No disagreement here FBBP. My R-value numbers don't include the significantly reduced infiltration benefit that ICF also provides...which is indeed long-term as you indicated. I only wanted to point out that the ICF effective R-value simply varies in accordance with the actual temp profile in a similar fashion as the electrical resistance of a capacitor/inductor circuit varies with the actual electrical power frequency and that ICF effective R-value can be easily determined for any climate. We need to know both R-value and infiltration rate when accomplishing HVAC design.

ICF should be less than wood construction for a single story? I wish some of you professionals were closer! I talked to 3 general contractors today (one which builds a good portion of most of the higher end homes in the area) and they all cringed at the first mention of ICF for the main floor. They basically just said it would be cost prohibitive and didn't really want to talk about it. His recommendation was to go with geo-thermal because "people know what it is and it will be good for resale", radiant heating (still need forced air for AC), SIPS sheathing, and ZIPS walls (both of which I need to research because I don't know what they are...)

Geo-Thermal is NOT a good ROI and can become a long-term maintenance nightmare. Plus upfront costs are high.

What state are you located in? There has to be a qualified ICF contractor out there.

I'm in Iowa. Yeah I'm not too excited about geo-thermal but people around here seem to think radiant floor heating and geo go hand in hand.

I did find one ICF installer, Eller Construction in Eldridge, Iowa which is very near us. I've got an email in to them.

While I hope and believe that electric will ultimately be the only residential fuel of the future, I am not a big fan of geo-thermal for the same reasons as Lbear. If you really want a complicated and expensive heat source, just a conventional heat pump would provide a highly energy efficient option. However, you should include the higher acquisition and higher annual maintenance costs when doing the heat source ROI analysis. Really, anything that can heat water that provides the best ROI is what goes hand-in-hand with hydronic radiant floor heating. That's another advantage of hydronic radiant floor heating, you have lots of flexibility with regard to heat source options. Heat sources likely need to get replaced about every 20 years or so, so selecting the best fuel source available in your area that will provide the best ROI over this period is very important too.

What would be your suggestion for heat source for hydronic radiant floor heating?

Right now with again, my low level of experience- I'm excited about:

ICF Construction
Hydronic radiant floor heating (With whatever heat source makes sense, so far I'm not a fan of geo thermal)
OR ductless mini splits
PV Solar/battery backup, grid connected.

If I can somehow achieve these things and be confident it's all being done properly, and NOT break the bank, I'd be ecstatic. I guarantee a home built like this in our area would likely be on the local news. It just doesn't seem to be important around here.

Posted By FBBP on 10 Dec 2015 12:37 PM
DAna - as the cost of any construction can vary dramatically across the country, it might be better to express the cost of upgrades as a percentage adder to the base building cost rather then an absolute number. In Calgary they don't even build code min. at 200/ft so to use that as a base makes little sense. I think you are suggesting that a well built home c/w with PV doesn't have to add more the 20 to 30% and maybe much less. This could still be over 600,000 in some parts of the country.

As a general rule, construction costs in Massachusetts are at least 15-20% higher than in the midwest. The raw land costs are considerably higher than similar plots in Iowa.

Concrete isn't dramatically more expensive in Massachusetts than Iowa, and there is a fair amount of ICF construction going on, but it's definitely more expensive than other ways to achieve identical or higher performance. Climate-wise the zone 5 locations of IA & MA are very comparable on insolation & temperature.

As Carter Scott's existence proofs have shown, the cost-adder of hitting levels where Net Zero is at least possible is very modest, less than 20%, usually less than 10% or sometimes even less than 5% after factoring in the reduced cost of mechanical systems once you're at the point where it can be heated/cooled by a couple of mini-splits.

The cost-adder of ACTUALLY going Net Zero Energy is tied up in the PV system, but that cost is now half what it was in 2010, and falling every year.

