Get some Sense... [sense monitoring solution]

[HankLloydRight]

If you only need hot water at that location at those times, then the water heater is superfluous.

First, folks, take a look at this article which explains my (common) situation:

http://www.chandlerdesignbuild.com/files/fhbDecJan08.pdf

The purpose of the 10 gallon aux tank is to buffer the cold water slug left behind in the tankless heater upon start-up.

In a world of free energy, I'd run the aux heater and the circ-pump 24x7. The aux heater alone draws a constant 2000w when the circ pump is running.

We just moved into this house, and got the first few electric bills over $500, I had to figure out what was going on. The first problem I found was that one zone of the HVAC was somehow switched to A/C and the others to heat. So in the middle of winter, the A/C was running to compete with the heater. Easy fix (we think the home inspector left it on A/C and we just didn't notice it. The house wasn't cold). But that didn't change our bill much the following month. I tracked the huge culprit down to the circ pump and the aux water heater. Actually, here's a graph of the energy usage before I put the circ pump on a timer:

Do you have the circ pump for when you will have large water demands, and the small tank for the rest of the time? If so, the new setup will only have the small heater on part of the time and the water will get colder in the intervening periods, more so as hit water is pulled from the tank.

So the bottom line is that we only need "instant" hot water upstairs in the morning for showers, and a few hours in the evening when my wife likes to take a bath (Coincidentally, we have the bathroom tile floor heater on the same schedule. ).

The circ pump and the aux heater work together. If the aux heater isn't on, the circ pump circulates cold water. If the circ pump isn't running, the heater keeps its tank at the set temp of 130 degrees but it doesn't circulate (which was causing my most recent problem with the 2kW spikes).

So simply tying the heater switch to the circ-pump timer with the relay should fix the problem and deliver hot water when/where needed based on the one timer, and not run the aux tank the rest of the day at all. This will kill the 2kW spikes I was seeing. That means if someone needs hot water outside of when the aux tank/circ pump are on, there's a short delay as hot water from the instant-on tankless heater gets up to the faucet.

I thought hard about getting Sense, but figured I could figure it out myself and save the $300 (I already have a two CT energy monitoring system from Efergy that works really well). I also don't like how they require you to install a 240 double breaker to power the device and detect actual voltages. I for one don't have any free space in my panel or subpanel. It would be nice if there were an alternate option. Anyway, I've knocked out most of the problems, so I'm not sure I need to spend the $300 for it anyway.

 

[mongo]

First, folks, take a look at this article which explains my (common) situation:

http://www.chandlerdesignbuild.com/files/fhbDecJan08.pdf

The purpose of the 10 gallon aux tank is to buffer the cold water slug left behind in the tankless heater upon start-up.

In a world of free energy, I'd run the aux heater and the circ-pump 24x7. The aux heater alone draws a constant 2000w when the circ pump is running.

We just moved into this house, and got the first few electric bills over $500, I had to figure out what was going on. The first problem I found was that one zone of the HVAC was somehow switched to A/C and the others to heat. So in the middle of winter, the A/C was running to compete with the heater. Easy fix (we think the home inspector left it on A/C and we just didn't notice it. The house wasn't cold). But that didn't change our bill much the following month. I tracked the huge culprit down to the circ pump and the aux water heater. Actually, here's a graph of the energy usage before I put the circ pump on a timer:

So the bottom line is that we only need "instant" hot water upstairs in the morning for showers, and a few hours in the evening when my wife likes to take a bath (Coincidentally, we have the bathroom tile floor heater on the same schedule. ).

The circ pump and the aux heater work together. If the aux heater isn't on, the circ pump circulates cold water. If the circ pump isn't running, the heater keeps its tank at the set temp of 130 degrees but it doesn't circulate (which was causing my most recent problem with the 2kW spikes).

So simply tying the heater switch to the circ-pump timer with the relay should fix the problem and deliver hot water when/where needed based on the one timer, and not run the aux tank the rest of the day at all. This will kill the 2kW spikes I was seeing. That means if someone needs hot water outside of when the aux tank/circ pump are on, there's a short delay as hot water from the instant-on tankless heater gets up to the faucet.

I thought hard about getting Sense, but figured I could figure it out myself and save the $300 (I already have a two CT energy monitoring system from Efergy that works really well). I also don't like how they require you to install a 240 double breaker to power the device and detect actual voltages. I for one don't have any free space in my panel or subpanel. It would be nice if there were an alternate option. Anyway, I've knocked out most of the problems, so I'm not sure I need to spend the $300 for it anyway.

