A COMPREHENSIVE STUDY ON DIFFERENT METHODS FOR AIR EXCHANGE RATES MEASUREMENT IN A NATURALLY VENTILATED DAIRY HOUSE | ||
| Misr Journal of Agricultural Engineering | ||
| Article 21, Volume 29, Issue 4, October 2012, Pages 1603-1620 PDF (847.64 K) | ||
| Document Type: Original Article | ||
| DOI: 10.21608/mjae.2012.101385 | ||
| Author | ||
| M. Samer | ||
| Assistant Professor, Cairo University, Faculty of Agriculture, Department of Agricultural Engineering, El-Gammaa Street, 12613 Giza, Egypt | ||
| Abstract | ||
| The major problem of natural ventilation is the lack of accurate, continuous and online measuring and controlling techniques for air exchange rates (AER) which is crucial for the quantification of gaseous emissions. Therefore, this papers aims at comparing four measurement methods and to recommend thereof one method for further developments. Thirty six experiments were performed to study the AERs in a naturally ventilated dairy barn through four summer seasons and three winter seasons. The AERs were determined using moisture (H2O) balance, heat balance (HB), CO2-balance and tracer gas technique (TGT). The statistical analyses were correlation analysis, regression model, ANOVA model and t-test. Continuous measurements of CO2 concentrations, temperature and relative humidity inside and outside the building were performed. The H2O-balance showed reliable results through winter seasons and slightly acceptable results through summer seasons. The error sources of H2O-balance are: the difference between the internal and external humidity levels which depend in turn on the accuracy of the used temperature-humidity sensors and their locations, the correctness of the used factors (e.g. the moisture produced by one cow and per mass unit), and the accuracy of the calculations of the humidity ratios. The HB showed acceptable results to some extent through summer seasons and unsatisfactory results through winter seasons. The error sources of HB are: the calculations accuracy of the net area of the different building components and the determination of the relevant overall heat transfer coefficients, the temperature difference which depends in turn on the accuracy of the used temperature-humidity sensors and their locations, and the sensible heat produced by the animals which depends on the physiological changes of the animals. The CO2-balance showed unexpected high differences to the other methods in some cases. The error sources of CO2-balance are: the use of calculation models for metabolic energy, the amount of CO2 produced per energy unit, the quantity of CO2 produced emitted from manure, variations of ambient temperatures and the location of CO2 measuring points. The TGT showed reliable results compared to HB, H2O-balance and CO2-balance. Therefore, the TGT should be further developed, where it delivers comparable results and is independent on the physiological parameters. The airflow rates (AFRs), subject to TGT, were 0.12 m3 s-1 m-2, 1.15 m3 s-1 cow-1, 0.88 m3 s-1 LU-1 (LU is livestock unit of 500 kg), 395 m3 s-1 and 470 kg air s-1 through summer seasons, and 0.08 m3 s-1 m-2, 0.83 m3 s-1 cow-1, 0.64 m3 s-1 LU-1, 275 m3 s-1 and 328 kg air s-1 through winter seasons. The AERs were 37, 81, 63 and 62 h-1 through summer seasons, and 40, 143, 61 and 39 h-1 through winter seasons subject to H2O-balance, HB, CO2-balance and TGT, respectively. | ||
| Keywords | ||
| Livestock buildings; Heat balance; Moisture (H2O) balance; Tracer gas technique; CO2-balance; Natural ventilation; Airflow rates; Air exchange rates; Gaseous emissions | ||
| References | ||
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