It's unlikely that the cost of batteries will make sense in the next few years at Iowa's low utility rates, but with incentives PV might be viable right now. Most but not all inverters being installed this year are battery-capable, but state & local utility regulations around how grid connected batteries are operated (and by whom) varies considerably.

As long as you plan the orientation and roof pitches to be able to exploit PV when the costs are financially rational in your area, having a heating system that is powered by electricity and having a building envelope with a small enough heat load to make it Net Zero, you can take it there when the time comes. If you cut up the roof lines with valleys & dormers, build only to code minimums and install a high temp gas fired hydronic heating system you're locked out of that cheaper energy cost future.

Geothermal can be cost effective in some locations, not so much in others, but there are design risks- far riskier than simply going with a high performance enclosure and using cheap mini-splits. Even in cheap geothermal cost markets, once the 30% income tax credit disappears it's very hard to make a lifecycle financial case against condensing natural gas.

So I could do grid connected PV (and yes, I believe Iowa has some incentives) and just make sure it's possible to connect batteries at some point in the future?

Would you just go with mini-splits at that point, assuming an excellent envelope?

Hydronic radiant floor heating (With whatever heat source makes sense, so far I'm not a fan of geo thermal) OR ductless mini splits

I'd consider AND. Ie, mini-splits plus radiant floors in some areas can be a nice combination. In some cases (crawl spaces, open web floor trusses), the radiant can be air based (vs low temp hydronic).

I would not rule out Geo off hand. Some areas it does make good cents because of the AC component but Dana sums it up quite well.

I like Jon's approach because the radiant can make the difference if you are at the low end of mini split capabilities. I'm not much in favour of air based hydronics. The problem is (and not a biggy) you still need ventilation so you go with a Unico system or a good exchanger depending on how big or convoluted the house is.

Both the radiant and minis can take advantage of the PV should you go that way in the future. If you think the minis can handle the whole load, still put pex in the basement slab. The cost is to low not to. As it would not be the primary heat source but rather floor tempering, you could get away with a water heater approach.

While my preference is ICF from footings to trusses c/w floor slab radiant, there will be a cost adder. The basement ICF always pays for itself straight up. The next storey becomes a numbers job. ICF is definitely more money then a code minimum 2x wall and in most cases I suspect more then 2x with foam or thick 2x with cellulose. The problem is that I'm not convinced that the later two will stand the test of time or the occupant abuse. Wood moves and moves more in climates that have extreme moisture or temperature fluctuations.

We see a number of wall stacks that rely on drying to the inside but we have no control over the inside wall treatment over time. If Molly home decorator puts vinyl paper over the drywall, will we get mould? If someone keeps high RH levels for health reasons, what is the result? Concrete and foam can with stand this and maintain the original design. Any of these designs will result in lower cost heating appliances so that may offset a portion of the cost on any of them.

I like everything you guys are saying. What about ICF from footings to trusses, zoned hydronic radiant floor throughout (comfort factor) with a couple of mini splits for backup heat in the VERY cold and to cover ductless AC with a PV installation?

As luck would have it, the back of our house will face more or less south, and although it has a couple of gables in it now, I think we could slightly change the design to get a nearly flat south facing roof.

Yes, if installing PV, given the rapid rate at which the battery technology and regulatory environments are evolving it would be silly to not have battery capability. Solar City (the largest residential installer in the US) already only installs battery-capable inverters. Once Tesla's giga-factory battery production facility in Nevada is up and running they plan to be installing a battery pack with every PV installation where ever the local regulators allow. (Tesla's CEO Elon Musk is the board chairman of Solar City, whose CEO is Lyndon Rive, a first-cousin to Musk.)

