Chapter Two |
| The worst times for solar collection are the early morning hours. There is not just one reason for this, despite what you may have "learned" from the solar experts.
The most intense (and therefore most useful) solar input is during the two hours before and two hours after solar noon. Solar noon is that time when the sun is highest in the sky - not necessarily at noon by the clock. If truth be told, the early morning hours of sunlight are pretty much a waste. The angle of inclination and the azimuth mean that not only is the intensity pretty low, but the reflection from windows or actual solar collectors is quite great. Lousy collection of energy. Having located International Solarthermics in the high Rocky Mountains in Nederland, Colorado, we often got lots of visitors worrying about the fact that sunrise was nearly an hour later than just to the east in the plains town of Boulder. The solar pyranometers and pyroheliometers that we used to instrument solar collectors in both towns soon told the tale: there was less than 3% difference in pre-solar noon collection. Now there was some additional difference due to the fact that the Degree Days for the two locations were quite different, owing to the difference between 5400 feet and 8500 feet elevations and quite different climatological ecosystems. Oh, sorry. That is just to say that it was typically colder and windier in Nederland than in Boulder. Duh... There was a larger difference in the afternoon readings. Why? Westerly collection is always greater in net BTU's because the outside temperatures on a daily basis are warmer after solar noon than prior to it. Because environmental temperatures are greater most afternoons, there is less loss by conduction, convection and radiation from any solar collector, regardless of how well it is insulated. Have you ever gotten sunburned on a cloudy day? Well, that occurs because of ultraviolet and low x-ray radiation penetrating the cloudiness to redden your exposed skin. Although the solar collector does not utilize that particular spectrum, there is still a quantity of visible light on most cloudy days. It was surprising to many of our visitors just how much heat was captured on a high cloudy day. That's why we recommend that folks open their window coverings, even on a cloudy, overcast day. Visible light enters the structure and is slowed to heat. Just lots less than on a sunny day. If you doubt this, on the next cloudy day in winter, go out and get into your car. As a moderately effective solar collector, you will feel that the car is much warmer than the outside temperature. This also accounts for our recommendations that real homes have modest fenestration on the west side. What is often overlooked by the solarists is the fact that real people live in their homes year-round. (Really) Summer sun directs upon the west side of the home much longer due to the changes in azimuth and altitude. (Much more than in winter) Lots of people do not like a super hot house in the summer time. One that can only be made habitable by adding air conditioning or a swamp cooler. Not all locations have the regular breezes that will allow cooling by the simple expedient of opening windows. Many folks are shocked by how far to the southeast the sun rises in winter and how far the to northeast it rises in summer. Thus, much of their design is predicated on some fantasy of a simple 180° arcing southern sun. One that exists only in imagination. We have a secret for you. The sun moves through an arc way less than 180° in winter and way more than 180° in summer. We can't tell you how often visitors to our facility would worry out loud about the fact that the sun disappeared after solar noon! Really, we kid you not! A kind of sequential thinking that went something like this: sun comes from east, then south, then west. South walls get no sun after noon. East walls only get sun in the morning. Dunno why they never took the time to observe the real world... With all of this instrumentation, we learned a number of other things. Although we originally oriented solar collector faces at an inclination of 35°, we discovered that a vertical collector (like the windows on your home) did not loose nearly as much energy due to reflectance from the glass face as we had anticipated. Indeed, a vertical collector at ground level with reflective surfaces on the ground before it operated within 4% to 5% of the efficiency of the angled collector, particularly once the collector surfaces were optimized for energy trapping. The advantage of this design was immediate - far less material was needed to fabricate the collector and pebble bed storage housing, and the unit was esthetically much more pleasing when integrated with a home. (Looked kinda like some sliding glass doors on the ground level) It was about this time that we finally began to get it ourselves. Solar collection, whether by a collector or by a home was a vibrantly dynamic process that involved tons of factors and you needed to account for all of them. A holistic viewpoint was necessary. The holistic approach was a bit painful for us in those early days when our livelihood depended upon selling licenses under patent to manufacturers of solar equipment. Because a rounded view of the processes involved led us to conclude that the most important components of the solar collector were some things we didn't sell: insulation and caulking. Simply insulating the home to R-19 in the walls and R-30 in the attic cut the size of the solar collector to one-third. When we first proposed these values as an excellent standard for all homes, we were featured on the front page of The Washington Post as radicals with harm in mind. They cited experts who opined in stentorous tones that "People will be killed by these recommendations. A sealed house with this much insulation will cause them to be suffocated in their sleep!" You've probably grown up in a world where (as it is in Colorado) it is the