Tekmar/Heat Timer - Where to locate condensate sensor?

Mike_Sheppard

Where is the best spot to locate the condensate sensor in an apartment building?I’ve seen people say that it should be on the end of the furthest steam main or the furthest radiator from the boiler room. The manual says undiscriptively “condensate line”.

I’ve worked with Tekmar and Heat Timer controls for 12 years now and I’ve seen sensors on wet returns, dry returns, steam mains, headers, radiators, boiler jackets, gas lines (yep, someone actually insulated a gas line and stuck the sensor under it), and in a room like a room temperature sensor.

Just wondering where you guys consider the best placement for the “condensate” sensor.


Edit: Picture attached of Heat Timer’s manual.

I’m thinking, when installing in a large apartment building, perhaps the furthest dry return would be a good spot?

EBEBRATT-Ed

I don't claim to be an expert on this. My understanding with Heat Timer is that that sensor serves as a "steam established" or "heat established" sensor and the control starts timing when the sensor gets hot.

Best place is on a dry return from the last radiator if two pipe or end of the steam main on a 1 pipe.

We had a Heat Timer go bad this winter and replaced it with a Tekmar which I was impressed with. Lower $$ We wanted to replace the sensor and followed the heat timer wires and lost them in the walls. Searched the whole building and could not find the sensor. Installed the new sensor on a return in the basement and I was sure we would have to go back and tweak the control but never herd back so I guess we lucked out. We did find the OA sensor and changed that

Mike_Sheppard

You are correct. Once the sensor reaches it’s set point it begins it’s calculated heating cycle length based off the outdoor sensor reading.

I was thinking the same. You lucked out with not having to tweak the control! I usually go back once to make some minor adjustments.

I’m more of a Tekmar fan as well.

sreja

We have a tekmar and I'm also a big fan.

As for where to put the condensate sensor, this advice is fine:
"Best place is on a dry return from the last radiator if two pipe or end of the steam main on a 1 pipe."

But in more flexible terms, you ideally want to put it somewhere that gets hot LAST (and then set the temperature trigger for it at a temperature that will be reached when heat has reached everywhere). So that might not technically be on the condensate line, and it's not critical that it is. You just want it someplace that has enough of a temperature difference that it roughly can tell the tekmar when heat has been generated and is starting to be received. Doesn't have to be too precise.

gfrbrookline

What are the benefits of a tekmar/Heat timer over a Honeywell Vision Pro 8k with 5 indoor sensors?

Dave in QCA

I installed a Tekmar 279 in the fall of 2008. It has been working fine and produces very even heat without any perceptible swings in room temperature.

HOWEVER. I am sure in my mind that there is an error in the factory recommendation for the placement of the condensate sensor on a two-pipe system. Here is why. The condensate sensor serves the function to determine when steam has been established in the supply piping. As you will note, on a 1-pipe system, the manual shows the sensor being installed on the runout to the radiator that is at the greatest distance from the boiler. The default setting for the sensor is 180 degrees. For the 2-pipe system, the manual shows the sensor being installed on the return piping of the farthest radiator. And, thus, the sensor will not see 180 degrees until the radiator is FULLY heated. The control will remain in the "establishing steam" mode even though steam is filling the radiators and is producing a great amount of heat in the space. This will cause WILD swings in room temperatures, causing the boiler to not fire again for a few hours. Wild overheated cycles is what the control is supposed to stop

I saw this as a serious error before I even began the installation. So, I installed the condensate sensor at the end of the longest steam main, making sure that it's on the top side of the pipe. When operating, the control switches from "establishing steam" to "heating cycle" when steam gets to the end of the main. This is also the exact same time that steam begins going into the radiators. So, in mild weather, a 6% cycle for example, will only warm the first portion of the radiators. Mild heat in mild weather. 1 cycle per hour. Room temperature shows zero fluctuation. In cold weather, for example, a 60% cycle will run the boiler for 36 minutes after steam is established, heating a significant portion of the radiators. And again, the room temperatures remain constant.

Mike_Sheppard

@Dave in QCA you bring up a great point. I didn’t think of that. Even if it were to be mounted on a dry return of a 2 pipe system down in the basement that condensate would have to make it though the radiators first. The temperature would likely have to be set lower than 180. Either that or the settings (boiler design % etc) would have to be dialed down to make up for the longer run time to “establish steam”

Dave in QCA

@Mike_Sheppard Yes, all of the gyrations that one would have to do to make it work as intended.... I mentally puzzled through all of those. But then, on an old 2 pipe vapor system such as ours, I find that with smooth even operation throughout most of the year, the outlet end of the radiator remains cold, and thus, the condensate is cold. The vast part of the year, if I touch the outlet of a radiator as it drops into the basement it is cold to the touch. Only when outdoor air temps get to the single digits do begin to feel any warmth, and then it might be 110F at the most. It's just not the place to check for "steam established". Now, if the system were to be made up of fin-tube convectors, then yes, it would be just fine. It would work great. Maybe that's what they were thinking.

