Tekmar 256 and Indirect Domestic Hot Water


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Old 12-23-09, 07:28 AM
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Tekmar 256 and Indirect Domestic Hot Water

I think I might have messed up in an attempt to save money and buying a less capabable outdoor reset control. I installed the 256 and it works great. It's cold outside now though, and I'm wondering if there'll be a problem getting hot water out of the taps when the weather turns warm and the boiler target temps are lower. The Argo controller the 256 is connected to does priority but the 256 controls the boiler temperature. Can I bypass the tekmar somehow so that the dhw water tank loop thermostat controls the boiler aquastat, maybe through the existing relay on the Argo?

Thanks.
 
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Old 12-23-09, 09:02 AM
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No problem.

http://tekmarcontrols.com/literature/acrobat/a256.pdf

See A256-3 (zone valve system) or A256-4 (circulator zoned system).
 
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Old 12-23-09, 09:29 AM
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Thanks very much xiphias. I guess I have to get another stand alone relay? I was really hoping to use the relay that is currently used on the Argo ARM-4P, using the priority feature as well.

Admittedly, it's a little hard for me to decipher the wiring diagram, especially the insides of the relay box.
 
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Old 12-23-09, 03:17 PM
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I can think of a way or two that you could still use the Argo to provide priority, but would still require the use of another relay.

Perhaps the easiest would require a relay with a 120VAC coil, and a SPST-NO (Single Pole, Single Throw, Normally Open) set of contacts.

The COIL would wire in parallel with the 120VAC to the indirect circulator, and would trigger whenever the circ was running.

The Normally Open CONTACTS would wire to the T T terminals on the boiler aquastat, in parallel with the wires from the 256.

Whenever the indirect circ was running, the 256 would be 'bypassed' and be able to fire up to high limit.
 
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Old 12-23-09, 05:39 PM
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Originally Posted by VelvetFoot View Post
Admittedly, it's a little hard for me to decipher the wiring diagram, especially the insides of the relay box.
Check out the specs on their Relay 003. That should give you an idea of how it can be done, which I think is similar to what Trooper is suggesting.

http://tekmarcontrols.com/literature/acrobat/d003.pdf
 
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Old 12-23-09, 10:03 PM
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Thanks for the help.

I think I figured it out. It works and nothing smoked.
I jumpered from the Argo terminals for zone 1 (dhw loop) to the Tekmar terminals that go to TT on the boiler aquastat controller.
I was careful to keep the right polarity (or is the proper term phasing) on the 2 sources of 24v ac.
So, then the dhw tank aquastat closes, the Argo acts like it normally would and starts and prioritizes Zone1 and the Tekmar starts the boiler if it wants (or not).
However, at the same time since the TT terminals are now also connected via the jumper by the closing dhw tank aquastat, so the boiler aquastat turns the boiler on and off until the dhw temp demand is satisfied.

I was nervous about the two 24 volt sources connected together, but I tested it pretty good and it works. I'm not gonna declare victory for fear of jinxing it, but it looks good.
 
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Old 12-24-09, 01:06 PM
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You must got some big ones... I guess being that the Argo panel is fused on the 24VAC secondary you were somewhat safe doing that... don't know that I would have risked frying something though...

Before you connected the two, did you happen to measure the 24VAC on each the Argo and the aquastat? Between two different transformers, there could be a volt or two of difference. Maybe more... if you look at the specs on a 24 V control transformer, you will see that the voltage has a pretty wide 'acceptable' window. This difference could be enough to overheat the transformers, even if they ARE in phase (yes, that's technically correct). So keep a finger on the transformers to make sure they aren't running too hot.

I would still recommend that you use the relay, just to be on the safe side.
 
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Old 12-24-09, 05:34 PM
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Yes, there was 1+ volts difference between the two transformers. Using my handy dandy Harbor Freight IR thermometer, I measured 108 F on the Argo with one zone running and 81 F on the aquastat controller transformer with boiler off. Doesn't seem that bad. Maybe I'll measure it with everything off later.