Ah, my misunderstanding. I thought the small tank was for the water in the pipes and was located at point of use, hadn't come across the hot/ cold/hot scenario.

So the circulation pump runs the water through the pipes back to the 10 gallon tank which is located by the main on demand unit?

Timer control of heater works, but be prepared for cooler water to start with. You may want to try disabling the element during the pump off time to simulate the new setup for family acceptance.

For optimal energy savings, have you considered a switch for the recirc pump in the bathroom (possibly with lower small tank temperature)? The loss due to the pump running may be higher than the standby loss of the tank.

Thinking with lots of assumptions:
3/4 copper pipe type L holds 0.025 gallon per foot. If the run is 40 feet, that is additional 2 gallon round trip. (No idea what the supply of return are)
That water is room temp say 65F. The tank may have cooled down to 110F. Just on straight mixing, the total volume of 12 gallons is at ((460+65)×2+(460+110)×2)/12-460=102.5 F.

The small heater is only able to raise that at a degree per minute ignoring losses from the pipes. If the tank ran 100% originally with the pump on, then it never put out enough heat to overcome the loss from the pipe run (at 130) so ability to catch up is questionable. But at least it isn't losing ground.

Thanks for letting me brainstorm

 

[HankLloydRight]

Timer control of heater works, but be prepared for cooler water to start with. You may want to try disabling the element during the pump off time to simulate the new setup for family acceptance.

I don't understand what you mean by turning off the element. Yes, I said above when the circ pump and aux tank is off, then there's a short wait for hot water from the tankless water heater. But this is only during the daytime when the demand for quick hot water is very low/none. The entire point of my posts is to explain that when the circ pump is off, heating the aux tank serves no purpose, since the standing water in the pipes is still cold. So the time it takes to get the warm water from the aux tank *or* the hot water from the tankless is about the same. So why even heat the aux tank to being with? I feel like you're not getting how the system works.

For optimal energy savings, have you considered a switch for the recirc pump in the bathroom (possibly with lower small tank temperature)?

Yes, there are many alternate solutions, like a switch in the bathroom or motion sensors. But even with those, there would be a wait for the hot water to circulate upwards. I'd rather just turn on the standby system at 8pm-11pm for demand anytime during those hours.

The loss due to the pump running may be higher than the standby loss of the tank.

No. The pump itself uses a tiny bit of power. Constantly heating the aux tank takes 2kW every 20 minutes to cover the standby losses.

The small heater is only able to raise that at a degree per minute ignoring losses from the pipes. If the tank ran 100% originally with the pump on, then it never put out enough heat to overcome the loss from the pipe run (at 130) so ability to catch up is questionable. But at least it isn't losing ground.

Again, this is not true. The aux tank, with or without the circ pump running can keep up with the loss. If it didn't, it would actually stay on 24x7. You can see in the graph in post #181 the heater cycling on and off when the circ pump was running constantly ..just cycling more frequently than when the circ pump is off.

 

[GatorGuy]

We just moved into this house, and got the first few electric bills over $500, I had to figure out what was going on.

Is that just for electric or water/sewage too??!

 

[HankLloydRight]

Just electric!!

I expect it to be about half that after fixing these things.

 

[mongo]

Hi, sorry if I'm not getting it, thanks for hanging with me.

Long post short: I'm not sure this will save energy and it might give too cool of water to begin with. Insulating the tank, lowing its set point to 120 (below main heater), or adding a heat trap on the aux tank outlet (if it not already there to reduce convention) might be a more effective solution.
You are only one who can judge what trade offs you want in terms of response and electrical usage.

I don't understand what you mean by turning off the element. Yes, I said above when the circ pump and aux tank is off, then there's a short wait for hot water from the tankless water heater. But this is only during the daytime when the demand for quick hot water is very low/none. The entire point of my posts is to explain that when the circ pump is off, heating the aux tank serves no purpose, since the standing water in the pipes is still cold. So the time it takes to get the warm water from the aux tank *or* the hot water from the tankless is about the same. So why even heat the aux tank to being with? I feel like you're not getting how the system works.

Not knowing the actual conditions (set point/ hysteresis, pipe length/ type, blah, blah blah), I'm not sure what the impact will be, but without the tank staying hot, the initial water temp when the circ pump starts will be lower due to pipe and tank mixing. The aux tank element has limited ability to cause a temp rise, so be sure that initial temp is adequate.

Yes, there are many alternate solutions, like a switch in the bathroom or motion sensors. But even with those, there would be a wait for the hot water to circulate upwards. I'd rather just turn on the standby system at 8pm-11pm for demand anytime during those hours.

