Design considerations for “Solar Heated” homes

Introduction: (Initial Observation)

Limited resources and high prices of fossil-based fuels have encouraged people to use solar energy as a heat source for homes. In order to use solar energy for heating homes we need to have methods to collect the heat in sunny hours, store the heat in some form, transfer the heat to the home at night or cloudy hours.
Solar heated homes also need to be energy efficient, so they can maintain heat for as many hours as possible.

In this project you can focus in one of the three basics of solar heated homes or you can study all 3 parts at the same time. For example you may want to focus on storing the energy and find methods or material that can store large amounts of heat and hold it for a long time.

Information Gathering:

Find out about what you want to investigate. Read books, magazines or ask professionals who might know in order to learn about the effect or area of study. Keep track of where you got your information from.

When gathering information, start your study by visiting the website of Energy Independent Housing. This website includes valuable information as well as drawings and models that you can make using paper, cardboard or balsa wood. Models can be a valuable addition to your project, specially if you input some of your own ideas on their design.

It is also good to see the design of solar collectors in another part of the same website.

Review the Energy Fact Sheet to learn about passive and active solar heating systems.

How to continue this project?

Being able to test different design factors is an important part of designing solar system homes. You will need to conduct at least one of the experiments proposed in this project to show that you are able to perform such experiments and use the results in your designs.

You should also make a model with paper, cardboard, balsa wood, wood glue or anything else that you can get hands on. Your model can help you to demonstrate the benefits of each design factor. You can also use your model as a part of your display.

Specific Heat Capacities Table

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

Following are three purpose that I suggest for this project.

The purpose of this project is to identify design considerations in solar heated homes that can contribute in

• collecting/ absorbing more solar energy
• storing energy
• re distribution of stored heat when needed

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Independent or manipulated variables that may affect the amount of absorbed solar energy are:

• The area of collectors
• The color of collectors
• The angel of collectors with sun light

Dependent variable is the rate of energy absorption.

Independent or manipulated variable that affect the storage of energy is the type of storage medium. Dependent variables are the specific heat and heat retention of the medium.

Independent variables that may affect the redistribution of energy are design variables such as size and position of energy storage tank as well as heat exchange method. Dependent variable is the rate of redistribution.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

Depending on the section of this project that you decide to focus, following are some sample hypothesis.

• Higher area of heat collectors result absorption of higher amount of heat energy. My hypothesis is based on my gathered information indicating solar energy is 1.5 KW per square meter.
• Black color on the surface of collectors result the highest amount of energy absorption. My hypothesis is based on my gathered information and the fact that black color absorbs a wider spectrum of visible light.
• A right angle between the surface of the collector and solar radiation will result the highest amount of absorbed energy. My hypothesis is based on my observation that when the angle of any flat board with the sun light beams changes from right angel, it forms a smaller shadow, so less sunlight will touch the surface.
• Water is the safest and best medium for storing heat and has a higher heat capacity and heat retention than other liquids such as oils and alcohols. My hypothesis is based on my observation that hot water stays hot for a longer time than oils.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1: Heat Retention

In this experiment we warm up our medium sample (water, salt water, oil, alcohol,..) to a certain temperature (for example 80 degree centigrade). Then we place the sample in a cooler that is in room temperature and record the temperature increase in the cooler. We will continue to record the temperature of the air in the cooler and make a graph. This graph will show us which of the tested material can store the highest amount of heat and retain it for a longer time.

1. Poke a small hole in the cooler’s top. CAREFULLY insert one thermometer so it extends all the way through the top then about a centimeter. Tape the thermometer in place with clear tape. Be careful not to move the thermometer around in the hole it made.
2. Place the cooler’s top on the cooler so it seals. Record the temperature inside the cooler after five minutes and write that temperature in your journal.
3. Fill one plastic bottle with water as your first sample medium. Place it in a pan of hot water. Use the other thermometer to record the temperature of the water in bottle for until it gets to 80º C. Write the final temperature in your journal.
4. Place the hot water bottle in the cooler. Record cooler’s temperature every two minutes for the first ten minutes then every ten minutes for five to 8 hour.
5. Prepare a graph that shows heat loss in the system over a day’s time.
6. Repeat the experiment with the same amount of hot salt water (Include as much salt as possible).
7. Repeat the experiment with the same amount (by weight) of dry sand.
8. Repeat the experiment with the same amount (by weight) of liquid oil.

Experiment 2: Heat capacity

Material that have a higher heat capacity take more time to warm up and take more time to cool off. So you want to design an experiment that would show the differences in heat capacity for equal volumes of different substances, and you want to be able to design the experiment and run it with things from around the house. A pan of simmering water provides a good, stable heat source. If you fill a Pyrex cup with different materials, you could show that some materials warm up more slowly than others, and then cool down more slowly as well. Following procedure is for testing heat capacity of water, alcohol, and air.

