a place for the growies

The early color renditions of the house prepared by The Architect showed the middle of the house (the thorax so to speak) clad in stained wood. I wasn't real happy about that wood. Don't get me wrong, stained wood looks awesome, and it looks awesome on the house. Wood adds warmth to the structure, and I'm all over that look achieved with subtle variations of color. However, the upkeep concerns me. That stained wood doesn't seem to fair well in our climate, at least not with quite a bit of upkeep. So instead of wood, the current design calls for Hardie board of a color yet to be determined.

To soften that side of the house (and provide some shade), The Architect added a wire mesh (think cow panel) trellis. The current thought is to have deciduous vines (The Architect refers to all plant life as "growies") grow up the trellis to provide shade and softness in the summer, something similar to the photo above of a MetroHouse in Austin just off of North Lamar.

Near our lot is a mixed use building that has gussied up their parking garage with a modern-looking sculpture grid. It's a neat look that might work well as a trellis when scaled down. In fact, something similar could also be used for the gate and the railings inside the house and on the back balcony. The one pictured above is made from tubular aluminum. Of course greater customization = greater cost, and aluminum tubes cost more than cow panel... I did, however, find a relatively affordable source of aluminum at speedymetals.com, so who knows. Perhaps this is a post-construction project...

Now that wood is off the table for the thorax, the question becomes: What to replace it with? Hardie board, yes, but what color? hmmm... Hard to say. Seeing some (white?) cedar weathered to a grayish lightness near our house makes me wonder if white cedar, left to its own devices, would, in fact, be a good choice. However, that weathered look may be due to the brutal drought we're presently suffering. Choices, choices...

[photos by mwah except (1) rendering of the house by The Architect and (2) white-weathered cedar from AltruWood]

I'll huff and I'll puff and I'll blow your wall down!

The passivhaus movement has gotten me interested in energy efficient wall and roof design. As it turns out, there’s more to a wall than nailing a few two by fours together and covering them with Hardie board. Ultimately, a wall needs to be designed to address expected weather conditions. A poorly designed wall will cost you money in increased heating and cooling costs and could, in wet and humid climates, reward you with a serious mold problem. Interestingly, there is a push and pull between designing walls for cold versus hot climates: design choices for hot sometimes work against choices you would make for cold and vice versa.

Down here in the hot and humid south, we have to mostly worry about heat and moisture. That makes me a little suspicious of the passivhaus standards which are strongly influenced by the climate in their German birthplace. Nonetheless, the goals of passivhaus are admirable but perhaps need to be adjusted for our southern climate.

A great resource I’ve found on wall systems is the Building Science Corporation website. They have a number of free PDFs about various building science topics, including those specific to various building climate zones across the United States. And they have quite a collection of articles on wall systems. They also have a nicely written general article about highly insulated wall systems for the United States. Building America, a program by the U.S. Department of Energy, also provides energy efficient building design suggestions, although they generally have less ambitious goals than other programs. Nonetheless, they have climate-specific resources, case studies, and economic analyses that are quite useful.

So what do these folks suggest for houses built in Austin, Texas?

We are building in Climate Zone 2. For this zone, the Building Science Corp recommends walls of R-15 (R refers to the amount of insulation; the higher the number, the higher the amount of insulation; 3.5 inches of your standard fiberglass batt insulation has an R-value of 11), windows with a U of 0.35 and an SHGC (solar heat gain coefficient) less than 0.25, a roof of R-40, a slab edge of R-5, and nothing for under the slab. A different article about a house built near Houston that strove to meet these standards passed on the slab edge insulation to avoid creating a potential pathway for termites. These R-values are probably lower than those of passivhaus standards, “probably” because passivhaus is about reaching certain energy use goals—the R and U values to get there depend on your house as whole. For comparison, the Louisiana passivhaus has walls of R-28, a roof of R-55, a crawlspace of R 16.5, and windows with U’s in the neighborhood of 0.20. The Austin passivhaus has walls of R-60, a roof of R-30, a crawlspace of R-30, and windows around U-0.25 to 0.30.

