiny constant heating loop running in the basement, but feel not spending money on SS/bronze pump and controls every few years it is a trade off.

If I wanted to be really green, I could take cold showers.....not going to talk the wife into that though.

Condoman

@edsut: No, sorry, cold water return. Never thought about the separate return when the addition was plumbed (by me). This bath is also the farthest from the indirect.

woobagooba

Lots of good info here ... https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_22_na.pdf

We decided to run a dedicated hot water return line while our walls are open, but leave it unused. My read of that Caleffi issue ... the potential legionella issues related to lukewarm water in any of the potable water lines has me passing on hot water recirc for now.

Zman

I had one of those installed in my house for a couple of years. The good news is that it will give you hot water instantly when you want to take a shower. The bad news is that you will need to wait anytime you want a drink of cold water. Your cold water will be noticeably warm.

edsut

@woobagooba: I assume that's only an issue if you leave the line idle for some length of time allowing "stuff" to grow where it shouldn't...

JUGHNE

The gravity system cools the water as it returns to the bottom of the tank.
It is then heated to about +130 before leaving the top.

Larry Weingarten

Hi, @edsut , I don't think anyone has mentioned demand control, yet. https://gothotwater.com/ is a good place to look and see if that fits your need.

Yours, Larry

edsut

@woobagooba: I'm still trying to understand how a recirculation system contributes to this issue any more than normal hot water that is left in a hot feed after the line is shut off and allowed to cool (say after a morning shower)? In this case (which is standard plumbing, no recirc involved) you have hot water that cools down to lukewarm and left in the pipe until the line is turned on again. So you still have luke warm water in a normal hot water line that isn't used. Know what I mean?

edsut

@Larry Weingarten: thanks, but quite pricey!!

edsut

@condoman: I'm liking the idea of building this myself, big cost reduction... Seems it could be done with a small arduino circuit that could detect the temperature by connecting to a clip-on-the-pipe thermistor and then control a relay to activate the pump. Agree?
Question though... When a pump is not running does it typically act like a closed valve or does water still leak through?

Dave H_2

To answer your question about the circ when the valve is shut and the taps are closed.......yes the circ still runs. The biggest problem everyone has with these types of systems is the programming of the circ. It is either poorly done or not done at all. Each one of those dip switches represents 15 minutes of circ run time. And then all of the pins are set for the couple of hours someone might use the water in the house. In reality, you should turn one pin on and then (depending if the run is short) turn the next two off. The water in the line is not going to cool off that fast. or if the run is really long, turn one pin on and the next off and so on and so forth.

Or use a learning system that can run the circ upon the demands of the homeowner and then run 5 minutes on, 10 minutes off during the learned cycles.

Dave H.

edsut

@Dave H_2 :
To answer your question about the circ when the valve is shut and the taps are closed.......yes the circ still runs.
So how does water circulate if all valves are shut? Does this stress the pump over time?
@Dave H_2 :
What you say about programming the timer makes sense...
With the systems that install completely under the sink (all-in-one-unit), does the pump then use both the timer and the sensor to turn on? For example, you use the timer to enable the system during the day, but that just establishes the period of time during which the sensor can turn on/off the pump. Is that how they work?

edsut

By the way... just a quick THANK YOU to all on this conversation... Its been very helpful so far!

Condoman

@edsut: There is no reason an arduino could not do the same thing as my timer circuit. I happened to have it already around from another project no longer in use.

I choose my parts so I can replace them as needed. In fact the circuits have backup parts already on hand.

I do not see and hot leaking to cold since they are all at the same pressure. The pump has an internal back flow valve also.

Alan (California Radiant) Forbes

@edsut We installed a Grundfos recirc. system like you've been originally talking about and it did not please me or the customer. The problem was that the thermostatic bypass under the sink is factory set to 100°F, so it closes when that temperature is reached when it should be 110° or 120°. It just wasn't hot enough. That was a few years ago and maybe things have changed since then.

