Rooftop Gardens A Green Alternative to Air Conditioning

Transcription

1 Rooftop Gardens A Green Alternative to Air Conditioning Define the Need: Rooftop gardens lower the maximum surface temperatures on roofs, but does this translate into changes in the internal temperature of the rooms in the building? Can a rooftop garden help conserve energy and lower your energy bill by keeping the internal temperature cooler on hot sunny days? This project will determine whether or not a rooftop garden can help keep a building cool. Background Research Would you like some sky vegetables for dinner? How about some fresh-cut roof flowers to put in vases in your house? Around the world, rooftops are being transformed into living green expanses. Besides beauty, rooftop gardens have a number of advantages, including growing food and taking carbon dioxide out of the air while releasing breathable oxygen. But can rooftop gardens also keep your house cooler and lower your energy bill? Imagine looking out over the rooftops of a city and seeing a canvas of living plants. All around the world rooftops are going green, especially in cities. These rooftop gardens are an environmentally friendly option that is gaining popularity. Living green roofs have many advantages, including providing more space for agriculture, adding beauty to the cityscape, and increasing the air quality. During photosynthesis, plants remove carbon dioxide from the air, and release oxygen. Over the course of a year, a single 1.5-meter by 1.5-meter section of a roof planted with grass produces enough oxygen to keep one human breathing for a year! Another advantage of rooftop gardens is the fact that they absorb heat and insulate the building better than traditional tar and gravel roofs. Because they sit in the direct sunlight for many hours, the temperature of traditional rooftops tends to rise above the actual air temperature. Then they radiate that heat back into the environment. If you live in a big city or have been to a mall with a lot of concrete buildings during warm months, you might have noticed the temperature difference between those areas and the suburbs or more rural areas. That is because when the heat is radiated back into the environment from the rooftops, an area with many buildings, like a city, can experience an increase in local air temperatures by as much as 5 7 F! This phenomenon is referred to as the urban heat island effect. However, rooftop gardens might be able to diminish this effect. Measurements from the Chicago City Hall show that on a summer day, when the air temperatures were in the 90's, areas of the roof covered in black tar rose to a surface temperature of 169 F, while areas planted with a rooftop garden only rose to 119 F that's a 50-degree difference (Chicago Department of Environment)! Rooftop gardens lower the maximum surface temperatures on roofs, but does this translate into changes in the internal temperature of the rooms in the building? Can a rooftop garden help conserve energy and lower your energy bill by keeping the internal temperature cooler on hot

2 sunny days? In this science fair project, you will find out by building two model houses one with a rooftop garden and one without and then you will compare how hot the inside of the houses get during the day and how they cool off when the sun goes down. Design Requirements: Materials and Equipment Garden clippers Photo storage boxes (2) of the same size, color, and shape. Tar paper; available at hardware stores (enough to cover two photo box lids) Strong double-sided tape, like carpet tape or foam mounting tape (1 roll) Sod (enough to cover one photo box lid) Exacto knife Thermometers (3). Clock or timer Lab notebook Heat lamp Heat lamp bulb Graph paper for analyzing the data. Experimental Procedure Design: Building the Box Houses 1. Using a pair of garden clippers or strong scissors, cut out two pieces of tarpaper that are the same size as the lids of the photo boxes. 2. With the double-sided tape, attach the tarpaper to the top of the photo box lids, as shown in Figure 1 below. 3. Place the lid of one of the boxes on the sod. Using the exacto knife carefully cut around the lid to get a piece of sod the same size as the lid. 4. Place the sod on top of the tarpaper lid of one of the boxes, as shown in Figure 1. a. The box with the tarpaper and sod lid will represent the rooftop garden house. b. The box with only the tarpaper lid will represent the traditional house. Figure 1. Design of a regular house and a rooftop garden box house.

