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{{Wikipedia}}
The principle of the thermosyphon system is that cold water has a higher specific density than warm water, and so being heavier will sink down. Therefore, the collector is always mounted below the water storage tank, so that cold water from the tank reaches the collector via a descending water pipe. If the collector heats up the water, the water rises again and reaches the tank through an ascending water pipe at the upper end of the collector. The cycle of tank -> water pipe -> collector ensures the water is heated up until it achieves an equilibrium temperature. The consumer can then make use of the hot water from the top of the tank, with any water used is replaced by cold water at the bottom. The collector then heats up the cold water again. Due to higher temperature differences at higher solar irradiances, warm water rises faster than it does at lower irradiances. Therefore, the circulation of water adapts itself almost perfectly to the level of solar irradiance. A thermosyphon system's storage tank must be positioned well above the collector, otherwise the cycle can run backwards during the night and all the water will cool down. Furthermore, the cycle does not work properly at very small height differences. In regions with high solar irradiation and flatroof architecture, storage tanks are usually installed on the roof.
='''Abstract'''=
Thermosyphon systems operate very economically as domestic water heating systems, and the principle is simple, needing neither a pump nor a control. However, thermosyphon systems are usually not suitable for large systems, that is, those with more than 10 m² of collector surface. Furthermore, it is difficult to place the tank above the collector in buildings with sloping roofs, and single-circuit thermosyphon systems are only suitable for frost-free regions.


'''Thermosiphoning''' is considered to be an [[appropriate technology]]. This process utilizes natural,[[renewable resources]] and the laws of basic [[thermodynamics]] to create movement of a heated supply of air or water. The entire process may be explained by the [[thermosiphoning effect]]:  When air or water is heated, it gains [[kinetic]] energy from the heating source and becomes excited. As a result, the water becomes less dense, expands, and thus rises. In contrast, when water or air is cooled, energy is extracted from the molecules and the water becomes less active. It also becomes more dense, and tends to "sink." Thermosiphning harnesses the natural density differences between cold and hot fluids, and controls them in a simple system that produces natural fluid movement. Several systems based on this technology are currently available, and may be read about in greater detail within the following text. 
[[Image:thermosyphon.gif|center]]


==''' Underlying Physics''' ==
== Abstract ==
Thermodynamics is the study of [[energy]].
''Also known as: thermosyphoning''
* [[1st Law of Thermodynamics]]- States that energy may be changed from one form to another, but cannot be created ordestroyed.
- Energy is always conserved.


'''Thermosiphoning''' is considered to be an [[appropriate technology]]. This process utilizes natural, [[renewable]] resources and the basic [[laws of thermodynamics]] to create movement of a heated supply of air or water. The energy source for this process is [[solar radiation]](or any other source of heat): the energy of the sun is captured in a [[solar collection]] device and is transferred to either air or water via conduction. The entire process may be explained by the [[thermosiphoning effect]]:  When air or water is heated, it gains [[kinetic]] energy from the heating source and becomes excited. As a result, the water becomes less dense, expands, and thus rises. In contrast, when water or air is cooled, energy is extracted from the molecules and the water becomes less active, more dense, and tends to "sink." Thermosiphoning harnesses the natural density differences between cold and hot fluids, and controls them in a system that produces natural fluid movement. Several systems based on this technology are currently available, and may be read about in greater detail within the following text.


== Underlying physics ==
Thermodynamics is the study of [[energy]].
* [[First law of thermodynamics]]- States that energy may be changed from one form to another, but cannot be created or destroyed. - ''Energy is always conserved.''


''This law may be applied to the movement of water in thermosiphoning system: Energy from the sun is directed and transferred (via conduction and convection) to either water, air, or another medium of choice. This natural process of heating eliminates the need for external energy sources such as fossil fuels or electricity.''   


it cannot be created or destroyed. In essence, energy can be converted from one form into another.  
* [[Second law of thermodynamics]]- States that in all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state. - The net return of a system is always less than that of which was initially put in.
Heat
Energy transferred as a result of temperature differences between two objects
Expressed as Q
First law of thermodynamics


==Physics==
''Energy is always conserved, however energy (or heat in this case) may often be lost in a given system (thermosiphoning) as heat. Adding [[insulation]] with appropriate [[R value]]s to the system and its plumbing may greatly reduce heat loss, and thus increase efficiency.''