No. The pump itself uses a tiny bit of power. Constantly heating the aux tank takes 2kW every 20 minutes to cover the standby losses.

Again, this is not true. The aux tank, with or without the circ pump running can keep up with the loss. If it didn't, it would actually stay on 24x7. You can see in the graph in post #181 the heater cycling on and off when the circ pump was running constantly ..just cycling more frequently than when the circ pump is off.

I understand the pump itself is low power, but the aux tank has to replace all the heat loss from the pipes, so the system is inefficient when running circ without water usage. I had thought from earlier post, that the heater did run all the time with the circ on.

The tank is "on" 24x7 which is the source of the spikes I was seeing. But when the circ pump runs, the heater for the aux tank is always on -- constantly warming the water circulating to the upper floors.

If it doesn't, that cuts the estimated power consumption.

With a on/off control to the tank, it very well may run most of the entire 3 hour window (if water usages does not trigger main heater). It will also make up for all the off time by heating the water back up to where it would have been. The reduction in electricity will be based on the drop in differential temperature due to tank cooling.

 

[Max*]

No. The pump itself uses a tiny bit of power. Constantly heating the aux tank takes 2kW every 20 minutes to cover the standby losses.

How long is that spike on for? Are we talking a minute every 20 minutes? Or are we talking 5 minutes every 20 minutes?


I have a tankless system too, I feel the pain of the initial startup. Gotta wait for 10-20 seconds for the hot water to kick on if no one used it for a while.

 

[HankLloydRight]

How long is that spike on for? Are we talking a minute every 20 minutes? Or are we talking 5 minutes every 20 minutes?

see post which started this discussion

Insulating the tank

Yes, I could do that, but it already has internal insulation, not sure how much more would help.

lowing its set point to 120 (below main heater),

Tried that. The result is taking a shower you get relatively hot water for 5 minutes (120 degrees) and then the hotter water (140 degrees) from the tankless heater reaches the shower and it's a shock of much hotter water. I've since reset both to 130 degrees so the transition is a constant temperature.

but the aux tank has to replace all the heat loss from the pipes, so the system is inefficient when running circ without water usage. I had thought from earlier post, that the heater did run all the time with the circ on.

Yes, it has to heat the tank and the water in the pipes. That's why I have the pump (and soon the heater too) on a timer only to turn on when hot water is needed most (actually, maybe an hour before needed).

To clear things up, there are only three modes:

Mode 1: (previous mode): Both Aux tank heater on and circ pump running 24x7. this caused high electric bills since the hot water was circulating hot water all day, even when not needed
Mode 2: (current mode): Aux tank heater on 24x7, circ pump on a morning/evening timer: This keeps the aux tank from heating the pipes when not needed, but does keep the tank itself up to temp by cycling the heater element every 20 minutes for a few minutes. When the circ pump is running, the heating element is mostly "on" all the time.
Mode 3: (future mode): Aux tank AND circ pump on the same timer (via SSR): Water in the aux tank is ONLY heated during the on-demand hours, and not during off-hours. During off-hours, hot water is only delivered by the main tankless hot water heater with a short delay at the faucet.

With a on/off control to the tank, it very well may run most of the entire 3 hour window

see post: Get some Sense...

 

[MP3Mike]

Mode 3: (future mode): Aux tank AND circ pump on the same timer (via SSR): Water in the aux tank is ONLY heated during the on-demand hours, and not during off-hours. During off-hours, hot water is only delivered by the main tankless hot water heater with a short delay at the faucet.

I'm not sure about the "with a short delay at the faucet" part. If the 10 gallon tank of water has cooled down it could take a long time to get hot water to a faucet. (A standard 2GPM faucet could take 5 minutes or more of running water before you actually get hot water.) If there wasn't a tank inline it would be a short delay.

But that all depends on how quickly the tank cools down, but I think you know the answer to that, is that it drops enough in temperature in 20 minutes to trigger the element to turn back on. Maybe a 5 degree drop? So ~4 hours to drop to 70 degrees? Sounds like that thing needs an insulation blanket stat. (And then maybe you wouldn't need to put the tank heater on a timer.)

 

[mongo]

Yes, I could do that, but it already has internal insulation, not sure how much more would help.

Double the insulation would cut the intermediate heating spikes in half (assuming convective loss is not a major issue).

Tried that. The result is taking a shower you get relatively hot water for 5 minutes (120 degrees) and then the hotter water (140 degrees) from the tankless heater reaches the shower and it's a shock of much hotter water. I've since reset both to 130 degrees so the transition is a constant temperature.

