Condensation, Modulation and Starvation

Brad White_9 · January 2006

> Three modes of fuel savings via a 
> condensing/modulating boiler?? 
> 
> 1) 
> Condensation savings: The lower the supply and 
> return temps, the greating the savings. 
> 
> 2) 
> Modulation savings: The more closely the boiler 
> output matches the load, the greater the 
> savings. 
> 
> 3) Starvation savings: The more 
> closely the supply reset curve matches the lowest 
> possible to just maintain desired indoor 
> conditions, the greater the savings. 
> 
> To my 
> amazement, the savings from 3) seem greater than 
> 1) and 2) combined! 
> 
> There is however a 
> "cost" for this savings. Unless both the boiler 
> and other (t-stats, TRVs, etc.) controls are 
> _I_both_/I_ changed, response to a call to 
> increase indoor temp--even in a single room--is, 
> at best, anemic. The emitter temperatures can be 
> so low and even (particularly in mild weather) 
> that _I_even with the same indoor temp_/I_ things 
> "feel" cooler. 
 
The emitter temperatures can be so low and even (particularly in mild weather) that even with the same indoor temp things "feel" cooler.

Mike T., Swampeast MO · January 2006

Three modes of fuel savings via a condensing/modulating boiler??

1) Condensation savings: The lower the supply and return temps, the greating the savings.

2) Modulation savings: The more closely the boiler output matches the load, the greater the savings.

3) Starvation savings: The more closely the supply reset curve matches the lowest possible to just maintain desired indoor conditions, the greater the savings.

To my amazement, the savings from 3) seem greater than 1) and 2) combined!

There is however a "cost" for this savings. Unless both the boiler and other (t-stats, TRVs, etc.) controls are both changed, response to a call to increase indoor temp--even in a single room--is, at best, anemic. The emitter temperatures can be so low and even (particularly in mild weather) that even with the same indoor temp things "feel" cooler.

Brad White_9 · January 2006

Your last sentence resonated with me

"The emitter temperatures can be so low and even (particularly in mild weather) that even with the same indoor temp things "feel" cooler."

This statement reflects experience I had when I had a Honeywell Centra controller (4-way mixing valve, weather responsive control). There was a pair of toggle settings which I never quite got the hang of, "W" and "WR", which were if I recall "straight weather-responsive" and "weather-responsive with room influence." (Or room responsive with weather influence was it?)

Anyway, in one setting the rooms overheated a bit and the other, with room influence tended to be too cool. Sort of a "cold 70" effect. So what seems to be needed is a positive radiant output, sort of a ski-jump at the bottom of the curve to assure the radiant effect is maintained.

Interesting stuff you are doing, Mike. Especially the "starvation mode" observation. My intuition says that the starvation mode begets better savings from factor 1 (more condensation) so long as it is supported by factor 2 (modulation at such low loads). I see them all working together in my mind's eye. Good brain food. Thanks!

Brad

Mike T., Swampeast MO · January 2006

My intuition says that the starvation mode begets better savings from factor 1 (more condensation) so long as it is supported by factor 2 (modulation at such low loads).

Most certainly interrelated, but [seemingly] more complicated. There really is an opportunity here for a new type of reset control. I hope both of my grandfathers will forgive me for this, but the Germans seem so blinded by their own sense of superiority that they fail to look beyond their borders for anything but conquest...

Unfortunately a US forced air furnace maker [seems] to be the closest to exploiting this control opportunity. It's out there for anyone to use and I'm more and more convinced each day that it will work nearly as well with more typically "American" systems as opposed to just TRVs.

Brad White_9 · January 2006

A German engineer once told me

that their ideal means of heating a house was to send the water out from the boiler, "as cool as would do the job and take it back as close to room temperature as possible".
This is the product of your recent experiment posting? Sitting back to watch this. Really interesting.

Mike T., Swampeast MO · January 2006

That's exactly what I've been experimenting with since the ending "shoulder" of the 2005 heating season.

The problem is that "as cool as would do the job" is subjective relative to how you define "job". What suits the climate, building construction, habitation style and personal preferences of Germany does not suit the climate, building construction, habitation style and personal preferences in the vast majority of the US. German-style economy can co-exist with American-style operation if the appropriate control scheme is employed.

