	Search *The Renewable Energy site for Do-It-Yourselfers*

Passive (and Active) Cooling

Passive cooling techniques (solar chimneys, thermal mass, ventilation, roof ponds, ...).
And, efficient active cooling techniques

Passive Cooling:

Passive Cooling Guides and Tools
Shading
Reflective Roofs
Cooling Towers $ Solar Chimneys
Earth Tubes
Reflectors
Tips

Questions?
Report Broken Links ...

Passive Cooling
The Energy Source Builder newsletter http://www.oikos.com/esb/51/passivecooling.html	A very good article that provides a simple method to allow you to determine which passive cooling techniques are best for your climate. This article is based on the book "Sun, Wind and Light" (see below).
Be Cool -- Natural Systems to Beat the Heat Preethi Burkholder with Claire Anderson How to get articles from Home Power ...	Home Power magazine article in issue 108 (Aug/Sept 2005) Very good article on simple techniques to prevent heat gain and to provide passive cooling. It includes a method to determine which cooling techniques will work best for your climate.
Passive Cooling -- Part 1 and 2 Cliff Mossberg How to get articles from Home Power ...	Home Power magazine article, issue 82 and 83 Article on passive design cooling techniques for hot humid climates with examples. Many techniques covered.
Lakeland, Florida -- Side by Side Test, Florida Solar Energy Center Comparison of energy of a home designed with many energy efficiency features to a same size conventional construction home. http://www.fsec.ucf.edu	This is a very detailed and carefully done study of two houses of the same size in Lakeland Florida. One house was built conventionally, and the other was equipped with a wide array of features to reduce energy consumption, including: reflective roof, internal duct system, thermal mass inside insulation, high efficiency and properly sized AC, well designed overhangs, and optimal windows. The measured energy consumption was 70% less on the house with low energy use features. A solar PV system offset and additional 22%, bringing the net energy use to near zero. The reports provide quite a bit of detail on the saving achieved by each energy efficient design feature.
Arizona Solar Center -- Passive Cooling www.azsolarcenter.com/technology/pas-3.html	A good overview of passive cooling strategies.
Passive Cooling for Your North Carolina Home North Carolina Solar Center NC Passive Cooling Guide (pdf)	Good guide to passive cooling houses in the SE humid and warm climates. From the NC Solar Center
Landscaping for Energy Efficiency South Carolina Energy Office Landscaping for Energy Efficiency (pdf)	Booklet on landscaping for energy efficiency. "Carefully positioned trees can save up to 25% of household's energy consumption". Several other energy saving "briefs" also available here.
Window Overhang Sizing Tool Sustainable By Design Solar Tools http://www.susdesign.com/design-tools.html	Properly sized overhangs on south windows keep you cool in the summer and collect sun in the winter.
Designing Shading Overhangs with Google SketchUp http://www.sketchup.com/ Caution: The free version of SketchUP does not allow you enter your latitude. For the sun model they assume a latitude of about 40 degrees North. This means if your latitude is near 40 degrees, the shadows will be accurate. However, errors in the sun's elevation and azimuth will increase as you go north or south of 40 degrees. Within the US (latitude 25 to latitude 50), the elevation angles can be off by up to about 12 degrees. Azimuth angles (particularly for south Florida) can be off by as much as 40 degrees.	SketchUp is a free 3D drawing tool from Google. In addition to be exceptionally easy to use as a general purpose drawing tool, it offers a shadows made by a built in sun. You can easily draw a wall with a window and overhang, and play the sun over it for various times of day and times of year. It could also be used to layout your whole house (with trees and sunspaces), and see how the sun plays over it. VERY easy to learn.
Shading Guidelines from Australia www.greenhouse.gov.au/yourhome/technical/fs19.htm	A good set of guidelines on a variety of shading techniques. Note that this is from Australia, so if you live in the northern hemisphere, you need to reverse north and south in the write-up.
Sun, Wind and Light -- Architectural Design Strategies, 2nd Edition G. Z. Brown and Mark DeKay	Details on a large number of specific design strategies for making effective use of the sun and wind, and natural lighting. It includes quantitative analysis techniques for each strategy. Intended for architects, but quite readable. Covers commercial buildings as well as residences. 2001 400 pages
Radiant Barriers, SouthFace.org -- Energy Fact Sheet www.southface.org Radiant Barrier Fact Sheet	A short but good Fact Sheet on radiant barriers from SouthFace.org.
