Duct Leakage

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Objectives
• Summarize Electric Power Measurement
• Learn about CO and CO2 measurement and
instrumentation
• Discuss next week field measurements
Portable (Field) power meter
and data logger
2
Single phase two wire
3
Single phase three wire
4
Three phase four wire
5
Electric power meters
Large variety:
+
power meter
with data logger
Inexpensive power meter
Power meter with power supply
6
Overview of CO2 and CO
• Why make these measurements in the field?
– Some background information
• Types of devices for each (overview)
• Pros and cons of devices (including accuracy)
7
CO2 - Standards & Guidelines
•
OSHA:
5,000 ppm (8-hr average)
•
ASHRAE (62-1999):
Cindoor – Coutdoor < 700 ppm
•
U.S. Navy (subs)
•
Observations in medical literature (Clark, 1996)
–
–
–
–
8
6,000 – 10,000 ppm
1,200 ppm @ 15 min (fatigue, lack of concentration, short. breath)
1,200 ppm long-term (calcium deposition in tissues)
> 2,500 ppm symptoms of oxygen deprivation in children
> 60,000 ppm (6%); possible narcosis / death (within minutes)
Carbon Dioxide (CO2)
•
Metabolic generation rate
•
Ventilation requirements
– ASHRAE Standard 62.1
9
Metabolic Generation Rate
• ASTM D6245
– Also ASHRAE Fundamentals Ch. 8 (2005)
AD = 1.8 for adult, 0.8 - 1.4 for kids
RQ = 0.83 when M = 1 met
RQ = 1 when M = 5 met
10
10
ASHRAE Standard 62.1-2007
11
CO2: Measurement Techniques
•
Non-dispersive infrared (NDIR) = most common
•
Electrochemical (reduce CO2 / generate current)
•
Photoacoustic (CO2 absorbs / T up to P pulse)
•
Potentiometric (CO2 to solution – changes pH)
•
Gas chromatography w/ MS or TCD
– High sensitivity
– High cost
12
Non-dispersive infrared (NDIR)
• Measures the infrared light absorbed by carbon dioxide as it passes through a flowthrough IR absorption cell
• Possible interference from other ionic species
- Interferences from other IR-absorbing gases are minimized by use of a
highly wavelength-specific detector
Issues:
…..
CO2: NDIR Detection
•
See ASHRAE PDS IV
•
Absorption of IR light (CO2 peak absorb @ 4.3 µm)
•
IR light source passed through narrow band filter
•
Higher CO2 = greater IR absorption
•
Interferences: H2O, CO, CH4 (absorp 4 – 7 µm)
•
Accuracy = 50 to 100 ppm up to 10,000 ppm
•
Hold calibration a long time ???
•
Cost: expensive for HVAC industry , affordable for
14
Field work
Electrochemical
• CO2 diffuses into the sensor through a porous membrane to
the working electrode where it is case electrochemical
reaction. This reaction results in an electric current that
passes through the external circuit. the counter electrode is a
reduction.
• Advantages/disadvantages:
– Can be very inexpensive
– Drifting,….
Carbon Monoxide (CO)
•
Major sources
–
–
–
–
•
16
Cigarette smoke
Incomplete bringing in HVAC and Cooking systems
Car exhaust
….
Standards
–
–
–
–
–
9 ppm (8-hour average) - NAAQS
35 ppm (1-hour average) – NAAQS
50 ppm – STEL/TWA – OSHA
400 ppm (15 minutes) - ACGIH
1,500 ppm (30 min) – IDLH (OSHA)
Example: Cooking – Natural Gas
17
Measurement of Carbon Monoxide
•
Electrochemical (common for hand held or home)
– Two electrodes
– Oxidize CO to CO2 – current generated
•
Biomimetic (gel cell)
– Synthetic hemoglobin – darkens in presence of CO
•
Semiconductor (wires of tin dioxide / ceramic base)
– CO reduces resistance
– High CO
•
Non-Dispersive Infrared Detection (NDIR)
18
– Used for emissions testing
– Absorption band
Instruments for CO andCO2 that you
will use
• HOBO U12 (datalogger)
• Telaire 7001 CO2 analyzer (NDIR)
• HOBO CO Analyzer (electrochemical)
• Specs:
• http://onsetcomp.com/products/sensors/tel-7001
• http://onsetcomp.com/products/data-loggers/h11-001
19
Lab exercises - next week
• PRC on Tuesday
– preparation
• Field
– Wednesday or Thursday
20
20
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