Yes, it has to heat the tank and the water in the pipes. That's why I have the pump (and soon the heater too) on a timer only to turn on when hot water is needed most (actually, maybe an hour before needed).

Mode 3: (future mode): Aux tank AND circ pump on the same timer (via SSR): Water in the aux tank is ONLY heated during the on-demand hours, and not during off-hours. During off-hours, hot water is only delivered by the main tankless hot water heater with a short delay at the faucet.

Thanks for this background. My major concern is that the tank will cool during the off period, the circ turns on, the water in the pipes cools the tank off even more, and then there is demand for water before the aux tank has heated things back up. So you could be back to the 120 (or colder) degree water case. (very dependent on aux tank cooling and pipe volume)
If you run the pump for > 30 minutes before needing water it may be mostly recovered. (energy usage may be about the same between keeping the water hot and reheating it, assuming no main water heater input. If it isn't, the tank is cooling way down which may be an issue at circ start.)

see post: Get some Sense...

Yeah I looked at that before my last message and again this time but couldn't see continuous/ longer aux draw. Isn't the circ usage after the 20 (assuming 8pm) mark?

 

[Max*]

see post which started this discussion

Seriously? The post that started this discussion has the scale in hours, not minutes. I can't tell if the thing is on for 5 minutes or 1 minute, or 30 seconds. I also can't tell at what rate your tool is sampling either. Both of these are pretty important to determine your potential savings, assuming you'll have any at all after you turn it off and then need to warm up the tank again.

I don't have Sense, I'm trying to make sense myself

I've identified most large energy sinks in my house, but I'm looking for suggestions on what people think this might be -- drawing about 2kW roughly every 20 minutes. We have gas heat and hot water, so that's not it. It could be the refrigerator, but I didn't think they pull 2kW.

All you said is it pulls 2kw about every 20minutes. But you never listed the duration.

If it's pulling 2kw for 1 minute every 20 minutes, you're spending <$15/month on this thing. While sure, that's money wasted, but the savings might not be as great as you think.
Whereas if it's pulling that 2kw for 5 minutes every 20 minutes, that's a different story.


You know what, it doesn't matter, just carry on. You're going to save a TOOOON of money by doing these 3 simple steps! Want more info, please click here

 

[HankLloydRight]

I'm not sure about the "with a short delay at the faucet" part. If the 10 gallon tank of water has cooled down it could take a long time to get hot water to a faucet. (

That's not how it's plumbed. Both the aux tank and tankless feed the main hot water supply. The tankless doesn't feed the aux tank and then to the main hot supply line. I could post a photo of the whole system, but that would just lead to more questions and confusion. The bottom line is I found the culprit causing the 20 minutes spikes. I'm going to get a $20 SSR and turn the aux tank off with the circ pump on the timer. Then I'm going to see how that affects demand during the day. If that doesn't work, I'll try something else.

All you said is it pulls 2kw about every 20minutes. But you never listed the duration.

Here's the graph expanded:

Shutting down the heater during off-hours won't change the experience much, as the pipes are cold already (no circ pump running), and instant hot water would be delivered on-demand, as it is now. So shutting down the heater and not having these spikes might only save a little energy, but keep the tank heated when it's not even needed?

 

[mongo]

That's not how it's plumbed. Both the aux tank and tankless feed the main hot water supply. The tankless doesn't feed the aux tank and then to the main hot supply line.

You have no obligation to us net critters, but a pic might really help.
If the tankless does not feed the aux, how are you avoiding the tankless cold water slug issue mentioned in the article you previously linked?

Do both the aux and tankless have cold water feeds that then tee together?

I'm going to get a $20 SSR and turn the aux tank off with the circ pump on the timer. Then I'm going to see how that affects demand during the day. If that doesn't work, I'll try something else.

That's why I suggested the $20 15A smart outlet (instead of relay/ SSR (and I do recommend the relay you poster over an SSR)), you can schedule it to be the same as the pump, staggered, or anything else.

Shutting down the heater during off-hours won't change the experience much, as the pipes are cold already (no circ pump running), and instant hot water would be delivered on-demand, as it is now. So shutting down the heater and not having these spikes might only save a little energy, but keep the tank heated when it's not even needed?

Agreed, but during the early time of the circ of mode of operation, a colder aux tank will have colder water in the pipes.

 

[HankLloydRight]

If the tankless does not feed the aux, how are you avoiding the tankless cold water slug issue mentioned in the article you previously linked?

