Ripping out Tekmar 306V's for Tekmar House Control 400 and 552 thermostats

tuffcalc

Hoping someone can maybe talk me off the cliff. I've just orderd 1x Tekmar 400, 4x wiring centre 313, 19x thermostat 552 to swap out my current system.

My current situation is as follows

19 zones
Thermostats - Tekmar 561 thermostats (with PWM control)
Tekmar 306V zone valve controllers.
Lochinvar knight boiler.

What's happening is that I'm getting roughly 2 to 5 minute on / 10-20 minute off cycles (with the thermostats running PWM control / in radiant mode). Across the 19 zones, this is causing the boiler to short cycle / go on and off quite a bit. The 306V has a room response signal that sets the setpoint on my lochinvar boiler based on the on/off cycle of the thermostats. The water is always between 85 - 110f, so very efficient.

My goal is to basically have my hydronic system act like my carrier. That is the thermostats communicate to the tekmar house control 400 how far each thermostat is from the setpoint and modulate the boiler based on that. This way I should get very long cycles (e.g., hours or more).

I called tekmar and they told me the house control 400 works on a 20 minute cycle. At the end of the cycle, it will recalculate the water setpoint based on outdoor temperature and indoor temperature feedback. This strikes me as exactly what I'm getting using the 306v's with room response.

Besides zone synchronization (which I don't really understand how it works) - am I gaining anything with the Tekmar 400 and 552 thermostats? Or am I better to just keep everything as is? Will the temkar 400 and 552s be able to communicate with eachother in real time and adjust the setpoint down/up as it gets closer/further from the set room temperature to keep the boiler running at exactly the heatloss of the house?

Thanks much

tuffcalc

I should add - my ultimate goal would be for the boiler to run constantly ... with the control modulating the boiler up and down to match the room temperature.

So in my 19 zone system, the largest load would always be on, and smaller zones can come on/off as needed. I'm fine with the thermal actuators firing on and off - but the boiler would constantly be modulating to meet the demand.

Zman

I suspect that your boiler is cycling because it's lowest turndown firing rate is higher than your load. All the controls in the world will not solve this problem. Did you put 19 zones on a WHN85? We really need to talk about keeping it simple "KISS".
I see a buffer tank in your future...

tuffcalc

Zman said:

I suspect that your boiler is cycling because it's lowest turndown firing rate is higher than your load. All the controls in the world will not solve this problem. Did you put 19 zones on a WHN85? We really need to talk about keeping it simple "KISS".
I see a buffer tank in your future...

Yes - I'm using a WHN85. 4 of my zones are at least 1000sq ft.

This could be happening because of the shoulder season, but I see no reason why the lochinvar can't dial down all the way to 10% while the other zones turn off/on around the 4 large ones (it's happening, sort of).

Maybe zone synchronization will help on the Tekmar 400.

Anyone have any actual experience with the Tekmar 400 and can weigh in?

Zman

I have more experience with the TN4 stuff. I am troubleshooting a 400 system this week. I have only read the manual but... i don't think is can solve your problem.

tuffcalc

Zman said:

I have more experience with the TN4 stuff. I am troubleshooting a 400 system this week. I have only read the manual but... i don't think is can solve your problem.

Do you know if the TN4 equipment calculates setpoint temperature in real time based on indoor/outdoor feedback - or does it calculate the setpoint based on cycle time on/off ?

nicholas bonham-carter

Have you done a heatloss, and radiation survey?
The results of this will show you if the 10% turndown is still too large for one zone.
A buffer tank will even out the system better than any controls.
Some people have incorporated the indirect into the heat storage aspect of this, without sharing the hot water for consumption, with the heating hot water.—NBC

tuffcalc

nicholas bonham-carter said:

Have you done a heatloss, and radiation survey?
The results of this will show you if the 10% turndown is still too large for one zone.
A buffer tank will even out the system better than any controls.
Some people have incorporated the indirect into the heat storage aspect of this, without sharing the hot water for consumption, with the heating hot water.—NBC

Yes - we did the calculations. Turndown is approximatley 8,000btu which almost matches a large zone.

Today we had some colder weather and the system seems to be working much better. The small zones click on and off, at least one larger zone is on most of the time so the boiler is getting a nice long burn time (albeit modulating up and down as zones are called).

I'm going to go ahead and replace the thermostats/controller with the tekmar communicating stuff. I think zone synchronizationw will be a big help to the short cycling in milder weather. I will report back once everything is in.

Zman

I am not sure if the TN4 calcs real time.
Keep in mind that with outdoor reset, the radiant output of the floors drops considerably as you reduce the water temp on warmer days.
I don't see a solution for you that does not involve either combining zones or adding a buffer tank.
The Tekmar controls do a lot of clever things, they cannot fix short cycling in a micro zoned system. Buffer, buffer, buffer....

tuffcalc

Zman said:

I am not sure if the TN4 calcs real time.
Keep in mind that with outdoor reset, the radiant output of the floors drops considerably as you reduce the water temp on warmer days.
I don't see a solution for you that does not involve either combining zones or adding a buffer tank.
The Tekmar controls do a lot of clever things, they cannot fix short cycling in a micro zoned system. Buffer, buffer, buffer....

I'm not understanding how the buffer tank will help. When a microzone calls the roomresponse SWT is generally low (say between 80 and 95f). The boiler cycles because of the PWM setting on the tekmar thermostat is set to turn off/on and pulse heat in the room. The lochinvar boiler is on but turned down (10% modulation).

How would a buffer tank change anything? The zones will still click on/off under PWM control.

