I am again considering installing an outdoor reset for my Buderus boiler. After reading many posts, I think that an indoor reset is also a good idea.

My system: Buderus G115 with an indirect DHW tank, two heating zones, a Taco ZVC404 zone valve controller, Taco 3 wire zone valves. 1 circ pump.

Does the 260 replace the Taco ZVC? From the wiring diagram, it looks like the T stat end switches get wired in to the 260. I would need to supply a new trans former too.



Thanks for any help.

 

No, two completely different animals.

The 260 is the reset module only, there are no zone controls on it... you would leave the ZVC as-is... the 'endswitch' on the ZVC is what would wire to the TT on the 260.

I believe that the ZVC panel has enough extra capacity on the internal transformer to power the 260 ... and there should be a terminal strip for the 24VAC in the ZVC panel.

 

Why not look into adding the Logamatic control to your boiler? It's made for it!

 

Indeed. Logamatic with the BFU room sensor would do this quite well.

 

Thanks Trooper, I was just briefly looking on the Tekmar site at wiring diagrams....hooking it to the end switch of the ZVC is much easier.

The Tekmar is less than half the cost of the Logamatic.....that's pretty much my reason for not going with the Logamatic.

 

Look at the new Tekmar Tn2 house controls.
Indoor / outdoor feedback (reset), contains built in (4 zones) switch for valves or pumps.
Pretty good value and it's 2 wire to boot.
I recommend you look at that over the 260

 

Thanks TO. But it looks you need to use the tn2 house control with tekmar thermostats too? With all of that, I'd be close to the Logamatic in price.

I'm really looking to do this outdoor reset as cheaply as possible. We only burn between 350-400 gallons of oil each year, so I'm not looking to spend a whole ton of money on this....but if I can save 10% on fuel costs.....that will be a help for sure.

I'd like to add the outdoor reset for sure. After reading a bunch more posts, it seems like the indoor reset needs some considerable time to get the location right. So maybe the indoor reset isn't really a priority fro me right now.....but I can add it later if I decide too.

I need an outdoor reset that will work with my Taco ZVC404, and will allow me to have the DHW priority. It seems like the Tekmar 260 is a bout the least expensive way to achieve this?

If the tekmar is wired to the end sw of the Taco ZVC, how does it know if the call is for a heating zone, or the DHW? Seems like I would have to remove my DHW from the Taco ZVC, and wire the aquastat and zone valve directly to the 260?

 

The 260 will not do DHW priority using a zone valve for the DHW. See section C2 of the manual.

 

Thanks xiphias.....I just downloaded the manual, and you're right. Not really sure how big a deal the priority is for us?

Maybe I ought to just go with the logamatic?

 

http://www.tekmarcontrols.com/litera...robat/a260.pdf

Take a look at 260-2

Your indirect a'stat would wire to the DHW demand on the 260.
The zone valve for the indirect also wired to the 260.

So, yes, you would be rewiring that part.

The priority is now coming from the 260.

I want to look at this a bit more, because I think there's an optional way to do this...

And by the way, it might be best if you did install a separate transformer. If you should somehow overload the transformer in the ZVC you wouldn't wanna trash it for that reason...

 

I didn't see the other discussion about the priority ... I'll look at that in a minute, but take a look at this diagram. It might work around that by retaining the priority in the ZVC panel, with a minimum of rewiring. The DHW A'stat and ZV could stay where they are.



If this isn't readable, or if you want the full size image, go here:

redhouse.jpg picture by JeffPicks - Photobucket

 

I need to refresh my memory as to what the "NORM-RESET" switch in the ZVC does...

I think this circuit does work around the lack of priority in the 260. When you set priority in the 260, what happens is it shuts off the boiler pump... and you can't have that. So set the priority in the 260 OFF, and in the ZVC - ON.

The ZONE 4 relay is used to tell the 260 that this is a DHW call.

I think this will work properly...

 

Thanks Trooper! Where did you find that diagram? i looked high and low to find something with both a ZVC and the 260.....guess I was looking in the . I didn't even see the z4 relay on the diagram last night.

Thanks again!

 

Yeah, now that this has come up, I dimly recall we might have had this discussion (priority with a ZV setup) somewhere else a long time ago. Also dimly recall it may have worked....

 

I found it in my head. Didn't exist till last night... unless as Xiphias has dim recollections, it might have been drawn previously and I reinvented my own wheel... I wouldn't be surprised if you looked through my entire 'collection' on photobucket if you find another very similar.

 

Thanks for doing that Trooper

Last night, I checked both end switches on the ZVC with an ohmmeter, and found that both were always closed during a call for heat, regardless of DWH priority. I never saw the zone 4 relay....sometimes it's hard to see the forest through the trees I guess.