Passive systems use only the natural density difference between hot and cold fluids to drive circulation. Since warm water rises and cold water sinks, no pump is needed. Passive solar water heaters place the tank above the collector, often on the roof or in the attic. Through a process called "thermosiphoning," cool fluid is pulled from the tank into the bottom of the collector, where it warms up and exits the top of the collector into the tank. The process continues until the fluid at the top of the collector and the bottom of the tank are the same temperature.
* [[Planck’s Law]]- the wavelength of radiation emitted from a surface is proportional to the temperature of the surface
The Thermosiphon Principle
Energy transferred as a result of temperature differences between two objects -''Dark objects absorb heat, while light objects reflect'' 
Solar water heaters make use of two naturally occuring phenomena for their operation;


Black objects absorb heat, and
''Darkly colored collection plates within the solar collector will aid in increasing solar absorption, thus increasing the amount of heat available to heat water or air in thermosiphoning. In contrast, reflective or lightly colored piping and storage tanks should be utilized as the light colors will help to reduce heat radiation out of the system.''
Hot water rises.
It's a simple system, where water is the only moving part.
Imagine a solar absorber filled with cold water. As the sun warms the collector, the water inside becomes hotter, expands, becomes lighter, and risers upwards towards the tank. The colder, heavier water is drawn down into the bottom of the collector, where it is heated, then moves upwards...and so on...and so on. 


This circular heating motion is called the thermosiphon effect. The greater the difference in temperature between the water in the collectors and the water in the storage tank, the faster the flow between them.
== Water heating ==


=== Passive ===
The passive thermosiphoning of water is the process of heating and moving water within a system without the need or use of electricity. This process functions by utilizing natual phenomena such as solar energy, gravity, and an available water source. A [[solar collector]], piping, and a water tank are materials required for the heating process. The flow of water is distributed into, within, and out of the solar collector. Cool water enters the bottom of the solar collector where it is then heated via [[convection]] by solar radiation. When water is heated it becomes less dense than cooler water, expands, and then rises (''flows'') through the piping. The heated water exits the top of the solar collector naturally.  The cooler and more dense water sinks and remains within the solar collector until it is heated. As the cool water is heated, it expands, rises, is pushed out of the top of solar collector, allowing cool water to flow into the solar collector. This process continues naturally until the temperature of the water reaches an equilibrium with solar radiation input.


Two types of thermosiphon water exchange systems are currently available: the close-coupled system, and the gravity-feed system.               


Thermosiphon systems rely on the natural convection of warm water rising to circulate water through the collectors and to the tank, which is located above the collector. As water in the solar collector heats, it becomes lighter and rises naturally into the tank above. Meanwhile, the tank's cooler water below flows down pipes to the bottom of the collector, causing circulation throughout the system.
==== Close-coupled system ====


= '''Water Heating''' =
Close-coupled systems function on the same principles of passive thermosiphoning mentioned above. The storage tank of these systems ''must'' be placed above the solar collector to utilize the water circulation driven by the passive thermosiphoning process.


==''' Passive''' ==
[[Image: Passive_water_heater_diagram_(2).jpg|thumb|upright=2|Schematics|right]]
The passive thermosiphoning of water is the process of heating and moving water within a system without the need or use of electricity. This process functions by utilizing natual phenomena such as solar energy, gravity, and an available water source. A [[solar collector]], piping, and a water tank are materials required for the heating process. The flow of water is distributed into, within, and out of the solar collector. Cool water enters the bottom of the solar collector where it is then heated via [[convection]] of solar radiation. When water is heater it becomes less dense than cooler water, expands, and then rises (''flows'') through the piping. The heated water exits the top of the solar collector naturally.  The cooler and more dense water sinks and remains within the solar collector until it is heated. As the cool water is heated, it expands, raises, is pushed out of the top of solar collector, allowing cool water to flow into the solar collector. This process continues naturally until the temperature of the water reaches an equilibrium with solar radiation input.