Building Science Corp attempts to balance cost with performance (and hand-in-hand with cost is the familiarity of the trades with high-efficient wall systems), hence the overall lower R values and higher U values than passivhaus. Furthermore, the Corp’s guidelines are independent of whole-house performance. As far as a wall is concerned, the amount of window coverage has a huge impact on the overall performance of the wall. For example, the wall for the Austin passivhaus is R-60, but those windows are R-4, greatly reducing the efficiency of the wall and the house as a whole (vampires probably have the most energy efficient homes around…).

I’ve also been following a blog by Gregory La Vardera who has recently been writing about wall systems. Something intriguing that he proposes is horizontally furring the interior side of exterior walls with two by twos. This gives a pathway for pipes and wires without compromising the insulation, and hence the R value, of the outside wall. Apparently, electricians and plumbers are notorious for hacking away at wall systems to get their job done, thereby compromising the energy efficiency of the design. Maintaining the integrity of the wall system is doubly important for homes that require some flavor of vapor barrier toward the inside of the house (typical for colder climates). A vapor barrier with lots of holes in it is hardly a vapor barrier. Fortunately, in hot and humid climates, the vapor barrier is typically toward the outside of the wall system.

I don’t know the gory details of what The Architect has planned for our walls at this point. The outer walls are two by sixes, and we’ve talked about closed-cell spray foam, although sprayed-in cellulose seems to be the preferred choice for greenies (and it’s less expensive than foam). We plan to use advanced framing, which minimizes thermal bridging (pathways for heat to move into or out of your house, usually through the framing). One builder we talked to felt that the roof was the most important feature in our climate and suggested a metal roof painted white to reflect the brutal Texas sun as much as possible. Passivhausers as well as others work to include thermal breaks in wall and roof design, especially in hot climates. Any hunk of wood or metal that extends from the exterior of the home to the interior provides a pathway for heat. A thermal break is generally accomplished by covering the exterior with non-structural insulation sheathing (this can also be accomplished with structural insulation such as structural insulation panels, what the cool kids call “SIPs”).

So, here is what I’ve learned about what should be done in our hot and humid climate:

From Building America (a Department of Energy program that strives to produce houses 30 to 50 percent more efficient than those that meet the 1993 Model Energy Code):

- Slab: Should have 6-mil polyethylene sheeting directly under it to control vapor and provide a capillary break (to prevent water wicking through the slab and into the house).

- Slab: Sub slab drainage should consist of a gravel capillary break beneath the vapor retarder.

- Slab: Don’t use sand anywhere; address differential drying and cracking through low water-to-concrete ratio and a wetted burlap covering during the initial drying.

- Walls: No vinyl wallpaper on the interior of exterior walls; wall coverings need to be breathable.

- Walls: No vapor barriers on the inside of outside walls

- Walls: Backprime all wood used on outside of house

- Walls: Create an airspace behind every outside surface and provide for drainage. This is especially important for brick and masonry.

- Walls: Use either interior gypsum board, exterior sheathing, or both as air flow retarders.

- Walls: Ensure that plumbing, showers, and tubs on exterior walls are properly sealed: These are often where the largest penetrations in the house occur.

- Ceilings/roof: No recessed lighting into unconditioned spaces.

- Walls: No need for a rain screen, but a need for a drainage plane/drainage space.

From Building Science Corporation on building in hot and humid climates:

- Walls: Need to dry to both the interior and exterior.

- Walls: Bricks are “reservoir claddings”: They store moisture. Sun that comes out after a storm can drive that moisture to the interior.

- Walls: The drying potential of a wall decreases with the level of insulation and increases with the rate of airflow.

