19,000 cfm x 0.018 Btu/ft3-F x 60 min/hr = 20,520 Btu/hr-F The initial heating coefficient, HC1, is: HC1 = 88,267 Btu/hr-F + 20,520 Btu/hr-F = 108,787 (Btu/hr-F) The internal heat gain, Qi, is: Qi = Qe x 3,412 Btu/hr = 200 kW x 3,412 Btu/kWh = 682,600 (Btu/h) The initial balance temperature is: Tb = Tia Qi / HC1 = 70 F - 682,600 (Btu/h) / 108,787 (Btu/h-F) = 63.7 (F) – The initial HDDs calculated with Tb = 63.7 F for are about: HDD(64 F) = 5,655 (F-day/year) The initial annual fuel use is: Qf1 = HC / Effh HDD(Tb) Qf1 = 108,787 (Btu/hr-F) / 0.90 5,655 (F-day/year) x 24 (hours/day) / 106 (Btu/mmBtu) Qf1 = 16,405 (mmBtu/yr) As before, heat transfer through the roof is: Qr = A / R (Tia-Toa) Thus, the heating coefficient for the roof, HCr, is: HCr = Ar / Rr The change in the heating coefficient from insulating the roof, is: HC, = A / R1 - A / R2 = A (1 /R1 1 / R2) HC – = 200,000 ft2 x (1/3 1/6) Btu/hr-ft2-F = 33,333 Btu/hr-F HC – The new heating coefficient, HC2, would be: HC2 = HC1 - = 108,787 (Btu/hr-F) 33,333 (Btu/h-F) = 75,454 (Btu/h-F) HC – The new balance temperature would be:
19,000 cfm x 0.018 Btu/ft3-F x 60 min/hr = 20,520 Btu/hr-F The initial heating coefficient, HC1, is: HC1 = 88,267 Btu/hr-F + 20,520 Btu/hr-F = 108,787 (Btu/hr-F) The internal heat gain, Qi, is: Qi = Qe x 3,412 Btu/hr = 200 kW x 3,412 Btu/kWh = 682,600 (Btu/h) The initial balance temperature is: Tb = Tia – Qi / HC1 = 70 F - 682,600 (Btu/h) / 108,787 (Btu/h-F) = 63.7 (F) The initial HDDs calculated with Tb = 63.7 F for are about: HDD(64 F) = 5,655 (F-day/year) The initial annual fuel use is: Qf1 = HC / Effh HDD(Tb) Qf1 = 108,787 (Btu/hr-F) / 0.90 5,655 (F-day/year) x 24 (hours/day) / 106 (Btu/mmBtu) Qf1 = 16,405 (mmBtu/yr) As before, heat transfer through the roof is: Qr = A / R (Tia-Toa) Thus, the heating coefficient for the roof, HCr, is: HCr = Ar / Rr The change in the heating coefficient from insulating the roof, HC, is: HC = A / R1 - A / R2 = A (1 /R1 – 1 / R2) HC = 200,000 ft2 x (1/3 – 1/6) Btu/hr-ft2-F = 33,333 Btu/hr-F The new heating coefficient, HC2, would be: HC2 = HC1 - HC = 108,787 (Btu/hr-F) – 33,333 (Btu/h-F) = 75,454 (Btu/h-F) The new balance temperature would be:
EnergyEfficientHVAC.docx