The brief for this particular medical company required the environmental control system (ECS) to maintain <3% relative humidity (RH) and 75°F temperature ±2° for the automated packaging of biotherapy reagents, some of which were highly sensitive to moisture and heat.
The medical HVAC system was to be located in an ISO 8 cleanroom space with ambient air from 65–77°F (18.3–25°C) and at 35–75% RH. In addition, some of the packaged items would include liquids that would introduce an evaporative load into the environment prior to the placement of heat seals. The heat sealing equipment would also introduce 400W of heat to the environment.
Finally, the machine would contain a stainless steel, pressurised dry-environment enclosure, air-locked to minimise the introduction of ambient air.
The solution
To dehumidify the system to the required conditions, Air Innovations introduced a desiccant dryer with pre-filtered air into the design. Re-circulated air is then returned to the acceptable ambient temperature and passed through HEPA filtration to maintain the cleanroom environment, while the hot exhaust is ducted away from the ECS.
The system was designed to sit below floor level, although the end location was ultimately moved onto floor level. The air change rate was designed to ensure a recovery time of less than 30 minutes any time after the doors opened.
The key specifications included:
- Relative Humidity controlled to ±0.5%, and set to <3% RH with 0.011µg/min continuous evaporation latent load plus moisture leakage loads
- Temperature controlled to 75°F ±2°F
- ISO 8 cleanroom level HEPA filtration (99.97% to 0.3µm)
- Environmental Control System designed to fit in a 37.5in by 52in trench
- PID (proportional-integral-derivative) loop controls for temperature and humidity
- Stainless steel 304 exterior
- Airflow designed for 90 cubic feet per min (equivalent to 0.04 m3/s)
- Maximum external static pressure of 1in (measured in inches of water gauge)
- Hot-gas bypass refrigeration control
- 1kW electric reheater.
The result
The medical environmental control system controls humidity to desiccant levels and maintains a steady temperature in the ISO 8 cleanroom space. The system also employs HEPA filtration. The solution not only meets all key specifications but also addresses humidity requirements through both the creation of a vapour barrier and the use of return air via a desiccant dryer to counteract internal evaporative loading. It also meets UL standards and features a stainless steel 304 exterior.
