Team 5 Solar Dryer

The goal of this project was to design an energy-efficient, time-saving, cost-effective solar-powered clothes dryer to be used in Penn State University’s entry home for the Solar Decathlon. The design constructed through this project uses a mere 1.115 kilowatts of energy per cycle of laundry, while a standard electric clothes dryer uses 4.6 kilowatts. Our dryer uses only 24% of what a standard dryer uses, demonstrating that the design does indeed meet the customer needs.

The Penn State Solar Decathlon Team is constantly trying to make each component of the solar home more energy efficient and easier to use, to meet their competition standards. One of these components would be the design of a solar dryer. Based on competition standards, the dryer must be able to be as energy efficient as possible, dry six towels in less than two hours, and must be able to be located in a convenient location in the home. To start this process, a Gantt chart was created to assign each team member specific duties, and to provide the team with an easy to follow schedule. Next, a mission statement was created to give the team guidelines to work by. Our design process then began with background research on current washers and dryers that are available on the market today, to get an understanding of what our solar-dryer should be able to do. A review of the customer needs, which in this case was the design competition standards, was completed again to keep the team on track with their goals. After the goals were clear to the team, we began working on generating concepts. The form of concept generation that we used was brainstorming, in which we generated as many concepts as possible, and narrowed down the best options. With all of this information at hand we produced a final design, tested the design, and made modifications to come up with a complete final product. This product was then analyzed for cost and energy efficiency. Each step of this process was important in determining the best solution for the problem given.

To keep our team on track, we created a Gantt Chart that allowed us to assign tasks and establish deadlines. The responsibility of each task for the project was assigned to a group member. By establishing these guidelines at the beginning of the project, our team was able to get organized and finish the project on time.

Traditional clothes dryers consist of three main parts: a rotating tumbler that spins the clothes, a heating element that heats the water in the clothes and a vent that allows the air to exit the dryer.

For the tumbler, a small motor is used for spinning. Due to the high ratio of the diameter of tumbler to that of the motor, a single belt is needed for the rotation.

For the circulation of air, air enters the body of the dryer through a large hole in the front of the dryer. The air then is sucked past the heating element into the tumbler. The heating element of the dryer is made of nichrome wire which is a good producer of heat as its fairly high electrical resistance allows it to get hot fast and as the alloy does not oxidize when heated. After hitting the heating element, the air passes through the clothes in the tumbler and moves through the front door and into the lint screen where it passes out of the dryer through a duct in the back.

The combination of the tumbler’s rotation and the hot air’s circulation causes the clothes to dry.

Patent number: 4514914
Filing date: Feb 16, 1984
Issue date: May 7, 1985

Patent number: 5809663
Filing date: Jul 17, 1997
Issue date: Sep 22, 1998

Patent number: 5755040
Filing date: May 9, 1997
Issue date: May 26, 1998

Patent number: 6973740
Filing date: Jan 14, 2003
Issue date: Dec 13, 2005

While retaining the basic concept of a clothesline, many variations of this clothes dryer have come onto the market.

i. Traditional clothesline: Very easy to install, this solar dryer consists of a strong string pulled taut between two locations to allow the user to hang clothes over it. Though these devices have a very low initial cost and no running costs, they do not dry clothes in all types of weather and are considered an eye-sore.

ii. Umbrella drying rack: This device consists of an umbrella like frame-structure across which wires have been pulled taut. It allows customers to dry a large volume of clothing in a small space. Made to be used outdoors, these models also have a low initial cost and no running costs. Like the traditional clothesline, these devices can be unhelpful in case of inclement weather.

iii. Indoor drying rack: Usually easily collapsible, indoor drying racks solve some of the problems seen in other clothesline-like devices. Since many are portable, they can easily be stowed away when not in use. However, the amount of clothing held by the dryers does not compare to the capacity of a long clothesline or an umbrella drying rack. Also, the drying period is heavily dependent on many outside factors leading a single drying cycle to take many hours.

I. Electric tumble dryer: this is the most common type of electric dryer. It uses a clothes tumbler and a heating element to force water out of clothes and then convert it to water vapor. Tumble dryers are very effective at drying clothes completely but have a high initial cost and require a large amount of electricity to be powered.

ii. Drying center: This system relies on the a heating element and strategic placement of clothes to help them dry. Similar to the concept of a heated closet, a drying center uses the heating element to evaporate water out of clothes.

