Indirect/storage tank issue (didn't seem to post first time)

AirborneTrav · May 2017

So I have run into an interesting problem that I was hoping someone could shed some light on. My company services a bed and breakfast that was running into a problem with one regular guest: he would show up, run the gigantic tub in one of the rooms until the 80 gallon Weil McLain indirect was cold, complain that he didn't have enough hot water, and get a refund. He was pretty much the only one that complained, but they ended up having us add an electric water heater as a storage tank, that we heated with a stainless 007 connected to the bottom inlet, circulating hot water from the indirect until the thermostat was satisfied. This has worked great since last June or July. He has stayed multiple times and hasn't been able to demand a refund. We got a call from them last week that another guest complained that they were only getting lukewarm water in the shower. The maintenance guy on site checked it out, got hot water at the shower, an

d chalked it up to the guy BSing him, until it happened with another guest. We initially suspected the mixing valve- replaced it, and it worked fine, until it didn't. I came here today and realized that while the stainless 007 is NOT running, we get tepid water out of the mixing valve. The second it kicks on, the mixed pipe out of the valve gets right up to temperature. I have posted a diagram of our setup, and it's open to critique. I really don't untestable how this just started happening, nor why it is happening in the first place. Anyone have any ideas?

heathead · May 2017

If it works fine when the pump is on, then the check valve is not working or is getting stuck at times and the flow is then getting by that. That would explain the warm water.

AirborneTrav · May 2017

That makes complete sense- kind of embarrassed I missed that, lol. Thanks for the help.

Mark Eatherton · May 2017

Is it a spring check or a swing check? It should be a spring check because it is in a downward flow position...

ME

hot_rod · May 2017

Ideally the check should be on the discharge side of the circ. The small internal checks shipped with most circulators these days should work.

Swing checks depend on a pressure differential to close and seal properly, not the best check for hydronic or pressurized water applications like that.

Dave H_2 · May 2017

Also another thing to look at is what is temp of the tank stored at and what is the setting of the mix valve.

Ideally, the minimum temp spread should be 27 degrees or more for the thermostatic element to work as its intended purpose. If the tank is set for 140, the mix valve needs to be set at 113 or colder.

You can also raise the temp of the tank in order to get more usable capacity from the tank. Since its an indirect, you can raise the water temp to like 150, mix at 115 and gain at least 25% (sometime even more) capacity.

In my own home, I have a 30 gallon indirect tank for 6 people and three full baths and never run out. I store at 160 and mix at 115. Everyone tells me I should have at least a 60 gallon tank but don't have the space in the mech room for it!!!

Dave H.

heathead · May 2017

Dave, I agree with the temp spread of 27 degrees. I know that is what it should be. Do people just run that hot and mix down. Does this apply to all mixing valves? I know I have a thermostatic mixing valve in the shower faucet also. Should that one also need the 27 degrees for optimum performance? What happens when it mixes with less that 27 degrees. Trying to learn why?

Does anyone make a valve that works with less differential? Do the electronic ones not need that high deferential? What are the model and makes of electronic versions?

I heat my water with mod/con and store my water at 126 degrees then once a week it goes to 140 for two hours to kill the stuff in the tank. I think at times the shower and the thermostatic mixing valve on the indirect are fighting each other, and not working ideally.

I am plumbing / planning a gravity hot water recirculation line. That looks like I am going to end up with a line for all sorts of stuff to grow. Does one just put a pump on that line that runs 5min every day to keep it from growing stuff. That line would also not be above 140 degrees because it is mixed down first. Or are the gravity recirculation lines just the place for leginares ? to grow.

hot_rod · May 2017

Do you have a pressure balance or thermostatic shower valve? Thermostatic types usually have two handles to adjust flow and another for temperature control. Pressure balance are usually single handle and less $$.

Thermostatic mixing valves will work with a differential below the 27° but they start to lose resolution or accuracy. You might feel small variations in temperature as that differential closes.

Gravity circulation may be tricky if it goes through the thermostatic, that valve has a lot of pressure drop.

Generally if a tank is set to say 126F, it probably stratifies to a higher temperature. I have seen solar tanks with a 15° or higher difference from sensor location to top of tank.

Yes an EMV would be accurate across all temperatures and wider flow rates. I've not seen any residential sized EMV, most are commercial, high flow valves.

While cranking up a tank temperature is a good way to extend DHW it does make a huge difference in scale precipitation and expected tank life. It also will require more frequent cleaning of the thermostatic valve. It depends on water hardness and amount of DHW that you use.

Pumped recirculation with a thermostatic mixer can cause some issues. Temperature creep or temperature droop occurs when no flow goes into the tank from the recirculation loop, and the valve losses temperature differential and fails to regulate.

