adding tekmar sensor 076 to control 260

CC.Rob_4

I added the indoor sensor not long after this thread back in December. Also implemented a setback timer using a simple programmable t-stat to start/stop UNOCC mode.

The results were phenomenal.

The heating system output was constantly tuned to the load.

FUEL USE REDUCTION = 8% compared to ODR-only

AVERAGE SUPPLY TEMP reduced by 40 degrees

COMFORT INCREASE excellent.

BOILER CYCLING reduced significantly.


Made possible in good part by education on the Wall. Thanks all!

CC.Rob_5

adding tekmar sensor 076 to control 260

I'm contemplating adding a tekmar indoor sensor 076 to my existing 260. The goal is to get closer to constant circulation and reduce variations in space temp. The present curve gets pretty close to constant circulation, but due to the setback, it's a bit high so we have excess input available for morning recovery.

This is a two-zone system with simple programmable thermostats that do a 2F overnight setback. Otherwise, setpoint is 68F. Thanks to a fortuitously balanced house, and a relatively open floorplan, I've found the sweet spot that represents the average temp of the two zones where the sensor would go.

Is there any benefit to adding the indoor sensor to this system?

From the 260 manual, it seems that the sensor is only active during a boiler demand, so any supply temp "fine tuning" occurs only when the stats are calling.

I am not using a timer, so the 260 is constantly in “OCC” mode.

My primary concern is accumulating errors during setback, when the indoor sensor would see space temps fall, yet OCC is still 68. Would this result in funky behavior during the period when reduced space temps are being maintained? (e.g., thermostat setpoint 66F -> makes a boiler demand -> 260 sees that OCC should be 68 -> jacks up the supply temp until 66F setpoint is reached and the stat removes the boiler demand? If this is a problem, is the only way around it to implement some sort of timer to put the 260 into unocc mode? I would like to maintain the convenience of the zone stats, so everyone doesn’t have to go mess with the 260 just to raise the space temp (not that they should, but sometimes they do…).

Thanks.

CC.Rob_4

bump.... anyone have some insight to share? I've searched through the archives and rummaged around the web to no avail. Thanks.

scott markle_2

setback

I think you should implement the timer so you have a global curve shift, and closer to constant circulation. The indoor sensor is useful because it will boost temperatures as needed and largely eliminate the pitfalls of slow setback recovery that are inherent to effectively adjusted ODR. I think the potential for the behavior you describe makes sense if you introduce the indoor sensor and continue to use the room stats to control setback. I don't think this would result in a fault, (ask tekmar )but it would defeat to some extent the advantage of lower temperature operation that you could be benefiting from in setback mode.

But wait ... as I consider this it occurs to me that Unless you are using a non-modulating condensing boiler the 260 can not provide the full reset range you would require for true constant circulation. You would need a mixing valve, or injection pump if your aim is constant circ., Because much of the typical heating load only requires water that is below the condensing threshold of a conventional boiler (140 or so).

radioconnection_3

indoor sensor

Having the indoor sensor would help boost recovery time, if needed, when going from unoccupied to occupied?

CC.Rob_4

piping

The system is capable of full reset. In practical terms the radiation is all fin-tube presently running between 110-170F.

I suspect that the average supply temp would drop at least 6-10F if the indoor sensor was running the show and constant or near-constant circulation was achieved. Plus reduce the amount of bouncing off the stats. The remaining issue is the convenience (or lack thereof) of simple adjustments to space temp by punching a button on a stat, now replaced with a trip downstairs and navigating a menu. Training on the 260 is a solvable problem, though. Thanks.