Two types of thermosiphon water exchange systems are currently available: the close-coupled system, and the gravity-feed system.               
===== Materials =====
* Solar Energy
* Solar Collector
* Piping
* Insulation
* Water
* Storage Tank
* Strong roof or other support system


=== '''Close-coupled System''' ===
===== Cost =====
* Current research ''(2007)'' suggests that passive thermosiphon water heaters may range from $500 to $6,500. Pricing may vary due to tank size, solar exposure, and geographical location 
* Many countries, states, and utility services provide incentives for [[renewable energy]] participation


In a close-coupled system the horizontal storage tank is mounted directly above the collector on the roof. Heated water is supplied at mains pressure. This arrangement is the most cost effective to install but efficiency is reduced in cool and cold climates by heat loss from the tank.
===== Pros & cons =====
Tanks are located above the collectors to take advantage of thermosiphoning. Thermosiphoning utilises flat plate collectors to heat the water, which returns to the storage tank, located above the collector. Cold, denser water flows through the collector heating up and is then returned to the tank. As the heated water is less dense, it rises to the top of the tank. For thermosiphoning to be successful, it is essential that a constant rise in the pipe work is maintained and that the correct diameter pipes are used as risers and headers.


'''''Pro's'''''
* Non-polluting
* Energy Savings ''- No electricity needed for passive thermosiphoning''
* Cost Effective
* Space saving - ''(ie. indoors)''


'''Cost'''
'''''Con's'''''
* Passive thermosiphon water heaters may range from $500 to $6,500. Pricing may vary due to tank size, solar exposure, and geographical location
* Tank exposure to external environmental condition may reduce efficiency, depending on geographical location
* Many counries, states, and utility services provide incentives for renewable energy participation
* Aesthetics - '' May be considered visually unpleasing''
* Strong support structure needed ''(i.e. roof)''
* Not suitable for extremely cold climates
* Location - must be positioned in an area with suitable solar exposure ''(i.e. south side of desired area)''


==== ''Schematics''' ====
==== Gravity-feed system ====
[[Image: Passive_water_heater_diagram_(2).jpg]]


Gravity-feed systems utilize the same principals of passive thermosiphoning as does the close-coupled system, however placement of the tank differs. Tanks are installed horizontally into a roof, which is often located directly above the solar collector. Once needed, the heated water within the storage tank takes the path of least resistance and moves via gravity down into the desired location. Gravity-feed systems require more piping/plumbing to distribute the heated water, and this factor should be taken into consideration when installing or purchasing a thermosiphoning system.


=== '''Gravity-feed System''' ===
===== Materials =====
In a gravity-feed system, the storage tank is installed in the roof cavity. These systems are cheapest to purchase but household plumbing must be suitable for gravity feeding, including larger diameter pipes between the water heater and the taps. A common alternative is to use a closed circuit gravity feed system to heat mains pressure water using a heat exchange.
[[Image:Passive_water_heater_diagram_2_(2).jpg|thumb|upright=2|Schematics|right]]


* Solar Energy
* Solar Collector
* Piping
* Insulation
* Water
* Storage Tank
* Strong roof or other support system




===== Cost =====
* Gravity-feed systems are typically the least expensive passive thermosiphoning water heaters
* Current research ''(2007)'' suggests that the cost may range from $400 to $5,500 ''(Not including the cost-if applicable- of installation)''. Pricing may vary due to tank size, solar exposure, and geographical location 
* Many countries, states, and utility services provide incentives for renewable energy participation


===== Pros & cons =====


== '''Active''' ==
'''''Pros'''''
* Non-polluting
* Energy Savings ''- No electricity needed for passive thermosiphoning''
* Cost Effective
* Space savings - ''(ie. indoors)''
* Aesthetics - ''(Horizontal tank placement)


