tekmar 152

Paul S_3

Can a Tekmar 152(2 stage) setpoint controller be used to stage 2 on/off boilers from outdoor temp? for example im in the process of installing a boiler room ....with 2 CI on/off boilers. whole house is infloor radiant.....i will be installing a Tekmar 360 with 4way valve and actuator and has boiler protection.....but i want to stage boilers too.....the Tekmar 374 gives me all of these options but a little pricey i would like to know what you guys think.... the only issue is the 152 doesn't have a WWSD feature because its applications are for indoor....i would put an outdoor stat in series to shut off staging....if DHW calls it will take priority over everything....please let me know if im over complicatings things... thank you Paul S

STEVEusaPA

Is this gas or oil? I like the 374, better for gas, but it doesn't matter if you're using the 4way for boiler protection-you would disable it in the 374. Does the price of the 374 exceed the price of a 360 and a 152, and the extra 'in-series' t-stat, plus wiring, labor, etc?

Paul S_3

its gas ....CI boiler need protection ....i think im just going with the 374....why would i disable the boiler protection in the 374 if its doing the mixing and staging...plus DHW priority.....your right about the cost...thanks

STEVEusaPA

Paul my experience with the 374 in my house, and I probably wont explain it correctly, is that enabling boiler protection only with the control for a radiant (low temps) system leads to short cycling, a lot of short cycling. It's better to do it with the piping. This may or may not apply to your situation, but it did to mine. The control will stop injection mixing at boiler minimum, so what happens? The boiler fires, gets above the minimum rather quickly, the injection mixing starts again, the boiler comes up to it's limit with ODR is in the 140 (minimum)-160 range, unless design day, and shuts off rather quickly. Injection keeps working, and round and round it goes. Now this is a multi, small zone system, so like I said, you may not have this problem.
My solution was a buffer tank, near constant circulation from buffer thru zones with odr curve adjusted, and the boiler's job is to charge the buffer when not in WWSD and/or charge the indirect.
In a nutshell I don't like that injection mixing completely stops when you drop below boiler minimum, considering the boiler can recover pretty quickly-I think it's more about the control's brain. Especially in the shoulder seasons when you're zone temps are say 90, and your boiler minimum is set at 130.
I stared at it, adjusted, recorded, tried different differentials, different combinations, stared some more the first heating season...mostly at night...mostly with my wife thinking I'm crazy.

Paul S_3

theres about 40 radiant actuators and 25 tstats .....system is all infloor radiant properly sized ... if the 374 can stage wouldnt that minimize the short cycling ? i wanted Lochnivars KHNs out of customers budget.....for some reason no one wants high wfficiency boilers.....expecially lochnivars .....other contractors installing naviens and are half my quote.....even though i explain the capabilities of the Lochnivars.....sorry to go off track