Procedure: Fill up a Pyrex measuring cup with either water, rubbing alcohol, or air, and then place it in a pan of simmering water. In the case of the air, use an empty cup and cover it with a sheet of plastic in order to keep the volume of air in the cup contained. Initially, the cup and its contents must be at room temperature. The temperature of the simmering water in the pan can be approximately 200 degrees Fahrenheit. Place a thermometer in the measuring cup in order to measure the temperature of the contents of the cup. Read and record the temperature every minute for ten minutes. Then remove the cup from the water and placed in a cold water bath. Measure and record the temperature of the cup’s contents every minute for ten minutes.

Record the results in a table like this:

Here is a table and a graph showing the results of the experiment. As you will see, the water did warm up more slowly than the alcohol, and both the water and the alcohol were slow to warm up compared to the air. In cooling, the exact reverse was true. The air cooled fastest, followed by the alcohol, then the water. This means that the water has the highest Heat capacity of the three, and the air has the lowest.

For heat capacity of metals such as Iron and copper click here.

Experiment 3: Investigating the effect of color on the absorption of energy from light

Material

• 6 Test tubes, each containing 35ml of water
• 5 Different colored papers – Red, Green, Blue, Yellow, Black, Clear.
• 3 40W Lamps
• 1 Clamp stand
• 1 Stop clock
• 1 Temperature probe

Procedure

Set up a test tube and a thermometer in a clamp stand, and placed the three lamps around it, at approximately 15cm from each bulb. Use a measuring cylinder to add certain amount of water to the test tube. (make it about half full). Then cover the outside of the tube in one color of paper, making sure that it is held tightly to the glass, and begin timing from the time when you turn on the lamps. After a set length of time (10 minutes for example), measure and record the temperature. Repeat the experiment for each color. Repeat the entire experiment several times and take averages of the results.

Sample Results

Sample Conclusion

As can be seen from the results, the test tube that was covered with black paper absorbed the most heat from the lamps. The other colors absorbed varying amounts of heat, but not as much as the black. We could improve this experiment by using copper tubes instead of using glass tubes – metals are better conductors and the energy would be conducted to the water more efficiently; we could also keep the same colors but paint them on to the copper tubes to investigate whether the conduction from the paper to the tube is affecting the temperature change in the water.

Experiment 4: Specific Heat Capacity

This experiment is for measuring the specific heat capacity of different fluids to test which would be most useful in a solar panel. Such experiments are performed many times and specific heat capacity of many material are known and are available in books and on the Internet. We have a sample table above in the gathering information section.

How much heat energy do we need to heat water,
and is water the best material to use in a solar panel?

Introduction:

Different substances contain different amounts of thermal energy depending on their nature, temperature, and mass. The heat capacity of an object is the amount of heat required to raise its temperature by one degree. The specific heat capacity is the amount of heat required to raise the temperature of the unit mass of a substance by unit temperature; it is measured in joules per kilogram per kelvin (Jkg-1K-1).

Specific heat capacities vary widely from one substance to another and from one range of temperatures to another.

The specific heat capacity of a substance can be found by measuring either the rise or fall in temperature of a sample of known mass under controlled conditions in a calorimeter. The total amount of thermal energy any body gains or loses is the product of its mass, its specific heat capacity, and its change of temperature.

Material and equipment:

• Thermometer
• Ammeter
• Voltmeter
• Copper calorimeter
• Electric heater
• Stop clock
• Measuring cylinder
• Digital balance

Diagram

Sample Procedure:

We first weighed the calorimeter, then added water to fill approximately three quarters of the calorimeter, and reweighed it. We subtracted the mass of the calorimeter from that of the calorimeter plus the water to find out the weight of the water. Next we measured the starting temperature of the water. We then set up the experiment and, using water as our first test liquid, we measured the voltage and the current supplied to the heater. We timed the experiment for 10 minutes, and after this period we recorded the finishing temperature. Lastly we took away the starting temperature from the finishing temperature to find out the temperature rise. We repeated the experiment several times, using both oil and water.

Sample Results:

We obtained our results using:

Energy in = Voltage x current x time (sec)
Energy absorbed by water = Mass x Specific Heat Coefficient x Temp. rise

Conclusion

We found that it takes half the time to heat up the oil compared to the water, because when we heated the same mass of liquid under the same conditions for 10 minutes the oil temperature rise was double that of the water. This would suggest that the specific heat capacity of water was double that of oil. This could be useful in solar panels because it heats up to a certain temperature more quickly. However, water would be able to absorb more energy per volume used and so might be more useful if there was a large amount of heat loss in the system. Another factor in the final choice would be which one is able to exchange the heat more readily to produce usable energy.

Materials and Equipment:

List of material can be extracted from the experiment design of each experiment.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Since we have proposed more than one experiment in this project, some sample results are following each experiment.

Calculations:

If you do any calculation for this project, write your calculations in this section.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

List of References