Climate Consultant, UCLA Energy Design Tools http://www2.aud.ucla.edu/energy-design-tools/ Note: the pshchrometric charts that this tool produces have an overlay indicating which type of cooling techniques will work well in your climate. A really nice tool.	Climate Consultant is one of the UCLA Energy Design Tools. It provides a variety of ways to visualize weather for a specific location. Weather data files are available for hundreds of locations. This is a brand new version, and is very easy to use. "It graphically displays climate data in either metric or imperial units in dozens of ways useful to architects including monthly bar charts, timetable charts, and psychrometric charts, sun shading charts, and sun dial charts." One of the most interesting charts is the Psychrometric chart with overlays that show the design strategies (e.g. passive solar, evaporative cooling, ..) will work for the location in question.
Radiant Barrier Pilot Project, Florida Solar Energy Center, D. Parker, J. Sherwin, and M. Anello http://www.fsec.ucf.edu	An FSEC evaluation of the energy saving for radiant barriers. Nine houses were monitored for attic temperatures and AC energy use before and after installing a radiant barrier. Bottom line was an about 10% reduction in AC energy costs, and a somewhat improved comfort level.
Shading Structures
Window (and house) Shading How to keep cooler, save money, and be green all at the same time Window Shading Techniques Gary	As much as half the heat gain to your house can come from unshaded windows. The sunny day heat gain from a hundred square feet of east or west facing window is the equivalent of running your furnace for several hours. This is my 2 cents worth on several effective and (mostly) inexpensive ways to shade your windows and cut down on house overheating, high AC bills, and greenhouse gas emissions.
Sun Screens http://sunbloxinc.com/ An article on this product: www.energyrefuge.com/archives/solar_screens.htm The screen material from Phifer: http://www.phifer.com/sunprod.htm And another -- there are lots of them: http://www.ezsnapdirect.com/ Exterior window shades -- search for shades: A similar screening from Real goods	This seems like a pretty good idea for reducing summer heat gain on windows. The shades block up to 90% of sunlight, and mount in vinyl frames (like bug screens). It looks like they would work on a wide variety of windows, including ones that would be difficult to handle with other shading techniques. They do the shading on the outside, where its most effect. It seems like a DIY version could be worked out. The Phifer SunTex material is said to be available at some home centers. Frames could probably be made from the same material that home centers sell for making insect screens.
Alnet DIY Rollup Shade Cloth Shades www.shade-cloth-diy.com/patio-enclosures/patio-enclosures.shtml	Plans for a simple rollup shade from shade cloth.
Trellis Cooling Pictures of the trellis and other passive cooling features here: www.inhabitat.com/2005/12/23/ecohouse-brazil/	ECO house in Rio de Janero uses an aluminum trellis to support plants that will shade the house wall from from sun.
Living Wall System http://www.eltlivingwalls.com	In addition to all the "green" benefits that these living walls provide, it seems like they could be very useful for reducing heat gain from walls that get a lot of sun. Lots of example photos and some "hot to" information at this website.
Trellis Shading DoItYourSelf.com Trellis Projects	Some sample projects/pictures that use an external trellis for shading. This approach works well on East and West facing windows where overhangs are not effective.
Shading Structures from 2007 Solar Decathlon A little more on the German entry: www.inhabitat.com/... Quite a few Solar Decathlon pictures from Inhabitat: www.flickr.com/photos/inhabitat/1636531291/	German entry in the 2007 Solar Decathlon had a nice porch/shading structure. Note the roof of porch is PV modules. Note that this would even work on east and west exposures. And, this nice overhang on the Urbana-Champaign entry. Click pictures to enlarge. Pictures from Inhabitat
Some Trellis or Plant Screen Ideas ...	These are some shading trellis or plant screen ideas excerpted from a discussion on the HomeEnergySolutions Yahoo discussion group Thanks to the folks at HomeEnergySolutions for the good ideas!!
The Green Shutter www.inhabitat.com/2006/03/08/green-shutter/	A pretty neat design for a operable shutter with plants for sun control.
Schiavello Vertical Garden From Inhabitat: http://www.inhabitat.com ...	This design seems as though it might work well for blocking unwanted solar gain on windows (particularly on difficult to shade east and west facing windows). For this purpose, it would best be installed outside the window on the ground or on a balcony. Judging from the comments, it might be good to think about some type of watering system.
Alnet DIY Awning Plans www.shade-cloth-diy.com/awnings/awnings.shtml www.shade-cloth-diy.com/awnings/retractable-awnings.shtml	Plans for a simple wood framed, shade cloth awning to provide window shade and reduce heat gain. Retractable version
Alnet DIY Pergola Plans www.shade-cloth-diy.com/pergolas/pergolas.shtml	Plans for a simple wood framed, shade cloth pergola from Alnet.