Active solar heating systems utilize an external energy source
'''''Cons'''''
In active systems (also known as pump systems or split systems), solar panels are installed on the roof and the storage tank is located on the ground or another convenient location, that does not have to be above the solar collectors. Water (or another fluid) is pumped through the solar collectors using a small electric pump.
* Plumbing and piping add additional costs to the system
* Aesthetics - '' May be considered visually unpleasing''
* Strong support structure needed ''(i.e. roof)''
* Not suitable for extremely cold climates
* Location - must be positioned in an area with suitable solar exposure ''(i.e. south side of desired area)''


Because active systems do not require a roof-mounted tank they have little visual impact, particularly when the solar collectors are mounted flush with the roof. However, active systems are usually more expensive to purchase and require more maintenance than passive systems.
=== Active ===
''Also known as: pump systems or split systems''


Active systems use more energy than passive systems because extra energy is required to pump fluid around the system. There are also additional heat losses in the pipes between the tank and the solar collectors. However, if renewable energy is used to power the pump and a high level of insulation is used for the pipes and tank, active systems can reduce greenhouse gas emissions as much as a passive system.
[[Image:water_heater_(5).jpg|thumb|upright=2|right|Schematics]]


==== ''Schematics'' ====
Active solar heating systems function on the same basis of the [[thermosiphoning effect]], however active systems utilize an energy source other than solar energy to help drive the process. This system installs only the solar collector on the roof, while the storage tank is installed on the ground or anywhere else below. These active water heating units require some external form of energy to pump the water throughout the system. By utilizing additional energy, these active systems are less cost efficient than passive systems. 
[[Image:water_heater_(5).jpg]]


== ''Materials'' ==
==== Materials ====
* Solar Energy
* Solar Energy
* Solar Collector
* Solar Collector
* Electrical energy
* Electrical pump
* Additional piping
* Insulation
* Water
* Water
* Storage Tank
* Storage Tank


=== Alternative Materials ===
==== Cost ====
* Current research suggests ''(2007)'' that active thermosiphon water heaters may range from $1,200 to $10,500. Pricing may vary due to tank size, internal piping requirements, solar exposure, and geographical location 
* Many countries, states, and utility services provide incentives for renewable energy participation


== Pros & Cons ==
==== Pros & cons ====


'''''Pro's'''''
'''''Pro's'''''
* Non-polluting
 
* Energy Saving ''- No electric needed for passive thermosiphoning''
* Money Savings
* Non-Toxic
* Cost Effective
* Cost Effective
* Space saving - ''(ie. indoors)''  
* Aesthetics - ''Storage tank not placed on the roof''
* Greenhouse gas reduction  - ''If insulated properly, it has the potential of polluting as little as passive systems.''


'''''Con's'''''
'''''Con's'''''
* Aesthetics
* Uses more energy than a passive system
* Strong support structure needed ''(ie. roof)''
* Requires more maintenance than a passive system
* Not suitable for extreme cold climates
* Heat loss - during the transfer from the solar collector to the storage tank below
* Location - must position in area with suitable solar exposure ''(ie. south side of desired area)''
* Pollutes some - from the electrical usage
* Location - must be positioned in an area with suitable solar exposure ''(ie. south side of desired area)''


=== Passive air exchange ===


[[Image: Water_heater(1)_(3).jpg|thumb|upright=2|right|Schematics]]


== '''Passive Heat Exchange''' ==
An example of a [[passive solar thermal]] heating system method is '''Thermosiphon Heat Exchange'''. It is based on the principle of natural [[convection]], in which air or water is circulated in a vertical closed-looped circuit without using a pump. Cool air indoors travels through a vent and is directed into an opening in the ''bottom'' of a solar collector. The air contained within the solar collector is then heated by the sun via [[solar radiation]]. Cool air is dense and will sink, while warm air is less dense and will rise. As the air heats up within the solar collector, it becomes less dense than the cooler air and rises. The warm air rises out of a vent in the top opening of the solar collector, moves into the desired area ''(i.e. indoors)'', and is replaced by cooler air. This air exchange process will continue until the indoor air temperature reaches an [[equilibrium]] with the temperature outdoors.