Zman

When the zones are clicking on with your present setup, the boiler is firing each time it happens. With a buffer tank, the energy stored in the tank will satisfy the load and the boiler will not fire on each pulse.
Your symptom is cycling on each pulse. Your problem is you have a bunch of loads out there that draw < 1,000 Btu on a typical day and boiler that cannot turn down that low. The solution is more buffer.

tuffcalc

Zman said:

When the zones are clicking on with your present setup, the boiler is firing each time it happens. With a buffer tank, the energy stored in the tank will satisfy the load and the boiler will not fire on each pulse.
Your symptom is cycling on each pulse. Your problem is you have a bunch of loads out there that draw < 1,000 Btu on a typical day and boiler that cannot turn down that low. The solution is more buffer.

Ok I see what you are saying...

So I'm satisfied I only need one zone to be on while the others are clicking on/off... this way the boiler turns down to between 10 and 20% modulation but does not shut off. I'm fine with the microzones going on/off as it only changes the modulation rate of the boiler AS LONG as one of the big zones is on. My goal is to have the boiler on as long as possible. If you can imagine, I had a fight hard to install the "undersized" WHN085 with the inspector.

I'll try the new tekmar controls with zone sync first. If that doesn't work I'll add a buffer tank as you suggest.

tuffcalc

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tuffcalc

Wanted to post an update if anyone ever ends up in the same situation as me.

I went ahead a ripped out my Tekmar 561 thermostats and 306V zone controls on my 19 zone system.

I installed the following:

1x Tekmar 400 House Control
4x Tekmar 313 Wiring Centre
19x Tekmar 552 Communicating Thermostats
1x Tekmar 486 Internet Gateway
Already existing - Lochinvar Knight 80k BTU boiler
This all feeds an approximate 5000sq ft house.

It's all working very well - night and day from the "dumb" controls I previously had (even thought the 561 was using PWM control, and the 306V could send a signal to the Lochinvar to change the setpoint based on the thermostat off/on time).

Here are my initial obvservations:

1. Zone synchronization works. It looks like the thermostats all start on a 20 minute cycle ... and the highest load bleeds into the next cycle ... so it looks like one big burn cycle to the boiler and runs for hours on end.

2. Indoor feedback seems to work very well. What's happening is that the system is finding an optimal setpoint and running the highest load zone continually within its 20 minute cycle while smaller load zones turn off before the 20 minute cycle ends. Last night it was 5c where I am, and the boiler ran for 12 hours straight (with at least one zone always calling) -- with the Tekmar modulating the boiler up and down as zones come on/off. The boiler spent most of its time hovering around a 10 to 30% firing rate, while changing the water setpoint every 20 minutes.

3. Buffer tank - many suggested it but it looks like I definitley don't need it. The Tekmar 400 modulates the boiler up (100% at the beginning of a cycle when the most zones are active) all the way down (10% towards the end of a cycle when few zones are calling). It works beautifuly.

4. I previously had the boiler firing off/on 10 or more times in an hour... now as I already mentioned, the boiler is running for many, many hours on end!

5. The Tekmar 486 gateway is very impressive. Nice simple GUI - and logs data to boot.

I was nervous removing my "newer" 561 thermostats with the 552's and the Tekmar 400 that has been out for over 10 years... but I'm glad I did. This "older" technology has really solved all my issues and I'm sure will get the most longevitity out of my boiler.

Turbo Dave

Outstanding. I have used the 400 series with the 532 and 552s for years with excellent results. The minimum supply temp provided to heat the coldest zone allows maximum condensing. I'm glad you are happy with the change.

tuffcalc

Update: it's been colder here the last week (between 35f and 19f). The boiler has been running for 4 days STRAIGHT modulating mostly between 10% and 40%.

Really happy with these tekmar controls.

Mike_Breault

Good day, I am with tekmar, and perhaps I can clarify what is happening with the 30x series zone pump / zone valve controllers, and the difference to the 400 series.(and Zone Sync.)

The original controls you had do not differ greatly from the Tn series you replaced it with expect for a couple notable details.

both thermostats use PWM. the TN series communicate, and have the capability of syncronous operations.

the 30x series pump or Zone control can send a signal to a mod con like the Knight, but there is a difference. it sends a temperature based signal.. meanining its send a voltage that =equals a termperature target and let the Knight (in this case) fire, but it does not monitor water temps, and it does not modulate the firing rate.. it says fire i want X° water,

The 400 series with a TN communications, monitors water temps and can modulate the firing rate directly to maintain a water temperature. rather than tell the boiler I want X°F water, its says fire lower, water is hot enough, or increase its not hot enough,

the TN stats differ in that when one calls for heat, will "poll" other thermostats, and all stats below set point, regardless of differential, will call for heat, and just disembark as needed. the house control notes and lowers firing rate.

Longer run times, bigger load, better comfort.

so while the tech is similar in both sets (PWM and Modulation), the TN is superior in application due to sychronous operation, and modulating the firing rate rather than a temperature based signal

Hope this helps.

Mike B

Zman

@Mike_Breault
Welcome to Heating Help.
It is awesome when manufactures reps chime in!

STEVEusaPA

Zman said:

@Mike_Breault
Welcome to Heating Help.
It is awesome when manufactures reps chime in!

Especially someone from Tekmar. Haven’t seen a Tekmar person on here for a while.

Mike_Breault

Thanks, Ive been a lurker here on my personal account for years learning, chiming in, but I recently moved from Watts to the tekmar division, and added this to my list of things, so I will be lurking professionally too.

Be well!