High school algebra, trig, geometry and a little calc thank you. Some refreshers at the University of Wisconsin, but Management it my strong suit. Thus my insistence on practical application, which is as much a part of engineering as hard math. Economy is the essence of good design, be it a bridge or a radiant slab. I know quite a bit about combustion having managed a condensing boiler manufacturing and feel confident that I can discern smoke from fire.

In Siggy's own word; " Finite element analysis is not guaranteed to predict reality with 100% accuracy. The simulation results are based on assumptions such as soil temperature, flooring resistance, tube spacing etc."

Your argument is that Siggy said so. Mine is that it makes good copy and makes the novice seem expert by the mere reference. If the argument in fact, is the thermal resistance of all that concrete over tube, we have to look logically at the thermal resistance of concrete at design water and air temperature. The ROI on raising tube, the material and labor to do it, simply can't be justified in the commercial installation of small low-load systems.

http://www.esmagazine.com/articles/the-effect-of-the-tube-depth-on-radiant-slab-performance?v=preview

The article starts by stating a theory, not empirical fact.

Tube should be placed in the center of a slab to achieve maximum heat transfer efficiency. This is a scientific fact and has been well documented...they clueless

Or maybe not. Siggy says (politely):

"This means there’s an optimal tube depth where the slab delivers maximum heat output. The simulations I ran suggest it’s about one-fourth of the slab thickness down from the slab surface."

http://smartgreenbuild.com/blog/download/449/

In Siggy's own word

Siegenthaler also said "In summary, tubing depth within a slab does effect thermal performance, in some cases significantly. This analysis suggests that provisions for maintaining the tubing at approximately 1/2 the slab's depth are justified and prudent."

The ROI on raising tube, the material and labor to do it, simply can't be justified in the commercial installation of small low-load systems

My consulting engineers, who do nearly exclusively low-load commercial buildings, appear to disagree. It was specifically noted that tube placement was very important in getting this system to high efficiency.

It would be helpful to hear how you enumerate those costs.

Just to be clear Badger, I don’t consider you to be a novice or less than capable. It’s just that I can’t forget the comment you made in another thread a while back where you stated that heat transfer and fluid dynamics are meaningless and that you don’t bother applying these principals when you do your residential designs. I am certain that you have lots of practical knowledge and experience with HVAC installations or you would be out of business by now. However, I don’t have a clue how you manage to design anything with that sort of attitude but maybe you have found a way… Mostly, I have just become of intolerant of folks who bad mouth engineering principals and engineers in general by claiming they know more and have more experience blah, blah, blah… Please kindly give us a break from all the BS. I for one would love to actually learn something new from all your practical experience.

I am so sick of the pointless OCD arguments about slab tubing height. If you want to insist on slab tubing raising... like I did for ten years, before I learned better... then by all means, continue. If you want to act like it's some litmus test for actual quality though, please go get tested for Aspbergers. It will be too soon if I never see this topic come up again.

As for sailaway, I'm in danger of ranting. I will summarize by saying IF you're serious about learning from experience, then please, start anytime.

Can you design a 5,000 sq ft house to run on a single 45 watt pump efficiently and comfortably? I'll tell you right now you can't if you care about laminar flow in our tiny pipes. But you can, and I do regularly, reliably and with great rigor, and achieve excellent comfort and efficiency while doing so. If the price to pay for that is a couple degrees of supply water temperature because of a miniscule boundary layer in my tiny radiant pipe, hey, I'm very comfortable with that value engineering. And I don't need to brush up on my integrals to prove it, either.

Sorry, I can't follow you. I did not say that I do not use engineering principles. I did not deny the the effect of raising the tube. I hold Siggy and his work in the highest esteem. I simply stated the fact that it is not worth the trouble to, raise the tube, in most residential applications or commercial for that matter, if the slab is but 4" thick.

I have been studying and using engineering for several decades now. You are all missing the point. It is simply one of practicality. I do not waste a lot of time trying to squeeze the last btu from my heat source, but use very sophisticated radiant floor software to CAD tube and determine loads for each room and specify the best heat source, distribution system and emitter available for the job and the client. This is professionalism and I the only licensed contractor, and RPA certified radiant floor designer on this blog, save Rob perhaps.

