Thermal Storage and Outdoor Reset

[BoiledOver]

This topic doesn't get much attention in the boiler forums. After searching threads here and elsewhere, most information did not address this concern without including boiler control. There are two simple ways to include outdoor reset while drawing from thermal storage. Injection using variable speed circulators or mixing valves, both controlled by an outdoor reset unit. The cost to achieve this can be $300 US and up. Since my system uses a stand alone wood fired boiler to heat storage, I do not see a need for additional boiler control.

The Tekmar 356 is a microprocessor-based outdoor reset control designed to operate a permanent capacitor, impedance protected or equivalent pump at varying speeds. The 356 also provides for boiler minimum protection and boiler operation.

The Tekmar 361 is a microprocessor-based outdoor reset control designed to operate a permanent capacitor, impedance protected or equivalent pump at varying speeds. The 361 also provides for boiler minimum protection, system pump operation, and boiler operation. As well, a tekmar indoor sensor can be connected to the control to provide indoor temperature feedback.

The Tekmar 356 and 361 fit the bill with additional features that some users would find useful. As you see, they employ the use of variable speed circulators and include boiler control.

There is a mixing valve controller option from Armatur that will do the job. They offer 2 models with outdoor reset, the LK110 and the LK130. Both mount directly to a mixing valve and receive input from an outdoor sensor. The LK130 includes input from an indoor sensor. The Armatur LK840 3-way mixing valve or valves from several others will pair with the controller. I have an LK130 controller mounted to a Tekmar 710 valve that work great together.

From info provided in the thread, Overnight Steady House Temps, I was made aware of the Armatur unit. The install was pretty simple and the results are a much appreciated good nights rest. The Grundfos 15-58 circulator runs 24/7 on the low setting and keeps things steady on the house side. Two things that could cause issue would be high winds, and solar gain. Both of those can be minimized with the use of indoor feedback. In the case of high winds, I found it necessary to adjust the outdoor reset curve slightly in extreme conditions. In the case of solar gain, I have the Grundfos 15-58 on/off controlled by the houses main thermostat set just above the Armatur indoor thermostat and will cut power to the circulator in an overshoot of indoor temp.

Results will probably vary with each system design and emitters used. Members @JohnDolz and @Sparky were very helpful in sharing advice of their experiences with outdoor reset from storage, thanks guys.

 

[TCaldwell]

Also Tekmar makes a 440 expansion module (floating point) that piggy backs connections to a 336 ( zone manager relay box). The reset curve could come from a reset module like a 423 that will manage multiple heat sources and provide 4 independent reset mix temps, controlled by their thermostats that provide indoor feedback and communicate with each other.
As you state there are many ways to skin the cat, however be aware that reset or mix control is limited by the circulators inability to respond to a control below 2vdc, whereas a 3 way valve will control from .5 vdc, that equates to 15 percent more range.
I’m my limited experience the success of odr is determined by low temp emitters providing even steady heat. Without them it’s only useful during the shoulder seasons to run storage lower possibly before the next firing, a relatively tight house is a must also.
I’ve been running on odr for 2 years and have been slowly replacing to lower temp emitters and radiant where possible.

 

[BoiledOver]

Yeah, Tekmar has a broad selection for just about any situation. For some folks, as in my case, who have moved to batch burning are looking for a basic controller to match their basic system. Most all users already have a boiler controller. A visual comparison to the indoor temp swings here.

BEFORE OUTDOOR RESET

WITH OUTDOOR RESET

 

[TCaldwell]

I like it, I think sparky has a LK mixer also, would be interested to hear from him and others on this.

 

[Karl_northwind]

I use the tekmar 356 regularly to supply from a hot water storage tank (large commercial water heater in my house, to GARNs in client's places) to run water thru a flat plate heat exchanger, with heating water on the other side. it allows me to maintain stratification on a GARN while still getting outdoor and indoor reset with mininmal power consumption. in one case, I used 2 of them to deliver 2 water temperatures to a place with panel radiators and in-floor.

otherwise I just use caleffi mixing valves. they seem to have the least bleed (from the cold side) thru of any of the mixing valves I've run across.