A centrifuge uses centripetal acceleration to force water out of clothes. While they are effective to an extent, they are incapable of getting clothes completely dry.

a. Manual compression – For this method, the clothes are wrung out to force the water out. While this method can remove a large amount of water in the clothes, they are usually damp afterwards. It is very difficult to achieve fully dried clothes using this method.

b. Centrifuge – This method involves rotating the wet clothes around a fixed axis. The centripetal acceleration from the rotation and the difference in densities of water and clothes causes the water to separate from the clothes. While more effective that manual compression, this method can also leave clothes damp.

c. Evaporation – Evaporation, which can occur at any temperature, occurs when high energy molecules near the surface escape into the surrounding atmosphere. As the temperature of the liquid increases, the number of molecules with energy to go into vapor phase increases.

For this project, our customer was the Penn State Solar Decathlon Team. We based our customer needs on their requirements for the solar home and the rules of the Solar Decathlon Challenge.

To fully determine the needs of our dryer, we asked a few questions to the solar decathlon team. Using their answers, we determined that the dryer could be placed anywhere in the house and that the dryer would need to dry at least 6 towels at one time. We were also told that a low-energy washer would be used to wash the clothes.

The rules dictated by the Solar Decathlon Competition stated that the dryer would be used over the course of the week that the solar home would be set up. It would also be used at different points of day, an important factor since this would mean that there would not be an equal amount of light at all times.

Design Project 2 presented the problem of designing a solar-powered dryer that would meet customer needs. It was discovered that customers were looking for a dryer that was energy efficient, cost-friendly, time-effective (could dry a large amount of clothing in as short a time as possible), aesthetically pleasing, and could be used for any type of clothing (including delicates).

For a conventional dryer, electricity is used to power the heating element, the fan and the tumbler. When combined, the fan generates hot air that flows through the clothes and helps extract water. The tumbler uses centripetal acceleration to push water out of clothes. The electricity in this case is supplied by the power grid.
For our design, the electricity is generated by a simple solar panel attached to the roof. The energy generated flows to the heating element and the fan in our dryer. The fan circulates the warm air and causes the water in the wet clothes to evaporate, thus drying the clothes.

U.S. Household Electricity Report estimates that 61 million households with dryers consume 66 billion kW of energy. This equals about 1081kW per household each year. Since a typical dryer cycle uses 4.6 kW of energy per cycle, this equals about 235 drying cycles each year or 4.5 drying cycles each week.
As per these calculations, our final dryer uses 1.115Kw of energy per cycle. This means that our system uses a mere 262.025kW of energy per year (for an average family).

Our team came up with different main concepts for the design of the dryer. We decided on using either a traditional dryer with a spinning tumbler, a closet-like space with adequate air circulation or a combination of the two. For air circulation, we planned on using a fan with either hot or cold air for the closet-like design while relying on the tumbler and hot or cold air with the spinning system. We also decided that while the main source of power for the dryer would be the sun, it would be able to use power from the grid if necessary. Finally, we had three main waste products that arose from the dryer cycle.

Our final concept consists of a closet-like dryer that used a fan and hot air to dry clothes. Our final decision was based on a combination of cost, energy used and time taken for drying. While the spinning tumbler concept has already proven its effectiveness in the current market, our team felt that the system is not as efficient with energy as we would like. A combination of the spinning tumbler and closet system, though ideal, seemed both expensive and wasteful. Our final choice was the closet system because we felt that it would have very minimal energy usage for a heating and fan system. We also felt that this system offers benefits such as fewer wrinkles in clothes, which cuts back energy costs and time in ironing, and a more gentle cycle for delicate clothes which is not seen in the tumbler system. We ran tests with a model that we built to finalize our design and decide if we wanted to use hot or cold air for circulation.

Our closet-like drying system is very easy to operate. The dryer is powered by through solar panels located on the roof. Once the on button is pushed the coils located on the bottom of the dryer begin to heat up while a fan turns on circulation warm air throughout the inside of the dryer. As the air circulates, the clothes begin to dry. This system is very good for preventing wrinkles and delicate clothing because there is no spinning and it just rests on hangers. As the clothes dry the warm air becomes moist so, there is a vent at the top in the back for vitalization. I will take approximately 45 minutes for your clothes to dry.

