Temperature Recovery Experiment

Mike T., Swampeast MO

For those who believe reset + low temperatures + hydronics = slow recovery, think again...

75 sq.ft. EDR radiator deeply set back--it and supply pipe stone cold. Good sized (14' x 16' room). TRV increased from minimum to the little red diamond.

In two minutes, the radiator was warm. In five minutes almost fully heated.

Image shows the air temp in the room on the left and Vitodens operation on the right. (Actual logged air temp at the beginning was 59.5°)

Red = supply; blue = return; grey = flue; dashed red = MY supply target; green = outside. NOTE: outside temp solar influenced. Separate thermometer very near temp sensor for boiler measured about 41° at beginning of the period, rising to about 45°.

Note that measured supply temperature was just a touch over 110° max. Air temp rise as much as 1.1° in 5 minutes was measured, with about 0.8° typical during the major part of the rise. Note that this is only a two-hour period. To me the room felt overly warm at the end of the period, but then again, I wear a sweater and am often doing both physical and mental work so enjoy temp around 68°.

Note that the burner even shut down during the time that the temp was still rising! (Outside temp hit the current modulation cut-off threshhold.) The mains are the buffer ;)

Will repeat in significantly colder weather, but I honestly don't except much difference.

Mike T., Swampeast MO

Please Notice

The relative rise in measured supply temperature compared to my target supply temp. (Again, the Vitodens will report a "boiler temp" VERY close to MY target.)

While outside temp is solar influenced, it didn't change much in the period. I've GOT to do something about that solar influence!!!

That radiator was pumping out lots of convective heat. I truly believe that there is a direct correlation between the differences in those two temperatures and the amount of heat being delivered to the space via radiation!!!

Plumbob

> For those who believe reset + low temperatures +

> hydronics = slow recovery, think again...


What this tells me is that the Viessman must have a "boost" function, probably using indoor temperature feedback. Notice that the supply temperature goes up to 110 (not a "low temperature" as you said, but rather high for the warm weather) and then drops sharply to 90 when the indoors gets close to 70. That's a very nice feature, but it doesn't disprove that reset + hydronic = slow recovery. It just means boost = fast recovery.

jp_2

target temp?

nice experiment!

would be intersting to show radiator temps on graph, that will correlate with radiation.

please explain "target temp"

lets see this experiement again when the temps are down in the teens. outdoor temp of 50F may not be a realistic example of set back.
I hardly consider firing up the woodstove at that temp. Now, late last night when I came home and the cabin temp was 15F and I wanted 60F, theres a set back challenge!

are those separate thermometers calibrated?
jim

Mike T., Swampeast MO

Those temps in the 60s are the room air temp--not outdoors.

Outdoor temp as measured on the North side in the shade was from 41° - 45°. Sorry those numbers are so small. Even the solar influenced (South) outside temp shows around 50°.

Curve hits 141° supply at 8° outside with a 0.8 ratio; rather low for iron rads and rather high for radiant floors.

Plumbob

Sorry, I misunderstood. I have now edited my previous post.

Mike T., Swampeast MO

Thanks. Will definitely do at lower temps. Am hoping for another "perfect" period with cloudy weather and outside temp hanging right around design. Have had a few of those in past years and always do LOTS of experimentation. At least this time I have a bunch more sensors.

Again, those outside temps are screwed up because it's a solar powered sensor that has to get some sun. Wasn't too bad with high sun and shade from leaves in the summer, but with low sun and no leaves, I'm getting some absurd solar influence. I've just ordered another remote-reading sensor so I can get the TRUE outside temp as well as the solar-influenced. Unfortunately, that fills my system and I can't add any more sensors without removing others measuring air temp in various parts of the house.

Outside temp (as sensed by the boiler) from 41° - 45° with the rise taking place mainly in the last 30 minutes or so.

"Target Temp" is based on a straight-line "curve" that produces 141° supply @ 8° outside with a 0.8 ratio.

Mike T., Swampeast MO

No problem. That statement containing "for those who believe" is not a slur in any way. It's a VERY common notion!

Considering my last similar experiment where I was watching the gas meter and raising even more iron in temp resulted in a rather small increase in burner output (nowhere near the max output) I have a feeling that this sort of response will continue right down to outside design temp!

jp_2

got it!

Mike T., Swampeast MO

The ONLY sensor attached into this boiler is for outdoor temperature. It has ZERO way of knowing actual indoor temp (even though it gives indoor temp adjustment dials).

Yea, there's a boost, but it is NOT a boost in supply temperature! As the house looses more heat, it adds more but without increasing the supply temperature above the target! Seriously!

The drop in supply temp was when outside temp rose to the point that the house was no longer loosing more than 22 mbh or so. Once that happens the burner cannot fire continually. Any time the house is loosing more, that burner fires and never stops!

Mike T., Swampeast MO

I'll try to repeat this evening

When outside temp is such that continual fire is required. You'll see that it does NOT boost supply temp...