Most people heating with mini-splits find it both quieter and more comfortable than traditional forced hot air heating, the current standard method of heating new homes in Iowa. There is a comfort upgrade to having warm floors, but not an efficiency upgrade. The mean radiant temperature in a Net Zero Capable house in zone 5 is pretty decent even without radiant floors, but you'll notice a difference in barefoot comfort. Whether that comfort up grade is worth anything, and if so, how much is really up to you, but it's a cost adder. For a slab-on-grade house it's cheap enough to install the tubing in the slab to give you that option down the line, should you decide that it's worth it. There is at least one reasonably inexpensive air-source hydronic chiller out there that would probably be able to cover the heat load of a Net Zero house in Iowa (Chilltrix), but there's some system design risk involved, and it'll be more expensive than a mini-split solution.

Fujitsu's mini-ducted mini-splits have decent air handlers and have a fully characterized output down to -5F (which is roughly your 99% outside design temp, maybe even colder- got a ZIP code?). They need only 9.5" of space for the air handler. Designing the house with the wall framing a foot taller than usual, and building a horizontal service chase under the attic above the finish ceiling to accommodate ducts, electrical & plumbing is a pretty cheap way to go, and gets around the room-to-room heat distribution issues that people tend to be leery about with simple wall-coils. It's a bit more expensive than wall-blob mini-splits, but not dramatically more. The biggest Fujitsu mini-duct cassette is a 1.5 tonner, and it's good 20,000 BTU/hr @ +17F (which is colder than your January mean temperature), and can throttle all the way back to 3100 BTU/hr @ +47F, which is an exceptional modulation range for 1.5 ton mini-splits, and would probably cover the load of a 2000-2500' Net Zero type house, but you have to do the load calcs as you develop and adjust the house design. Some houses are better heated with a single wall blob for the more open living areas, and a mini-duct cassette for the bedroom areas- it varies, and you can think about it as you drill down on design details, if you think you'll be going higher-R + mini-splits.

Carter Scott's Net Zero Energy houses typically have one ductless wall-head per floor, and no supplemental heating- most people are fine with it. All of the Devens houses monitored in this mini-split study were built by his company:

http://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/monitoring-mini-split-ductless-heatpumps.pdf

FWIW: The most expensive ductless solution I've personally been involved with in Zone 5 was a pair of 2-ton 3-zone multi-splits serving a ~3200' house that was substantially below current code min, at about $15K up front, reduced to about $11 K after local subsidies. A propane-fired ducted system with a 3 ton AC condenser proposed for the same place was quoted at about $25K. A fully ducted 2-zone Carrier GreenSpeed heat pump + a 1-ton mini-split was proposed by yet another contractor for about $40K. Even at code-min a ductless solution may be cheaper to install than typical gas-fired hot air + central AC. You have to have the load numbers hammered out in advance, and push (sometimes aggressively) on the ridiculously oversized heating & cooling solutions. Had the house actually NEEDED equipment as big as the propane furnace and 3 ton AC, the price difference would be enough to bring the load down to something even smaller, if that price difference were applied to the building envelope in new construction.

Bottom line: You have to think of the building envelope and mechanicals as part of a system, and adjust accordingly. If you do it right you save a ton of cash up front on the mechanical systems, and another chunk o' change every year thereafter. The highest efficiency mechanical systems have a lifecycle much shorter than the lifecycle of insulation, and don't provide as much comfort, with the exception of radiant heating & cooling. Accept that radiant heating & cooling is really a luxury, and decide whether it's a luxury worth the price quoted. The high performance builiding envelope is also a luxury (it's not required by code), but it's a luxury that also saves on operating costs. It's more than just a financial calculation of the Net Present Value on future energy savings, but those future energy savings can be quite large relative to the cost. The cost of natural gas is currently at historical lows, and is widely expected to double in the next 15 years (wholesale price). The cost of grid tied solar is going to be much cheaper than residential retail rates soon enough, and even at current ductless efficiency it's heat output of will be cheaper than gas by 2030 (even in Iowa.) It's hard to build-in energy price deflation & deflation into a simple NPV calculation, since the error bars are large.

Posted By rgonyer on 11 Dec 2015 04:51 PM
I like everything you guys are saying. What about ICF from footings to trusses, zoned hydronic radiant floor throughout (comfort factor) with a couple of mini splits for backup heat in the VERY cold and to cover ductless AC with a PV installation?

