Need help with a Taco PC600 Post Purge Timer Card

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Old 09-28-14, 07:44 PM
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Need help with a Taco PC600 Post Purge Timer Card

Hot water gas boiler, two zones each with their own Taco 007 pump all controlled by a Taco SR504EXP (yes, it's a four zone control and we only have two). There is an ODR set to maximum differential of 20. Boiler supplies only heat, no domestic hot water.

I bought a Taco PC600-3 Post Purge Timer Plug-In Card to work in conjunction with the system as a means of cutting back on short cycles. I thought if it ran down temperature within the boiler that it would run longer cycles, and that no heat will be lost. It's ok if the rooms slightly overshoot thermostat setting.

How should I set it up to have the accessory card run the pumps for a short while after the thermostats are satisfied?

Am confused by description mentioning a priority zone when I don't believe there is one.
 
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Old 09-28-14, 07:49 PM
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Trooper, the forum pro, will stop by and help you out.

I am confused though. You have two thermostats tied together controlling two zones of heat ?
Sort of defeating the purpose of two zones.
 
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Old 09-28-14, 08:27 PM
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It is

But it seemed counterproductive to have two thermostats running at the same time as when one was satisfied and shut off, the other would kick on and the system was sorta constantly being called on for heat. So I jumpered the thermostat wires within the 504 box and sometimes when it's ok to have part of the house colder than the other simply flip an added a microswitch which can isolate the jumped wires. That's my own mickey mousing, but the real question is how to properly add this accessory board.

Having two zones maxed out for size within the pump limits (75 feet of baseboard per zone) controlled by one thermostat has worked out well for the most part. Regardless, the boiler short cycles a lot and I was hoping this post purge would allow the boiler to be colder when it starts up and therefore cut back on short cycles.

I was also thinking of replacing the ODR with one which has more than a 20 degree differential, but that's another chapter.

Just want to know how to connect this accessory board as we are totally confused by the priority zone etc. What's the normal way of setting it up?
 
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Old 09-28-14, 08:31 PM
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Hi OldGuy (PJ too!),

On the Taco panels, one of the 'channels' is switchable to 'priority' mode.

This is typically used with an indirect water heater.

When the priority zone (the water heater) calls for heat, and priority is turned ON, that zone will heat normally, but it will EXCLUDE the other zones from calling for heat. i.e. giving priority to that channel to give the fastest recovery time to the water heater.

The post purge card is intended to dump the excess boiler heat into the indirect water heater as a 'storage battery' of sorts.

It CAN do what you want it to, but with caveats:

If you move one of the zones to the priority channel and switch priority ON and install the PC600 card, when that zone calls for heat, it will work normally and the pump will run after the heat call is ended for however long you have it adjusted to (maximum of 10 minutes).

The caveat:

When that zone is calling for heat, the OTHER zone can't get any if it calls at the same time. It will have to wait until the priority zone is finished.

If the OTHER zone is currently running when the priority zone calls for heat the priority zone will 'take over' and the OTHER zone will shut down until priority is finished it's call.

Not really what you want to hear, is it?

There are other ways to do what you want, but they involve strap on aquastats mounted on the boiler hot supply line. I can explain further if you are interested... tomorrow.
 
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Old 09-28-14, 08:33 PM
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I am confused though. You have two thermostats tied together controlling two zones of heat ?
Sort of defeating the purpose of two zones.
I'm confused too!

Where was this mentioned?

So what you are saying is that when EITHER zone calls for heat, BOTH zones run?
 
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Old 09-29-14, 05:31 AM
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Explained

I initially posted a comment which was way to detailed and perhaps confusing. So I cleaned it up and made it simpler. PJMax responded while I was editing it. So yes, his appreciated comment may seem unfounded but it's not at all.

I could be mistaken, the priority zone appears to be the far right terminals within the box and is presently unused. The leftmost two terminal sets are wired.

How will the card work if it's simply plugged in and priority is left turned off (not called for as domestic hot water is not sourced from the boiler).... will it do anything without the priority zone turned on and does the box need to be rewired to accommodate?

