Posted By Snooks on 22 Aug 2013 12:13 AM
All that is fine, but don't tell me the ground is warm when trying to sell me geothermal and then tell me the ground is so cold that I need over kill in insulation. The Insul-tarp is said to have an R value of 7.5 and when 7 feet under and the ground is 50 degrees or more, I am comfortable with it. Seems to me a thermal break is more important than pilling up insulation. I am an accountant and not an HVAC pro, so I realize I don't have formal training but there is "common sense" in what I am saying (Science too for that matter). If there is a thermal break then I am not heating the ground. I guess one could argue that I want the geothermal effect in my slab before I turn on the heat. Let that warm ground raise the temp of the slab before the heat comes on. What really is the difference? Global warming is said to be science too, but to each his own. I am just a homeowner trying to make choices in a very confusing and distorted world.

Really?   The don't list an R-value in the current spec. In the "fact sheet" they say it tests at R5.9 @ 75F, but that's at full loft, before the bubble pack inevitably gets crushed &/or fills with moisture. They also do a sleight of hand and try to sneak in the R-value of the slab it self, the sand & gravel & dirt underneath etc. to weasel another R0.9 out of it for a whopping R6.8, but in a radiant slab you can't use the R value of the concrete. The R-value of the soil below varies quite a bit with actual grain size and moisture content, and  about half the R-value is the bubble pack, which never does as well in the field long term as it does in an ASTM C518 test plate.

If InsulTarp performed at even R3 over the long term I'd be overjoyed, but putting a radiant slab even over R6.8 would be a huge waste of energy at central IL subsoil temps.

The very definition of "thermal break" is indeed piling up insulation. Insulation is what impedes the flow of heat from the warmer side to the colder side, breaking the flow of thermal energy.

If you have very deep dry sandy soil and your slab is 10s of feet above the local water table and you manage surface water VERY carefully you might make out OK on the seasonal heating of that somewhat insulating thermal mass of soil, but it's really not the way to go. With clay soils with some moisture content forget about it.

Common sense should tell you that there's no way to, "Let that warm ground raise the temp of the slab before the heat come on.". Heat moves only from warm to cold. The room temp will ALWAYS be above the ~55F subsoil temp, and before the heat comes on the heat flow will ALWAYS from the room to the slab, and from the slab into the ground.

One of my degrees is in physics (the other is mathematics, but I work as an engineer), and I can tell you there is simply no way to beat the raw physics here. To move heat from 55F dirt into a slab that needs to be raised a few degrees above room temp takes a ground source heat pump, but it takes an energy input to accomplish that feat.  Still, the amount of heat you can move will be ~3-5x as much as the raw energy used by the pump, which is what makes it superior to electric boilers from an operating cost point of view.  I won't try to describe the working fluids and phase changes from liquid to gas to fluid that makes these things work, but they DO work. It's how you can make ice cubes in a 5F freezer in a 75F room, and how you can cool your room to 70F on an 100F day with an air conditioner- the basic technology is more than 100 years mature, the basic science even older.  Bringing the temp of a slab up to 75F by pumping heat out of 55F dirt isn't a very challenging design constraint.

A 55F ground temp is fine for a GSHP a great temp for both heating and cooling, since you can pull a lot of heat out without freezing the soil (changing it's heat transfer characteristics and net efficiency of the system) and you can pump a lot of heat into the soil during the cooling season without raising the temp of the soil far above room temp where it would be losing both efficiency & capacity.

Snooks, I can understand your wanting radiant floor heat in the basement, it makes for very comfortable basement living space. It's unfortunate that your under slab insulation is lacking. If you are intent on installing a radiant floor heating system, you'll have to take that into account when calculating your total heating load so as to accurately size your boiler.

Apparently, you have access to natural gas in your home, so it makes economic sense to use gas as your energy source over electricity. You probably get your electric power from Commonwealth Edison, and although they offer reduced rates for electrically heated homes, it's still not going to compete cost-wise with NG.

The biggest barrier to installing a high efficiency mod-con boiler is likely to be its technical complexity. I'm not aware of any all-in-one NG fired mod-con boilers similar to the Uponor Radiant Ready 30E.

If the technical complexity of designing/building a hydronic system is daunting, you can purchase component assemblies to significantly cut the time and risk of a DIY project. Check out Precision Hydronics, for example.

--Clark

As a DIY it's easier to hack in a heat-exchanger-isolated loop on a condensing tanke hot water heater like a Polaris o Vertex than it is do properly design a system around a mod-con boiler.

But without a careful heat load calculation we have no idea as to what your actual peak water temp requirements would be, and with the ground-lossy slab it'll be a bit higher than a well insulated slab, all else being equal. But it still might make it at domestic hot water temps (most do.)

Gas is almost certainly going to be your cheapest option, at least within the lifespan of a hot water heater or boiler. But if you're going to air condition, ductless mini-split heat pumps that both heat & cool will be cheaper to heat with during the shoulder seasons.

