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This powerpoint illustrates the research done on the passive cooling methods of earth tube systems and solar chimneys in Florida\'s sub-tropical climate.
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Passive Cooling in Florida
Applying the passive cooling techniques of natural
ventilation and earth tube cooling to Florida’s subtropical
climateJack Vitek
Stetson University
Department of Environmental Science
April 8th, 2009
Introduction Conditioning homes in subtropical climates consumes more
energy than any other building/structural cost
The implementation of passive cooling techniques would drastically reduce our energy consumption
“Air conditioning is commonly used to achieve thermal comfort in commercial buildings in the hot and humid Southeast Asian Region. Typically, air-conditioning accounts for 60% of electricity consumption in such situations.” – Vangtook, Chrarattananon (2005)
The research and analysis was done to determine whether the passive cooling techniques of earth tube systems and natural ventilation can passively cool a building in a subtropical climate like Florida
Florida Warm and
humid climate with high annual precipitation
Similar Climates
Southeast Asia (India, China, Thailand)
Australia Sub-Tropical
South America
Study Area:Comparing Climates
Average Temp
Average
Humidity
Average
Rainfall
Expected Findings Research shows that far less energy is consumed
when the passive cooling techniques are incorporated with conventional HVAC systems than without them in regions similar to Florida
Furthermore, it seems the use of multiple passive cooling methods will further increase the energy efficiency and conditioning efficiency of the building
However, passive cooling methods, when used alone, do little to maintain constant humidity when compared to conventional methods
Background:Conventional Methods
HVAC Systems: A conventional method of cooling and conditioning the climate within a give area. The three functions of heating, ventilating, and air-conditioning are closely interrelated.
If solar chimneys, EAT systems are “passive” techniques because the require no energy, HVAC systems would be considered “active”.
Background:Passive Cooling Techniques
Passive solar cooling: “the removal of heat of the building environment by applying the natural processes of elimination of heat to the ambient atmosphere by convection, radiation and evaporation or to the adjacent earth by conduction and convection (Jain, 277).”
Most Common Techniques: Water-roof evaporation, solar chimneys, earth to air transfer systems, vegetative shading, vegetative roof
Techniques Researched: Natural Ventilation (solar chimneys), earth to air transfer systems
Background:Earth to Air Transfer Systems
“An earth tube is a long, underground metal or plastic pipe through which air is drawn. As air travels through the pipe, it gives up or receives some of its heat to/from the surround soil and enters the room as conditioned
air during the cooling and heating period.” – Lee, Strand (2007)
Pic
ture
1P
ictu
re 2
Background:Earth to Air Transfer Systems
Importance of Tube Length The longer the tube is
underground, the longer the air inside the tube is exposed to the soil condition through the pipe walls (Figures to right)
“As the pipe length increases, the inlet air temperature
decreases due to the fact that the longer pipe provides a longer path over with heat
transfer between the pipe and the surrounding soil can take
place give the same overall heat transfer coefficient of earth tube.” – Lee, Strand (2007)
Background:Earth to Air Transfer Systems
Importance of Pipe Depth
The temperature of the soil depends on its depth, therefore making the depth of the pipe very important
“As the pipe depth increases, the inlet air
temperature decreases, indicating that the earth tube should be placed as
deeply as possible.” – Lee, Strand (2007)
Pic
ture
3
Background:Earth to Air Transfer Systems
Importance of Air Velocity (inside pipe)
Increased air velocity inside the tube limits the amount of time air can be conditioned
“As the air flow rate increases the inlet air temperature increases in all locations, since the air spends less time in the tube and thus in contact with the lower soil temperature.” – Lee, Strand (2007)
Importance of Pipe Radius Increased pipe radius allows
for more air intake, and by doing so, limits the amount of air to pipe contact
