Using a mixing valve to help with stratification

[brack86svo]

Is there any way to use a mixing valve to keep water circulating through a zone to a preset temperature before sending the cooled water back to my storage tanks? I can't figure out how it would be plumbed to make it work, or if it's even possible.

I installed Alpha circulators, running them on auto, and that has helped a little. The biggest problem I have is with heating my DHW. When there is no demand, the return temperature is a little high, so I would like to keep circulating it unit a set temperature, I just can't figure out how that would work, or if it's even possible.

 

[maple1]

More than one Alpha? What's your zone & control setup?

I have one Alpha, with 4 heating zones & 1 DHW zone all with zone valves. I simply throttled my DWH flow by closing the isolation ball valve some. It's likely only 1/4 open or so. Pump reads 1 GPM when just it is open.

 

[brack86svo]

More than one Alpha? What's your zone & control setup?

I have one Alpha, with 4 heating zones & 1 DHW zone all with zone valves. I simply throttled my DWH flow by closing the isolation ball valve some. It's likely only 1/4 open or so. Pump reads 1 GPM when just it is open.

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.

 

[maple1]

Do you have a circ on the dhw side of the dhw hx's too?

 

[brack86svo]

Do you have a circ on the dhw side of the dhw hx's too?

I do not. I have considered it, but was trying to not add the expense. I may have to go that route and see how it works.

 

[maple1]

Not sure what your dhw setup is, but I have an 80 gallon electric tank. I use a Johnson A419 controller. Probe is tucked in at the bottom inlet. When it gets to setpoint, it opens the zv on that circ. The end switch in the zv starts the alpha same as my other zones calling would. Along with opening the zone valve, the Johnson at the same time starts a small B&G Ecocirc on the domestic side, using a relay parallelled with the zv wires. That setup works very well, the alpha doesn't run long to charge the tank up, and the return temps are quite low. Forget what exactly, I'll try to check the temps next time I see it running when I'm down there.

 

[brack86svo]

May have to give that a try. I can use my CBW web relay to control the Alpha and DHW circulator. I have a sensor at the top of the water heater, I just need to install one at the bottom and have it be the one to control the pump.

Thanks for the input.

 

[velvetfoot]

I'm not sure if it's relevant but here is my setup.
I have a bypass around my measly 120 gallon tank with a electric mixing valve controlling the return temperature to the boilers. I have it set at 155 now. The water gets pumped from the boilers, and then through the zones if a zone circ is running because of a call for heat, and then, if the water is not above 155 it gets recirculated back to the boiler.

This way hotter water goes to the baseboards, with just excess heat going to the tank.

The valve is a three way electrically operated valve controlled by an analog controller.
I have oil and pellet boilers and a small tank.

I'm not sure it's worth it, but I like the idea of a controlled return temp and higher output temps.

 

[Mike Fromme]

I use a 'backward' mixing valve on my primary loop to recirculate the water through the zones before it returns to storage.

 

[maple1]

That's a tidy looking setup.

(Have we met before? )

 

[Mike Fromme]

Yeah, I used to poast here more often. But my research into how to create spontaneous combustion via large chunks of concrete has taken up all my free time lately.

 

[maple1]

Suspicions confirmed - ha ha.

 

[stee6043]

Lots of fun discussion here. I'll offer one thought up - I think you're throttling your AWHX too much. Most coils are setup to run most efficiently in the 20 degree temp change range. You're pushing 40. I understand that you're doing this to control mixing in your tanks but I'd argue you're doing more harm to your overall efficiency than good.

You'd have to confirm with some actual tests but I'd argue you might get better usability (longer storage life) out of your tanks if you let 150 degree water go back into your tanks vs the 130. My coil stopped being useful at right about 140 degree supply water. That's the point that the blower was running far too long to heat the house.

My two cents only.

 

[brack86svo]

I installed a Taco 003 on the DHW side and that helped with recovery and return temperature to the tanks. It still is an issue as the tanks cool, since less heat is transferred. It also seemed to take a lot out of the tanks to get the DHW back up to temp. I need to work on a pressure switch, and try to utilize my FPHX to heat the incoming water better, perhaps with separate zoning of the sidearm and FPHX.

I agree that the flow through my AWHX is causing an efficiency issue, so I may have to make some changes there. Currently, the outlet temperature from my air handler is 120*, which is fine but, as storage cools, so does the out let temp due to throttling the flow. My storage is too small to maintain the temperatures I need in between burns. May have to go back to idling the stove, and basically using storage for times when the fire goes out for whatever reason.

 

[maple1]

Your sidearm & FPHX (DHW setup) isn't on a separate zone now?

Also with the Ecocirc on my DHW side, I have the ability to adjust flows on both sides of the DHW HXs to get decent dTs & lower return temps. Not sure what the 003 runs for flows, suspect it's quite a bit more than the Ecocirc. Also, my plate is a 20 plate - not sure what yours is. I started a burn this morning, my 80 gallon DHW tank was around 115°. I got it up to the 145 range pretty quick - didn't time it, but don't think any much more than a half hour. That's with 160 boiler water. I didn't think to look & see what my HX in/out temps were when it was doing that (have temp guages for all 4, along with at the 2 element locations of the DHW tank). Think the Ecocirc is set somewhere around the half-speed area - forget that too.