law that new homes must have R-19 in the walls and R-30 in the attic, so you have already concluded that these so-called experts were wrong. Ironically, one of the experts cited in that article was an engineering professor from Denver University in Colorado (kindness prevents us from mentioning his name) He stated bluntly that everyone knows that you shouldn't put any insulation in your attic because you will prevent the solar heat gain from the roof from penetrating the attic and entering the home. It seems to be an attribute of solar energy that lots and lots of folks who have never actually done any real research are moved to angrily state that "It is a well-accepted fact that (insert your own stupid myth here) is true in the solar community." We can't tell you how often we hear that same comment today. Holism. What does it mean in this context? It means looking at any problem from all sides, allowing all aspects to be considered. For us, it became an advocacy of active solar as opposed to passive solar applications. Why? Because most folks - not all, certainly - demand comfort in their castles. A builder would be sued if he built a home that was too cold (i.e. less than 70° F) at night or too hot (i.e. more than 76°) in the daytime. Sued, you exclaim? Yeah, unless that builder would be lucky enough to sell the home to an all-out passive solar enthusiast. That is not to demean the enthusiast - heaven forbid - instead, bless them for their commitment. Passive solar involves uncontrolled thermal masses to capture and release heat collected from solar inputs. Unfortunately, uncontrolled means uncontrolled. Worse yet, the passive solar afficionado invariably has nothing but scorn for any reasonable backup that does have control. At best, he or she will reluctantly concede that one may have a wood burning stove or a fireplace for supplementary heat. Saints preserve us from installing natural gas or propane or (gasp!) electrical heat! Active solar entails collecting heat that really is not needed in the daytime in most circumstances and storing it for recovery when it really is needed - namely, at night and on really cloudy days. As we saw earlier, most homes on most days need no supplementary heat if solar energy is available through the home fenestration. Folks who live in well-insulated homes can attest to the fact that the furnace seldom, if ever, turns on after mid-morning. Next, we need to talk about storage of thermal energy. Folks who know nothing about thermodynamics often advocate storing thermal energy in water. Unfortunately, this is a bad decision based upon partial information. Water, of course, is a much more efficient way of transferring heat than is air. But when storing heat in a tank, very little stratification occurs. This means that the highest temperature is in contact with the walls of the container. No mater how well the tank is insulated, the higher the temperature, the higher the Delta-T or differential temperature between the water and the surroundings, so heat loss is as high as it possibly can be. So, despite the disadvantages of heat transfer using air as a medium instead of water, the practical advantages for thermal storage became predominant. Using 1-1/2" to 2" washed (not crushed) river gravel as a storage medium created a multitude of benefits. Due to the great surface area of the pebbles, heat transfer from the air to gravel was high while the air was circulating. However, once forced air circulation ceased, air circulation in the pebble bed stopped, since the pebbles interfered with natural convection. Even more importantly, conduction in the quiescent pebble bed is extremely minimal. Why? Because the heat in a given pebble could conduct heat to an adjacent pebble only through that one extremely small point where the two touched. Similarly, heat transfer through the walls of the storage container insulation is also extremely minimal because the conduction portion is limited to the aggregate of the points of contact with the wall, far less than 2%. An unexpected phenomenon was the extreme stratification of temperatures within the pebble bed from the "hot" end to the "cold" end. The air flow through a pebble bed is designed so that hot air from the solar collector enters the pebble bed on the so-called "hot" side and exits on the "cold" side. But heat being removed from the pebble bed is channeled in the opposite direction, entering from the "cold" side and exiting from the "hot" side. In instrumented pebble beds insulated with R-30 insulation, the hot side of the test bed was still at 120° F after a full 30 days of stasis. Water tank storage, on the other hand, lost all heat in the 30 day period, assuming the external or room temperature. In our lectures around the country, we often posed the following problem to engineers in the audience in an attempt to highlight the problem with sequential, as opposed to holistic, thinking: a typical shower requires 15 gallons of hot water. If the home has a 40 gallon hot water heater, how many showers could be taken before the water was not comfortable? The answer is not 2 or 2 and 1/2 showers. Instead, the answer is but one. Why? Because when you take a shower, hot water is removed from the top of the tank, typically at about 120°, to mix at the shower head. However, each gallon of hot water that is removed is replaced from the cold water supply at a temperature between 33° and 55°, depending upon the time of year. 15 gallons of "cold" water mixed with 25 gallons of "hot" water will result in a tank temperature of about 90°. That's fully 8 degrees colder than your body temperature - far too cold for a comfortable shower. Are you beginning to see what the notion of holistic reasoning is all about? Ya gotta look at everything, not just some isolated factor. Like the sun being most powerful from the south. Or thinking that once solar noon is passed, solar collection ceases from the south. Unfortunately, when it comes to building a