An example of a [[passive solar thermal]] heating system method is '''Thermosiphon Heat Exchange'''. It is based on the principle of natural [[convection]], in which air or water is circulated in a vertical closed-looped circuit without using a pump. Cool air indoors travels through a vent and is direccted into an opening in the ''bottom'' of a solar collector. The air contained within the solar collector is then heated by the sun via [[solar radiation]]. Cool air is dense and will sink, while warm air is less dense and will rise. As the air heats up within the solar collector, it becomes less dense than the cooler air and rises. The warm air rises out of a vent in the top opening of the solar collector, moves into the desired area ''(ie. indoors)'', and is replaced by cooler air. This air exchange process will continue until the indoor air temperature reaches an [[equilibruim]] with the temperature outdoors.


'''Cost'''
==== Materials ====
* Passive thermosiphon water heaters may range from $500 to $6,500. Pricing may vary due to solar exposure and geographical location 
Keep in mind: ''the bigger the solar collector, the better.''
* Many counries, states, and utility services provide incentives for solar energy participation
=== '''Schematics''' ===
[[Image: Water_heater(1)_(3).jpg]]


===Materials===
'''Solar collector'''


'''Frame'''
- 6 vertical 2-by-6-inch boards -sideboards
- 2-by-6, and a 2-by-8 boards - top sill
- lag screws - recommended, but not necessary for attachmant   
'''Glaze'''
- corrugated polycarbonate panels
- 10 panels - 26 in wide by 8 ft high
- Pairs of panels overlapped over 1-by-1-in vertical wood strip - makes 4-foot-wide panels for each bay
- ultraviolet-resistant coating - apply to sun-facing side to extend longevity
'''Solar absorption plate'''
- 2 layers black metal window screen - attached across the top and bottom of bays
'''Vents'''
- holes cut through building’s siding
Note: - plastic flaps will prevent back flow of air through upper vents at night


== Pro's & Con's ==
==== Cost ====
* Current research ''(2007)'' suggests that passive heat exchangers may range from $55.00 to $400. Pricing may vary due to size of collector/s, insulation of area to be heated, solar exposure, and geographical location. 
* Many countries, states, and utility services provide incentives for renewable energy participation
 
==== Pros & cons ====


'''''Pro's'''''
'''''Pro's'''''
Line 124: Line 180:
'''''Con's'''''
'''''Con's'''''
* Increased maintainence - (ie. covering during times of low solar radiation)
* Increased maintainence - (ie. covering during times of low solar radiation)
* Geograpgical location
* Geographical location may alter effectiveness
* Requires manual colsing of backdraft dampners at night
* Requires manual closing of back draft dampers at night
* South facing installments preferred


 
== References ==
= References =


* National Renewable Energy Laboratory (NREL) Dynamic Maps, GIS Data, and Analysis Tools- Solar Maps (2007)  
* National Renewable Energy Laboratory (NREL) Dynamic Maps, GIS Data, and Analysis Tools- Solar Maps (2007)  
Available: http://www.nrel.gov/gis/solar.html
Available: http://www.nrel.gov/gis/solar.html
    
    
* Citarella, Joe. "Thermosyphons - Better Approach to CPU Cooling?" Overclockers. 5 August 2005. <http://www.overclockers.com/articles1246>.
* Citarella, Joe. "Thermosyphons - Better Approach to CPU Cooling?" Overclockers. 5 August 2005. http://www.overclockers.com/articles1246
 
*Reysa, Gary. "Build a Simple Solar Heater" Mother Earth News. January 2006 http://www.motherearthnews.com/Alternative-Energy/2006-12-01/Build-a-Simple-Solar-Heater.aspx
 
*"Part 2: A Tour of Renewable Energy Applications." http://www.uneptie.org/pc/tourism/documents/energy/11-26.pdf


* Mirmov, N. I., Belyakova, I. G. "Heat liberation during vapor condensation in a thermosiphon." Journal of Engineering Physics 43(3), pp.970-974, 1982.
* Mirmov, N. I., Belyakova, I. G. "Heat liberation during vapor condensation in a thermosiphon." Journal of Engineering Physics 43(3), pp.970-974, 1982.


