WARM UP #2A


OBJECTIVES: In this exercise you will:

Learn about Energy Scheming:
how to do numerical input
how to change roof pitch
how to adjust graph zero lines
how to associate a takeoff

Learn about energy:
what the difference there is in the algorithms for walls and roofs vs. floors
what sol-air temperature is, and how gain varies for roofs vs. walls
see how absorptivity/conductance affects heat gain

Learn about architectural design implications:
how surface orientation affects energy (SWL #20, #27, #28, #31,#33)
how color is an energy as well as architectural issue (SWL #54)



PROCEDURE:

1) Download the Warm Up 2 file to the desktop.

2) Position Netscape as a 2" wide strip on the right hand side of the screen.

3) Double click on the Energy Scheming folder.




4) Drag the Warm Up 2 file from the Desktop over the Energy Scheming application icon to open it.




5) The Energy Scheming window should appear on the left and the Netscape window on the right.




6) The Warm Up 2 building file has its climate set to Phoenix, the building type is defined as residential, and the building size is 1200 sf. You will see that the Draw layer has three squares in it, labeled "Wall", "Roof", and "Floor", already taken off. Each of these represent an element of equal area (100 sf) and R-value (R-16.1), but having different orientation.




7) Select Graphic report from the View menu and click on the calculation icon to let Energy Scheming calculate. The graph format is already set.




8) In a previous exercise, we saw how heat transfer through the wall is driven by the area and R-value of a wall and the temperature difference between both surfaces of a wall. Let's explore the effect of climate on the exterior surface temperature. Select Project from the Define menu.




9) This brings up the Select Climate dialog box. Click on the User Defined Climate button.




10) This brings up a small dialogue box to select the type of climate procedure to use. Set it for All new values, as shown, and click OK.




11) The General Climate Information dialogue box will come up next. Fill it in as shown. The purpose of this climate is to try to isolate temperature and radiation effects. Much of what is being input for this climate is unimportant and so is not realistic. When you are done click on the Input Average Data button.


12) You are now asked to fill in average day data for each of four days. Fill out the screens as shown, clicking Next Day after finishing each day.





 

The following warning may pop-up because you are creating a fictitious climate. It's okay that some of the values may be out of range. Click on the button "Leave it as it is and don't show me this message again.":



13) When you complete the final day you will be returned to the Select Climate screen with the new climate selected. Click on Review Selected Climate to see the climate data that Energy Scheming has created. Click OK on this screen and the following two dialogue boxes.




14) You have just created a climate with four evaluation days -- a high temperature/low radiation day, a high temperature/high radiation day, a low temperature/low radiation day, and a low temperature/high radiation day.


15) Select Graphic Report from the View menu and set the Graph floating palette as shown.

They should be:

High temp, low radiation

High temp, high radiation

Low temp, low radiation

Low temp, high radiation


16) Click on the calculator icon to let Energy Scheming calculate again.




17) When it is done you may have to drag the graph handles of the graphs in order to eliminate overlapping bars.


Please answer the following questions using the graphic report:

18) In what climate conditions is the heat gain through the roof greater than the heat gain through the wall and why?

Since heat rises, heat gain through the roof will always be greater than heat gain through the wall regardless of the climate condition.
On cloudy days (low radiation), heat gain through the roof is greater than gain through the wall because of the reflectance of the clouds on a horizontal surface.
Both sunny days (high radiation/low temp and high radiation/high temp) show greater heat gain through the roof than the wall because the sun is higher in the sky and shines more directly on a horizontal surface than a vertical one.
Heat gain through the roof is greater than that through the wall on hot days (high temperature) because of night sky radiation.


19) The heat gain through the wall on a hot sunny (high temperature/high radiation) day is greater than on a cold sunny (low temperature/high radiation) day because:

the angle of the sun is lower.
a higher ambient temperature raises the delta T, which drives heat transfer.
the surface temperature of the wall is raised only by direct radiation.
the thermostat is set lower.


20) Heat gain and loss through the floor is mostly driven by:

ambient outside temperature
roof heat gain and heat loss
radiation level
the sun's altitude angle


21) If the flat roof was replaced by a 12:12 pitched roof facing north,

the sun would never shine on it, so there would be no heat gain through the roof on high radiation days.
the sun would sometimes shine on it (summer morning and evenings), but the heat gain on low temperature/high radiation days would be reduced.
the heat gain and heat loss on cloudy days (low radiation) would remain the same.
the heat gain and heat loss for all days would remain the same, since only the ambient outside temperature drives the heat transfer through a roof.


NOTE: To replace the flat roof with a north facing roof in Energy Scheming , remember that a flat roof takeoff is done in plan and a pitched roof takeoff is done in elevation. Don't takeoff the same area twice!



First open the roof specification and delete the takeoff in plan using the thumbs down tool.





Then add a north facing roof by first adding a north elevation (double click on New Elev, and select a north orientation). Open the North elevation icon and in turn the Roofs specification. Click on Detailed Roof Design and type in 16.10 for Total R-value (gain and loss) to match the previous roof takeoff. Then takeoff exactly 100 sf (since the roof is angled, the area of the takeoff will not fill the entire square).


Click here if you would like to see the correct answers.


Go to:

Exercise #2A

Cool Down #2A


Return to: Topics Page

Navigation  

Back to Class Home Page