taco RMB+DHW


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Old 03-24-08, 04:02 PM
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taco RMB+DHW

How would you hook this up?

buderus 215
buderus indirect dhw
taco RMB
4 zones of in slab heat

I want my RMB to control my boiler with outdoor reset. to get water hot enough for the DHW i would pipe that circ pump in before the RMB. I do not want to wire the DHW demand through the RMB because if it senses a demand it will start mixing water for my floor heat. If i hook the DHW aquastat directly to the boiler i bypass the RMB sending it all the way to 180 no matter what the temperature outside is. I also lose priority not having the DHW circ wired to the radiant switching relay.

what would you do?

my 2 ideas are 1) hook the dhw aquastat to a switching relay that is hooked to the dhw circ pump. this wouldnt be connected to the boiler or turn on the boiler when it started circulating but the RMB would kick on the boiler when the temp started dropping just as it would with normal heat loss not running for a long period, giving the RMB total control.

2) same as above but have both the DHW demand and the RMB demand hooked to the boiler. When the RMB calls for heat it will heat the boiler to its calculated temp. When the DHW calls for heat it shoots up to 180 regardless.

To me it seems like bypassing the RMB would make me lose some efficiency but then again maybe that boiler always needs to be at 180 to heat that tank of water up...i dont know, im no boiler technician. THANKS!
 
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Old 03-24-08, 04:20 PM
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For starters, you do want the boiler to go full temp for the DHW call. That's pretty much a given. If you try to run the DHW with low temp water from the boiler you won't be satisfied with the recovery...

Treat the DHW as a high temp zone ...
 
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Old 03-24-08, 05:00 PM
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If I get this straight, all of your central heating is through the RMB?

Normally an RMB is used to add a low temp circuit to a high temp circuit. Ideally you would have an ODR controller on the high circuit and the RMB would supply the temp curve and flow for the low temp circuit.

So you'd need to have a primary boiler circuit. Make it parallel primary for the indirect and use a Tekmar 260 or something like that.
 
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Old 03-24-08, 05:45 PM
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thanks for the quick replies. now to clarify a few things. Ok, so my DHW pump is on the primary loop, it is communicating with the boiler and is wired totally independent from the secondary loop(RMB) since they are independent is there a way i can connect something to give DHW priority? all house zones are on circ pumps with a taco switching relay. My understanding is that i cant hook it up to the same relay because when DHW calls for heat, the rmb will think its mixing water for the floor heat and thats not good.

The reason im not just going for a tekmar 260 is because the RMB has all of the control capability....minus the DHW haha. The only reason i have this problem is because i got the RMB 1/2 price......stupid good deals Otherwise i would have the tekmar or the logomatic.

I guess in my dreams i thought i would be real efficient keeping the boiler cooler with the outdoor reset, but in reality the DHW needs more heat for faster recovery. So my DHW will kick the boiler into full gear and my RMB will kick it on just as much as it needs to.
thanks again
 
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Old 03-24-08, 07:23 PM
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I think even with the RMB the boiler is going to operate full temp. It's going to MIX to get the radiant to the lower temp. That's why they call it a MIXing block. It mixes SOME of the high temp water from the boiler with the return from the radiant loops to target the temp that is required for the radiant, while allowing the boiler to run in NON condensing territory.

Boiler protection is one of the things that the RMB does, by sensing the return to the boiler and preventing it from going below the condensing point. The only way that you can run the boiler at a lower temp is with a condensing boiler.

You can still do priority... you would need a relay that is set up to interrupt space heating calls to the RMB when there is a DHW call.

But I'm confused again ... you must have a mixing valve already, correct ? So don't you just need to replace that mixing valve with the RMB ? Isn't there a pump in the RMB also ?

My understanding at this point is that you have an RMB sitting in a box waiting to be installed into a system that is all together and working. I'm assuming that you've got manual fixed mixing valves, correct ? And you are trying to determine how to replace those mixing valves with the RMB, and run DHW priority, correct ?
 
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Old 03-24-08, 09:49 PM
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to help you understand my situation, not just the RMB is in a box, the whole mechanical system is. Im building the house as we speak (well waiting for snow to melt mostly right now) and im just getting everything together and planning how it will be laid out. The RMB can be used as a complete outdoor reset boiler control. If its 50 outside it may calculate that the boiler only needs to make the water 160 instead of 180, it then uses that 160 water to inject into the heat circuit that will be maintaining approximately 100 for the in slab tubes. This is my understanding of this particular system and outside reset controlers in general. Money is saved by not heating the boiler up to 180 if you only need 150 to get things done and not constantly keeping it that high when there is no demand. And condensing isnt an issue because there is a low limit built in....kept at about 140 for the g215. After a little more research i think what i will do is put the DHW demand to TT on the boiler aquistat, put the RMB demand to TT on boiler aquistat. when the DHW calls for heat the boiler will crank up to the high limit, when the RMB calls for heat the boiler will go to the calculated temp. The DHW relay needs to block the demand from the RMB to make it priority though...what kind of relay would do that without actually being tied into the RMB's brain? I cant just use one of my slots on my taco switching relay and flip the priority switch because that demand will still cause the rmb to start circulating. Sorry, this is probably confusing the way im writing it, but i greatly appreciate peoples input!
 
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Old 03-25-08, 02:44 PM
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Gotcha...

If you wanted to wire up a relay you could use a Honeywell 8222 series. I would set it up so that when the indirect aquastat called, it would fire the relay. One set of the relay contacts would then go the the TT input on the aquastat. The boiler demand signal from the RMB would run THROUGH the relay on the second set of contacts, using the Normally Closed contacts. Those contacts would OPEN when the A'stat called and prevent the call from the RMB from reaching the boiler.