Temp in that room is still 65.8°. I turned the TRV back down to minimum after I saw a leveling of the room temp.

jp_2

no indoor sensing?

forgive my ignorance on reset controllers. but what happens on a real cold windy day compared to a cold calm day?
without sensing indoor temps, won't indoor temps vary calm to real windy days- infiltration, higher window losses, bunches of kids coming and going?

is it similar to:
I've noticed with constant floor circulation, the system almost seems to control itself once you find that magic supply temp. all last winter I hardly adjust supply water by more that 10F. and the room seemed to have nearly constant temp.

thanks
jim

Plumbob

> Yea, there's a boost,

> but it is NOT a boost in supply temperature! As

> the house looses more heat, it adds more but

> without increasing the supply temperature above

> the target! Seriously!


Well, I understand the Viessmann does that by varying the flow rate. I am not sure how that can work well because the effect of the flow rate on radiation's BTU output is very weak. But assuming that's how it works, it is just like a boost! The supply temperature remains the same, but the pump speed is boosted based on the return temperature. The supply temperature will then need to be higher than needed to hold a steady indoor temperature with high flow, but when the flow rate is very slow (in 'hold temperature' mode rather than recovery mode), the return temp will be low, and that's the important thing.

Anyway, the main feature here (NOT a part of 'standard' reset) is variable flow rate pumping and the resulting load-dependent boost.

Som time ago I looked for pumps that can be controlled based on setting/varying a flow rate or a pressure drop across the pump. As far as I could determine at the time, it is not easy or cheap to do this.

Mike T., Swampeast MO

I've noticed with constant floor circulation, the system almost seems to control itself once you find that magic supply temp. all last winter I hardly adjust supply water by more that 10F. and the room seemed to have nearly constant temp.

The Vitodens LEARNS that "magic" temperature!!!!!!!!

The thermostatic radiator valves (TRVs) are sensing indoor temp and open/close themselves automatically to achieve the desired setpoint. But, they can ONLY "communicate" back to the boiler by changing the temperature in the supply and return and the total system flow rate.

My reset curve is set to ALLOW for cold, windy days; doors left open for a while, etc. The TRVs just throttle down the flow when the actual temp is higher than required.

This is an old 2.5 floor house with the radiation sized by the "Mill's Rule" with a bit extra thrown into sleeping rooms (all on 2nd floor) to allow "airing". Insulation/weatherization has only served to make the radiation in the sleeping rooms even more oversized. My reset curve is set to give about 10 degrees of "headroom" to the least over-radiated space--the entry hall and twin parlors where one radiator (due to freezing) was replaced with one half the original size. This is also the curve that I used for my radiant bath floors--single-temp constantly circulating system.

The Vitodens maintains MY curve even if part of it can only be measured in the boiler itself.

Are you with me before I continue?

jp_2

trv's

so each rad has a little bit of self control with the trv?

is there no zone valves then? if so, what controls them?

is there only one reset curve?

what control controls the radiant floor temp? how can that be adjusted?

what if your folks are visiting and being old they complain the house is too cold? my dad will jack up the tstat to 75F, just like my grandfather did. how does it/you handle this?

so far so good!
sorry for all the question
thanks
jim

Mike T., Swampeast MO

The speed of the pump is controlled by outside temperature alone. Pump is at the factory settings and is maybe up to 45% rotational speed. Outside temp changed actually rose, so pump speed decreased.

But, I did open a TRV which reduced delta-p which in turn increased the flow at the same pump speed.

No, this is not "standard" reset by any means! It is the ability of the boiler to almost exactly match the load at any given time regardless of outdoor/indoor conditions.

Ron Schroeder_3

> I've GOT to do something about that solar

> influence!!!



How about shading the house with Solar Photovoltaics. ;-)

Ron

Mike T., Swampeast MO

so each rad has a little bit of self control with the trv?

Each rad has COMPLETE and independent self-control via the TRV.

is there no zone valves then? if so, what controls them?

When every radiator has a TRV "zoning" ceases to have
meaning. Each TRV forms its own "zone" but they combine to form a whole. There is no "on" or "off", only modulation.

what control controls the radiant floor temp? how can that be adjusted?

In my case it's controlled by the reset curve and the mean radiant temperature of the space. No adjustment is necessary. The radiant spaces run 5 degrees above the average temp of the spaces surrounding. Remember--this is engineered for baths--you ALWAYS feel a surrounding warmth when you walk into one of my baths...



is there only one reset curve?

Yes, and it is set to provide adequate headroom for weather and the desires of the occupants.

what if your folks are visiting and being old they complain the house is too cold? my dad will jack up the tstat to 75F, just like my grandfather did. how does it/you handle this?

If grandpa only wants one room really warm, the response and rise is quite rapid (see experiment). If he insists that the entire house be made warmer it's going to depend somewhat on the outside temp. The closer you get to outside design temp and the more closely your Vitodens meets this loss, the less reserve you will have to increase the ENTIRE home. Remember that any space set back in temperature gives you reserve...

hr

jp

when I lived and worked in Montana, a plumber I worked with lived in a tepee.

Talk about some deep setbacks.

Camp fire in the center, smoke flaps the whole deal. Lasted two winters

Think he keeps his home about 78° these days Ahhh to be young again...

hot rod

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Mike T., Swampeast MO

Down to 61.5°

Another day