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

3

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

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 theAH 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

8

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

9

Some examples of power measurements

Fan power for air movement Heat generated by thermal manikin

10

AC or DC current source

Voltage and Current

V [V] R [Ω]

I [A]

11

Power measurement

• V = IR

• P = VI = I2R

Are these for :A) AC or B) DC or C) both?

V [V] R [Ω]

I [A]

12

Single-Phase vs. Three-Phase

Ref: Tao and Janis (2001)

Single phase 3 wire system

Common for US residential buildings

For three phase:

P = √3 E IV-V

Or

P = 3 E I V-N

13

Voltage measurement

R [Ω]

I [A]

voltmeterV

Current measurement

I=V/Rshunt

14

Other methods for current measurement

Measure Induction

15

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.

Use magnetic flux

AC circuits Reminder - Quick Reference

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/accircon.html#c1

Check for this class

Check for your general education

17

Power factorVoltage current phase

Power:P()=V()·I()

P()

18

Power factor Voltage current phase shift

Devices in electric motors

Voltage current phase-shiftPower factor

P()

P=I·V·cos Φ Power factor = cos Φ

20

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.

21

Portable power meter and data logger

22

Single phase two wire

23

Single phase three wire

24

Three phase four wire

25

Electric power meters

Power meter with power supply

Inexpensive power meter

Large variety:

power meter with data logger

+

26

Power control

Lab exercise •Measure the power consumption of variable power transformer (Variac)