As for experience, I am a Charter Board Member of the original Radiant Panel Association and set on the technical committee that wrote the first US standard. I hold a Master plumbers license in Minnesota and the cities of St. Paul and Minneapolis, where I also hold a Master Steam and Hot Water heating license. I stay in business by using science and good sense to give my customers good value.

If you want to get technical lets talk about lets fight over the 100% parasitic loss of circulators and how folks could save $10 or more dollars per year by turning the speed from spd 2 to spd 1. Or, we could go on about comfort, the main feature of radiant panels. We could start with the geometry of "Nevins chamber" (Nevins & Feyerherm, 1967). But none of this really answers the OP's question.

It is OK to show off as long as some reasonable good comes of it. So far it is the tedious, both to use and to hear about, "free" heat load "program". I will stop, if you will.

That’s very impressive Badger and precisely why I think you should more openly share your practical installation knowledge and experience on the forum. For example, perhaps start a thread why we always place expansion tanks near the boiler outlet and close to the pump inlet before distribution to the manifold circuits. I could provide the math (and create/share the software) for properly sizing the tank. Or perhaps a thread about best practices for efficiently placing distribution piping in general. I am sure that you have many tips you have acquired over your many years that many of us engineering types would welcome and could likely benefit from.

Relative to my comment about you being overly dismissive of engineering principles, I went back and reread the thread that I referenced:

Ignorance

It was Rob who actually made this comment and I just incorrectly assumed that you were of this same ignorant mindset given how you responded in that thread. I am very happy to hear that you believe that adhering to engineering design principles is important…and my sincere apologies for putting you in this ignorance camp. Both good engineering design practices and good installation practices are critical to achieving a good hydronic radiant floor heating system outcome.

You win the award for the most ironic link title ever. You did reread that whole thread before you reposted the link, right? Did you ever figure out how to fill a residential radiant system without upsizing the pump first? Or are you still going to insist that if I have a two story house I need a pump capable of pushing about 20 ft of head in the system?

I've done both differential and integral calculus. Fun stuff. Frankly though a little algebra and some realistic assumptions will solve 99.99% of engineering problems we care to consider with enough rigor to satisfy anyone. And I don't use math as an excuse to ignore reality.

I'm an electrical engineer with math & physics degrees, and even the simple crayon-on-napkin arithmetic works for MOST of this stuff (and a good deal of what I get to do to make a living too.)

The number of hydronic designers/installers who don't even bother with the napkin are many (but I s'pose those are the guys Rob & Morgan get to clean up after.) There's a shocking wealth of ignorance out there in the HVAC biz, but the notion that it needs to be engineered & tweaked to the last 2% is just silly.

I wonder if we can get this blog to go to face time! it could get more lively!!
Dan

Why? Do you have the popcorn-concession all fired up? :-)

"electrical engineer with math & physics degrees" Now the veil is lifted and all truth revealed!

I knew you were different, but thought you might be a Nufi.

To Sailer's point.

Pump to low-mass boilers and away from vents, expansion tanks and temptation.

Sizing expansion tanks has nothing to do with the size of the boiler, rather the volume and the design temperature of the system attached thereto. Like boilers most expansion tanks are over-sized. The sin is not the same since an over-sized expansion tank causes a temporary and exclusive expense while the over-sized boiler garners lifelong sorrow.

If we can get folks to insist on ACCA Manual 'J' heat loads performed by experienced technicians, designer or even professional engineers, we will have more efficient, comfortable and yes Greener HVAC systems.

Pass the popcorn :-).

Badger, who said "sizing expansion tanks has nothing to do with the size of the boiler"? Not me. I only suggested that you consider starting a thread about where and why in the system an expansion tank should be installed. I thought that you might have a more practical hands-on way to better explain this than I could. I can certainly provide the expansion tank sizing equation (and create/share the software too) if there is any interest. As you indicated, the expansion tank sizing largely depends on system volume and on the design operating temp (or perhaps more accurately it depends on the hydronic fluid density ratio at the design operating temp versus the initial fill temp). There is also a dependency on the static pressure during the initial fill and the pressure relief valve rating, but I am sure I would confuse many people if I tried to explain this.