I think the decision whether to go hydronic, ductless mini-splits, or something else (e.g., direct vented NG heaters) in the basement would depend on the need to air condition the basement space. Cooling might not be needed at the basement level during the summer, especially with Snooks' basement floor being a significant heat sink. My basement slab is insulated at R10 and the walls at R22. Basement temperatures stay right around 70F all summer without supplemental air conditioning (beyond the spill over from cooling the above grade space). Depending on how the basement space is going to be used, the superior comfort afforded by radiant heat may or may not be that important. For me personally, I'd hate to give up the radiant basement floor heating, purely from a comfort standpoint. This environmentally controlled space (for temperature, humidity and dust) doubles the practical living space of our house.

I have no personal experience with mini-split systems, so I'm not about to poo-poo them. Stlll, for new construction I'd want to see them in action and get some trustworthy testimonials before budgeting for their relatively higher cost when less expensive options are available.

--Clark

"This is how Carter Scott builds most of his Net Zero houses on the cool edge of climate zone 5. " FYI, I clicked on the link and CS states he uses the Zip system sheathing: "CS: We have found that a triple system works best: 1.The Zip System (sheathing with an air barrier built into it) on the exterior walls; 2.The low density spray foam, and 3.The air sealing of the dry wall on the inside."

Posted By Surfsup on 22 Aug 2013 09:47 PM
"This is how Carter Scott builds most of his Net Zero houses on the cool edge of climate zone 5. " FYI, I clicked on the link and CS states he uses the Zip system sheathing: "CS: We have found that a triple system works best: 1.The Zip System (sheathing with an air barrier built into it) on the exterior walls; 2.The low density spray foam, and 3.The air sealing of the dry wall on the inside."

He has definitely evolved away from the closed cell foam, and more toward cellulose, but he still uses a lot of foam (though open cell is far less of an issue than closed cell).  His typical wall stackups are usually more than a foot thick with a full foot of fill, and that's a whole lot o' foam at any density:

Blankets are for beds, certainly not for insulating under any slab. It is the worst kind of gimmick and akin to bubble wrap for shear unmitigated gall. The effect of using the questionable R-value of assorted soiled, as Dana astutely points out, is to have to "charge" the soil. Much like heating a pool the first of each season. The cost to heat up the soil, usually about two feet down, until no the heat wants to go up instead down will cost more than proper insulation...about R-10 in most basements, most cold climates. Not the end of the world, just not optimum.

Most basements will not benefit from typical DX cooling, but dehumidification is usually wise.

Yikes! Your research missed a few fine points.....

"All that is fine, but don't tell me the ground is warm when trying to sell me geothermal and then tell me the ground is so cold that I need over kill in insulation."

Actually closed loop geo design temps are as low as 30F EWT. It's not that we literally take warmth from the ground, we take heat energy and amplify as well as combine it with existing BTU's. Think of a conventional central air conditioner. It collects heat energy from a 72F house and releases it into outdoor air raising the condenser discharge temp above outdoor temp.
In other words we are taking heat energy from the home and heating the outside. Based on your theory, we then could use less insulation in the walls of the home (with no impact on cooling efficiency).
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" The Insul-tarp is said to have an R value of 7.5 and when 7 feet under and the ground is 50 degrees or more, I am comfortable with it. Seems to me a thermal break is more important than pilling up insulation."

Both are important, the bigger the break and higher the "R" the better (though there is such a thing as diminishing returns which an accountant will understand). Warmer migrates to cooler. The higer the temperature difference, the quicker it moves. The less insulation employed, the higher the water temperature must be, the greater the temp. difference the quicker your energy dollars go bye bye......

"I am an accountant and not an HVAC pro, so I realize I don't have formal training but there is "common sense" in what I am saying (Science too for that matter)."

Yes science, and refrigeration principles (or collection/amplification of heat energy) all apparently not "common sense". In fact some of geo is counterintuitive without more than cursory education on it.

"If there is a thermal break then I am not heating the ground."

This is a thermal barrier of very low quality. You will heat the ground and the energy will be wicked away from your home (with your energy dollars).

" I guess one could argue that I want the geothermal effect in my slab before I turn on the heat. Let that warm ground raise the temp of the slab before the heat comes on. What really is the difference?"

Well you are correct in that "one" is arguing that point. The difference is you are talking about temperature and everyone else is talking about heat energy and the cost to move or create BTU's. A common layman mistake.

" Global warming is said to be science too, but to each his own. I am just a homeowner trying to make choices in a very confusing and distorted world."

Some are confused by numbers and tax code. Education moved you out of that confusion. With education you can move from your current confusion.

" Which always amazes me with some HVAC guys. On one hand there is so much warmth in the ground they talk geothermal and on the other hand they argue you can't get enough insulation under the basement slab. Puzzling to me how both conditions can exist, but I don't want to get into that here."

No you shouldn't want to get into that here. You should have gone into it before pouring your slab.

Sorry if I sound harsh, but perhaps a few years from now someone will resurect this thread and avoid the same mistakes.

Regarding your insulation, something is better than nothing (which is what we used years ago). So it will still work or you can get with an energy pro and see if you might be better served (long term) by abandoning the radiant in favor of forced air. This will be dollars and "sense" (right in a bean counter's wheelhouse).

Good Luck.
j