circulating pump for Econoburn

[Woodrookie]

First fire today for my Econoburn outdoor 200! Everything seems to be going well except the circulating pump has not kicked on. Is it supposed to run continually or only once it reaches a certain temperature? RIght now the unit is at about 70 degrees. Thanks, John

 

[b33p3r]

If 200 is same as 150, the circulating will kick on at 150* and continue to circulate until temp falls below 150*. +- a couple degrees.

 

[Woodrookie]

Excellent, thanks for the info. I will keep monitoring it... Just out of curiosity, do you know why its set up like this? Is it some sort of safegaurd against something?

 

[b33p3r]

The recirc pump circulates to get boiler up to usable temp,150*. The primary to house will take over after that. If the wood boiler temp falls below 150* the recirc will come back on and primary shuts off to bring the boiler back up to usable temp and prevent cold shock to boiler. As in my case, I pump wood boiler through oil boiler. If temp fell below 150* on wood boiler and primary kept pumping, my oil boiler would maintain the wood boiler which would waste alot of oil! However its mostly about cold water shock in wood boiler.

 

[Woodrookie]

got it..interesting stuff. I'm new to all this and not very mechanically inclined but learning all the time. Anyway, the pump kicked on and we're up and running.

Note to propane deliver guy: from now on, just keep right on going past my house!!

 

[Piker]

The recirc pump circulates to get boiler up to usable temp,150*. The primary to house will take over after that. If the wood boiler temp falls below 150* the recirc will come back on and primary shuts off to bring the boiler back up to usable temp and prevent cold shock to boiler. As in my case, I pump wood boiler through oil boiler. If temp fell below 150* on wood boiler and primary kept pumping, my oil boiler would maintain the wood boiler which would waste alot of oil! However its mostly about cold water shock in wood boiler.

Based on the position of the thermocouple that is used to switch between the near boiler and system circs... there is no real return protection in this control structure. Last I knew, and on all the ecoburns i have installed, the thermocouple was at the very top of the boiler vessel... about as far away from the return line as possible. The back of the boiler can be hit with 50° water for several minutes before a change is registered at the top of the boiler.

Real return protection needs to be in the form of an injection loop or thermostatic mixing valve.

I think that the controls as designed were intended to be run with forced air heat exchange systems like most outdoor wood boilers... for this, where thermal shock isn't really an issue, the control structure serves it's purpose. Hydronic emitters can be a different story, however... A large radiator zone, or a radiant slab, can return very cold water for a period of time. Even a large baseboard zone that has been sitting idle for a day can return room temperature water to a boiler that's 180.

If the location of the thermocouple has changed, someone let me know...

cheers

 

[ewdudley]

Real return protection needs to be in the form of an injection loop or thermostatic mixing valve.

I think that the controls as designed were intended to be run with forced air heat exchange systems like most outdoor wood boilers... for this, where thermal shock isn't really an issue, the control structure serves it's purpose. Hydronic emitters can be a different story, however... A large radiator zone, or a radiant slab, can return very cold water for a period of time. Even a large baseboard zone that has been sitting idle for a day can return room temperature water to a boiler that's 180.

If the location of the thermocouple has changed, someone let me know...

I don't see that changing the boiler temperature sensor location would be workable. If the boiler sensor is moved towards the bottom of the boiler then it would see cool return water sooner, but then the top of the boiler would be susceptible to getting too hot before the relocated sensor is hot enough to permit the circulator to run again.

It seems to me the only way out is like you say, some sort of boiler recirculation loop that mixes cold return with hot supply in order to maintain acceptable return temperature.

If the system load flow is constant enough it could be as simple as to provide a parallel path back to the boiler with a manual or automatic proportioning valve that would mix in plenty of hot supply water back to the boiler.

For my oil boiler I set up a fat recirculation loop with its own circulator that runs whenever the load circulator runs. I downsized the load circulator to be matched better with load requirements, which makes the load flow only about one third of the recirculator flow.

This way the boiler temperature drops for the most part uniformly, and the boiler sensor at the top of the boiler can stop the circulators before the whole boiler is filled with cool water. I didn't want to spring for a variable speed injection control or a Danfoss for an oil boiler we wouldn't be using much any more, so I thought this approach would work good enough. But it turns out that it works great, cycling the cirulators in about a four or five minute cycle with a 10 degF hysteresis on the low limit control.

--ewd

 

[kabbott]

I use sensors on the inlet and outlet of my boiler. My bypass circ comes on based on stack temp so it starts as soon as I build a fire no matter the water temp. That keeps
from getting hot spots on startup from no flow. My boiler loop comes on at 150. Both circulators are VS via the nimbus/NFCS so I can control both inlet and outlet temps and
so far works great. I would put a nimbus on the draft fan but it is capacitor start... may need a little re-engineering

Kris

 

[Chris Hoskin]

Is there a down side (real or perceived) to a Termovar type thermostatic mixing valve? Why are folks trying so hard to re-invent that wheel?

hoping to learn something,

Chris

 

[kabbott]

Is there a down side (real or perceived) to a Termovar type thermostatic mixing valve? Why are folks trying so hard to re-invent that wheel?

hoping to learn something,

Chris

If you don't have the system to control the VS pumps the termovar may make more sense... I already had the NFCS so...

