Eatherton-Real Time Load

Boilerpro_3

Figuring heat loads is so complex a thing to try to break down. Another variable I've wondered about is how much heat from the ground traveling up a masonry sturcture effects the load. Soooo many variables!

Boilerpro

gasfolk

How to use the Eatherton-real-time load?

Does anyone know how Mark Eatherton uses real-time loads?

When he sizes from a real time load, does he add any safety margin? Does he worry about unusually cold weather? Besides sizing, does he get other useful info from the real-time load?

I have read his excellent articles (and will reread them).

Thanks,

gf

[Deleted User]

Follow your gut instincts...

and the guidelines of the articles. Make certain you compensate for internal electrical useage, most of which converts to some form of thermal energy. Make sure you're crediting any external electrical usage to avoid over crediting. Look at the weather patterns, and adjust accordingly.

All in all, I don't think you'd need to compensate upward by more than 15%, and that's just a gut figure too.

Bottom line, by properly sizing the physical plant to the real time load requirements, you are cutting out the fat, that causes excessive short cycling. The study I'm currently doing has the boiler running for 7 minutes, then resting for about 10, then running for 7 and so on and so forth. The on off cycle portion of the graph looks like a solid black line because the short cycling is so close, and this was at design conditions outdoors.

My ModCon turns on when it gets cold outside, and stays on until it warms up, and I reduced my gas consumption by 60% over the old GFA furnasty that used to reside here....

Granted, there are some "system efficiency" changes, but a savings is still a savings, regardless of how you get there. I went from 150K btuH furnace down to a 50K Munchkin T-50. And we are quite comfortable...


Thanks for reading.

ME

gasfolk

Do you need a weatherman?

Hi Mark,

Do you make any adjustment for part-load efficiency? For example, if the real-time load (at design temp) is tiny for the existing boiler (say, less than 33%) does your estimate change? Have you done follow-up real-time loads on your (smaller) replacement boilers, and if so, does better part-load efficiency of a smaller boiler yield an even smaller real-time load estimate?

Would it create havoc if the local weatherperson announced a particularly good night (low temp, some wind) for measuring real-time load? Might too many homeowners learn of over-sizing too quickly?

Thanks again; we really appreciate your experience and generosity.

gf

[Deleted User]

Tough to do...

I just completed the monitoring of a 1,000,000 btuH boiler that I know is oversized, but the only data I have access to is the run time of the gas valve per given degree day of exposure, the "clocked" input to the appliance on an real time hourly basis, and the combustion efficiency of the appliance. It ain't perfect by any means, but it gets you a lot closer than guessing...

The problem with attempting to do an after the fact replacement audit is that we used mod con boilers, and we'd have to set a gas meter with pulsed output to monitor the boiler. The proof is in the pudding. 30 to 60% reductions in fuel consumption. Also, substantially increased comfort levels in those apartments surround the boiler room...

HTH

ME

Boilerpro_3

Been sizing that way for about 10 years

but you have to be careful..part load efficiencies, compensate for accelerating air leakage at lower temps. I always like to take an overnight load reading at design temp, but then you you have to compensate due to thermal mass. A massive structure delays the full impact of low temps for a couple days.

boilerpro

[Deleted User]

Which is why....

I like to get at least a weeks worth of data befoe I pull the trigger. I've not seen the lagging phenomenom that you are addressing. Maybe the mass acts as a thermal buffer??

I did see the actual thermal lagging in an R value test done on my own home. There's a real time delay in the transfer of energy in and out of the house caused by the insulation. I'll look around and see if I can find them data from that experiment.

ME

Boilerpro_3

Mark

My info comes from early studies done with concrete floors used as absorbers for solar heat. Its been awhile, but I believe it took about 24 hours for heat to travel through 3 to 4 inches of concrete. This certainly would cause thermal lagging.
The second source is from experience. My mother's home in Chicago could go for 3 days of 90F daytime high weather before we ever needed to turn on the AC. Anyone else with a masonry structure has also related this experience
Even insulation has mass, so thermal lagging will occur.
I am really glad to see this method of determining load becoming more widely known. I use it as a tool when trying to convince someone that the boiler being proposed by a competitor is the wrong size. I just ask them for a few months worth of fuel bills, run the calcs, and show them through common sense the proper sized boiler.

