Dual Eternal Tankless Installed Correctly?

[rfco81]

Hello-

This is directed at anyone who has experience installing the Grand Hall Eternal Tankless water heaters in a dual (or more) unit installation where two or more units are installed and using the BUS connection to communicate production based on demand.

I had these two units installed in my home three months ago by a local "reputable" plumbing company. Unfortunately the install was flawed from the beginning because they sent out plumbers who were inexperienced with installing these in dual configuration. The first round of problems came from them not knowing how to put it into multi-unit mode, then they broke a pin on a board which had to be replaced. Once they got htat done and the multi-unit configuration on the dip switches set, things seem to have been ok. I have noticed though the 'sandwich' effect every so often and sort of randomly since the units were installed.

We run these at 130f which should be hot enough to burn and not tolerate holding my hand under the water. While it gets close to being that hot, it's still not as hot as I would expect.

This evening I was in the utility room and decided to do some laymens testing to see if things were working. What I noticed was: The output line on the 1st unit was nice and warm, where the output line on the 2nd unit was luke-warm at best. The way the piping is setup, the 2nd unit's output line connects up with the 1st unit's and they blend the water out to the main feed to the mana-bloc.

I've included some photos below. The plumbing company swears they are hooked up properly because we can turn on tons of faucets in the house and they do lose pressure but not too much. I'm hoping someone can just tell me it's normal for the 2nd unit's output line to feel luke-warm while the main unit is nice and hot but I have a feeling something is wrong because I looked at the installation manual and it mentions a recirculation pump, which does not exist in my world presently.

Thoughts?? Thanks so much to anyone with some helpful advice on these things.

Images:

Unit#1 (Master)

Unit #2

Both Units Side by Side

-Ryan

 

[havasu]

I'm just wondering why the dual set up? How big is this house? What climate are you in?

 

[rfco81]

The house is 5,000sq ft 3 levels wth 5.75 bathrooms , I am in the Denver metro so we swing between fairly warm in the summer to mild and somewhat cold in the winter. I purchased the home in April of this year and it had a generic (contractor grade?) unit installed that was way under-capacity - could barely take 1 shower without having the sandwich effect throughout the entire shower. I told the plumbing company that I wanted to have the ability for at least two or three showers plus maybe a load of laundry to be going at once without losing pressure or having the sandwich of cold water in there.

They said the way to accomplish that was to have two of these units installed, so I did. I'm not entirely convinced on their competency level with installing these things (the installers were mystified at the "networked" setup of these units for one) and although I'm and IT guy and nowhere near the skill level of a plumber, common sense tells me if luke-warm water is coming from one unit and mixing directly with the very hot water from the 1st unit, something isn't quite right?

Thanks!
-Ryan

 

[havasu]

Yeah, I myself can't understand that with such an elaborate set up, a return line wasn't also built into the system with a recirc pump. Since I am not familiar with your units, I believe your best bet would be to call the manufacturer and ask them personally, because you are correct, something just doesn't seem correct. It may be as simple as flipping a few switches on the control boards of the units.

I also know on tanked dual water heaters, the hot outlet of one unit goes into the cold of the second unit, but not exactly know how a tankless system would work. I do see an obvious lack of hot water pipe wrap, which I surely hope has been corrected since these pictures have been taken.

 

[IFIXH20]

Turn off power to unit 1 -- open a couple fixtures to see if unit 2 is working properly or close the red handle shutoff valve above unit 1, then open fixtures to test unit 2 .
You could have a flow sensor problem. I would also check with the manufacturer to make sure it is ok to have the expanison tank on the hot side of the system

 

[Beni]

AH... I know this one.

One side of the heaters is piped in series while the other side is piped in parallel. With dual water heaters you want both inlets and both outlets to be piped the same, either series actually called reverse return with the inlet feeding from one side and outlets feeding to the other, or with parallel with both heaters feed from the middle with balanced piping sizes and lengths to each heater.

So looking at the "both heaters side by side" photo, what your want to do is remove the front parallel piping after the vertical valve and starting from the left heater with pipe up ell right to tee at right unit and continue past tee at right unit and reconnect to the vertical valve connection (by the pex piping). Can't tell if that is supply or discharge, but based on the expansion tank and the 1/4" branch above the center tee is probably the supply.

As its piped, the left hand unit always sees more flow rate as it has the less pressure drop thru it. The right hand unit see's less flow rate. Weird that the right hand unit has a valve in the connection, yet the left does not.

Reverse return is a whole lot easier to pipe and get right BTW. It works for more then 2 heaters in series too.

Good luck

Beni Bacon PE, CIPE

 

[IFIXH20]

AH... I know this one.

One side of the heaters is piped in series while the other side is piped in parallel. With dual water heaters you want both inlets and both outlets to be piped the same, either series actually called reverse return with the inlet feeding from one side and outlets feeding to the other, or with parallel with both heaters feed from the middle with balanced piping sizes and lengths to each heater.

