Presentation on theme: "Heating Losses- Infiltration and Ventilation ARCH-432."— Presentation transcript:
Heating Losses- Infiltration and Ventilation ARCH-432
Attendance Which civilization made it a point to layout whole cities to take advantage of passive heating? In what direction did the city streets run? A. Greece B. Rome C. Egypt D. Persia E. Babylonia
Attendance Aeschylus pronounced Ess ca less One of the earliest writer of Greek tragedy – before him plays had single actors who could only respond to a chorus (group of people). Aeschylus increase the tragedy to two actors with dialog.
Big Picture MomentroofExteriorwall Glassconduction Floor Infiltration and Ventilation Ceiling Partition
Five main types of heat loss 1. Transmission (conduction) 2. Infiltration (convection) 3. Ventilation (convection) 4. Radiation (radiation) 5. Moisture migration roof Exteriorwall Glass conductio n Floor Infiltration and Ventilation Ceiling
Summary of Heat Losses Wall Roof Floor Windows Doors Infiltration Ventilation Envelope Losses
What You Need To Know The difference between ventilation and infiltration Calculation methods for both ventilation and infiltration
What You Need To Be Able To Do Calculate infiltration/ventilation loads Be able to reduce/mitigate infiltration and ventilation loads Employ techniques for increasing ventilation effectiveness
Terms Infiltration Exfiltration Ventilation Direct Outside Air System (DOAS)
Infiltration The uncontrolled introduction of outside air into a building.
Infiltration The uncontrolled introduction of fresh air into a building. 1. Most subjective of all losses 2. Oftentimes the largest of all heat losses. Sometimes comprises up to 30% of the total heating load. 3. Ends up being an educated guess
Why Is This Important? All buildings leak A tight building will leak.5 AC/H A leaky building can leak 3 AC/H Regardless of climate, air leaking into walls causes problems
Ventilation The mechanical introduction of outside air (OA) to: Replace Oxygen Dilute contaminants Pressurize the building
Infiltration Calculation Methods Crack method Air Change Method Averaging method (I dont know so Im going to throw a dart method)
Crack Method Presumes that an accurate estimate can be obtained by estimating the rate of infiltration per foot of crack for doors and windows CFM = Ft. of Crack x Infiltration Rate Q S = 1.1 x CFM x (T 2 – T 1 ) in BTU/HR
Add Infiltration Through Open Door Determine Door Usage ת = Number of People per Minute Determine CFM per person (D) CFM = ת x D LEED-NC Credit EQ 5 for providing vestibules.
Infiltration by Crack Method Add CFM from Crack losses to CFM for Open Door losses
Mitigate These Losses How do you reduce or mitigate these losses? (Review)
Mitigation Strategies Pressurization Q S = 1.1 x CFM x (T 2 – T 1 ) Vs. Q S = 1.1 x (CFH/ft of crack x ft of crack)/60 x ΔT You own the variables!
Infiltration Variables Review Wind velocity and direction Stack effects Corner rooms Exhaust fans on or off Pressure zoning Frequency of use Maintenance
Air Change Method Often used in residential construction and in large warehouses and similar buildings CFM = A.C.H. x Volume (ft 3 )/60 or CFM = Volume (ft 3 )/Frequency (minutes)
Air Change Method Uses same formula for sensible Equals one room change Designer will use 0.3 to 2.0 air changes per hour (ACH) Occupancy Climatic condition (i.e. winter vs. summer) Construction (tight or loose) Least accurate of the three methods Q sens = 1.1 x CFM x T
Heat Loss Due to Infiltration Infiltration Btu H = 1.1 x CFM x (T i – T o ) CFM = (ACH x volume) / 60 min per hour
Heat Loss Due to Infiltration Infiltration Please Note: For tight construction use 0.5 for ACH. For medium construction use.85 for ACH. For loose construction use 1.3 for ACH. For really bad construction use 2.0 for ACH For the summer months (cooling) use 70% of the winter values.
Btu Hour Loss due to Infiltration Main Area CFM Ht.W.L.1.10air exch.vol. In cf/ 60 Temp. Ch. 1246.6674.661.100.541,803.63348.367629,123.19 Btu Hour Loss due to Ventilation Main Area Ht.W.L.1.10sf cfm exchangeOccup. Temp. Ch. 1246.6674.661.103,483.640.18034.847666,983.35 RaRp Occup/ 1000 0.18510.00 Infiltration & Ventilation
Heat Gains Due to Infiltration Latent Load BtuH = 4500 x (air exchanges x (volume) /60) x (W Final – W Initial ) (W Final – W Initial ) = Difference Ratio Pounds of Moisture per dry air
Heat Loss Due to Ventilation Ventilation Btu H = 1.1 x [(R a x square feet of building ) + (number of people in the building x R p )] x (T i – T o )