RATE OF HEAT LOSS THRU SLAB/EDGE
Last Post 06 May 2015 08:53 AM by sailawayrb. 6 Replies.
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bob lightUser is Offline
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04 May 2015 06:11 PM
I AM TRYING TO FIGURE OUT MY BASEMENT RATE OF HEAT LOSS THROUGH THE SLAB EDGE AND INTERIOR FLOOR USING  SIEGENTHALER'S MODERN HYDRONIC HEATING.  HIS FORMULAR ON PAGE 30, EQUATION 2.7 STATES   Qslab    =    (L)(DeltaT)/1.21+0.124(Redge)0.0103(Redge)squared.
On the next page he plugs in some numbers, = (L)(DeltaT)/1.21+0.124(Redge)+0.0103(Redge)squared. 
Since I started both formulars at the same point, one should see they are not the same and will give different results.  In addition in his example I came up with 2700/2.89 not 2700/3.619.  So I have three numbers to play with.  I am at a stand still until I get some advice.  I appreciate any help you can give me.  I know we have some experts out there.  Thanks, Bob
sailawayrbUser is Offline
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05 May 2015 07:46 AM
Yes, the correct answer is 2700/2.89 as you indicated and is NOT 2700/3.619 as John Siegenthaler indicated. There should be a "+" before the 0.0103 in equation 2.7. We actually pointed out that error to John Siegenthaler several years ago...along with several other errors too. Please also be aware that you should use the average slab temp if the slab is heated and NOT the indoor room temp. Please note that we use the correct Siegenthaler equation in the heat loss software on our website:

Borst Heat Loss Analysis Software

I should also note that the hydronic radiant floor heating design software on our website assumes that the exposed floor heat loss is calculated using the indoor room temp as would normally be done, and the hydronic radiant floor heating design software then subsequently factors this exposed floor heat loss to be higher based on the design average slab temp as determined by the software. This make more sense since you don't know what this average slab temp will be until you actually do the design... We found this to be a deficiency in John Siegenthaler's hydronic radiant design software several years ago as well and we refined our hydronic radiant floor heating design software to better address this:

Borst Hydronic Radiant Floor Heating Design Software

Anyhow, I hope this helps and you are no longer at a stand still, LOL!
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
bob lightUser is Offline
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05 May 2015 11:17 AM
sailawayrb, appreciate the correction and yes I've found numerous mistakes as well. I will check out your site as I get along to verify what I think I know.  I plan on putting a temp sensor in the slab for the hell of it so I will know the slab temp.  I still have a problem in putting the pex in the slab and plan on doing 2/4 inches of EPS foam below and and 2" of XPS on top then the PEX, followed by 1.5 of crete, and lastly tile.  I can't see directly heating the slab as most do with the PEX in the slab even though I've been told to do so.  Some rocks are harder then others
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05 May 2015 01:03 PM
Yes, slab temp control feedback is likely more important than indoor temp control feedback. Outdoor temp feedback is also very important too. By important, I mean having the control capability to maintain the indoor temp at the desired comfort level without having indoor temp over- or under-shoot issues.

Where do you see the benefit in layering and using so much insulation in this manner? I don’t know where you are located, but why not just put 2-6” below the slab and place the PEX in the slab?
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
bob lightUser is Offline
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05 May 2015 04:32 PM
Perhaps I have to much time on my hands.  I have a real problem with craft telling me this is how we do it without backing it up with some expertise facts.  All the radiant heat guys say to put it in the slab because it works better that way.  In my thinking it cost much more to heat a 4" slab 2400sq ft to keep the tile/rooms up to temp.  If the PEX is in the 1.5" of crete below the tile insulated from the slab which is insulated from the ground then it would appear to be less costly to keep the tile/rooms up to temp with less loss to the ground.  Now I do not have the knowledge or experience in this and I am to old to do this house wrong and do the next one better.  So I don't have a problem listing to you experts unless this is the way its always been done.  Another problem I have seen countless times is the concrete guys hire the cheapest laborers to spread the mud and they don't care about not damaging anything in their way. To prevent this I will be sitting there with my rifle.  We lost alot a very good craft with the down turn several years ago and they don't appear to be coming back which is why I will be doing most of my building.  The house will be at approx 7300ft level with average yearly temp 15-69 degrees located 60mi east of Salt Lake City, Ut.  If you have some studies you could refer me to I would appreciate it.
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05 May 2015 04:35 PM
Energy is conserved. Once the slab is heated up, heat loss is heat loss and the mass of the slab is basically irrelevant to energy usage, and you're in a climate where you won't go from stone cold to heated all that often. Insulate the slab well. The only reason not to do the slab would be lead/lag time and properly controlled in most homes that shouldn't be a problem.
Rockport Mechanical<br>RockportMechanical.com
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06 May 2015 08:53 AM
You already have John Siegenthaler’s book, “Modern Hydronic Heating”. There really isn’t anything currently available that is better than that…even given the obvious typos. My vote would also be to just put all your insulation under the slab and just properly do a conventional slab-on-grade HR emitter as detailed in John’s book. There is really no need to over-think this, risk creating other problems, and increase your cost unnecessarily.

LOL, if you like rifles, you might like these too:

Borst External Ballistics Software

Borst Bullet Ballistic Coefficient Software
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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