- Walls: Clad and tape exterior walls with 1 to 4 inches (2 inches recommended for hot and humid climates) of non-structural exterior insulation sheathing (such as expanded polystyrene [EPS], extruded polystyrene [XPS], or polyisocyanurate [polyiso], rigid fiberglass, or mineral wool)

- Roof: 4 inches of nonstructural exterior sheeting, preferably in 2-inch lifts where the lateral seams between sheets are staggered between the lifts.

- Roof/ceiling: Use gypsum board as air barrier; however, that means that there shouldn’t be any ceiling penetrations.

Images respectfully cribbed from Building Science Corporation.

cool blog: Green House, Good Life

While considering making an offer on our lot, we walked and drove around the neighborhood, getting a feel for potential future environs. Besides the trees and nice streets and (generally) well kept lawns, we noticed a nice Craftsman-style house going in a few blocks away (a good sign, methinked).

In addition to walking the hood, I poured through the neighborhood newsletters to learn about issues and whatnot and was pleasantly surprised to find an article about the house and its various green amenities, especially its geothermal. "Hmmmm", I hmmmmed to myself, "I hope we get to meet these folks someday."

Then, a couple-few weeks ago, I got my first comment on this blog, and it was by Devon, one of the owners of that house! Because she's a blogger via Blogger (soon to be named something else [grrrrr...]), I was able to track her back to her blog, Green House Good Life, and lo and behold it was the same Green green house a few blocks away! I devoured the blog over the course of a long weekend (If you're building or thinking of building, it's a darn good read) and thoroughly enjoyed it. Well written, informative, and helpful. I highly recommend it. It's still an active build blog as Devon and her hubs continue to polish the house (solar anyone?) and work on the landscaping. And we're so fortunate to have nice folks right around the corner to learn from (and lean on?) as we embark on our own build.

objects in mirror are closer than they appear

The Architect surprised us at a meet-a-potential-builder meeting with a scale model of our house. Purdy darn cool! I made a made-to-scale poorly dressed me and she (and cat) to try and put things into perspective. And holy gibbering garbanzo beans: The house seems huge!

One of our (first world) struggles is understanding the size and scale of the house and rooms and whatnot. Having a little me and she (and cat) helps (note that the Isetta is not at the proper scale...).

[photos by mwah!]

getting hot and bothered about geothermal

The Architect has been hot about geothermal and, having a degree in geophysics and hearing about the potential energy savings (up to 50 to 60 percent!), I’m warming up to the idea. However, that geophysics degree cuts both ways, so I’ve not been entirely convinced, especially since we heard the city’s HVAC guy allude to heat buildup issues.

Ground source heat pumps have been around for quite awhile. The first ground source heat pump (coils in trenches) was installed at a home in Indianapolis in 1945. Since that time, more than a million systems have been installed across the United States. Despite that, it’s still considered an innovative technology, primarily because there are not many system installers and, despite the one million installations, not all that common.

First, a word about terminology: Merriam-Webster defines geothermal as “of, relating to, or utilizing the heat of the earth’s interior.” Traditionally, geothermal refers to tapping into the earth’s heat for energy. For example, Iceland is a world leader in green energy due, in large part, to its geothermal resources. Geothermal as used in the context of HVAC systems is actually a ground source heat pump. Yes, heat from the earth is harvested to heat the home (albeit with a heat pump), but the earth is also used to dump heat accrued during the cooling season. Other names for this technology are geothermal heat pumps, earth-coupled heat pumps, earth exchange systems, and GeoExchange systems, the latter a protected trade name. Despite the usage of geothermal in the title of this post, I will use the term “ground source heat pump” because it’s a more technically accurate term than geothermal.

Ground source heat pumps use the earth to increase the efficiency of heat transfer for air conditioning and as a source of heat for heating. Below a certain depth, typically 10 to 20 feet, the earth is at a constant temperature, reflecting an average of the year’s overall temperatures (unless you live near a magma body, in which case you probably shouldn’t be living there!**). For example, the ground temperature in northern Minnesota is about 37 degrees F while the ground temp in Austin, Texas, is about 71 degrees F. Given that the ground temperature is a function of the average air temperature and air temperature is governed in large part by the sun, ground temperature is a form of stored solar energy.