1. cheaper-pump + nimbus<$130
2. no flow restriction from thermo valve
3. precise control of temps-type the new temp in the web interface and that's it.
4. MOST importantly because it's cool and I can... :coolsmirk:

The Econoburn setup and some discussion with Nofossil gave me the idea to go this route. I think it's a shame Econoburn does not take this to the next step
to be able to actually control the return temps.

Kris

 

[Chris Hoskin]

thanks for your thoughts Kris. By the way, reason number four above is one of my FAVORITE reasons!

Wife: "why do you need to do that?"
Me: "need? oh, need has nothing to do with it!"

 

[ewdudley]

Is there a down side (real or perceived) to a Termovar type thermostatic mixing valve? Why are folks trying so hard to re-invent that wheel?

hoping to learn something,

Danfoss and Termovar are great solutions, but my temperament won't allow it. What do they cost, upwards of $200 for just the valve? Should be a $45 part, but it isn't, and I ain't paying it whether it works better or not, nor whether it I can afford it or not.

What is so hard about plumbing in a zero dollar salvaged 007 and leveraging the existing control and ending up with return temperature cycling in an adjustable 10 degF range? Shouldn't some wheels be reinvented?

 

[pybyr]

Danfoss and Termovar are great solutions, but my temperament won't allow it. What do they cost, upwards of $200 for just the valve? Should be a $45 part, but it isn't, and I ain't paying it whether it works better or not, nor whether it I can afford it or not.

I looked at a mix valve that a local friend was installing for his gasifier+ storage system, and it looked literally like an automotive thermostat in a really uncomplicated cast housing. I agree that this is one item where someone has a profit margin that is a bit excessive.

I've got an Azel 777 setpoint control with pulse duration modulation that's going to handle the return protection on my Econoburn (by switching between the main circ and near circ pumps if the return gets too cool).

Just need to start wiring it up with all the other relays, differential control, etc. Hopefully, that'll start next weekend, as I finally now have nearly all the parts on hand.

 

[ewdudley]

...
I've got an Azel 777 setpoint control with pulse duration modulation that's going to handle the return protection on my Econoburn (by switching between the main circ and near circ pumps if the return gets too cool).

Just need to start wiring it up with all the other relays, differential control, etc. Hopefully, that'll start next weekend, as I finally now have nearly all the parts on hand.

I'm going with a PID duty-cycle modulation controller for return temperature control on the wood boiler as well, since the wood boiler is not as simple, predictable, and controllable as the oil boiler, although I'm set up to run the boiler recirculator all the time instead of switching back and forth.

The weak point in cycling motors on and off is normally the relay contacts, which are typically rated for 100,000 cycles under load, unless they're overloaded and then they'll crap out pretty early in the game. So a longer cycle will of course lower the number of cycles over time, but at some point you lose tight enough control.

Just going by the looks of them I would recommend not using an Azel type unit to switch even a dinky motor; you'd probably be better off using the Azel to switch the coil of a socketed ice-cube relay that can be replaced easily and cheaply when it goes bad.

--ewd

 

[pybyr]

...
I've got an Azel 777 setpoint control with pulse duration modulation that's going to handle the return protection on my Econoburn (by switching between the main circ and near circ pumps if the return gets too cool).

Just need to start wiring it up with all the other relays, differential control, etc. Hopefully, that'll start next weekend, as I finally now have nearly all the parts on hand.

I'm going with a PID duty-cycle modulation controller for return temperature control on the wood boiler as well, since the wood boiler is not as simple, predictable, and controllable as the oil boiler, although I'm set up to run the boiler recirculator all the time instead of switching back and forth.

The weak point in cycling motors on and off is normally the relay contacts, which are typically rated for 100,000 cycles under load, unless they're overloaded and then they'll crap out pretty early in the game. So a longer cycle will of course lower the number of cycles over time, but at some point you lose tight enough control.

Just going by the looks of them I would recommend not using an Azel type unit to switch even a dinky motor; you'd probably be better off using the Azel to switch the coil of a socketed ice-cube relay that can be replaced easily and cheaply when it goes bad.

--ewd

Thanks for noting that potential concern Elliot. The Azel's contacts are rated 10 amps, and the circulators that I'll be switching are under an amp. I did just send an inquiry to Azel to see what they thought/ recommended.

 

[ewdudley]

Thanks for noting that potential concern Elliot. The Azel's contacts are rated 10 amps, and the circulators that I'll be switching are under an amp. I did just send an inquiry to Azel to see what they thought/ recommended.

Let me maybe backpedal.

Working from memory I was confusing the Azel with the ubiquitous 'JLD7100'/'TET7100' type of cheap PID temperature controllers that are rated for three amperes, on a good testing day.

The argument for a using a separate relay in the case of the rated-for-ten-amperes Azel would be valid on its face with respect to moving the potential point of failure to a more replaceable component, but less compelling.

Cheers --ewd