Alnet DIY Trellis www.shade-cloth-diy.com/garden-designs/garden-designs.shtml	Plans for a simple wood framed, shade cloth trellis fro Alnet
Elegant Shade Structure Popular Mechanics www.popularmechanics.com	Plans for a very elegant shade structure. This could be used as a standalone shade structure or adapted to shade a house window. Very detailed plans.
Windsor Shade shelter California Redwood Association www.calredwood.org/ref/pdf/shelter.pdf	Detailed plans for a free standing shading structure. Could be used for yard/deck shade, or to shade a window.
Rollup shade plans From Charlie's Green House www.CharliesGreenhouse.com The Plans (pdf)	Plans for a simple rollup shade from Charlie's Greenhouse in Seattle.
Shade Sails ,,,	Shade Sails (or Solar Sails) are fabric membranes supported by fixed anchors, and positioned to provide shade. They are laid out and tensioned in such a way as to be very resistant to winds. They can be used to shade decks, porches, play areas, windows, ... They can be very nice looking indeed, and can handle some difficult shading problems. Example photos, and design information here ...
Reflective Roofs
Comparative Summer Attic Thermal Performance of Six Roof Constructions, Danny Parker and John Sherwin, Florida Solar Energy Center, 1998 The full paper ...	This is an excellent paper that compares the attic temperatures for 6 different roof constructions. Following the findings of this study can have a major impact on your cooling costs. If you don't have time to read the full paper, here is my quick summary of the findings...
Cool Metal Roofing www.wbdg.org/design/coolmetalroofing.php	Reflective metal roofing can keep your house cooler and save on cooling bills.
Measured Cooling Energy Savings From Reflective Roofing Systems In Florida: Field And Laboratory Research Results, Parker, Barkaszi, Chandra, and Beal Florida Solar Energy Center www.fsec.ucf.edu/en/publications/html/fsec-cr-1220-00/ Measured and Simulated Performance of Reflective Roofing Systems in Residential Buildings, Parker, Huang, Konopacki, Gartland, Sherwin, and Gu. www.fsec.ucf.edu/en/publications/html/fsec-pf-331-98/ Measured Roofing Material Reflectivity's ... A sampling of commercial sources ...	Actual measurements of reduction in cooling energy for 8 homes in Florida before and after coating the roof with a reflective (white) coating. Cooling energy savings averaged 20% just by going to a more reflective roof. The papers cover both roofing materials that are reflective as well as coatings that can be applied on existing roofs. The paper on Roofing Material Reflectivity is good and surprising.
Cooling Towers & Solar Chimmneys
Ventilation Rates for Solar Chimneys Energy and Buildings -- 32 www.ecaa.ntu.edu	Paper provides measured ventilation rates and room temperatures achieved by four solar chimney designs.
Passive Air Conditioning -- Low Energy Cooling Tom Elliot www.thefarm.org/charities/i4at/lib2/aircool.htm	Another writeup on evaporative cooling towers with some design information.
How to Stay Cool in the Hot Desert (with less power) Charles Van Meter http://millennium-ark.net	A passive cooling tower that uses wind and water evaporation for cooling. No blowers -- only electric demand is a small water pump. Some design rules, and several years operating experience.
Reflectors
Reflector/Shades, Steve Baer, Zomeworks Corporation http://zomeworks.com/files/sunbenderTM/reflector-shades.pdf	A good paper by Steve Baer reviewing the use of seasonally moveable reflectors to increase solar heat gain in the winter, and reduce unwanted heat gain in the summer. A nice mix of solar physics and practical how-to that Steve has gained in the building of many of these types of reflector systems over the years.
Earth Tubes Earth tubes are tubes buried in the ground deep enough to take advantage of the more even year round temperature at depth. Air from outside the house is run through the earth tubes to heat or cool it before it is introduced into the house. In the summer, the earth is cooler that the outside air temperature and the air will be cooled as it goes through the tubes, and the opposite in the winter. This is a simple, energy efficient means of pre-heating or pre-cooling air, but there are a number of things to consider -- so do your homework carefully.
EERE -- Earth Tube Cooling A fact sheet from the EERE site: EERE on Earth Tubes	The EERE on earth tube cooling. They seem to be a bit "cool" to the idea -- and, I think they make some good points.
Performance of Single Pass Earth-Tube Heat Exchanger: An Experimental Study, Girja Sharan, Ratan Jadhav Data from an Earth Tube experiment: Earth Tubes2003-01-07GirjaSharan.pdf	An interesting paper with some actual data on a real earth tube -- this might be helpful in designing your earth tube. The data includes temperatures along the tube, airflows, fan power, and COP.