Caleffi now has a 520 mixer kit with the valve designed to eliminate those problems if you use the recirc port provided. The valve also closes off if cold supply is lost. Here is a look and some more info on Legionella.

hot_rod · May 2017

From a Purdue study, probably older than most of us here. It shows a good example of mineral precip from 120- 160°F

heathead · May 2017

Hot Rod,

Thanks for the Purdue Study. I think if more people saw that it would make one think about the storage temps. Its not all back and white but a balance. I will look at the instructions to the 520 mixer for the re circ port connection. I am trying to wrap my head around no flow into the tank from rec line or temp creep. I have to understand that better in my mind. Yes the shower valves are themostatic, I won't go back, to pressure balance. Set it and adjust slightly during a shower. I think I only adjust it because my body get used the hot water as the shower goes on. The only problem with thermostatic shower valves is when it fails is that the hot and cold can mix together in the valve and be hard to find the one valve that is causing problems. Thanks for all your feedback have learned a lot from you over the years of reading posts.

hot_rod · May 2017

If you have hard water conditions cleaning or rebuilding thermostatic devices, either point of distribution or point of use is just going to be an ongoing requirment. I know of commercial hotel properties that have a staff dedicated to thermostatic valve maintenance.
Softened water helps a lot, but you can still have high TDS with soft water, so minerals are still circulating.

There is not a lot to fail inside thermostatic valves, some o-rings and a wax "pill" Rebuild kits are readily available for the shower valves I imagine.

I feel one of the most reasonable anti-legionella methods it to elevate the tank and entire DHW loop temperature, above 140F daily for a 1 hour period.

If the tank can handle all your DHW needs at 120°F, really no need to maintain it at 140° or higher 24/7.

That anti legionella function has been in all our solar controllers for 6 years or more and I suspect most boiler controls that are Euro based also have that function already load in.

For buildings with multiple loops or branches our ThermoSetter will automatically allow the loops to run up to a higher temperature. A second cartridge senses high temperature and forces the valve to full open. So one valve balances and provides thermal anti legionella function.

Jean-David Beyer · May 2017

About mixing valves with lower differential, here is one by Caleffi:
"Minimum temperature differential between hot water inlet and
mixed water outlet to ensure thermal shutoff function: 18°F (10°C)

"Minimum temperature differential between mixed water outlet
and cold water inlet to ensure stable operation: 9°F (5°C)"

It is for this valve:
https://www.caleffi.com/sites/default/files/file/01092.pdf

I use it between my storage tank that runs between 140F and about 160F and the house that I do not want to supply over 120F. Works fine.

You might wish to ensure that it has a high enough flow rate for your needs.

There has been a lot of discussion (long ago) here about my using this valve in this way, but the consensus seems to be that it is OK, provided I do not try to set it over 120F, and I do not set it over that.

"The Caleffi 5213 series is a high performance combination thermostatic and pressure balanced mixing valve and is ASSE 1070 Listed (temperature can not exceed 120°F)."

hot_rod · May 2017

Correct you are. That is a point of use valve, ASSE 1070 intended to be used at fixtures but certainly can be used at the tank also.

Differences from a point of distribution ASSE 1017 valve as you mentioned, maximum 120° setpoint, lower Cv at 2.
The adjuster also needs to be tamper proof, requiring the cap to be removed, it has a hex socket built into the cap for adjusting.
Chrome plated as it is often exposed in commercial applications.

I have used them for radiant mixers also as it has tighter temperature control and tighter differential tolerance. Just be aware of the low Cv.

Here is a Cv calculator for all.

In the last column enter the Cv of the valve, and the flow rate you expect the valve to be used at. pressure drop in psi and ' of head.

Here is an example of a 2 Cv valve with an 8 gpm flow.

It can be used for any valve or device really, not just Caleffi.

One valve I see on the market, 3 Cv 3/4" shows a max flow of 19 gpm! here is what the pressure drop would be

heathead · May 2017

Hot Rod,

Thermosetter 24 v activated valve looks like the golden ticket. It will enable the flushing of the lines at times when water would not be used. Easy to control and tie into the boiler and Hot recir circulator with relays.

Thanks for the product idea.

Jean-David Beyer · May 2017

Another reason I used that point of use ASSE 1070 valve, with lower flow rate is because I am the only user of hot water in my house. I do have a dishwasher and a washing machine that I sometimes run at the same time as I take a shower.

This valve will hold the set temperature at much lower flow rates than the larger valves (about 1/2 gallon per minute). If I am taking a shower and everything else is off, I still want it to regulate.

Indirect/storage tank issue (didn't seem to post first time)

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