Logic/ control tree help please

[pybyr]

With cooler weather on the horizon in VT, I need to get back to work on planning and finishing my control system (to date, I've run by manual "wire nut logic"). [and I tend to have 'too many projects not enough time' which is why this is just now back to competing for front burner]

My system consists of an Econoburn 150, a 1200 gallon storage tank (unpressurized)(with a plate heat exchanger to tie in to the pressurized boiler system), and a water-air heat exchanger in ductwork for a single heat zone to the house.

Plumbing of the system is by primary/ secondary, with pumps, so it'll be easy to manage which way the hot water is coming or going as between the different heat sources/ loads [yeah, I know that valves can be more elegantly simple/ efficient, but I found it easier to get my head around the pumped system and have confidence that the physical plumbing layout would be right the first time].

I'm going to be using an Azel solar differential control to manage charging of the storage from the boiler, and an Azel DST 777 setpoint controller with variable pulse width modulation to provide return water temperature to the boiler. Already have those parts on hand.

I'm leaning towards using some Auber instruments PID temperature controllers for the other temperature sensing/ switching
http://www.auberins.com/

[by the way, I invite input on whether thermocouples will be OK for the temp. ranges involved, or whether I should go with 3-wire RTD sensors]

And then I plan to use relays if/ as necessary to get the right pumps flowing under the right conditions.

But, since I am better at lateral/ creative thinking than linear thinking, I am having a hard time with the initial stages of charting out a logic/ control tree.

I am familiar with the basic idea of "and" and "or" switching, which is what I plan to use the PID controls and relays for; I've done that (relays as and/ or...) on other projects, but not with something with this range of inputs and operating states.

So, where I'm struggling is in the aspect of what 'layer' of the switching/ input parameters/ operating modes to start mapping both the functional and electrical schematics.

I actively seek experience and wisdom to help me move forward on this.

Thanks

Trevor

 

[kabbott]

50 views and no bites on this one???

Trevor could you post your plumbing layout or a link to it? I know I have seen your layout before but don't recall the details.

Will the econoburn control the 'near boiler' pumps or will your external controls handle everything? I think your system is fairly simple plumbing wise
but a picture would go a long way.

I to was a bit overwhelmed when I started the rules for my NFCS. I found that just writing out an 'if/then' list for each pump worked for me. I will admit going back and streamlining
the rules a bit (like 3 or 4 times ;-) )

Kris

 

[pybyr]

Thanks Chris-- and I hope some others join in too--

here is my diagram

https://www.hearth.com/econtent/index.php/forums/viewthread/21524/P15/

The Econoburn can control the near boiler pumps, unless there is reason to do otherwise.

Thanks

 

[sdrobertson]

50 views and no bites on this one???

I'm one of the views, but this stuff is over my head. I do look forward to the explanations as I'll learn some more.

 

[Piker]

50 views and no bites on this one???

Trevor could you post your plumbing layout or a link to it? I know I have seen your layout before but don't recall the details.

Will the econoburn control the 'near boiler' pumps or will your external controls handle everything? I think your system is fairly simple plumbing wise
but a picture would go a long way.

I to was a bit overwhelmed when I started the rules for my NFCS. I found that just writing out an 'if/then' list for each pump worked for me. I will admit going back and streamlining
the rules a bit (like 3 or 4 times ;-) )

Kris

I do not believe the econoburn two-pump controls to be adequate for boiler return tempering with thermal storage systems. If I recall correctly, the use of a mixing valve or loading unit when using storage was something we added to the owners manual when I worked as a sales rep for them. Given the location of the thermocouple that controls the boiler's circulators (which is installed from the factory about as far away from the return line as you can get) you can actually get several minutes of cold water returning to the boiler before the thermocouple can sense a temperature change. Wide temperature swings are hard on the boiler plate and refractory of a low mass gasifier, and can produce quite a bit of condensation inside the boiler as well, depending on actual return temps of course. The controls were more or less designed around using the boiler without storage and through a heat exchanger in the plenum of a forced air furnace with a relatively low delta t... for this, the control logic is sufficient. Even hot water systems with large radiators or radiant floor require you to be careful with return temps on any of the low mass gasification boilers that are on the market... even without storage. I would, for instance, never install a Solo Plus without return protection.

hope this helps.

cheers

 

[kabbott]

Thanks Chris-- and I hope some others join in too--

here is my diagram

https://www.hearth.com/econtent/index.php/forums/viewreply/655002/

The Econoburn can control the near boiler pumps, unless there is reason to do otherwise.

