2 thermostats, 2 pumps, 2 relays, how to set up


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Old 02-09-10, 07:04 PM
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2 thermostats, 2 pumps, 2 relays, how to set up

Residence (mine), mod-con boiler, 2 zones

Zone 1 (main zone) is converted gravity, cast iron, heating most of the downstairs and all of the upstairs. Second (smaller) zone is RFH under tile, covers kitchen and adjacent small addition. Open floor plan so these rooms do get some heat from zone 1. Each zone has a thermostat and a Taco SR501 relay. No mixing from the boiler, runs between 110 - 135 F. Three pumps on the system: a return pump upstream of the boiler, one pump for radiator loop, one pump for RFH loop. No outdoor reset (I know ...). Overall happy with this system, in our second winter now, got lots of help here along the way.

When the RFH is calling but the rads aren't, the boiler tends to short cycle because the RFH gpm draw is low, so boiler quickly overshoots temp and shuts down. But RFH loop keeps calling, so that soon the temp in the primary loop drops and the boiler cycles again. Most often happens because the RFH is calling to up the slab temp, not because room temp is low.

To help minimize that short cycling I want to try running the RFH loop whenever the rads are running, to boost the floor temp up in that zone when the boiler is already running (and condensing), but also maintain the ability for the RFH to call and run separately from its own stat. I expect this will boost the floor temps higher than we have them now but that is OK and I want to try it out.

So, current setup:
Main stat calls ==> boiler called, pump for radiator loop kicks in
Addition (RFH) stat calls ==> boiler called, pump runs for RFH loop

desired setup:
Main stat calls ==> boiler called, pumps run on both loops
Addition (RFH) stat calls ==> boiler called, only RFH loop pump runs (as before)

How to do it?

Can I do this with existing relays? I considered taking the RFH pump off its relay and running it from the orange wire on the boiler, but then would the RFH pump continue to run when the boiler is called but temp is already up? I'm thinking no, but I dunno ...

Sorry for the long post. Current controls diagrammed in images, p2 is "radiator pump" and p3 is "RFH pump."


 
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Old 02-09-10, 09:00 PM
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You might be able to do this with what you have... here's what I'm thinking:

On the RFH relay,

Remove the jumper from H to 3

Move the hot wire to the circ to 3

Jump from H to 4 NO

(basically reversing those two wires...)

Run a wire from the Radiator relay, 4 NO, the same one that goes to the pump, over to 4 NC.

I think this will run the RFH pump whenever the radiator pump runs and the RFH t'stat is NOT calling.

When the RFH t'stat calls, it pulls the relay in and runs the pump from the 4 NO hot...

Draw it out, think it out, and decide if that will do it... I believe it will.

P.S. Something that needs to be checked... the current rating on the 501 relays...
you need to check that because this setup will require that the relay in the radiator
pump box be able to carry the current of BOTH pumps.

P.P.S great drawings!
 
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Old 02-10-10, 06:59 AM
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Trooper, since he is zoning this system with pumps I'm guessing he is also using flochecks. Could this be as easy as opening the flocheck on the RFH and when the rads call the pump will also cause water to flow through the RFH also, and when he wants just that zone that pump will come on and he'll have it. I know it dipends on how this is piped, just a thought.
 
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Old 02-10-10, 07:37 AM
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That is a good thought spot!

How about that sbarr? Can you open the flow check to get flow in that loop? Worth a shot...

Looking at the drawings, the wiring changes I suggested would be quite simple the way it's layed out. The "box above relays" looks as though it has the hot feed to the radiator pump in it. It's probably wire-nutted... simply drop a wire into that wire nut, and down into the RFH relay and connect to 4 NC... that, and reverse those other two wires... here's a diagram of what I'm thinking...

And again, CHECK THE CURRENT RATING ON THE RELAY!

 
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Old 02-10-10, 07:58 AM
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Trooper,
Your concern of amperage is probably not a problem as the SR501 is good for 5 amps on the contacts.
 
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Old 02-10-10, 08:14 AM
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Thanks for the posts!

There are flow checks on the manifold, downstream of the RFH pump, so that won't solve it. And the loops are in parallel, with the RFH loop coming off the primary loop. I can post up a pic of the piping if folks are interested but I don't see any way around it other than an electrical one.