As an unrelated comment only for clarification, I have been messing around with the thermostat connections within the 504 because I noticed that quite often when two zones were active that when one thermostat became satisfied the other was ready to start a cycle. As a result, the system seemed to be on a lot more than it had to be, and to encourage fuel savings I tried running it such that one thermostat would control both zones. With one thermostat turned way down, I used the other to control both zones. It's my own experimentation and am of the impression that it assures a larger load for the oversized boiler if both zones are calling for heat simultaneously and that both simultaneously may cut back on short cycles and keep the place uniformly comfortable. Of course, we lose the benefit of two zones and there were times that I'd "unjump" the hacked wires in the 504 and keep one part of the house colder than the other. But when all was said and done, that didn't seem worth doing as the boiler ran just as much either way. Perhaps this is all part of the joy of a modern oversized boiler. It does seem that the post purge card would force the boiler to be a colder temperature than without it, and that would encourage a longer cycle. I'm also considering replacing the Burnham OEM ODR with one which has more than a 20 degree differential and that would also benefit by warm weather shutdown. First choice now would be the Taco PC-700 which would plug into the 504 box, and maybe use the same outdoor sensor, although I haven't gotten to check the resistive values yet to see if they are the same. Can at least use the same sensor wire for sure. No need to respond to this paragraph, it's only for clarification and thanks for listening.
 

Last edited by thatoldguy; 09-29-14 at 05:48 AM.
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Old 09-29-14, 05:50 AM
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How will the card work if it's simply plugged in and priority is left turned off
That's a good question, and I don't have an answer for it!

I would say try it out and see what happens.
 
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Old 09-29-14, 06:17 AM
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NJT, this has to be a first for you... never seen a question posted you couldn't competently handle or help out with somehow!!

I don't believe I can do this, but if you can would you mind changing the title of this thread to: "Need help with a Taco PC600 Post Purge Timer Card"

Fully expect to mess with the card and figure out what it does, but there must be clear instructions for it somewhere to maximize one's use of it.

Clear, but not helpful instructions:
http://www.taco-hvac.com/track_file....wnload_id=8197
 

Last edited by thatoldguy; 09-29-14 at 06:34 AM.
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Old 09-29-14, 07:13 AM
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this has to be a first for you
Ha! Your prize is in the mail!

I have to confess that I've never used the PC600 card, and as you say, the instructions are not the best in explaining all the various conditions.

I do suspect that turning the priority off will still allow the post purge to operate that channels pump though...
 
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Old 09-29-14, 07:36 AM
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Thanks for changing the title.

Will continue to try learning more about this card before messing around with it, and will post what I find for the benefit of others probably about the same time as the first snow falls.

Unless, of course, someone else can fill in the void.
 
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Old 09-29-14, 03:31 PM
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Well, if this thing won't do what's expected, is there a simple device I can put inline with each circulator which will continue to power it for xx minutes after it's told to shut off?
 
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Old 09-29-14, 04:26 PM
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I think with the priority turned off it will do what you want, but only on the zone that you move over to that 'channel'.

So my suggestion would be to put the zone with the highest heat loss on that zone. If they are balanced, pick the one that you think you might like a tad warmer.

There isn't really anything 'simple' aka 'pre-made' that will do what you want... that I'm aware of. On my old boiler ( which was a SINGLE ZONE, ONE PUMP ) I implemented a post purge by strapping an aquastat onto the boiler supply pipe and wiring it's contacts across the circulator relay in the aquastat.

When the water hit the strap on aquastat setpoint, the contacts closed and 'bypassed' the circ relay in the aquastat. The pump would continue to run until the boiler water cooled to the differential setting of the aquastat. I think I used 30F as the diff and had the setpoint at something like 140F or so. As long as the water hit the setpoint, the circ would continue to run until the boiler was down at 110F or so.

I would NOT suggest this approach on the 504 panel without 'reverse engineering' it to be certain that bypassing the pump relays won't cause some damage...

And STILL, since you have MULTIPLE pumps, you would only be able to do this with one channel anyway... unless you engineered some setup with relays and logic that would do what you want with BOTH or EITHER pump.

My advice is to try it with what you've got and see how that works out.
 
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Old 09-30-14, 06:32 AM
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If inclined, I would incorporate a PLR (programmable logic relay)
IDEC Corporation - FL1E-H12RCC - Programmable Controllers - Logic Controllers - Allied Electronics

These devices feature 8 inputs that can control up to 4 outputs with individual time delays…along with many other complex logic blocks.

Wire the circulator outputs to the PLR inputs
Wire the PLR outputs to the circulators
Program the PLR with “Delay Off Timers” set to 10 minutes.

When call-for-heat ends, the PLR timer(s) retain power to the circulator(s) for the programmed time setting.

Individual On/Off Delay timers requiring no learning curve to program are another solution, but at twice the price.
 
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