Question for Econoburn owners....

[kuribo]

Hello-

I have an Econoburn 200 (indoor model) and have been wrestling with my system design prior to install. I would like to configure my system to control the boiler output temp to a steady supply temp, send the water to my 1000 gallons of storage in a "one and done" manner, using variable speed pumps, one as the primary boiler loop circulator and one as the storage circulator. Nofossil does something quite similar in his system using regular circulators and his control system (incidentally, he has gone above and beyond in answering my questions- thank you!). I would like to use ecm pumps with temp set point control, such as the Viridian pumps from Taco instead of the older style circulators. However, there are some devils in the details with them that are complicating my efforts and his control system does not function with ecm pumps...Soooooo.....

That's the background, here's the question for Econoburn owners: the people at Econoburn tell me that their boiler controller is set up so that the boiler circulator turns on at start up with the boiler fan, then off at 150F. It then turns on the storage circulator. If the water into the boiler falls below 150F, it turns the boiler circ back on, and turns the storage circ off. Rinse and repeat. It toggles back and forth between the two circulators to fill storage and protect the boiler. I believe this is called bang-bang control. They also tell me that the user can dial in the boiler output temp and that the controller modulates the boiler fan to maintain this selected boiler output temperature. I am wondering how accurately and how tightly modulating the fan actually controls the boiler outlet temp through the burn. Econoburn has told me to within a few degrees but I would like to hear actual owner experiences before I abandon my variable speed pump approach...You know, trust, but verify! Thanks.,,

 

[__dan]

I'm sure the NFCS has relay outputs to turn the circs on and off. That's really all you can do externally with an ECM pump. The ECM is basically similar to an AC synchronous motor that come with its own VS drive, optimized for the application. You would not separate the two until you get in the larger sizes, 5 hp or so, where you would buy the drive and motor seperately.

So you could certainly use ECM temp setpoint circs with any control system that turns them on and off, letting the circ do its own thing as intended, speed control with its own algorithm and sensors. Standalone digital controls.

The part where you say the Econoburn swaps circs under load, me I would beat up on the factory if they told me that. The boiler would be on its own short primary loop, basically a pumped bypass, and tap loads off that with closely spaced tees. The boiler circ is always on when the boiler is over the circ launch temp.

You could load storage with a VS injection pump that has built in boiler protection sensing, a second sensor on the boiler return, and ramps as boiler return temp exceeds the low limit setpoint.

There are a variety of ways of doing it. I would probably draw it three or four times differently myself. Just what you said made no sense in a time when the industry should be making progress on best practices. That's why I would first go back to Econoburn and see what they say, They should know the boiler and its application best.

 

[kuribo]

Well, the toggled circulators in a bang-bang control scheme didn't seem the most elegant way to do this to me either but that is what they do....The problem with the variable speed temp set point circulators like the Taco Viridian is that they have a minimum flow that is above what is required to maintain boiler protection and/or keep the boiler output at a steady temp with decreasing boiler output. In other words, at the beginning and end of the burn cycle, you can't slow the flow down enough through the boiler to maintain the boiler output setpoint or run the storage circulator slow enough to maintain the boiler return setpoint. I talked with the Taco engineer who is responsible for programming the Viridian and he strongly recommended against using one in the boiler primary loop to control boiler output temps because he thought it a bad idea to stop flow through the boiler....of course, one could set these ecm pumps up with a bang bang control as well, but that kind of defeats the whole purpose, I would think...Here is the Econoburn recommended piping schematic:

 

[__dan]

Well, the toggled circulators in a bang-bang control scheme didn't seem the most elegant way to do this to me either but that is what they do....The problem with the variable speed temp set point circulators like the Taco Viridian is that they have a minimum flow that is above what is required to maintain boiler protection and/or keep the boiler output at a steady temp with decreasing boiler output. In other words, at the beginning and end of the burn cycle, you can't slow the flow down enough through the boiler to maintain the boiler output setpoint or run the storage circulator slow enough to maintain the boiler return setpoint. I talked with the Taco engineer who is responsible for programming the Viridian and he strongly recommended against using one in the boiler primary loop to control boiler output temps because he thought it a bad idea to stop flow through the boiler....of course, one could set these ecm pumps up with a bang bang control as well, but that kind of defeats the whole purpose, I would think...Here is the Econoburn recommended piping schematic:

View attachment 174574

Yep, just quickly as I'm out the door.

See the straight supply to return boiler piped loop. That's essential to the boiler. Pumped bypass to maintain suitable return temp above 140. That circ is always on when the boiler temp is above the launch temp. Pretty good drawing so far.

