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Experimental Analysis of Condensation Rate in Conductive Cooling Systems for Dairy Cattle

Perano, Kristen M., Shelford, Timothy J., Gebremedhin, Kifle G.
Applied engineering in agriculture 2018 v.34 no.2 pp. 425-436
agricultural engineering, air, air temperature, cooling, cooling systems, dairy cows, dewpoint, heat exchangers, heat stress, linear models, relative humidity, sand, sawdust, surface temperature, thermocouples, water content
Conductive cooling for dairy cattle is an emerging technology that holds promise as a way of relieving heat stress. A conductive cooling system using modified Dual Chamber Comfort (DCC) waterbeds from Advanced Comfort Technologies as heat exchangers placed in the stalls of dairy cows was tested. Rate of moisture accumulation in two types of bedding (sand and sawdust) was studied for two levels of relative humidity (RH) of air (~60% and ~75%). Four bedding thicknesses were considered in this study and were 0.5, 2.5, 7.5, and 20 cm. The experiment consisted of the following: (1) two waterbeds cooled by circulating water at 4.5°C, and (2) two more waterbeds (control) where the water in the waterbeds was not cooled. Moisture content of the bedding was measured in duplicate at three locations on the surface of each waterbed for each of 20 treatments (sand and sawdust bedding measured at both ~60% RH and ~75% RH and at five bedding thicknesses/sampling depths). The moisture measurements were conducted before and after 2 h of cooling. In cases where the bedding thickness was 2.5 cm or more, the temperature of the bedding was measured at three points using thermocouples: (1) at the surface of the waterbed, (2) at mid depth, and (3) at 0.5 cm below the bedding surface. Mixed linear models were used to calculate the condensation rates and the equilibrium temperatures. In all treatment combinations, the surface temperature of the cooled waterbeds was at least 7.5°C lower than the dewpoint temperature of the air. For the 0.5-cm thick sawdust, condensation rates, calculated in percent increase in dry basis of moisture content per hour (% d.b. h-1), were 3.5% d.b. h-1 higher for the cooled waterbeds than that for the control waterbeds at the ~75% RH. For 0.5-cm thick sawdust at ~60% RH, the condensation rate for the cooled waterbeds was 3.1% d.b. h-1 higher than that for the control waterbeds. Similarly, the condensation rates for the 0.5-cm thick sand were 2.0% d.b. h-1 higher for the cooled waterbeds than for the control waterbeds at the ~75% RH conditions and 1.3% d.b. h-1 higher at the ~60% RH conditions. The condensation rate for the 2.5-cm thick sand bedding measured at the top surface of the waterbed (the bottom 0.5 cm of the bedding) was statistically significant but negligible (0.1% d.b. h-1). No other treatments yielded any difference in condensation rate between the cooled waterbeds and the control waterbeds.