Your air handler could be adding inefficiencies too, not knowing much about that (air leaks? ducting? etc.) - also the size of your AWHX. Think bigger is better there (i.e. oversize), to handle lower temps better.

 

[brack86svo]

They are not on separate zones. When I originally did the install, there was no storage, so the outlet from the boiler just circulated through everything in the house. My FPHX is a 20 plate that is installed to heat the domestic before goes into the water heater. Right now, it does little to nothing to heat the water with it throttled. I basically need to zone it, and have the circulator pumping storage wide open when a hot water faucet is being used. Is this how you have yours setup?

When I was looking at small circulators, I didn't even realize the ecocirc was adjustable. I chose the 003, and may end up regretting that. Running the circulator on the DHW side, has helped the delta T's by about 15 degrees, allowing me to open the valve used for throttling the alpha a little bit.

Not sure of the BTU rating of my AWHX. It was the biggest I could fit in my air plenum at the time.

 

[maple1]

I think I (or we) must have been missing something.

My setup heats the water in my DHW tank, whenever it cools off below a certain setpoint. It does that whether the DHW is being used or not - running hot water has no play in it. Sounds like yours is somehow dependant on DHW being used?

I installed my sidearm first, in a usual way sidearms are installed - the bottom of the sidearm is Td into the bottom inlet port of the DHW tank (it is bottom fed), the top of the sidearm is Td into the relief port which is up high on the side of the tank. So water circulates (recirculates) through that loop - constantly, when I used convection & just the sidearm. I later added the FPHX, and the Ecocirc - in series with the sidearm. My flows are very low through both sides of the exchangers.

And the way you last explained it - does that mean your DHW exchangers are in the same loop as your WAHX? If so, they each have different demands so that might be conflicting them & your system. But there should be no need to pump with any kind of speed though the FPHX for DHW, mine works great with an indicated 1gpm on the Alpha - but again I don't think I have a clear picture of your setup. That's what I really like about the Alpha - on multiple zones, you can throttle (or open up) each for its demands & the circ will keep up. Or slow down if it gets down to only one throttled zone being called. If all your stuff is on one zone, throttling one thing will throttle everything on that zone.

 

[brack86svo]

The current setup goes from storage to the Alpha, then to a 3 way zone valve. De-energized zone valve, the water is sent through the sidearm. Sidearm is plumbed to drain the valve on the bottom to the port on top of DHW (typical T installed with relief valve on top). From sidearm it goes to FPHX, then to return on storage tanks. FPHX is hooked into series of the cold supply to the DHW in a cross flow manner. With the throttling I'm doing to slow storage flow through the sidearm, I'm making the FPHX useless. I need to either move it in a manner close to your setup, or zone it off, and have full flow from the alpha when cold water is being drawn into the DHW (as a preheater for the water going into the DHW)

When the 3 way zone valve is energized via the house thermostat, the alpha sends water through the AWHX, bypassing the DHW till the call for heat is completed.

To clarify, before I added storage, flow came from the boiler, through the side arm - FPHX - AWHX. Now the DHW and AWHX are separated.

We are already planning to replace our current 50 gallon water heater with a 80 gallon heat pump style in the spring, so I think the extra 30 gallons of capacity will help in the heating season, in regards to my current issue anyway.

I hope how I explained it makes sense.

 

[woodsmaster]

I've been thinking of adding a buffer tank to recirculate my water until it drops to a set temp then sending the water back to storage and replacing the cooler water with hot water from storage. Curios to see what other ideas are out there to do this without an extra tank.

 

[velvetfoot]

I have this tank: http://woodboilers.com/froling-energy-tank-119-gallon-indirect-water-heater.html
The temperature can get pretty low and I can still have hot enough dhw.

 

[woodsmaster]

That tank is a little pricey for me. I was thinking l could spend about $300 and have a buffer tank, aquastat and a small pump.

 

[brack86svo]

That tank is a little pricey for me. I was thinking l could spend about $300 and have a buffer tank, aquastat and a small pump.

Yeah, that tank is half the price of my boiler. I'm sure it's a nice tank, just way out my price range. I need to replace my water heater in spring, so i'm going to go with at least an 80 gallon for that.

 

[velvetfoot]

I didn't spend that much, but if it ever goes kaput, I don't think I'll replace it in kind, but even a normal indirect tank of 120 gallons is not cheap.

 

[woodsmaster]

That's why I have an electric water heater with a side arm, a. poor mans indirect. i can;t see spending that kind of money on something that I don,t really need. To many other things i want.

 

[Mike Fromme]

I've been thinking of adding a buffer tank to recirculate my water until it drops to a set temp then sending the water back to storage and replacing the cooler water with hot water from storage. Curios to see what other ideas are out there to do this without an extra tank.

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.