* Design and Performance of a Compact Thermosyphon. Aniruddha, P., Yogendra, J., Beitelmal, M,Patel, C., Wenger, T.  
* Design and Performance of a Compact Thermosyphon. Aniruddha, P., Yogendra, J., Beitelmal, M,Patel, C., Wenger, T.  
Woodruff School of Mechanical Engineering. 2002. <http://www.hpl.hp.com/research/papers/2002/thermosyphon.pdf>.
Woodruff School of Mechanical Engineering. 2002. http://www.hpl.hp.com/research/papers/2002/thermosyphon.pdf
 
== Interwiki links ==
 
* [[Wikipedia:Thermosiphon]]


*"Part 2: A Tour of Renewable Energy Applications." http://www.uneptie.org/pc/tourism/documents/energy/11-26.pdf


{{Solar navbox}}


{{copyedit|Integrate merged content (first section -  "Abstract" marks the start of the second article.) This will require some understanding of the tech - not ''just'' a copyedit job. }}


--[[User:Fatima|Fatima]] 12:39, 5 October 2007 (PDT)
[[Category:Passive solar]]
{{stub}}
[[Category:Solar]]
[[Category:Solar hot water]]
[[Category:Solar hot water]]
[[Category:Heating and cooling]]
[[Category:Heating and cooling]]
[[Category:PH261]]
[[Category:PH261]]
{{PH261 Page}}--[[User:Hoffster|Hoffster]] 09:29, 6 December 2007 (PST)

Revision as of 23:12, 26 November 2013

The principle of the thermosyphon system is that cold water has a higher specific density than warm water, and so being heavier will sink down. Therefore, the collector is always mounted below the water storage tank, so that cold water from the tank reaches the collector via a descending water pipe. If the collector heats up the water, the water rises again and reaches the tank through an ascending water pipe at the upper end of the collector. The cycle of tank -> water pipe -> collector ensures the water is heated up until it achieves an equilibrium temperature. The consumer can then make use of the hot water from the top of the tank, with any water used is replaced by cold water at the bottom. The collector then heats up the cold water again. Due to higher temperature differences at higher solar irradiances, warm water rises faster than it does at lower irradiances. Therefore, the circulation of water adapts itself almost perfectly to the level of solar irradiance. A thermosyphon system's storage tank must be positioned well above the collector, otherwise the cycle can run backwards during the night and all the water will cool down. Furthermore, the cycle does not work properly at very small height differences. In regions with high solar irradiation and flatroof architecture, storage tanks are usually installed on the roof. Thermosyphon systems operate very economically as domestic water heating systems, and the principle is simple, needing neither a pump nor a control. However, thermosyphon systems are usually not suitable for large systems, that is, those with more than 10 m² of collector surface. Furthermore, it is difficult to place the tank above the collector in buildings with sloping roofs, and single-circuit thermosyphon systems are only suitable for frost-free regions.

Thermosyphon.gif

Abstract

Also known as: thermosyphoning

Thermosiphoning is considered to be an appropriate technology. This process utilizes natural, renewable resources and the basic laws of thermodynamics to create movement of a heated supply of air or water. The energy source for this process is solar radiation(or any other source of heat): the energy of the sun is captured in a solar collection device and is transferred to either air or water via conduction. The entire process may be explained by the thermosiphoning effect: When air or water is heated, it gains kinetic energy from the heating source and becomes excited. As a result, the water becomes less dense, expands, and thus rises. In contrast, when water or air is cooled, energy is extracted from the molecules and the water becomes less active, more dense, and tends to "sink." Thermosiphoning harnesses the natural density differences between cold and hot fluids, and controls them in a system that produces natural fluid movement. Several systems based on this technology are currently available, and may be read about in greater detail within the following text.

Underlying physics

Thermodynamics is the study of energy.

  • First law of thermodynamics- States that energy may be changed from one form to another, but cannot be created or destroyed. - Energy is always conserved.

This law may be applied to the movement of water in thermosiphoning system: Energy from the sun is directed and transferred (via conduction and convection) to either water, air, or another medium of choice. This natural process of heating eliminates the need for external energy sources such as fossil fuels or electricity.

  • Second law of thermodynamics- States that in all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state. - The net return of a system is always less than that of which was initially put in.