Heat naturally flows from higher temperatures to lower temperatures via conduction. A heat pump induces heat to flow from a lower temperature to a higher temperature, hence the word “pump”. A standard air conditioner is an air source heat pump. It pulls heat from your inside air and transfers it to the outside air. A refrigerator is also an air source heat pump, pumping heat from the fridge interior and transferring it to the exterior (which is why it’s important to keep those coils on the back dust free and breathable). The reason ground source heat pumps are more efficient than air sourced heat pumps is because the temperature difference is greater at the heat sink. Dumping heat into the ground at 71 degrees F consumes a whole lot less energy than dumping heat into the great outdoors at 104 degree F.

There are several types of ground source heat pump systems, including closed loop and open loop. I’m only going to dwell on closed loop systems because (1) that’s what’s most common in Texas and (2) the water conservationist in me is appalled with open loop systems which commonly pump groundwater and then dispose of it. There are also horizontal loop and vertical loop systems. Again, because they are most common in Texas and in urban settings, I will focus on vertical loop systems.

A typical HVAC system, such as the one we have in our current house, has an air handling unit inside the house and a condensing unit located outside. The air-handling unit moves air from the house into the unit and over cool evaporator coils coursing with chilled refrigerant. The heated refrigerant is then moved to the condensing unit where the refrigerant is cooled and condensed (which is why there’s always a fan blowing out there) before it’s moved back into the house to start the whole cycle over again. An HVAC system using a ground source heat pump works in a similar way except that instead of transferring heat to the air via a condenser the heat is transferred to the ground by first transferring the heat to a water/antifreeze solution via a heat exchanger and then pumping that solution through tubing buried in the ground. The tubing forms a loop through which the water is circulated such that the solution is cooled by the time it makes the full loop. The cool thing about this (besides the resulting conditioned air) is that there is no need for an outdoor condensing unit: more room outside and no fan blowing and going all summer!

Heating in a typical HVAC system is accomplished by pulling air into the air handler and across an electric heating element or a gas-heated element. A ground source heat pump works in the opposite direction during the heating season where the coils on the inside are now used as a condenser instead of an evaporator and the earth tubing is used as a source of heat instead of a sink.

The length of the tubing exposed to the earth is an important consideration and is a function of the thermal properties of the ground at your particular location, how big of a system you need (tonnage), ground temperature, groundwater flow, the diameter of your borehole, what you fill the borehole with, and how close your boreholes are to each other (or any other ones in the area).

Distance between boreholes is important to prevent thermal interference between the boreholes. The rule of thumb is 20 to 25 feet between each borehole with about 150 to 300 square feet of land per ton of system capacity. Ideally, borehole spacing should be based on the more specific thermal attributes of your location. The National Ground Water Association says that rules of thumb should not be used when sizing these systems (I include them here as a screening test. For example, if your contractor wants to place your boreholes 5 feet apart, you may have an issue and can start asking questions). There are manual and numerical methods for calculating the length of borehole needed to achieve the desired cooling and heating effect. Hopefully your contractor knows how to run these numbers. Given that a lot of assumptions are made on thermal properties, you'll want to go along with any safety factors built in, even though it may increase the cost. While it's possible to test and quantify the thermal properties at your location, this is typically not done unless your system is expected to require more than 100 tons of cooling.

There needs to be a good thermal connection between the borehole and the earth. Early ground source heat pumps struggled because installers used non-thermally enhanced grout (grout is the stuff that backfills the borehole around the tubing). Thermally enhanced grouts can reduce the depth and number of boreholes. When grouting, it’s critical that the grout doesn’t bridge in the hole creating large air gaps. Air is a terrible heat conductor and will greatly decrease the efficiency of your system. Being a hydrogeologist, I have some experience with drillers. Drillers are infamous for cutting corners on the way to getting the job done, especially if they’ve fallen behind (it’s difficult to check their work when it’s hidden…). Therefore, it’s critical to have a technician babysitting the rig and the roughnecks. Preferably the technician can cuss like a sailor: It was sitting on drill rigs that I learned how to use the f-bomb as a noun, verb, adjective, and adverb, often all in the same sentence.