And yes, the pump runs according to the timer and often deadheads when the bypass is closed, but it's a weak enough pump where it doesn't matter.

edsut

@Alan(CaliforniaRadiant)Forbes: seems that temperature problem would be easily solved if I took @condoman's approach and built my own. Bad news on that front is that I really wouldn't save any $$ doing that. Grainger wants $280.00 just for the pump! I can buy a full system and install under-the-sink for about $320.00.
Based on all this info, I think I am going to go with the under-the-sink system (using cold-water return).

Thanks again to all who contributed! I will keep this conversation posted on my status.
I really like this forum!

Condoman

@edsut: The Armstrong Astro 225SSU is half that price at Zoro.

Jean-David Beyer

The problem was that the thermostatic bypass under the sink is factory set to 100°F, so it closes when that temperature is reached when it should be 110° or 120°. It just wasn't hot enough. That was a few years ago and maybe things have changed since then.

I have a similar Taco system and as the customer, I am frustrated by it. My frustration is partly the design of my house, and partly the design of the system. I get the hot water from my indirect hot water heater that runs between 140F and about 155F with an automatic mixing valve that puts out about 122F water. This then goes through a small ECM pump into the concrete slab upon which the house is built. The slab also has the pipes for the radiant heating zone downstairs. Think of it as a heat sink. Now the Taco ECM pump is plugged into their smart control that watches my hot water usage over a week and then runs the ECM pump at those same times the following week. But it runs ON for five minutes and OFF for 10 minutes.

By the time the hot water gets to the kitchen sink (and the dishwasher), I cannot get it over about 110F and even that takes over five minutes to do it. If I turn the hot water off, it cools down in about five minutes. Also, the non-adjustable clever valve under the sink is set for 118F or something like that, so it never shuts off. Hence the cold water is usually too hot.

Furthermore, I keep irregular hot water usage hours, so what it learns one week is not very appropriate the next week. If I do not use enough hot water for (I think) 36 hours, it assumes I am vacation and forgets what it learned. It also forgets if the power goes off, so I stuck a UPS in there.

STEVEusaPA

I still think my idea has some merit. Bronze circ, hot water recirc line back to indirect.
To elaborate:
Flow switch on hot water line out to fixtures. In my case the master bath is on the other side of the house and the only room requiring hw recirc.
-Flow switch closes contacts to energize a control (circulator).
Timer (circuit) allows circ to run 30 seconds (for my situation), then timer locks out circ (control) for 15 minutes. This is long enough to take a shower or in my wife's case the circulator may come on for another 30 second cycle in 15 minutes.
Practical operation.
Walk into bathroom, turn on hot water faucet for a full second to activate flow switch. Pop off your clothes, turn on shower, hot water in 7 seconds.

ChrisJ

JUGHNE said:

The gravity system cools the water as it returns to the bottom of the tank.
It is then heated to about +130 before leaving the top.

How does that work with a checkvalve?

I wouldn't want my heater pulling water from the bottom of the tank. I also thought it was somehow against code?

ChrisJ

I don't see the circulator running without any return being much of an issue.

If it's a centrifugal pump there should be less of a load on the motor than if the water is flowing. As long as the water in the pump housing keeps the seal etc cool enough I would expect it to be fine aside from wasting power.

I'm using a Taco 006 and an aquastat on my system with a return. I didn't want water from my tank heater going through the cold side.

JUGHNE

The recir water returns to the bottom of the tank by gravity.
There is a swing check valve that allows a trickle flow into the tank induced by the same flow up thru the hot supply.
A nearly closed ball valve controls the flow.
I might have nearly a 10 foot drop from under the farthest lav sink to the basement floor. And the return line has slope on it to induce the flow.

If there were not enough flow to open the swing check then one would drill a 3/16" or less hole in the flapper.