Keep it up, common sense may someday rule!

Boilerpro

Maine Doug_28

Thermal lag

Lots of thermal lag in my building. The radiant slab is 18 yards of concrete. The walls are 3 course of brick, a foot thick. The foundation is mortared granite, a foot thick at the top to about 2 foot thick at the bottom. The walls and ceilings and floors of the downstairs vault and main floor vault are 18 inches thick. The main floor vault is also steel lined with 2 doors, one is 3 inches and the main door is about 5 inches thick. The main floor is wood over concrete, the underside of which is the downstairs ceiling which is of course exposed to the radiant floor.
Run out of oil and it can take 3 days to get chilly.
I wish the controls had a weather forecast attachment since the outdoor reset does not know that as soon as the sun comes up the outdoor temp will go up again. So from 3am to 6am, it still thinks it has to be injecting when it could just sit for awhile. Unless the forecast is cloudy and snow and more cold.
Takes a long time to make a temp change in the building but is quite stable once you get there. Too bad we don't have a ModCon.

Boilerpro_3

Doug

I would try to add indoor feedback to that system....Outdoor reset has limitations and high mass buildings and homes with high passive solar gains (especially with high mass radiant)really become problematic with outdoor reset. You're may even be better which just a thermostat on the wall.

Boilerpro

gasfolk

Any Practical Issues?

Hi Boilerpro, Mark, and Maine Doug, always glad for your thoughtful comments.

Boilerpro, can you elaborate on your experience in sizing by real-time load? What steps do you take? Have you had any failures, call backs, unexpected consequences? Any advice to someone trying this for the first time?

In case anyone missed the links, the Eatherton articles are

Eatherton-Real Time Loads, Part 1

Eatherton-Real Time Loads, Part 2

Eatherton-Real Time Loads, Part 3

Eatherton-Real Time Loads, Part 4

Thanks,

gf

gasfolk

Any Practical Issues?

Hi Boilerpro, Mark, and Maine Doug, always glad to read your thoughtful comments.

Boilerpro, can you elaborate on your experience? When sizing by real-time load, what steps do you take? Have you had any failures, call backs, unexpected consequences? Any advice to someone trying this for the first time? Cautions for the homeowner thinking about downsizing? Thanks.

In case anyone missed the links, the Eatherton articles are

Eatherton-Real Time Loads, Part 1

Eatherton-Real Time Loads, Part 2

Eatherton-Real Time Loads, Part 3

Eatherton-Real Time Loads, Part 4

Thanks,

gf

gasfolk

Any Practical Issues?

Hi Boilerpro, Mark, and Maine Doug, always glad to read your thoughtful comments.

Boilerpro, can you elaborate on your experience? When sizing by real-time load, what steps do you take? Have you had any failures, call backs, unexpected consequences? Any advice to someone trying this for the first time? Cautions for the homeowner looking for a rough estimate?

Anyone else had the courage to try this? (In case anyone missed them, links to the Eatherton articles follow.)

Eatherton-Real Time Loads, Part 1

Eatherton-Real Time Loads, Part 2

Eatherton-Real Time Loads, Part 3

Eatherton-Real Time Loads, Part 4

Thanks,

gf

Brad White_41

Great set of Mark's articles.

Just one minor issue, the second link takes me back to the thread page -leaving out the all-important page 2!

FYI

Thanks-


Brad

gasfolk

Thanks Brad...

Link corrected above. (BTW, I'm still chuckling about your chimney and white smoke comment.)

Any thoughts on this topic? If not quite at outdoor design temp, could one simply crank the stat, wait for steady indoor temp, then clock? Say, if you need 10F and you've got a week of steady 25F, could you bring indoor to a steady 85F then clock the boiler?

Best regards,

gf

Maine Doug_28

Thanks Boilerpro

It does seem like a case for a simpler solution. I may just get another VisionPro to use multiple sensors for averaging. Maybe I will borrow the sun room VPro stat to try it in the main area first.
A couple of shots of the space at the start and after some improvements. Uninsulated steam pipes and all.

[Deleted User]

I wouldn't...

At that point, you will be raising the mass temeprature a lot more than it would normally be raised. I doubt the system would actually be capable of doing that. Instead, just take what you saw during the 25 degree week, and project/extrapolate it to the design conditions you anticipate seeing. Heat loss is a linear function.