Thanks

Ummmm, Is it just me or does that link take me right back to this thread???

If the Econoburn is not up to controlling the boiler/return protection pumps then just use the external controls for them to.
I assume this is setup with two pumps on the boiler, One is just a bypass pump?
Are the pumps variable or multi speed or single speed? I Would start with return protection... boiler reaches set temp and bypass pump comes on...when return reaches set temp boiler loop comes on and bypass loop stays on... when return reaches yet higher temp bypass loop turns off and boiler loop keeps running.That should take care of the boiler as long as your sensors
react rather quickly.

I am not sure how the differential controller will interact with the other controller, On my system no pumps run unless something is calling for heat, be it the storage or domestic
or baseboard heat (unless the boiler overheats and then it will dump to the baseboard even if house is not calling for heat).

 

[in hot water]

I agree that it would be nice to use some variable speed functions. It's a great way to provide return protection, accurately and efficiently.

I like this method better than restrictive thermostatic valves. It is also great for mixing down temperatures to radiant or low temperature zones.

A step further would be out door reset on the heating pumps. The V/S function is done with a triac relay, maybe these relays could be imbedded in the No-Fossil control circuit board.

hr

 

[Piker]

just a quick note on thermostatic mixing valves being restrictive... while this is true, depending on delta T from the storage tank, it may or may not be an issue. I have become quite fond of the loading pumps in lieu of the standard thermostatic mixing valves. The loading units are less restrictive, and are capable of closing the recirc loop completely once the return water comes up to temperature. Very smooth operation, and no need to install a bypass valve on the recirc loop to make them work properly like the regular termovar valves.

A variable speed injection loop is certainly the cats meow when it comes to return protection... a little pricier than a loading unit... and the loading unit being pricier than a standard termovar. It's fair to say that all three methods can be made to work nicely on most systems.

cheers

 

[rkusek]

I think this the link to prbyr's schematic https://www.hearth.com/econtent/index.php/forums/viewthread/21524/P15/

 

[jebatty]

This may have come up before with the posting of your plumbing layout. Ideally you want counterflow on the HX. Although you have reversible circs on the storage side of the HX, which is good, you will get counterflow only when either charging the tank or when discharging, as the system supply side of the HX pumps in one direction only. I have never seen performance charts of plate HX's plumbed parallel flow vs counterflow to know what the difference on approach temperature actually is.

 

[jebatty]

Some comments on the solar differential controller for charging the storage tank. The plus side of the Azel is the ability to set the differential between 0.8 to 17.9°F. I originally used a Steca solar differential controller, but it had a fixed differential of 8F, which did not allow charging the tank higher than about 180F, although maximum boiler output is higher. I wanted to be able to charge my tank up to maximum boiler output temperature.

What I did was simply run the charging circ(s) whenever the boiler was firing and supply temperature over 160F. Since I fire the boiler only when I need to charge the tank (I draw all needed heat from the tank), in actual operation boiler output always is above tank temperature, so I always want to charge the tank when the boiler is firing. The only exception is when the wood load burns down and boiler output temperature begins to fall. The solution I found that works best is not a differential controller, but instead a low limit controller for the charging circs that operates based on flue gas temperature. Mine is set at 200F. In operation charging begins when boiler supply temp is over 160F, and charging continues until flue gas drops below 200F. This was easy to do with the Tarm, as it has an internal low limit controller that shuts the Tarm down at the temperature setting of the low limit thermostat. I just wired this circuit into a relay, so when the Tarm shuts down, the relay contacts also open on the charging circ(s) and charging stops.

The Azel, with the ability to set a closer differential, should not result in the issue I had. But also, my solution saved me perhaps $200 by not needing a differential controller.

 

[pybyr]

Thanks everyone for the input so far (and for the correction on the link to my earlier diagram) (and I edited my post above to have the correct link).

Let's assume that the flow paths that I have in the plumbing are reasonably OK and they are what they are, 'cause I am only going to pick up wrenches and blowtorch if something really doesn't work after I have a control system in place and running.

And regarding the near boiler piping and controls/ low temp protection, based on some earlier input from Nofossil when I spoke to him at the big Expo this past May, I am going to use the Azel setpoint control to throttle back the flow when the temp drops, so as to keep the boiler from hovering at low temperatures. [this is a separate/ additional Azel control from the differential one that'll be used to determine the basic charging of the tank]

So I'm still back to needing some input to get myself unstuck on the basic topology of the larger system controls.