The check keeps the recir line from becoming a cold supply when hot is used and cold comes into the bottom of the tank.

tim smith

I installed a little modified recirc at my house, oversized my recirc pump a little and installed occupancy sensors that would pick us up at door to bathroom. Recirc pump would turn on and stay on for appx 5 min. With in 20 sec I had hot water at tap. Saved having the heat loss of the recirc line running all the time. Worked out well.

rick in Alaska

I have a push button switch under the kitchen sink, that is connected to a two minute timer, that activates the return line pump, and works well. But, I do like Steves idea of a flow switch activation. Then all fixtures would be able to control the pump, and without any wiring.
Rick

ChrisJ

I like the fact that when I go into any bathroom at 2AM I get burning hot water within 2-3 seconds of turning on the faucet. There's no wait time, no ramp up time, nothing. Hot water, bam, right there.

The pump runs for about 40 seconds every 20 minutes.

At 30 watts I come up with 0.04kwh per day. $0.125 per month to run the pump like I do, or $1.50 per year.

For my insulated piping I come up with roughly 500 btu/h loss which I come up with roughly $65 per year

So, less than $6 a month for hot water within a few seconds any time of day and by letting things cool off more isn't going to drop that cost a whole lot.

STEVEusaPA

ChrisJ said:

I like the fact that when I go into any bathroom at 2AM I get burning hot water within 2-3 seconds of turning on the faucet. There's no wait time, no ramp up time, nothing. Hot water, bam, right there.

The pump runs for about 40 seconds every 20 minutes.

At 30 watts I come up with 0.04kwh per day. $0.125 per month to run the pump like I do, or $1.50 per year.

For my insulated piping I come up with roughly 500 btu/h loss which I come up with roughly $65 per year

So, less than $6 a month for hot water within a few seconds any time of day and by letting things cool off more isn't going to drop that cost a whole lot.

It's probably better than that as you aren't wasting water waiting for it to get hot.

JUGHNE

Also, the water that is wasted used to be hot, but that heat was lost to the basement.

ChrisJ, your annual $65 heat loss is not all a waste. For 4 months it contributes to heating your house at probably the efficiency of your steam system.

For me it may be 4-5 months of heating, I use that logic to justify my constant trickle flow gravity recir, which I am sure is frowned upon by some.
But I have no pump or control investment initially or replacement there of.

A friend in the HVAC business realized that his recir pump had failed but still had quick hot water, his system was gravity flowing thru the dead pump.
He left it as is.
I wonder if your system is gravity flowing between pump cycles, to give you the instant hot water. You could power it off for a couple of days to find out.


Erin......I dout thenk the spelchucker feature is warking.....is that my problem or the Wall's.

ChrisJ

JUGHNE said:

Also, the water that is wasted used to be hot, but that heat was lost to the basement.

ChrisJ, your annual $65 heat loss is not all a waste. For 4 months it contributes to heating your house at probably the efficiency of your steam system.

For me it may be 4-5 months of heating, I use that logic to justify my constant trickle flow gravity recir, which I am sure is frowned upon by some.
But I have no pump or control investment initially or replacement there of.

A friend in the HVAC business realized that his recir pump had failed but still had quick hot water, his system was gravity flowing thru the dead pump.
He left it as is.
I wonder if your system is gravity flowing between pump cycles, to give you the instant hot water. You could power it off for a couple of days to find out.


Erin......I dout thenk the spelchucker feature is warking.....is that my problem or the Wall's.

That's true,
However for the summer months I'm also paying to remove that heat besides just create it so I feel summer / winter balance out enough for me to just count the loss alone over 12 months.

AdamInEvergreen

Just joined this forum and am browsing old posts. The simple fix I did was to put my Circulator in always on mode then plug it in to a smart plug. I use the app on my phone to set a routine of On - Wait Four Minutes - Off. We just turn it on when we need it so there is no unnecessary run time.

Pre covid when I actually got up at the time time every day I had a schedule set so I knew there would be hot water waiting at 5:15am. Helped me get out of bed consistently. 

MikeAmann

I realize this post is old, but nobody thought of running the water HALFWAY back to the tank, if that was even possible in the OP's situation.
Ideally, a dedicated line all the way back to the water heater, returning the water as close to the cold inlet as possible would be best. But if that is not possible, then what about a return line to as far back in the loop as he can get? A semi-dedicated return line.