We will be building a 2 story house in Austin, TX area with a full subgrade basement out of ICF (R-40) 3 stories total\.  We will have "Quiet cool fans' on the ceiling in just about every room on the 1st and 2nd floor.  We have a fully insulated large chase going up the the middle of the house.

My no a/c plan is to utilize the cool 55* air of the basement.  We will have 2 HEPA fresh air intakes in the basement. One for just the basement and another that will bring the outside air into the basement to cool in, then it will pass a humidifer and get sucked up to the top floors. I'm thinking of using the same Quiet Cool fan ($500) but instead of sucking hot air from the ceiling and pushing it outside, it will suck the cold air from the basement ducting (specifically for the top floors) and push it through ducts in the floors to the rest of the house.

So the basement air would be gathered from the HEPA air intake, then next to a large humidifer.  Another HEPA air intake would bring air into ducting between the basment slab and raised floor, flow through a path to be cooled by the basement, then blown up the chase.  Inside the chase are two dehumidifers, one at each level before the air dispurses to each room vent.

Do you think this will work?

Groundwater temperatures in Austin are about 72 to 74 F (http://mb-soft.com/solar/soilmap.gif), so I don't understand how you will get 55 F air out of your basement. If basement temperatures are 72 F, I would guess that the house temperatures might be 84 F or higher during the summer. Dehumidifiers will add heat to the house, since the latent heat of vaporization is released during condensation, plus the waste heat from the device. In a well-insulated house, you might be able to grab the coolest of the air during the night, and then shutdown ventilation during the heat of the day. But during the heat of the summer, the outdoor low temperatures might be on the order of 80 F, so it would only get warmer from there.

People survived in Texas for many years before air conditioning was introduced (maybe around 1940). I grew up for a while in Houston without air conditioning, and it is worse than Austin. I slept with a fan blowing on me. You will not be walking around the house with long jeans on during the summer. You should plant some shade trees if the lot does not already have them.

Well, crap! Thank you for your reply.  I'm assuming since it says "Ground Water" that is temperature is taken at the depth they hit water, so in Austin, 100+ feet depending location?

Is a root cellar impossible then in TX because the basement wont get lower than 75*?

Methinks the only way a basement in Austin gets to 55F if via stratification of the conditioned air, or leaks in basement-routed ducts overcooling the basement  or something.

The most efficient way to cool new construction in TX is to design & orient it to limit summertime solar gain.  The highest efficiency mechanicals in the world don't make up for a inappropriate/bad design.  Whether the walls are R40 ICF or R3  cheez-whiz, controlling the solar gain by design is everything in that climate, and wall-R barely means squat for cooling loads. I'd even argue against R40 walls in that climate- the typical R20-22 minimum ICF offering is more than enough wall-R particularly for a mass wall- spend the money on something other than more EPS. Or maybe R40 was some dynamic mass modeling "equivalent-R" number for the ICF you were looking at? (A true R40 ICF has 10 inches of foam, something like 2 or 2.5" on the interior, the rest on the exterior.)  Spending the money on a mass-roof & high-R roof would be money better spent than anything over R20 for ICF walls.

Reducing or even eliminating west facing windows, and shading the south facing windows with overhangs is just for starters.  Model the thing with DOE2 or BeOpt, and be prepared to make changes.  Cutting the cooling load by 2/3 or more in the design phase is both cheaper and more comfortable, but don't kid yourself that you'll be comfortable completely sans-AC unless you do even more load-killing, and possibly incorporating more thermal mass fully inside the building envelope.  You may be able to get the peak load under the capacity of a 2 ton ductless with a lot of careful design, and with a high mass interior pre-cooling with an even smaller unit might be able to ride the daily peaks without being uncomfortable.

Large chases running up the middle of a 3 story house adds a lot of stack effect, and will drive air infiltration if you don't make the roof and basement extremely air tight to the outdoors.  Air sealing the chase and other penetrations between the basement and first floor (including weatherstripping the door to the basement stairs) can reduce that quite a bit.

