Abstract
The investigation reported here was conducted to provide data necessary for an estimate of the radiant heat load to housed animals and a design of thermal radiation environment in opentype livestock barns under summer condition. The experiments were carried out in 5 existing barns, each roof of which had different resistance of total heat transmission and surface absorptivity for solar radiation. The results were obtained as follows:
1) The average rate of downward all-wave radiant heat were measured as 400-500kcal/m2.h. in the barn on a sunny day, and these values were equivalent to 60-80% of the outside horizontal solar radiation.
2) The downward radiant flux and the temperature difference between inside roof surface and inside air decreased as the thermal resistance of the roof increased. When the absorptivity of the roof surface was high, the effects of the thermal resistance on such reductions were highly significant, but scarcely appeared for the roof having low absorptivity.
3) The thermal resistance of the roof being high, the radiant flux depended on the outside air temperature, but it depended on the solar radiation while the thermal resistance was low.
4) To provide below 1°C temperature difference between the inside roof surace and inside air on a sunny day, the required thermal resistance of the roof were estimated as 0.6m2.h.°C/kcal for the absorptivity being 0.7, and as 0.5m2.h.°C/kcal for the absorptivity being 0.4, respectively.
5) Provided with low thermal resistance of the roof, it was seemed that decreasing the absorptivity of the roof surface was equivalent to increasing the thermal resistance of the roof for modifying the thermal radiation environment in opentype barns.
6) It was considered that the upper hemispherical effectual radiation temperature was a resonable index to evaluate the thermal radiation environment within livestock barns.