The tankless output and the aux output both Tee into the main hot water line. The tankless output ALSO goes into the input of the aux tank. So if water is demanded and the circ pump/heater aren't running, hot water is only drawn from the tankless (the circ pump pumps return water into the tankless, so if that's off, there's no flow through the aux tank and only the tankless). In theory the water in the pipes and the slug are the same cooling temp.

That's why I suggested the $20 15A smart outlet (instead of relay/ SSR (and I do recommend the relay you poster over an SSR)), you can schedule it to be the same as the pump, staggered, or anything else.

But I want them on the exact same schedule. No need to maintain two different switches/schedules. The relay accomplishes this without added complexity.

 

[mongo]

The tankless output and the aux output both Tee into the main hot water line. The tankless output ALSO goes into the input of the aux tank. So if water is demanded and the circ pump/heater aren't running, hot water is only drawn from the tankless (the circ pump pumps return water into the tankless, so if that's off, there's no flow through the aux tank and only the tankless). In theory the water in the pipes and the slug are the same cooling temp.

I am so lost, unless you meant to say the pump returns to the aux tank...

Realizing you just bought this house, any idea why the aux isn't in series with the instant unit (with pump returning to their union)?

But I want them on the exact same schedule. No need to maintain two different switches/schedules. The relay accomplishes this without added complexity.

No idea on how hard they are to setup (DST and such), I thought using the outlet plus a plug and socket might be easier.

 

[HankLloydRight]

I am so lost, unless you meant to say the pump returns to the aux tank...

You are correct, I mean the circ pump returns to the aux tank. Sorry.

Realizing you just bought this house, any idea why the aux isn't in series with the instant unit (with pump returning to their union)?

I believe it's plumbed exactly as indicated in the article I posted. There are valves to adjust the flows between the pump, aux and tankless. In a perfect world where the circ pump and aux tank can run non-stop, yes it should be in series with the tankless. In this case, I'm glad it's not so I can create other flows and plans.

No idea on how hard they are to setup (DST and such), I thought using the outlet plus a plug and socket might be easier.

The switch is simple to install as any SPST light switch. The aux tank is hard-wired in, so I'd have to install an outlet box, outlet, and plug on the tank, and then use a smart outlet in addition to the smart switch I already have, and create two identical schedules. The scheduling for the switch is done on the smartphone and in the cloud, so it knows about DST and with the relay (takes 2 minutes to install), operates on the same schedule.

 

[mongo]

You are correct, I mean the circ pump returns to the aux tank. Sorry.

No problem, thank you for explaining the system, it is a interesting approach.

I believe it's plumbed exactly as indicated in the article I posted. There are valves to adjust the flows between the pump, aux and tankless. In a perfect world where the circ pump and aux tank can run non-stop, yes it should be in series with the tankless. In this case, I'm glad it's not so I can create other flows and plans.

Gotcha, the valve set up the primary flow paths for the different modes via adjustable flow restriction.

The switch is simple to install as any SPST light switch. The aux tank is hard-wired in, so I'd have to install an outlet box, outlet, and plug on the tank, and then use a smart outlet in addition to the smart switch I already have, and create two identical schedules. The scheduling for the switch is done on the smartphone and in the cloud, so it knows about DST and with the relay (takes 2 minutes to install), operates on the same schedule.

I see, instead you can tuck the relay into the existing wiring space and use some flexible conduit for the 120V control line?

I hope you update us on what the results of the change are.

 

[dhanson865]

Over the weekend it's now detected:
1. fridge
2. fridge light
3. garage door opener (1/4)
4. heat pump
And some other stuff

there are now so many devices it doesn't fit in a screen shot, but it's learning.

I learned that lights in my fridge are 3x40 watts = 119 watts showing on Sense... almost as much as running the fridge!

I replaced my 40w refrigerator lights with 6w LED bulbs from Lowes. Nothing fancy, just the $1.50 utilitech non dimmable LED bulb(s). In my case it's 1 for the freezer section and 1 for refrigerator section.

They don't run often so it's not much of a saving on electricity directly but less heat into the cooled space, I figure it's worth doing.

 

[mongo]

I replaced my 40w refrigerator lights with 6w LED bulbs from Lowes. Nothing fancy, just the $1.50 utilitech non dimmable LED bulb(s). In my case it's 1 for the freezer section and 1 for refrigerator section.

They don't run often so it's not much of a saving on electricity directly but less heat into the cooled space, I figure it's worth doing.

Especially worth it when the door is accidentally left ajar (and the fridge doesn't have a light timeout).

 

[GatorGuy]

Just electric!!

I expect it to be about half that after fixing these things.

Yikes. My whole utility bill for a 4600 Sq ft house is less 75% of that.