Fermentation Design 95 Convection and radiation depend upon whether the tanks are insulated or not, and the ambient air temperatu especially during the winter. Measurements of convection and radiation heat losses are, on average, 5% or less of total heat of fermentation(winter and uninsulated tanks) 2. Heat Loss by Evaporatio a. If fermenters have level indicators, theaverage evapo- ation per hour is easily determined b. Calculate pounds of water/hour evaporated from psychometric charts based on the inlet volume and humidity of air used, and at the broth temperature The exhaust air will be saturated, Determine heat of vaporization from steam tables at the temperature of the broth= HEy= Btu/lb Q2=HEy X(b water evap/hr)=Btw/hr Evaporation depends upon the relative humidity of the compressed air, temperature of the fermentation broth and the aeration rate. It is not uncommon that the loss ofheat by evaporation is 15 to 25%ofthe heat of fermentation. Modern plants first cool the com- pressed air then reheat it to 70-80%relative humidity based on summertime air intake conditions. Conse- quently, in winter the air temperature and absolute humidity of raw air are very low and the sterile supply will be much lower in relative humidity than summer conditions. Therefore in the winter more water is evaporated from the fermenters than in the summer. ( Water can be added to the fermenter or feeds can be made more dilute to keep the running volume equal to summer conditions and productivity in summer and winter equal) 3. Heat Removed by refrigerant a. This is determined by cooling the broth as rapidly as possible 5%F below the normal running temperatureFermentation Design 95 Convection and radiation depend upon whether the tanks are insulated or not, and the ambient air temperature, especially during the winter. Measurements of convection and radiation heat losses are, on average, 5% or less of total heat of fermentation (winter and uninsulated tanks). 2. Heat Loss by Evaporation a. Iffermenters have level indicators, the average evapo￾ration per hour is easily determined. b. Calculate pounds of waterhour evaporated from psychometric charts based on the inlet volume and humidity of air used, and at the broth temperature. The exhaust air will be saturated. Determine heat of vaporization from steam tables at the temperature of the broth = HEV = Btu/lb. Q2 = HEV x (lb water evaphr) = Btuh Evaporation depends upon the relative humidity of the compressed air, temperature of the fermentation broth and the aeration rate. It is not uncommon that the loss of heat by evaporation is 15 to 25% ofthe heat of fermentation. Modern plants first cool the com￾pressed air then reheat it to 70-80% relative humidity based on summertime air intake conditions. Conse￾quently, in winter the air temperature and absolute humidity of raw air are very low and the sterile air supply will be much lower in relative humidity than summer conditions. Therefore, in the winter more water is evaporated from the fermenters than in the summer. (Water can be added to the fermenter or feeds can be made more dilute to keep the running volume equal to summer conditions and productivity in summer and winter equal.) 3. Heat Removed by Refrigerant a. This is determined by cooling the broth as rapidly as possible 5°F below the normal running temperature