On-demand circulation

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jrogers99

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Hello all! I'm excited to have found this forum! I have attached what my setup looks like for a visual. I don't have a timer or an aquastat but I'm trying to circulate my hot water with my two tankless heaters. The loop in the diagram is about 160' of 1" Pex-a around the house. I have a Grundfos Alpha2 right on the outlet of the second water heater pushing water the 160' around. It's a 2 story house and I have to pump it up about 21' from lowest to highest point which I'm not sure matters when it's a closed system? Obviously when water is demanded it's an open system but the house pressure takes over.

Anyway....I set the pump on any speed and it registers 1 gpm but it doesn't kick on either Tempra water heater. They're plumbed just like in the pic attached. Is it because the Alpha2 has a head height of only 16' or so? Do I need a pump that moves faster? I'm getting ready to move back into the house after a full remodel and I want this system to start moving hot water around the "loop". I think I should probably add a timer too. Thank you for any ideas on how to get this going!!! I'm sure I'm just missing something!
 

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breplum

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do you have a way to purge air from both sides of your pump?
You are likely air locked.
You are correct, the pump size should make no difference.
Of course you should have a timer.
Can't your plumber help you?
 

jrogers99

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breplum...thanks for the response. I am the plumber...unfortunately. But...I just plumbed a six bathroom house so I'm on a roll! Anyway, I had read something about air lock but don't know enough about it. I read that you could put a relief valve or something of that nature into the line. The pump is on there with a ball valve on the inlet and outlet so it can be replaced at any point. Any thoughts on getting rid of air? Out of the whole country....I can't believe you're in Lafayette and I'm in Danville! Thank you again!
 

breplum

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The addition of tees with hose bibbs between the ball valves and the pump.
Both sides.
Then you can use a short hose (typically we carry washing machine hoses for this) and purge into a bucket.
You must have solar p.v. if you have electric water heaters.
 

breplum

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If your mechanical space is concrete, you could loosen the flange and let air/water spurt out, but that is a mess and not nice for the pump
 
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jrogers99

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I did a little research and found that this pump is self-venting and there is zero noise in the system. I just can't seem to get the flow to kick it on. The Tempra model comes on at a minimum flow of .5 gpm which technically should be activated with the Grundfos showing movement at 1 GPM.
 

breplum

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Do you have internal check valves ? Could they/one be hung up?
BTW, the white plastic internal check valves Grundfos makes, break down with the chloramine and hot water and fail after a couple of years.
Be prepared to add in-line check valve.
That self-venting is interesting but may not be enough unless you wait?
 

Diehard

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Just tossing out the following if it is found not to be an air lock issue.

As you said and @breplum confirmed, pump size should not make any difference in a closed system, as far as height is concerned. What would affect the flow rate would be the pressure loss. But with 1" tubing, pressure loss should be minimal. [Something like 0.1 psi(about 1/4 foot of head) per 100 feet at 1 GPM. Or 0.3 psi(about 3/4 foot of head) at 2 GPM per 100 feet. If we estimated a total of 300 feet with losses for fitting, that would still only be a couple of feet of head loss or less.]

Now the head loss can some times be substantial through those tankless units. I didn't look for what it is through a Tempra 20.
But what troubles me is the fact that, from the sounds of it, you have a multiple speed circulator and the flow rate never changed. Almost like you have a flow restriction somewhere.

Now another thought is the fact that those water heaters don't kick on until they reach a least 0.5 gpm. So if you are, in fact flowing at 1 gpm it should be kicking on.

I know those tankless units can be pretty sophisticated. I would pass it by the manufacturer of those water heaters. Don't mention that you are not a plumber.

