Attic Fans

Solar Dynamic Attic Fan

One day one man or woman discovered that a planted seed, when left to the "elements", would grow, all by itself. And the whole world changed. Tribes of foraging nomadic peoples became societies of farmers, and the word "home" became a necessity and the Cave became home. And the "Elements of Nature" became an adversary. And man's continuing battle with the "elements" has become as old as his wish to leave the cave.

The "elements", Wind, Rain, and Sun, needed to be tamed, so we watched and learned. And with time we found ways to master them, and make some of them work for us. With that, we've created community, society, and a semblance of order. Eventually evolving to word we call "technology. With the social acceptance of shelter, the cave has become a forgotten part of man's past Today, it is our mastery of these elements that has allowed us to completely take them for granted, and the knowledge we'd gained for their mastery is now unknown to virtually all of us. And today with all of our new homes, cars and overhead, our new found technology is telling us that the most economically feasible place a person could live, in this perfectly structured society, would be in what is called today an "Earth structure", or "a cave". It would do us all well to remember that while we may be able to counteract the elements, and to even harness some of their foreseeable affects. We are still very much accountable to them. This document deals with one simple aspect of many concerning the elemental Impacts on a Home: "The Suns Compounding Influence."

"Oppression"

Glossary of Terms:

Heat gain: is the rate by which the suns impact compounds.
Heat load: is the compounding temperature created by sun's impact.
UBC: Uniform Building Code

Temperature Inversions

The natural ventilation of a home is, for the most part, a lost architectural protocol. The basis of the concept lies in maximizing the full potential for heat relief of the home through utilization of all natural resources available at the building site. The Natural Resources to be assessed are:

1. Existing trade winds, and known yearly wind flow patterns and/or Naturally occurring breezes flowing through the existing draws in the land, specifically through the warmer months

2. Any potential heat sink's that will either trap or draw warmer air, such as a larger canyon or gully. These geographic anomalies all have natural updrafts at their rims, and temperatures at the bottoms can be 10-15 degrees warmer. Rivers, all-seasonal streams or any full-seasonal body of water. This is very important as wind blowing over water can be as much as 10-15 degrees cooler then ambient, and in the heat of the day, evaporating water will create a natural up draft, usually drawing cooler air to the water source.

3. Planning for the use of any Existing Shade potentials.

4. Pre planning of the homes floor plan to maximize all aspects of exposure

The Foundational Theory's for Natural Ventilation

Hot air rises, expands, and looses its moisture.
Cold air sinks, contracts and hold's its moisture
And, they will not mix.

This is fundamental to understanding the Natural ventilation process, and with it we can begin to determine the steps of sun impact a typical home will experience throughout a summer day.

A New Day

Light of dawn brings heat-load. Light creates change. Light is photon irradiation, it is not matter, but it affects all things of matter. It makes electrons move faster, and that makes friction- HEAT. The heat you feel from the sun is not actually coming from the sun, it is a reaction to light that all matter must have. That's what sunlight is. This is what sunlight does.

The light of a new day peers quietly and quickly over a horizon, and all things in its path begin to warm from its touch, the pollen in the air, the morning dew, and any east facing roof of a home. This touch is gentle at first, but the affect compounds, soon the air of the day has become turbulent with uneven air pressures, as the first temperature inversion of the day begins. Fog, heavy with humidity from the dew of the grass, begins to spiral up with other expanding gases, and then become gusts, and then winds. And all surfaces under the sun just get warmer and warmer, and any air beneath any surface (i.e.-roof) begins to warm and expand and that heated air permeates every surface it comes in contact with. This is oppression. Our "Shelter" is under attack.

An attic is basically a partially vented closed environment, sitting atop another sealed structure we call a "home". It will by design, have two openings, one's at the bottom (called soffit ventilation) and one at the top (ridge vents, or airhawks). When that environment is exposed to the light of the day, a positive pressure dynamic of both heat and air is created, it's end result will be an amazing compounding retained heat load of s much as 180 degrees on a 100 degree day, directly impacting the attached sealed structure (the home) under the attic. An open-beam or cathedral ceiling home is simply an oversized attic with an even larger heat-gain and load potential. The attics of most homes will experience as much as a 70 degree increase in heat gain during the day. Peak attic temperatures as high as180 degrees are common place in localities where a typical afternoon temperature of 90-95 degrees is normal. Even with modern insulation standards (R-30 or better), this can increase the interior temperatures of a home by as much as 30 degrees.