And remember, the IECC requires contractors to use the 97-1/2 percentile rule. In other words, the temperature used for calculating the heating system sizing is based on that temperature in which the temperature will be above it for 97-1/2 percent of the heating season. For Denver Colorado, that temperture is 0 degrees F, not 15 degrees below as many contractors use. That ends up significantly oversizing the equipment, which causes short cycle issues for the balance of the heating season.

ME

Boilerpro_3

Ahhh, be careful,

Heatloss from a structure is NON LINEAR....air leakage rates increase as its gets colder. The ACH rate at 20F outdoors may be .6 ACH, but at -5F it will be higher like 1.2ACH. Heat load due to air leakage multiples as it gets colder..bigger temperature difference AND bigger leakage rate. This is why it can be pretty hard to extrapolate. Like your first response said, at some point you have to use instinct.

Boilerpro

Brad White_9

Boilerpro-

> Heatloss from a structure is NON LINEAR....air

> leakage rates increase as its gets colder. The

> ACH rate at 20F outdoors may be .6 ACH, but at

> -5F it will be higher like 1.2ACH. Heat load

> due to air leakage multiples as it gets

> colder..bigger temperature difference AND bigger

> leakage rate. This is why it can be pretty hard

> to extrapolate. Like your first response said,

> at some point you have to use instinct.

> Boilerpro

Brad White_9

Boilerpro- Curious about that ACH rate part

Boilerpro-
I take into account such things as temperature in say a high rise where stack effect can be a form of entertainment sometimes. But in a house of one or two stories? The motive forces of wind are about the same (outside density being heavier than inside density, granted). But absent an open chimney and the adiabatic aspects, where did you get the information you suggest that ACH doubles with temperature alone? (If I am reading that right?) Not a challenge, just curious. This is the first time I have heard that suggestion outside of taller buildings at least.

Please elaborate.

Thanks!

Brad

Boilerpro_3

Sizing method

I have rarely done the full real time measurement that Mark has, however, I nearly always use the next best data resource....historic usage reflected on gas bills. I also look closely at the efficiency of the equipment. When equiment is so oversized, standby losses can be very large, so firing efficiency does not reflect the actual efficiency. Also this real efficiency varies with load. With a big old monster with no stack damper and an atmospheric burner, I assume an efficiency about 20 to 30% less than firing efficiency. A more compact modern unit running in a converted gravity system , but twice the size needed is probably closer to 60 to 65% efficient. Again, some instinct and knowledge go a long ways.
After determining (guesstimating?) the efficiency during the months usage being reviewed and doing the muliplication to get actual btu's output, I extrapolate like Mark does. However, with the non linear nature of air leakage, you have to give yourself some extra btu's. For a typical, well maintained older frame structrue, I add about 15%. For a loose structure higher, and with tighter high mass structures, maybe none needs to be added due to the thermal flywheel effect of the mass.
Somewhere in the files of posts here, I gave a detailed explanation of my methods, but they parrallel Mark's with a few additions.
I used only this sizing method on my first small commercial project..about a 10,000 sq ft masonry and concrete church...and it overestimated the load by about 10%.... a heck of alot closer than other mehtods. It has served me very well for the past ten years. I usually use both a conventional load analysis and this method as a double check. If I see a big difference, I lean strongly to the usage based calculation.

Boilerpro

Boilerpro_3

Digging...

back into my old IIT textbook that I still use regularly.
Design Inltration Rate (ACH)for winter: Heating: Wind speed = 15 mph
ASHRAE Heating and Cooling Load Calculation Manual, 1979,

Medium tight construction goes from .9ACH at 20F to 1.2ACH at -10F.

Not double, but very significant. I can also feel it in my old home. In 20F weather, very little cold air comes up the old holes in the floors from the old radiator piping, in really cold weather, quite the draft. Just think, A 20 foot chimney has a pretty good draft....that's about the same height as the interior of a home.

Boilerpro

Boilerpro

Unknown

I'm still not getting article 2. can't find it on their site either.. CONSPIRACY???

gasfolk

Eatherton-Real Time Loads, Part 2

Hi Rob,

Have attached part 2 below. If this doesn't work, please email me and I will forward a copy.

gf

Unknown

well, it downloads as "attachment.cfm", but if I renamed it as a .doc it works just fine. Thank you very much!

