Passive Solar Cooling
Across America, today’s buildings consume 39 percent of our nation’s primary energy and 70 percent of our electricity. This is more energy than any other sector of the U.S. economy, including transportation AND industry. The air conditioning electricity requirement for hot humid states like Florida is about 10 percent more than the electricity consumed in the rest of America. Sadly, Florida unwisely produces about 40% of its electricity from dirty coal and 40% from expensive imported petroleum – giving Florida very unhealthy (deadly) air pollution, and huge volumes of greenhouse gas emissions, which contribute to man-made Global Warming, which provides thermal energy for deadly Florida hurricanes.
Eliminating conventional power-company air-conditioning in hot humid climates is both extremely important, AND a challenging technology education issue for environment-damaging business-as-usual architects, builders, and homebuyers. This material is therefore a very important portion of Zero Energy Design’s goal for Abundant Energy In Harmony With Nature.
Many so-called “energy experts” have incorrectly stated: “Passive solar systems do NOT work in hot humid climates like Florida.” This statement is partially correct IF you constrain your simplistic thinking to conventional single-shell houses, but this ignorance is quite false IF you understand the powerful science documented by Zero Energy Design.
We hope that the reader will remain open to the practical cost-effective easy innovative implementation that we recommend herein. The ZED “Thermal Buffer Zone architectural design pattern” creates a whole new environment of exciting opportunities for using solar energy and state-of-the-art Zero Energy Design to eliminate most expensive conventional summer cooling requirements in hot humid climates.
The ZED Thermal Buffer Zone (TBZ) (introduced in Chapter Eleven) is extremely valuable thermally and aesthetically both winter AND summer. Two small Delta T’s are always better than one larger Delta T, whether the exterior is below freezing with wind chill, or hot and humid with a high apparent temperature heat index. The beautiful large glass area of a ZED solarium is ONLY possible with a Thermal Buffer Zone design, since it would be a thermal disaster on a single-shell home in a hot climate. In quick summary, the ZED Thermal Buffer Zone summer design:
(1) Helps reduce or eliminate most conventional cooling energy requirements, and
(2) Allows the most attractive visual home designs, and natural daylight throughout the entire home, of ANY architectural alternative design pattern available today.
To order a copy of the U.S. DOE / ORNL Workshop handout CD-ROM Click here
We introduce “Passive Solar Cooling – Use Sunshine To COOL Your Home” in Chapter Six of our ZED eBook. Everything we discussed there applies to Thermal Buffer Zone home cooling. (You may wish to review Passive Solar Cooling before you proceed.)
We start with the basics of summer energy conservation, cool roof, radiant barrier roof decking, no west facing glass and well-insulated (low infiltration) roof, ceiling and walls. We make sure that things like clothes dryers and fireplaces are NOT sucking cool air out of the inner living quarters, and replacing it with hot, humid, dirty, unfiltered air from outside. We eliminate incandescent lighting and inefficient appliances. Minimized photovoltaic systems give us some solar-powered electricity to work with.
Where auxiliary air-conditioning and interior dehumidification are required part of the time, we are careful to NEVER run any air ducts in any unconditioned space (like the garage or the attic).
This is EXTREMELY IMPORTANT. It can be implemented in many clever ways. In a single-story house, higher ceilings can be used. Vents can be hidden in spaces above kitchen cabinets, lowered hall ceilings, false vaulted ceilings, etc.
Earth Sheltered Thermal Buffering
2400 years ago, the ancient Greek city planners accurately determined that the most desirable place to locate buildings was the South / Southeast side of a hill (or mountain) with a nice view to the South (like the city of Priene). If you can find and afford such a near-perfect piece of real estate, consider yourself very lucky. A cut into the hillside, and an Earth berm buffer zone on the North (east and/or west side, and optionally an Earth covered roof with greenery) is a VERY ENERGY EFFICIENT, esthetically pleasing Zero Energy Home location.
The energy requirement for such a beautiful Earth berm home will be the minimum possible. In the hottest climates, a cool tube, with downhill condensation drainage can be used for hot Summer days, but the Earth berm will probably eliminate the need for a cool tube, since much of an Earth sheltered house is underground (depending on site characteristics).
Get More Great Information Sources in Larry Hartweg's 800 page book on
Passive Solar Heating and Cooling Techniques
"Zero Energy Design"
Absorption Chillers
In the more tropical portions of the Southern U.S., where air temperatures peak above 90 degrees Fahrenheit in the day, humidity is high, and overall low night time temperatures remain above 80 degrees, a solar-powered “absorption chiller” can be used to reduce air temperature and humidity in the interior living quarters down as low as any human could possibly desire.
The absorption chiller concept is unfamiliar to most homebuyers, architects and builders today. They are skeptical about everything that they do not understand.
In the 1920’s, this reliable, low-cost, noiseless, phase-change, absorption cooling technology was used extensively in “gas refrigerators”, especially in urban-and-rural homes that had no electricity. Many modern designers are not familiar with the characteristics or economics of absorption cooling. It revived for use in Recreation vehicles, and now for Zero Energy Homes.
A water-based absorption chiller can inexpensively drop the temperature down to 40 degrees. Other non-water versions can go well below freezing for making ice, etc. When powered by concentrated solar energy (instead of 1920’s natural gas), absorption chillers cost almost nothing to operate, and have essentially nothing in them to wear out (as do today’s noisy, expensive, electromechanical freon-compressor-based air conditioners and refrigerators, which have to be replaced at high cost every few years). The heat source causes circulation, fluid/gas phase change, and cooling.