Drilling is a messy business; therefore, it’s critical to keep the inside of the tubing clear of mud and dirt. According to some experts, lack of cleanliness has caused many a system to fail or serve at a less-than-ideal efficiency.

A shallow water table helps to enhance the thermal connection to the earth because the fill materials will likely become saturated with water. Even enhanced grout typically has lower thermal conductance than the ground itself; therefore, smaller diameter boreholes tend to have better performance (but they increase the chance of bridging…).

High-density polyethylene pipe is typically used for the tubing. High-density polyethylene pipe typically has a 50-year warranty with independent tests suggesting a 200-year lifespan. Pipe joints should be thermally fused (that is, melted together). This material and fusing is what is used for natural gas lines (with a reported 1,000 year expected lifespan). Other methods of joining pipes have been shown to fail over time.

Most installers use geothermal transfer fluid, something the cool kids called GTF, which consists of water and methyl alcohol (to prevent freezing), in the tubes. If the tubes leak for some reason, you won’t have a hazardous waste site on your hands.

Using a ground source heat pump will impact temperature in the earth, albeit locally. Ideally, you live in a place where the amount of heat you put into the ground during the cooling season equals the amount of heat you pull out of the ground during the warming season. Because of unretrievable heat loss around the fringes of your boreholes, this ideal climate would require slightly more cooling than warming. Unfortunately, very few of us live in this ideal climate; therefore, the ground will have a net heat loss or heat gain resulting in a decrease or increase in ground temperature over time. This overall change in ground temperature will decrease system efficiency over time. That’s the bad news. The good news, at least for homeowners, is that this typically only happens with larger commercial systems (many more system tons; therefore, many more boreholes) and not home systems (although it could if the system is not designed properly). Nonetheless, boreholes need to be spaced farther apart in Texas than elsewhere in the country because of our cooling dominated climate.

Design software typically only considers the conduction of heat in the ground. The movement of heat via groundwater flow (advection) is another potential source of heat dissipation; however, water has to be able to flow quite freely for there to be a benefit. Given that our lot is over the Austin Chalk and that groundwater doesn’t move very fast through the chalk (it still has a fraction of its original seawater in it, fer cry eye!), only considering conduction makes conservative sense. The density of the Austin Chalk as well as its lower porosities and saturated condition maximizes its thermal properties.

An addition to a ground source heat pump system that can bleed off some of that heat and also save energy is a device called a “desuperheater” (I picture the little guy on Fantasy Island opening the water heater closet and yipping “De Superheater! De Superheater!”). A desuperheater harvests heat from your central air conditioner’s compressor to heat your water (according to my engineer bride, desuperheaters are also used at power plants). For a ground source heat pump, instead of dumping all that heat into the ground, it gets used to warm your water. Brilliant! A supplemental heat rejector to deal with our cooling-dominated climate! In fact, desuperheaters are highly recommended for cooling-dominated climates (they don’t help you out at all when you’re not using your air conditioning).

A desuperheater can provide about 5 to 8 gallons of hot water per hour per ton of cooling capacity. In an average climate, it can provide 20 to 40 percent of a home’s hot water )and you gotta believe that's higher here in Texas). It provides a greater cost benefit in homes with electric water heating than gas water heating because heating water via electricity tends to be more expensive. Given Austin’s warmer-than-average climate, a desuperheater can reduce water heating energy costs by 85 percent (!!!) if you heat your water with electricity and by 60 percent if you use gas. Given that heating water by natural gas is already 60 percent less expensive than using electricity, the cost saving are considerably less (48 bucks a year for gas versus 152 bucks a year for electricity). However, despite the lower savings, there should be a hidden efficiency benefit for the entire system by using the desuperheater as a pre-earth circulation heat rejector.

