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An interesting bit about tekmar boiler controls....Boilerpro

Boilerpro_3
Boilerpro_3 Member Posts: 1,231
A few months ago I visited a home where I installed a Burnaham 207 and a tekmar outdoor reset control with DHW. I found it, in my opinion, short cycling. I checked with tekmar and discover their controls are programmed with a minimum cycle length of a minute or less, if memory serves (like I said, it has been a few months). It was running only a 10 degree system differential with a constant space heating demand (the control is dialed in very tight)on a 45 F rainy day (design here is -5F). To me this is much too short of a cycle length that will lead to condensation in the vent, sooting of the boiler, and poor flame efficiency. The tekmar literature always lead me to believe that the differential would be increased under light load in order to improve boiler efficiency. With a minimum cycle length like that, I think trouble is heading tekmar's way. Wonder what Glenn at Burnham, Noel at Slantfin and the folks at Weil- McLain would say about having thier boilers operating like that.
Just bringing to light a serious concern of mine for others to comment on.

Boilerpro

Comments

  • Bart
    Bart Member Posts: 14
    re:tekmar

    Were you running a continious circ zone?
    I have always made the 24v boiler demand only on a call
    for heat, and have always got the 071 sensor as close to
    the supply outlet of the boiler and well insulated as possible. The control usually works well with the differental set to Auto.
  • Hmmmm

    I thought the differential widened for that reason, myself. I have some homework to do, now.

    Noel
  • Tekmar Control Differentials

    Dave,

    Depending on the model and age of the Tekmar control, there are various functions that have to be properly programmed in order to help assure proper boiler run times. The newer controls have to be programmed with the type of system you are running and the type of boiler you are using (low mass or large mass). The Auto differential setting on the newer controls will readjust to achieve proper running times. The older controls will have a dial to set differentials.

    Another factor that will affect running times is boiler sizing relative to system loads. As we all know, many boilers are somewhat oversized (particularly replacement boilers). When Indirect applications are prevalent, many boilers are sized to satisfy both indirect and system loads simutaneously. Sizing to the larger of the two (system or indirect loads) and using the ability of DHW priority is a much better way to go. Take a close look at your control and the way it is programmed. Generally these controls will operate with proper running cycles provided setup and sizing is correct. Hope this helps.

    Glenn Stanton

    Burnham Hydronics
  • Boilerpro_3
    Boilerpro_3 Member Posts: 1,231
    Glenn, the control was set to auto Diff.

    This is what concerns me...A one minute or so firing cycle is OK, according to tekmar programmers! The control is a 260 boiler control. In auto diff, the factory programmed minimum on time is 1 minute or less, no matter what the on site settings. I told the tekmar tech about the problem and this short of a cycle was within the controls specs.

    Most of the tekmars I've been putting in for the last 8 years have been multistage units, from the older 252's and 254's to the newer 261's and 262's. I've never seen short cycling on the first stage boiler of these controls when using cast iron, only on the second stages, due to the stored heat in cast iron boilers and intermittant pumping of the latter stages. P/S piped, staged, intermittant circulation cast iron boilers really seem to need a firing delay to let the pump move some of the heat out of the boiler to see if it can satisfy the control requirements before it begins the firing cycle.


    Boilerpro
  • Boilerpro_3
    Boilerpro_3 Member Posts: 1,231
    At the time...

    I was doing my bucket time there was a constant space heat demand.... 260 control reset curve tuned in very tight..... so space heating pump almost never shuts off all winter. See my above post to Glen Stanton.

    Boilerpro
  • Normally

    there would be a delay in the ignition of the burners Dave. On a call for heat, the boiler relay will bring on the pump and then the sequence for opening of the damper and subsequent ignition sequence. This would generally account for almost a minute of clock time. Standing pilot models would be shorter of course. Your comments interest me a bit and I will contact Tekmar on Monday or Tuesday to discuss this. By the way.....is this one a Model 260?

    Glenn
  • Boilerpro_3
    Boilerpro_3 Member Posts: 1,231
    Glenn, what I have been seeing...

    Is that when the second stage boiler is already hot (often quite hot due to heat soak because the pump shuts down with the burners), and when it is turned on again, the pumps turns on and begins dumping the heat from the boiler into the system loop. The firing sequence also begins, opening the damper. However, all the heat stored in the hot castings and boiler water from the previous firing cycle satisfies the controls requirement and the boiler is shut off before the main burners light. Just an added observation and the reason I am going to start using time delays on the burners of my staged boiler installations. If you take a look at tekmar's new 268, it can stage the pumps on first and then the burners.