 

[Sparky]

I installed the LK 130 just about a year ago. The system has worked great, I have run my tank down to 130 degrees (during the day) and still have a warm house. My second floor has petite 7 radiation and it works great with the system. I also run radiant heat on the first floor and the works well too. My burns a very consistent too. 180 lbs a day (except on below zero days) I was burning 300 lbs a day. There are a couple of things that I have noticed. One is the indoor thermostat doesn't have a large effect on the system (IMO I think the outdoor temp controls the system) I'm not sure if the indoor thermostat controls anything. I would like to know how @BoiledOver made out with his set up. Also the second thing was the below zero nights I would turn the bypass screw and manually open valve all the way or it would be cold in the am, Now I am not saying it's not operator error (I don't think it is) But i am always looking to learn something new especially burning wood. Other than that the system works great my house is so much more consistent temperature wise and I am glad i installed it.

 

[nhtreehouse]

Great topic. As many have mentioned, there are many ways to remove the fur from this particular cat. Great to read of other people's experiences!

I'm mixing my house supply water using ODR out in the boilerhouse and then passing that through the underground pipe. Of the many viable solutions, I picked a tekmar 3 way valve, like the one BoiledOver uses, only mine is on 1" pipe. For the mixing motor I used the 0-10 volt control motor tekmar makes, the tekmar 742. That leaves me needing a way to control the motor with a 0-10V voltage, and I'm using an EasyIO controller for that. I'm sure the LK solutions are very good as are the tekmar controls. Here is my mixer (don't mind the wires hanging out all over the place, I'll get to tidying that up over the summer!):

Right now, I've implemented a standard ODR formula in the controller:

TMIX = 65 + RR * (TINSIDE-TOUTSIDE)

My vastly oversized panel rads will work great with a reset ratio (RR) of 1.0, while my less oversized rooms want more like 1.2. TCaldwell is talking about multiple ODR curves for different heat emitters - pretty interesting. I see lots of ways to improve this formula and you'll see some non-linear ODR formulas out there. But this got me going, and getting going was the first goal.

So far so good, and while I've got a lot to learn, so far I've learned these things:

1) ODR allows me to send 120 degree water to the house on moderate days, that water is circulated through oversized panel radiators. With a low flow rate, these drop 25 to 35 degrees, meaning my return water is less than 100 degrees. This cold water puddles nicely in the bottom of the tank, and becomes the new "cold" source to the 3-way valve. So on the hot end of the valve I could have 180 and on the cold, 90, with the mix being 120. For every gallon I'm sending out the mix port, only 0.33 gallons comes from the top of the tank, with the balance from the house return/bottom of the tank. I believe this drives stratification in the tank and thus gives a bit more life to my storage. Obviously when the top of the tank is around 120, I'm out of gas, the controller is driving the mixing valve all the way to the hot stop, routing all hot water to the mix port. With this setup it's not untypical for the tank to have a delta T of around 100 degrees, this pic was taken about 18 hours after a burn finished, on a warmish day (Hello Stratification!):

2) Using ODR not only gives more effective use of the tank, but it also means that I don't ever really want to charge the tank to 180 top to bottom. When that happens, the mix valve is all the way to the cold side, routing all "cold" water to the house. Obviously as time goes on, the house will strip some heat from that water and the mix valve will be able to regulate. But putting it simply, if you give 180 degree water to both the hot and cold ports, expect around 180 on the mix port.

3) It works. Just two days ago I got a panel rad hooked up in a room which has no other heat besides a woodstove. The rad I installed is not big enough to meet the entire room's loss, so it finds a "happy place" when fed with ODR water. That happy place is where the heat emitted by the radiator meets the heat lost from the room. As it turns out that was about 55 degrees, not so comfy. But here is the kicker... The room was pretty much constant at that temp for like a day and a half. As the outdoor temp dropped, the ODR shoved hotter water into the rad and the balance point was met. I left for an overnight away (amazing having "central" heat), came back, and the room was 53 degrees. And it was like 5 degrees last night.

4) Today when I came home I got a good look at what an "empty" tank looked like - about 800 gallons of 90 degree water and then a thermocline with 120 at the top of the 1000 gallons. I don't think I'd get that without ODR. I was using a RR of 1.20, which I think drove up my return temps from the earlier pic.

5) the obvious thing - distributing lower temp water should be more efficient in terms of heat lost off piping, underground, etc.