Scroll down about halfway to Peter Pfeiffers rules of thumb for designing green houses in Austin- there are real golden nuggets of the hard-truth in there:

http://www.greenbuildingadvisor.com...conference

“Don’t underestimate the value of discussing the obvious. If your new windows leak air because you didn’t do any air sealing — because you didn’t use any low-expansion foam — then you won’t get the energy benefit you expect. I know of one owner who spent $30,000 to replace all his single-pane windows with new double-pane low-e windows, and because of air leaks, there was no change in his energy bills.”

“If you do Manual J modeling, then there is something you can get whenever you model one of your houses — and that is intuition. You’ll notice that a living room that faces west needs about half of the cooling tonnage of the house. So intuition tells you that for your next house, you had better cut back on unshaded windows facing west. In a lot of houses, the AC load is being dominated by sunlight coming in through west windows. So, from looking at the Manual J report, you might realize that maybe you don’t have to worry so much about wall insulation, but maybe you should worry more about unshaded west windows.”

“Shade your windows. The overhangs on my house save us more energy than the solar panels on the roof. They also enhance the living quality, because we don’t have to close our blinds; we don’t get glare. Overhangs add comfort and durability to the home.”

“Shading your windows is often more effective at reducing energy use than replacing your windows with new low-e windows.”

“If a home has a swimming pool, the pool pump is often the single largest consumer of energy in the house. Changing a HERS rating from HERS 55 to HERS 40 is a drop in a bucket compared to replacing a pool pump with a more efficient pump.”

“Buy a lot on an east-west street. East-west streets are better for passive solar design than north-south streets.”

“You want a centrally located air handler with short duct runs. I prefer an airtight all-metal duct system — no flex duct. You also want one centrally located tank-style water heater. That’s much better than three tankless water heaters. We stopped doing tankless water heaters.”

Of course we have a good roof plan, it will be quad deck (ICF but for floors & roofs) with r-40 wth metal roofing on top of that.  The entire house has 6-8 ' deep of covered wrap around porch to shade the windows (that will be low-e and sealed to the 9's).

And I essentially WANT a stack effect in the hot climate.  Cold air will enter the basement on the north side of the house  and exit out the top attic vent. As I said in my first post, I will have quite a few fans that suck the hot air out and push it outside. I don't know why I would NOT want the air to come up from the basement.  You need to bring fresh air into your house somehow, seems like the best place to bring it in from is the coolest side and the lowest point.

I'm not a tool, don't plan on spending $30k on windows without sealing them.

Why insulate to those high levels if you are just going to be pulling outside air through the home? How do you plan to reduce the humidity levels in the summer?

"Cold air will enter the basement on the north side of the house and exit out the top attic vent."

Where is this cold air coming from again? Deep (30') ground temperature maps that I looked up using google show Austin to be ~71 deg F. At 10' deep the ground temperature will swing ~ +/-5 deg from that during the seasons, so you are looking at ~75 deg F ground temperature at your footings during the summer. I would hardly call that cool. Barely comfortable and then only if humidity is controlled.  And if you start pulling in 95 deg F plus air from outside in July, your basement will quickly become 90+ F degrees.  There is just not enough heat transfer there, especially if you have insulated walls in the basement.

Posted By Calm Rhino on 01 May 2012 08:08 PM
Of course we have a good roof plan, it will be quad deck (ICF but for floors & roofs) with r-40 wth metal roofing on top of that.  The entire house has 6-8 ' deep of covered wrap around porch to shade the windows (that will be low-e and sealed to the 9's).

I think that you will find the porches to be a great asset in providing shading to limit heat gain into the windows.  Plus, they provide a nice place to hang out during the evenings away from the west side of the house.  Get yourself a nice porch swing.  They make some in Gruene near New Braunfels that I found very comfortable.  In the old days, folks would just sleep outside on the porches to take advantage of the breezes. 

You might pay particular attention to the metal roof materials/coatings.  I would think that a metal roof would be a cool roof since it reflects much of the sunlight.  However, uncoated metal is a poor infrared radiator, so even though they reflect a lot of sunlight, they can still get pretty hot since they don't have a good way to reject the heat that they absorb.  You may have already checked into cool roof coatings, but if not, you might want to look into that.