[Deleted User]

Tell me more please..

In my 33 years of doing this, I've NEVER come across this phenomenon, and I trained under some of the best in I=B=R, a LONG time ago...

I'd have thought that SOME ONE would have pointed that out, and made darned sure that it was taken into consideration at "design" conditions.

Now wind induced infiltration is a whole nuther ball of wax, but compounded cold infiltration? Are they saying that the cold causes the structure to shrink, compounding infiltration around doors, windows and other seals?

Never hoid of it.

I will double check the data I've collected, which is a LOT and with a LOT of differing exposures and see if what you say holds true. I always just looked at it from the coldest weather potential seen and extrapolated it to design conditions.

As Ahnold siad, "Ahl be bach"...

Still learning, after all these years.

ME

[Deleted User]

A quick check of a recent audit proved...

the exact opposite.

At design conditon a 70 degree difference the building used 4,573 btu's per degree hour. (70 X 4,573 = 320,000 btuH)

At a 52 degree F difference, the building used 5,548 btus per degree hour, for an hourly total of 288,444.

At a 35 degree difference in OSA versus 70 degree F. the building used 9,473 btu's per degree hour. (35 x 9473 = 331,555 btuH)


MY INTERPRETATION IS THAT WITH THE EQUIPMENT BEING SO GROSSLY OVERSIZED, IT'S EFFICIENCY SUCKS AT ANY CONDITION OTHER THAN DESIGN CONDITION, AT WHICH POINT IT IS STILL 33% LARGER THAN IT NEEDS TO BE. Sorry for all the yelling:-)

In any case, the energy consumed per degree difference went down, not up.

So much for theoretical information. Real time data on a minute per minute and hour by hour basis trumps all...Ain't no disinformation hiding in these numbers.

ME

Brad White_9

I am glad we share the same inner skeptic, Mark

Nothing against Boilerpro, I am still open to learning, but in 28 years on the design side, I have never taken into account an increase in infiltration except in high rise construction.

Granted that breeze you can tolerate when it is 50F outside feels a whole LOT different when it is -5F outside!

I can see how at first blush your findings may go to increased efficiency at lower ODT's but the loss slope is still the loss slope. I will dig in a little deeper at my end.

Still, I will check my ASHRAE archive. In the years 1977, '81, '85 there were different infiltration methods uses, some simple multipliers of volume depending on how many exposures. Proves only one thing: Absent objective measurement, it is only a guess. Give me measurement.


Best,

Brad

[Deleted User]

It's like my pappy used to say...

If'n ya don't learn something new EVERY day, you were either A, gone fishing, or B, weren't paying attention. And if you were gone fishing, and you didn't learn something new, you weren't paying attention.

I try and keep an open mind to anyone who is willing to post infomation on this forum, right wrong or misguided. I find it intersting however, that we put so much faith into the theoretical side of things, and it ends up being so grossly over sized. Big is NOT better when it comes to heating plant. I hold no ill will towards BP either, and I appreciate his input and experience in the mix. Not many people have the moxy nor cajones to do things differently out of the box. He obviously does.

Off to educate 50 building inspectors today about hydronic radiant heating at the Colorado ICC Education conflagration.

Have a good day.

ME

Brad White_9

Colorado ICC Day

Excellent gig, ME. Getting the AHJ's on board en-masse cannot hurt the cause. No one better than you to lead the charge.

Grade hard, grade fair. And for God's sake, I hope they are "paying attention"