Obviously indoor feedback of some sorts is required to deal with the effects of solar and other heat gains, like pesky humans and their cooking and bathing habits. In my case, I'm using a Euro system of constant pressure pump, low flow rates, ODR mixed water and TRVs on panel radiators. If the sun comes out (or if I fire up the woodstove, like I did this afternoon), the TRVs start to shutdown the flow rate in the radiator, reducing it's output. I have my panel rads hooked up to a radiant manifold and can watch the flow meter and from the flow rate, I can easily deduce which loops are throttling flow meaning that the room is in regulation. Changing the pump speed (or shutting it off), or using the indoor temp to reduce the water temperature all see like viable options.

Since I've put this together I've come to learn that there is another type of mixing valve - one without a rotating spindle like the LK and Tekmar valves. It's a 3-way valve and it has a fitting for a TRV on it - meaning it will attempt to regulate the mix port to whatever the TRV senses. At first this might seem stupid - who is going to put piping in their living spaces so the TRV can see the room temp? But there are remote thermostat heads with capillary tubes which will screw onto the TRV fitting. Think aqustat(-ish), Euro-style, electrons need not apply. Apparently these valves and control heads are used for some Euro radiant floor setups. So instead of bang-bang (on/off) control of a pump at a fixed speed, they regulate the temperature of the water supplied to the floor to meet the room loss. Interesting concept. Still noodling on how that all works with just proportional control, which is what a TRV is.

That's what I've figured out so far. I know there are those on this site which don't care to use ODR, and that's cool. I personally have learned so much from the hearth archives that I thought I'd try and give back - so here is what I've learned so far.

 

[TCaldwell]

Chris, who makes the trv regulator your talking about, I’ve heard about a Sampson valve, wonder if they work in a similar way?
For a long time lurker turned boxes full of supply house parts to putting it together singlehandedly, your learning curve appears very fast!

 

[Karl_northwind]

Chris, who makes the trv regulator your talking about, I’ve heard about a Sampson valve, wonder if they work in a similar way?
For a long time lurker turned boxes full of supply house parts to putting it together singlehandedly, your learning curve appears very fast!

Look on page 24 of the Caleffi catalog. they have a number of different variants. 472 is probably what you'd want.
typically I think you'd have a circulator running the floor loop (s) full time, with the Thermostatic valve introducing hot water via some closely spaced tees to the floor water and the air sensor in the room. floor water heats up to match the heat loss of the room.

 

[maple1]

Today when I came home I got a good look at what an "empty" tank looked like - about 800 gallons of 90 degree water and then a thermocline with 120 at the top of the 1000 gallons. I don't think I'd get that without ODR.

I see the same thing quite regularly without ODR. Well, not quite the same thing, because I only have Slant Fin baseboard (although it seems to be oversized) - so mine is more like 125-130 at top and 105-110 at bottom. I would really like some lower temp emitters, or cast iron rads, but with what I have now likely just throwing more Slant Fin at it would be the cheaper & simpler way to get my depletion temps lower. (Plus my better half seems to have an aversion to cast iron rads for some reason). I have quite low flows pumped by an Alpha on low dp setting. When storage is hot, it functions as a typical baseboard system - flows stopping & starting. But as storage temps decrease the flows become longer until they get to the constant stage. So the last portion of my storage use (Maybe 2-4 hours? Maybe longer? Depending how cold it is out), my system is practically doing the same thing as an ODR system would be - flowing constantly with no mixing. Until it gets to the point of not being able to keep up with heat loss - then I need to light a fire again. So I don't think adding ODR would do much for me on getting more mileage out of my storage - that would need to come from more or better radiation.

 

[nhtreehouse]

Hey Tom,

LTL here, the long time lurker. Thanks for the compliments ... Been a long road but well worth it, as you well know.

The ones I saw were in the Hydronics Alternatives Price List. #5021 is a 3/4 diverting valve - non electric controls heads are there too. I believe they import Hertz from Europe. Could be wrong on that, but I thought I saw a Hertz on the room control.

I checked out the Caleffi part numbers Karl_northwind mentioned. I think the 472 is the room control, but I looked up all the valves mentioned in the product data sheet and didn't see a 3-way diverting valve. I'm sure they are out there from other manufacturers. Everything on the datasheet was a radiator fitting or towel bar fitting.

otherwise I just use caleffi mixing valves. they seem to have the least bleed (from the cold side) thru of any of the mixing valves I've run across.