Edit: I took off the jumper off and measured the temps again and they were comparable, so I hope I'm okay on that.

Thanks again.
 

Last edited by VelvetFoot; 12-24-09 at 06:07 PM.
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Old 12-24-09, 10:02 PM
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I measured it again with nothing on (setback) and the Argo transformer seems to be in the high 90's, so there is an effect. I'm hoping it won't be fatal. Perhaps I will look into the alternatives mentioned.
 
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Old 12-25-09, 04:29 AM
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I don't know, I measured it again with no thermostat closed and jumper disconnected and reconnected and saw no difference. I'm hoping for the best.

I did look at the link to Tekmar relay 003 and 004. That'd be a way to go for sure. I'm thinking power it off the 24 v thermostat rather than the 120 v circ pump. The relay would separate the two 240 v sources.

Anyway, thanks, and Happy Holidays.
Luckily the weather seems to be holding out for our long drive today to NYC and back.
 
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Old 12-25-09, 08:37 AM
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It would take a while... hours... before the transformer temperatures stabilized...

I'm thinking power it off the 24 v thermostat rather than the 120 v circ pump. The relay would separate the two 240 v sources.
What 240 V sources are you talking about? Typo? you meant ' 24 V ' ?

How would you do that? If you wire the 24V relay coil in PARALLEL with the aquastat, it won't work... the Argo uses DC coils in their panel, with diodes rectifying the AC... the leakage through the coil across the connections might/could cause the argo relay to be 'always on'... and if you wire it in SERIES with the wires to the Argo... it won't work... with the voltage drop across the coil of the series relay, you would probably only have 12 V to each coil...

Trust me, the easiest way to do what you want to do is with a 120VAC coil wired across the indirect circ, and the normally open contacts of that coil wired across the TT terminals of the boiler aquastat. Safe for the equipment, simple to wire.

R4222 Relay

Socket and mounting plate

For not much more money, you could also use an SR501 or R8845 ... might be a bit 'overkill' though...
 
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Old 12-25-09, 09:04 PM
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Yes, it was a typo.
Thanks very much for your help.
Not too expensive.
What I meant that instead of using a 120 volt relay, use a 24 volt relay and use thermostat voltage via the Argo to switch the boiler aquastat control.

Just one more question:
Do I really have a valid concern about not producing adequate hot water in the summertime if boiler temp target is in the neighborhood of 140F?

Thanks again.
 
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Old 12-26-09, 07:35 AM
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Originally Posted by VelvetFoot View Post
Do I really have a valid concern about not producing adequate hot water in the summertime if boiler temp target is in the neighborhood of 140F?
No concern if you implement the relay system as described by A256-3 or -4, which is basically Trooper's suggestion as well. On a DHW call, the boiler is allowed to operate up to its aquastat limit temperature. It will not be limited by the space heating target temperature.
 
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Old 12-26-09, 08:01 AM
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I can't grasp your idea... the boiler aquastat doesn't use a 'voltage' to trigger it, it's a 'contact closure' on the T T terminals that does that. The voltage that triggers the relay in the aquastat is sourced from the aquastat transformer itself.

There are multiple ways you could do this of course... another way would be if you used an 8845/501 type relay... which have multiple normally open contacts available for use. Mount that, supply it with 120VAC, connect the aquastat from the indirect to the T T (or R W) terminals so that the aquastat fires that relay. Then, wire one set of the contacts to the T T terminals of the Argo, and another set to the T T terminals on the boiler. This will bypass the 256 control during indirect call.

Maybe what you are thinking is to 'rob' the 24 VAC from the Argo panel to power a relay? YES... that would work also, as long as the Argo had a few hundred milliamps extra capacity to run the relay... and actually, this might be the best approach, because all you would be dealing with is some low voltage wiring... use a 24 V relay with DOUBLE POLE contacts... Is this diagram what you were thinking?



This relay would work, and will plug into the same baseplate as the other I posted previously.