Another Night and humidity enters the picture

At the end of the day with the dusk, the air becomes much cooler and heavier with water. Surfaces cool and contract, and the heat of the day is dissipated rapidly with the cooler temperatures as light of day falls to the dark of night. During this time the air in the attic also cools and vents, and the oppressing heat of the day is replaced with the contracting cool of the night. And slowly, all night long the positive pressures of the day once again return to ambient, as do the temperatures.

The following morning the cycle starts all over again, and now we have a new previously undisclosed element to be considered. The cooler air of the evening before, now sitting in the attic (along with the humidity and condensation that accompanies all cooler air) will not vent, as the heat grows, some of that air may find a soffit ventilation, but most will simply go where the heat isn't. When the sun begins it's relentless assault, that humid air is now being literally pumped into the attic's insulation blanket, and then into the roofing, and into the walls. Years upon years of this exposure and it becomes very easy to see this as a primary source for the occurrences of mold and mildew.

This is the cycle of Temperature Inversion, it is cyclic and for 1000's of years we were smart enough to deal with it using common sense to combat it's effects by simply situating homes locations, windows, gable vents and openings in accordance to the natural winds of the home' geography. But all that went away when we discovered that the cost of building homes was a lot cheaper when they all looked the same regardless of which way the wind blows, and that central air conditioning wasn't all that bad a way of life, if you could get past the respiratory diseases, and the on going costs. Well, the cost has now become an issue, the mold has always been an issue, but now the lawyers are getting involved. The Public Eye is now focusing on attic heat as a problem and unfortunately, there's a whole bunch of finger pointing going on with very few answers. On the other hand, the good thing about this is that there is focus. It does not take rocket science to figure out what you're reading here. By recognizing and utilizing the resources present at the building site and understanding the greater effect this temperature Inversion can have on the potential for natural ventilation, a whole new rediscovery of understanding can be expected and accepted.

The existing Attic Ventilation process of today

The first attempt at attic ventilation from the 1930's all the way into the '60's was possibly the most effective. Larger gable vents at either end of a home could provide the possibility of flow through ventilation provided the distance between the vents wasn't to long. Unfortunately, these larger gable vents generally became a source for water leaks, birds, bugs and a host of other issues. In addition to severely limiting emerging architectural designs of the day. New technology and architectural design captured the public, and declared the end of natures hold on the homes of the 21st century. Instead of working with nature, technologies we're being developed to fortify against it. From those day's to the present, design and placement of cookie cutter homes into a development that maintained positive natural resource utilization has never been considered economically feasible. Heat gain was supposed to become a "non-issue". A.C could handle the heat. Furnaces could handle the cold. Air purifiers could handle the air. Theoretically. It sounds good but it never has worked, and never will.

Uniform Building Code had pretty much become an established practice by 1966. The country had gone through some hugely profitable construction years and liability issues now required some level of standardization, still UBC soffit ventilation did not become code until 1974, and then it stated simply that all home's would have: "1.15 sq. ft of input air per cubic ft. of attic space, and an equal amount of exhaust." The concept: "Hot air rises, and as it does ambient outside air will be drawn in through the soffit ventilation. This is still the standard by which homes are built today. It didn't work then and still doesn't today.

New Ideas

The idea of a ridge vent first surfaced in 1957, the idea being that as hot air "rose", a draft could be created that should/could vacuum an attic space. Further study should that in addition any consistent breeze could also aid in this process, if they could find a way to prohibit driving rain. Ridge vents became an accepted option in the early 1970's. For the most part, they did offer a marginal level of success (temp drop of about 20 degrees) provided the ridge vent traveled the whole ridge. For the most part this product has not worked to it's fullest potential, manufacturers are still inventing different designs in hopes of finding something more efficient, but for the most part home builders have discovered that doubling up the passive ventilators can accomplish the same thing at much less cost.