EBEBRATT-Ed

Tekmar or heat timer all those systems work on some theory that the system they are applied to is balanced which most probably are not.

Most of these are old originally coal fired systems and I see these controls as a "band aid" to an old system because in most cases it's the only thing you can do short of manual operation.

Still it gives you warm weather shut down. And finding the right location for the "steam established" sensor can be problematic but it's a lot better than a boiler running wild and opening windows but they are far from a perfect control system.

@gfrbrookline

The heat timer or tekmar advantage is

1.warm weather shutdown with an outside air sensor`
2. the boiler starts and warms up the piping. When heat reaches the end of the system the "heat established sensor" starts timing the length of the boiler cycle based on outside air temp and the settings the installer programs into the control.

So boiler shuts down if outside air says no heat is needed. Boiler cycle is longer or shorter based on outside air temp.

gfrbrookline

@EBEBRATT-Ed Thanks for the info but still don't see the advantage. Since I am heating the interior space if I am running averaged sensors in the interior spaces to call for heat why would that not be better than using and outside temperature to dictate the run time.

I can see the benefit with hot water heat because you can adjust the temp of the water needed to heat the space but with steam if the system is balance and insulated I don't see how you would have a gain over a vision pro unless you had a large building and could not have enough senors to provide adequate input.

Mike_Sheppard

@gfrbrookline this was more geared towards large apartment buildings as I noted in the first sentence. I’m sure there are better options for a single family home.

gfrbrookline

Thanks @Mike_Sheppard . I have a 7 unit condo building and have just been looking for ways to make the old system work better.

EBEBRATT-Ed

@gfrbrookline

Sorry about that. Heat timer/Tekmar control is for steam boilers where you cant have stats in each apartment of multifamily units. For smaller buildings what you suggest would be better


basically just a timer that runs the boiler based on outside air. starts timing when pipes get hot.

Tekmar works good and is much less $$$$$$

Dave in QCA

The Tekmar 279 has the option for one, two, or more interior sensors. However, even with interior sensors, the Tekmar does not operate in the same manner as a thermostat. Like @EBEBRATT-Ed said, it operates like a timer. However, the timer is affected by two factors. Primary effect on the timer (length of cycle) is the outdoor temperature. At the beginning of each cycle, the Tekmar looks at out door temperature and calculates a length of steam cycle. It also looks at the indoor sensors. If the indoor temperature is above or below the target, it will adjust the steam cycle accordingly. So, it determines in advance, the length that the cycle is going to be.

JohnNY

Here in NYC, we see and install both Heat-Timer and Tekmar products in most of the buildings we service. The exceptions are where buildings are controlled by an Allerton or similar DDC control network or BMS.
I only ever see the system sensor located on the drop to the wet return off the steam main. Flexibility in programming is enough to make that location work well for nearly any system.
Of course, there are exceptions.

I should add that the heating cycle of many Heat-Timers is not activated by a system sensor but by a pressuretrol or vaporstat at the boiler which works well and eliminates the need for the long run of wire needed with the system sensor.
This is not an option for Tekmar but is common with Heat-Timer, which is a far better product. Nothing wrong with Tekmar. I use the 279, 260 and other models frequently, but the functionality of the Heat-Timer line blows Tekmar away.

Mike_Sheppard

@JohnNY I know Heat Timer has the pressure sensor option for establishing steam, but I’ve never seen one actually used. I’ve only ever seen the temperature sensor.

Does the Heat Timer pressure sensor work well with the low steam pressures these systems run?

Dave in QCA

On most systems, It might work, but it won't work well. Pressure will not build until the radiators are fully heated, in most cases. So, rather than providing just the right amount of steam to the radiators based on the outdoor temp, it is going to fully heat them. Of course, if the system has fin-tube convectors, it might work fine. On our system, we never build pressure.

Now, if the system is fully orificed, and pressure is established in the mains as soon as the mains are filled with steam, but before the radiators have begun to heat, a pressurestat to signal steam established would work great.

JohnNY

It's fairly common here and it works fine. On a mid-rise or high-rise building the pressure is going to rise. A pressuretrol or vaporstat will start the cycle at 10 oz or 1 psi, whatever it is, and the remaining run time fills the last radiators. It doesn't matter how you get this done...with pressure or temperature...it's a balancing act and it usually takes some human intervention to get right and you don't always have access to the parts of the system where a sensor would do most good.

gfrbrookline

@EBEBRATT-Ed and @Dave in QCA thank you for the clarification. I appreciate your help.