If you’re using electricity to supplementally heat your water, you can get a single tank, although some recommend a separate buffer tank for the desuperheater regardless of the energy source. If you are using gas, you’ll need a separate desuperheater tank to preheat the water before it goes into your water tank (haven’t quite figured out why yet…). Kind of a bummer, but there are desuperheater tanktoppers to reduce the footprint of the extra tank. An added plus of a tanktopper is that it pre-preps you for solar water heating (something to consider for the non-cooling months). And yes, you have to have a tank for the desuperheater (the harvested heat has to be stored somewhere); however, none other than the U.S. Department of energy says you can use a desuperheater with a tankless water heater.

Here’s a comparison of annual cost between different types of heating and cooling systems in Austin according to Action Mechanical Systems:

Heating AC Hot water Total

All-electric: $864 $689 $179 $1,732

Natural gas: $418 $689 $75 $1,182

Geothermal: $182 $415 $27 $624

A ground source heat pump with a desuperheater can result in energy bills 64 percent lower than an all-electric system and 47 percent lower than a natural gas system. That’s rather amazing! And according to the American Society of Heating, Refrigerating and Air-Conditioning Engineers (I hear their conferences are off the hook…), maintenance costs for ground source heat pumps are 11 percent lower than a natural gas system and 17 percent lower than all electric air source system.

Designing and installing a ground source heat pump requires some special skills and experience. It’s recommended that the contractor be certified by the International Ground Source Heat Pump Association and have considerable installation experience. Engineers and system designers can become Certified GeoExchange Designers via the Association of Energy Designers. Drillers should be certified by the International Ground Source Heat Pump Association. In addition, the State of Texas licenses water well drillers for the drilling of closed-loop geothermal wells.

But what about cost? Unfortunately, up-front costs for these systems can be quite a bit more than a standard system (one source suggested twice as much). In defense, practitioners point customers to the much lower cost to heat and cool after the system is put into service. One source noted that a geothermal system can be a money maker right away if the additional costs are wrapped into a home loan. For example, if financing the additional cost of the geothermal system adds $40 a month to your house payment but you’re saving $70 a month, you’ve just put an extra $40 a month into your pocket. A pretty convincing financial argument assuming you have some headroom on your financing. There also may be financial incentives to take the edge off. Last I checked, Austin (may) offer a $500 to $1,250 rebate depending on the efficiency of the system and whether or not you include a desuperheater. The feds may offer a rebate as well.

Some folks around the corner from us (we met them via the blog) recently finished a Craftsman-style green house (literally and greenily!) with a ground source heat pump, and they were kind enough to give us a tour (they even showed us their desuperheater, which I now have a far greater appreciation for…). They seemed pretty happy with their system.

So, after almost writing a thesis on this topic (sorry...), where does that leave us? I’m just about convinced that we should put one in. Next step is to talk with a ground source heat pump contractor and see what the cost difference is. As you know, it’s all about the green: the green green and the Benjamins…

Sources used for this post:

Geothermal Heating & Cooling Systems

Geothermal Heat Pump Design Manual

Heat Pump Water Heaters

Builder Guide: Improve Energy Efficiency with Desuperheaters

Residential Heat Pump Water Heaters

Advances in Modeling of Ground-Source Heat Pump Systems

Guidelines for the Construction of Vertical Boreholes for Closed Loop Heat Pump Systems

An Information Survival Kit for the Prospective Geothermal Heat Pump Owner

Retrofitting the Workforce: Geothermal Heat Pumps (focused on Texas)

GeoExchange

** As you go deeper the temps gradually increase because of the geothermal gradient caused by a molten hot core bleeding heat to the surface.

