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When the Problem Is Heat

How to keep the heat outside when you live in the desert Southwest and daytime temperatures can top 100°F

Posted on Jul 14 2014 by Scott Gibson

If you have problems dealing with the heat, you probably wouldn't like the desert Southwest, especially when conventional air conditioning is simply too expensive to use on a regular basis.

That seems to be the case for a GBAGreenBuildingAdvisor.com reader who's trying to learn more about building in a climate where the challenge of staying cool far outweighs the minor and occasional inconvenience of staying warm.

"I live in the low desert southwest near Phoenix," Anneal G writes in a post at GBA's Q&A Forum. "Living is very different here than in cold weather areas. And very different than Florida or humid areas of Texas."

Outside temperatures are more than 100°F in the shade for five or six months at a stretch, and may hit 115°F. At night, low temperatures may be only 95°F for a couple of months. Humidity is very low, and there are few drought-resistant trees to help.

A lot of people work at home, and few of them set their air conditioners to anything less than 79°F.

"We need to keep heat out rather than keep in or keep cool in and heat out, and this is apparently handled different than in cold weather," Anneal asks. "But how? That is what I would like to know.

"I am not looking for perfection like the Passivhaus. Just what should an average person with a low-to-medium budget really ask for to build a basic energy-efficient home in my low desert environment?"

Anneal's query is the focus of this Q&A Spotlight.

Start by orienting the house correctly

GBA senior editor Martin Holladay suggests that Anneal follow the recommendations in one of his articles, Hot-Climate Design. In that article, Holladay recommended that homes in hot climates be oriented so that the long axis of the house has an east-west alignment; have a hipped roof with wide roof overhangs; have as few east-facing and west-facing windows as possible; include details that keep the windows shaded; have all ducts inside of the home's thermal envelope; include adequate roof insulation or ceiling insulation; have a thermal envelope that is carefully air sealed; have energy-efficient appliances and lighting; and have ceramic tile flooring rather than carpeting.

Orienting the house so its long axis runs in an east-west direction means that in the middle of the day, the angle of the sun on south-facing windows is high, writes Dana Dorsett, and that allows much of the heat to be reflected. By shading windows with overhangs, most of the direct solar gain is blocked.

"East- and west-facing windows get sun on them when the sun is lower in the sky, and the incident angle on the windows reflects very little of that solar energy," Dorsett adds. "By having the longer axis running east-west means less window area on the east and west sides to soak up the heat. If possible, design for no west-facing glass and minimal east-facing glass."

North-facing windows are the best for daylightingUse of sunlight for daytime lighting needs. Daylighting strategies include solar orientation of windows as well as the use of skylights, clerestory windows, solar tubes, reflective surfaces, and interior glazing to allow light to move through a structure., Dorsett says, since it's shadow-free and never as harsh as direct sunlight.

A simple gable roof with the ridge running east-west also would give Anneal the most productive rooftop solar (PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow.) installation.

"Even if you don't install it on day one," he says, "within 5 to 10 years the costs are expected to fall by more than half (again!), which will make it one of the cheapest energy sources available. The average installed cost of PV right now in much of the U.S. is about $4/watt, or about $40/square foot. In some places it's getting down closer to $2/watt or $20/square foot."

In Arizona, an array with a capacity of between 10,000 and 15,000 watts should cover most if not all of an air conditioning bill, providing the attic is well insulated.

What about adding thermal mass?

Anneal wonders about the differences in building techniques between Florida, another hot spot, and Arizona. "I am a little confused about that, too, since rammed earth, adobe, and straw-bale construction are mentioned in this area for thermal mass (?) but the (Florida) Hot-Climate Design article mentions only needing 2 inches of rigid foam (R-10) for the walls," Anneal writes. "I would have thought more than R-10 would be needed for the walls? Am I missing something else?"

Adding thermal mass to exterior walls is expensive, says GBA senior editor Martin Holladay, but it is an effective strategy in hot climates.

