Solar Powered Attic Fan

¶ … attic fan is an essential part of a building in that it helps in the regulation of the temperature of a building by reducing the heat energy level in a building's attic. It does so by getting rid of the hot air that is accumulated in a building.

The attic fan helps in the regulation of temperature by the exhaustion of the hot air by through the blade action. Due to the fluctuating nature of the temperature, it is necessary for the fans system to be automated by employing thermostats. An attic fan even though is surrounded by a number of controversies as regards its effectiveness in energy conservation, still remains to be an integral part of a building's design as ventilation to every space in a building is of utmost importance.

TABLE OF CONTENT

Introduction

History of the Photovoltaic cell (Solar Panel)

The construction of the solar panel

Photovoltaic systems in residential homes

Operation mechanism of an attic fan

Determination of the attic ventilation requirement for the attic fan

The attic fan design

Conclusion

15'Bibliography

Introduction

An attic fan is a necessary part of any home whose owner intends to achieve the necessary and proper ventilation and moisture level. Due to the current energy crisis that has hit the world couple with the global economic crunch, it has become necessary for governments, corporations and individuals to devise newer methods and techniques that rely on alternative energy sources. The solar energy for example is one of the best renewable sources of energy that can be utilized in the achievement of the necessary electrical power to drive both domestic and industrial devices such as fans used in the ventilation systems.

Apart from being an affordable source of electrical energy, the solar also offers an environmentally friendly alternative in that it does not emit any form of wastes that have always been associated with other energy sources such as coal and nuclear sources.

When the room temperature rises above 80 "F, t become uncomfortable to stay in the room.Therefore, it becomes necessary to invest in some for of an air conditioner. The advent of the solar powered attic fan brings peace of mind to a home owner in that he can decide to shut the windows and turn on the fan with the knowledge that the device can help in getting rid of the excess heat in the rooms while saving him over 35% on costs associated with home cooling.

The rise in temperature in the houses with attics is caused by the super heated air that gets trapped in the attic and then gets redistributed in the lower rooms through conventional air circulation.

History of the Photovoltaic cell (Solar Panel)

The word "photovoltaic" is derived from the Greek word ph-s which means "light" while the "voltaic" part of the name is which means electricity is derived from Volta, an Italian physicist.

The operation of the solar panel is dependent on a phenomenon referred to as the photo-voltaic effect which was discovered way back in 1839 by Becquerel, a French physicist. The building of the first solar cell however was actualized in 1883.That fete was achieved by Charles Fritts.He built the very first photovoltaic cell by coating the junction of Selenium, a semiconductor with a very thin layer of gold. The junction formed is what exhibited the first characteristics of a photovoltaic cell in history. It is worth noting that the efficiency of the first construction was just a mere 1%.It is the work of Sven Ason Berglund that led to the increase of efficiency of the solar cell. Sven had a series of patents that were geared towards increasing the efficiency of the photovoltaic cell. In 1946; Russell Ohl came up with the modern junction semiconductor. He patented the invention which he discovered as he worked on a sequence of experiments that lead to the development of the first transistor, a device that has indeed revolutionized modern electronics.

The modern day solar panel technology was discovered accidentally in 1954 at the Bell laboratories. While doing an experiment on semiconductors in the Bell labs, it was accidentally discovered that the doping of silicon with particular dopants (impurities) resulted in substance that was very sensitive to light. It was the work of D. Chaplin, C Fuller and G. Pearson that led to the invention of the first device capable of transforming energy of light into electricity. The result of this was an increase of the photo cell with an efficiency of 6%, which was high at that time.

The initial demonstration of a solar battery was done in 1954.Later on, further research was into the usage of the photovoltaic cell was funded by the government after its applicability was shown through various platforms. The photocell was used to power spacecrafts and geostationary satellites viably. Such funding and research has enabled the creation of the more efficient photovoltaic system capable of achieving over 80% efficiency. The current energy crisis and green energy policy has resulted to event further research and development regarding this energy source. The solar cell now boasts of a myriad of application from domestic, government to military application.

The construction of the solar panel

The diagram below illustrates the operation mechanism of a basic photovoltaic cell.

A very thin semiconductor wafer is designed and treated in a special way in order to produce an electric field. One side of the wafer has negative potential while the other has a positive potential. The action of light energy on the solar cell causes electrons and "holes" to migrate in opposite directions on the solar cell. The attachment of an electrical conductor to the opposite sides of the semiconductor wafer results in a compete circuit and hence electrical current flow is initiated. The generated electricity can then be used to power any type of a desired load. The load in our case is a motor driven fun.

Photovoltaic systems in residential homes

The photovoltaic system for residential homes should be designed in such a way that they can provide or rather supply half or three quarters of the residence's energy requirements. Such a system would typically be able to produce power of between 1-3 Kw.

Since different homes have different energy requirements, it is necessary to first of all evaluate the total electrical loading of the household before choosing any given system to install.

It is best practice to install the largest system that one's budget can allow. This is for the following reasons.Firstly, there is almost the same installation cost involved regardless of the system size and secondly, other PV system components such as the inverter are sized for a wide range of power outputs up to 5Kw.Therefore the nearer your system is to the 5Kw benchmark, the more savings one realizes.

