GARN Control Wiring

[deerhntr]

Hope everyone is heating well without Saudi Oil this holiday season,

I have a Control wiring question for you GARN users out there. Hopefully "Hearterman" will add his experience and expertise to the answer as well.

I am in the final phase of bringing my GARN up, and I am finally working out my controls for the system. My current House system is a Oil fired HW heater wired in a "Tankless" Configuration. The Boiler has a honeywell 8124A triple aquastat that controls the boiler, and sends back to my ZONE control board(ARGO ARM-6P) ZC-ZR. The End switch on the ARM-6P feeds X-X to T-T on the 8124A. I have a attached a jpg schematic of the current configuration for clarification.

What I would like to do, is use the X-X from the isolated switch on the ARM-6P as the master control for my GARN. I think that would require that I jumper ZC-ZR on the ARM, and run the GARN as a "COLD START" boiler. In a manual configuration, I would disable my oil-fired boiler.

For a more automatic control, my thinking is to use an aquastat in the GARN TANK to sense a low temperature condition, and then switch a set of relays that would "reconfigure" my existing oil boiler back to the "Tankless" mode, Disable the GARN control, and allow the Oil boiler to act as a back-up. On the GARN tank temperature rise above a setpoint, The relays would switch back to the GARN mode, and switch off the OIL boiler.

My final control solution would be to use a NON-Fossil controller to run everything once I get the kinks out.

So for now, I am just trying to get the GARN up and running, with the most basic of control. That would be disabling the Oil boiler completely with manual switches. I will then workout the backup/switch over control, and then finally switch everything over to the NF controller.

SO MY QUESTION: What do you think, will it work, or am I way off in the weeds somewhere? Comments, or suggestions are encouraged....I can stand the heat!

 

[Jim K in PA]

Russ,

Not sure if you have this figured out already, but I am a bit confused by your description. What do you mean by GARN "control"? The GARN has a timer that runs the fan, and that's it. Are you referring to a pump control?

For a simple configuration, which is what I am running right now (full manual backup), I have my oil boiler configured for cold start (jumper ZF-ZC). I also have my oil gun isolated with a 20A toggle switch. This allows the Honeywell to function normally, thinking the oil burner is running, but my oil furnace is actually bypassed as far as water flow. I am using a TACO ZVC-406 in place of your ARGO for the zone vlaves, but otherwise it's the same setup. I have my end switch on the TACO controlling my primary and secondary pumps (via a TACO SRC-606 out near the GARN), so that as soon as a T-stat calls for heat, the P&S pumps kick on. My house circ is wired through the Honeywell, and kicks on when the heat motor zone valves open. This results in a 30-45 second difference between when my P&S pumps start and when the house circ starts. My HX is in the basement, about 120' from the GARN, and 30 seconds is more than enough time to have hot water circulating in the GARN side of the HX when the house circ kicks on.

You can certainly use the end switch on the ARGO to control more than one relay.

 

[deerhntr]

Russ,

Not sure if you have this figured out already, but I am a bit confused by your description. What do you mean by GARN "control"? The GARN has a timer that runs the fan, and that's it. Are you referring to a pump control?

I'm sorry I wasn't more clear. I was really thinking about two levels of control, the first being the switching between two boilers, GARN being master, and Oil HW being Back-up/Slave. Then the second level of control being once the master or back-up has been selected, how is the pump control, zone control, aquastat control is configured for that selection.

For a simple configuration, which is what I am running right now (full manual backup), I have my oil boiler configured for cold start (jumper ZF-ZC). I also have my oil gun isolated with a 20A toggle switch. This allows the Honeywell to function normally, thinking the oil burner is running, but my oil furnace is actually bypassed as far as water flow. I am using a TACO ZVC-406 in place of your ARGO for the zone vlaves, but otherwise it's the same setup. I have my end switch on the TACO controlling my primary and secondary pumps (via a TACO SRC-606 out near the GARN), so that as soon as a T-stat calls for heat, the P&S pumps kick on. My house circ is wired through the Honeywell, and kicks on when the heat motor zone valves open. This results in a 30-45 second difference between when my P&S pumps start and when the house circ starts. My HX is in the basement, about 120' from the GARN, and 30 seconds is more than enough time to have hot water circulating in the GARN side of the HX when the house circ kicks on.

You can certainly use the end switch on the ARGO to control more than one relay.

In essence, That is exactly what I plan to do for my manual selection between GARN and OIL. My oil boiler aquastat(HW 8124A) is configured in "Tank-Less" mode, although the DHW coil is not used. Therefore the ZC-ZR never holds off my zones, my argo board does that via the priority zone which is an in-direct DHW heater.

For my pumps, I have a couple of SR-501s that will be enabled by the end switch as you stated.

So, yes GARN Control Wiring was a bad choice of words, although I was trying to gain a little more insight into the overall system control than just the pumps. And I was curious how others had done their system control, given the TOTAL lack of any system control discussion in the GARN documentation.

And, yes I do know the GARN has a timer on the fan and that is it. You did leave out the low water lock-out for that fan..... But, I guess for control you could also add opening the door, loading the firebox, and striking the match. But I'm not aware of anyone who has automated that process yet. That may be an assigment for over the winter

Thank you for you input. You are always very helpful.

 

[Jim K in PA]

There are a number of ways to slice the control and piping watermelon. I think that is why Dectra provides just a rudimentary piping diagram, and no control strategy.

