Specifications S14 - Commissioning-hvac.org

IEA Annex 40
Final Report Subtask B2
Development of Functional Performance Testing procedures
Air Quality Sensors in Buildings
and HVAC systems
Date: 01/06/2005
Authors:
Cleide APARECIDA SILVA
Jules HANNAY
Jean LEBRUN
University of Liège
Laboratory of Thermodynamics
LIEGE
Christophe ADAM
Philippe ANDRE
Patrick LACÔTE
University of Liège
Department of Environmental Sciences and Management
ARLON

1 Description of the considered object
This specification concerns the air quality sensors installed in the building and in the HVAC
systems. A more general information about sensors validation is given in generic FPT,[12], to
which an automatic reference is done whenever required.
1.1 Operating principles
Two types of pollutants are generally measured in building and HVAC systems: the CO2 and
VOC ( volatile organic compounds) sensors.
1.1.1 CO2 sensors
CO2 is not a pollutant as such, provided it remains in the acceptable range. The CO2
concentration is nevertheless a good indicator of the occupancy rate, as well as of the activity
level in a room or in a building. CO2 sensors are usually measuring the absorption in a part of
the infrared range by the measured gas. Thermal energy associated to the absorption process
is proportional to the gas concentration.
Figure 1 gives the rates of CO2 generation for several activities, [11].
Figure 1: Rates of CO 2 generation for various activities
The rate of CO2 production varies with diet and health, as well as with the duration and
intensity of physical activity. The more exertion an activity entails, as measured in metabolic
equivalent task (MET) units, the more carbon dioxide is produced [11].
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1.1.2 VOC sensors (multi-gas sensors)
The VOC (volatile organic compounds) sensors are based upon the absorption of inorganic
ions on a porous heated surface. This modifies the electrical resistance of a semi-conductor.
Those detectors are sensible to a wide range of organic components, as well as to other
molecules (Figure 2). They are also very sensible to tobacco smoke.
Figure 2: Resistance variation of a VOC sensor to different gases
(Air, CO, Methane, Ethanol, Propane, Hydrogen)
1.2 Data provided by the manufacturers
Data are generally provided as "data sheets". Typical examples of data sheets, corresponding
to a C02 and to VOC sensors respectively, are given in Figures 3 and 4.
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Figure 3: Example of CO2 sensor data sheet
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Figure 4: Example of air quality sensor data sheet
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1.3 Problems to be considered
1.3.1 General problems
All problems listed in the reference document [12] are relevant for air quality sensors.
1.3.2 Specific problems for air quality sensors
Furthermore, air quality sensors have to fulfil specific installation and calibration
requirements, and attention must be paid to sensors location and connection:
• Sensors should be located in the return ducts, not too far from the grille;
• If located in the rooms, sensors should not be too close to occupants, not too close to
windows and correctly vented;
• Sensors have to be continously connected.
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2 Description of the testing procedures, [12], [13]
For commissioning sensors, a number of methods are available, ranging from basic "visual"
inspection operations to advanced validation methods. The most advanced methods are
providing "self-calibrating" characteristics to the sensors [12].
2.1 Visual observation of measuring results
2.1.1 Summary of the test specifications
This "basic" method consists in observing the measuring results of the measurement for one
or for several variables and to check if there is no major problem.
Typical "obvious" problems are :
- interruption of measurement
- values out of range for a long time
- apparent random evolution of measurement
• Objectives and sequence of the test : Detection of anormalities in the sensors readings
• List of operational conditions to test : Current operation of the HVAC system
• Requisite : None
• Required material : None
• Time required for the test execution : Short : time required for observation of
measurements (display on screen, printing of output file, ...)
2.1.2 Preparation phase: evaluation of available data and of expected
performances
- Measurement points available for the test: all air quality measurement points are
potentially concerned by this test procedure;
- No specific measuring techniques required
- Data helpful for this testing procedure :
- information about problems having occured in the past
- technical data about sensors : expected "noise", theoretical time constant, expected
range of variation, ...
- scheme of the HVAC system showing sensors location
- No additional instrumentation required.
2.1.3 Execution phase
2.1.3.1 Summary of the test method
This "basic" test method consists in using the BEMS to observe the evolution of typical
sensor readings.
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2.1.3.2 Experimental method
- Select typical variables to display on the BEMS;
- Observe evolution of selected variables
- Optionally, print selected graphs or save for future processing.
2.1.3.3. Contents of the test report
- Date and time
- Current operation of the system
- List of selected variables
- For each selected variables :
- typical evolution
- comments
- Summary of test results.