Passive Annual Heat Storage, John Hait, 1983 http://www.earthshelters.com/	This book by John Hait is mostly about his Passive Annual Heat Storage home design, but it does have a section on earth tubes and how they are used on his houses. An interesting all around book.
The Natural Home Building on Earthtubing: http://www.thenaturalhome.com/earthtube.htm	Describes the way in which earth tubes are used in their house design. They also describe an earth tube system using water rather than air in the pipes: http://mb-soft.com/solar/alternwa.htm its hard for me to tell whether they have actually built one of these or not.
Earth Tube Cooling -- Leopold Legacy Center Aldo Leopold Earth Tubes Paper	A large commercial application using earth tube cooling. Some design numbers provided.
Analysis, Design, and Prelimnary Testing of Solar chimney for Residential Air-Conditioning Applications, Gang Wang, Bing Chen, Mingsheng Liu, Joerg Henkel, University of Nebraska, Lincoln	This paper looks at the feasibility of using a solar chimney to drive flow through an earth tube. Both analysis and testing are provided.
REHAU Air - Ground Heat Exchangers http://export.rehau.com/ ...	This company makes components for earth tube heating and cooling systems. The downloadable pdf provides some useful information for designing earth tube systems. (thanks to Charles for finding this)
Earth Tube Design Notes... Gary	These are just some thoughts on earth tube design based on nothing more than reading the articles above.
Cooling Tips
Water bed cooling	Randy suggests that in hot climates sleeping directly on the water bed bladder will be cooler. Remove all the coverings except for a sheet or two, and let the water conduct heat away from your body. The temperature of the water in the bladder will be the average of the last few days, and cooler than body temperature. After more experience, Randy adds that during the cooler season, you want more insulation (e.g. a blanket) between you and the water bladder to keep it from getting to chilly. Its a mater of adjusting the amount of insulation between you and the thermal mass.
Efficient Active Cooling These schemes cool using a small fraction of the energy used by conventional AC units.
Whole House Fan for Cooling Whole House Fan pdf (240K)	For relatively dry climates with cool nights, whole house fans are very effective in reducing or eliminating the need for refrigerated AC. I have had a whole house fan in my last two houses, and would not be without one!
Whole House Fans Tech Sheet (pdf) PG&E	Another good guide on using and installing a whole house fan.
Energy Star Ceiling Fans www.energystar.gov Getting the Most from Your Fan, Chris Calwell and Noah Horowitz Home Energy Choosing and Installing a Ceiling Fan, Fernando Pages Ruiz, Fine Home Building Magazine (very good how-to on installing ceiling fans)	Ceiling fans are an efficient cooling method for some climates and conditions, especially when the use of a ceiling fan allows less use of AC. Energy Star ceiling fans use half as much energy as typical non Energy Star fans. Note the directory of approved fans, and the attention to making any light that might be included with the fan an efficient one. If you have several ceiling fans in your house, using energy efficient fans could save you as much as 1000 KWH a year, so its worth finding good ones and sizing them for the space. Some thoughts on choosing an efficient ceiling fan ...
Ceiling fans with aerodynamically designed blades http://www.fanworks.com/vari-cyclone.htm	Ceiling fans with "Gossamer Wind" technology blades move about 40% more air for the same power use. Models are available that operate at 12 or 24V, and can be operated direct PV or battery. FSEC paper: Performance and Applications of Gossamer Wind™ Solar Powered Ceiling Fans
Solar Attic Vent Fan http://www.arttec.net/Solar/5-21-06/May21-06.html	Guy Marsden describes how to install a solar powered attic vent fan. The fan lowers his attic temperature by abut 20 to 30F, which reduces heat transfer through the ceiling. Adding attic insulation and sealing plumbing and wiring penetrations through the attic ceiling are other ways to lower heat transfer from the attic to the living space.
Innovative Design Eliminates Cooling Equipment Energy Source Builder #36, December 1994. http://www.oikos.com/esb/36/Inno_Des.html	Article describes a house in Davis, CA (103F summer design temperature) with no refrigerated air conditioning system. The system uses night time ventilation and thermal mass to provide cooling. An evaporative cooler is operated at night to cool thermal mass.
Night Breeze Cooling System http://www.davisenergy.com/nb_page.html Home Energy Magazine article Kicking the Air conditioner Habit (pdf)	This is sort of a highly sophisticated version of a whole house fan. It eliminates or reduces the need for refrigerated air conditioning by using cool night air to pre-cool the house for the next hot day.
