Using a mixing valve to help with stratification

maple1

Minister of Fire
Sep 15, 2011
9,922
Nova Scotia
Just adding a bit of info re my DHW heating setup & temps.

I started a burn a while ago, and decided to charge my DHW tank up & note the various temps.

The DHW tank was at 133/120, and top & bottom element locations. (I wouldn't normally start a charge at these temps, but would rather just wait until it fell to it's normal calling point).

After about 10 minutes of circulating, the exchanger temps were:

Boiler/supply side: 160 in, 127 out.

DHW side: 103 in, 132 out.

For whatever that is worth, for comparison....
 

Beagle Dad

Member
Sep 17, 2014
46
Ottawa Ontario
I have Alpha pumps and valves on the outlet of my heat loads, based solely on your posts.

I run three Alpha's. One on the boiler, one on the DHW and Air water heat exchanger, and one for the radiant floor in the garage.

The DHW and AWHX are on a 3 way zone valve. When call for house heat, the valve sends water just to the AWHX. I throttled that back with a valve to the point where I get 170* in, and about 130* out. When no call for heat, the water circulates through a sidearm, then plate for DHW. I have that choked off so I'm getting 140* return. Alpha reads from 0 to 1 GPM when running through DHW, between 1 and 2 GPM for AWHX.

The Alpha for the garage radiant runs all the time. It circulators water just through the outer edge of the concrete via a manifold with zone valves. When a call for heat, the other three zones open. This was to keep the outer loop from freezing, since I did not insulate the perimeter of the concrete or foundation.

So I have two problems with this setup personally, I'm sure there are lot more for the people in the know. One problem with using a manual valve to throttle water flow, as the storage cools, so does the output of the AWHX. I figured if could have a set return temperature, I can better tune the blower speed to make sure I am getting a good heat output, plus extracting as much useable heat as I can before sending it back to storage. The other problem is I am not getting as good of performance with my sidearm and plate setup as I was with full flow. My logic was that I'm not moving the water through them quick enough. I don't know if that is even the case. I am getting better stratification but, seemed to have sacrificed performance at the heat loads.

In regards to my DHW, I lost 20 degrees of heat by throttling the flow back. I have never been able to get the DHW up to the same temperature of my storage. With 180 water, the DHW would get to 160. Now the best I can get is 130 to 140 and recovery time is much worse.

Thermostatic mixing valves work well to control the return water temperature back to the storage tank(s). I use the Honeywell AM10R mixing valve to control the water temperature back to my storage for my in duct heating coil. I have 4 loops on my storage system which all incorporate a mixing valve to maximize the storage tank stratification.

Duct Heating Coil.JPG
Forced Air Coil Piping.JPG
 

huffdawg

Minister of Fire
Oct 3, 2009
1,447
British Columbia Canada
I use a buffer tank between the demands and storage . I have a house loop that supplies the house demands from the buffer tank, the dhw tank gets its heat from this loop. I am thinking if I had a Delta t circ. for the house loop , that I would be able to send cooler water back to the buffer tank by it regulating the delta t.

I hope this isnt hyjacking your thread B86 . I have been trying to think of ways to send cooler water back to the buffer in order get better stratification in the storage tanks. This thread got me thinking again .. oh oh.

links to my basic system configuration , workin in real time. http://96.54.66.117/public/huff.html

http://96.54.66.117/

note.. buffer to storage tank piping is replumbed utilizing opposed circs. from top of buffer to top of storage , with the bottom of tanks being connected with one continuous length of pipe.

Huff
 

brack86svo

Member
Jan 18, 2013
127
Central PA
Thermostatic mixing valves work well to control the return water temperature back to the storage tank(s). I use the Honeywell AM10R mixing valve to control the water temperature back to my storage for my in duct heating coil. I have 4 loops on my storage system which all incorporate a mixing valve to maximize the storage tank stratification.

View attachment 188873 View attachment 188874
That's exactly what I was looking for, just wasn't sure how to hook it up to make it work. Now that I see it, it makes sense. I ordered the AM101R, will try to get it hooked up this week and report back. With my setup, I'm fighting a losing battle. I have my returns going in the top of the tanks. The return pipes extend down into the bottom of the tanks but, I have some heat transfer between the hot water at the top, and the cooled water getting pumped to the bottom. I never considered stratification when I was putting everything together. At this point, I'm trying to salvage a flawed design.
 

Beagle Dad

Member
Sep 17, 2014
46
Ottawa Ontario
If you can install a thermometer on the return water to see what is going on. I used a Winters TBM20025B6 from Amazon. This thermometer does not require a well only 1/4" connection.