    Boilerpro
  • hydronicsmike
    hydronicsmike Member Posts: 855
    Will look into this on Monday.

    Boilerpro, would you mind emailing me your number?

    Thanks.

    Mike
  • hydronicsmike
    hydronicsmike Member Posts: 855
    Mr. Dave

    It was interesting to see your post regarding this short cycling issue here on the wall. Its great, but when you argue about someone’s product, you should get all the facts down so we all know what the issues are. Just to be fair to the manufacturer.

    Any comments after this are based on a previous conversation you had with Randy, a customer service representative at tekmar on March 26, 2003.
    I understand that on your job we are dealing with a 260 Boiler Control.

    As Glenn said, the (Auto) Differential changes based on load response and could fluctuate between 2 and 42°F
    In your case, however, you failed to mention that you installed a 3-way thermostatic mixing valve in the return to protect the boiler from cold return water, which is great. But you also stated back then (with tekmar) that your Boiler Minimum setting was set to OFF. –Why?

    What happened in your case, most likely, was that the Control has targeted a supply temperature below 140°F, which means that your thermostatic mixing valve diverted most of the boilers flow right back into the boilers return and not past the supply sensor. I am wondering why you would set the Boiler Minimum to OFF in the first place. I mean we are talking non-condensing boiler. That’s the reason you installed the mixing valve to begin with. With the 3-way thermostatic changing the flow rate across the boiler sensor constantly to accommodate Boiler Return Protection, the Control sees (assumes) a constantly changing load. Once the return temperature is satisfied by the thermostatic mixing valve, the flow past the supply sensor increases drastically since not much flow goes through the mixing valve anymore. Now all of the boilers water makes it past the sensor and pretty quick, the boiler target has overshot. If the boiler has been running for at least 30 seconds, we'll turn it off. Why would we keep it running? 30 seconds is the minimum on-time that has been in place for years without problems. If we were to meet the target in less than 30 seconds, then the differential widens.

    Solution:
    Set the boiler minimum on the 260 to 140°F. Dial your thermostatic mixing valve down to 125-130°F for return protection and you will see that there will be a much more constant flow rate across the boilers supply sensor and the control will do what it is designed to do. A 10°F Boiler Differential that the Control is running on right now, definitely tells me that the control is thinking Light load at the moment.
    Also, wire your boiler pump to the pump contact on the Control, so it doesn't just run while the boiler is firing. We need flow past the sensor when there is a demand on the control.

    When you mention flue gas condensation, may that have (even remotely) anything to do with a 30ft exposed masonary with an 8" aluminum liner and no rise off the draft hood?

    Dave, anything stated in this message was in good intentions. You should give us a call and we'll get things straightened out. Don't we always?
    Why make a statement as such? It is easy to be taken the wrong way.

    Regards,

    Mike


    PS. Glenn, is a 30 second cycle length damaging your boilers?
  • hydronicsmike
    hydronicsmike Member Posts: 855
    Dave,

    I fully agree on having the boilers pre- and post purged. I don't know if using a time delay relay will be the best solution. How about setting a manual differential greater than the one you have, if you aren't satisfied with the Controls (auto) logic?

    Like you said, the 264 and 268 have adjustable post purging times, where the pre purging is based on the boilers mass setting. AND, a seperate interstage delay.

    Mike
  • Boilerpro_3
    Boilerpro_3 Member Posts: 1,231
    Mike....

    I had no intention of bashing your products or your company and apologize if that is how is appeared. I was only intending to raise a concern in a forum of many excellent professionals, such as yourself, Glenn Stanton, Noel Murdoch and many others. I have used your control products almost exclusively since I began in the business due to their greatly above average design and value.