As luck would have it, the back of our house will face more or less south, and although it has a couple of gables in it now, I think we could slightly change the design to get a nearly flat south facing roof.

The resistance heat is usually the back-up for the mini-split, not the other way around. When it's below 0F the efficiency of a mini-split is only about 2 and at -15F it's less than 2. But when it's 35-40F outside a right-sized mini-split would have an efficiency of about 4, using only 1/4 the power of an electric boiler to keep the place up to temp. If you're going to combine an electric boiler radiant floor with mini-splits, run the radiant with a floor thermostat at a constant temperature, and let the mini-split modulate with the load to keep the room temperature up. But in a high-R house a radiant slab can EASILY keep up with the load, and if you set the floor temp much over 70F it could be carrying the lion's share, at truly pathetic efficiency compared to the modulating heat pump.

So much to learn, but I also know 1000% more than I did a week ago. Thank you to everyone!

My zip code is 52726. It's near the north end of the zone. Last winter (This was extreme), we had a few days that were -20F actual temps. But it does happen. We also have summers that have 95F+ days with very high humidity.

Also, this will be a walk out basement style ranch home, with probably around 40% of the basement walls above grade.

You could go with either mini splits or HR and be very comfortable if you have an energy efficient building envelope. I don't think you will need any backup. However, I would suggest putting the PEX in the slab even if you elect to go with mini splits. That way you could cost effectively have HR in the future if desired. If you have a southern exposure, you should consider passive solar heating too.

Your 99% outside design temp is about -3F (same as Davenport/Moline), and your US climate zone is zone 5A. That is a climate where cold climate mini-splits do well and even some ducted ones. Even though the fully specified capacity may stop a -5F or -15F, the Fujitsus will keep going at any temperature. The Mitsubishi Hyper Heating series is fully characterized at -13F (-25C), but will automatically shut down somewhere around -20F (specs say it could be as warm as -18F), and will auto-start once the temp rise to -15F or so. Even though it might hit -20F once or twice in a decade, there's no reason to rule them out, as long as it has a bit more capacity at -3F than your calculated heat load at -3F.

Sized correctly so that it covers -3F load but is still modulating at +47F (the temp at which it's minimum output is also characterized in an HSPF test) you'll get a seasonal average COP of at least 3 or better. If it's undersized so that it's running full-blast all the time, or so oversized that it's cycling on/off any time it's over +25F it'll struggle to hit a seasonal average of 2.5, but will still pull at least 2.0 (half the power use of an electric boiler.)

For a finished walk-out basement type house you'll probably need a mini-split for the basement, and another for the first floor. The heat load and heat gain of the basement zone is going to be a fraction of that upstairs (unless it's facing west and has large sliders on the walk out, causing very high sensible cooling load peaks.

In a high-R house be careful to not over-glaze the house, or you'll end up with uncomfortably high daytime cooling loads on sunny days in winter. You don't need to increase the glazed area to get a decent amount of passive solar. Limiting west facing glass to the minimum required for daylighting is important for bounding cooling loads. The temptation is to increase south facing glass for wintertime gain, but it's not a good idea. With high-performance windows the additional cost of bigger windows is more expensive energy than PV solar + mini-split, and it makes it more likely that you'll have uncomfortable overheating issues.

Back of the house faces basically due south. Let's see if this layout link works....

http://s346.photobucket.com/user/rgonyer/media/Newhouse_zpsglub1gjw.jpg.html?sort=3&o=0

There are a ridiculous number of unnecessary corners (particularly the bump outs & back on the front of the house) which increases the thermal bridging of the framing and the ratio of exterior surface to conditioned floor area. Not counting the garage or the fireplace, I'm coming up with 26 corners (including the hard to air seal high-thermal bridging non-perpendicular corners at the master bedroom and kitchen. There also appears to be a snow-trap a the Study bump out at the intersection with the porch roof, and potentially a snow-trap valley between the garage gable and large dormer gable (hard to tell without ridge line indicators over the floor plan.)

