Does this thermostat exist?

Gooch

I've got a radiant staple up floor. Currently running a tekmar 562 WiFi stat. Ivery got hardwood floors so I'm using a floor sensor with a max floor temp. The 562 would be perfect if I could use the floor sensor but not have to select radiant floor on the status. When radiant floor is selected on the status it does what it call PWM(pulse width modulation) 1.5 degrees below the set points and the system runs 100% of the time. Between neg. 1.5 and positive 1.5 degrees it cycles and this is my problem. It is short cycling the boiler. I would much prefer it to just operate 100% of time when 1 degree below set point the off 100% when set point is reached. Does a stay exist that operates this way?

Jamie Hall

Is the thermostat controlling the boiler directly? Seems to me that there are better ways to control such a system...

Gooch

The stat controls a pump relay, But yes when the stat calls it signals the relay and the relay end switch fires the boiler. I'm running an HTP UFT-80 Modcon. how would you suggest this be controled?

Ironman

Is the outdoor sensor installed and is the ODR curve PROPERLY set up on the boiler? If both of these are true, and the boiler is PROPERLY sized to the load, then you wouldn't need the floor sensor - in fact, you wouldn't need the stat.

Jamie Hall

I do hope that one of the radiant pros chimes in on this -- I'm a steam guy, but what I do know and have read is that this shoud be controlled using an outdoor reset for the boiler, to vary the temperature and firing rate of the boiler (that's the mod part of mod/con) and a separate pump and circulation to run the radiant.

Gooch

Yes the ODR is installed and set. I want the floor sensor for protection. I do not want to over heat my solid wood flooring. This is not the only zone feed by the boiler. The boiler for this zone alone would be oversized.

Ironman

That's not the proper way to control the floor temp. The correct method is to use a mixing device that limits the SWT to the floor.

What other type of emitters do you have? What's the maximum SWT the boiler is sending to the system? Do you have a secondary mixing device for the floor? What type?

Gooch

The boiler also serves my basement slab, backup fan coil (for when the staple up radiant cant match the btu loss due to my floor max limit for protecting my hardwood) and DHW(priority).the max SWT for ch is 110*. The staple up is wirsbo plates with 1/2 he pex. The system works great and I understand what the status is trying to do, but the staple up just doesn't have the issue with overshoot that the basement slab could have. I'm not willing to operate the system without overheating protection for my flooring.

Ironman

What's controlling the SWT to the staple up? Is 110* the max SWT to it? If so, there's no chance of over-heating it.

Gooch

110* is the max the boiler will supply. I've got the max floor temp set to 80*. To keep the house at 70 the floor hovers around 78*. This is measured at the bottom of the sub floor.

HVACNUT

Are there seperate input temps for different circuits programmed into the HTP boiler? Sounds like that is the case and your boiler is short cycling in direct relation to its radiant heat call at 110 degrees. If you pipe in a thermostatic mixing valve, set that to 110 and reset that circuit to high temp space heating, the boiler will modulate with the ODR and use some return water to extract BTU's eliminating short cycling.

Gooch

No, there is only one temp for CH needs, the top of the ODR curve is set to 110* The short cycling is a direct result of the stat's operating process.

Gordy

If the ODR is properly setup the thermostats duty is nothing more than a high limit device. The ODR drives the system.

Gooch

I agree but this stat won't function that way, is there one that will allow for what I'm looking for?

Gooch

Anyone?

ratio

I think what Gordy means is that if the stat has to turn off the heat the supply temp is, by definition, too high. Are there significant solar gains?

pecmsg

I wouldn't worry about overheating the hardwood floors, the'll take more heat then your feet or the pets will.

Why is this control shutting down the boiler and not that zone?

Gordy

Like @ratio said. You need to tweak the ODR. If the curve is precisely set then the thermostat is not even needed. Its only function becomes a high limit for solar gain, cooking, wood burner/fireplace, many people for a party. Any kind of internal, or external gain to the envelope that would skew room temps from the ODR strategy.

Gordy

I should ask if you are 100% sure it is set up correctly?

Gordy

Also,any time you try to keep a tight setpoint range there can be unintended consequences.

I'm curious of the piping control strategy. When the hydro air supplements it only gets 110*, and the radiant, and hydro air work together. All so you don't over heat the radiant?

Having mixing valves on both radiant zones would allow independent temps, and allow the hydro air to operate at a higher temp.

Gooch

The forced air never runs so I'm not worried about feeding it with a higher temp. It shuts the boiler off since there is no longer any calls for heat. If the basement were calling at the same time the zone would shut off but the boiler would continue to run.

Gordy

Usually depending on loads the two different radiant assemblies would require different supply temps on a reset curve. That doesn't mean they couldn't be the same however. I believe the uft only allows one supply temp on a reset curve plus dhw.

Something is a miss. You should not be cycling in a 3 degree range. Unless the staple has a high load. Tstat location?

I guess my point is with the two different assemblies is they act different. Concrete has mass, the staple up has much less mass. You are also pushing through sub floor and hardwood to get the heat to the space. An insulator verses a conductive medium.

If you are shooting 78 on the back side what is the actual floor temp above? That's where you need be concerned.

Gordy

It would be helpful to go into detail of the cycling on the staple up zone. On time verses off. How long each is. Pwm tries to achieve near constant circulation. Maybe you need to drop the reset curve.