I think I see what you are saying - when the valve is all the way at one end, say, routing all hot water to the mix, there is some % of cold which still comes through. I noticed that when I emptied the tank the other day - mix was a couple degrees lower than the hot. As I understand it, they do that so water can expand/contract without busting something. At least I think I read that somewhere. Probably only an issue when running out of storage and you just cannot quite get all hot out to the mix port. During normal operation you wouldn't notice it.

Any idea how the Tekmar 3 way mixing valves compare to the Caleffi valves in this respect?

 

[BoiledOver]

I think I see what you are saying - when the valve is all the way at one end, say, routing all hot water to the mix, there is some % of cold which still comes through. I noticed that when I emptied the tank the other day - mix was a couple degrees lower than the hot. As I understand it, they do that so water can expand/contract without busting something. At least I think I read that somewhere. Probably only an issue when running out of storage and you just cannot quite get all hot out to the mix port. During normal operation you wouldn't notice it.

Any idea how the Tekmar 3 way mixing valves compare to the Caleffi valves in this respect?

I experienced the same partial mix with a Honeywell valve. The Tekmar 710 is 100% at either stop, I have no experience with the Caleffi valves.

 

[salecker]

Today when I came home I got a good look at what an "empty" tank looked like - about 800 gallons of 90 degree water and then a thermocline with 120 at the top of the 1000 gallons. I don't think I'd get that without ODR.

I see the same thing quite regularly without ODR. Well, not quite the same thing, because I only have Slant Fin baseboard (although it seems to be oversized) - so mine is more like 125-130 at top and 105-110 at bottom. I would really like some lower temp emitters, or cast iron rads, but with what I have now likely just throwing more Slant Fin at it would be the cheaper & simpler way to get my depletion temps lower. (Plus my better half seems to have an aversion to cast iron rads for some reason). I have quite low flows pumped by an Alpha on low dp setting. When storage is hot, it functions as a typical baseboard system - flows stopping & starting. But as storage temps decrease the flows become longer until they get to the constant stage. So the last portion of my storage use (Maybe 2-4 hours? Maybe longer? Depending how cold it is out), my system is practically doing the same thing as an ODR system would be - flowing constantly with no mixing. Until it gets to the point of not being able to keep up with heat loss - then I need to light a fire again. So I don't think adding ODR would do much for me on getting more mileage out of my storage - that would need to come from more or better radiation.

Hi Maple
My experience is about the same as yours.I have no ODR and don't seem to have any issues without it.We have cast iron rads in our upstairs and a home made unit heater in the basement,it is a regular unit heater with a squirrel cage fan so it's not as noisy as the industrial fan that was on it.
At -40 ish we will draw the tanks down to 110F ish before the backup oil boiler fires up at 105 F ish. The cold temp water still produces heat out of the CIR's.My system dosn't allow for stratification because the water is always moving.
I am blown away by sparky's wood use...
There is probably more to the story but at -40 we don't burn that much wood and all we have is spruce.On -40 days we go through 1 cart of wood my wood cart measures about 4ft long and 2.5 ft high.On -20C average we go through 2 carts in 3 days.
I have read about ODR since i started reading here,still haven't seen how they would help my system without leaving the KISS zone.If i am mistaken i would really like someone that knows the fine points of Outdoor resets to show me how they would benefit my system.
Thanks Thomas
Thomas

 

[TCaldwell]

I live about 2-1/2 hrs south of sparky, not knowing his setup or house size, I burn about 180lbs down to about 0degf, odr mix temp max at 0 degf is 145. Any lower if there’s wind involved I have to up the curve to 160.
Right now it’s 40 outside, mix temp is 112 and radiant odr mix is 100.

 

[maple1]

On the wood use I'm still working at the 4 cord section of my basement woodpile. It should take me just into March before it's gone. So guessing it might end up at 5.5 cords for the whole winter? Not sure how that translates to pounds. It's something like a 20/80% soft/hard mix with quite a bit of the hard being rotten but dry. Not all high quality stuff.

 

[Bad LP]

My RFH zones have ODR. Baseboard zones are what they are. House has very even heat but it's also an open design. ODR works well and there is a maximum temp setting that is very important for my wood floor areas.

If I had to build another house it would be 100% tile in the living and bath areas.

