Tekmar 279 Steam Controller Questions

cubicacres

Has anyone installed a Tekmar 279 steam controller for a single-pipe steam boiler (WMC EG-75) in a large house or small apartment building before (about 4,000 sq ft)? We have one indoor sensor Tekamar #76 for the coldest apartment, the condensate sensor on the end of the steam main just outside the boiler room, and the outdoor sensor on the North wall to install. How long/how many hours has it usually taken for a typical install without any problems?

cubicacres

Thanks. We'll see if we can identify the old outdoor sensor conduit. The condensate sensor could be in the boiler room like you mentioned, or we could go another 5-10 feet further just outside the boiler room wall to the last radiator, since it's just on the other side of the boiler room wall. The indoor sensor is already wired-up from the coldest apt room to the boiler room as a basic thermostat, so hopefully just a quick replacement using the same wiring if possible. We're hoping the auto-settings with the outdoor/indoor/condensate sensors should calibrate things pretty well for us.

I wonder if our old thermostat still wired-up in the boiler room that used an indoor sensor & an outdoor warm-weather sensor/shut-off could use the same wiring for the Tekmar to save time? The electrical panel box is about 10 feet away, just outside the boiler room, so maybe not too bad of a job in any case, if new electrical needs to be run.

cubicacres

Great. We noticed it was about 40 degrees today at the property, and it ran for about 33 minutes with the burners on the whole time before the LWC seemed to cut it off for a few minutes. The sight glass water level varied almost an inch during that time, but didn't seem too crazy. Then the burners fired-up again a few minutes later with a lower sight-glass reading, and ran for about 8 minutes before shutting down. Not sure if the thermostat was satisfied, or it was the LWC stopping it again. The main vents had stopped intermittent puffing/venting about mid-way through the first 33 minutes, I think.

cubicacres

When we have it installed next week, we're planning on using:

68 deg indoor design (same as target temp/room occupied temp for indoor sensor, right?)

72 deg outdoor design, since -4 deg was Milwaukee design day used in the WMC Installation Guide with our 68 deg indoor target

100% boiler design % for now with the auto heat-curve used with the indoor sensor in charge of demand, but we can decrease that in the future-or does the auto & indoor sensor take care of this automatically every time?

cycle=auto, which we plan to use. Or if we select it, I think defaults to 60 minutes unless we change it.

No setback/boost/unoccupied settings for now.

cubicacres

We saw the LWC at 33 minutes started going on & the sight-glass was on the low-end of the range it had been the last 33 minutes. It only shut off for a few minutes, not the 10 it should have waited for the condensate to return if it was shutting down the burners. Maybe some condensate returned naturally & let it start up again before the 10 minute pause for the LWC was over? The LWC did seem to blink & go on after the next 8 min burner run, so maybe running low on water by then?

So far the auto-water feeder is at 4 gal since install 3 weeks ago. It just turned from 3 that it's been steady at from the install date (when they went from 0-3 gal the first day trying to keep the burners firing with the LWC cutting them out) to 4 yesterday.

JohnNY

I have about 75 tekmar 279s installed in the field. The majority are on 1-pipe steam.

cubicacres

So far that 33 minute run time we noticed was without the Tekmar added yet-just the temporary basic thermostat controlling it from one of the apartments on a 40 degree day (maybe the tennants set it above 70?, we didn't check it so we can't be sure what it's at for the next few days until the Tekmar install this week). We also still need to replace the near-boiler insulation, so hopefully that's part of it, rather than our new boiler being too small for the system. Our slant/fin smart phone app heat loss calc. showed around 130,000 BTU/HR heat loss (others ranged from 120,000-160,000 online), compared to our 247,000 Gross or 185,000 Net EG-75 boiler.

It sounds like you'd recommend adjusting the cycle length a few times during the heating season, rather than relying on the auto settings & letting the indoor sensor communicate with the outdoor sensor & condensate sensor to target the indoor "Room Occupied" & "Indoor Design" desired indoor temp setting?

cubicacres

So the estimated heat loss of 130K BTU/HR per the heat loss calc. of our building compares to the 247K BTU/HR Gross Output the boiler makes heating all the main piping, risers, and radiators in the building?

That's the rationale behind sizing it to 52% to balance the loss rate with the BTU production rate over time, right? Would this suggest running the boiler 100% of the time 24/7 if it were set at 52% instead of higher?

Here's what I read in the Tekmar 279 manual (attatched PDF) pages 6 & 7:

When an indoor sensor(s) is connected to the control, the
Room setting becomes a Room Target temperature. The
control measures the current air temperature in the room
using the indoor sensors. The control then automatically
shifts the heating curve so that the measured room
temperature reaches the Room Target temperature.

The Adjust menu includes a setting called Cycle that
determines how often the heating system will run. During
each heating cycle the boiler is turned on once, and the
boiler is turned off once. Each building has a natural heat up
and a cool off rate. This is determined by many factors such
as the size and length of runs in the steam heating system,
the size and mass of the radiators, and the heat loss of the
building. The factory default is 60 minutes. When using
optional Indoor Sensors, an automatic setting is available
that allows the control to learn the natural temperature
swing of the building. If the optional Indoor Sensors are
not used, then the only method of adjustment is trial and
error by the installer.

Does this suggest we can try the indoor sensor & auto settings to get us the best burner firing times, or is manually adjusting for about 20-30 minutes of burner firing time by changing a few settings better to be sure we get maximum efficiency?

Our tenants did raise the temporary thermostat in their place from 60 to around 65-70 deg. this week, so that setback recovery from 60 could explain some longer run times the last few days & the extra gallon of water per the water meter? We added 2 gallons this past week. Or maybe a few radiators are still squirting since they're larger vari-vents than the old radiator vents and still need to be turned down. We did this on one that was too hot & squirting, along with shimming it from level towards the supply valve a little, with small tile squares instead of the carpeting it was shimmed with :-)

cubicacres

Thanks. Tekmar Tech support reccomended similar trial & error by starting with the auto settings for now, then watching how it runs (they called it the "Bucket Method" = sit on a bucket in the boiler room & watch what happens over time :-). The indoor sensor should adjust the heat curve automatically, and the 60 minute default cycle time on auto is reccomended by Tekmar as a starting point. He noted we could increase it to 100 minutes if desired. A short cycle time of say, 20 minutes could be problematic if at 50% boiler size, and only 10 minutes or less to run, which seems to make sense. Once we replace the near boiler insulation & get some colder days, it will be interesting to see how the Tekmar runs on the system.