Thanks

Trevor

 

[kabbott]

and an Azel DST 777 setpoint controller with variable pulse width modulation to provide return water temperature to the boiler. Already have those parts on hand.
Trevor

Sorry I missed that^^^

So the boiler/bypass loop can be switched via the Econoburn and control of bypass loop handled by the dst 777 . The storage charging will be handled by the differential controller.
The primary loop pump is easy, it needs to run when any LOAD pump is active. That can be done with an extra set of relay contacts on each load pump, just wire the contacts in parallel
and drive the primary pump with them.

Which leaves only the plenum pump correct? The room thermostat can control the plenum pump directly maybe?
So you only need logic to decide BOILER or STORAGE based on their temps?

I don't think I would even use another control. Just use relays... If the boiler pump is running a call for heat will turn on the plenum and primary pump... if the boiler pump is not running
a call for heat will turn on plenum, primary and storage discharge pumps. If the boiler and storage are cold an aqua-stat could kill the storage pumps so they won't run if not moving any
heat, And could also turn on warning light, buzzer, whatever(HEY I'M COLD DUMMY FEED ME SOME WOOD)

The Econoburn will turn on boiler pump whenever it is hot.
The diff controller will turn on storage pumps and primary pump whenever the Econoburn is x degrees hotter than storage.

I may be missing something else, let us know....
I love puzzles. :cheese:

 

[Donl]

Just an observation. If you haven't already notice the flow on the secondary to the furnace plenum is flowing in the wrong direction.

 

[ewdudley]

...

So I'm still back to needing some input to get myself unstuck on the basic topology of the larger system controls.

...

Need to divide and conquer by identifying sub-systems that can be controlled independently once their inputs have been identified, kind of a bottom-up-and-done, top-down-now-what iterative process.

What I normally do is sit down with paper, pencil, and eraser and write down a list of the symbols I'm going to use to refer to all the signals and active components of the system, along with six or eight words to describe each of them.

For instance for your system:

EconoBurnCallForLoad. 24VAC from EconoBurn. Boiler is running and (presumably) needs to get rid of heat.

PEconoBurnRecirc. EconoBurn recirc pump.

KEconoBurnRecirc. PEconoBurnRecirc activation relay.

PEconoBurnInject. EconoBurn boiler loop return water injection pump.

PWMEconoBurnRetCtrl. 24VAC Azel DST 777 control signal.

KEconoBurnInject. Relay that actually powers PEconoBurnInject.

PPrimaryCirc. Primary loop circ pump.

And so forth, reworking the list iteratively the make the symbols more and more consistent and meaningful to yourself and whoever might be tasked with working on the system.

Meanwhile edit an official theory-of-operation document that describes the goals and functions of the system strictly in terms of the list of official dictionary you're developing. For instance:

"Once the EconoBurn is lighted and until it shuts itself down, it activates signal EconoBurnCallForLoad whenever it senses that its supply temperature is above 150F. Signal EconoBurnCallForLoad activates PEconoBurnRecirc through relay KEconoBurnRecirc. EconoBurnCallForLoad also activates PWMEconoBurnRetCtlr, which modulates return water temperature via KEconoBurnInject/PEconoBurnInject."

Off to the side you may or may not want to write some logic equations that condense the theory of operation into anding and oring of signals.

Now you're ready to draw schematics for whatever portions of the system that are fully described and get them out of the way.

So now we know how PEconoBurnRecirc and PEconoBurnInject are controlled, but what other implications are there for EconoBurnCallForLoad being true?

By way of example I would assume that PPrimaryCirc would need to run whenever EconoBurnCallForLoad is true, and also the temperature of the primary loop at the point where PEconoBurnInject draws return water would need to be less than e.g., 140F. So we need to inject cool water into the primary loop from storage in order to maintain this maximum temperature, or none at all if heating load is sufficient, but the point is that we can develop logic for pulling cool water from storage independent of what the loads of the system are doing, decribe that logic in the theory of operation, draw that portion of the schematic and get that out of the way.

And so forth until you have a completed system. YMMV.

Cheers --ewd

 

[pybyr]

Just an observation. If you haven't already notice the flow on the secondary to the furnace plenum is flowing in the wrong direction.

Thanks for the suggestion, but all of the points on my primary loop consist of Taco Twin Tees, which have two ports side by side, rather than in sequence, so they are ambivalent about which is exit and return-- I just couldn't depict them that way.

They're a really neat product because you get the equivalent of closely spaced tees in one compact fitting, but they're really more like "side by side tees"