Heat Gains into a Building Solar Gains Shading

Attendance What improvement did George Ravenscroft (1618 – 1681) develop to make glass windows economically feasible? Made it square Added color to make it more attractive Added lead oxide Learned how to bevel the glass Made it thinner He added lead oxide to the glass to make it much easier to form and cut. This allowed glass blowers to make panes of glass much more quickly, making glass windows widely available.

What You Need to Know How solar radiation effects cooling loads

What You Need to be Able To Do Be able to calculate solar loads Develop strategies to limit/postpone/utilize solar loads

Terms Fenestration Solar Heat Gain Factor (SHGF) Shading Coefficient (SC)

Sunlit Glass QS = solar gain + conduction Fenestration sun rays reflected energy transmitted glass window conduction solar gain (radiation) Fenestration “Any opening in the external envelope of a building that allows light to pass.” QS = solar gain + conduction

Glass - Conduction Calculated the same way as heating for conduction Qconduction = U  A  TD

Calculating the Solar Gain Q = SHGF x A x SC where: SHGF = Solar Heat Gain Factor A = Area SC = Shading Coefficient I. Calculating the Solar Gain A. Q = SHGF x A x SC x CLF where: SHGF = Solar Heat Gain Factor A = Area SC = Shading Coefficient CLF = Cooling Load Factor

Solar Heat Gain Factor (SHGF), Table 2-15A Do you see the three variables? I. Solar Heat Gain Factor, Table 2.8 A. A function of: 1. Latitude 2. Direction 3. Month B. Based upon clear glass, 1/8” think C. Based upon no shading D. Based upon the 21st day of the month E.. Units are BTU/hr-ft2

Shading Coefficients Table 2-16 I. Shading Coefficients, Table 2.8 A. Adjustment factor to take into account shading. B. A lot of research has been done on shading 1. ASHRAE re: fabric styles

Shading Strategies Fins Overhangs I. Shading Types A. Fins 1. Popular in the 50’s and 60’s 2. Executive Office Building on 15th St. is a good example.

Shading Strategies Adjacent Buildings I. Shading Types A. Adjacent buildings 1. May completely shade the entire window 2. Our classroom is a good example of this. 3. Use Solar Heat Gain Factor (SHGF) for North facing glass to account for this type of shading. See Table 6.6

Shading Strategies A completely shaded window is similar to a North facing window

Accounting for Shade In the Northern hemisphere, use the North Column

Effect of Glass on a South Wall Glass – Conduction QC = U x A x (T2 – T1) QC = .47 x (24 x 4) x 17 QC = 767 Btu/Hr Glass – Solar QS = SC x A x SHGF QS = .90 x (24 x 4) x 29 QS = 2,505 Btu/Hr QT = 2278 Btu/Hr Wall – Conduction QC = U x A x TETD QC = .26 x 377 x 19 QC = 1,875 Btu/Hr

LEED EA Credit 1 Credit 1 – Optimize energy performance (1 to 10 points) Building orientation Harvest free energy Sustainable strategies Harvest free energy Building orientation Appropriate envelope design Use of thermal mass to balance temperature variations Natural ventilation Use of appropriate glazing Earth-coupled heat pumps Turning off lights when daylight is available

Cooling Peak Load – Sum of All Cooling Loads at Peak Conditions Sensible Latent Roof = 14,253 Btu/Hr WallS = 1,875 Btu/Hr WallN = 593 Btu/Hr WallE = 2,162 Btu/Hr GlassS = 3,272 Btu/Hr GlassN = 797 Btu/Hr People (30) = 7,350 Btu/Hr 4,650 Btu/Hr Ventilation (372) = 8,184 Btu/Hr 7,083 Btu/Hr Infiltration = 0 0 TOTAL 38,486 Btu/Hr 11,733 Btu/Hr