Flue draft inducer

[hwater85]

Looking for some advice and direction. I want to install a draft inducer for a DIY Switzer/Garn boiler im planning to build. Id like the inducer to be controlled via flue gas temperature. I've looked for high temp thermostats, but 240f seems to be the highest. I must be looking for the wrong components or in the wrong direction.
Basic control needs would be manual override for start up and then the temp sensor will kill power to the fan when flue temps drop below 250f.
Any help would be greatly appreciated.

 

[brenndatomu]

Thermocouple and a PID or PLC controller...

 

[TCaldwell]

This is a feedback loop, as above you’ll need a type k ungrounded thermocouple, a pid controller to accept the thermocouple temp signal, scale the temp signal range to a controller output, weather it be 0-100 pct or rpm or cfm. Determine a controller setpoint , possibly being optimal flue temp. Next you will need a 3/4 or 1 hp 3 phase motor that’s inverter friendly with rated temp bearing garn uses a 56c frame size , and lastly a inverter to control the speed from the pid controller output. Automation direct will have everything probably about a grand.

 

[hwater85]

OK I've got a new problem. I'm looking at belt driven blower fans rated at 300-500 degrees, i believe this is the type of setup that Switzer is using on his boilers. Anyone out there running on of Garys boilers could steer me in the direction of a brand, type or size that you are using with success. I really like this blower setup compared to the Garn blower, as the belt drive keeps the motor away from the heat and you have multiple pulley size ratios to control cfm.
The main problem is that Industrial blower fans come with Industrial price Tags. Just wondering if I'm looking in the wrong direction?
Again any advice or information is greatly appreciated.

 

[hwater85]

This is a feedback loop, as above you’ll need a type k ungrounded thermocouple, a pid controller to accept the thermocouple temp signal, scale the temp signal range to a controller output, weather it be 0-100 pct or rpm or cfm. Determine a controller setpoint , possibly being optimal flue temp. Next you will need a 3/4 or 1 hp 3 phase motor that’s inverter friendly with rated temp bearing garn uses a 56c frame size , and lastly a inverter to control the speed from the pid controller output. Automation direct will have everything probably about a grand.

Ive been searching some older posts. It looks like you are running a 2hp motor on your garn. Is this still the motor your using and if so, how does it work compared to a 1hp?
I just priced out a 500CFM @ 2''SP blower with a 1hp 3 ph motor. $2000 plus tax and shipping. YIKES!!

 

[TCaldwell]

I did some testing early on with a 2 hp, settled on a 1hp, I think it was a iron horse inverter duty from automation direct, the gs2 inverter they sell was the match for it, both were under 700 . The 60 hz / 3450 rpm through the garn internals is about 260 cfm.
that’s good for 400kbtu +\- at full burn.

 

[hwater85]

Ok.
thanks for the response.
With the high priced quote on the blower fan, I’m now contemplating a direct drive Garn fan setup.
I really wanted to go with the belt driven blowers
But haven’t found one with a practical price point.
thanks again Tom
Adam.

 

[TCaldwell]

Have you researched a fan yet, continental fan is one manufacturer, it will be difficult to determine cfm until you know a static pressure through the boiler.

 

[hwater85]

Have you researched a fan yet, continental fan is one manufacturer, it will be difficult to determine cfm until you know a static pressure through the boiler.

I’ve researched fans for several days.
3/4-1hp units.
9-10” radial Blades.
350-500 CFM at 2”SP.
400f degree rating.
$1700-2100. Plus tax and shipping.

 

[TCaldwell]

350 - 500 cfm is likely too high for a garn style, too fast through the combustion chamber causing incomplete combustion. Resonance time And turbulence in the combustion chamber cause heat equating to a complete burn. Too much cfm won’t allow this to happen.

 

[TCaldwell]

Automation direct,
Marathon inverter duty 1hp E2000, 564$
GS3-21P0 inverter for above 255$
My inverter is the earlier version GS2, so ask them about motor compatibility.
Also my motor mounted on the garn face with a insulating gasket ( as are all garns). The above motor bearings lasted a year, I replaced them with bearings with a better dust seal, for 15$, still going strong.
You’ll need to determine the fan style once you’ve determined where it’s going.

 

[hwater85]

350 - 500 cfm is likely too high for a garn style, too fast through the combustion chamber causing incomplete combustion. Resonance time And turbulence in the combustion chamber cause heat equating to a complete burn. Too much cfm won’t allow this to happen.

350CFM is really the starting point for most industrial blowers. But with the VFD and the size of my primary and secondary intake dampers, im thinking slowing the air down shouldn't be much of a problem.
I'm building the heat exchangers like a Switzer, 2 passes of 9- 2'' sch40, I really like Gary's design for the heat exchangers, it allows me to adjust the amount of tubes being used for heat exchange. If my flue temps are too cold I can adjust air speed and heat exchange capacity.
I'm picking up the steel tomorrow morning. Really excited about building this boiler.

 

[TCaldwell]

Is your p/s air control like Gary’s( door flaps ) or actual butterfly dampers, you must have a pic of what it’s going to look like

 

[TCaldwell]

350CFM is really the starting point for most industrial blowers. But with the VFD and the size of my primary and secondary intake dampers, im thinking slowing the air down shouldn't be much of a problem.
I'm building the heat exchangers like a Switzer, 2 passes of 9- 2'' sch40, I really like Gary's design for the heat exchangers, it allows me to adjust the amount of tubes being used for heat exchange. If my flue temps are too cold I can adjust air speed and heat exchange capacity.
I'm picking up the steel tomorrow morning. Really excited about building this boiler.

There’s a lot of red flags going up based on what I’m reading here, just want to make sure your not going down the rabbit hole, could you call me about 8:30 this evening?

 

[hwater85]

Id like to thank Tom for taking the time to talk last night. He helped shine some light on some potential problems and how i may best correct them. Im going to steel yard this morning. Ill try to post a pic if this rain will ever stop.
Happy Friday

 

[JohnDolz]

Id like to thank Tom for taking the time to talk last night. He helped shine some light on some potential problems and how i may best correct them. Im going to steel yard this morning. Ill try to post a pic if this rain will ever stop.
Happy Friday

Tom is a super smart dude and I have found him to always be amazingly helpful!