Objectives Blower door and duct bluster measurements - Theory and lab

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  • Objectives Blower door and duct bluster measurements - Theory and lab
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  • 2 Infiltration/Leakage Measurements (Calibrated Fans) Flow going through fan is calibrated to pressure rise across fan If you measure pressure, than you know flow Requires very smooth inlet and outlet conditions Often have to restrict flow to get measurable pressure signal for low flows Examples: Blower door and Duct Blaster 2
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  • Fan Pressurization In 1970s, smoke evacuation fans used to find air leakage 1. Install blower door 2. Use fan to create artificial pressure difference between inside and outside 3. Use smoke stick (or cigarette, etc.) to visualize flow patterns. 4. Seal leaks
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  • Quantitative Blower Door How many points should you measure? How can you estimate uncertainty? http://www.energyconservatory.com/products/products1.htm#pd16
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  • Test Data 1000 ft 2 house, 10 ft high ceilings Two-point test 1688 CFM at 51 Pa 1048 CFM at 24.5 Pa What is ACH 50 ( 50 ), C?
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  • Answers 50 = 1 ACH C = 131.07 CFM/Pa n n = 0.65
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  • Reporting blower door data Flow (or air exchange rate) at a given pressure Equivalent Leakage Area What are dimensions of c?
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  • Comment Blower doors do not measure air exchange rate Why not? What do they measure?
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  • 11 Blower Door Misc. All windows and doors to outside closed Why? What about buffer spaces? HVAC off Hard to do on windy days Watch out for buckling linoleum floors and fireplaces Flow direction change/ring change can be discontinuous Remember to record before and after reference pressures with fan covered 11
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  • More Blower Door Tests Measure component leakage What fraction of leakage is due to a certain component? Tape off component and repeat test What are issues with this approach? Series leakage paths Air leaks to attic and then to crawlspace and then to outside
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  • Residential Component Leakage ComponentRangeAverage Walls18-50%35% Ceilings3-3013 Windows/Doors6-2215 Fireplaces0-3012 HVAC3-2818 Other Vents2-125
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  • Duct Leakage Responsible for enormous energy losses (20-30% is not uncommon) Comfort Outdoor air pollution Contaminant spread
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  • Duct Leakage Excluding registers, grills, diffusers Ducts leak to the inside Ducts leak to the outside (mostly an American problem) Ducts leak on the supply (positive pressure) side Ducts leak on the return (negative pressure) side What are we concerned from the perspective of: Energy?, Indoor air quality? Comfort?
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  • Duct Leakage Method 1 Blower door subtraction Two successive blower door tests 1. Normal 2. With duct registers sealed (with tape) Difference is total duct leakage Is this supply, return, or total? Is this inside, outside, or both? Problems and limitations?
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  • Duct Leakage Method II Duct pressurization Tape registers Use Duct Blaster (calibrated fan) to do a blower door test of the ducts Is this supply, return, or total? Is this inside, outside, or both? Problems and limitations?
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  • Duct Pressurization Test Extension How do you measure exterior leakage? How do you measure supply and return leakage separately? How do you measure duct leakage at operating conditions?
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  • 21 Reporting Duct Leakage Are we interested in absolute amount of leakage or relative? If relative, relative to what? ASHRAE Standard 152 defines: s supply leakage fraction r return leakage fraction 21
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  • 22 Air Handler Flow Measurement Often need to know flow through air handler Historically many methods, all problematic: Non-uniformity of flow (i.e., very turbulent) True Flow Plate Specialized type of orifice Replaces filter Gives air handler flow Pressure correction 22
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  • Other Duct Leakage Testing Methods Nulling test Measures duct leakage at operating conditions Also measure air handler flow Very intensive to set-up and also sensitive to wind Delta-Q test Only uses a blower door and does not require taping registers But mathematically problematic
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  • 24 Nulling Test Step 1: Install Duct Blaster fan in doorway to building, turn on air handler and zero* out any pressure imbalance What does the flow through the fan equal? Why is this test sensitive to wind? Under what conditions will this test fail? 24
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  • 25 Nulling Test (cont.) Step 2: Second Duct Blaster is installed in HVAC system, return side sealed off, air handler fan turned on, and air flow rate is adjusted to match supply plenum pressure under normal conditions Step 3: Step 1 is repeated What is flow through Duct Blaster installed in door this time? 25
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  • Summary of Nulling test Use a Duct Blaster as envelope fan to null out change in envelope pressure caused by unbalanced duct leakage First with normal operation unbalanced leakage Second with return isolated and a Duct Blaster assisting the AH fan so there is no return leakage supply leakage Difference is return leakage Measures leakage directly thought to be accurate Very sensitive to wind
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  • General Comments about Fan Tests Buildings are complicated, go slowly and methodically Practice/experience are key Practical matters (HVAC turned on, someone stepped on a tube, wind, etc.) are very important Cardboard and tape are useful research tools/skills