The tap for the loads, fine except return that load immediately adjacent with a closely spaced tee. That's because of differences in the flow rates between the boiler and the load. Multiple independent loads may have sequential sets of closely spaced tees in the boiler bypass loop.

Then instead of bang bang (I'm assuming the load short cycles while the boiler circ is always on), you would use this:

http://tekmarcontrols.com/products/hvac-systems/361.html

Which will VS a standard 007, and it will go down to nothing, essentially off then on at the lowest speed, in auto. I have this feeding my slabs and when the slabs have been running every day for a while, the return temp is high and the mix demand is very little. It also does boiler return protection with a second sensor and will not ramp up the load until, or maintains above, the boiler return temp over the low limit.

So, very close to what the factory diagram shows. A high flow pumped boiler bypass loop with the loads tapped off that as boiler return temp allows. I would tap the secondary with the VS injection pump. If you have a straight DHW load that is high flow, delta T through the DHW tank will be not huge, so boiler return protection is probably less of a concern. Just a second set of closely spaced tees, dedicated zone circ for the indirect DHW, and straight boiler water with no mixing.

If the flow rate of the ECM circ is above what works, you can probably throttle that with a (fixed) valve in series to get the low flow rate necessary.

As I said, I would draw it a few times then go a few rounds with Econoburn about the application. That's what they are there for.

https://www.hearth.com/talk/threads/pellet-boiler-cycle-monitoring.152539/#post-2050479

 

[kuribo]

I think they don't show closely spaced tee's because the boiler circ shuts off at 150F and the supply circ then takes over- they never have the two pumps running at the same time, toggling back and forth. Siegenthaler mentions this approach in his biomass-hydronic heating pdf- see below.

I want to send a flow to storage that varies with the boiler output from 0gpm to about 5gpm at a steady 180F out of the boiler, returning from storage at a steady 85F, mixing with 180F water in the boiler loop to return to the boiler at 150F. The flow through the boiler loop would vary from 0gpm up to about 15gpm...

Since the ecm pumps will not pump flows less than 2gpm or so, I will have to go with regular pumps and controller like the tecmar if the toggle method suggested by Econoburn with the fan controlling the output temp doesn't seem to be sound....

Thanks for your replies, much appreciated!

PS here's the pdf of the Siegenthaler lecture:

 

[__dan]

I talked with the Taco engineer who is responsible for programming the Viridian and he strongly recommended against using one in the boiler primary loop to control boiler output temps because he thought it a bad idea to stop flow through the boiler....

View attachment 174574

I read it again. This I see as a problem, a misunderstanding of operating requirements.

If you have a low mass load and expect warm return water pretty quick, like conventional baseboards, the pumped bypass is small and just adds tempering water to raise the return temp.

If you have an elephant load like storage, the load can easily stomp the boiler operating temp, return and supply, down into its condensing range, over its entire full fuel load burn time.

So the roles reverse, the pumped boiler bypass is big and adding the load happens only a little at a time over the burn cycle, because the instantaneous load of storage will stomp the boiler if too much is added in too short a time.

First would be the factory supported piping diagram.

Second would be the sequence of operation.

Third would be selection of controls and circs to achieve the first two. Not choosing the controls and circs first. I did not intend to put item 3 before items 1 and 2.

The Econoburn will have a minimum necessary flow rate while firing under load. That's the bypass circs job. Always on and fixed speed is fine. It never should slow down, which aligns with what the the Taco engineer is saying and the intent of the Econoburn piping diagram.

The load circ's job is to vary the added load so it does not happen instantaneously and stomp the boiler down into the condensing range. Getting the piping and operating sequence right will indicate the right solution in controls and circs.

There was discussion on the board where one of the posters was in discussion with Taco to get them to add a reverse acting feature to the ECM products. Since adding load is cooling the return, the reverse acting fixed temp sensing ECM circ has to slow, to raise the boiler return temp, or maintain it over the low limit setpoint. If this product is now on the market, most likely it will be less expensive and more robust than the Tekmar 361 with an 007, since you would not be using most of the 361's added features, only the boiler return protection with VS adding of the load.

There is certainly some progress that may be made there.

 

[__dan]

Toggling one circ or the other at 200,000 btu output is a non starter for me. No way I could see to put it into the hands of the customer and not expect something the future will frown on. It is not foolproof while the average customer certainly is.