The latest "answer" is really more promotional then anything else. Solar board is foil-backed roof decking, and recently it's become the darling of the high-tech house builders. It's installation is timely as it simply goes down where standard roof deck once did, so there's little to no extra expense in labor, and because it's a recognized energy-saver product there are added financial incentives for a homebuilder to want to sell it. There are many different products being offered by the lumber companies so there are aggressive retail campaigns underway. These products can make a difference to heat gain (about 20-30 degrees), and they definitely have a down side, because of the way it works (reflecting the heat back at the roofing, the potential for roofing life is greatly diminished. So, needless to say, roofing companies are very excited about the future of these products. The AC people seem to be somewhat in different, probably because the product really doesn't provide much for them outside of a little better environment for their AC's to operate. In addition, even though the product is fairly new to construction, it has become very apparent that in certain situations excessive humidity and condensation will be an on going issue, and as of yet there doesn't appear to be any answer or acknowledgment of the problem.

Another product somewhat like Solarboard is Radiant Barrier, it comes in various styles and manufacture. Radiant barrier is typically a foil or Mylar sheet role product that can be installed either on the floor of the attic or up against the roof rafters depending on which theory you hang your hat on. Obviously, the rafter installation mirrors the functions of Solarboard and because of the air space of the rafters, popular belief is that it is more effective, it is much less expensive and after-market friendly. The attic-floor installation creates a secondary seal of the home from the attic. Generally this is of no importance what-so-ever as most AC units in attic spaces are in the attic and leaving them exposed to the heat substantially reduces the effectiveness of the process. There are some who "tent" the AC units but the effectiveness of this process is not clear, and the over all integrity of the installation would be suspect at best. There have to be 100's of different manufacturers of these products now and to be sure they're over all effectiveness is pretty much established. (max temp drop-around 30 degrees). The Installation process is highly critical, as any leak will undermine everything. The real downside to these products is the resulting humidity. Condensation is a critical problem with any reflective barrier and a barrier trapping heat with any timber exposed has to be a high consideration. Unfortunately these products also have a very short sales history. So any recorded results of their effectiveness at this point would still be largely conjecture. We can verify initial temperature drop, and a substantial humidity gain. The long term ramifications are still unknown. Some of these products do have Energy-star certification.

There is also an alternative method of attic manufacture being experimented with that can only be described as a totally sealed attic. Super Insulated and air tight, it is believed that all heat gain will remain in the encapsulated attic space and actually become a heat-sinc of sorts, further cooling the home. I have had limited exposure to this, and I have to admit it sounds interesting. I can say that field testing has shown a limited amount of success and a growing issue with humidity and condensation. Along with a horrific labor cost, but then all new ideas require investment.

All of the processes mentioned so far are generally or moderately effective in their application, but over-all they fail because of the "fortify against" philosophy. The real issues are not being addressed at all, The dynamics of the daily temperature inversion, and the accompanying control or lack of control of humidity. While it is true that the deflection of heat gain can have an effect on heat loading, all of the above mentioned processes end up creating more heat in a concentrated area that can only result in a condensation issue somewhere within the spectrum of that temperature spread. Condensation is a natural result of colder air coming in contact with warmer air. On a surface that will not absorb, it can condense, on a surface that does absorb, it will saturate. Water evaporates with clashing temperature. Therefore the key lies in maintaining ambient temperatures, and it really isn't as difficult as it would seem.

In nature we can naturally seek the comfort of shade beneath a tree. There are no walls and because the sun cannot penetrate the canopy of leaves and branches the air beneath remains un-heated and therefore cooler (holding it's water), heavier and concentrated. So why do our homes not work in a similar fashion? We even construct walls and insulate them much like the cave we emerged from, and we still have heat.

We believe the answer lies in terms called "positive and negative pressurization". The canopy of a forest works through layers of cover, eventually it is that air space between the branches that renders the sun's impact impenetrable and yet still allows for air convection. So, as the sun's light penetrates the top of canopy of the forest and it warms, the air is warmed and starts to raise and expand and gust's become breezes and up drafts. Fleetingly opening the canopy to colder air down below, and that cooler air warms and begins to raise. Now, at the edges of the forest where the sun's light has been neutralized by the cool of the forest a strange dynamic begins. Because of the cooler air's affinity to contract, and the warmer air's affinity to expand, ever so slowly, air is drawn into the forest as the "warmed" cooler air begins to rise and expand (positive pressurization), and as it does the "warmer" air at the edge of the forest, air begins to cool. This in it's most natural form is "negative pressurization". And I believe the proper management of it, can solve ALL of our home heat gain and ventilation issues.