I don't know how firm you are about not having air conditioning, but you might save the option to add a small capacity unit to your well insulated house if your other strategy does not work out.  (Obviously some of us are skeptical.)  You certainly can live without it, but not too many folks in that area do.  You might justify the energy use for a/c by adding some solar PV to offset the energy use.  Austin is pretty good for solar insolation, and probably has some good local rebates in addition to the federal rebates.  Costs are sometimes ~$1.75 per Watt after rebates.  However, there is a tradeoff between having trees for shading versus no shading for solar PV.     

Thank you everyone for your responses.

Of course the air coming into the house in July would be 100 degrees in the daytime but I don't plan on running the fans during the heat of the day, just in the morning and at night. But I do think I will probably need an a/c for the summer, dang. But I would much rather opt for trees for shade and go with wind instead of solar power. And 1.75 /w after rebates? That is amazing, I will definitely need to go check those out.

Does anyone here have a basement in Teas?

Front porch swings in Gruene? I'll take any excuse to go to that town, LOVE it there!! Wish I could eat at the Gristmill EVERY single day!!

And thanks for the tip about cool roof coatings, I did not know that they had to be coated, makes sense.

Posted By Calm Rhino on 02 May 2012 01:54 AM
Thank you everyone for your responses.

...snip...

And thanks for the tip about cool roof coatings, I did not know that they had to be coated, makes sense.

I do not know what is available for metal roofs to try to change the emissivity characteristics (make them a better infrared energy radiator).  I would check and see if anything is available.  A disadvantage of coating a metal roof is that you might introduce a maintenace issue to a roof that normally is maintenace free.  Life is full of tradeoffs. 

The going price for PV systems including installation before rebates is about $4.50/W.  The federal rebate is 30%.  Local rebates that can include utility, city, or state rebates are highly variable.  You might check out http://www.austinenergy.com/Energy%.../index.htm for rebates in your area.  Solar panels actually shade the roof, so that is one way to cool the roof.  You could also consider a pole mount in the yard if you have the room in a shade-free area, and if codes allow it.  Generally in cities, people mount panels on the roof, while in the country people sometimes use pole mounts.   

There are CRRC rated cool roof metal finishes for metal roofing, and are worth looking at. Galvalume has reasonable color range of cool-roof metal finishes, as do others. See: http://www.coolrmetal.com/color-card/

A PV array on the south facing roof brings the heat-reflectivity of the roof back down to black composition-shingle levels, but shades the roof deck, and if the pitch of the roof is higher than 3:12 there will be some amount of convection cooling. It's a waste to put cool-roof metal under PV since it would absorb, not reflect the infra-red emitted from the back side of the PV, but the net benefit of PV far outstrips the heat-gain issue. See: http://blogs.scientificamerican.com/solar-at-home/2009/10/27/the-albedo-effect/

There's really no such thing as "cool air" even at night in Austin mid-summer, so you won't be cooling with outdoor air. Mid-summer dew points are also quite high (the mean dew point in July is over 70F!) so even when the air temps might be useable for sensible cooling, the net increase in latent-load wouldn't be worth it. A nighttime ventilation approach to cooling can often work in drier parts of the country. You really DON'T want to preserve stack effect for cooling purposes in Austin!

Wraparound porch, yes. Low-E windows, on all but the south side. Trees... well... it depends. Shading the west side with trees is of higher benefit than the south side, and still allows you to utilize passive gains in the winter. The sun is pretty high in Austin in July- the house would need to be built under the canopy of a mature forest to get much benefit from trees on the south side.

Wind is almost always a net-loser compared to PV for single-family homes, especially if sited anywhere near trees. But even on the windswept valleys of central TX it takes a pretty tall tower to reap the benefit, and unlike PV there is a maintenance schedule to deal with- it's a mechanical beast, after all. When it's all said and done, rooftop or ground-mounted PV almost always delivers more kwh/year per $ invested, and is lower maintenance to boot.

I'm still baffled as to why money is being spent for R40 walls here, when the net benefit over R20 mass walls is miniscule in this climate.  The lifecyle benefit of R40 walls in that climate is more expensive than (un-subsidized) photovoltaic solar electricity at current prices(!), which means you'd be better off spending the money on pole-mounted PV than on the "extra" R20 of EPS on the walls.

To get a handle on how to make the efficiency upgrades rational, download a (freebie!) copy of D.O.E.'s BeOpt tool, which was designed expressly for that purpose.  It's WAY better than trying to do it with heating/cooling load tool.  Designing the house for the site & climate factors to minimize both cooling and heating energy use while optimizing your utilization of money toward that end is what this tool is all about.

