Tank less question

icy78

Hello all I have a question on a rheem tankless RTGH-95DVLN. Issue is p1 codes. The p1 code is insufficient flow. However with a digital gauge I am seeing 4.4 GPM on pump curve on a closed loop heating system, yet I still get a p1 occasionally. Any input on this? Bad sensor maybe? I suspect this is calculated through temperature rise through the heater?Any suggestions welcome. Thank you. Tech support could only tell me to change the filter. Yup.

icy78

Let me put this a different way. Is there a way I can measure 28fthd across the pump but its actually not moving water? Taco 0011-F4. In other words , can you measure a differencial but the pump is actually deadheading?

Zman

You have discovered one of the differences between a boiler and a hot water heater. The high resistance of the water heater is OK with 60 psi of domestic water against it, not so good in a heating system.
Yes, I believe a deadheaded circ will show a pressure drop. It is still converting energy after all. In any event, you should not operate any circ that far from the center of it's curve. It wastes energy and greatly shortens the circs life.
I am guessing this is not piped primary/secondary? Do you have a sketch?

icy78

Here it is. Is this a misapplication?

Zman

Using a water heater as a boiler is a misapplication. Your drawing does not show circulators for each mixed zone. Do you have them?
If you can find pressure drop Data for the water heater, you can determine proper pump size for the application. In a quick search I was unable to locate one.

icy78

Not my install. But our co. did it! Boiler was nixed as too expensive by the owner. I don't know the research/sizing that went into this if any. However it is my problem now and I don't want to bandaid it, I want to do it right and I want to lay it out to the install crew or whoever how this needs to be done correctly. There is some type of memories stop valve to set flows for each coil and all the coils where verified as warming on startup a couple years ago there have been no issues until recently. The last thing to happen was we had lost two pumps on this system which appears to be from the high head and running on the wrong side of the curve, so I was asked to go look at this system and I found air in the system, and no bleaders so I had them put in the Honeywell micro bubble separator and move the tank and the fill to where you see them now on the drawing. Each heating coil has a 3 way valve and all the zones heat together and/or separately. I am an R guy mostly, that is taking on this kind of service call, because I want our company to improve, not bandaid. SO I am really appreciative of you responding. More data. 12 psi system pressure. 61ftHD discharge and 33 ftHD suction. Two zones heating at the time verified by temp rise.

Zman

If that is the only circ in the system it is doing a whole lot of work. The mixing valves and whatever balancing valves that are downstream are adding to the problem.

Operating that far up on the curve is absolutely causing the premature pump failures. It may have always run that way and may not be your immediate problem. If it is moving 4.4 GPM at 30 degree delta, that would be 66,000 Btu/hr.

I don't know that model but would venture to guess that the water heater has a flow switch tells it to heat. I would start troubleshooting there.

icy78

Thanks Zman. I agree. I spent an hour earlier this evening trying to find Rheem data. No luck. Salesman will be in Thursday, we'll ask him. Apparently he ok'd this useage. Found lots of info on Rinnai and others so its fusstrating that Rheem is so secretive.

icy78

Well no new info from anyone who installed this so I went back to the site. HERE'S what I see.

Taco 0011 circ.
1" piping to 6 zones with 3-way valves
Verified piped right and 3 ways are correct.

28fthd on circ.
DeltaP on heater alone is 25fthd.

Shows occasional low flow.

Heater audibly ramps up and down with me manipulating a ball valve for varying flows.

So: I throttled the valves on both sides of the circ to obtain 23fthd. It runs longer and low flow is no longer shown. Pump curve shows 10 gpm at that head and the point is now closer to the middle of the curve. But with inlet and outlet throttled, is that a good number?
However now I'm short of flow thru a couple of coils. Probably needs balancing.

Another thing. The 3-way valves have a 1.9cv. I know that means 1.9 gpm at 1 psi drop. But how do I measure that drop AND is that maybe too high a cv. I did find out that this heater can do 9.75 gpm at 16ft deltaP. I'm just thinking tho that they are referring to a 60 psi inlet pressure ala domestic hot water. Not about 25 psi in this closed boiler loop.

Im confused.

Zman

This one is pretty hard to follow.

According to your drawing, you would have no flow through the coils. There must be a balancing valve that is not shown.
I don't understand how throttling the circ valves is increasing flow. Or are you opening a balancing valve of some sort?

The data you have on boiler is helpful. That is pretty high resistance but workable.

The 1.9 cv number is a tough one. A valve like that is not designed for a heating system.

Maybe you could verify the piping diagram and include these valves. Pictures always help.

icy78

(For some reason I cant do pics). My drawing is wrong. It shows the supply looping into the return. It does not do that. There are BV s on each coil and bypass. I have made enough disturbance at work about it now that engineering is looking at the 3-ways ,because I noticed that if I throtled the pump down a BIT, I would lose flow thru the coils. Thanks for your input. I will update when I have new info.

icy78

Well after doing some reading and pondering what you all have commented, I say the whole install is messed up. It should've been P/S and the Cv of the valves is too low. At work I have said that to treat the customer right we need to eat the cost of doing it right. The company is certainly big enough to do this and not notice the cost. I guess I'll see what happens. It's a tough spot to be in , where as a tech I know my company (that i work for) did it wrong and I have to cover it up somehow. That's not going to work for me I'm thinking.

hot_rod

If you want to stay with that "heater", a separator or better yet a small buffer tank, with all those zones, would clean up the piping and flows.

Size the boiler circulator to get the best performance through it, and the distribution circulator, maybe a delta P for that side.