There is a lesson to be learned here also. Success lies in finding balance. The darkest forests are generally also the wettest, and maybe the hottest or coldest. Regardless, generally the air is almost unbreathable because of the overwhelming molds, which will only be found in limited air flow, and limited light situations. Their presence is part of the process, as they grow on decay, they will choke out the sun, without the sun, photosynthesis stops, foliage withers and dies, and eventually the health of the forest returns.

So, we have a model for successfully ventilating a home, and we've already got one element in place by recognizing the need for soffit ventilation. The second element will either be an 80 ft. dramatically louvered attic, … or a fan. I know this is not an exciting answer. Attic fans have been around since forever, and unfortunately there has never been much published success in their use, and frankly I would concur the 110 volt fans of today really aren't very plausible solutions. Their cost to operate will never return enough to pay for what they might save, their motors fail far to often and are expensive to service, and have significant potential as a fire hazard. But perhaps of highest concern is their thermostatic operation makes them reactive to the environment rather then proactive. 110 volt fans are thermostatically controlled, effectively putting them behind the 8 ball to begin with.

But I would reply there is alternative technology that has not been applied in a way condusive to success. The problem is multifaceted, and the fans being foisted on the public today are not capable of answering all the issues that make up the problem.
1st Heat gain and Heat load compounds, once the process has had a chance to begin it is impossible to reverse, short of blocking the sun..
2nd In 1974 UBC soffit ventilation requirements became standard, and attic fan requirements were adopted based on a 1 to 1 rate of air exchange. Any secondary air flow restriction because of heated air expansion was not part of the equation. As a result, the established CFM requirements were based on total volume of air exchange rather then negative air pressure maintained. And because of this, and the subsequent failure of fans to keep up, the process of negative pressurization was largely abandoned as ineffective.
3rd The issues of humidity and heat cannot be separated, one begets the other. Any attempt to treat them separately via mechanical isolation must be site specific, extremely expensive, as well as only marginally effective in the long term.

So, this discourse draws to a conclusion. The sun is both the cause of our problems and I believe it may well offer us the solution. Photovoltaics in particular, present very unique attributes that perfectly suite attic ventilation because of it's timely operation at the temperature inversion points of the day. The temperature inversion points of the day are right after dawn, and right after dusk. At night the world begins to cool, warm objects (like houses) give off their gained heat, and it is replaced by the cool of the evening. In the morning, with the dawn the whole process starts over again. A solar powered fan operates pro-actively, when the sun comes up, it's on. Creating air exchange before the sun's light can impact the roof and heat gain can begin, and as the roof warms it will already be exchanging the cool wet air of the night before, at such a rate that heat load cannot be established. And at night, it's off, allowing the residual heat gain of the day to vent itself naturally. The question then becomes, why would this fan in particular work while others didn't. The answer lies in application and truer definition, and probably politics.

We have proved empirically that our 20 watt solar fan exchanging 1275 CFM of air, with UBC (Uniform Building Code) soffit ventilation will effectively keep an attic of 1600 sq. ft. at/or very close to ambient temperatures throughout the day. That is an established fact backed up by 20,000+ units and 13 years of experience. It is also a statement no other product addressed here will make. And in addition, we also know that a 10 watt fan moving 850 CFM installed on a home with as little as 1000 sq.ft of attic will not keep an attic cool. It will retard its rate of loading, but eventually the sun will catch up and the fan will be overwhelmed. And in fact (2) 10 watt fans (850 CFM ea. or 1700 CFM total) installed on a 1200 sq. ft attic won't stop it either.

This is significant, because it means that the combined resistances offered by the soffit ventilation and the compounding heat gain require a higher negative pressure to keep heat load at bay. NOT MORE AIR, …but HIGHER PRESSURE. (Unofficially, we figure 1053 CFM per every 1000 sq. ft. of attic). We also know NO fan can catch up. Once oppression has begun, it cannot be reversed. The key is stopping it before it can start. One might think then that more CFM's is better, but that has not proven to be the case. Conversely, because of the set air resistences offered by soffit ventilation, and the suns impact on the roof, we've found that increasing air flow to handle more then approximately 1600 square feet of attic is equally ineffective. It's a balance.

Discussion authored and presented by:

Ron Buckner
National Sales Manager
Solar Dynamics Inc