Air Quality Sensors in Buildings and HVAC systems

Transcription

1 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

2 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 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]. 2

3 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. 3

4 Figure 3: Example of CO2 sensor data sheet 4

5 Figure 4: Example of air quality sensor data sheet 5

6 1.3 Problems to be considered General problems All problems listed in the reference document [12] are relevant for air quality sensors 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. 6

7 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 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,...) 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 Execution phase Summary of the test method This "basic" test method consists in using the BEMS to observe the evolution of typical sensor readings. 7

8 Experimental method - Select typical variables to display on the BEMS; - Observe evolution of selected variables - Optionally, print selected graphs or save for future processing 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 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 8

9 2400 CO2 concentration [ppm] /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 9

10 2.2 Diagnosis tests 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) Preparation phase: evaluation of available data and of expected performance Cfr Execution phase 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 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 Contents of the test report Date and time Selected (or generated) operational conditions 10

11 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 , [7] ISERMANN, R. Supervision, fault-detection and fault-diagnosis methods: an introduction. Control Engineering practice, vol. 5, n 5, pp , 1997 [8] ASHRAE Fundamentals Chapter 14: Measurement and Instruments [9] Sontay Limited, [10] [11] MURPHY J., BRADLEY B., Using CO 2 for Demand-Controlled Ventilation, Engineers Newsletter, Volume 31 No. 3, [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. 11