To order a copy of the U.S. DOE / ORNL Workshop CD-ROM Click here
Get More Great Information Sources in Larry Hartweg's 800 page book on
Passive Solar Heating and Cooling Techniques
"Zero Energy Design"
Contact ZEDmaster@ZeroEnergyDesign.com
Video, Passive Solar COOLING - For Hot Humid Climates
Zero Energy Design Cooling With Sunshine
The summer performance of the ZED Thermal Buffer Zone (TBZ) is very different from the way it operates in the winter. Instead of a totally-sealed attic, in the summer we open large peak roof vents to exhaust thousands of cubic feet per minute of the warmest air from the top of the TBZ. 2,000 cfm is the MINIMUM roof exhaust rate on most Thermal Buffer Zone homes in areas with a significant cooling requirement.
The TBZ roof vents can be operated manually from inside the insulated attic space (twice a year – spring and fall), or they can be automated with an intelligent minimum-cost sensor-based “enthalpy” control system (discussed in Chapter Two) for more precise hourly temperature and humidity control on larger homes.
The operating cost for the roof vent motors and control system is low. A small amount of electricity is required to quickly open or close any vent, and then no further power is necessary to hold them in the open or closed position. The power to drive the high-volume upward airflow comes mostly from natural convection – warmer less-dense air rising like a hot air balloon. If there is a breeze outside from any direction, it can enhance the exhaust airflow rate by creating a slight vacuum.
Our large 1979 indoor swimming pool home had over 7,000 cfm roof vent capacity, in a climate that peaked at 110 degrees Fahrenheit. It continuously exhausted hundreds of thousands of BTU’s of warm air 24-hours a day in the hottest part of the summer.
If a Thermal Buffer Zone home includes a swimming pool, swim spa, hot tub, koi pond, waterfall, etc. in the TBZ solarium, dehumidification ventilation becomes a design issue that must be carefully dealt with. Heated pools MUST be covered when not in use to minimize undesirable large-volume water evaporation. The pool cover can be a movable floor, to increase usable sunspace area (a dance floor, sports court, etc.).
A properly ventilated TBZ significantly REDUCES humidity in the summer. As a large volume of TBZ air rises by convection, it gradually becomes warmer and less dense. This increases its capacity to hold water vapor, which it then draws out of the house through the high-volume roof vents, reducing the absolute humidity in the TBZ.
When the high-volume TBZ roof vents are open, warm air rises toward the top of the TBZ like a hot air balloon through the south AND north sides of the TBZ. Instead of a natural convection circular up-and-down winter airflow LOOP, ALL SUMMER CONVECTION AIRFLOW IS UPWARD AT ALL POINTS. There is NOTHING that causes TBZ air to fall downward from the top of the home in the summer with the roof vents open. The density of TBZ air decreases as it rises, and continuously draws more heat and humidity out of the thermal buffer zone “automagically.”
If ZED-recommended cooler, less-humid TBZ replacement is introduced near the center of the crawlspace with unrestricted airflow in all directions, then the upward airflow rate through the north and south sides of the TBZ will be “automagically” determined by north / south / east / west temperature (and thus air pressure) differentials during different hours of the day. This is far superior to conventional central air conditioner systems, which always deliver the same airflow rate to all rooms, regardless of the fact that eastern rooms need more cool air in the summer morning, and western rooms need more cool air on hot afternoons.
Automatic self-regulation is one of the most powerful assets of any intelligent natural-convection airflow design, summer or winter. In essence, in the summer, the hottest exterior walls of the Thermal Buffer Zone architectural design pattern automatically receive the largest volume of cooler, less-humid replacement airflow, with no electrical control systems to make it happen effortlessly, using free Mother Nature Airflow Intelligence.
To order a copy of the U.S. DOE / ORNL Workshop CD-ROM
Click here
Get More Great Information Sources in Larry Hartweg's 800 page book on
Passive Solar Heating and Cooling Techniques
"Zero Energy Design"
Contact ZEDmaster@ZeroEnergyDesign.com
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Earth Temperature Cool Tubes
1979 Hillside Cool Tube Filtered Fresh Air Intake (before being packed in sand and buried). In hot locations where necessary and feasible (such as south-facing hillsides or low-water-table areas) large-diameter underground “cool tubes” can lower the outside replacement air temperature for the sunroom and attic, which are buffer zones between the interior temperature of the home and exterior temperature extremes. When warm outside air passes through the underground cool tube (surrounded by ambient temperature earth), condensation forms on the walls that must be drained off (just like the dehumidification process of an expensive high-energy-consumption conventional air conditioner). This is why hillsides are the best location for the use of cool tubes. ZED NEVER allows ground water, condensation, mold or mildew to accumulate inside a cool tube. This design factor is critical.
Cooler, dryer air from the cool tube is then input to the solarium thermal buffer zone (by natural convection created by turbine vents with no fans, thermostat or electricity). The cool dry replacement air is not added directly into the living quarters interior, unless the owner intentionally leaves the sunroom interior doors open on mild days or nights. Cool tubes are NOT for every house everywhere (there are several critical design issues), but where applicable, they are a nice tool of Zero Energy Design..
If a Thermal Buffer Zone (TBZ) Home includes a swimming pool, swim spa, hot tub, koi pond, waterfall, etc. in the TBZ solarium, dehumidification ventilation becomes a design issue that must be carefully dealt with. Heated pools MUST be covered when not in use to minimize undesirable large-volume water evaporation. The pool cover can be a movable floor, to increase usable sunspace area (a dance floor, sports
To order a copy of the U.S. DOE / ORNL Workshop CD-ROM
Click here
Get More Great Information Sources in Larry Hartweg's 800 page book on
Passive Solar Heating and Cooling Techniques
"Zero Energy Design"
Contact ZEDmaster@ZeroEnergyDesign.com
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