Downward losses (heatboy)

heatboy

Wrightsoft and Wirsbo’s ADS heat loss software both raise the heat loss of any building as you lower the under slab insulation values. Because of this, I get, in my opinion, erroneous calculations leading to larger than actual heat looses and over-sized heating equipment. This is something I would love to see ASHRAE look at. HR? Am I off base on this? With slab projects, going from R-5 to R-2.5 raises the heat loss by 40%, according to the programs. This makes no sense to me considering once the area under the slab equalizes, (you can't stop it from doing so) your system becomes oversized. Doesn’t it? Help!

hb


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hr

I'll find out more

I have been searching the ASHRAE abstracts section lately. It seem there has been research and papers published on this topic. Dr. Kilkis at Watts Radiant has done a lot of research in this area. Mr. Lenman has modeled this, I understand also. Probably still find his take in the Progressive Mechanical archives.

As I understand talking to geothermal designers, the heat transfer to soils is a very complex thing to model and predict. So many variables, even the most powerful computers struggle to come up with an answer.

To my way of thinking doubling the R value will affect the amount of time for the temperature in the slab and in the ground to stabilize.

The July 2000 issue of the RPA (Under slab Insulation cover story) newsletter cites some of the studies on this topic. Beaver Plastics in Calgary modeled the loss and graphed it. ASHRAE Handbook 27.10 has detailed information and calculations on under slab insulation, I understand.
Run the calcs on Watts Radiant Works also. They update and apply the latest ASHRAE materials into that software often.

Paramount in my mind is the edge loss and perimeter banding. As for the middle of a slab 7 feet deep in a basement hmmmm. How's that for an answer.

I'll get the two other RPA research committee members on this question. Unless, of course, you would like to tackle that question for the research committe

hot rod

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Earthfire

groundloss

IGSHPA may be able to come up with some answers on that one .One of their test projects for the last year has been an earthcoupled ice control system for a bridge.With all the testing they do at Oklahoma State they may have some insights as to what is happening under the slabs.

heatboy

hr

Do you have Lenman's article? I lost my Prog Mech stuff when my computer died a while back. I would like to read it. Can you paste it here or e-mail me?

I'll look into the Watts Radiant software.

hb

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Mi39ke_2

reposts

Hi Jeffrey,

Since ProgMech is a non-commercial private list, it might be best to get the author's permission before reprinting. Yeah, most of the people who contribute in that forum are very forward-thinking and open, so maybe it wouldn't be a problem, but you never know...some personality clashes may come into play.

Contact me via email (or give me a call) if you have trouble accessing the archives through Yahoo. You should be able to search for what you are looking for from there.

Best,

Mi39ke

hr

focus your search,hb

to somewhere around 2/2/2000 maybe around 11:31 ish
hot rod

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heatboy

It sounds like.....

Tomas agrees with our assertions. I think (g). I realize soil types may have an effect on downward losses, but how much, I'm not sure anyone knows. In my areas of work, soil types run the gambit from clay to sandy to shale. Tough call on how much is really needed. Push the insulation envelope or cover my a** with larger equipment?

hb

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eleft_4

downward

hr,
we use to use coal dust to keep pipes from freezing in to shallow of a trench, after thawing them out. Something about keeping the pipes dry, it worked. Maybe it will work under radiant panels also.

Al

hr

40% oversize, oh my aching back

40% is a big number, considering the building loss, in the structure per say, hasn't changed. At least to my way of thinking. Why not oversize a tad with a modulating boiler. The boiler could simmer down after that questionable downward loss is handled and limp along at a lower firing rate. Seems the best of both worlds. Heck you can even get a virtually noise free,wall hung, German brand, in silver that should cover that range the calcs print out

You are correct, we need to re- examine that downward loss issue with various R values. That makes at least two experts that question the numbers. Not counting you and I of course :0

hot rod

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hr

Coal dust?

That is a new one on me. I guess you could always light it up if it didn't keep thre pipes from freezing. Just don't use pex in the trench

hot rod

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Gary Fereday

> That is a new one on me. I guess you could always

> light it up if it didn't keep thre pipes from

> freezing. Just don't use pex in the trench

>

>

> hot rod

>

> _A

> HREF="http://www.heatinghelp.com/getListed.cfm?id=

> 144&Step=30"_To Learn More About This Contractor,

> Click Here to Visit Their Ad in "Find A

> Contractor"_/A_

Gary Fereday

Coal dust?