Brad White_9 · January 2006

Cool

is indeed subjective as is the notion of comfort. Physiology is unique to each of us. A woman in her early 50's having "her own personal summer" will be at odds with a 20-something in a sleeveless. (Cat fight!

I am so bad....

So we rely on numbers, a comfort index with a range of temperature and humidity. No other way to define it. But I think we have both recognized that at low emitter temperatures there is a modest chill, you almost want to tap the accellerator to remove it. The beauty of radiant flux!

My German acquaintance did observe that if your design coldest temperature occurs at night (just before dawn historically), then you should also take into account that this is normally a set-back period (10-15 degrees below occupied setpoint) that a good engineer (he glared at me) should take that into account as a design basis. In other words assume a higher daytime design temperature.

Remember that during the early days after WWI, it was the Germans in the throws of hyper-inflation that created essentially the Crock-Pot, using little fuel to cook at low temperatures over time. How efficient can a country be? They are almost Swiss for crying out loud.

Mark Adams · January 2006

Hey, I tried this...

> Three modes of fuel savings via a

> condensing/modulating boiler??

>

> 1)

> Condensation savings: The lower the supply and

> return temps, the greating the savings.

>

> 2)

> Modulation savings: The more closely the boiler

> output matches the load, the greater the

> savings.

>

> 3) Starvation savings: The more

> closely the supply reset curve matches the lowest

> possible to just maintain desired indoor

> conditions, the greater the savings.

>

> To my

> amazement, the savings from 3) seem greater than

> 1) and 2) combined!

>

> There is however a

> "cost" for this savings. Unless both the boiler

> and other (t-stats, TRVs, etc.) controls are

> _I_both_/I_ changed, response to a call to

> increase indoor temp--even in a single room--is,

> at best, anemic. The emitter temperatures can be

> so low and even (particularly in mild weather)

> that _I_even with the same indoor temp_/I_ things

> "feel" cooler.

Mark Adams · January 2006

I've been experimenting..

with this exact concept in my new home. The system is a WM Ultra 80LP, 3/4 of the home on fin tube and 1/4 on underfloor radiant. It is primary/secondary with zone valves and the radiant is done with a Taco RMB-1 on ODR.

Playing with the system settings on the Ultra, I can get a very aggressive reset curve that causes the system to run 24/7. It follows the outdoor temps nicely and the house is warm. My wife and duaghter tell me it's a bit cooler than they like, or were used to when I was letting the Ultra control per its built in defualts. Mind you, I have NOT told them I am experimenting here!

The real problem with this, for me, is that I like to sleep in a cool room; 61F is good. So, in the morinng, the setback is ended, a heat call goes out, but the water temp delivered to the fin tubes does not raise the temp to 68F for about 4 hours. With no setback, this would be excellent.

There are a few settings that really make this interesting. One is the reset curve stuff and the other is the temperature boost. The Ultra can, if desired, raise its boiler temp in 18F increments every X minutes (set 0-30 min) up to the point where it is at its max output temp which on mine is 174F. If set to zero, this increase never happens and recover from setback is more like waiting for solar gain to get things up to temp. Set for 30 minutes, you get 30 minutes at the temp called for by reset, another 30 min at the previous + 18F, another 30 min at previous + 18F, etc. So, eventually, the stats can be satisfied after setback.

Bottom Line? I've yet to find the sweet spot of quick setback, low temp with continuous flow when occupied and 2 women who don't ask why its cold when the stats read 68F. BTW, this is in WNY, just outside of Buffalo. The Ultra and the Taco almost provide the ideal in this regard, but some custom programming would really polish it off.

Happy New Year!

jerry scharf_3 · January 2006

check out my post on heating model

Mike,

I just posted the heating model for perusal. This is what I'm planning to implement next on my "lab." (Oh, I know the other occupants never signed up to live in a heating lab.)

The thing about this is it takes a large number of temp sensors. You need 2 per zone (one for room MRT and the other for return water temp), 1 per manifold and a number near the boiler.

As soon as the current dust settles, I will change from controlling the boiler set point to controlling the boiler modulation directly. The Munchkin "tekmar interface" allows this with the right configuration setting.

jerry

Mike T., Swampeast MO · January 2006

Jerry:

You have primary/secondary piping, right?

In my self-taught way I reverse "primary" and "secondary" considering "primary" to be the heat source (boiler) and "secondary" the emitters (load). Sorry for that...

Anyway, how many secondary (load) sources from the primary (boiler) loop?

