The Influence of Building Equipment and Operation on the Air Exchange Rates throughout a Naturally Ventilated Dairy Barn

Abstract

Naturally ventilated barns have gained wide acceptance worldwide, due to the easy design and the low energy consumption. The inside climate and the air exchange rate (AER) of such buildings is mainly affected by the outside conditions. The AER has a great influence on emission fluxes. There is no reference method for AER estimation in naturally ventilated barns but several methods with different pros and cons and each with uncertainties have been used. The aim of this study is to evaluate the influence of side curtains of a naturally ventilated barn on AER as well as the reliability of tracer gas technique in AER quantification throughout these kinds of barns. The AER and the emission fluxes were measured in a naturally ventilated dairy barn in north Germany. The AER was estimated using two methods. The first one is the concentration decay of radioactive isotope tracer-gas Krypton (85Kr-M) with two different evaluation procedures: (1) AER obtained from the sum of impulses for all 85Kr-detectors (sum-85Kr-M), and (2) AER obtained from the arithmetic average of the single 85Kr-detectors (average-85Kr-M). The second method is the CO2-mass balance model (CO2-M). The meteorological parameters were recorded inside and outside the barn, as well as the concentrations of ammonia (NH3), carbon dioxide (CO2) and methane (CH4). Pearson correlation analysis was performed and linear regression models were fitted. On this basis, the influence of the side curtains on AER was investigated and evaluated. The AERs, derived from CO2-M, were 35.314.6 h-1 and 22.07.1 h-1 for opened and closed side curtains, respectively. The 85Kr-M resulted in higher AERs values compared to CO2-M by 0.150.13 for sum-85Kr- M and by 3.661.17 for average-85Kr- M. The emission fluxes according to CO2-M were during the summer seasons 124, 538 and 45,600 g d-1AU-1 for NH3, CH4, and CO2, respectively. During winter seasons they were 64, 348 and 42,700 g d-1AU-1.