Energy is always conserved, however energy (or heat in this case) may often be lost in a given system (thermosiphoning) as heat. Adding insulation with appropriate R values to the system and its plumbing may greatly reduce heat loss, and thus increase efficiency.

  • Planck’s Law- the wavelength of radiation emitted from a surface is proportional to the temperature of the surface

Energy transferred as a result of temperature differences between two objects -Dark objects absorb heat, while light objects reflect

Darkly colored collection plates within the solar collector will aid in increasing solar absorption, thus increasing the amount of heat available to heat water or air in thermosiphoning. In contrast, reflective or lightly colored piping and storage tanks should be utilized as the light colors will help to reduce heat radiation out of the system.

Water heating

Passive

The passive thermosiphoning of water is the process of heating and moving water within a system without the need or use of electricity. This process functions by utilizing natual phenomena such as solar energy, gravity, and an available water source. A solar collector, piping, and a water tank are materials required for the heating process. The flow of water is distributed into, within, and out of the solar collector. Cool water enters the bottom of the solar collector where it is then heated via convection by solar radiation. When water is heated it becomes less dense than cooler water, expands, and then rises (flows) through the piping. The heated water exits the top of the solar collector naturally. The cooler and more dense water sinks and remains within the solar collector until it is heated. As the cool water is heated, it expands, rises, is pushed out of the top of solar collector, allowing cool water to flow into the solar collector. This process continues naturally until the temperature of the water reaches an equilibrium with solar radiation input.

Two types of thermosiphon water exchange systems are currently available: the close-coupled system, and the gravity-feed system.

Close-coupled system

Close-coupled systems function on the same principles of passive thermosiphoning mentioned above. The storage tank of these systems must be placed above the solar collector to utilize the water circulation driven by the passive thermosiphoning process.

Schematics
Materials
  • Solar Energy
  • Solar Collector
  • Piping
  • Insulation
  • Water
  • Storage Tank
  • Strong roof or other support system
Cost
  • Current research (2007) suggests that passive thermosiphon water heaters may range from $500 to $6,500. Pricing may vary due to tank size, solar exposure, and geographical location
  • Many countries, states, and utility services provide incentives for renewable energy participation
Pros & cons

Pro's

  • Non-polluting
  • Energy Savings - No electricity needed for passive thermosiphoning
  • Cost Effective
  • Space saving - (ie. indoors)

Con's

  • Tank exposure to external environmental condition may reduce efficiency, depending on geographical location
  • Aesthetics - May be considered visually unpleasing
  • Strong support structure needed (i.e. roof)
  • Not suitable for extremely cold climates
  • Location - must be positioned in an area with suitable solar exposure (i.e. south side of desired area)

Gravity-feed system

Gravity-feed systems utilize the same principals of passive thermosiphoning as does the close-coupled system, however placement of the tank differs. Tanks are installed horizontally into a roof, which is often located directly above the solar collector. Once needed, the heated water within the storage tank takes the path of least resistance and moves via gravity down into the desired location. Gravity-feed systems require more piping/plumbing to distribute the heated water, and this factor should be taken into consideration when installing or purchasing a thermosiphoning system.

Materials
Schematics
  • Solar Energy
  • Solar Collector
  • Piping
  • Insulation
  • Water
  • Storage Tank
  • Strong roof or other support system


Cost
  • Gravity-feed systems are typically the least expensive passive thermosiphoning water heaters
  • Current research (2007) suggests that the cost may range from $400 to $5,500 (Not including the cost-if applicable- of installation). Pricing may vary due to tank size, solar exposure, and geographical location
  • Many countries, states, and utility services provide incentives for renewable energy participation
Pros & cons

Pros

  • Non-polluting
  • Energy Savings - No electricity needed for passive thermosiphoning
  • Cost Effective
  • Space savings - (ie. indoors)
  • Aesthetics - (Horizontal tank placement)

Cons

  • Plumbing and piping add additional costs to the system
  • Aesthetics - May be considered visually unpleasing
  • Strong support structure needed (i.e. roof)
  • Not suitable for extremely cold climates
  • Location - must be positioned in an area with suitable solar exposure (i.e. south side of desired area)

Active

Also known as: pump systems or split systems

Schematics

Active solar heating systems function on the same basis of the thermosiphoning effect, however active systems utilize an energy source other than solar energy to help drive the process. This system installs only the solar collector on the roof, while the storage tank is installed on the ground or anywhere else below. These active water heating units require some external form of energy to pump the water throughout the system. By utilizing additional energy, these active systems are less cost efficient than passive systems.

