The thermal performance of a low-cost, hoop-type swine building (3.55 × 5.7 × 10.3 m) was evaluated under the winter weather conditions of Central Japan. The hoop building had two curved roofs made from 2.5 cm diameter tubular steel pipes each covered with a reflective film. There was a 20 cm air space between the inner and outer covers through which the exhaust air flowed. A positive-pressure ventilation fan and an air distribution duct were used to supply the fresh air. The evaluation was conducted for three opening configurations of the air distribution duct (one, two, or four holes on a cross-section of the duct) and presence or absence of an internal curtain. Furthermore, the effect of replacing the reflective film with a PVC film for the east side cover on solar transmission and thus the internal temperature rise was quantified. The building was simulated to house 30 pigs at a body weight of 70 kg. Resistive heating wire was used to simulate the sensible heat generation of the pigs at 131.5 W/pig at 10°C temperature.

The inside temperature averaged 6.9°C higher than the outside temperature during the minimum ventilation period. As the exhaust air passed through the double-layer air space, 25.4% of exhaust heat transferred back into the building and 74.6% lost to the outside. When replacing the reflective covers with the PVC film covers on the east side, the internal temperature rise increased to an average of 7.6°C with a maximum of 12.7°C. The magnitude of temperature rise was proportional to the transmitted solar radiation, as evidenced by the higher temperature rise during the day and significantly reduced temperature rise at night. To eliminate the effects of cold, nocturnal radiation, the PVC film cover should be covered by the regular reflective cover at night. One-holed air duct had a tendency to produce drafts in the pig occupied zone (POZ, 1.2 × 0.7 m), whereas four-holed air duct tended to have less mixing effects on the air. In comparison, the combination of two-holed air duct and use of the internal curtain was found to be the best in achieving warmer air temperature and minimizing drafts in POZ.