As far as control logic for the oil boiler relative to the GARN, I was pretty hung up over this issue last year, but had no time to work out the solution. After living with the GARN for a season, I came to the conclusion that for ME, automating my backup oil furnace is no longer a priority, or a necessity. I still have my oil boiler piped into my house-side plumbing, but was sorely tempted to just delete it altogether. Prudence, however, dictated that I leave it there, but I did need to simplify the means of switching over. Hence, I have two ball valves and a single toggle switch to throw to go back over to oil. Simple enough to explain to anyone, and be done by anyone.

But, if one were to incorporate an automatic backup system, IMO the simplest and easiest means starts with plumbing the house side with the oil (or whatever) furnace as a secondary loop on a primary loop that feeds the zones. Use a single aquastat/sensor in the house primary loop to switch on the backup unit when the cut-in temp is met. When you refire the GARN, and keep the water temp above that lower cut in temp, the backup goes dormant again. With the closely spaced Tees there are not EBVs to control to divert flow through the backp furnace. This does require more pumps, but is overall a simple means of accomplishing automatic backup.

Anywho, that's my take on it.

 

[Gooserider]

My take would tend to be using the same signal for both systems...

Use a make-on-rise aquastat on the Garn to control the coil on a double throw relay. Route the "call for heat" wires to the common contacts on the relay

if the Garn is hot the relay closes, and you use the normally open contacts to send the heat call to the Garn circs and turn on whatever other zone valves or other pumps are needed to get the heat to the distribution system...

If the Garn is not hot, the relay opens, and you use the normally closed contacts to send the heat call to the fossil burner, and again let it feed it's signals to the needed pumps and zone valves...

The distribution system controls are responsible for getting the heat from the inputs to the calling circuit, but this should be the same task whichever unit is calling.

You get automatic switchover, and minimal need for changes to the existing circuits.

Gooserider

 

[deerhntr]

My take would tend to be using the same signal for both systems...

Use a make-on-rise aquastat on the Garn to control the coil on a double throw relay. Route the "call for heat" wires to the common contacts on the relay

if the Garn is hot the relay closes, and you use the normally open contacts to send the heat call to the Garn circs and turn on whatever other zone valves or other pumps are needed to get the heat to the distribution system...

If the Garn is not hot, the relay opens, and you use the normally closed contacts to send the heat call to the fossil burner, and again let it feed it's signals to the needed pumps and zone valves...

The distribution system controls are responsible for getting the heat from the inputs to the calling circuit, but this should be the same task whichever unit is calling.

You get automatic switchover, and minimal need for changes to the existing circuits.

Gooserider

Thanks Goose,

That is basically what I plan to do once I get the kinks out of my manual operation, and develop a little history of use. I will then be able to chose my set points better, and not add any complexity to my initial start-up/debug.

BTW, I am now plumbed, and have done an initial fire. I am currently debugging my House side of the HX. I have a TACO VDT pump on an injection loop with the HX. The pump does not seem to be varying speed to meet varying demand. I didn't get done till late last night, but I think I have to work on a better placement for my supply and return sensors. I will work on that today.

Thanks for the input

 

[Jim K in PA]

After looking at your piping schematic in your blog, I see you are running the existing furnace in series. My suggestion certainly would not work if that is the configuration you want to stay with as far as piping. We ran our furnace in series last winter, and this year I re-piped the house side distribution to eliminate that, since I found a substantial amount of standby loss was occurring through the oil furnace heat exchanger and flue. If your oilfurnace has an automtic damper, that will help reduce that standby loss.

Goose's suggestion to put the aquastat/sensor on the GARN is best, since it eliminates issues with pipe cooling during stagnation (no heat call) causing a false low-temp switchover with a pipe mounted aquastat/sensor. Did you install a temp well in one of the front bungs on the GARN?

 

[deerhntr]

After looking at your piping schematic in your blog, I see you are running the existing furnace in series. My suggestion certainly would not work if that is the configuration you want to stay with as far as piping. We ran our furnace in series last winter, and this year I re-piped the house side distribution to eliminate that, since I found a substantial amount of standby loss was occurring through the oil furnace heat exchanger and flue. If your oilfurnace has an automtic damper, that will help reduce that standby loss.

Well......the series vs. parallel piping is a long and painful story. To shorten it...1) I wanted parallel to minimize standby losses as you describe, 2) To get the job done, I had to go with the series plumbing for the time being. I had to change HVAC contractors at the 11th hour, and wanted to get up and running before the end of the year. 3) This was also the preferred method GARN tech support suggested with the VDT Injection PUMP. So... this what we have, and for now we are heating

Goose's suggestion to put the aquastat/sensor on the GARN is best, since it eliminates issues with pipe cooling during stagnation (no heat call) causing a false low-temp switchover with a pipe mounted aquastat/sensor. Did you install a temp well in one of the front bungs on the GARN?

Yes, I was thinking of this type of system switch over all along. With that in mind, I do have a temp well, and I am also working on some maxim/dallas "one-wire" temp sensors for monitor and control functions. I ran 16 twisted pairs of cat5 in conduit in my trench just for this use.

I have a very interesting story to go along with my VDT pump that I will share at another time. Still have some loose ends to tie up.

Thanks for all of our help Jim, and Merry Christmas and Happy New Year!