DPST relay 24VAC coil

You can of course use the Tekmar 003 relay for this... even better if it's a)cheaper and b)comes with the socket. Just adjust the wiring to match the drawing above.

Yeah, both A and B ...

Tekmar 003 @ PexSupply

Yes, I believe you will find that the 140 temp won't be enough to give you adequate recovery time on the indirect during the summer.
 

Last edited by NJT; 12-26-09 at 08:17 AM.
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Old 12-26-09, 12:22 PM
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Originally Posted by NJ Trooper View Post
Yes, I believe you will find that the 140 temp won't be enough to give you adequate recovery time on the indirect during the summer.
But just to be clear, the whole point of this exercise is to allow the DHW call to 'bypass' the tekmar ODR, so that the boiler aquastat is the high limit on DHW calls.
 
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Old 12-26-09, 01:23 PM
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Ya know... I was just thinking about this a bit more in depth... if I understand the connections you originally made, there is a serious flaw in that scheme.

Your jumpers from the input to the Argo from the indirect were/are going to the T T connections to the boiler, right?

So, what happens when one of the HEATING zones calls? The TT connections are going to pass that contact closure BACK to the indirect input of the Argo... at which point the Argo would think a priority call was coming in, and take priority control.

It's what might be called 'positive feedback', and would cause all kinds of weird things to happen. This is what causes P.A. systems to HOWL! The indirect could overheat, the house could get cold because the heating circ would stop. The system would be 'latched up' until the priority timer in the Argo timed out and gave control back to the heating call...

So, you really do need that relay.
It's never as easy as it seems at first glance!
 
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Old 12-26-09, 01:50 PM
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Thanks guys for the incredible feedback (so to speak ).

I'm still irrationally resisting the additional relay.
When the aquastat on the water tank closes, the TT terminals are joined as well as the terminals on the Argo because the tank aquastat wires as well the wires to the TT terminals are on one set of terminals on the zone 1 terminals on the argo. When a demand for heat occurs via a room thermostat, the TT terminals are joined via the Tekmar reset control. The TT terminals are energized before they are joined in both cases - the circuit just isn't completed.

I think your original objection is still potentially valid. In effect I am creating a voltage source from connecting the low sides of two nominal 24 volt transformers with a potential 10% difference in voltage between the two.

So far, so good though. I haven't seen any problems yet.

If it does crap out, I'll be sure to post here, if nothing else as a warning to don't do stupid things.

Thanks again for the incredible input.
 
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Old 12-26-09, 03:45 PM
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Here's a rough sketch of my concern:



What you can do to prove/disprove whether or not this is true:

1. Turn aquastat on indirect all the way down so that you know it is not calling for hot water.

2. Turn one of the room t'stats up to generate a call for space heating.

3. Watch the LEDs on the Argo panel. If I'm right, the priority LED and the LED for zone 1 indirect pump will light, the indirect pump will run, and the space heating zone circ will stop, and that corresponding LED will go out.
 
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Old 12-26-09, 05:28 PM
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You are correct, sir.
I didn't see that at all - just focused on the indirect- it seemed to be working.
Anyway, I disconnected the jumper.
Will be ordering relay and base as you suggested.
Hoping to stick with 24 volts.
Thanks again for all your help.
 
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Old 12-26-09, 05:48 PM
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I would use the Tekmar... looks much easier to wire. The base has 'compression' type connections, just stick the wire in and tighten the screw. And all the wiring being low voltage can be done with regular thermostat wire which you can buy by the foot a HD or Lowes.

There are terminals in the Argo panel marked 24VAC and COMMON, correct? That's where you would pick up the voltage to use for wiring the indirect aquastat to the coil of the relay.
 
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Old 12-26-09, 06:11 PM
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Glad you boys have figured that out....
 
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Old 12-26-09, 06:35 PM
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Yep.

On the right track.
 
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Old 12-29-09, 08:06 PM
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Well, I think I have it working. I'm going to keep my eye on it to make sure it is indeed doing what it's supposed to do.

 
 

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