PROPOSAL OF JAPANESE STANDARD OF THE MEASURING METHOD OF AIRFLOW RATES OF BUILDING EQUIPMENTS

Transcription

1 PROPOSAL OF JAPANESE STANDARD OF THE MEASURING METHOD OF AIRFLOW RATES OF BUILDING EQUIPMENTS Y. Utsumi 1, S. Hayakawa 2, T. Kurabuchi 3, and H. Yoshino 4 1 Department of Architecture, Miyagi National College of Technology, Natori, Japan 2 Department of Architecture, Nihon University, Tokyo, Japan 3 Department of Architecture, Tokyo University of Science, Tokyo, Japan 4 Department of Architecture, Tohoku University, Sendai, Japan ABSTRACT The measuring method of airflow rates of building equipments is important and is required in many standards, codes, etc. and the committee of the ventilation planning in the building of SHASE (Society of Heating, Air-conditioning and Sanitary Engineering), Japan is about to propose the standard for The Measuring Method of Airflow Rates of Building Equipments. It is aimed to ensure the quality of indoor environment and the performance of HVAC system under the situation that the existing methods are in the variety but less information for the choosing and its feasibility is available. The applied principles are 1) to collect available methods and provide the standard to practitioners which are feasible, 2) to include most of the methods applicable and available at this moment, 3) to cite and/or mention the existing standards, and coded, etc. and 4) to indicate the feasibility of the methods to practitioners. This paper provides overview of the measuring methods of airflow rate in buildings and also the framework of the proposed standard. KEYWORDS Standard, Japan, Airflow rate, Measurement, Building equipment INTRODUCTION Background and purpose Ventilation is necessary for the human activities in buildings, and its major purposes are to provide fresh air to breathe and to exhaust contaminants with adequate amount of airflow rate and resultant IAQ. In general, there should be the procedure that ensures proper airflow rate in the phases of designing, delivery, etc. and regular inspection is carried out for ventilation system. On the other hand, insufficient airflow supply may occur after moving in houses where occupants mainly operate ventilation system. Recently the commissioning, Cx, including airflow rate is being common in design, construction, maintenance, etc. in Japan. Many activities exist after 90s and, for example, Manual for the Assessment of Indoor Environment (SHASE 2005) was published. This paper describes the measurement method and related standards of airflow rate of ventilation system, and also proposes the framework of a new standard of airflow measurement method of building equipments. Buildings and ventilation system in the scope The measuring methods of airflow rate of building equipments are specified in many standards, codes, etc. They are in the variety but less information for the choosing and its feasibility, therefore, it is preferable for practitioners to have methods and standards that are available and feasible. In this Corresponding Author: Tel: , Fax: address: utsumi@miyagi-ct.ac.jp

2 context, the principle of the proposed standard would be; To include most of the methods applicable and available at this moment To cite and/or mention the existing standards, and codes, etc. To indicate the feasibility of the methods to practitioners The building usages are office, houses and schools, and not for factories that may have a large space. Building ventilation equipment system in the scope is shown in Figure 1. The hatched area besides indoor, HVAC system and heat exchanger are dealt, and the measurement of each component of ventilation system, such as air supply, air exhaust, air intake of the system, air exhaust of the system, fan, duct, results in the measurement of the system. Outdoor Air Inlet Filter Cooling coil Heating coil Return air Humidifier Supply duct Air supply indoor Supply fan Air exhaust Outdoor duct Exhaust Return fan duct heat exchanger Exhaust Air System and equipments in the scope Figure 1. System and equipments ion the scope MEASUREMENT METHOD OF AIRFLOW RATE AND ITS APPLICABILITY Classification of airflow measuring method and ventilation standards The common measuring method may be into four types as followings. Multi-points measuring method of duct flow Tracer gas method of duct flow Flow-hood for air supply and air exhaust k-factor method (pressure difference method) The ventilation standards and codes can be also classified by applied phases; In designing, to estimate airflow rate and flow paths In construction phase, to measure airflow rate of each equipment and to adjust airflow in the system In maintenance phase, to execute regular inspection of the system performance The standards and codes used in some phases Applicability of airflow measuring method To acquire the exact airflow rate on-site, it is important to choose adequate method according to the airflow component and to understand the performance of the component. The method may be chosen considering; the component to be measured the location to be measured

