Laboratory HVAC: Supply & Exhaust Duct Design
An important aspect of laboratory HVAC system is the ducts. There are two key elements to factor in for laboratory duct design – the primary supply ducts and the exhaust ducts – to ensure the performance and safety of the laboratory environment.
Typically, for the supply duct, the general practices for all buildings can be used in the selection of duct materials for laboratories. This is because most supply ductwork may not encounter sufficient concentrations of hazardous laboratory materials.
However, the exhaust duct systems design requires more considerations due to the hazardous materials contained in the exhaust airstreams.
In this blog, we compare the key design elements recommended by ASHRAE for the laboratory duct design.
| ELEMENT | DESCRIPTION | SUPPLY DUCT | EXHAUST DUCT |
|---|---|---|---|
| Ambient Temperature | Higher ambient temperatures relative to the supply air temperature can create condensation on the outside of the ductwork. Condensation on ductwork can eventually cause corrosion of the ductwork. | Y | Y |
| Duct velocities and pressures | Low-pressure ductwork is often made of thinner material than higher pressure ductwork, but it requires a larger duct to move the same volume of air as a high-pressure system. | Y | Y |
| Length and arrangement of the ductwork | Lengthy runs of ductwork result in larger supply air heat gains or losses and require additional cooling and heating capacity or additional insulation. | Y | Y |
| Nature of hood effluents | Knowledge of the current and future effluents and their possible concentrations is necessary to assess the materials required to handle the exhaust. | Y | |
| Effluent Temperature | Effluent temperature is also a concern for condensation. High-temperature effluents can cool off significantly in a lengthy section of duct. | Y | |
| Variance in exhaust air volume | Knowledge of variance in exhaust air volume helps in maintaining needed duct velocities. | Y | |
| Flame spread and smoke developed ratings for duct materials | Knowledge of the rating for the materials considered for ductwork is required to meet national, local, and state regulations. | Y |
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