Operation mechanism of an attic fan

Without the attic fan, room temperature can soar up to over 160 "F. The attic fan aids in cooling the room through the creation of a positive air movement the attic. The action does not rely on the action of the wind and also does not require excessive passive venting. The action of excessive passive venting is not ideal in that it results in the too much moisture infiltration in the room which results in the creation of precipitation such as snow or rain. The mounting of an attic fan is usually done on the roof of a house towards the back end at about distance of two feet from the peak of the roof. Its action of temperature regulation is aided through the action of a thermostat which automatically switches it on and off accordingly when the desired room temperature is achieved. The thermostat therefore ensures that the attic fan runs only when it is necessary and hence also helps in energy conservation and safety.

The advantages of an attic fan are as follows:

First on foremost, it helps in the lowering of room temperature by about 10 degrees. Through is action of temperature regulation, the life span of roofs is increased since it keeps shingles cooler. If a humidistat is included in the assembly, the fan helps in keeping the attic dry during the months of winter. The attic fan also helps in saving up to 35% on air-conditioning costs.

The total savings obtained by the use of an attic fan also depends on a variety of other factors. Such factors include the color of the roof, the degree of shading of the house, the level of insulation of the house and the overall efficiency of the home cooling system.Roughly, it has been estimated that the return on investment of an attic fan takes about three years. That is to say the installation pays for itself in a period of about three years. It is also important to invest in a high quality attic fan. The fun should be protected with a durable screen. The screen helps in keeping away pests. The choice of metal in the construction is preferable since it does not crack over a period of time as plastic does. A high quality thermostat is also necessary since it helps in energy conservation and is also time saving since it eliminates the need of the home owner climbing up to the attic in order to reset the fan. It is also necessary to include a firestat that helps in shutting off the fan incase of a fire outbreak. The fan's motor should be thoroughly lubricated at all times to ensure smooth operation.

There exist two types of attic fans. The roof top type and a gable-end type. The diagram below shows the effect of the attic fan on the overall ventilation of the house.

Determination of the attic ventilation requirement for the attic fan

1.Determination of the attic area's square footage to be ventilated

In order to determine the area of the attic to be ventilated by the attic fan, one need to multiply the length of the attic by the attic's width.

For example: Let's assume we have an attic whose length is 50 feet by 25 feet. Then it follows that the attic area to be ventilate d would be 50' x X 25'= 1250 square feet.

2.Determination of the required total net free area..

After determining the attic square footage, divide it by 150 in order to get the net free area needed to effectively ventilate the attic

Calculation:

1250 sq. ft + 150 = 8.333 square feet of net free area.

3.Determination of the required amount of intake and exhaust net free area.

In order to achieve an optimum performance in the attic ventilation, a balance must be achieved between the intake and the exhaust vents. This is achieved in calculation by dividing the result of step 2 by two.

Calculation

8.333 + 2= 4.16

4. Conversion to square inches

Ventilation product's specifications are usually listed in square inches. Therefore we must convert our calculations to square inches. To do this we multiply the results obtained by 1.

Calculation:

4.16 sq. ft x 144 = 599 sq. in. Of intake net free area and The attic fan design

The fan should be highly efficient in the exhaustion of air from the attic. The fan includes highly optimized airflow blades with a twisted configuration. The blades should be capable of achieving a rotational speed of up to 600 RPM.The choice of material for the blades should be plastic. That means that the blades can be remolded on to a hub in order to form one piece (unit).Metal too can be used in the design of the blades.

The assembly can then be mounted on an exhaust outlet possessing a conical shaped diffuser on the roof. The other alternative is to have the fan assembly in a portable form. This arrangement allows for the fan to be moved anywhere where need for ventilation arises. The blades are put in motion by the action of a solar powered motor. The blade and motor assembly should be capable of achieving approximately 1050 cfm while at the same time utilizing no more than 17 Watts.

The arrangement below portrays the basic configuration of the attic fan design.

The following factors are the most important in the design of the attic fan:

a) Uniform flow

In order for the fun wheel to impart a uniform stream of air of required velocity and pressure over the entire net attic area, the wheel must possess two very important characteristics.

i. The blades should be narrow at the tip as that is the area where the velocity is highest. The blade should then widen towards the hub. The widening of the blade towards the hub should is done in order to achieve more blade area that is required because of lower blade velocity.

ii. The blade's angle of rotation to the plane of rotation should be minimum at the tip and should increase towards the hub. It is necessary to calculate the width and angle for each point of the blade in this manner in order to achieve uniform velocity and pressure.

It is paramount to maintain uniform velocity and pressure over the blades because of the following reasons:

In case certain areas of the blade do not have same pressure as other portions of the blade, then there will be back flow of air in those points. Such points are located near the hub in blades such as the ones for an airplane propeller.

Inequality in the discharge velocity also results in power wastage in excess velocity pressure. Because velocity pressure increases as the square of velocity, inequality in discharge velocity, if translated converted into velocity pressure, would result to a higher velocity pressure. A good example being that fans which develop most of their velocity and pressure near the tip of the blade usually have very low efficiency.

b) Hub size.

The hub's aerodynamic purpose is to prevent back flow of air through the center of the fun and hence it increases the fan's efficiency. The hub should never be too large or too small. A large hub would result in an increase in velocity pressure. That would result in loss of efficiency due to the small net opening. A very small hub also results in the deterioration of air flow near the hub.