Indoor Reset

Mike T., Swampeast MO

LOW!

How low will depend upon how far the soapstone is from the stove.

bruce pirger

Indoor Reset for Indoor Gain

OK, I think I am finely making progress...

I will burn a woodstove nearly continuously all winter, so a type of indoor reset must be employed to not blow us out of the house. I just assume burn as little oil as possible. But I do want to have the floors warm, especially the concrete slab!, and also the fire will go out...

So, I need outdoor reset, indoor reset, and the mixing control on the radiant heat. I have attached the basic drawing....My, it looks like all those standard examples...LOL...imagine that.

So, the pump on the manifolds runs continuously, the mixing valve is controlled by the controller to adjust the water temperature as mandated by the outdoor and indoor reset and controllers' temperature curve.

So, the question is....Just how does the controller respond to the indoor reset?? One way would be to select a lower temperature curve....one way would be to push the entire curve down (maintaining slope) so that the mixed water temp is lower for a given outdoor temp with a warm indoor temp.

Right?

So the question is, just how do the various controllers actually automatically introduce this indoor reset feedback? It'd be silly if it heated the boiler temperature up, in response say to a lower temperature outside, but then just mixed the mixing valve very low due to the high indoor temp. Seems like picking the correct controller algorithm here is the key to minimizing fuel consumption.

Does anyone know exactly how the Vitotronic 200 would handle this? I see in the Technical Data Manual it says the indoor reset control must no influence the underfloor heating circuit...maybe this means not turn off the circulation??

There is a wide range of adjustment indicated for the heating curve slope and offsets...but I'm not sure if this is determined automatically based on the outdoor and indoor resets.

Anybody know just how this works in the Vitotronic 200?
Thanks!

Mike T., Swampeast MO

Attachments won't load...

>Technical Data Manual says the indoor reset control must not influence the underfloor heating circuit...

I'm presuming this means that indoor reset shouldn't modify the underfloor in ANY way as it is intended to be used for SUPPLEMENTAL radiation when the underfloor is INADEQUATE. Quite the opposite of what you want to do!

>I will burn a woodstove nearly continuously all winter, so a type of indoor reset must be employed to not blow us out of the house. I just assume burn as little oil as possible. But I do want to have the floors warm, especially the concrete slab!, and also the fire will go out...

Tall order. If the wood stove is on the concrete slab, it might be impossible to keep the floor warm without blowing you out of the house at moderate outside temps.

I also presume that the area most influenced by the wood stove is on a separate "zone." If so, I believe a Danfoss FHV-A room temperature control (or similar) is MOST appropriate in this area for this zone. It would only change the flow/temperature in THAT zone, not the entire manifold. Finding it's proper position in the space (not too close to the stove--not too far away) could be really tricky! If the stove area has more than one run of tubing from the main manifold, you'd need one of these on each run. This should provide the indoor reset you desire while ensuring sufficient temperature is available for other areas while not allowing the slab to get too cold.

Since your goal is to use the least oil (not the least wood), I think [THINK mind you] that you would: use the wood stove exclusively as long as possible into the heating season, then turn on the underfloor. Then, cut back a bit on the wood burning until is gets (and stays) quite cold outside--logic being the inherent waste (and wait) of making big changes in temp of the slab.

I'm sure it's not impossible, but unless you could come up with some way to automatically vary the manifold temp based on the current output of the wood stove-but ONLY if it's not too cold outside AND not too cold in other spaces inside...you see it's getting very complicated...a big part of your indoor "reset" will have a lot to do with how much wood and draft you give to the stove.

>There is a wide range of adjustment indicated for the heating curve slope and offsets...but I'm not sure if this is determined automatically based on the outdoor and indoor resets.

I SERIOUSLY doubt the controller is designed to deal with your circumstance. I believe you would have NIGHTMARISH control problems if you try to influence the entire underfloor circuit with indoor reset. Unless the wood stove heats the entire home quite evenly (highly doubtful) you'd never be able to find an appropriate place for a single indoor reset. Again, I believe those Danfoss FHV-A room temp controllers hold the key here.

Mike T., Swampeast MO

Attachment finally loaded...

Still looks to me like FHV-A's on each tube circuit in areas "open" to the stove are most appropriate.

Mike T., Swampeast MO

Design flash if...

...if stove is located inside a corner of nearly any height and...

if tubing is not installed and...

if you lay a/an underfloor tube circuit(s) in the area most affected by the output of the stove [I'm presuming you've designed so that your circuits are similar in length] and...

if this works:

Install SOAPSTONE lining (with a radiant barrier behind the stone) in the corner behind the stove. Project height of lining about 15 degrees above stove top at nearest proximity.

Use a Danfoss FHV-R (floor temp controller(s)) IN the SOAPSTONE controlling the closest circuit(s).

STILL use FHV-A (room temp controllers) in any loop in any area still open to the stove.

I could write about why the properties of SOAPSTONE suit this application but you would be bored and I'd be wasting time.

This will actually compensate for the output of the stove whether used or unused (presuming you're using constant circulation and reset).

hydronicsmike

What you need, is a ....

...tekmar 363 Universal Reset Control with an 063 RTU and 3 remote Air Sensors 076/077. You are absolutely right. You need Outdoor Reset with Indoor Feedback in this system. You may want to consider using Slab Sensors as well, which could be the 072 or 073 Sensors. Visit www.tekmarcontrols.com.

Send me an email if you have further questions.

I hope this helps. Regards,

Mike

bruce pirger

Woohoo! I'm learning...that is the EXACT controller and set up I determined over the weekend...with the slab sensor to maintain a minimum temp.

Thanks guys!

Dan, just received your books. I like your style.

corey

Different approach

Very interesting (and common) problem. Talk about a moving target! Most folks just suffer with the inherent temperature swings woodstoves provide. It's part of their 'charm', right? If you're cold (or hot), just move your chair...

Assuming your house is not yet built...
Infloor radiant is great by itself, but if you were to use radiant panels or baseboard, you could use TRVs to make each panel (or run) essentially self-adapting to the dynamics of your wood heat source.
I have seen this work great as a retrofit at a ski house.
For new construction, this approach could save a lot of money and complexity. TRVs are much cheaper to implement than micro-zones or challenging control schemes.
If the woodstove affects a very open floor plan, it could be otherwise very difficult to achieve any reasonable temperature balance at the far corners as the output of the woodstove varies.

Secondary benefit:
If the woodstove is located on an inside wall or towards the center of your interior space, having the hydronic heat source emit from the outside walls may actually feel more 'even' to the occupants when the stove is running than infloor would.
Just a thought. Best of luck with your project.

Mike T., Swampeast MO

FHV essentially is a TRV

intended for radiant applications. It's position in a loop is irrelevant as it is a simple two-way device--what does matter is the physical location of the temperature sensor (actuator).

One modulates the valve based on air temperature, the other based on slab temperature.