This would be very easy to confirm with Econoburn. All you need is a simple number, their minimum flow rate through the boiler, and pick a fixed speed boiler bypass circ that will guarantee that, always on. Then add load to maintain at or above boiler return temp, let the load circ control calc and VS to make HW return target temp. .

Get one more number from Econoburn, their recommended and max delta T through the boiler. I'm guessing it's between 10 and 20 F and not more than that.

You should be able to forget about the boiler supply temp. You are saying the Econoburn will ramp the fan speed to respond to HWS temp?, so there's some crude modulating firing rate? Anyways, to achieve the target HWS you want, you would set the Econoburn;s firing control to that, then set the return temp setpoint (controlled by the VS load circ) so the return temp will fall in the desired range. Once dialed in, flow through the boiler and delta T will probably fall in a stable range, so you would be able to set HWS by setting target HWR.

The problem I would see with toggling the circs is cold start performance, which is very frequent. Once storage is returning 140, you don;t need the bypass circ, but you would not need to fire the boiler either.

 

[kuribo]

Yes, I was one discussing the Taco ecm with reverse acting control here in the past. The problem with using them in the application as I have described is that they do not vary speed from 0 to 100, but more like 20-100. Thus, as I explained above, they will over cool when the boiler is near the beginning or ending of the burn cycle.

To control the output temperature of the boiler to a fixed point as the output climbs and falls at the tails of the burn cycle, varying the flow of water through the boiler with a variable speed circ is perhaps the most accurate way to obtain a fixed supply temp, I would think. That is unless we hear positive reports from other Econoburn owners about the stability of the built in fan modulation control of supply temp....

I prefer to look at this as a heat balance: the boiler is putting out a varying amount of BTU's into the primary loop where it is moved via a varying, though relatively high flow, low delta T. This is removed by a high delta T, varying, but relatively smaller, flow, to storage. I calculate the ratio of primary to secondary flows to be at a 3:1 ratio throughout the burn.

Both flow and delta t need to be considered. I may be returning 80F from storage, but at a small flow rate, so that there is an energy balance between what the boiler is putting into the primary loop and what is being removed to storage.

 

[kuribo]

I think toggling would work ok if you were sending the water back and forth through storage so that you were returning 120-140-160F water to be heated to 180f, but with a "one and done" approach, I need a steady 180F supply temp so that the as the last gallon of 80F water leaves the bottom of the tank, it is replaced with a gallon of 180F at the top....That's the theory, I know there will not be perfect stratification and some mixing will mean that return temps will climb a bit....

I do need to discuss this more with Econoburn. They promised to send me a complete theory of operation for their controller. The manual is short on details.

This approach using two variable speed pumps to control boiler output temp and return temp is being used by Nofossil and is well documented on his web site with real time system performance....Becomes kind of addicting to watch....Check it outbroken link removed)

 

[maple1]

What is it that you are hoping to accomplish by supplying a steady 180 from the boiler?

 

[kuribo]

One and done storage filling.

 

[maple1]

OK - but is there an advantage to one & done, or a gain to be had? Just trying to understand the reasoning.

I am thinking that having supply temps at 180 for the whole burn might be a little bit of an efficiency hit - the hotter boiler wouldn't scrub quite as much heat out of the gasses before they exit compared to one that was 160 for a good part or most of the burn.

 

[Bob Rohr]

OK - but is there an advantage to one & done, or a gain to be had? Just trying to understand the reasoning.

I am thinking that having supply temps at 180 for the whole burn might be a little bit of an efficiency hit - the hotter boiler wouldn't scrub quite as much heat out of the gasses before they exit compared to one that was 160 for a good part or most of the burn.

I wonder the same? It sounds like you are trying to turn a high mass boiler into an instantaneous/ tankless type of heater? So low flow high delta T. That is opposite of what a typical hydronic heat source is designed and intended to do?

 

[kuribo]

Higher delta t to storage means smaller plumbing, smaller pumps, smaller fittings, less heat loss, etc. Losses on burn efficiency should be at least offset by improvements in system efficiencies. The delta t through the boiler would be a steady 30F, which shouldn't be an issue. Of course, it could be set at 20F as well, would just mean higher flows through the boiler loop....

 

[lotawood]

I think I want a one and done like Kuribo. My thoughts were the advantage of keeping the storage stratified.

On my system with the high mass concrete radiant floor using the hot water, things stay stratified pretty well.

When the boiler is fired, the hot water at the top of storage turns into cold water for an hour or more.

It would be better to just add one and done hot water and keep the stratification.

 

[kuribo]

Any Econoburn owners who can comment on the stability of the outlet temps as set by the controller???