Yes, ACCA Manual J written by mechanical PE Hank Rutkowski (and I believe still updated by him) is certainly an approach that I for one will continue to endorse.

Rob, clearly it is YOU who need to re-read that thread. The OP wanted to fill his system USING HIS EXISTING PUMP and asked if the elevation had to be considered when doing this. Again, the correct answer to THIS QUESTION is YES. The reason of course is because for this situation the system is still OPEN. The system will not become CLOSED until the hydronic fluid travels all the way up and thru the circuits and then back down to the pump.

I never suggested upsizing the OP's pump such that it could be used for this purpose...you apparently inferred that...or more likely this was an intentional obfuscation as I have often seen you do on this forum when a topic is beyond your knowledge. Granted, this OP was pretty confused, asking bad questions, and likely dealing with a poorly designed or installed system. However, I also seem to recall that he had several HVAC "experts" unsuccessfully try remedy his problem at significant expense to the OP.

When one properly designs a hydronic system, the pump is sized for a CLOSED system so as to provide the required design flow rate at the design head which results from the hydraulic friction generated in the system at this design flow rate. If you have ever actually used software to design a CLOSED hydronic system, you can confirm this is indeed true because there are no elevation change software inputs. Please see our DIY hydronic radiant floor heating design software as an example:

Borst Hydronic Radiant Floor Heating Design

If you have ever actually used software to accomplish an OPEN system pipe and pump design, you will see that there are indeed required elevation change software inputs. Please see our DIY Darcy-Weisbach and Hazen-Williams pipe and pump design software as examples:

Borst Pipe & Design (Hazen-Williams)

Borst Pipe & Design (Darcy-Weisbach)

Our Hazen-Williams formula based software is limited to water at 60 degrees Fahrenheit at turbulent flow rates, which is typical of most water work projects. It can actually be used for designing both OPEN and CLOSED systems as explained in the associated instructions.

Our Darcy-Weisbach formula based software is NOT limited to only water at 60 degrees Fahrenheit at turbulent flow rates, and is considered by many to be more accurate than Hazen-Williams formula based software. It can be actually be used for designing both OPEN and CLOSED systems as explained in the associated instructions.

Since our company also does hydroelectric projects in addition to hydronic floor heating, we have to be fluent in designing both OPEN and CLOSED systems.

Anyhow, I sincerely hope this exposition gives you a better understanding of fluid dynamics and how pumps should be properly sized for both OPEN and CLOSED systems.

Dan, I wouldn't suggest getting too lively. I saw the sample hydronic design on your Blueridge website and I re-discovered the definition of LOL.

Hey its the OP!

I originally asked about types of insulation for under a slab. Then I mentioned the reinforcment detail. Some of you guys went seriously sideways.

Just to clarify I mentioned "PEX mid slab" because thats where it ended up after chairing the rebar so it was effective, and trying to maintain decent cover over the PEX so it didn't get damaged and we could trowel the mix without the aggregate bumping into the PEX and ruining the finish.

Now where is that popcorn?

John7

Congrats John. It ended up where it belongs...or at least where we like to see it placed... I am sure Dana has the popcorn heading your way!

sailaway. the fact that you couldn't figure out how to fill a system without worrying about pump size speaks volumes. protip: the pump is completely irrelevant to the system fill. that was what I was talking about in the thread you referenced. I am surprised you can't garner such a basic understanding from my posts. but then, maybe you're too busy formulating ad hominem attacks and casting completely baseless aspersions to read for comprehension.

I am quite experienced with both open and closed system design, thanks.

I have been wrong and even confused on some threads, absolutely: our passive solar discussion is an example, and I admitted it, and apologized. I have never intentionally obfuscated anything in my life. And I haven't yet seen you once even acknowledge a misstep. Because of course you don't make any. Which is why every radiant system in america pushes at least 1 GPM per loop, right?

Posted By BadgerBoilerMN on 25 Apr 2013 06:26 PM
"electrical engineer with math & physics degrees" Now the veil is lifted and all truth revealed!

I knew you were different, but thought you might be a Nufi.

...which I clearly AM, but that's never going to stop me, eh?

Too funny...Now I can say one of my best mentors is a Nufi! Grand fun...hehehehee