I'm pretty sure you could also use a 'packaged' relay...

Drawback to this is that there is no LIMIT to how long the priority call would last... better controls will only allow a priority DHW call for a limited amount of time. If it's REALLY cold out, the house temp could drop during a DHW call. Limiting the time for a DHW call would prevent that. I suppose you could always wire up a timer to the relay as well if you found it to be a problem . (my guess is you won't)

But, the relay will work... here's one possibility:



When the DHW is not calling, the boiler demand from the RMB travels through the relay. When the DHW calls, the relay energizes, interrupts any calls from the RMB, and closes the TT on the boiler.

Do you have a proposed piping diagram drawn up yet ?
 

Last edited by NJT; 03-25-08 at 03:24 PM.
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Old 03-25-08, 03:34 PM
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No, that won't do what you want ... never mind ...

If the RMB gets a heat call, it's still gonna fire up and go ... so the relay is pointless... might as well just tie both the DHW demand and the RMB demand in parallel to the TT on the boiler like you said ... if you didn't have the zone panel, this would work.

must be a way, lemmee think some more ...

OK, you need to interrupt the demand from the SR to the RMB ... that's what I was thinking a few posts back, just got ahead of myself ... I'll rework the drawing.
 

Last edited by NJT; 03-26-08 at 02:30 PM.
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Old 03-25-08, 07:00 PM
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Taco SR503, indirect on priority. Parallel primary loops, the RMB forming the secondary. Protection is the big unknown. Could be avoidable if flows are right yet on the other hand might really need an ESBE for optimal service life.

So a simple Taco relay... and there's your future high temp if even wanted. The RMB forms one secondary loop, well injected loop. I'm just not sure if the boiler primary has enough flow compared to the mixing pump to not be a condensing candidate.
 
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Old 03-26-08, 02:28 PM
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The RMB will provide the boiler protection... it's basically a 260 without the DHW ... there's a sensor, and he will set boiler min at 140 ...

I agree that the indirect should be wired to the SR, along with it's circ pump, but here's the rub:

When the SR sends the boiler demand, it's going to be sending it to the RMB, and the RMB will fire up... NOT what we want to happen.

There needs to be a relay that knows when it's a DHW call, and bypasses the boiler demand around the RMB.

I've got an idea which I'm gonna draw up, when I get a chance, maybe later this evening.

akstyle, you still with us ?
 
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Old 03-26-08, 02:59 PM
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The RMB does have a boiler sensor and allows protection... I didn't realize that. This should be what you need...

http://www.taco-hvac.com/uploads/FileLibrary/RMB10.pdf
 
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Old 03-26-08, 05:09 PM
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I haven't fully perused that drawing yet... I think AK is using circs to zone though ... did you happen to notice if there was one that used SR instead of ZC ?
 
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Old 03-26-08, 05:42 PM
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Good catch Trooper, I was thinking this was ZVs.

There are 24 diagrams and none seem to be for this.

How does this sound?

Start with this diagram and pretend it's an SR504 or 506 for the low temp circs.

http://www.taco-hvac.com/uploads/FileLibrary/RMB03.pdf


Add another SR503.

I would pipe the indirect as parallel primary meaning it has its own loop and just uses one circ. The aquastat connects to the leads for zone 1 (jump it for priority) and the circ gets powered of zone 1.

Instead of the RMB connecting to the boiler, it would instead have those leads going into zone 2. Furthermore, zone 2 would then control the primary pump for heating instead of the power coming from the RMB.

Leaves a future high temp zone but one with no protection.
 
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Old 03-26-08, 07:03 PM
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I wish the descriptions at the Taco site were a bit more informative ! 14 is close to what I was thinking with the relay to interrupt the heat demand from the SR to the RMB ... and 13 also... with the 'packaged' relay ...

I've still got another idea, but if AK don't come back, I'm not gonna spend the time on it .
 
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Old 03-26-08, 08:15 PM
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Oh what the heck, I had nothing better to do anyway:

I'm pretty sure this will work. PLEASE! check this work carefully before commencing to use this drawing !

 
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Old 03-27-08, 02:41 PM
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I noticed one minor drawback to this scheme.

If any zone t'stat calls during a DHW call, the zone circ for that/those zones will run. No heat call will pass to the RMB though, so the zone circ will simply run until the DHW call is complete, at which time the RMB will fire up and run.

Not a big deal really...
 
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Old 03-27-08, 08:40 PM
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you guys are my heros. I have been at work and didnt check back in a few days. I didnt imagine i would get this much help and i want you guys to know that i am VERY thankful and your time on here is much appreciated. Yes all zones are circ pumps. I just glimpsed at your drawing, i will print it out after this. Up until i saw that i was thinking of just making no priority and seeing how it did, if it would keep up to my liking great, if not i would look for another solution. When its 50 below next winter though i dont know if thats when i want to find out HA. Im going to absorb this into my brain and ill post back if i have any questions. Thanks again guys.
 
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Old 03-28-08, 03:11 PM
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Oh man, now I can't get my hat to fit ! a Hero! whoa!

naahhh, we just like this stuff...

I _think_ ... NOT SURE ... that if you used an R8222D DPDT relay instead, you could use the second set of contacts to open the ZC / ZR jumper on the Taco SR and disable the circs during a DHW call ...

Grady... you reading ? Do you know if that would work ?
 
 

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