Lab Duct blaster

advertisement
Objectives
Blower door and duct bluster measurements
- Theory and lab
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:
2
– Blower door and Duct Blaster
2
Fan Pressurization
•
1.
2.
3.
4.
In 1970s, smoke evacuation fans used
to find air leakage
Install blower door
Use fan to create artificial pressure
difference between inside and outside
Use smoke stick (or cigarette, etc.) to
visualize flow patterns.
Seal leaks
Quantitative Blower Door
•
•
How many points should you measure?
How can you estimate uncertainty?
http://www.energyconservatory.com/products/products1.htm#pd16
Test Data
• 1000 ft2 house, 10 ft high ceilings
• Two-point test
– 1688 CFM at 51 Pa
– 1048 CFM at 24.5 Pa
• What is ACH50 (λ50), C?
Answers
• λ50= 1 ACH
• C = 131.07 CFM/Pan
• n = 0.65
Reporting blower door data
• Flow (or air exchange rate) at a given
pressure
• Equivalent Leakage Area
– What are dimensions of c?
Comment
• Blower doors do not measure air
exchange rate
– Why not?
• What do they measure?
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
11
reference pressures with fan covered
11
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
Residential Component
Leakage
Component
Range
Average
Walls
18-50%
35%
Ceilings
3-30
13
Windows/Doors
6-22
15
Fireplaces
0-30
12
HVAC
3-28
18
Other Vents
2-12
5
Duct Leakage
• Responsible for enormous energy losses
(20-30% is not uncommon)
– Comfort
– Outdoor air pollution
– Contaminant spread
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?
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?
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?
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?
Reporting Duct Leakage
• Are we interested in absolute amount of
leakage or relative?
– If relative, relative to what?
• ASHRAE Standard 152 defines:
– αs supply leakage fraction
– αr return leakage fraction
21
21
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
22
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
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
24
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
25
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
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
Download
Related flashcards
Create Flashcards