Bottom line, the number of corners and different roof pitches make it more expensive to turn this into a high performance house. Try to limit the total number of corners to 8. A "T" topology has 6 outside corners, two inside corners. The bump-outs and dormers give it some drama, but you can do a lot with transitions in cladding type without destroying inherent shape efficiency.

Re-configuring how the bath and utility room next to the study are configured so that the north wall of the study is a continuous plane with the north wall of the bath & laundry gets rid of 4 corners.

You can get rid of another three by moving the foyer and wall for the short hall to the Great room north to be at the same plane as the study as well.

Moving the fireplace completely inside the Great room and making the west wall a single plane on the exterior rather than the interior gets rid of another 4 corners, and improves the drafting of the unit. Making it an EPA approved wood stove or wood burning insert would be even better. If you move the west walls of the Great Wall out to match the insulated west wall of the fireplace bump out it's more conditioned space, but with less thermal bridging from framing, and about the same exterior surface area. The only additional exterior surface that adds its at the roof, which is higher R than walls in most houses.

Flattening out the windows on the south side to make it a single plane (except for the step back for the Great Room) then makes it a T topology except for the corners that intersect the garage. Since the garage is at least semi-conditioned space, the impact on thermal performance of those corners is small. But it's probably not difficult to address those better too.

Reducing the total number of roof planes and going with shed roofs rather than a gable perpendicular to the main roof to gets rid of valleys, and reduces the amount of snow-trap points. (The porch/foyer gable intersecting the wall of the Study bump out looks like real leak hazard. The kick out flashing would have to be pretty tall to keep it dry under record-snow year conditions.)

The architect may get less fun out of simplifying the footprint, but it makes the builder's job a lot easier (especially if you're going for better-than-code air-tightness), and it lowers the thermal performance requirements of the walls to hit any particular load number.

Dana, I really appreciate your analysis. The non-perp bump out at the kitchen may be hard for us to get rid of (Well, hard for my wife to get rid of ;-) ) but I can use all this input and talk to our designer. Something that bothers me, why don't builders/designers notice these types of issues? Maybe we just don't have this type of skill in our area.

Posted By rgonyer on 16 Dec 2015 02:37 PM
Dana, I really appreciate your analysis. The non-perp bump out at the kitchen may be hard for us to get rid of (Well, hard for my wife to get rid of ;-) ) but I can use all this input and talk to our designer. Something that bothers me, why don't builders/designers notice these types of issues? Maybe we just don't have this type of skill in our area.

Architects are often more concerned about the visual aesthetics of both the exterior & interior than mundane functional aspects such as energy efficiency (or snow-trap roof lines, in snow country.) Really great curb-appeal isn't necessarily at odds with aesthetic or functional issues, but those are often pushed onto the engineers' & builders' plates.

Builders definitely notice things like complicated framing & sheathing issues, which no only undercut efficiency, they usually result in higher labor costs and higher material scrap rates, all of which get bid into the quote.

Designers & builders of high performance houses are more attuned than the average, since that's their stock in trade. You can build a pretty efficient house at code-minimum R-values if you pay close attention, but you can't hit Net Zero Energy at current code minimums.

Beginning in 2020 all new homes in California will be required to be Net Zero. Given the volumes at which houses are built in CA (even the US climate zone 5B sections of CA), there should be rapid narrowing down on what it takes to actually achieve that cost effectively. A rectangular footprint "shoe-box with a gable" is pretty good starting point, but it doesn't have to be simplified to quite that degree. But the 28-corner multi-plane bump-outs and ornamental dormered roof look is probably not going to make it in the post-2020 CA world, at least not in the cooler parts of the state.

The odd-angle corners on the back of your are bit of a PITA to thermally break and air seal. It's a weak point, but it's do-able.