Mike T., Swampeast MO · January 2006

Your German acquintance exactly described the control philosophy of the Vitodens yet I'll be damned if I can understand how structures with high mass exterior walls and exterior insulation can drop anywhere near 10-15 degrees overnight in their relatively mild and predictable climate.

Perhaps you only get the "feeling" of increased heat during the period of least heat loss?

Mike T., Swampeast MO · January 2006

emperical truth: "exact conformity as learned by observation and or experiment between judgments or propositions and externally existent things in their actual status and relations"

so...

"emperical truth" must then change when the "actual status and relations" are related to human desires and the whims of nature

No wonder I quit statistics class twice and accepted the "F" both times.

Mike T., Swampeast MO · January 2006

Thanks Mark! VERY helpful!

May I play "question box"?

Have you been able to measure any difference in fuel consumption with the changing settings?

Which rooms have radiant floors? What general heat transfer mechanism in the radiant areas?

Zones? Master, remaining bedrooms and general living space perhaps?

Presuming that you're using daily setback, which areas? Are the radiant areas set back as well?

Your personal preference is to "sleep cool". In the perfect world would you "wake warm"? Perhaps wake cool to a warm bathroom for SSS and then a return to a now warm bedroom for dressing?

What is the preference of the wife? The daughter?

Mark Adams · January 2006

> May I play "question box"?

>

> Have you been able

> to measure any difference in fuel consumption

> with the changing settings?

>

> Which rooms have

> radiant floors? What general heat transfer

> mechanism in the radiant areas?

>

> Zones?

> Master, remaining bedrooms and general living

> space perhaps?

>

> Presuming that you're using

> daily setback, which areas? Are the radiant

> areas set back as well?

>

> Your personal

> preference is to "sleep cool". In the perfect

> world would you "wake warm"? Perhaps wake cool

> to a warm bathroom for SSS and then a return to a

> now warm bedroom for dressing?

>

> What is the

> preference of the wife? The daughter?

Mark Adams · January 2006

The A's to the Q's

Have you been able to measure any difference in fuel consumption with the changing settings?
--No, not yet. This is the first year in the home. The propane gauge is not precise and I have to normalize this to HDD. More to follow.

Which rooms have radiant floors? What general heat transfer mechanism in the radiant areas?
--The radiant is in the 21x14 kitchen and the two bathrooms. It is Onyx staple up with radiant insul barrier.

Zones? Master, remaining bedrooms and general living space perhaps?
--Zones are Kit and baths together, great room-den-mud rm-foyer together and 3 bedrooms on a zone.

Presuming that you're using daily setback, which areas? Are the radiant areas set back as well?
--All zones get set back. The bedrooms and great room the most at 68-62 overnight and the kit/baths at 70-65F.

Your personal preference is to "sleep cool". In the perfect world would you "wake warm"? Perhaps wake cool to a warm bathroom for SSS and then a return to a now warm bedroom for dressing?
--Yes, exactly!

What is the preference of the wife? The daughter?
--They like it warm during all waking hours. What a surprise :-) If the system is on aggressive starvation, they will turn on the fireplace while watching TV in the late evening.

Need more???

Best regards,
Mark
Clarence, NY

jerry scharf_3 · January 2006

I always thought

the loop that has the exp tank is the primary and the others are secondary. As long as we can follow each other, it's fine.

The boiler is PS, there are 14 zones hanging off 3 manifolds. All zones are radiant: radiant floors, radiant ceilings, radiant walls, and suspended aluminum radiant panels.

I have the close Tees now, but may convery that to a LLH or similar if I see much difference between system return and boiler return. I have the webstone P/S fitting with the valve, power purging is wonderful.

The zone valves are proportional, so all the water in the system is moving almost all the time.

jerry

Mike T., Swampeast MO · January 2006

You're correct regarding the nomenclature, but for some reason I still say (and think) it the wrong way...

Is there a common feed line in the secondary (emission side) piping? If so, try placing a surface-mount sensor there. Insulate around the sensor well. Log the temp if possible. Compare to the supply temp reported by the boiler--change the supply curve and see if you find a predictable difference.

gasfolk · January 2006

Loss of Core Warming?

Could the "cold 70" sensation be from reduced MRT because reduced loss of BTUs in the supplies are not warming the core of your home and conducting to the interior surfaces?

