The heat transfer fluid systems designed by Fluor include liquid phase heating and cooling, vapor phase heating and combination liquid and vapor systems. The operating temperatures have varied from read sub-zero for cooling or greater than 700°F for heating applications. Since many batch and semi-batch processes require both heating and cooling in the same equipment, such as jacketed reactors, we have designed many heat transfer systems involving a single heat transfer fluid but with multiple temperature levels for heating and cooling. Where control of process temperature was critical, we designed systems to operate in temperature ranges as close as ±1°F.