    The description of the piping in your post is incorrect, as often happens when trying to communicate over the limited media of a phone line. The piping is as follows.
    The Esbe thermostatic mixing valve ispiped P/S to the main system loop and pump. The control's sensor is on the system loop piping, not the boiler supply. Therefore, the flow across the sensor is not effected by the boiler's pump. It is also nearly constant during the heating season, since the heating curve of the control is set very closely to the heat loss curve of the home and the system circulator is almost always on. During my time I was watching operation, probably nearly an hour, the system pump never shut off. The control was only running about a 10F differential when it was short cycling the boiler.
    The attached picture shows a similiar residential installation, however, there is only one boiler instead of two. The Esbe valve is on the left pipe leading into the return of the boiler. This installation has a check valve on the boiler supply that is not necessary is the installation in question. The system pumps are pumping away from the boiler's P/S tees and then the compression tank and air separator. This piping arrangement is intended to allow for any system water temp that is necessary, hence the boiler minimum supply can be set to off. I have several other installations using this configuration with two boilers using a 252, a 261 and a 262 and none have first stage short cycling. Boilers run at proper temp while the system water is fully reset based on outdoor temp. It is a less expensive, and not as elegant, alternative to injection pumping. I apologize for the poor quaility of the photo, it is pre-digital camera.

    My concern about chimney condensation and short cycling is that the liner will never get a chance to warm up before the burners shut off. I have seen this before, as have others on this Forum.
    In the installation in question, the boiler is a 198,000 btu/hr input Burnham 207, hence the 8 inch aluminum liner in the exterior wall chimney. The chimney is the connector, since there are no other appliances connected to the chimney, from my understanding of vent design. So the connector height is 30 feet. B-vent runs from the chimney liner to the boilers vent damper to help ensure the chimeny is as warm as possible. As you stated, this is not an optimum configuration, but quite common, which was all the more concern when the boiler was short cycling.
    You should have recived my phone number via E-mail, however, the computer was acting a little strange this morning so there may have been problems.

    Boilerpro
  • Mike

    > It was interesting to see your post regarding

    > this short cycling issue here on the wall. Its

    > great, but when you argue about someone’s

    > product, you should get all the facts down so we

    > all know what the issues are. Just to be fair to

    > the manufacturer.

    >

    > Any comments after this are

    > based on a previous conversation you had with

    > Randy, a customer service representative at

    > tekmar on March 26, 2003. I understand that on

    > your job we are dealing with a 260 Boiler

    > Control.

    >

    > As Glenn said, the (Auto)

    > Differential changes based on load response and

    > could fluctuate between 2 and 42°F In your case,

    > however, you failed to mention that you installed

    > a 3-way thermostatic mixing valve in the return

    > to protect the boiler from cold return water,

    > which is great. But you also stated back then

    > (with tekmar) that your Boiler Minimum setting

    > was set to OFF. –Why?

    >

    > What happened in your

    > case, most likely, was that the Control has

    > targeted a supply temperature below 140°F, which

    > means that your thermostatic mixing valve

    > diverted most of the boilers flow right back into

    > the boilers return and not past the supply

    > sensor. I am wondering why you would set the

    > Boiler Minimum to OFF in the first place. I mean

    > we are talking non-condensing boiler. That’s the

    > reason you installed the mixing valve to begin

    > with. With the 3-way thermostatic changing the

    > flow rate across the boiler sensor constantly to

    > accommodate Boiler Return Protection, the Control

    > sees (assumes) a constantly changing load. Once

    > the return temperature is satisfied by the

    > thermostatic mixing valve, the flow past the

    > supply sensor increases drastically since not

    > much flow goes through the mixing valve anymore.

    > Now all of the boilers water makes it past the

    > sensor and pretty quick, the boiler target has

    > overshot. If the boiler has been running for at

    > least 30 seconds, we'll turn it off. Why would we

    > keep it running? 30 seconds is the minimum

    > on-time that has been in place for years without

    > problems. If we were to meet the target in less

    > than 30 seconds, then the differential

    > widens.

    >

    > Solution: Set the boiler minimum on

    > the 260 to 140°F. Dial your thermostatic mixing

    > valve down to 125-130°F for return protection and

    > you will see that there will be a much more

    > constant flow rate across the boilers supply

    > sensor and the control will do what it is

    > designed to do. A 10°F Boiler Differential that

    > the Control is running on right now, definitely

    > tells me that the control is thinking Light load

    > at the moment. Also, wire your boiler pump to

    > the pump contact on the Control, so it doesn't

    > just run while the boiler is firing. We need flow

    > past the sensor when there is a demand on the

    > control.

    >

    > When you mention flue gas

    > condensation, may that have (even remotely)

    > anything to do with a 30ft exposed masonary with

    > an 8" aluminum liner and no rise off the draft

    > hood?

