paging hydronics_mike - 1 more t-256 question -

soot_seeker_2

hi mike - this post is from the previous thread further down but i wanted your thoughts on it. (slight editing).

i called tekmar this (tuesday) morning. i couldn't reach mike (you) as he was busy on the line but i spoke to 'paul' (excellent rep). after explaining my situation (above) and expressing my concerns about cold starting a 25 yr old (soot prone) JOT, we agreed it might be best (and easiest) to just jumper the demand loop terminal and let the t256 continuously govern the reset temp all the time (not just during demand). [so you guys had the right ideas (above) as to how the demand loop worked - thank you.] the rep explained that tekmar is very 'cold-start' oriented & that is why you'll basically see many of their application drawings designed according to that point of view. the rep indicated that tekmar's research has shown that cold-start is really the way to go (with few if any historical problems) and that those less inclined to go that route may not be giving the boilers enough credit to hold up under that operation. certainly, the fuel savings are far greater - so it's always something to consider.

with regard to the demand wiring, the only big difference between the two setups is that the t256 control is cut out during periods of non-demand (allowing possible cold-start) as opposed to maintaining a minimum reset temp. naturally, i like the idea of the greater fuel savings associated with cold-starting and it would probably be fine for the cold months where the boiler temp would rarely get a chance to really drop that low as to become a sooting problem - but my real concern was for the fall and late spring periods where the cycles would be less & the boiler temp might actually go cold for a period of time between demands ( trust me, my boiler doesn't like that & eventually throws a soot fit). i thought that this might be solved by jumpering the demand loop and lowering the boiler temp minimum (allowing a lower idle temp) - but that wouldn't really work since it would also alter the low end of the terminal curve and throw-off the target point for the radiators during real cold snaps.

so here's the next question.

if you have a situation (like above) where you would want the idle (no demand) boiler temp to be lower than the terminal curve minimum but you DON'T want it to go completely cold, why not just jumper-out the demand loop (t256 'always on') *AND* wire the heat demand signal from the zone valves/circ pumps/master relay control/ etc.(inverted thru a relay) to the 'unocc' loop instead and adjust the unocc value such that it shifts the curve down parallel during 'no demand' (closed unocc loop) to give you a lower idle temp - but will never let the boiler go too low since the t-256 is always 'on' and then flip back (open loop @ unocc) to the OCC (value) setting which would put you back on the regular terminal curve during a demand?

i thought this would work if the 'boiler min' value gets shifted down with the 'unocc' setting. does it?

otherwise any problems with this idea that you can see?

ss

hydronicsmike

Hey Soot

A Boiler Minimum always is and stays the Boiler Minimum, no matter how much a curve is shifted. (The same for any Boiler Maximum Setting [not applicable in the 256, but plenty of other Boiler Controls tekmar has]) I see what you are trying to do and it 'could' work. However, the Boiler Minimum is usually programmed to be 140°F, which is the lowest one should ever run a Cast Iron Non Condensing Boiler to prevent condensation.

So to answer your question, it is not practical to do and the Boiler Minimum would still (and definitely should) stay the same anyways.

If you want to further your Energy Savings, it would actually be best to use a Mixing Device to run a Baseboard (Fin Tube Convector), as during mild load conditions, the water temperature on the Mix Side can be lowered below any Boiler Minimum and therefore increase the Energy Savings and greatly improve the Comfort Level by minimizing or even eliminating temperature swings and expansion noises.
Anyways, feel free to call me at any point, should you think I could help you further. Would be very happy to talk to you and discuss all your options.

!! Keep in mind that if you apply a permanent demand on the 256 (Jumper terminals 7 "T" to 9 "Com") you will have to have continuous flow past the Boiler Supply Sensor and a Pressure Bypass should be used. Also never run the Boiler Pump of the internal Pump Relay in the Boiler. This would cause your pump only to run while the Boiler is actually called to fire. In many cases, this is known to create Boiler Short Cycling, which is usually not too good on a Boiler, nor does it help the overall Efficiency or Fuel Consumption, due to the Supply Sensor cooling off while there is no hot Boiler water flowing past it.!!

Hope this helps.

Best Regards,

Mike

soot_seeker_2

hey mike

hey mike,

thanx for the info / conversation today. i gather we got cut off at the end. i tried to call you back but your line was busy. if you should have a good longtime contact at peerless or tekmar that might be familiar with the specs of the 1980's vintage peerless boilers then by all means please let me know either here or by the phone number on file at tekmar.

ss

hydronicsmike

Hey Soot

try my Rep in PA, he has been Reping Peerless for years. His name is Roger Prevost and he is Quality Equipment Sales in Pottstown, PA 610-495-9800. If he doesn't know the answer to your question, he will know who you should talk to at Peerless. Tell him Mike sent you.

Thanks for calling. Enjoyed the conversation. Feel free to call back at any time, should we be able to be of further assistance.

Regards,

Mike