New Radiant System Install Flow Rate Troubleshooting

SuperTech

Ditch the heat trap nipples, or pipe into the drain valve. I believe @hot_rod and @HomerJSmith are both correct. 

diyinstaller

Ta-daaaa:



Now the question is whether the perforated end causes enough pressure drop. I'll cut it off, reinstall, and remove the heat trap diaphragm washer I found on the hot side which appears to be something like this:
source: http://waterheatertimer.org/New-water-heater-making-noise.html


There was no heat trap mechanism found on the cold side.

HomerJSmith

I know you're an engineer and over think things.

I'm reminded of an engineer joke.--Two engineers were talking and one engineer said, "Where'd you get the new bike?" The other engineer said, " A woman rode up on a bike, ripped open her blouse and said, "Take what you want.", So I took the bike." The other engineer said, "Good Choice."

Drain the tank and flush it out and re-pipe the return to the drain. Do it! Do it for my sake, I have a 100 dollars riding on it.

diyinstaller

Good news: problem solved. Trimming the end of the dip tube and probably a little help from removing the heat trap washer on the hot outlet got me up to 3gpm at max circulator speed. Basically the same flow I measured when I bypassed the water heater .
I left the pex lined nipples, there didn't seem to be any obstruction in those as the heat trap function was provided by the washer I removed. The U-shaped routing on my connectors and significant length of vertical pipe coming out of my walls shall suffice as a heat trap.

HomerJSmith

Bad news, I'm out 100 bucks, but I was right about the dip tube.

Good job!

HomerJSmith

Here's something to think about.

The return from the HX goes into the cold water line above the tank. The thermostatic mixing valve depends on a temperature differential to function properly. You probably have hot water coming from the HX at the connection to the mixing valve.

Could that create a problem with the mixing? Inquiring minds want to know.

diyinstaller

If I had to do this over I would probably pipe directly to the drain, and you're right that would have solved it. Since all my plumbing was already routed to the cold inlet I decided to see if I could get that to work first. Since I'm getting the same flow rate as when I bypassed the heater completely I don't think I'll need to do much more.

I understand the overthinking stereotype, but good engineers think just enough to get the job done quickly and with success and can balance overthinking against knowing when to just get their hands dirty to find the answer.

One of the tip offs was yesterday evening after installing the pressure gauge right after the HX outlet. I noticed the pressure would vary almost 5 psi as I turned up the circulator. Theoretically there shouldn't be much hydraulic resistance between the outlet of the HX and the water heater. Thought about it more this morning before I started working on it. This made me think the issue was downstream of the HX and could be the water heater itself. Then I thought that maybe I should bypass the water heater first, especially since that was a pretty easy amount of work took me less than 5 minutes including digging the 3/4" nipple out of a bag of irrigation plumbing I had in the shed. Then it was a matter of some google sleuthing to learn about water heater dip tubes and I was off to the races.

diyinstaller

@HomerJSmith
I think you're on to something. I should probably tee the return in after the tempering valve tap.

I have to think more about what happens when a hot water tap is opened. What I do know is that yesterday I saw the flow meter go to zero when somebody opened a hot water tap in the house. If that's the case, there is no flow through the heating system when hot water is running and the tempering valve should only mix pure cold water. I just checked again and when the hot water turns on the flow reduced by about 0.5gpm Yesterday it must have gone to zero because my flow rate was so low in the first place. What this means to the heating system performance when hot water is on is something I have to figure out.

Since I plumbed my return upstream of the tempering valve I'll probably be mixing in hot water instead of cold when the heating system is running. Worst case is that the water is warmer than intended at the shower I suppose. I should probably resolve that.

hot_rod

Here are a few typical dip tubes. Some brands use a tube with slots down the side for that swirl action.
Also a dielectric nipple with anode rod combination, so the hot exits those slots in the nipple/ rod.
I think a seriously restricted dip tube would show up when you use hot water?
You may damage the flare end on the tube removing it, if it is stuck in the connection.

diyinstaller

@hot_rod
I don't think the restriction on the dip tube is noticeable at a hot water tap because the water pressure is in excess of 40psi. At those pressures, relative flow rate probably doesn't change much with this element of resistance present or not. My circulator is producing flow using just over 5psi (13ft head at peak), at this pressure, this much resistance creates a significant relative flow difference (in my case almost halves it).
probalby best illustrated by drawing the two system curves with and without the resistance and the operating points for the flow provided by ~40psi street pressure vs flow provided by ~5psi circulator.
Plus there are flow restrictors in faucets and showers that are probably masking any pressure deltas, I'm guessing they might be pressure compensating?
I also just turned on my hot water faucet and didn't notice anything different:)

hot_rod

Are there checks on the thermostatic mix valve? They should always be included, especially in instances where the valve may see a pressure imbalance between H&C.

diyinstaller

@homerjsmith
I take that back, I did plumb the tee correctly, I've been looking at it for too long. The return is tapped in downstream of the cold water supply to the tempering valve. Tempering valve gets pure cold water.
I have to think this through but when hot water tap is opened, big pressure drop occurs there it has to draw through the water heater and will presumably draw more through that path than the tempering valve. The pressures around the tee junction where the supply comes back in should ensure the flow goes from the return back into the water heater as the cold supply is flowing into the heater also. I don't foresee the heating system return backflowing into the tempering valve cold inlet. However I haven't thought this through thoroughly. Also, I'm sort of relying on the schematic from Siegenthaler's book establishing this as a soundly functioning installation.
@hot_rod
Yes, the spec sheet says it has checks in it. However I don't think that's the issue that Homer was concerned about. I think he was concerned that the cold inlet on the tempering valve wouldn't be getting cold water while the heating loop was running.

EBEBRATT-Ed

@diyinstaller

Good job troubleshooting!

Alan (California Radiant) Forbes

You may not heave enough ceiling height to get the dip tube out. But it should be a straight piece of plastic tubing with no restrictions although it's been awhile since I pulled one out myself and these manufacturers are always coming up with something new.

diyinstaller

@Alan (California Radiant) Forbes
Luckily my garage has a tall ceiling. Plenty of room to pull it out as evidenced by the photo I snapped when I removed it.

Thanks everybody for all the help with the troubleshooting.

Lesson learned is that the dip tube in a tank style water heater can be a significant restriction for a circulator you might typically spec in a hydronic system. Either plumb the return into the drain tap, spec a water heater with auxiliary taps on the side, or modify the dip tube to remove the restriction. Modifying the dip tube will result in less turbulent mixing of incoming cold water and could affect heating performance.

I estimated the restriction of the dip tube before modification is equivalent to 550ft of 3/4" PEX (pipe size coefficient = 0.14203)

There are also heat trap devices typically installed in the inlet/outlet nipples, these may also contribute to losses so they may also need to be removed. If removed, the connections should be routed to provide a U or a loop to maintain a heat trap.

Also, if anybody is interested i have an 007e used for only a couple hours pumping water on the heating loop side that I swapped out for an 0018e. Message me if you're interested.

Alan (California Radiant) Forbes

Thanks for bringing your problem here. I think we all learned a LOT.