Except, adds Dan Kolbert, in areas where it doesn't cool off very much at night. "Sooner or later," he writes, "the mass will heat up, too, and then what?"

This is certainly the case where Anneal lives. Temperature data over the past three or four years shows that high temperatures in July and August can range as high as 116°F, while low temperatures are in the high 80s.

"Dan is right," Holladay adds. "Once summer weather sets in, and nighttime low temperatures are higher than your indoor temperature, thermal mass does no good. Under those circumstances, you still want good old-fashioned insulation.

"The reason that less insulation is required in Phoenix than in Fairbanks is that your delta-TDifference in temperature across a divider; often used to refer to the difference between indoor and outdoor temperatures. [the difference between inside and outside temperatures] is smaller," he adds. "Even when it's 110 degrees outside, your delta-T is only 30 or 40 degrees. In Fairbanks, the delta-T can be 120 degrees."

Design a form appropriate to climate and site

Malcolm Taylor suggest Anneal look at the work of architects who have developed successful designs for similar climates. He cites the work of Australian Glenn Murcutt, plus a house designed for the California desert by Lloyd Russell.

The Russell house features a steel canopy that shades the house, plus garage-style doors that can be rolled up to let in light and air.

But the California house ignores the Passivhaus-like strategies that work well for almost all climates, says John Brooks: extremely airtight building envelopes with ample insulation, not too many windows and careful window orientation and shading.

"Overhead doors and sliding glass pocket doors are almost impossible to make airtight," Brooks says. "The canopy is a cool idea but [it] seems to be doing a very poor job of shading the glass ... not to mention the concrete thermal bridge."

Not so fast, replies Taylor. It was only recently that we stopped designing buildings to reflect their location and climate. The availability of cheap energy allowed designers to make a one-size-fits-all kind of house that could be built anywhere from Alaska to Arizona. "So we end up with an inappropriate basic shape we then try and make work by upping the efficiency of the building envelope," Taylor says. "At that point the only way to do this is to create the hermetically sealed enclosure characteristic of Passive Houses. Why not step back to look at the solutions that were always used before the advent of the ubiquitous modern tract house?"

Not every detail of the California house necessarily works, he adds, but the problem with Passivhaus design is that it seems arbitrary or inappropriate, he says. "They sometimes take on the superficial form of the region — say, barn-like in Vermont — but none of the essential elements that reflect the local climate," he says.

Our expert's opinion

Here's what GBA technical director Peter Yost had to add to the mix:

My first thought on key elements of design and construction for hot-dry climates is: Use the GBA Strategy Generator! It’s a great place to start to gather up ideas for your climate, by stage of construction.

And then for some thought-provoking examples go to these GBA Green Home projects:

I know that none of these homes are in exactly your climate, but each has some key design elements relevant to your environment.

My second thought is: check Building America resources from Building Science Corporation on design and construction for hot-dry climates:

No surprise that takeaways from all of these resources reflect insights already shared by Martin Holladay and company, but here several to round out the issue:

  • Airtightness is key in any climate, no less so in hot-dry climates. And airtightness is as much about comfort and air quality as it is energy efficiency.
  • Keep all HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. ducting and equipment in conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. . And this is as much about thermal comfort and air quality as it is energy efficiency.
  • Decide how “active” you want to be in operating a home to reject heat. Window coverings can play a key role in managing solar gain (most effectively from the outside but inside as well), but their effectiveness is often tied to occupancy engagement.
  • Real energy efficiency is always an integration of excellent design, materials, and construction. Look for architects or builders who are willing to guarantee the performance of their work.


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1.
Mon, 07/14/2014 - 13:59

Solar screens?
by Eric Sandeen

Helpful? 0

Any experience w/ solar screens like Pfifer Sun-Tex? I guess if he's building from scratch, he has the chance to do proper overhangs, and might not need that, but maybe it's a decent retrofit approach?