    >

    > Dave, anything stated in this message

    > was in good intentions. You should give us a call

    > and we'll get things straightened out. Don't we

    > always? Why make a statement as such? It is easy

    > to be taken the wrong

    > way.

    >

    > Regards,

    >

    > Mike

    >

    > PS. Glenn, is a 30

    > second cycle length damaging your boilers?



    Although we would desire a much longer cycle length, it may not be neccessarily be harming the iron, but it isn't doing much for the longevity of the boiler controls! Thanks for handling this one. I meant to call you today but I was busy with a group of contractors here in Lancaster from the beautiful state of Maine. Thanks again.

    Glenn
  • Mike

    Although we would desire a much longer cycle length, it may not be neccessarily be harming the iron, but it isn't doing much for the longevity of the boiler controls! Thanks for handling this one. I meant to call you today but I was busy with a group of contractors here in Lancaster from the beautiful state of Maine. Thanks again.

    Glenn
  • hydronicsmike
    hydronicsmike Member Posts: 855
    Dave.

    I know that your work is top notch. I don't know if you remember, but we worked on a job together about 2 years ago. I think you even sent me pictures. I have since sent customers your way at least twice. Don't know if they ever materialized, but....they were not too far from Amboy.

    In this case, something is just going wrong and we'll fix it. What I should get, is a piping diagram that is as built and installed. I will once again look into the Controls logic. Out of how many we sold, this is the very first complaint I get and we'll get to the bottom of that one.

    I am sorry if I wasn't bang on with the system description, but I went by what was written in that particular phone report of the conversation you had with Randy that day. Let me have the mechanical, I'll dig into the Control and we'll get her straightened out.

    It's 11:50PM and I am still thinking about this one. I love my job!!!

    Regards,

    Mike

    PS. Thanks Glenn. As always. I am missing you on the WETSTOCK III list.
  • Stemmer
    Stemmer Member Posts: 4
    controls

    Morning All.
    Reading this with interest I wondered why any external control would be utilized when you have a combination heating / domestic load requirement. Typically, i use an electric zone valve on each load with an end swith. Wire all the end switches back to the boiler. As each loads thermostat / aquastat calls for heat, it opens the zone valve which fires the boiler. The pump runs off the pump relay from the boiler. When all is satisfied, the boiler is shut down. This also eliminates any hassles when there is only a domestic demand and no heating demand. If a 3 way is used to protect from LRWT it doesn't cause any problems unless the boiler operating control is set too low. If there is a low temperature loop within the system, control the loop, not the boiler.
    Also, when I do utilize a Tekmar controller, I have been installing the water sensor in the return water side, system side of a mixing valve if there is one. This will increase the cycle time of the appliance. Remember to set the controller down, it thinks its looking at the supply temperature. Good luck.
  • hydronicsmike
    hydronicsmike Member Posts: 855
    And Dave,

    no phone number in my mailbox this morning.

    Mike
  • Boilerpro_3
    Boilerpro_3 Member Posts: 1,231
    Hey Frank...

    > Morning All. Reading this with interest I

    > wondered why any external control would be

    > utilized when you have a combination heating /

    > domestic load requirement. Typically, i use an

    > electric zone valve on each load with an end

    > swith. Wire all the end switches back to the

    > boiler. As each loads thermostat / aquastat calls

    > for heat, it opens the zone valve which fires the

    > boiler. The pump runs off the pump relay from the

    > boiler. When all is satisfied, the boiler is shut

    > down. This also eliminates any hassles when there

    > is only a domestic demand and no heating demand.

    > If a 3 way is used to protect from LRWT it

    > doesn't cause any problems unless the boiler

    > operating control is set too low. If there is a

    > low temperature loop within the system, control

    > the loop, not the boiler. Also, when I do

    > utilize a Tekmar controller, I have been

    > installing the water sensor in the return water

    > side, system side of a mixing valve if there is

    > one. This will increase the cycle time of the

    > appliance. Remember to set the controller down,

    > it thinks its looking at the supply temperature.

    > Good luck.



  • Won't be there Mike

    Due to prior commitments in New England, I will be unable to attend. My partner, Ron, will not be able to attend either. maybe one of these days we will mmet!

    Glenn
  • hydronicsmike
    hydronicsmike Member Posts: 855
    ISH-NA??

    gonna be there?
This discussion has been closed.