Evaporation of water to the ambient air is generally a cost-effective solution to alleviate heat
stress but is also critically discussed due to its increasing effect on indoor humidity. The
objectives of this study were to investigate the impact on indoor temperature, humidity, and
ventilation rate using a high-pressure fogging system inside a mechanically ventilated research
facility for fattening pigs. Data were sampled quasi-continuously throughout four fattening
periods, including information on water consumption and energy use of the fogging system, as
well as on the averageweight gain of the pigs. It was found that for the pigs, the positive effects
of the reduction of sensible indoor temperature exceeded the negative effects of the increased
humidity, mirrored e.g. by a reductionof the temperature–humidity index (alert situationswere
reduced from 15.5% to 0.8%) and an increased weight gain of the animals during hot summer
conditions. Main effects were achieved on days with mean daily outside temperatures above
14 1C, during which water consumption of the fogging system averaged 4.9 ld1 pig1.
The evaporation characteristics, such as the evaporative fraction as well as the time
constant for reaching a steady state, were evaluated using a transfer-functionmodel. Both were
influenced largely by temperature and saturation deficit. While the evaporative fraction was
100% during steady state and 63% of steady state was reached within 65 s during warm and dry
ambient conditions (28 1C; 53% relative humidity RH), the evaporative fraction dropped to 89%
and 65% for moderate (21 1C; 69% RH) and cold/humid (131C; 83% RH) indoor conditions,
respectively, and the time to reach steady state was nearly doubled for the latter. The
information about such evaporation characteristics is crucial for an accurate control of fogging
and ventilation.