With the savings you report, might slightly raised indoor thermostats warm your living space with a fraction of the BTUs saved by starvation, improving comfort while remaining economical?

gf

gasfolk · January 2006

Loss of Core Warming?

Could the "cold 70" sensation be from reduced Mean Radiant Temperature (MRT) because reduced loss of BTUs in the supplies are not warming the core of your home and conducting to the interior surfaces?

With the savings you report, might slightly raised indoor thermostats warm your living space with a fraction of the BTUs saved by starvation, improving comfort while remaining economical?

gf

jp_2 · January 2006

2=3

seems to me that your #2 and #3 are the same thing, just said in a different way? you have a controller and a control.

Ron Schroeder · January 2006

And if it can't modulate low enough (or with an unmodulatable boiler) there is #4), the often neglected wider boiler temperature differential and/or a buffer tank..

Mike T., Swampeast MO · January 2006

Yep! BUT, the buffer can get awfully large...

Ron Schroeder · January 2006

True, but the fuel savings from reducing short cycle losses can be huge (I have seen 50% savings without changing the boiler). And with an inside out indirect as the buffer tank, you only need one device.

Mike T., Swampeast MO · January 2006

Not quite the same.

Regardless of the control system you can modulate the boiler on any number of different curves to achieve nearly identical indoor conditions.

1 + 2 = 3

You just have to find the ideal settings to exactly produce 1 and 2. Indoor reset with proportional feedback to the boiler comes the closest if you can find the perfect location for the indoor sensor in an ideally balanced single-zone system.

Mike T., Swampeast MO · January 2006

I have no problem believing that!

Not all boilers/control systems offer that adjustable differential. There is a "differential" setting on the Vitodens by the way (completely undocumented in the standard US boiler literature), but I've received two wildly different explanations of what it does... It's easy to find in the boiler itself, but I wouldn't go changing the factory setting!!!

gasfolk · January 2006

Core Temp?

Mike,

What about your core temperature? Do you think the reduced loss of BTUs from the supply pipes into the core of your house is reducing MRT in your living space?

gf

Mike T., Swampeast MO · January 2006

"Core temp" is definitely way down as I'm also keeping the entire home cooler than last year. I won't lie and say it's particularly comfortable. Sweater in my office (sleeves always down), heavy comforter when I sleep here, IR lamp when drying off with the warmer-heated towel, sleeves down most of the time when doing physical work of renovation. Still give the master suite (including office) one blast of forced warm air on many mornings--shut it off when temp reads about 66°.

The reduced space temp alone however does not seem anywhere near enough to account for more than 50% reduction in degree day adjusted fuel consumption compared to the boiler curve in use this time last year.

Weather has been unusually warm and for the last 15 days measured supply temp has averaged only 73° or so with occasional, short "bursts" of boiler operation when the outside temp drops below 35° or so.

Outdoor temp has to drop to the 20s before I really feel that wonderful radiant "glow" of big standing iron--but even then the air is still quite cool...

Mike T., Swampeast MO · January 2006

Just a few more...

Do the zones seem to recover at a similar rate? Are the setback and recovery manual or automatic via "smart" thermostats?

Is the adjustable staged boost of the Ultra linked to an independent timer-based operation? Or more likely the result of a heat call, e.g. as long as a thermostat is calling the boost is initiated at the set rate until all calls are satisfied? If the latter (as I suspect) I certainly see the conundrum. Set the curve to produce a nearly continuous call for heat and the boost must be zero.

Mark Adams · January 2006

More Q&A

Do the zones seem to recover at a similar rate?

---NO. The radiant takes an hour or more extra.

Are the setback and recovery manual or automatic via "smart" thermostats?

---HW 8100 series. Smart, and I cannot turn the "smarts" off for some reason. The setup codes are not in the menu. Odd.

Is the adjustable staged boost of the Ultra linked to an independent timer-based operation? Or more likely the result of a heat call, e.g. as long as a thermostat is calling the boost is initiated at the set rate until all calls are satisfied? If the latter (as I suspect) I certainly see the conundrum. Set the curve to produce a nearly continuous call for heat and the boost must be zero.

---The latter as you've guessed. The Ultra can be told at what intervals you want the boost and it keeps boosting until the stat is satisfied. BUT, Once up to speed from the first setback of the day, the temp does not boost often assuming a 30 minute setting.

Mark

Condensation, Modulation and Starvation

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