New Evaporative Cooling Systems -- An Emerging Solution for Homes in Hot Dry Climates with Modest Cooling Loads Southwest Energy Efficiency Project Evap Cooler Report (pdf) Evaporative Cooler Assessment from ToolBase: http://www.toolbase.org Two stage evaporative coolers: www.homeenergy.org ...	Good and detailed report on a new generation of evaporative coolers that are more efficient, use less water, and require less maintenance. These cooler in a relatively dry climate can save 90% compared to compressor driven conventional air conditioning!
PV Powered Evaporative Coolers http://www.southwest-solar.com/ www.oksolar.com/products/air_conditioner.htm Some notes on a DIY one: www.voltscommissar.net/competitive_edge.htm	These evaporative coolers use low HP 12V fans that can be powered by PV arrays.
Night Sky Roof Water Spray Cooling system www.pnl.gov/TechReview/whitecap/whitecap.html EERE report ORNL gov report The first link above provides the most complete design information, and describes three different roof spray system designs. While these papers seem to be aimed primarily at commercial applications, residential applications may well be workable, simple, and energy efficient. Most beneficial for dry climates.	"This innovation spray-cools water on the roof at night and applies the cooled water to reduce subsequent cooling loads. On clear nights, the sky is much colder than outdoor air, contributing to high water cooling rates through a combination of evaporation and sky radiation. Overnight, NightSky systems can typically cool a large storage volume (preferably two gallons per square foot of roof surface) to a final temperature as much as 12 degrees below the minimum night air temperature." Seems like a very promising way to reduce the energy cost of cooling. The 5600 sqft prototype described in the first link achieved an EER of 149.
Hydronic Cooling Energy Source Builder, Issue 53 http://www.oikos.com/esb/53/hydroniccool.html	An article from the Energy Source Builder Newsletter on using hydronic heating systems for cooling, including radiant floor systems.
Some Information on Designing and Building Evaporative Pad Cooling System Ohio State University Fact Sheet http://ohioline.osu.edu/aex-fact/0127.html	Information for designing and making your own evaporative pad cooling systems. I have seen systems of this type in greenhouses for cooling.
Florida Zero Energy Test House Florida Solar Energy Center The Report (pdf)	A home constructed in a very difficult cooling climate (central Florida) to see if a combination of passive cooling techniques to reduce heat gain, high efficiency AC, efficient appliances, and a fairly large PV rig could produce near zero net energy use. The home was largely successful in meeting these goals. Net energy use was only about 18% of a control house built to current codes. Pretty good detail on how much energy each feature saved. My 2 cents would be that the passive cooling, high efficiency AC, and efficient appliances contributed 67% the of the savings, while adding little to the cost of the house. The 4KW PV rig contributed the other 33% of the savings, and probably cost about $40,000.
Theoretical Evaluation of the NightCool Nocturnal Radiation Cooling Concept Danny S. Parker Florida Solar Energy Center (FSEC) New report on the NightCool performance in test buildings: Experimental Evaluation of the NightCool Nocturnal Radiation Cooling Concept: Performance Assessment in Scale Test Buildings, Danny S. Parker, John R. Sherwin Florida Solar Energy Center (FSEC) Daily performance of the test buildings, http://infomonitors.com/ntc/ Note: I would tend to NightCool in the Experimental area, so, if you go after this, bear in mind you may suffer the "being a pioneer" learning curve. Please let us know how it comes out.	This is a simple, building integrated, cooling scheme that uses nighttime radiation cooling from a metal roof to cool air in the attic space. Attic air is then circulated into the living area to provide cooling. A simulation model is used to predict performance in various climates -- the scheme works very well in dry areas, and fairly well even in very difficult moist-warm climates (e.g. Florida). One of the attractive features of this system is that the roof is very conventional -- no massive ponds or moving insulation. There is the potential in some climates to use the same metal roofing/attic system for space heating in colder weather. The new test report shows the results for two 10' by 16' structures that were built to compare NightCool performance to conventional AC in Florida. Very interesting and promising results. Tests of a a simple dehumidification system using desiccants are now underway.
Turbo Kool Evaporative Cooler http://www.turbokool.com/ Install Manual (pdf)	This is a small 12 VDC evaporative cooler that is intended for RVs, construction equipment, ... but might work well in any small space. The fan draws 4 amps, and the company says it will run directly off a 60 watt solar panel.
Plans for Evaporative Coolers www.igcusa.com/Catalogs/Coolair%20Install.pdf	Detailed plans for making evaporative coolers. Intended for greenhouses, but may be adaptable to other situations.
Odd Active Cooling These schemes cool using a small fraction of the energy used by conventional AC units.
Mist Cooling For Large Outdoor Areas	A very simple mist cooler for large outdoor areas. Intended for cows, but I don't think they will mind if you use their idea.