Materials

  • Solar Energy
  • Solar Collector
  • Electrical energy
  • Electrical pump
  • Additional piping
  • Insulation
  • Water
  • Storage Tank

Cost

  • Current research suggests (2007) that active thermosiphon water heaters may range from $1,200 to $10,500. Pricing may vary due to tank size, internal piping requirements, solar exposure, and geographical location
  • Many countries, states, and utility services provide incentives for renewable energy participation

Pros & cons

Pro's

  • Money Savings
  • Cost Effective
  • Aesthetics - Storage tank not placed on the roof
  • Greenhouse gas reduction - If insulated properly, it has the potential of polluting as little as passive systems.

Con's

  • Uses more energy than a passive system
  • Requires more maintenance than a passive system
  • Heat loss - during the transfer from the solar collector to the storage tank below
  • Pollutes some - from the electrical usage
  • Location - must be positioned in an area with suitable solar exposure (ie. south side of desired area)

Passive air exchange

Schematics

An example of a passive solar thermal heating system method is Thermosiphon Heat Exchange. It is based on the principle of natural convection, in which air or water is circulated in a vertical closed-looped circuit without using a pump. Cool air indoors travels through a vent and is directed into an opening in the bottom of a solar collector. The air contained within the solar collector is then heated by the sun via solar radiation. Cool air is dense and will sink, while warm air is less dense and will rise. As the air heats up within the solar collector, it becomes less dense than the cooler air and rises. The warm air rises out of a vent in the top opening of the solar collector, moves into the desired area (i.e. indoors), and is replaced by cooler air. This air exchange process will continue until the indoor air temperature reaches an equilibrium with the temperature outdoors.


Materials

Keep in mind: the bigger the solar collector, the better.

Solar collector

Frame - 6 vertical 2-by-6-inch boards -sideboards - 2-by-6, and a 2-by-8 boards - top sill - lag screws - recommended, but not necessary for attachmant Glaze - corrugated polycarbonate panels - 10 panels - 26 in wide by 8 ft high - Pairs of panels overlapped over 1-by-1-in vertical wood strip - makes 4-foot-wide panels for each bay - ultraviolet-resistant coating - apply to sun-facing side to extend longevity Solar absorption plate - 2 layers black metal window screen - attached across the top and bottom of bays Vents - holes cut through building’s siding Note: - plastic flaps will prevent back flow of air through upper vents at night

Cost

  • Current research (2007) suggests that passive heat exchangers may range from $55.00 to $400. Pricing may vary due to size of collector/s, insulation of area to be heated, solar exposure, and geographical location.
  • Many countries, states, and utility services provide incentives for renewable energy participation

Pros & cons

Pro's

  • Low cost
  • Energy saver
  • Pollution reduction
  • May be used to cool electronics

Con's

  • Increased maintainence - (ie. covering during times of low solar radiation)
  • Geographical location may alter effectiveness
  • Requires manual closing of back draft dampers at night
  • South facing installments preferred

References

  • National Renewable Energy Laboratory (NREL) Dynamic Maps, GIS Data, and Analysis Tools- Solar Maps (2007)

Available: http://www.nrel.gov/gis/solar.html

  • Mirmov, N. I., Belyakova, I. G. "Heat liberation during vapor condensation in a thermosiphon." Journal of Engineering Physics 43(3), pp.970-974, 1982.
  • Design and Performance of a Compact Thermosyphon. Aniruddha, P., Yogendra, J., Beitelmal, M,Patel, C., Wenger, T.

Woodruff School of Mechanical Engineering. 2002. http://www.hpl.hp.com/research/papers/2002/thermosyphon.pdf

Interwiki links


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