Power

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Objective
• Summarize house ventilation/infiltration and
duct leakage
• Power measurement
– Review/learn
• Electric power
• Electric power measurements
• Instrumentation
Summary of last week lab
measurements
• Not quite successful filed work
– ……
– …..
–…
• Data are posted on the course website
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
3
3
Duct pressurization
Duct and house
pressurization
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.) untapped register,
etc. are very important
• Cardboard and tape are useful research
tools/skills
Why to know about power measuring
techniques
• Used fro any kind of energy consumption
monitoring of building and/or building
systems
• Electric power is used in various indoor
environment experiments to generate heat
source
8
Some examples of power measurements
Fan power for air movement
9
Heat generated by thermal manikin
Voltage and Current
I [A]
V [V]
AC or DC current source
10
R [Ω]
Power measurement
• V = IR
I [A]
• P = VI = I2R
Are these for :
A) AC or
B) DC or
C) both?
11
V [V]
R [Ω]
Single-Phase vs. Three-Phase
For three phase:
P = √3 E IV-V
Single phase 3 wire system
Common for US
residential buildings
12
Or
P = 3 E I V-N
Ref: Tao and Janis (2001)
Voltage measurement
I [A]
V
voltmeter
R [Ω]
Current measurement
I=V/Rshunt
13
Other methods for current measurement
Measure Induction
14
Electric energy vs. Electric power
Electromechanical induction
watt-hour meter
Counts the revolutions of an metal disc which rotates
at a speed proportional to the power.
15
Use magnetic flux
AC circuits
Reminder - Quick Reference
Check for this class
Check for your general education
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/accircon.html#c1
Power factor
Voltage current phase
Power:
P()=V()·I()
17
P()
Power factor
Voltage current phase shift
Devices in
electric motors
18
Voltage current phase-shift
Power factor
P()
P=I·V·cos Φ
Power factor = cos Φ
Some facts about Power factor
• Low power factor is expensive and inefficient
• Utility companies charge large commercial and industrial
customers an additional fee when power factor is less than
about 0.95.
• Low power factor reduces an electrical system’s distribution
capacity by increasing current flow and causing voltage drops.
• Increasing power factor you can reduce electric bills and
enhance your electrical system’s capacity.
20
Portable power meter
and data logger
21
Single phase two wire
22
Single phase three wire
23
Three phase four wire
24
Electric power meters
Large variety:
+
power meter
with data logger
Inexpensive power meter
Power meter with power supply
25
Power control
Lab exercise
• Measure the power consumption of variable
power transformer (Variac)
26
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