Could it be Gilsonite! a fine powder used to insulate pipeing underground. Its a petroleum type product. Does not harm iron pipe, & will not deteriorate. is not fire proof (burnes easily). Sometimes used to overcoat asphault paving. Mined in eastern Utah, kind of like solid oil.

heatboy

Slab areas

hr,

When I said 40%, I meant just the slab areas have 40% higher loads according to the programs when comparing R-10 to R-2.5. You can imagine, with a 5,000 square slab that makes quite a difference in sizing. The loads with R-2.5 are actually higher than a standard Manual J load and that shouldn't be, in my mind anyway. When you placed the sensors under your slab, did you install different types of insulation? Can you post the pictures again? Thanks!

hb

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hr

two types of underslab insulation

and one area uninsulated. I went with 1" Foamboard, and 1/2" Insultarp. Mainly due to the similar R- value claims. I am interested in the response time differences, and how the ground below responds, and the length of time for the 12" deep sensors to equalize.
I also have a sensor located away from the slabs 12" deep to see what temperature that probe will go to.
My thinking is the loss does not change that much with 1" as compared to say two inch. Certainly 40% seems huge. I'll bet after a certain time period the sensors 12" below the slabs will all read the same, regardless of how thick the insulation is.

A freezer floor application would be an excellent way to show this also. In those cases the floor is cooled, often well below zero. The radiant system keeps the ground from freezing and heaving. I have to find out if anyone has probed and data logged one of those. Talk about some delta T maintaining 40 degrees soil below a -30 degree slab. I have never done one but understand 6 inches! of insulation is used. There are several of these in my area, I've been in one of them at minus 25.

hot rod

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heatboy

Another wondering.

What do you think 8"-10" of 3/4" modified stone would do? Reduce or increase downward loss. Since there are small air pockets in the stone, it should slow down the rate of heat transfer since air is an insulator. Or, not?

hb

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hr

I always thought pea gravel

would make the best material under a slab. It seems like it would trap lot of air. Similar to the insulating qualtities of sand.
Other plus's with pea gravel it is self compacting. If you have ever run a compactor over it you will see that feature.
You can have it delivered in a redi mix truck so placement is easy, just "chute" it in place like concrete. You can get a real accurate sub grade with small diameter aggregrate. It also allows great drainage should errant, "rouge" water appear. Not to mention nice to kneel on
Road base or base rock with sand type binders doesn't drain as well, and they definitely need to be compacted.

I suppose a soil scientest could give us more info on conductivity of various "earth products" Still think we should be embracing the geo thermal experts for info in this field. Maybe Duncan has a OK State contact person. I'll check with David Springer, he seems to be connected with the geo experts also.

hot rod

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Mi39ke_2

From the big book...

From that "big bad-boy of a book" by Watson and Chapman (just got it from the RPA bookstore yesterday), regarding concrete slabs that are brought up to temp in the fall and allowed to discharge at the end of the heating season:

"The ongoing loss through the backside may also be relatively small if surrounding materials and soil are kept dry, are porous, and not compacted, so that heat conduction is minimized. In most climates the ground temperature, approximately 5 to 10 feet inside of the perimeter and 2 to 3 feet below the heated slab, will remain at the stable year-round temperature indigenous to the region, usually just above or below 50 degrees."

Art Pieterman

This is really interesting,

as I really don't know much about the technical aspects of our heatloss program. I work for HeatLink in Canada as a local rep. I just looked at a heatloss I did a couple of days ago for a 14,000 sq. ft. slab-on-grade Ford dealership and I played with the R-values for the slab. The load with R-5 underslab was 139K, and with only R2.5, the load only increased by 2K to 141K. The program we use is an MS Excel spreadsheet designed in-house by our engineer in Calgary. The only thing that I am 100% sure on is that as a systems designer, HeatLink stands behind their heatloss 110%. In my few years with the company, we have yet to have any complaints about equipment being undersized due to the loads that our heatloss spits out.

One of the things I do know is that HeatLink worked with Beaver Plastics somewhat and wholeheartedly agree with the information that they have sent out about under slab insulation.

What would be interesting to me, is to take my heatloss on this dealership and redo on Wirsbo's program to compare the two.

Art

eleft_4

it was

100% coal, very fine. I don,t see much chance of catching fire under a slab or drive way for that matter. It's not a new one. We did it as far back as the late 1950's. Al

heatboy

Maybe it's me.........

I like your numbers much better than mine, Art! Does anyone else have any comparisons for under slab losses?

Always learning.

hb

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David Van Wickler

IMO

the perimeter and edge are the important concerns since heat loss is directly related the delta T. Below the slab could be a multitude of materials that could be a detriment to the downward heat loss like water levels, clay, etc, and under these conditions full slab insulation is required in addition to some other type of lab drainage, removal of offending material(clay) and backfilling with stable fill(gravel).

I design for a 8-12 foot perimeter and 2" rigid along the edge, and a below slab temperature of 70F. This reduces the delta T and lowers the heat loss but insulation is still required.

I have sen a fair number of boilers run for a week straight at design temperature and not make hi limit due to no edge, perimeter or under slab insulation, so it is required.