BEW

Boilerpro_3

Hey Mark,

My only explanation for the changes in published infiltration rates in colder weather is the stack effect through the home. Back to the chimney analogy. The higher the temp difference between the bottom of the chimney and the top, the stronger the draft. If you look at a home, it is nothing more than a chimney with a very broad cross section. In colder weather the draft created at the top by air leakage increases the suction at the lower portions of the house, so air leakage increases. If you have increased air leakage rates combined with a higher temperature differential, you should see a non linear curve.
Your analysis of your data about the efficiency of a boiler dropping off wildly at low loads fits with both the old IBR efficiency chart I have for atmospheric equipment and the changes in fuel usage patterns with the stage fired heating plants I've installed. The percentage reductions in fuel use are much higher in the shoulder seasons than in the coldest months. I expect the same patterns when going from on/off boilers to Modulating. I have 3 Prestiges in as of last fall and I am keeping tabs on these, but the condensing aspect of these may throw off the numbers. I may be installing some modulating Raypak atmospherics and would like to see how they do. The Raypak lit that I have read only show about a 2% drop in firing efficiency from low (20%?) to high fire, so the numbers should work fairly well.
Another bit of interest. My helper has noticed increased drafts at those same radiator holes whenever the damper closes on his newer atmospheric vented draft hood boiler. These drafts apparently did not exist with the old boiler with a continuously open draft hood vent connection. I suspect the chimney draft was counteracting the draft through the home, reducing the air leakage rate though the living spaces. Another HMMMMM?

Living and learning,

Boilerpro

Brad White_9

Stack Effect

I can see the merit when looked at in detail here, BP.

While it is true that a house or any space with elevation (it has to have volume or else is it really a space?) is defacto a chimney. The gradient in a house is so small. Yes the stack effect does increase with temperature.

Key point is, what comes in can only be equal to what goes out. If the home is sealed naturally the better. That was a point I acknowledged in my first posting on this sub-thread, of increased infiltration at lower ODT's.

It is not the stack effect and drafts themselves that increase, it is the "potential" to have them increase. No house being airtight, whatever does leak in will increase accordingly, I fully concede. May just not be that much.

Now, let's take a house that is two storeys, 10 feet on the first floor and 9 feet on the second floor.

Say it is zero degrees outside and 72 inside.
The stack effect potential in inches WG is 0.0428.

Say it is 40 degrees outside and 72 inside.
The stack effect potential in inches WG is 0.0175.

(Basically every degree difference begets an Delta-P gradient of 0.005 inche WG in a building of this size.)

Say it is 72 degrees outside and 72 inside (Cancel out the temperature effects and just deal with elevation):
The stack effect potential in inches WG is practically zero (not enough to measure and not heat loss anyway!)


Just for fun: Here is the pressure gradient over the 1250 feet that is the Empire State Building when it is zero out and 72 degrees inside: 2.1843 inches WG.

Living and Learning....

Brad

Boilerpro_3

HMMMMM

that .04 sounds like the typical high range of recommended draft in most chimney's. What we need here now is a "typical" cross section of the total of all leaks in a home. From what I remember, it is alot larger than most would think... the size of a 6 inch flue, for example. I'm not sure if you have that data? We may be talking more air flow than one would first think.

Boilerpro

Brad White_9

Are you sure the decimal point is in the right place?

I had thought that a chimney about 30 feet high would draw about 0.10 inches (top of my head) at stack temperatures in the 350 range. I will have to check that out....

Boilerpro_3

That .04 is recommended draft....

not what is typical. I had one a year ago pulling .4 inches at about 45 feet...it used to be for coal.

Boilerpro

Brad White_9

For a 33 foot chimney

with 350 degree flue gasses, I get 0.2372 inches (more or less! ) on a zero degree day.

Maybe the 0.04 is a minimum? Or a cold value but on a warmer day? I do not get a 0.04 value until it is about 30 degrees outside with a 72 indoor temperature, so I think that is a median winter value and a minimum at light-off.

Ron Schroeder

Brad

.04 is recogmended adjusted WC in flue pipe before the draft regulator, not ion the chimney itself.

Brad White_41

That makes a lot more sense, Bruce

Thanks.

One of my missing links of knowledge is on the burner tech side. My next task...

Ron Schroeder

I figured that the light would come on

because I know your at homew;-)

gasfolk

Boilerpro...

After much interesting (and educational) reading of Boilerpro's old posts...

Boilerpro Real-Time Sizing Method

It was surprising to read how often this issue of sizing by fuel usage has been discussed on The Wall over the years. You guys are really patient to be willing to discuss it again.

Thanks,

gf

gasfolk

Boilerpro...

After much interesting (and educational) reading of Boilerpro's old posts...

Boilerpro Real-Time Sizing Method

It was surprising to read how often this issue of sizing by fuel usage has been discussed on The Wall over the years. You guys are really patient to be willing to discuss it again.

Thanks,

gf