DSCF6189.JPG
 

Attachments

brack86svo

Member
Jan 18, 2013
127
Central PA
I will be adding 2 more gauges, ordered them when I ordered the mixing valve. I'm going to be adding one to the return line to the tanks so I can adjust the mixing valve. I'm not sure about the other one yet. I already have one after my DHW heat exchangers, and one after the AWHX. I may just out the other one on the mix side of mixing valve.
 

brack86svo

Member
Jan 18, 2013
127
Central PA
Mixing valve is installed and doing exactly what I was hoping so far. I have it set to about 140*. My main goal was to be able to utilize my FPHX to heat the water coming into DHWH. With the mixing valve set at 140*, I am heating the DHW to about 150* through the sidearm. I started a fire last night and once the DHW got up to 135*, the wife took a shower. With the FPHX cooling the water even more in the loop, I was returning 120* to the tanks, and DHW never dropped below 130*, 50 gallon water heater, about 15 minute shower. When I did the throttling with a valve that Maple1 uses, my FPHX was no longer effective, as the water from the tanks was slowed down so much, that there was no heat transfer. With the mixing valve setup, it draws only the hot water it needs from the tanks to stay at the 140* set point of the mixing valve.

I put a few locust splits that were in the 8" range last night, and they are still going now. I normally would have split those up by hand but, it was raining last night. That being said, I'm not sure how much this setup will help stratification yet, at least not till after the boiler stops putting heat into the tanks.
 
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Beagle Dad

Member
Sep 17, 2014
46
Ottawa Ontario
Good to hear you are getting the results you wanted, These little valves are a cost effective way to control return water temperatures back to the storage
 

brack86svo

Member
Jan 18, 2013
127
Central PA
Good to hear you are getting the results you wanted, These little valves are a cost effective way to control return water temperatures back to the storage
Thanks for sharing your setup. It's working better than anything else I've tried so far. Fire finally went out around 2. So far, I've lost 5 degrees at the top of the tanks, and 30 degrees at the bottom. Before, the most I would see is a 20 degree difference, usually less.
 

Bob Rohr

Minister of Fire
Jan 9, 2008
1,268
SW Missouri
Hot water goes through the zones. When it gets to the mixing valve if it's still hot it goes back through the zones. If it's cold it goes to storage.
View attachment 188748

It would be interesting to see flow meters on those "P" circulators. It looks like they go in and out of series with C-1? It's not a primary secondary piping according to the way the returns tie back to the loop?

It seems if C-1 and P-1 were running, there would be some high flow and velocity. As P2 and P3 power on what does the flow rates in P1 look like?
 

Mike Fromme

Burning Hunk
Apr 18, 2014
213
Maine
It would be interesting to see flow meters on those "P" circulators. It looks like they go in and out of series with C-1? It's not a primary secondary piping according to the way the returns tie back to the loop?

It seems if C-1 and P-1 were running, there would be some high flow and velocity. As P2 and P3 power on what does the flow rates in P1 look like?
It was a bit of a compromise... I originally had an oil boiler only with supply and return headers zoned with circulators.

When I added the wood boiler I didn't want the time or expense of redoing what was already there. With that setup all I needed to do was connect the headers to create a loop and then T into it for the wood boiler supply and return. By creating that 'primary' loop I could then use the diverting valve to limit return back to storage. Otherwise I could have left them as headers.

The downside as you said is the 'c' pump is in series with the with the 'p' pumps. The best solution would probably be zone valves but I'm not sure it's worth the $$ to switch everything around... There 8 zones with a large variety in piping; an indirect, modine for the basement close by, distant baseboard loops etc. I'd have to change the piping to reverse return or add some sort of pressure differential bypass to make it work. And then I'd be relying on a single pump to get heat into house. Not something I'm crazy about when it's below zero for two weeks straight.

I had thought about switching the 'p' pumps to delta P pumps but I'm not sure how pumping in series would affect them...

Lately I've been thinking delta T pumps would be the best answer. But what I have works very well at the expense of some extra kilowatts. Even with low storage temps the baseboard keeps the house warm until it gets into the teens... So I wonder if delta T pumps would slow down too much when storage is at ~120 to get enough heat out of the baseboards? Or at least as much as I do now.
 

velvetfoot

Minister of Fire
Dec 5, 2005
9,973
Sand Lake, NY
You wood burning people with big storage are thinking about controlling the supply temperature from storage. With my pellet/oil two pipe setup to a buffer, I've been controlling the boiler return temp for fast return from setback and letting pump run times just get longer, like maple1. I can see advantages to lower temps, but not at expense of setback return.

I'm thinking with a two pipe layout (like I have), a bypass around storage with an electrically controlled 3 way mixing valve could control boiler return temp as well as loop supply temp when operating only on tank. Only one valve. The controller I have does two different sensors-a sensor on the supply could be added to the existing boiler return sensor, with a switch that changes the controller's temp. sensor input depending on if the boiler is on or not.

Reset would be nice (which I don't have). Also a way to override it to get max temp when in setback recovery.

I think electrically operated mixing valves have a lot of potential, especially when paired with a sophisticated control system (which I aint got).