For a rough cut as to where you need to start thinking more carefully about R-values, take a look at Table 2, p.10 of this document.  Austin is on the cool edge of zone 2, so anywhere you're over the recommended R values for zone 3 you may want to consider dialing it back a bit, spending the money elsewhere. You'd get more benefit taking some R out of the wall, and boosting the R value of the roof to R50, but given that it's a roof with a decent amount of thermal mass, maybe not.  A cool-roof finish takes a big chunk off both peak and average roof temps, and the thermal mass averages that (now lower) temp over time- a sufficiently long time that the re-radiated heat to the night sky brings down the average as experienced by the interior.

Optimizing window types by orientation and shading factors can let you find the right balance between passive gains during the heating season and heat rejection during the cooling season.  Low-E, sure, but the south facing glass may want to be a higher SHGF than on the other sides, using overhangs on the south side windows to kill the summer heat, but allow at least some gain in the winter.

How were you planning to heat this place? The heating outside design temp for Austin is +30F, and though your heat loads are likely to be pretty low, they're still non-zero. With R20+ walls, U0.30-0.34 windows, and a careful passive heating design/analysis the could be pretty close to zero though.  The key is to design it to heat (mostly) passively without boosting the sensible cooling loads.

To put Dana's thorough analysis into perspective; if you have to turn off the lights to cool off the house in winter, you spent too much on insulation...

This is why they make Architects and Mechanical engineers.

To be fair, we often assist Architects - and others - in evaluating windows and certain aspects of construction such as overhangs using advanced heating and cooling load design software. Good software will even allow for a large shade tree looking over the new sun room.

Ok, PV sounds like the way to go but I'm pretty sure I'm doing my calculations wrong as for how many I would need for 6000w. Seems like it would be more roof space than I have and I really don't like pole mounting. I'm really liking the UGE with the wind and PV.

And that makes total sense about the walls. The walls would be r-40 not for R value but because I need the thicker panels for the siding and cabinets, etc I'll be mounting on the inside and out. I could drop it though, think about different siding.

And as far as heating, at the top of the air chase is a lookout tower (3rd floor, 144 sq ft) with windows on all sides except the south. They will have shutters on during most months but during the few winter "days", I'd open the shutters, let the heat in and blow it down the chase for extra warmth. But since the ground is always right about 70*, even in the winter, I can still be cycling my basement air up because the "cool 70* air" will be considered "warm 70* air" in the winter.

I was talking to a contractor who specializes in basements in Texas and he says his basements stay about 65 -70 degrees, depending on if they have ceiling fans or let hot come down from the upstairs. I'm thinking of having a "two space" basement air flow system. The first where air comes in from outside, gets cooled and dehumidified (1500 sq ft). The air will be there from for 8 hours (cooling from 8 pm to 4am)(intaking air from 4am-12p). Then it will get blown to the main basement area (1500 sq ft) and be there for another 8 hours (4 am to 12p). THen during the main hot hours of the day, that air will be cycled up to the rest of the house , 12 to 8pm? so it will just be on a cycle. Or am I completely off my rocker?

With the entire house being a thermal mass, all the spaces will want to be the same air from the basement and with an r-50 roof and whole house fans sucking the hot air from the ceilings and pushing it outside. My main concern will be keeping the upper floors cool and pumping the heat out.

IN addition to the air being cooled in the basement, the double hung windows on the 1st and 2nd floors will be opened at the top in the morning and in the night, and while the fans are sucking the hot air out, that will bring a cool breeze in. I may be completely off my rocker though.

Or am I completely off my rocker?

It appears that what you are neglecting to consider is that heat is a quantity. Just because you have a cool space or a warm space doesn't mean you can get any amount of heat or cooling from there.

For example, in order to blow a significant amount of heat down from your lookout tower, you'd have to calculate the amount being generated up there by insolation. The rest of the warmth is just what has escaped up there from the rest of the house. Once you started a fan to circulate, you'd rapidly find that what was coming down was not noticeably warmer.