So looking at the "both heaters side by side" photo, what your want to do is remove the front parallel piping after the vertical valve and starting from the left heater with pipe up ell right to tee at right unit and continue past tee at right unit and reconnect to the vertical valve connection (by the pex piping). Can't tell if that is supply or discharge, but based on the expansion tank and the 1/4" branch above the center tee is probably the supply.

As its piped, the left hand unit always sees more flow rate as it has the less pressure drop thru it. The right hand unit see's less flow rate. Weird that the right hand unit has a valve in the connection, yet the left does not.

Reverse return is a whole lot easier to pipe and get right BTW. It works for more then 2 heaters in series too.

Good luck

Beni Bacon PE, CIPE

If i am not mistaken the water heaters are pipe parallel and expanison tank is on the hot side of the system

 

[rfco81]

Great info and advice everyone - thank you. I am going to try isolating the second unit this morning and see what the results are then it sounds like a call to Grand Hall is the next step to see what they have to say about the setup. I think from everyone's input on this post that my suspicions of it not being 'quite right' are being confirmed. I'll update the thread when I get an answer from the mfr. And to answer one of the questions in the thread - there is no wrap on the piping - those pics were taken only a couple of days ago on 9/24. I'm surprised our city code inspector didn't call them out on that - they sure did on a lot of other things!

 

[Beni]

If i am not mistaken the water heaters are pipe parallel and expanison tank is on the hot side of the system

Yes they are pipe parallel, but the the inlet and outlet piping is not balanced. That is the piping is not the same configuration with unequal lengths of piping between the inlet piping and outlet piping. This causes unbalanced flow between the heaters.

From a hydraulic standpoint with unbalanced piping, one heater will always work harder then the other and the full recovery/ output will not be obtained. I've seen this in commercial installations too. Though never for the ones I've designed ;-).

Generally while true balanced parallel piping works fine, a reverse return (where the inlet and outlet piping feed 180 degrees apart, is much more forgiving and is much easier to balance.

A direct return piping where the inlet and outlets feed from the same side is also imbalanced and should be avoided where two or more heaters are installed. (Just FYI)

Good engineering practice is to place the expansion tank on the cold water side. Its easier on the rubber diaphragm in the long run.

Beni Bacon, PE, CIPE

 

[Beni]

I'm surprised our city code inspector didn't call them out on that - they sure did on a lot of other things!

Oddly enough it's not really addressed in the plumbing codes. Though sometimes its in the appendix's. It gets missed many a times. The manufactures data might have a diagram for parallel heater installations, but who reads instructions.

Its not all that uncommon to see. Alas, many an engineer would miss that too..

Here's a link showing a typical reverse return parallel piping:
http://www.waterheaterrescue.com/pages/WHRpages/English/Troubleshooting/lingopages/in-parallel.html

Beni Bacon PE, CIPE

 

[phishfood]

What is this reverse return of which you speak?

I have an install of dual tankless high capacity heaters coming up at some point, and don't want to showcase my ignorance by screwing it up.

 

[IFIXH20]

What is this reverse return of which you speak?

I have an install of dual tankless high capacity heaters coming up at some point, and don't want to showcase my ignorance by screwing it up.

reverse return is the way you pipe cold & hot water lines to the water heaters - reverse return lesson friction and help with balancing the system meaning Reverse Return system will work together better --- Direct Return system, one unit will work a little harder, that is why manufacturer recommend having temp controls set different on Direct Return piping systems.
direct return piping = first in first out
reverse return piping = last in first out
Reverse return only applies to multi water heater installation.
hope this make sense -- engineering mumbo jumbo

 

[Beni]

reverse return is the way you pipe cold & hot water lines to the water heaters - reverse return lesson friction and help with balancing the system meaning Reverse Return system will work together better --- Direct Return system, one unit will work a little harder, that is why manufacturer recommend having temp controls set different on Direct Return piping systems.
direct return piping = first in first out
reverse return piping = last in first out
Reverse return only applies to multi water heater installation.
hope this make sense -- engineering mumbo jumbo

Ah, Great way of explaining it. Much clearer then my mumbo jumbo for sure..

The key is that the supply and return lengths are exactly the same for each heater back to the point of connection on the distribution piping. That way the pressure drop is the same to each heater and the flows balance, and life is good.

The reverse return arrangement works for any number of heaters or hydronic boilers in series.

 

[phishfood]

Do I have it right in this sketch?

 

[Beni]

Yes, the top is what I call a balanced piping arrangement, which works well for two units, but gets overly complicated with three or more units.

The lower sketch is the reverse return. It uses two fewer elbows and works even for 6 units in line.

Its important in either configuration to use the same type and size fittings and valves for each heater. Adding an extra fitting or valve to one and not the other effects the flow hydraulics.

The photo from the original poster shows how exactly not to do it. The installer did one side like the top sketch and the other side like the lower sketch. It results in a unbalanced flow where one heater works harder. Sometimes doing all the work.