Photo from Wikipedia Commons.

the appliance from hell: the lowly clothes dryer

One thing that’s neat about passivhaus is the unholy fixation practitioners have on heat sources and sinks. Stuff you (or at least I…) don’t think about. Like the thermal impact of flushing a toilet. While that impact is (presumably?) minor, some thermal impacts are not. The one impact that has kept me up at night sweating and shivering in the corner is the appliance from hell, the lowly clothes dryer.

Before considering the lowly clothes dryer in the context of passivhaus, I thought of that white jiggly box in our house as something to (ahem) dry our clothes. You put clothes in, you turn it on, you come back later: dry clothes! Instead, I now see it for what it is: A well camouflaged thief—an embezzler, really—who skims off the top and steals your money.

The crime the dryer commits is multi-faceted. First, it pilfers your cool air. Just plumb takes it. I was enjoying that cool air, fer cry eye! And I paid to cool it! That's right, the dryer pulls air from its surroundings to do its deed. Second, it then uses valuable electricity to warm that cool air to drying temperature. Begin sobbing here. And third, it ejects that air to the outdoors, creating a negative pressure in the house through which hot air seeps back in as make-up air from Gawd knows where, which I then have to cool so the dryer can warm it up again. It’s a miracle I’ve gotten any sleep at all lately!

Amazingly, there isn’t a dryer on the market (that I am aware of) that uses outdoor air to dry your clothes unless your dryer is already outdoors such as in the garage or on an unconditioned back porch. The dryer in our current house is on our back porch. I figured we were low-rent: turns out we are passivhaus pioneers! Tellingly, the local passivhaus dude plans to put his dryer on a back porch.

There are options. Such as the helpful suggestion by the passivhaus creator, Dr. Wolfgang Feist, to dry your clothes on a clothesline. And while I find drying clothes on a clothesline vaguely romantic (we indeed do it from time to time), it’s not a good all-the-time option. There is also something called a “drying closet” which is essentially an enhanced indoor clothesline in a rather large box. There are also condensing dryers, built for cases where there is no place for an exhaust. However, reviews of these critters are mixed with none other than the Canadian government advising against them.

Our current dryer had to get serviced recently, and I took the opportunity to gaze at its innards to see if I could connect hosing to supply it outside air. The repairman thought I was nuts (“Dude: It doesn’t use that much air!” “But, dude, have you seen that sucker blow! It‘s 200 cfm!!!”). I’m thinking we’ll chose our next dryer based on whether or not we can make this modification.

Given that it seems to be getting hotter around here (two days of record-setting temps at 105 degrees…), I’m hoping that manufacturers will start making appliances for different climates. For example, having a fridge with a condenser that could be placed outside (we don’t put our AC condensers in the house, now do we?). Until that time, it appears you’ll see me stumbling about town with dark bags under my eyes (and higher electric bills).

can you overinsulate?

I was wondering about this in a recent post: can you overinsulate? Apparently I'm not the only one. Reduced to first principles, heat flows as heat flows, so it seems that what's good for keeping heat in is also good for keeping heat out. My bride (the engineer) and I have chatted about this from time to time (it's that kind of exciting relationship...), and it's mentioned in this article and debate over at Green Advisor: perhaps it's due to temperature difference. The temperature difference in Minnesota is larger than the temperature difference in Texas. Up north, you may be fighting to keep the T at 75 inside while it's 10 below zero outside (a difference of 85 degrees!). Down south, you may be fighting to keep the T at 75 inside while it's 105 outside (like today...), a difference of "only" 30 degrees. Perhaps this is why energy recovery ventilators work better (greater efficiency) in heating climates than in cooling climates?

Furthermore, there are a lot of heat sources in a house: the stove, the computer, the TV, the cat, you. In a heating climate, these heat sources help you. In a cooling climate, they hurt. And there's the humidity issue. I like the comment in the article about someone sometime designing appliances for a hot climate. I'm still losing sleep over how a clothes dryer takes indoor (cool!) air, warms it up, and then disposes it the outdoors. Not cool! (so to speak...). Certainly not efficient.