Same goes for the basement cooling concept. Down there, what you could get in the way of cooling would be limited by the volume of air passing through and how fast it could lose heat to the cooler surfaces. It wouldn't be too long before your basement was heated and there would be little benefit to be derived from the airstream passing through.

What are you coming up with for the solar panels you need to get to 6000 watts? Without going into specifics for your location, you can think about 200W per panel or 10-15 watts per square foot. That gives you either 400-600 square feet total, or 30 panels which are usually about 3' X 5' or thereabouts. That is an array 100 feet long or two arrays about 50' long each.

A 6,000 W DC solar PV system in Austin is in the ballpark to power everything and meet most or all of the a/c cooling load for a new, well-insulated house, unless there were plasma TV's, shop equipment, extra freezers, etc. You can size PV systems by what you need based on previous experience and modeling for a new house, or based on how much you can fit on a roof. If there is a size limit, then choosing PV panels with a high efficiency is an advantage.

If there is freedom to orent the house (in azimuthal angle), a roof facing due south or 5 deg. W of due south with a pitch of 7:12 would be ideal for solar PV in that area.

I agree with ICFHybrid that you would really need to do some heat transfer calculations for how fast you could dump heat into the ground if you pulled hot air into the basement for cooling. You would immediately find that you don't want an insulated basement, but rather, you want to heat sink the basement to the ground. You might be able to find some calculators for "earth tubes" that would help demonstrate heat transfer to the ground. In fact, earth tubes might be a more efficient way to cool the air before it enters the house. The well insulated basement would work well for an air-conditioned house, or one where the air was precooled with an earth tube. I don't think earth tubes would work great in the Austin area, but it would be the most efficient way to accomplish what you are trying to do.

You could also consider making the basement the living area during the heat of the day rather than trying to blow that air into the rest of the house. You might find it a bit humid, but cooler than the rest of the house. (Dehumidifying will add heat.)

Dehumidifying with a mini-split would remove heat, but most would also be lowering the temperature, which you wouldn't necessarily want to do on humid but not too warm days. The Daikin Quaternity series is the only one I'm aware of that can dehumidify without changing the temperature, unless you WANT it to. It's capable of dehumidifying while heating as well as cooling, and you can set both temperature & relative humidity set point. Most others with dehumidification modes will only dehumidify while cooling, and most don't have a dehumidistat- it'll keep on going until you set it to some other mode no matter how dry it gets.

I'd be very surprised if basements in Austin were ever 65F in summertime without air conditioning. If the air-conditioned air is allowed to stratify it might, but with subsoil temps already north of 70F, the direction of heat flow would be out of the slab into the basement, if the basement were actually 65F. I can believe 65F basements in mid-winter for conventional poured concrete foundations, but with ICF it would be warmer.

Setting aside the latent load issues for the moment, fans moving air in/out of the house use substantial power too, and if there isn't a large temperature difference it's effective coefficient of performance is abyssmal. It takes a LOT of 70F air to remove the heat stored in the thermal mass of the house at 80F. By contrast, modulating variable refrigerant volume heat pumps such as mini-splits have PHENOMENAL coefficients of performance when the temperature differences are low, especially when moving heat from a warmer house to cooler air. Inverter drive air source heat pumps such as mini-splits would likely use less power than any grid-powered heavy-ventilation scheme, and they wouldn't be introducing latent heat in the process. Cooling off an 80F house with 75F outdoor air with a mini-split at low speed the COP would approach double digits, and at high speed would be at about 5.0, whereas with a whole-house fan it might be less than 1. See figures 14 and 18 in this document:

http://www.nrel.gov/docs/fy11osti/52175.pdf

without those "meters... up close" again dana, would the IQ var refg GSHP be considered practical?
I saw another thread too.
What about GSHP credits that would kick in?
What about more inclusive GT/Solar comprehensive contracting that is fair and legitimate?

What if heating HW  2 or just 3 would just be an asset with a mini as the add-on , since it does not heat HW (unless latest models are)?

What if it were contracted as on the side of a GSHP  sold, then but at a 'contractor's special' value?

All about eStar credits for sales profits on that GT/Solar contracting , and with HW tank or system as legitimate combined inclusive...

Hmm...-  calculating got me in trouble at least once in 50 years.






(Credit and maybe any additional Utility rebate considered, if applicable: consult your tax adviser)