3 measuring period measuring precision the size of measuring equipment, the configuration of measuring system, the period needed for preparation, the procedure of acquired data processing, cost, etc. Table 1 shows the relation between measurement method and targeted component, considering uncertainty and feasibility. Applicability decreases from double circle to triangle. Also it should be noted that the environment conditions, that is, outdoor temperature, indoor temperature, humidity, wind speed and direction, etc. may be within the allowed range of the method and that the small capacity of ventilation system in house is likely to be affected the measurement devices because of small fans. Table 1. The relation between measurement method and the component Method Multi-points measuring method of duct flow Tracer gas method of duct flow Flow-hood without pressure compensation Flow-hood with pressure compensation Pressure difference method (k-factor method) Part to be measured Duct Duct Air supply, exhaust Air supply, exhaust Ventilation equipment Certainty Feasibility comment Common method Complicated configuration Portable Portable Manometer needed BRIEF DESCRIPTION OF AIRFLOW MEASUREMENT METHOD Multi-points measuring method of duct flow The airflow velocity distribution in a duct is measured to estimate the intake air volume and supply air volume. The configuration is shown in figure 2. The duct section, circle or rectangular, is divided into equal area subdivisions, at the location of the anemometer in this case (see figure 3). The representative air velocity at each subdivision is measured and the mean velocity Vmean[m/s] is calculated. Flow rate Q[m3/h] is derived with equation 1, where S[m2] is a section area of the duct. Q = 3600 x S x Vmean [m3/h] (1) This method is commonly applied and many variations, e.g. simplified and precise procedure. The location of the measurement, the number of subdivisions, and the choice of equipment, e.g. anemometer(astm 2007), pitot tube(astm 2006), propeller, etc., are important. This method may have within 10% of uncertainty. Tracer gas method of duct flow Known amount of tracer gas is injected into the duct and tracer gas concentration at the leeward is measured. The instrumentation is indicated in figure 4. The ratio of injection rate to the leeward tracer gas concentration provides the mass airflow rate Fu[kg/h] by the equation below. (ASTM 2004)

4 Duct diameter D Flow rectifier anemometer Figure 2. Multi-points measuring method of duct flow <150mm 16 to 64 subsections Measuring points Figure 3. An example of subdivisions of duct section Fu = (CI - CD) / (CD - CU) x FI [kg/h] (2) Where CU [kg/m3]: windward mass concentration of tracer gas, CD [kg/m3]: leeward mass concentration of tracer gas, CI [kg/m3]: mass concentration of injected tracer gas, FI [kg/m3]: injected flow rate in mass This method has characteristics such as; 1) applicable to the case that air speed is low where anemometer cannot be used, 2) no effect from the temperature, the humidity, etc. in duct, 3) no need to measure the duct section area, 4) air flow can bi not straight, 5) instrumentation may be complicated. Also the choice of tracer gas should be careful not to cause any hazard. Generally the accuracy depends on the tracer gas analyzer, the location and numbers of tracer gas sampling concentration. C U C D F U F U +F I C I,F I Figure 4. Airflow measurement by tracer gas method

5 Flow-hood for air supply and air exhaust The flow hood is adapted to the air exhaust device or air supply device according to its size. The average air velocity is automatically measured by the equipment and multiplied by the section area, same to equation 1, and the airflow rate is indicated on the equipment panel display (see figure 5). As the equipment itself gives the flow resistance and it may change the airflow rate, there are two methods; 1) without pressure loss compensation, and 2) with pressure loss compensation. Former method is; 1) easy to use, 2) portable, 3) battery driven. However it cannot be used with large or complicated shape of airflow device, and is not adequate for long term measuring, e.g. more than 1 week. The products in market can measure up to 4000[m3/h]. Though the latter is more accurate than the former because the auxiliary fan generates the lost pressure by the attached device (JIS 2000, ANSI/AMCA 1999), the equipment is much larger in most cases. Other characteristics are; 1) applicable to inlet and outlet, 2) a variety of air velocity measuring equipment is available, 3) can attach flow rectifier to avoid biased flow. Air supply or exhaust ceiling hood downward for supply and upward for exhaust measurement and display holder to grab Figure 5. Configuration of flow hood measuring device manometer Manometer for velocity Ps Experimented fan Pn Chamber A Chamber B Auxiliary blower Damper for airflow rate adjustment nozzle Figure 6 Principle of flow hood method with pressure loss compensation