 

[JohnDolz]

This topic doesn't get much attention in the boiler forums. After searching threads here and elsewhere, most information did not address this concern without including boiler control. There are two simple ways to include outdoor reset while drawing from thermal storage. Injection using variable speed circulators or mixing valves, both controlled by an outdoor reset unit. The cost to achieve this can be $300 US and up. Since my system uses a stand alone wood fired boiler to heat storage, I do not see a need for additional boiler control.

The Tekmar 356 is a microprocessor-based outdoor reset control designed to operate a permanent capacitor, impedance protected or equivalent pump at varying speeds. The 356 also provides for boiler minimum protection and boiler operation.

The Tekmar 361 is a microprocessor-based outdoor reset control designed to operate a permanent capacitor, impedance protected or equivalent pump at varying speeds. The 361 also provides for boiler minimum protection, system pump operation, and boiler operation. As well, a tekmar indoor sensor can be connected to the control to provide indoor temperature feedback.

The Tekmar 356 and 361 fit the bill with additional features that some users would find useful. As you see, they employ the use of variable speed circulators and include boiler control.

There is a mixing valve controller option from Armatur that will do the job. They offer 2 models with outdoor reset, the LK110 and the LK130. Both mount directly to a mixing valve and receive input from an outdoor sensor. The LK130 includes input from an indoor sensor. The Armatur LK840 3-way mixing valve or valves from several others will pair with the controller. I have an LK130 controller mounted to a Tekmar 710 valve that work great together.

From info provided in the thread, Overnight Steady House Temps, I was made aware of the Armatur unit. The install was pretty simple and the results are a much appreciated good nights rest. The Grundfos 15-58 circulator runs 24/7 on the low setting and keeps things steady on the house side. Two things that could cause issue would be high winds, and solar gain. Both of those can be minimized with the use of indoor feedback. In the case of high winds, I found it necessary to adjust the outdoor reset curve slightly in extreme conditions. In the case of solar gain, I have the Grundfos 15-58 on/off controlled by the houses main thermostat set just above the Armatur indoor thermostat and will cut power to the circulator in an overshoot of indoor temp.

Results will probably vary with each system design and emitters used. Members @JohnDolz and @Sparky were very helpful in sharing advice of their experiences with outdoor reset from storage, thanks guys.

Happy to hear that it has worked out for you!

 

[JohnDolz]

I installed the LK 130 just about a year ago. The system has worked great, I have run my tank down to 130 degrees (during the day) and still have a warm house. My second floor has petite 7 radiation and it works great with the system. I also run radiant heat on the first floor and the works well too. My burns a very consistent too. 180 lbs a day (except on below zero days) I was burning 300 lbs a day. There are a couple of things that I have noticed. One is the indoor thermostat doesn't have a large effect on the system (IMO I think the outdoor temp controls the system) I'm not sure if the indoor thermostat controls anything. I would like to know how @BoiledOver made out with his set up. Also the second thing was the below zero nights I would turn the bypass screw and manually open valve all the way or it would be cold in the am, Now I am not saying it's not operator error (I don't think it is) But i am always looking to learn something new especially burning wood. Other than that the system works great my house is so much more consistent temperature wise and I am glad i installed it.

Regarding Indoor Controller, I have no experience with the components you are using but I can tell you that mine differently factors in. My controller allows me to toggle from Outdoor Control to Indoor Control to "Both" this allows me to see the different flow temps based on each setting (i.e. if I get up early while recovering from setback I can see that my Both flow temp is quite a bit higher than the Outdoor flow temp). This compensates for the windy days, solar gain, etc.

 

[JohnDolz]

Great topic. As many have mentioned, there are many ways to remove the fur from this particular cat. Great to read of other people's experiences!

I'm mixing my house supply water using ODR out in the boilerhouse and then passing that through the underground pipe. Of the many viable solutions, I picked a tekmar 3 way valve, like the one BoiledOver uses, only mine is on 1" pipe. For the mixing motor I used the 0-10 volt control motor tekmar makes, the tekmar 742. That leaves me needing a way to control the motor with a 0-10V voltage, and I'm using an EasyIO controller for that. I'm sure the LK solutions are very good as are the tekmar controls. Here is my mixer (don't mind the wires hanging out all over the place, I'll get to tidying that up over the summer!):

View attachment 222716

Right now, I've implemented a standard ODR formula in the controller:

TMIX = 65 + RR * (TINSIDE-TOUTSIDE)

My vastly oversized panel rads will work great with a reset ratio (RR) of 1.0, while my less oversized rooms want more like 1.2. TCaldwell is talking about multiple ODR curves for different heat emitters - pretty interesting. I see lots of ways to improve this formula and you'll see some non-linear ODR formulas out there. But this got me going, and getting going was the first goal.