May I assume you had those heaters running without the recirculation loop?
 

jrogers99

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Thank you Diehard & breplum! I did install a 400 amp service to the house and put on a PV array and yes, that's why I'm using electric...dual electric at that just for the volume (4 kids). So the Grundfos Alpha2 does have an autoadapt feature but also a "set" feature so I've put the unit to run continuously on the lowest speed. I've actually tried all the speeds but the lowest would seem to be the best to try. I didn't use the grundfos check valves and put in direct inline 1" ones in the PEX line just as my original diagram showed. At all faucets in the house I get full water and the Tempra tankless shows the GPM I'm demanding. When I open another faucet, it shows higher GPM as I open more taps as the two tanks adjust for volume. So, my flow seems to be great. I could purchase another pump with higher head pressure, more push, etc. but as Diehard calculated (and as I assumed) that shouldn't be the problem. I know I'm just missing something and I'm appreciating any and all suggestions. Thank you!
 

jrogers99

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Do you have internal check valves ? Could they/one be hung up?
BTW, the white plastic internal check valves Grundfos makes, break down with the chloramine and hot water and fail after a couple of years.
Be prepared to add in-line check valve.
That self-venting is interesting but may not be enough unless you wait?
In order to vent if needed you just run the pump on the speed of III and it purges.
 

jrogers99

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Just tossing out the following if it is found not to be an air lock issue.

As you said and @breplum confirmed, pump size should not make any difference in a closed system, as far as height is concerned. What would affect the flow rate would be the pressure loss. But with 1" tubing, pressure loss should be minimal. [Something like 0.1 psi(about 1/4 foot of head) per 100 feet at 1 GPM. Or 0.3 psi(about 3/4 foot of head) at 2 GPM per 100 feet. If we estimated a total of 300 feet with losses for fitting, that would still only be a couple of feet of head loss or less.]

Now the head loss can some times be substantial through those tankless units. I didn't look for what it is through a Tempra 20.
But what troubles me is the fact that, from the sounds of it, you have a multiple speed circulator and the flow rate never changed. Almost like you have a flow restriction somewhere.

Now another thought is the fact that those water heaters don't kick on until they reach a least 0.5 gpm. So if you are, in fact flowing at 1 gpm it should be kicking on.

I know those tankless units can be pretty sophisticated. I would pass it by the manufacturer of those water heaters. Don't mention that you are not a plumber.

May I assume you had those heaters running without the recirculation loop?
The diagram that I posted in the original post was actually given to me by the manufacturer who is working with me and says I shouldn't need a small tank heater to jumpstart and my setup is fine and the 1" PEX line is smart to overcome pressure loss and should work beautifully!
 

Diehard

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You say, you set the pump on any speed and it registers 1 gpm. I take that as meaning you had it at the highest speed and it still only registers 1 gpm. Granted the heater should kick in at 0.5 gpm but it's very strange if the gpm never changes with the different speeds. Which Grundfos Alpha2 model do you have? The 15-55?
I'm not totally familiar with the controlling features of this pump but looking at the curves shows that at the lowest speed, the pump is only capable of 3 feet of head. What happens when you set it for "High constant speed"?

Did the manufacturer of the heater mention, or does their literature state, what their pressure loss is through their unit?

Do you realize that 100 feet of that tubing holds about 3 gallons of water and at 1 gpm that equates to about 3 minutes. That would make that 1 gpm a bit slow, I would think.

Another thing I just realized is, the circulator is on the line feeding the fixtures rather than on the return. Which means every bit of hot water use at the fixtures must go through the circulator. Running or not. ???

Another thought...with a closed recirc loop subject to changing temperatures, why don't they recommend an expansion tank?
 

jrogers99

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Yes, any speed registers 1gpm. It's the 15-55 (actual pic of it below). I bought it for the Auto adapt feature which I'm now realizing doesn't work for this setup. No matter which of the 3 speeds it's on...gpm doesn't change. I do hear the pump making the change in speed.

The manufacturer did say that I may need a booster pump because I'd probably lose between 15-20 psi through each unit. The pressure seems to be fine. The house has great water pressure and I have it set right now a bit high to overcome that pressure loss (~70psi) and still get good pressure with multiple faucets on.
The reason behind the 1" line was thinking about volume needed with, say, 3 showers on simultaneously. I do think that makes the 1 GPM slow and that is still my thought. I just don't want to randomly go changing the pump even though I'm thinking that is the next step and get one that has a 30' head for instance which would, I think by default, give me better pressure.

Tempra didn't recommend an expansion tank and essentially said, which I understand, just make sure the activation speed of the pump is greater than the activation speed of the Tempra (.5gpm). As I'm writing this email I'm thinking that since I have two Tempra's does that mean I have to overcome .5 gpm per unit for a total of 1 gpm? In that case maybe I do need a more powerful pump. They said the expansion tank wasn't necessary in this setup because of the size of my recirc line.

