How should engineers write a performance specification that avoids unsuitable substitutions?

State the target relative humidity and tolerance, the design temperature range and the calculated moisture load. Define the required technology, airflow at duty, filtration class and any enclosure rating for outdoor plant. Include the controls and BMS integration points needed for commissioning and monitoring. Many projects use DEHUM supplied Dantherm or DriSteem as the basis of design, with equal considered where full compliance with performance and controls is demonstrated. This keeps design intent intact and reduces whole of life risk.