Taco ZVC406 with mix of N/C and N/O Zone Valves

CoalBoilerGuy

I want to have a Taco ZVC406 Zone Valve Control Module cycle my coal boilers circulator only when one or more of the zone valves on my system are open.  Unlike most boilers a coal boiler must make heat continuously, whether the

home needs it or not, otherwise the fire goes out.  Therefore it needs a temperature reducing "dump zone".  My concern is that my aquastat linked high temperature "dump zone" valve is of the normally open type, whereas all of the homes regular thermostat linked zone valves are of the conventional normally closed type.  The dump zones zone valve is continuously energized to force it closed, and it only opens when my high level boiler set point temp of 210 deg. F. is reached, at which time it opens and dumps the boilers excess heat. 



Here is the crux of my problem:  Since the single normally open zone valve is continuously energized under normal conditions, yet it is closed while energized, and the Taco ZVC406 runs the circulator whenever it senses one or more energized zone valves, will my circulator be running continuously (and worse yet, shut off right when it is actually needed the most if the dump zone valve opens due to excessive boiler temp while all of the other zone valves are closed), or will I be able to somehow wire the ZVC406 to cycle the circulator only when one or more of the N/C zone valves are energized and open, and/or when my N/O dump zone valve is de-energized and therefore open?

Alan (California Radiant) Forbes

ZVC 406

That's a tough one.



I'd use an SR501 pump relay as follows:



1) Wire the end switch of the ZVC406 to TT on the SR501.

2) Provide power to the SR501 and make sure terminals H and 3 are jumpered.

3) Connect the pump neutral to N and hot to terminal 4 N/C.

4) Install a jumper between the R terminal and terminal 5 N/O.

4) Connect the NO zone valve to terminal 6 and the 24V terminal next to T-T.



When the end switch opens on the ZVC406, the pump is energized and the NO zone valve is de-energized to the open position.

CoalBoilerGuy

Taco ZVC406 with mix of N/C and N/O Zone Valves

Thank you much Alan!  I don't have either of these units yet.  After I wire the end switch of the ZVC406 to TT on the SR501, are all of the other connections you mention done within the SR501?  Basically I'm confused regarding which of the instruction steps involve connections to the SR501 and which involve connections to the ZVC406 (or if some of the instructions in addition to step 1 involve wires being connected to/from each unit).

Alan (California Radiant) Forbes

ZVC406 and SR501

Yes, only step 1 has to do with the ZVC406.  All the other wiring is on the SR501.  You can see a product description of the SR501 here:



http://www.taco-hvac.com/uploads/FileLibrary/SUB101-053SnglSwtchRly.pdf?PHPSESSID=b78381eb2a92de5fce8ef34b84b7bfd9

CoalBoilerGuy

Taco ZVC406 with mix of N/C and N/O Zone Valves

Alan, many thanks again!!!



One last question remains. All of my N/C zone valves will be connected to the bottom "zone valve" connectors on the ZVC406, but the single N/O zone valve will be connected to the SR501 relay.  What do I do with the open zone valve connection block on the ZVC406 that would normally have had the N/O zone valve wired to it.  Do I jumper it in any way, or just leave it open?

Alan (California Radiant) Forbes

ZVC406

Just leave it open since the SR501 will control that zone valve.

CoalBoilerGuy

Taco ZVC406 with mix of N/C and N/O Zone Valves

Alan, does the Aquastat switch that is signalling to the N/O zone valve still get wired into one of the 'thermostat" blocks along the top row of the ZCV406, or does it also need to be tied into the SR501 relay somehow?

Alan (California Radiant) Forbes

Aquastat

Tell me more about the aquastat.  Does it close on a temperature drop?  What temperature is it set to?  Is it wired in series with the zone valve?  Is there a transformer wired in?

CoalBoilerGuy

Taco ZVC406 with mix of N/C and N/O Zone Valves

It is a Honeywell L6081 dual aquastat.  I will be wiring my 'normally open' zone valve through the high temperature "break on rise" (normally closed) side, and setting it to break (and thereby open the zone valve) at a temperature of 210 degrees F.  My intent is (or was) to place this leg of the dual aquastat onto one of the Taco ZVC406's "thermostat" blocks.  This arrangement should cause the normally open zone valve to open when my boilers temperature reaches or exceeds 210 degrees F., sending flow through my "dump zone" so the boilers temperature drops.  As I understand this, the normally open zone valve will then be closed again when the boiler temperature falls by the aquastats fixed "differential" of 10 degrees F, or to 200 degrees F.  By placing the aquastat on the ZVC406 it will be 24 VAC.  The transformer is built into the ZVC406.   Originally I was going to wire this normally open zone valve into the lower zone valve block of the ZVC406 right below where the upper block with the aquastat on it sits.  Then I realized that this will mess up my circulator function as per my first post in this thread.



The reason why I desire to use a normally open zone valve for my "dump zone" is that in a power outage it will fail open and form a "gravity loop" to draw away heat from my solid fuel boiler that is going to be making heat for some time before the fire goes out during a power outage, with all of my other zone valves failed closed, and a circulator that has stopped running.  It seems like the prudent thing to do.



 

Alan (California Radiant) Forbes

ZVC406 and L6081

Yes, you're right.  It should all work fine except that the circulator will not turn on.  You could wire a relay to the 24 volt connections (the lower block of your aquastat zone) to turn the pump on using the NC connections.  Make sure it's a "double throw" relay.



Are you using the L6081 because you happen to have one laying around?  Just be careful to make sure no voltage mixes between the two controls.  The switch contacts on the L6081 should be "dry", otherwise damage will occur to one or both controls.



If you are using the L6081 only as a high limit control, it might make more sense to purchase and use a plain old L6006A aquastat that requires no power input.  Just for simplicity sake.  It will "break" on a temperature rise.



Whatever you do, document it well and write down the sequence of operation for anyone that comes afterwards.  Leave it in the boiler room for all to see.

CoalBoilerGuy

Taco ZVC 406

To my knowledge the Honeywell L6081A is only a dual set of isolated switches.  It shouldn't matter if one switch is wired for 120V service, and the other for 24 VAC serivce, or am I all wrong here?  I have not purchased this aquastat yet.  Does anyone out there know the answer to this?  How about the very similar Honeywell L4081B dual aquastat?

CoalBoilerGuy

ZVC406

I have had what should be a reliable source (the coal boiler manufacturer) confirm that the L4081 is dry and that there should be no problem having 24 VAC on one leg and 120 VAC on the other.  The L6081 is essentially the same unit as far as I can tell, sans with one side that is SPDT instead of both sides being SPST.