Gooch

The only thing that is causing the short cycling is the PWM of the state. I have no storage mass to the boiler so anytime a zone calls for heat it lights the boiler. It works just fine with a max temp of 110.

Gooch

Maybe I'm not clear on how it is working. I have 2 zones. Basement and main floor. Basement is served via infloor. Main floor is served via uponor track. The fan coil can feed both and is intended as a backup only in the event of an issue with either floor. The boiler is piped P/S. The boiler only has 2 supply Temps. One for heating. One for DHW. The ODR is installed and set up as such: 60*outside=90*swt/-4*outside=105*(I lowered this and have had no issuesuch but didn't solve my problem.)

My controls work as follows. The basement slab is on a heat only air stat. The floor runs maybe twice a day. The upstairs is using the noted tekmar. 2 stages of heating and 1 cooling. First stage heat is the floor. Second is the fan coil. Cooling is my central air.

Both stats feed into a tekmar pump relay. And the end switch of the pump relay feeds the t/t on the boiler.

Because both floors work with the same temp I see no need to complicate the system with mixing valves.

My problem is the tekmar stat is trying to deliver small amounts of heat by cycling on and off. I do not know how it determines how long to cycle for but it seems to be on for 3 or 4 minutes and then off for 3 or 4 minutes. I'd much prefer it to operate like the basement stat that it runs until set point is reached and not fire again until it would be half to 1 * below setpoint.

Gordy

Like I said the concrete floor has a different characteristic it is slow to charge, and slow to release coupled with a low load of a basement.

So you want a non pwm thermostat that can still control the hydro air?

Gordy

Why not switch with the basement zone, and see how things act. That costs nothing then move forward from there if the main floor gives desired results. See also if the basement floor cycles on pwm.

Ironman

I believe your problem lies in how you've set the stat up. If I understand you correctly, you've set the "Max floor temp" to 110*. Set it higher to at least 120*. That won't damage your floor. Also set the minimum floor temp to 70*.

The radiant floor setting that uses PWM is for a HIGH MASS floor; than means a slab. Your staple up is LOW MASS. If the above changes don't correct the problem, then try selecting a different type of emitter for the first stage so the PWM is disabled.

You want the boiler or a secondary mixing device to limit the SWT to the floor, not the thermostat. The "Max floor temp" is a SAFETY feature, not a CONTROL feature.

Gooch

> @Gordy said:
> Like I said the concrete floor has a different characteristic it is slow to charge, and slow to release coupled with a low load of a basement.
>
> So you want a non pwm thermostat that can still control the hydro air?

I want a non PWM stat that can still control the hydro AND has a floor temp input. Maybe I'm being overly cautious about my floor tempspace with the hardwood.

> @Gordy said:
> Why not switch with the basement zone, and see how things act. That costs nothing then move forward from there if the main floor gives desired results. See also if the basement floor cycles on pwm.

Good thought. I wish the tekmar wouldn't force me to select rfh when I select a floor sensor. Simpler yet I'll just disable the floor sensor and remove the rfh setting.

> @Ironman said:
> I believe your problem lies in how you've set the stat up. If I understand you correctly, you've set the "Max floor temp" to 110*. Set it higher to at least 120*. That won't damage your floor. Also set the minimum floor temp to 70*.
>
> The radiant floor setting that uses PWM is for a HIGH MASS floor; than means a slab. Your staple up is LOW MASS. If the above changes don't correct the problem, then try selecting a different type of emitter for the first stage so the PWM is disabled.
>
> You want the boiler or a secondary mixing device to limit the SWT to the floor, not the thermostat. The "Max floor temp" is a SAFETY feature, not a CONTROL feature.

Max floor temp is not the temp of the water but the actual temp of the floor.

Ironman

Gooch said:

> @Gordy said:

> Like I said the concrete floor has a different characteristic it is slow to charge, and slow to release coupled with a low load of a basement.

>

> So you want a non pwm thermostat that can still control the hydro air?



I want a non PWM stat that can still control the hydro AND has a floor temp input. Maybe I'm being overly cautious about my floor tempspace with the hardwood.



> @Gordy said:

> Why not switch with the basement zone, and see how things act. That costs nothing then move forward from there if the main floor gives desired results. See also if the basement floor cycles on pwm.



Good thought. I wish the tekmar wouldn't force me to select rfh when I select a floor sensor. Simpler yet I'll just disable the floor sensor and remove the rfh setting.



> @Ironman said:

> I believe your problem lies in how you've set the stat up. If I understand you correctly, you've set the "Max floor temp" to 110*. Set it higher to at least 120*. That won't damage your floor. Also set the minimum floor temp to 70*.

>

> The radiant floor setting that uses PWM is for a HIGH MASS floor; than means a slab. Your staple up is LOW MASS. If the above changes don't correct the problem, then try selecting a different type of emitter for the first stage so the PWM is disabled.

>

> You want the boiler or a secondary mixing device to limit the SWT to the floor, not the thermostat. The "Max floor temp" is a SAFETY feature, not a CONTROL feature.



Max floor temp is not the temp of the water but the actual temp of the floor.

I know, but 120* is still safe, particularly if you're sensing the sub floor.

Gooch

120* is 35* over the recommended safe setting. Granted it would never get to it.