3 Measuring the Temperature in the Box Houses 1. Put the three thermometers all in one place (a tabletop or counter with the same amount of lighting and heating) for 15 minutes. 2. Put one thermometer in each of the boxes. 3. Place the boxes on the same tabletop or counter, with the same amount of lighting and heating. 4. Place the third thermometer on the table between the two boxes. This is the external thermometer and represents the outside air temperature around the box houses. 5. Let the thermometers and boxes sit on the tabletop undisturbed for 30 minutes. External Internal of Rooftop Garden House Internal of Traditional House Starting Heated 1st Cooling Table 1. Data for the temperatures of each thermometer 2nd Cooling 6. After 30 minutes, record the temperatures in the data table in the lab notebook. These are the starting temperatures. a. One at a time, open each of the boxes and quickly read the temperature on the thermometer. b. Read the temperature on the external thermometer. 7. Now place a heat lamp above the box houses. Space the boxes and external thermometer such that they are getting equal lighting from the heat lamp. The lighted heat lamp will provide warmth and simulate what happens to the houses during a hot, sunny day. 8. After 1 hour under the lighted heat lamp, record the temperatures using the same technique as in step 6. These are the heated temperatures. 9. When done recording the temperatures, turn off the heat lamp. This is as if the sun has set for the day. 10. Then record the temperatures as the boxes cool down. a. After 15 minutes, record the temperatures using the same technique as in step 6. These are the first cooling temperatures. b. Then wait an additional 15 minutes and make a second temperature recording. These are the second cooling temperatures. 11. Repeat steps 1-10 four more times for a total of five experimental trials.

4 Analyzing the Data 1. The line graph shows the progression of temperature from starting, to heating, to cooling for each of the photo box houses. a. The y-axis (the vertical axis) is the temperature, and the x-axis (the horizontal axis) is the progression from starting, to heating, to cooling. b. There are three graphs, each with three lines (one for each photo box house and one for the external temperature) consisting of four data points (temperature readings). Conclusion Rooftop gardens, or green roofs, have many benefits. They are aesthetically pleasing, reduce the heat island effect, reduce the amount of carbon dioxide, reduce air pollution, reduce heating and cooling loads, lengthen roof life by two to three times, reduce sound reflectance and transmission, reduce rainfall run-off impacts, and remove nitrogen pollution in storm water runoff. By analyzing the data, it was found that the rooftop gardens kept the internal temperature of the house stable. There was less change in the internal temperature of the rooftop garden house than there was in the traditional house because the rooftop garden house took longer to heat up and cool down This engineering project supported the thought that a rooftop garden is a viable green option and is beneficial to the home s inhabitants.

5 Bibliography California Academy of Sciences. (n.d.). The Living Roof. Retrieved April 20, 2008 from The City of Chicago's City Hall Rooftop Garden: Green Buildings, Roofs & Homes. The City of Chicago's Official Site. Accessed December 18, Dictionary.com. Lexico Publishing Group, LLC. Accessed December 21, (Source of some vocabulary definitions, with some adaptation) Green Roof Basics. City of Chicago. Accessed January 4, Green Roof: Morgan Processing and Distribution Center, USPS Sustainability Fact Sheet. Last updated August U.S. Postal Service. about.usps.com/news/electronic-press-kits/greennews/greenkit-5.pdf Accessed January 16, Roof Garden. Last modified June 24, Wikipeida, The Free Encyclopedia. Wikimedia Foundation, Inc. Accessed June 24, Roof Top Gardening. Published December City Farmer, Canada's Office of Urban Agriculture. Global Ecovillage Network Oceania & Asia Inc. Accessed December 20, Rooftop Gardens. USA Home and Garden. Accessed December 21, Rooftop Gardens from Around the World, Garden Plants and Gardening Forum. Updated December 7, The Grow Spot. Accessed January 4, Slutz, Sandra (Science Buddies). Rooftop Gardens: Are They a Cool Idea? Last edit date: May 12, Science Buddies. Accessed August 12, Urban Heat Island. Last modified July 29, Wikipeida, The Free Encyclopedia. Wikimedia Foundation, Inc. Accessed June 24,