It reminds me of an article some 5-6 years ago that resurfaced. Someone claimed that radiant heat allowed you to design with 0 air changes per hour since there is no convection..........................that article is missing some serious air infiltration conditions that have nothing to do with radiant heat.


Really important is intial start up or set back. I have sat down and looked at start-up conditions and a slab on grade will draw about 3X the steady state BtuH load. SO protect the boiler from this condition. Primary/secondary piping alone will NOT protect a boiler. If the slab draws 300,000BtuH and the boiler is only capable of producing 100,000 BtuH the boiler will lose the battle and drop it's supply temperature 20F above the return.

David Van Wickler

Heat loss - what numbers do you trust

From what I know, you can see a lot of different heat load values from different programs. indoor air temp and ACH being the greatest variables.

There have been many times that a customer would call and say comp X had a lower heat loss and didn't need plates, etc.

A few years ago a distributor that switched mans, called me with a problem. he was using comp X program because he thought it was easier and performed periemter banding clacs. But it habitually underestimated (IMO) the heat loss - not that it was inaccurate but that it was too critical and "exact". WHen the church could rise above 62F the "exact" was wrong. He bought a second boiler to replace one of the two.

Fudge is good when it's not too much.

heatboy

Thanks for the input, David!

On the subject of start-up and set-back. On initial start-up (first cool weather), the energy needed to overcome such a small load is minimal, correct? So, the boiler sized to heat that 100K load at design should be more than adequate during seasonal start-up when the load would be 5K. If you are starting up a slab for the first time in the dead of Winter, that's a different scenerio. Granted, boiler protection, if needed, has to be incorporated in mechanical design regardless of the other issues. P/S piping only assures flow through the boiler and, I concur, does nothing to protect from condensation.

I also agree with your point of insulation is needed. I'm just unsure how much is needed before it becomes diminished. Edge insulation always has been a challenge. There again, a thermal break is needed, but when you have 10" to 12" footers and the first loop is 6" from the wall, that could be up to 16" or more of concrete the energy has to travel through. Concrete guys aren't really fond or 2" of polystyrene on the inside of the footer, which, around here, is mostly the case.

How far off am I (g)?


hb


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hr

Put the numbers to it hb

What is the worth to the customer for insulation? Saving $0.05 per heated square foot, in utility costs balanced against the up front cost of entire slab insulation. Compared to saving $0.25 per heated square foot, makes the choice easier in favor of spending 40 cents per square foot for insulation.

Slab on grade compared to basement 5 to 7 feet deep would be different also. ASHRAE numbers I have seen show a number between 0.021- 0.032 btus/hr/sq.ft for basements 5-7 feet below grade. Say you use the high side of that on a floor that requires 120 degree supply to provide 20 btus per sq. ft. So .032X (120-20) = 3.2BTU/sq. ft. loss downward. Multiply that times the cost of energy with the efficiency factor accounted for and you have a cost to operate difference. Thats IF you agree that thew loss is consistent throuhgh out the heating season.

It the vagueness that throws me for a loop. What is the actual downward loss on each and every job? Back again to soil types, moisture, etc, etc. It seem real hard to get a real accurate number for the "what ifs!"

The 1-1/2 - 2" edge to footing insulation done to the best of your ability--a must, in my opinion. Perimeter for 4 feet good idea. Entire slab with R-2.5? I say why not on residential applications at a $.40 cost per square foot investment. If nothing else the response time is helpful for shoulder season ramping.

The hardest decision I face is the payback for entire slab when you start looking at 6,000, 10,000 or larger slabs. The cost for 2" of foam under those size areas get pricey. Does the downward loss in the middle of a large shop building amount to enough to warrant spending thousands of dollars to get to R5 or 10?

Like everything else in the radiant selection process, boilers, controls on and on. Is it worth it to the customer to spend an additional 2-3 thousand for top of the line brands if the listed efficiencies are identical to the less expensive brands? Depends! Present the options. Some buyers will others won't.

For loss calcs run the numbers based on formulars that are known (the ones you most trust and present the options to the buyer.

I too wish the loss issue was more black and white when it comes to calculations. It may never be

hot rod

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David Van Wickler

Cold concrete is still cold

Even in the fall - concrete that is 60-65F is still cold. yes the surface is going to be 70-72 depending on indoor air temperature but initial load is still on the high side.

Snow melt - cold start - hold on baby - we are suckin' down some BtuH's, primary/secondary or not.

David Van Wickler

good points and if I may add,

R-value is still R-value and does not mind soil type, porosity, etc. And a little oges a long way when compared to none at all. And it's sure is a mister trying to squeeze it in under an existing slab.

Concrete guys shouldn't mind as long as it's not under the footing.