It sure looks like it should work just fine. If the ZVC is rated for 4 zone valves, and I'm only using three....do you think it's ok to run the 260 off of the ZVC transformer? Or should I just go ahead and install a second one?

Thanks again for the help guys!

 

I would say yes, should be no problem. You won't draw more than a few hundred milliamps from the ZVC transformer to run those two relay coils in the 260. Try it and monitor the temperature of the transformer when everything is calling... maybe look at the voltage also... you should be able to tell if you are overloading it.

I think that if you checked them again with the NORM-RESET switch in the RESET position, you would find they BOTH operated with a DHW call, but only ONE operates with a HEAT call.

The PRIORITY switch in the ZVC only blocks a HEAT call from getting through when there is a concurrent DHW call.

By the way, if you 'right click' the schematic, and click 'View Image' in the dropdown box, you can see it full size. Then click the 'back' button to return to the forum.

 

Excuse me but could you recommend a site which explains how to use photobucket to share links/photos on the forums?

 

No, sorry, I don't know of any sites like that... but it's real easy.

You set up a free account at Image hosting, free photo sharing & video sharing at Photobucket and upload your pics to a PUBLIC album. You and then use the 'image' and 'url' icons to either post the image location or the album location into the forum.

But I would rather we didn't turn this person's thread into a discussion of how to post pictures... so hopefully this will suffice.

 

Based on this info, I'll most likely go ahead and order the 260. Just to conform a couple things:

The boiler output on the 260 (terms 11,12) gets wired to TT terms on my Honeywell L7248 aquastat, and the circ pump gets moved from the aquastat over to the 260. All other wiring at aquastat(burner wiring) remains intact.

There is no by-pass piping, so i should set the low limit to 140° to prevent condensation?

And lastly, will the 260 run off a generator? I have no problems running my boiler off either of my generators right now. I have an old Honda EM2200, and a newer Coleman Powermate 6200.

 

get a cheap(er) UPS to power the Tekmar.
It will clean the genie power up consideratbly.

 

Yes, correct.

Maybe even a bit higher... certainly no lower. The actual setting should be based on the average temp in the boiler and the return water temp.

I like the idea of a small UPS myself. You could get some pretty long run times on one if all you are powering is the 260 and the ZVC...

What primary control and aquastat do you have?

 

The small UPS is a great idea...thanks TO!

The aquastat is a Honeywell L7248C, and I can't remember what the primary is....it's been awhile since I've had the front cover off the burner. It's a Riello burner though. I can check tomorrow if it's important.

 

Not really important... just wondering if any 'electronics' is involved... some generators are pretty 'dirty' sine waves. Some are pretty good... when electronics gets involved, the cleaner the sine wave, the better. Another idea is to use pure sine wave inverters, and a 12 V battery. One guy that used to come here does just that... runs them off the battery in his truck. When the battery gets low, he finds an excuse to run the truck down to the liquor store for more beer and to recharge the battery.

I re-did the diagram to show powered from the ZVC panel.

 

Thanks for the help guys. I'm going to go ahead and order the 260, and I'll most likely get the indoor sensor as well.

 

Before I go ahead and order the 260, I think that I could actually use a 256 if I'm not going to use an indoor sensor.

If I wire the DWH as pictured above, but instead of going to the 260, I would just take those wires going to terms 3&4 on the 260 and wire them to TT on the aquastat......seems like it should it work to me?

I've been searching various threads on adding the indoor sensor, and I should probably start another thread with my questions on that before I make a final decision. Going with the 256 over the 260 would save me almost $200.

 

Depending on your return temperatures over the course of a heating season, you might be able to rock the house with one or more indoor sensors (you can ladder them to get an average of different locations/zones; see http://www.tekmarcontrols.com/sb/sb018.pdf).

The real advantage of indoor sensing (in general, not just the 260's flavor) is that you are supplying the heat needed based on the actual load of the building. That's a very good thing.

The potential downside in your case is (perhaps?) not having the boiler piped to provide a full range of reset temperatures while protecting the boiler from condensation. However, with oil, you can go down to around 115F return temp before you really start having to worry about condensing. So if you have a low deltaT in your heating loop(s), you might supply something like 120-125. Depending on your heat loss and emitter characteristics, that might be a common temperature. Or not.

The major disadvantage of simple outdoor reset is that the control is tied to a supply temperature for a given outdoor temperature, and can chase the differential around that but is otherwise limited.

 

I don't think the 256 has the DHW capability... so something might need to be jiggered with another relay to get that to work properly. If the control doesn't know that it's a DHW call it will try to recharge the indirect with whatever space heating temp it is currently using, and that will KILL the recovery time on the indirect.