“As the pipe radius increases, the earth tube inlet air temperature also increases due to the face that higher pipe radius results in a lower convective heat transfer coefficient in the pipe inner surface and lower overall heat transfer coefficient of earth tube system.” – Lee, Strand (2007)
Background:Earth to Air Transfer Systems
Other Important Factors Soil Temperature – Directly effects air
inside tube Soil Composition – Determines how well
soil can hold temperature Pipe Thickness – Influential in air to soil
temperature transfer Pipe Composition – Influential in air to soil
temperature transfer
Background:Natural Ventilation & Solar Chimneys
Buoyancy Driving Force (stack effect) – due to temperature difference between indoor and outdoor air temperatures (Bassiouny & Koura, 2007) – Picture A
Aeromotive – wind driving force - Picture B
Solar Chimneys use both types of natural ventilation to passively cool the structure Picture
B
Picture A
“Natural ventilation is not only regarded as a simple measure to provide fresh
air for the occupants,
necessary to maintain
acceptable air quality levels, but also as an
excellent energy-saving way to
reduce the internal cooling load of housing located in the
tropics.”- Boonsri,
Hirunlabh, and Khedari (1999)
Background:Natural Ventilation and Solar Chimneys
Importance of Air Gap
Provides area for stack effect to exist between solar chimney and building inlet
Usually located in south façade or in roof
Importance of Solar Chimney’s Positioning
Air gap and solar chimney must receive solar radiation in order for stack effect to occur
Solar Chimneys located on the south façade of a building are most common due to solar exposure
Chungloo & Limmeechokchai
(2006)
Background:Natural Ventilation & Solar Chimneys
Importance of Air Gap Provides area for stack
effect to exist between solar chimney and building inlet
Usually located in south façade or in roof
Importance of Solar Chimney’s Positioning
Air gap and solar chimney must receive solar radiation in order for stack effect to occur
Solar Chimneys located on the south façade of a building are most common due to solar exposureBassiouny & Koura (2007)
Importance of Façade Material
Wall material has an influence on the air gap’s ability to insulate heat, creating the stack effect
Importance of Ventilation Input & Air Gap Output
The amount of input and output air allowed must be regulated (airflow)
Degree of “openness” of input/out
When the respective vents are opened (time of day)
Liping & Hein (2006)
Literature Review:Earth to Air Transfer Systems
Passive Cooling Tech.
Data Source Information Covered
Earth to Air Girja Sharan, Rantan Jadhav (2000)
Single pass earth tube buried 3 m below surface, ambient air is pumped through blower Air at constant velocity
Earth to Air Kwany Ho Lee, Richard K. Strand (2007)
Importance of:Pipe RadiusAir FlowPipe LengthPipe Depth
Earth to Air Jens Pfafferot (2003) Importance of:Ground TemperatureSoil CompositionHeat Transmission
Literature Review:Natural Ventilation & Solar Chimneys
Passive Cooling Tech.
Date Source Information Covered
Natural Ventilation Wang Liping & Wong Hien
Design and importance of façade in natural ventilation
Solar Chimney Sudaporn Chungloo & Bundit Limmeechokchai
(2006)
Solar radiation’s effect on solar chimneyAir gaps, stack effect and south facing façadesConnect solar chimneys and natural ventilationACH (Air Changes per Hour)
Radiant Cooling Prapapong Vangtook & Surapong
Chirarattananon (2005)
Energy consumption of A/C in hot humid climate A/C = 70% energy consumption in households
Solar Chimney Ramadan Bassiouny & Nader S.A. Koura (2007)
Description of solar chimney Increase of solar radiation on air gap increases air flow rate Spraying water
Discussion:What Was Learned?
2-6 degrees temp. difference in outdoor and indoor temperature
Little information addressing the regulation of humidity
Cannot condition a structure as effectively as mechanical methods can in hot humid climates
EAT & Natural Ventilation produced cooler temperatures
No to little energy consumption
Combination of passive and active systems to reduce (not eliminate) energy Night Ventilation
Discussion:Where to Now?
Continued/Increased development of humidity regulation in passive techniques
Increased application of passive cooling techniques alongside mechanical
Promote cost benefits of applying passive techniques
Increased popularity in United States
Questions
Thank You