2.
Mon, 07/14/2014 - 14:36

How does an architect or builder guarantee performance?
by John C Hansen, LEED AP

Helpful? 0

Scott,
How would an architect or builder guarantee the performance of their work? Would you give us some examples please?
I read with interest your last bit of advice to your readers who want to have a home built for themselves. You wrote: “Look for architects or builders who are willing to guarantee the performance of their work.”
While I agree that this is good advice to prospective home buyers, I wonder if that is even possible. I recall at one time in the past there was a builder in the Chicago suburbs who built homes that came with a guarantee related to energy usage (efficiency).
No longer in the Chicago area, this builder currently has two communities in Texas and their website promotes the builder as “one of the nation's foremost leaders in residential, energy-efficient construction, as well as a pioneer in green-building.” I no longer see on their website any mention of any performance guarantee for their current product.
So, I wonder if anyone has ever tackled the challenge of actually finding the architect or builder who would even consider guaranteeing the performance of their work. I know that many articles aimed at builders recommend that they write performance specifications for their trades (subcontractors), but that too is a really challenging bit of advice. Just how many HVAC contractors would ever venture a performance guarantee? It just does not seem practical when so much depends on the successful performance of the building envelope and the workmanship of many other contractors whom they have no control over.


3.
Mon, 07/14/2014 - 14:48

On performance guarantees
by Scott Gibson

Helpful? 0

John,

It was actually Peter Yost who suggested looking for an architect or builder who would guarantee the performance of their houses.

Still, I spoke with an architect in Louisville, Kentucky, last week who guarantees heating and cooling costs will be $45 per month per 1000 sq. ft. of floor area. He is Gary Watrous of Watrous Associates Architects, who specializes in passive solar designs.

There may very well be others who do the same thing, even if the specifics are different.


4.
Mon, 07/14/2014 - 20:44

Count me out
by Malcolm Taylor

Helpful? 0

I sure wouldn't guarantee building performance unless the owner promised not to live there. Occupant behaviour is too large a determinant of energy use. Talk to landlords who include utility costs in the rent for some real world experience on how that can effect behaviour.


5.
Mon, 07/14/2014 - 22:44

When you're hot, you're hot
by w d

Helpful? 0

Scott, good article on the design demands of a truly hot environment.

Eric has speculated on the value of solar screens in a properly oriented and designed new building. When it's 95F overnight and 115F during the day, screens and low shgc windows may help stay lower in that range but most homeowners I know would be begging for thermal relief. One item that might be overlooked: When the sun is bright on a hot day and even if the window is fully shaded by overhang, it's possible to feel radiant heat through a 1990s vintage window. Stand next to the window (room at say 75F) with a magazine or solid object in hand. Close your eyes and pass the magazine between your face and the window. The difference you feel is influenced by indirect light from semi-reflective surfaces outside. In the Southwest, the South side front yard may be a patch of sand and stone; maybe a cactus. There's no lush lawn nor bushes nor trees to blunt the sun's relentless scorching. Placement of a solar screen or grate outside the window can reduce this effect and if the sun shines directly on the window at times, the window treatment serves double duty. If a grate or screen is incorporated in a shutter, the device can be stored in place. A decorative shade sail could reduce some of the indirect heating as well. Of course, if we shift to retrofit instead of new construction, window treatments can be a cost effective option and LBNL is said to have a study that will quantify the options, the economics, and even some of the intangibles.

Somewhere on Anneal's list I'd also look for a cool roof option.


6.
Tue, 07/15/2014 - 08:01

performance guarantees
by stephen sheehy

Helpful? 0

An architect would have to be crazy to provide an energy performance guarantee. He or she has little or no control over whether the builder complies with plans and specs. A few observation visits during construction are not enough to ensure the design gets built as it is drawn.

I suspect the architect's professional liability insurer would not cover such a guarantee.

As Malcolm points out, the homeowner is a big uncertainty. I can envision an owner in Vermont setting the thermostat at 75 in January, while sleeping with the window open.