6 k-factor method (pressure difference method) The airflow device itself has some hole to measure the pressure difference and an inherent coefficient, k-value, to calculate airflow rate (Johansson 1998). The pressure differences are between room and inside the device and between two points inside the device (see figure 7). The location can change for air supply and exhaust. It is common in North Europe but not produced in Japan at this moment. The airflow rate is derived by the following equation. The pressure can be assumed to be the combination of static and dynamic pressure. Q = 3.6 x k x ΔP 1/2 [m3/h] (3) Where k [L/s/Pa 1/2 ]: k-value ΔP[Pa]: pressure difference k-value is set with each equipment P measuring point q=k P indoor Figure 7. The configuration of k-factor method THE FRAMEWORK OF PROPOSED STANDARD The content of proposed standard There are four types of the measuring methods of airflow rate in buildings as described above. The standard is being proposed based on the principles; 1) to collect available methods and provide the standard to practitioners which are feasible, 2) to include most of the methods applicable and available at this moment, 3) to cite and/or mention the existing standards, and coded, etc. and 4) to indicate the feasibility of the methods to practitioners. The content at this moment is indicated in table 2. The purpose and scope have been expressed and the way to choose the method for chapter 4 is summarized in table 1. Chapter 5 Airflow Measuring Method specifies the common four types in terms of measuring configuration, principle and characteristics with the information on; Characteristics Principle and airflow rate derivation Instrumentation Procedure Measurement uncertainty Related standards, etc. and reference Chapter 6 Certainty of Measurement Results specifies the performance of each method according to the catalogue, experiment, etc. Chapter 7 Measurement Report explains the required general data at the measurement such as; Title of the measurement

7 Date and time Location Personnel Organization The name of measuring method Measured data Air flow rate result The proof of calibration Table 2. The content of proposed standard of The Measuring Method of Airflow Rates of Building Equipments Chapter Description 1. Purpose Including the background 2. Scope Possible users and applicable fields 3. Terminology Technical terms, etc. 4. Airflow Measuring Method and its Applicability Indicating the way to choose 5. Airflow Measuring Method 5.1 Multi-points measuring method of duct flow 5.2 Tracer gas method of duct flow 5.3 Flow-hood for the airflow inlet and outlet 5.4 Pressure difference method ( k-factor method ) Describing available methods in terms of principle, procedures, error, etc. 6. Certainty of Measurement Results For each method 7. Measurement Report Typical reporting format CONCLUSIONS It is important to provide the practical measuring method of airflow rate in buildings in the shape of authorized standard common to many countries. The methods are classified into four types; 1) multi-points measuring method of duct flow, 2) tracer gas method of duct flow, 3) flow-hood for air supply and air exhaust, and 4) k-factor method. After defining the scope and purpose, four methods in are described briefly in terms of principles, characteristics, etc. Also the table to choose the method for users is shown. Based on these issues, a new standard The Measuring Method of Airflow Rates of Building Equipments is proposed and explained concerning to the framework. Though the standard draft is almost completed, it is necessary to survey more related existing standards, etc. and to continue the revising. ACKNOWLEDGEMENTS This research and the providing the proposal are in collaboration with the committee of ventilation planning, leader Prof. H. YOSHINO, of SHASE, The Society of Heating, Ai-conditioning and Sanitary Engineers of Japan, and also ISO TC163/SC1/WG10 committee, leader Prof. H. YOSHINO, supported by Japan Testing Center for Construction Materials. The authors acknowledge the related members and their supports.

8 NOMENCLETURE CU [kg/m3] windward mass concentration of tracer gas CD [kg/m3] leeward mass concentration of tracer gas CI [kg/m3] mass concentration of injected tracer gas FI [kg/m3] injected flow rate in mass Fu [kg/h] mass airflow rate k [L/s/Pa 1/2 ] k-value ΔP [Pa] pressure difference Q [m3/h] volume airflow rate S [m2] the section area of the duct, hood, etc. Vmean [m/s] the mean air velocity REFERENCES 1. SHASE (2005), Manual for the Assessment of Indoor Environment, Study on Standardization of Measurement Procedures for Assessing Indoor Environment and Energy Performance of HVAC Systems, SHASE-M , ASTM D (2007) Standard Test Method for Average Velocity in a Duct Using a Thermal Anemometer, ASTM D (2006) Standard Test Method for Average Velocity in a Duct (Pitot Tube Method), ASTM E (2004) Standard Test Method for Volumetric and Mass Flow Rate Measurement in a Duct Using Tracer Gas Dilution, JIS B 8330:2000 (2000) Testing methods for turbo-fans 6. ANSI/AMCA Standard , (1999) "Laboratory Methods Of Testing Fans for Aerodynamic Performance Rating" 7. P. JOHANSSON (1998),ANDERS SVENSSON : Metoder för mätning av luftflöden i ventilationsinstallationer, BYGGFORSKNINGSRÅDET