So far so good, and while I've got a lot to learn, so far I've learned these things:

1) ODR allows me to send 120 degree water to the house on moderate days, that water is circulated through oversized panel radiators. With a low flow rate, these drop 25 to 35 degrees, meaning my return water is less than 100 degrees. This cold water puddles nicely in the bottom of the tank, and becomes the new "cold" source to the 3-way valve. So on the hot end of the valve I could have 180 and on the cold, 90, with the mix being 120. For every gallon I'm sending out the mix port, only 0.33 gallons comes from the top of the tank, with the balance from the house return/bottom of the tank. I believe this drives stratification in the tank and thus gives a bit more life to my storage. Obviously when the top of the tank is around 120, I'm out of gas, the controller is driving the mixing valve all the way to the hot stop, routing all hot water to the mix port. With this setup it's not untypical for the tank to have a delta T of around 100 degrees, this pic was taken about 18 hours after a burn finished, on a warmish day (Hello Stratification!):

View attachment 222717

2) Using ODR not only gives more effective use of the tank, but it also means that I don't ever really want to charge the tank to 180 top to bottom. When that happens, the mix valve is all the way to the cold side, routing all "cold" water to the house. Obviously as time goes on, the house will strip some heat from that water and the mix valve will be able to regulate. But putting it simply, if you give 180 degree water to both the hot and cold ports, expect around 180 on the mix port.

3) It works. Just two days ago I got a panel rad hooked up in a room which has no other heat besides a woodstove. The rad I installed is not big enough to meet the entire room's loss, so it finds a "happy place" when fed with ODR water. That happy place is where the heat emitted by the radiator meets the heat lost from the room. As it turns out that was about 55 degrees, not so comfy. But here is the kicker... The room was pretty much constant at that temp for like a day and a half. As the outdoor temp dropped, the ODR shoved hotter water into the rad and the balance point was met. I left for an overnight away (amazing having "central" heat), came back, and the room was 53 degrees. And it was like 5 degrees last night.

4) Today when I came home I got a good look at what an "empty" tank looked like - about 800 gallons of 90 degree water and then a thermocline with 120 at the top of the 1000 gallons. I don't think I'd get that without ODR. I was using a RR of 1.20, which I think drove up my return temps from the earlier pic.

5) the obvious thing - distributing lower temp water should be more efficient in terms of heat lost off piping, underground, etc.

Obviously indoor feedback of some sorts is required to deal with the effects of solar and other heat gains, like pesky humans and their cooking and bathing habits. In my case, I'm using a Euro system of constant pressure pump, low flow rates, ODR mixed water and TRVs on panel radiators. If the sun comes out (or if I fire up the woodstove, like I did this afternoon), the TRVs start to shutdown the flow rate in the radiator, reducing it's output. I have my panel rads hooked up to a radiant manifold and can watch the flow meter and from the flow rate, I can easily deduce which loops are throttling flow meaning that the room is in regulation. Changing the pump speed (or shutting it off), or using the indoor temp to reduce the water temperature all see like viable options.

Since I've put this together I've come to learn that there is another type of mixing valve - one without a rotating spindle like the LK and Tekmar valves. It's a 3-way valve and it has a fitting for a TRV on it - meaning it will attempt to regulate the mix port to whatever the TRV senses. At first this might seem stupid - who is going to put piping in their living spaces so the TRV can see the room temp? But there are remote thermostat heads with capillary tubes which will screw onto the TRV fitting. Think aqustat(-ish), Euro-style, electrons need not apply. Apparently these valves and control heads are used for some Euro radiant floor setups. So instead of bang-bang (on/off) control of a pump at a fixed speed, they regulate the temperature of the water supplied to the floor to meet the room loss. Interesting concept. Still noodling on how that all works with just proportional control, which is what a TRV is.

That's what I've figured out so far. I know there are those on this site which don't care to use ODR, and that's cool. I personally have learned so much from the hearth archives that I thought I'd try and give back - so here is what I've learned so far.