2.1.4 Illustration Example
CO2 tests are currently used in order to identify the airflow rate supplied to an air-conditioned
zone. An example of monitoring device, including a CO2 is shown in Figure 5.
Examples or recordings performed in two zones are shown in Figure 6. It appears here that
the probe installed in the office B3708 has an offset which should be corrected.
Figure 5: Example of monitoring device
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2400
CO2 concentration [ppm]
2000
1600
1200
800
400
0
19/03/02
00:00:00
19/03/02
12:00:00
20/03/02
00:00:00
20/03/02
12:00:00
21/03/02
00:00:00
21/03/02
12:00:00
Time
CO2_B3708
CO2_B3508
Figure 6: Examples of evolutions of CO2 concentrations
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2.2 Diagnosis tests
2.2.1 Summary of specifications
This method consists in performing test cycles. In other words, the system is brought into
specific operational conditions where an expected and easily predictible relation between
sensors can be observed.
• Objectives: detection of the qualitative response of a sensor to a given sollicitation for
which the expected response is known.
• Operating conditions: typical conditions which involve a predictible behaviour of the
sensor response (eg “breathing” above a CO2 sensor and checking an increase of the
sensor response).
• Pre-requisite: the “artificial” configuration of the system should concern fault-free
components
• Required material: None (if using the BEMS).
• Required time: Short (a few minutes for each test).
2.2.2 Preparation phase: evaluation of available data and of expected
performance
Cfr § 2.1.2.
2.2.3 Execution phase
2.2.3.1 Summary of the test method
The test method consists in generating (or taking profit of) some specific operating conditions
and in observing the behaviour of pre-defined sensors.
2.2.3.2 Experimental method
Testing conditions are either generated or are naturally occuring and presenting “interesting”
characteristics. In both cases, the method consists in observing (or recording) the behaviour of
some selected variable.
Example: moving the fresh air damper and observing the CO2 concentration at air discharge.
2.2.3.3 Contents of the test report
Date and time
Selected (or generated) operational conditions
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For each condition:
- Description of the operation imposed
- Method to generate (or obtain) it
- Variables to observe
- Typical evolution
- Comments
Summary of tests results.
3 References
[1] SELLERS et al “HPCBS Control System Design Guide”. California Energy Commission.
Public Interest Energy Research Program, 2003
[2] DEXTER, A.L. ; PAKANEN, J. editors. IEA Annex 34 final report, IEA ECBCS, 2002
[3] VISIER, J. Ch. Editor “IEA Annex 40 final report”, IEA ECBCS, 2005
[4] XIAO, F.; WANG, S. “Sensors fault diagnosis for re-commissioning of AHU monitoring
instruments”. IEA Annex 40 working document n° , 2002
[5] WANG, J.-B.; WANG, S.; BURNETT, J. „FDD and soft fault estimation in
commissioning BMS monitoring instruments of central chilling plant”. Proceedings System
Simulation in Buildings 98, Liège, 1998
[6] YOSHIDA, H.; KUMAR, S.; MORITA, Y. „Online fault detection and diagnosis in VAV
air handling unit by RARX model”. Energy and Buildings, vol. 33, n°4, pp 391-410, 2001.
[7] ISERMANN, R. “Supervision, fault-detection and fault-diagnosis methods: an
introduction”. Control Engineering practice, vol. 5, n°5, pp 639-652, 1997
[8] ASHRAE Fundamentals Chapter 14: Measurement and Instruments
[9] Sontay Limited, www.sontay.com
[10] http://www.madur.com
[11] MURPHY J., BRADLEY B., “Using CO 2 for Demand-Controlled Ventilation”,
Engineers Newsletter, Volume 31 No. 3, 2002 - www.trane.com
[12] APARECIDA SILVA C., HANNAY J., LEBRUN J., ADAM C., ANDRE P., LACÔTE
P., FPT S09: “Sensors of HVAC systems” , Laboratory of Thermodynamics and Department
of Environmental Sciences and Management, University of Liège, Belgium
[13] LIU M., CLARIDGE D.E., “ Tools and Equipment for Continuous Commissioning”,
Annex 40 – subtask B2, mars 2001
[14] CUEVAS C., LEBRUN J., LACÔTE P. ANDRE P., “Recommissioning of VAV
boxes “,september 2002, Laboratory of Thermodynamics and Department of Environmental
Sciences and Management, University of Liège, Belgium.
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