With our model, the team used a Remington hair dryer to simulate the flow of hot air through the system. The hair dryer has five settings, with five being the highest. On the fifth setting, the hair dryer uses 1.875 kW of energy. Since we used the hair dryer on the fourth out of five settings, to determine the amount of energy used in the model, we multiplied the 1.875 by 4/5 (or 80%) for a total energy usage by the model of 1.5 kW/cycle. However, the hair dryer used utilized an overly high amount of energy that would not make sense for an actual solar-powered dryer, so our team was forced to utilize other methods of heating and air circulation to output a more accurate energy usage for the dryer. We decided since our actual system would use heating coils as a heating element, we used the energy from a toaster (which also utilizes heating coils), at 1.0 kW of energy. For air circulation, we used the energy from a standard portable fan, at 0.115 kW of energy. By adding these two values together, we were able to come out with a much lower amount of energy used by the actual dryer of 1.115 kW of energy per cycle. A standard electric clothes dryer uses 4.6 kW of energy per cycle. Our design uses a mere 24% of what a standard dryer uses. From this data we could conclude that our design met the goal of the project.

To ensure that our model would meet the needs of the customer most effectively, we ran several tests to determine which design would do this. To test our design, we generated a model that was proportional in size to the actual design. The model consisted of a cardboard shell with a plastic lining and measured 1’ x 1’ x 2’. A plastic rod across the upper half of the box held the wet towel for drying. A Remington hairdryer was then used on its fourth highest setting with hot air to see how long the towel took to dry. The test ran for twenty minutes, and the previously weighed wet towel was weighed again to see how much water was lost in the process. The test was again ran with cold air this time to see the difference between hot and cold air. After this test, a third test, of hot air, was ran to see if the results from both hot air tests were consistent. The data collected from each test is shown in the table below:

Trial	Initial Weight	Weight With Water	Final Weight
1: Hot Air	51.8 g	140.3 g	88.5 g
2: Cold Air	51.2 g	147.3 g	130 g
3: hot air	51.2g	143.4 g	92.8 g

To determine the cost of working on and creating a model of our team’s dryer, we followed the guidelines to determine the initial NRE cost. This was done by first calculating how many hours total our team worked on the project. We estimated that each person worked an average of 6 hours per week over the span of seven weeks, for a total of 42 hours per person. Since there were four members of our team, we multiplied this number by four to determine that a total of 168 hours was worked. It was assumed that each member of the team was getting paid as part of an internship or co-op at an hourly rate of $18/hour. This rate was multiplied by the overhead rate of 1.8 (which includes facilities, vacation, workman’s compensation, sick leave, and healthcare) for a rate of $32.40/hour. This rate was then multiplied by the 168 hours worked for a total labor cost of $5443.20. Since mostly all of the materials to make the actual model were provided, the only portion of our model that needed to be included in the material cost analysis was the hair dryer that was used to simulate the flow of hot air through our model. The Remington hair dryer used had a cost of approximately $30.00, giving our team the model cost of $30. The labor cost ($5443.20) and the model cost ($30.00) were added together for a total cost of $5473.20.

Our team concludes that this design meets the needs of the customer: energy efficiency, length of drying time, and ease of use, very effectively. It meets the design standards for energy efficiency in that uses solar energy only to operate the dryer, and uses only 9kW of energy per load (appx. high due to large electricity use of a hairdryer). Our dryer design also meets the requirements for length of drying at a low 45 minutes. Finally, the dryer is easy to use, and can be located in a variety of locations in the home, because it is operated independently. The design process we followed helped us to meet the needs of the customer and create a successful product.

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2. Deming, Charles P. Dual energy input cycle for a dryer. Whirlpool Corporation, assignee. Patent 4226026. 1979.

3. "How Clothes Dryers Work." How Stuff Works. Nov.-Dec. 2008 <http://www.howstuffworks.com>.

5. "Low Energy Clothes Dryer Patent." Grayhatch.com - Thinking Outside the Box. Nov.-Dec. 2008 <http://grayhatch.com>.

6. Meyer, Robert W. Stationary clothes drying apparatus. Whirlpool Corporation, assignee. Patent 6973740. 2003.

8. Perque, Allen J. Portable, solar powered clothes dryer. Patent 5809663. 1997.

9. "Remington Solutions Gemstone Ceramic + Ionic Styler." Remington. 5 Dec. 2008 <http://remington-store.com>.

Power	Main Design	Air Circulation and Temperature	Output
Solar	Closet System	Hot air with fan	Water
Solar	Spinning tumbler	Cold air with fan I.e. only fan	Warm air
Generator	Combination of heated closet and spinning tumbler	Hot air with spinning tumbler	Chemical waste
Generator		Only spinning tumbler