I'm at my day job, will have to revisit this tonight, drawing out Troopers suggestion which sounds like a good one. You are correct about the wire nut and hot feed in the "box above relays." And I'll check the rating on the relay - will post back ...
 
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Old 02-10-10, 02:01 PM
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Trooper, the purpose for no.3 terminal is to power 4no or 4nc. If you jump H-4NO that will bring a direct 120v to that terminal. Then if you bring a wire from rad. relay 4NO to 4NC when that zone calls that will bring another 120v when that terminal is activated. That means you'll have 120v to 4NO and 120v to 4NC at the same time. The only way 3 gets powered I believe is if you jump H-3. Without that jumper how is the pump that you put on 3 going to get powered. By jumping from H-4NO which makes that a direct feed on the RFH what will make the pump operate when he wants just that zone.
 
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Old 02-10-10, 04:07 PM
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not sure what you mean spot!

You can run the relay 'backwards', there's no problem with that... wiring it this way creates an OR condition on the Radiant pump... it will be powered by one OR the other of the contacts...

There are four conditions:

1. Both relays OFF. No pumps run.

2. RADIATOR relay ON, FLOOR relay OFF. 120 goes to both pumps... the RAD pump picks it right off the NO on it's own relay, and 120 is passed to the NC on the FLOOR relay, which passes it to the FLOOR pump and it runs also.

3. RAD relay OFF, FLOOR relay ON. RAD pump will not run, FLOOR pump will contact NO on it's own relay which is HOT and it will run.

4. BOTH relays ON. RAD pump will be powered by 120 from it's own relay, as will the FLOOR pump from the HOT on NO.

Verschtenen ja?
 
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Old 02-10-10, 04:26 PM
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spot, I re-read your post to try and understand your concern... and I think I know what you are thinking... maybe...

On a SPDT (Single Pole Double Throw) relay, there is a 'movable contact', the 'arm', which can also be called the 'common' terminal.

Then, there is a Normally Open contact which 'makes' with this 'arm' when the relay is energized, and a Normally Closed contact which 'makes' with the arm when the relay is NOT energized.

We generally see these relays used with the SOURCE applied to the 'arm','common' terminal, but there is no reason they can't be operated in the other direction.

In other words, TWO sources, ONE load, powered from either source.

Let's look at another example, using audio...

Say you had two audio amps, and one speaker. You wanted to use EITHER of the amps to power the speaker. You would connect one amp to the NO and one to the NC, and the speaker on the ARM. Flipping the relay (or switch) would send either/or of the amps to the speaker.

Say you had two speakers, and one amp, now you would connect the amp output to the ARM, and one of the speakers to the NO and one to the NC. Flipping the relay (or switch) would send the amp to either/or of the speakers.

Does this make any sense? or am I 'over explaining' (in case you haven't noticed, I have a tendency to do that!) ?

Beer 4U2
 
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Old 02-10-10, 06:02 PM
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Trooper, I understand what you're saying and in that context it make sense. Sometimes I too overthink things. After all your wiring is done which terimal will turn on RFH pump when running alone. I realize the pump is on 3 but where does 3 get power. Are you saying that 4NO will power 3 when called.
 
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Old 02-10-10, 07:22 PM
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Yes. When the floor thermostat calls, and that relay pulls in, 4 NC will 'break', and 4 NO will 'make' with 3 and the pump will get power from the feed on 4 NO.
 
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Old 02-10-10, 09:46 PM
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The wiring and logic look good to me. I'm glad you two hashed it out, made me pay attention and I'm feeling comfortable with the details now. As stated, relays are fuse protected at 5A.

So I'll start by just flipping the jumper and the feed at the RFH relay. If that runs the floor pump when the floor stat is calling as expected, then I'll bring over the hot from 4NO(rads) to 4NC(floor).
 
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Old 02-10-10, 11:26 PM
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OK it's been working fine, manually switched on and off a few times, all 4 states are good.



On to monitoring the consequences now, see if running it like this is useful or a harebrained idea ...
 
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Old 02-11-10, 10:29 AM
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sbarr, whatevers happens, great schematics.
 
 

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