outdoor rest

Rocky_2

Sounds like you just need boiler reset and DHW production. If that is the case, the Tekmar 260 does those two things. If you do not have the tekmar thermostats then resetting the boiler temp and controlling the DHW production is about all you can do from a control standpoint to increase your efficiency. Have literally installed hundreds of the tekmar 260's. They perform well and are very reliable.
Hope this helps,
Rocky

Jim_109

Outdoor reset

Which Tekmar outdoor reset do you recommend for the following application? One oil fired boiler, 2 zones, possibly adding a third zone and an indirect hot water heater.

The tekmar website, has many outdoor reset options.

I am looking to save energy which they all do, what other features should I look for? THANKS!

Glenn Sossin_2

Indoor Outoor Reset

If this is for an existing installation, the easiest and least expensive way is to use a tekmar 256 for heating demands, bypass it on a demand from the indirect.

Basically, this will intercept the TT demand signal from your heating circulator relays and create its own variable high limit function by opening and closing the TT circuit in accordance with boiler system temp and outdoor temp.

Demand from your indirect aquastat relay will still go directly to TT of the boiler and operate of it's pre-set high limit.

Hope this helps you.

Paul Rohrs_4

Or...

You can choose from a wide selection of PDF's available on their website. A260-3 with zone valves, A260-4 with zone pumps.



Regards,

PR

ALH_4

Reset

The only thing using the 256 doesn't do is provide DHW priority for faster tank recovery.

Boiler temp reset w/o dhw priority: 256
Boiler temp reset w/dhw priority: 260

The tekmar 260 control also provides a relay capable of running the DHW pump directly. This saves a relay for the pump and pays for part of the control upgrade. A Danfoss thermic valve might be a good addition to the 256 or 260 to prevent flue gas condensation under any condition.

Mixing (for low temp zones) w/o dhw: 356
Mixing (for low temp zones) w/dhw priority: 363

Mixing can either be done with an injection pump or with a mixing valve. The equipment for injection is less expensive, but the temperature setpoint of a mixing valve is a little more accurate. Also, using a mixing valve saves at least one pump and the electricity to run it.

There are also Tekmar Net 4 controls depending on the connectivity you would like between the thermostats and the boiler control.

CC.Rob_3

while the 260 is nice

(I have one), I discovered that it has a rather limited processor that overestimates supply temps at lower outdoor temps. In my case, this overestimation costs about $50/yr in wasted BTUs at current gas prices. Kind of bummed me out to know that in 8 years it will have cost as much in wasted energy as the unit itself. Their higher-end controls (the 262), or perhaps an even simpler direct reset ratio control, might be worth looking into.

(The technical reason is that the processor appears to experience a quantization error in a couple temperature bands, one low, one high. Have conversed with tekmar about this. Likely a bit depth issue, but beyond a basic description and acknowledgement of the issue, I think the details are proprietary.)

This is not a rant against tekmar, per se. The control appears to be an otherwise fine product. Just would have been nice to see in the literature that the 260 doesn't actually follow the characterized heating curves shown in the literature with the precision purported. They might have up-sold me rather than lost my purchase decision.

CC.Rob_3

while the 260 is nice

(I have one), I discovered that it has a rather limited processor that overestimates supply temps at lower outdoor temps. In my case, this overestimation costs about $50/yr in wasted BTUs at current gas prices. Kind of bummed me out to know that in <=8 years it will have cost as much in wasted energy as the unit itself. Their higher-end controls (e.g., the 262), or perhaps an even simpler direct reset ratio control and DHW priority scheme, might be worth looking into.

(The technical reason is that the processor appears to experience a quantization error in a couple temperature bands, one low, one high. Have conversed with tekmar about this. Likely a bit depth thing, but beyond a basic description and acknowledgement of the issue, I think the details are proprietary.)

This is not a rant against tekmar, per se. The control appears to be an otherwise very fine product. Everything I've ever read about tekmar company and products suggests they are first rate. Their tech support and customer service when I inquired about the above was truly excellent and very forthcoming. Just would have been nice to see in the literature that the 260 doesn't actually follow the characterized heating curves shown in the literature with nearly the precision implied. They likely would have up-sold me....

Glenn Sossin_2

Priority

Agree, there is no priority function built into the 256, however, it sounds as if this is a very simple system, no primary secondary involved. If so, you can add a priority function by a second DPDT relay as shown.

Be aware if the indirect aquastat is never satisfied, your heating relay will never get power to operate in this diagram. On most modern circ heating relays,there is a built in timer function that would eventually allow the heating circs to run if the indirect called for an excessive period of time. You can't use this timer function however. You have to wire your indirect demand around the reset control because when the indirect calls for hot water, you want the boiler to fire all the way up to the high limit regardless of the outdoor temp.


The attacment provided should work for you. I would try it without priority to confirm there are no demand problems for either heat or hot water. Most likely this will be the case. You would do this by simply applying 120V power directly to the L N contacts of the ARM3-P and not supply it's power throught the AR-822 4NC contact.

Hope this helps you.