new home, most solar enthusiasts go into sequential mode. Most are, understandably, environmentalists, wanting to preserve our precious natural resources. Laudable, if implemented. Were that it were so... We saw in the first chapter that many environmentalists will build a log cabin as the environmentally sound thing to do without even considering that they are hogging the wood that could go to build 10 or 12 homes. Similarly, they will insert it in the midst of trees with no consideration of fire hazards to the structure or from the structure if they use (as is typical) a woodburning stove. If environmentalists of this ilk were environmentalists, chimney cleaners would be everywhere. Tried finding one lately? The trees block solar inputs to the home. So even more wood is burned. Ever noticed that somehow it is OK to burn wood inefficiently but awful to burn any other fuel? Yet others insist that the only clean heat (aside from solar) is electrical heat, because it doesn't pollute. Yeah, right. Perhaps not in the vicinity of the house. But electrical energy is 3 times as expensive as other energies for a reason. Due to a combination of problems, such as peak usage times and transmission line losses, only 1/3 of the energy produced at the coal burning power plant is ever delivered to you, the end user. And, of course, there is never any pollution from the power plant. Our favorite environmentalists are arrogant beyond belief, looking down with contempt at the ranchers and farmers who surround them and provide them with safe and inexpensive food as environmental despoilers. It is a truism that only the environmentalists care about the environment. Everyone else is a rabid polluter and savage environmental destroyer. We try not to confuse such as those with facts, since their minds go into the ether whenever we try. Facts like the ranchers and farmers loving the land they own, being much more careful stewards of the environment because their livelihood depends upon preserving it and nurturing it. Not to mention their love of the land their parents and grandparents handed down to them. The loud ones would be dismayed to know what the farmers and ranchers think about their clots of subdivision homes clustered on tiny city lots, cheek on jowel with each other, listening with rapt attention as their neighbors flush the toilet. Ever thought of just how "environmental" gazillions of homes plopped in the middle of the wilderness really are? We get a kick out of the environmentalist who calls 911 to complain about an elk in the garden and could someone come out and shoot it? Somehow, protecting the environment is always much more comfortable if it is someone else doing the protecting. But, back to building logical homes. We hope you agree that a log cabin ain't the best solution. Straw bale and tire houses both have an intrinsic appeal to folks wanting to opt for an alternative to the traditional forms of construction. Nothing wrong with that. Especially if the home is being built by the homeowner. Labor costs don't really matter in such a situation and they shouldn't. It is more like a quest and we should all laud such efforts. But damn few people have the time or inclination to endure the hardships of erecting such structures, no matter how satisfying it might be. That means that most people will need to buy a home built in a factory (a so-called modular home) or one built by a contractor. Here's a little secret. General contractors are generally not terribly altruistic or philanthropic. The dirty bastards want to make a profit! Yes, we know that is a deplorable situation. Wouldn't life be better if contractors would build a house for free? But, even if they did build for free, the enthusiasts would be disappointed to learn that most, not all, people think straw bale houses and tire houses and berm houses are really ugly. Yeah, we know those ordinary folk are unenlightened clods who are desperately in need of an education. But most of them prefer homes that look like homes. Like the homes they grew up in. Comfortable and controlled like the homes they are used to. Try selling a new home made out of paper or stinking tires or moldy hay. Argue that it is every bit as good. See how many you sell to ordinary folk. The enlightened contractor will indeed endeavor to "build green". It's only good business. Using plentiful pine siding in lieu of the less expensive vinyl siding is one such concession that we recommend. We also recommend asphalt/fiberglass shingles for roofing instead of the probably more aesthetically pleasing wooden shakes. Why? Because fire is a danger and wooden shakes are just plain reckless. Sustainable forest wood products are to be preferred, if practical. But if some mill is doubling the price of a product because they have "certified" it to be sustainably grown, the contractor is going to look elsewhere. If he or she didn't, the house price would balloon out of reach for the potential home buyer. Plus, truth be told, nearly all wood available from your local lumber yard is from "sustainable" sources. Damn little virginal forests being logged anymore, unless you are specifying an exotic wood like bubinga. Weyerhauser and Boise Cascade grow their own stuff these days. Yeah, wood is really simply another crop like beans or peas. Marketability of the ensuing structure must be the prime consideration. There are seclusion people and there are view people. The building site must be chosen with one group or the other in mind. But if view is selected, then the house plan must emphasize that view with all appropriate fenestration, regardless of the orientation. If you are appealing to the seclusion folks, obviously a lot without trees won't do. Ain't no use building a home no one will buy. Or building one you can't sell for a profit. If you ignore these realities as a builder, you won't be a builder long. Ya gotta pay your help and your subcontractors. The rascals are really insistent about that...
|