I know I am on thin ice here (Sales guy asking an Engineer a design question) but based on #2 it sounds like you are feeding both ends of your mixing valve directly from storage, why did you do this vs. feeding the cold side of the valve with the return water from the house? This would allow you to heat the entire tank to 180 (I push my top to 195 +/- a little).

Regarding your point #5 not everyone here would agree that this result in greater mpg.

Must agree with TCaldwell - most impressed with what you have done!

 

[maple1]

I know I am on thin ice here (Sales guy asking an Engineer a design question) but based on #2 it sounds like you are feeding both ends of your mixing valve directly from storage, why did you do this vs. feeding the cold side of the valve with the return water from the house? This would allow you to heat the entire tank to 180 (I push my top to 195 +/- a little).

I was wondering that also but then thought I must have mis-read something or not understood.

 

[nhtreehouse]

maple1 and JohnDolz, I could entirely be wrong on the lower tank temp thing (#2 above), and would be happy to be corrected. My tank is piped "2-pipe", but there is a lot more to it than that. I'll put together some drawings tonight and try and explain what I've seen. When I wrote the original post I based it on what I was seeing that day in the boilerhouse, but I might have been doing some testing where the house was isolated and that might have screwed up the results.

More later - and I may be having humble pie for dinner.

 

[JohnDolz]

maple1 and JohnDolz, I could entirely be wrong on the lower tank temp thing (#2 above), and would be happy to be corrected. My tank is piped "2-pipe", but there is a lot more to it than that. I'll put together some drawings tonight and try and explain what I've seen. When I wrote the original post I based it on what I was seeing that day in the boilerhouse, but I might have been doing some testing where the house was isolated and that might have screwed up the results.

More later - and I may be having humble pie for dinner.

I may have just misunderstood what you were trying to say. The way my system is set up Return from the house comes into the cold port of my mixing valve, this way I am using minimum hot water (top of tank) to mix that water UP to the desired temperature. The way I read your post it seems like you are using cold water from the bottom of the tank to COOL top tank water DOWN to your desired temperature. Like I said I could have just misread you. By the way I eat humble pie often and it is quite delicious!

 

[nhtreehouse]

maple1 and JohnDolz, you're right and I'm wrong, humble pie eaten for dinner last night.

But there is a lot more to it. What I saw in the boilerhouse last night confirmed the issue I'm having when the bottom of the tank is hot, and the mix temp is not controlled. And shame on me for not seeing it sooner, like when I was piping it out.

This might be of interest to some, if not, go ahead and ignore me now.

My tank to boiler is piped "2-pipe." But I have a vertical tank, and getting the mixer piped in from the top of the tank and the bottom of the tank was a bit tricky, as it's about 15 feet from one port to the other. I know I stared at the piping for a long time before sweating it in, and at the time I thought it was just fine. Here are a couple of annotated shots - taken 90 degrees from each other.

Side view, Mix goes to the house, Rtn is the house return. These exit the wall, turn 90 degrees and go into the underground piping. The piping on the outside is surrounded by a huge foam box. You can see the thermistors for Mix and Rtn - more on that later:

Front view - tank on the right, boiler on the left, Lk thermovar just out of view to the left past the strainer.

So, in theory, Rtn flow from the house enters the 2" tee and flows upwards through the piping marked "cold to 3-way", enters the cold port on the 3-way valve and goes back to the house via the Mix pipe. This works fine when the boiler is off, the thermovar is closed and there is no "boiler flow".

What I'm seeing in the boilerhouse is that when the thermovar opens, hot water is bleeding into the cold side of the 3-way valve. The PID loop closes the valve slightly to compensate for the warmer "cold" water. After the first lap through storage, the thermovar opens completely, and the PID looses control, closing the valve completely, shunting all cold water to the mix. But, the cold port on the valve is a mix of the Rtn water and the boiler return flow. Those are approximately 85 and 160 degrees in last night's experiment.

I setup the datalogger to get to the bottom of this and the results surprised me. This is during the burn, in the middle, the boiler shuts off and for the right half of the graph we're running off storage:

Mix is the dark green trace, Rtn the neon green trace. Yellow is the PID control (pid_out) - it should be around 300, which corresponds to 3V control to the valve, and roughly 30% open. When the pid_out signal goes to 0, the valve is shunting all cold water to the mix port.