7.
Thu, 07/17/2014 - 20:31

When you're hot, you're hot, EXCEPT...
by Michael Ginsburg

Helpful? 0

Its summertime in southern Arizona and, yes, it gets hot just like northwest Phoenix area.

Is it possible to be cool in a home where ambient temps ALWAYS hover around 75F? without a forced air system cycling intermittently throughout the 24 hour day? How could this be?

A well insulated ice chest with a block of ice will maintain cool temps for a longgggggg time. It's as simple as that.

The same is true for a house (ice chest) and the temperature controlled concrete floor (block of ice).
The enormous thermal mass capacity of a 4.5" thick slab for the entire home does just that, noiselessly, consistently, evenly and everywhere in the home - no varying and intermittent micro climates created by a blowing forced air system. And, with a 3kWh PV system the electric bills have been April, May, around $12 each month. June was just under $28 (almost half was standard customer service charges). July is coming soon but probably will be around $40.


8.
Wed, 07/23/2014 - 23:10

Thanks!
by Anneal G

Helpful? 0

Wow, thanks guys. I am so grateful for you taking me seriously.
I only just saw this after posting on "Designing Houses That Keep Their Cool"
Posted on Jul 4 2013 by Alex Wilson
Thanks again.


9.
Thu, 07/24/2014 - 12:58

Post from another blog
by Anneal G

Helpful? 0

This is comment I posted on "Designing Houses That Keep Their Cool" Posted on Jul 4 2013 by Alex Wilson.
http://www.greenbuildingadvisor.com/blogs/dept/energy-solutions/designin...
Figured this is a better thread for it.
"Phoenix is not high desert
by Anneal G

Thank you for taking the time to consider warm weather areas.

The low altitude southwest is a unique situation. It is not high desert like Las Vegas or even most of Tucson. It is frustrating that low altitude and high desert are generally combined into the same environment. They are not. Yet the population here is fairly significant. According to World Population Review, Phoenix is the 5th most populous city in the United States and the Phoenix metropolitan area is home to 4.33 million people in 2013. I dare say in the winter it doubles where I live with “snowbirds” or winter visitors so, as a guess, it may be 1/3 higher in the general metropolitan area in the winter?

But, the winter isn’t an issue here. It’s beautiful, open window time. It’s the long hot season that is an issue. I don’t think anyone living here year round complains that their inside temp is too hot at 79-80F with ceiling fans running, in high summer. When it accidently gets to 77F…burr. Seriously.

My non-professional observation is: it is the sun that is hot here and the air is much cooler. I know that sounds stupid but it just feels as though the sun is hotter here. Even in the winter, when you get in the car in the late morning, it is hot. When it is 105F in the shade it is at least 120F in the sun. As soon as it gets a little cloudy ;-) the temp drops dramatically to maybe 100F in the shade so to me keeping the sun off the bldg. via roof overhang or something makes a big difference.

I would like to know if something like a second wall/vertical louver fence a specific distance from the house would provide some kind of protection. Not just, yea, anything would help, but some specific scientific insulating/cooling value? Like if it is 12” from bldg it acts like magnifier holding the heat in but if it is 18” it would protect but 24” it does nothing. It seems to me that might be inexpensive if it would work. And some heat reflective surface for the exterior siding that doesn’t blind you or reflect heat onto the neighbors house? The article mentioned roof materials certified by the Cool Roof Rating Council or the Energy Star Roof program. Can they be used as siding?"


10.
Tue, 07/29/2014 - 15:12

They Make Shade Fabric
by Kevin Dickson, MSME

Helpful? 0

Coolaroo fabric is quite economical. It allows just the right amount of air through it, which is critical.
http://www.coolaroousa.com/en/shade-sails

You're right that the sun is the problem, but a well insulated house just needs shade on the windows.
For a poorly insulated house, it might be cheaper to shade it than insulate it.

shadecanopy2.jpg


11.
Wed, 07/30/2014 - 11:36

Shading exterior walls...
by Michael Ginsburg

Helpful? 0

Do you need to shade a highly insulated ice chest that has a block of ice in it? No.


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