I think I had worked something out for this at one time,... I'll look.

 

You're correct Trooper, the 256 doesn't have DHW, but.....if, using your drawing in post #24, I take the wires from the zone 4 relay that were going to terms 3&4 on the 260, and wire them to the boiler aquastat on the TT terms....it would not send a call to the 256 at all. The ZVC would be using it's DHW priority and sens a direct call to the boiler at full temps.

Thanks for the help xiphias....I'm still considering the indoor sensor(s). I do not have any bypass piping, but thats not say that I couldn't add a bypass at some time. I guess I'm still a bit confused about using the indoor sensors. I currently have two zones, and two T stats. We setback 4 degrees at night and during the day when nobody is here. Do I keep my current T stats in place, and add the sensors nearby? Can we still keep our setback? Any info is greatly appreciated....

Thanks!

 

Straight outdoor reset pretty much means giving up setback. Which is not altogether a bad thing (see the tekmar essays for why).

But the indoor sensors plus a simple timer (I use a Lux TX500 thermostat, aka Ace Hardware ATX500) can do multiple setback periods if you wish. Works great. It can also allow/deny DHW calls during setback periods. That's nice; keeps the boiler from doing DHW when you might not need it for 8+ hr.

If the thermostats are in a good location, then near them is fine. You'd set the thermostats for a degree or two above the tekmar setpoint. That way the thermostats generate a continuous call for heat (thus letting the tekmar do its thing) and act as a high limit to stop the call for heat when you go above setpoint, e.g., heat gains due to cooking, occupancy, solar, wood stove, etc.

 

Ok.....so it looks like the 260 with indoor sensors will be a better fit.

We have an 1800 sq ft house, two floors, with a somewhat open floor plan. Is it better to have one indoor sensor in an average temp area, or two sensors, one on each floor?

 

Right, I think. You would of course have to remove the connection to the 24 VAC source and just use the Z4 relay as a 'dry' contact closure. IOW the Z4 normally open contacts would wire in parallel with the 256 wires to T T on the boiler aquastat. I think that's what I was thinking...

You would be in somewhat 'uncharted' territory though. When the DHW calls for heat, it operates the Z4 relay, but it ALSO still operates the ENDSWITCH.

This may not be a problem though, but I think it's worth considering the scenario. The 256 will see the DHW as a 'boiler demand' and attempt to run the boiler. That attempt will be bypassed and over-ridden by the Z4 relay closure. IF there is a problem, it would be in the 256 possibly being confused by the fact that it will not be able to shut off the boiler when it's target temp is reached. It will see the boiler temp overshooting it's target. Whether or not this will have any effect on it's brainiac, i.e. changing 'learned' parameters for it's PID logic or not is a question only Tekmar will have the answer to.

 

Yeah.....I forgot that the endswitch also closes on a DHW call.

xiphias has me just about sold on the 260 anyways......thanks for the help guys!

 

I knew he could do it! He's awesome that way!

 

I'm not advocating one way or the other (I think). Every installation is different, and behaves differently.

As to whether one vs. two sensors, that depends. If you do indeed have an average spot, maybe try one. Otherwise, go two. Remember, there's all kinds of games you can also play with the output of your emitters (e.g., for baseboard, close the dampers in places that have too much output) to 'balance' the house.

 

I don't think you can use two... there is no way to connect two such that you end back at the nominal resistance value. The next step after one is four. This connection would be series/parallel and the total will show the same resistance as one.

 

Can two be used if you parallel two 10k resistors with the two sensors? Just wondering out loud here.

I'll see if I can find an average spot in the house. I've been adjusting the dampers over t he past few months to make an attempt at evening out the system....and I have things pretty close...within a degree or two right now. If I could just get my wife to leave things alone though....

 

One sensor is probably fine. Between damper adjustments and ability to use thermostat as high limit it should work out. For average, you want to be away from point sources of intermittent heat such as the kitchen, walls that get a lot of sun, the room with the fireplace, etc., and you want to be on the low end of average rather than the high end. Easier to reduce output than suffer with not enough.

Keep in mind that there will still be some issues with how the control can respond with less than full-reset range. It really works best with systems that can handle water down to nearly room temp (75-80). It should figure out how to compensate for that by playing with the differential, firing cycles, etc.

 

No, that won't work... what will happen is that you will end up reducing the sensitivity of the thermistor...

There nothing wrong with using two thermistors right next to each other though... if you only wanted to do two locations...

 

OK....I'll find a good spot for one sensor and see how that works.

I should set it to auto diff and see how it works for a few weeks then?

As far as measuring return temp to figure out the DeltaT.....can I just strap a thermocouple to the return line and monitor the temps? I definitely don't want to risk damaging the boiler with too low of a temp.