So the first very disturbing thing is that during the first lap through storage, the PID is constantly decreasing, which says the cold port on the valve is getting warmer. Unfortunately, I didn't have a sensor on the cold port of the 3-way valve. The hot port is "hF', the teal trace above and is roughly constant. command is the setpoint for the Mix temp. T6 is my bottom tank sensor, PID error in red.

A zoom in:

On the left hand side, the boiler is finishing it's first lap through storage, and when the teal hF line starts to increase, the thermovar is wide open. The cold port on the 3-way valve gets more hot water, to the point where the PID goes to zero and the mix is unregulated. At the peak on the hF trace, it looked as if I was going to overshoot the storage capacity, so I kicked the house circ on the highest constant pressure - "3", possibly doubling it's flow from ~1gpm to 2gpm. It's an alpha and it said there was 2 gpm going to the house. The PID loop woke back up and started regulating. Then a few minutes later, I decided we would be Ok on storage, so I kicked the alpha back to Auto. PID looses it's mind again, and the mix (dark green) goes unregulated.

That all said, I believe I created a really nice gravity flow problem in my piping. It's only really a problem when the boiler circ is on, and the thermovar is open to some degree, and it's really a problem when the thermovar is all the way open. I'm thinking that it's more of a problem with low flow and low mix temp (it was above freezing for the duration of this little experiment).

I'm certainly open to other explanations. Injection mixing? Wouldn't think that was possible, but...

I'll add some more temp sensors for the next burn in a couple of days. Hopefully will confirm what I saw during this run, but with temp logs for the mixer "cold" port, and the thermovar mix port.

 

[BoiledOver]

These questions do not require an answer for me. I appreciate different angles of thinking when troubleshooting an issue, so enter the questions as an aide to you.

Does the alpha circ have its check valve? Can an adjacent gravity flow trespass the zone circuit? Is your house circ pulling away from the Tekmar 3-way mixing valve? Could the rotation be reversed on the Tekmar 742? Is your flow temp sensor far enough down stream of the Tekmar mixing valve? Mine is mounted one foot beyond the circ.

It doesn't appear, to me anyway, that your plumbing is a problem. In fact, mine is the basically the same. The ODR module from Armatur will take the 3-way to either dead end rotation and remain until a conditional input prompts a reverse motion. The ends are 100% closed one way or the other with the Tekmar 710 mixing valve. Could your ODR controller be malfunctioning?

 

[JohnDolz]

My tank to boiler is piped "2-pipe." But I have a vertical tank, and getting the mixer piped in from the top of the tank and the bottom of the tank was a bit tricky, as it's about 15 feet from one port to the other. I know I stared at the piping for a long time before sweating it in, and at the time I thought it was just fine. Here are a couple of annotated shots - taken 90 degrees from each other.

Side view, Mix goes to the house, Rtn is the house return. These exit the wall, turn 90 degrees and go into the underground piping. The piping on the outside is surrounded by a huge foam box. You can see the thermistors for Mix and Rtn - more on that later:
View attachment 222893

Front view - tank on the right, boiler on the left, Lk thermovar just out of view to the left past the strainer.

View attachment 222894

So, in theory, Rtn flow from the house enters the 2" tee and flows upwards through the piping marked "cold to 3-way", enters the cold port on the 3-way valve and goes back to the house via the Mix pipe. This works fine when the boiler is off, the thermovar is closed and there is no "boiler flow".

What I'm seeing in the boilerhouse is that when the thermovar opens, hot water is bleeding into the cold side of the 3-way valve. The PID loop closes the valve slightly to compensate for the warmer "cold" water. After the first lap through storage, the thermovar opens completely, and the PID looses control, closing the valve completely, shunting all cold water to the mix. But, the cold port on the valve is a mix of the Rtn water and the boiler return flow. Those are approximately 85 and 160 degrees in last night's experiment.

.[/QUOTE]
Definitely not suggesting your piping is wrong, just telling you what I have gong on here. If I were to apply to way my system is piped to your picture I would tell you that the vertical return to the 3 way valve would be teed before it hits the boiler flow. The thinking being the return water will get "sucked up" to the mix valve and the "boiler flow" will take the path of least resistance heading straight back to the boiler. I got the book "Plumbing Away" but honestly only looked at the pictures so please take anything I write with a grain of salt.