And yes, as the 1" pex is run around the house (which I estimate the full loop is about 180-200' it has 1/2" pex lines off of it to each fixture. The line is run around the house to be ~within 5-10' from each "outlet" whether it be a shower, sink, etc.

My thought was the 1" line stays circulating around and as water is demanded at a fixture, the hot water will only be a few feet from each fixture.

I'm on the search for another grundfos with "more power" that may overcome the start issue. Any recommendations (Grundfos, Taco, etc) are definitely welcome in addition to what the problem truly is!! Thank you!
 

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Diehard

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Yes it does sound like you need a more powerful pump. Particularly if the head loss is fairly high through the tankless unit. The trouble is, you shouldn't have to go buy a different size pump not knowing the approximate size you need. You should have a better idea what your total head loss will be, at a particular flow.

For the manufacturer to say that you may need a booster pump because you'd probably lose between 15-20 psi through each unit is useless information without the flow values. He's probably talking about pressure loss when water is being used at or near the rated capacity of the units and not at the flow of the recirculation system.
You say you have great pressure. When you say you have it set to overcome that pressure loss (~70psi), is 70psi the cold water pressure setting or is that the loss you are overcoming? Just curious.

Are you somewhat familiar with reading pump performance curves. In brief, a pump can only pump at a flow and pressure, at a point on one of those curves.
A system curve, which a designer would plot or consider, is based on the piping systems pressure losses at various flows and would run from bottom left to upper right. Where it intersects with the pumps performance curve is what the pumps actual flow and pressure would be.
So if you look at the curves below,which represent 3 different pump speeds, you can see that if that pump was, in fact, pumping 1 gpm it would have had to be at a pressure of 3 ft for the slowest speed, about 7.5 ft the 2nd speed and around 18 ft for the fastest speed.
Now just as an example, I've plotted a sample system curve(in red) representing pressure losses through a piping system. As the flow through the system increases, the pressure loss increase. And where those curves intersect is what the actual flow vs head pressure the pump would be pumping.

Sorry if this is too much to digest but I had to give you an idea of how it works

Grudfos Alpha2 15-55.jpg
 

Diehard

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How does that series arrangement work?
Is the first unit set at a lower temperature than the second?
I would have thought, particularly since you wanted to get plenty of flow, that they would have been set up in a parallel arrangement.

EDIT: Looking back at the comments you said,
"As I'm writing this email I'm thinking that since I have two Tempra's does that mean I have to overcome .5 gpm per unit for a total of 1 gpm?" Being in series, each unit would be seeing the same flow rate. Also, the recirc loop flow is only going through one unit.

EDIT: Regarding that circulator showing only 1 gpm at every one of the 3 speeds, I would ask Grudfos if that made and sense or if they had any idea what would cause that. Can't hurt.
 
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jrogers99

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Hey there....I can read a curve as I used to do quite a few calculations building a few koi ponds with waterfalls, etc. So, I do understand the relationship between pressure, head height to overcome, etc. I don't understand it perfectly but understand it enough to know that somewhere in that equation is my problem. I am running a lot of volume in the 1" pex line. The way the Tempra's are setup is as follows....the first unit is set at a lower temp than the second. Then, when the second gets a hold of it (where the loop is) it is only heating the water a bit so it can run more volume. Then, as more volume is demanded as in a multiple shower arrangement, more water will be pulled through the first and get "preheated".

The 70 psi is where I have the incoming water pressure set at. I could have it at 100 psi but that's hard on the joints. I may raise it a bit because I am losing some of that pressure through the Tempra's in the hot line.

I like the ideaq of asking Grundfos what they think. I haven't done that yet and I will now and will let you know what they think. Thanks!
 

Diehard

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Sounds good.
Keep in mind that the house water pressure is strictly to satisfy your needs for water volume and pressure and has nothing to do with the circulation loop.

Be sure to let us know if you find out anything from Grudfos. You may get lucky and get to talk to someone with experience.
If possible try to speak with engineering.

Oh yeah...and try to find out the pressure drop through those tankless units AT A SPECIFIC GPM. The lower the GPM the better but we can always estimate it if we have something to work with.
 
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