Results and Discussion
Spatial variation:
Differing spatial trends in air temperature and moisture level were observed in the barns. In the naturally ventilated barns, no set pattern existed for the dry-bulb and dew-point temperatures within the quadrants. The time-averaged hourly temperature curves for Barn NV-NY appeared like loosely woven strands of string with different strands in different order throughout the day. In a naturally ventilated barn, this is a logical consequence of the wind direction not being consistent throughout the day and from day to day. An exception was that from about 6 to 10 AM the northwest and southwest quadrants were consistently cooler than the eastern quadrants, and almost equaled outside temperature. This time period likely coincided with cows being out of the barn for milking and more prevalent westerly breezes (latter could not be verified). The temperature curves for the other two naturally ventilated barns appeared as tightly woven strands or ropelike. For a given set of wind conditions, one could find a small rise in indoor temperature in the downwind direction in these barns. The tight weave of the curves illustrates that wind direction was not predictable and/or the temperature rise within these barns was very small due to good air exchange (on a per-cow basis).
The tunnel-ventilated barns displayed more discernable trends. If a change in temperature existed, the temperatures increased with the designed airflow pattern, where outdoor air entered endwall inlets and was exhausted from fans on the opposite end. The data showed that air was picking up sensible heat and moisture as it traveled through the barns. This pattern was most evident in Barn TV-NY, the longest barn where the spreads in time-averaged temperatures were consistently 4 to 5°F (Figure 4). Temperatures within Barn TV-OHC were so close that the representative curves overlapped one another. Data for Barn TV-OHW showed similar trends with slightly more spread than Barn TV-OHC. Consequently, the time-averaged interior air temperatures in the shorter (160-foot) barns were within 2°F of ambient air temperature during the day and were no more than 4°F warmer at night, while the long NY barn (>850 ft.) had interior temperatures that ran 4 to 5°F warmer than outside during the daytime and 8 to 9 °F warmer at night.
The THI varied throughout the barns with the dry-bulb and dew-point temperatures from which this index is derived. In the naturally ventilated barns, THI patterns existed for any given time or weather conditions, but not on a time-averaged basis. In the tunnel-ventilated barns the maximum differential (compared to that outside) in time-averaged THI ranged from about 1 within Barn TV-OHC to nearly 4 in Barn TV-NY.