Overhang

Earlier this semester the engineering service project class took a trip to the habitat for humanity house that is being built on Woodruff Street. While visiting there, I noted the gable roof runs from north to south. The wall that faces the south has no shade from the roof. Searcy is in the northern hemisphere above 23.5˚ meaning that the sun is always in the southern sky. The point of this is that the windows on the south wall will let sun in all year long which will heat the house. The heat is good in the winter, but bad in the summer when you are trying to cool the house. Improving the efficiency of the house is easy here by shading the windows. Good windows on the south side of the house are a good thing, because they can significantly lower the heating cost of the house. The windows will have to be shaded in the summer, or all of the energy you saved in the winter will be used in the summer to cool the house. The purpose of my task was to find the best length of overhang that will shade the windows in the summer and let the sun in during the winter. To do this I first had to find the climate of Searcy. The average Temperature was helpful, but I could not find an exact date for the cut off between summer and winter. I was then shown a web site that could calculate the heating degree days (HDD) and the cooling degree days (CDD). The link is provided [|DegreeDays]. A HDD is the amount of heat in degrees that the heater has to produce per day to keep the house at the desired temperature. CDD are the same, except for the air conditioners. One flaw with this was the web site only had temperature for the last year. With the data from the web site I graphed the HDD and the CDD, seen below. Witch gave me the exact cut off dates April 22nd to September 19th as seen on the first graph. The next part of the task was to find the position of the sun was on those days so by consulting the analemma plot we see that the sun is 11˚ north of the equator on April 22nd and 2˚ north on September 19th. That means at 12 noon on April 22nd the sun is 90˚ above the latitude line of 11˚ north. Now the sun is not in the same place on those days so we compromise with 6˚ which puts the cut off dates at April 7th and September 7th. April 7th is good but looking at the second graph September 7th is still very hot, so 4˚is a beater option. Now that we can find the angle that needs to be cut by, taking Searcy’s latitude 35.25˚ and subtracting 4˚. The overhang and the distance from the roof line to the middle of the wall must make a 31.25˚ angle. So if the south facing wall is 8ft tall than the overhang need to be tan(31.25)*8/2=.607*4=2.43 or 2ft 5”. In the future more data from degreedays.net needs to be gathered in order to find a more constant temperature for Searcy. This will help chose beater on cut off dates. Also the number of windows needs to be looked at to see if the sun can do the heating in the winter. Last but not least it need to been shown how much the sun will heat a room though a window. I recommend a 2ft 5in overhang for the south facing wall in Searcy Arkansas.
 * **ROOF OVERHANG STATUS REPORT** ||
 * ||  ||   || Final Report [[file:Overhang.pdf]] ||   ||
 * **Project Description:** |||||||| Design the roof overhang to be as energy efficient as possible. Having long enough to shad the windows in the summer but allow the sunlight to shine in the windows in the winter. ||
 * **Project Sponsor:** ||||  || Sponsor Rep: ||   ||
 * **Program Manager: Rich Wells** ||||  || **Project Manager: Grant Arthur** ||   ||
 * December 1, 2010 ||  ||   ||   ||   ||
 * **Accomplished This Period:** ||  ||   ||   ||   ||
 * Searcy Arkansas is located at 35 15' 2" north and 91 44' 10" west. The longest day of the year is June 22nd which also has the greatest sun angle, in Searcy the sun angel is about 79*. On average the three hottest moths are June, July, and August. A two foot overhang will shad the ground under the wall from May 20th to July 20. ||
 * **Objectives to Next Reporting Period:** ||  ||   ||
 * Find height of walls and windows. ||
 * November 9th to November 16th ||||||  ||
 * **Accomplished This Period:** ||
 * Found the angle of the sun though out the year. ||
 * **Planned But Not Accomplished This Period:** ||
 * Ø Highlight the deliverables and/or tasks that were expected to be completed but were not. ||
 * **Objectives To Next Reporting Period:** ||
 * The cut off dates for having the sunlight comeing in the window. ||
 * **Risks/Outstanding Issues/Problems:** ||
 * The cut off dates for having the sunlight comeing in the window. ||
 * **Risks/Outstanding Issues/Problems:** ||

HDD & CDD Sun Position