In the stringent world of controlled environments, Deep Cooling In Cleanrooms HVAC design is not optional, it’s vital. Moisture, even in trace amounts, can provoke condensation, microbial growth, or particle adhesion. Many pharmaceutical, biotech, and semiconductor processes demand tight control of dew point, temperature, and humidity. In the first lines of any cleanroom HVAC spec, designers must ensure that the dew point is actively managed alongside sensible heat loads.
In this blog, we will clarify what “deep cooling” means, how dew point control works in practice, and how to align such systems with GMP, ISO 14644, NAPRA, and other regulatory frameworks. We’ll also highlight some energy trade-offs and practical design approaches.
What Is “Deep Cooling” in Cleanroom HVAC Design?
In HVAC parlance, “deep cooling” refers to the deliberate overcooling of air below the dew point (or “subcooling”) to extract moisture, followed by reheating to the target supply temperature. In cleanrooms, this technique is frequently the go-to for dehumidification. You might also see it implemented as chilled-water or DX coils that operate at low entering-coil temperatures (e.g. 40 °F entering water or equivalent in DX setups).
By cooling below the dew point, latent heat is removed (moisture condenses), and that moisture is drained off. The air then is reheated to ensure the delivered air doesn’t overcool the space. This two-step method decouples humidity control from temperature control.
Deep cooling thus becomes essential when humidity or dew point is the more critical constraint than temperature. In such cases, the cooling coil must operate at full capacity, even if that pushes supply air colder than the nominal temperature setpoint. Later, reheaters or bypass schemes bring it back to comfortable or process-safe levels.
Dew Point Control: The Underlying Psychrometrics
To appreciate deep cooling, we must revisit dew point. Dew point is the temperature at which air becomes saturated (100 % relative humidity) and water vapor begins to condense (well at least theoretically). In a cleanroom, you rarely want air at 100 % RH, because condensation triggers contamination risks.
By cooling air below its dew point, moisture condenses and is removed, reducing absolute humidity. Then, the air is reheated to maintain a safe relative humidity (e.g. 30 %–50 %), depending on the application. The final supply air has lower moisture content but remains above freezing or condensation risk in the space.
This approach contrasts with simpler RH control methods that rely solely on desiccants or membrane dehumidifiers without cooling. Deep cooling is often more robust when external air loads or internal latent loads vary significantly.
Implementation Options: Chilled Water, DX, and Hybrid Strategies
Chilled-Water Deep Cooling with Reheat
Large installations frequently use chilled water systems for deep cooling. A central chiller cools water (e.g. 2 °C to 7 °C) which flows through air handling coils. Mixed return air is chilled below its dew point, moisture condenses, and then that cold, dry air is reheated as necessary.
Many HVAC design guides for cleanrooms specify dual coil systems: one coil addresses the make-up air (handling latent + sensible loads), and a second handles internal, process‐generated heat (sensible load) with minimal further dehumidification.
DX (Direct Expansion) Systems
In some smaller or modular cleanroom setups, a DX system is used. Here, refrigerant is expanded directly in a coil inside the air handling unit. The coil can cool air below its dew point to condense moisture, and then reheating or bypass strategies bring air back up as needed.
DX systems simplify the plumbing and are more compact, but they can limit flexibility when loads fluctuate widely. Also, achieving very low dew points via DX may push equipment to its performance boundary.
Hybrid and Free Cooling Approaches
When ambient conditions are favorable, free cooling (or economizer cooling) can reduce reliance on mechanical refrigeration. In cooler seasons, external air or chilled water bypassing the chiller can help maintain lower dew points with lower energy.
In some district or campus settings, deep lake or deep water source cooling may assist or substitute part of the cooling load. (Though it’s less common in cleanroom use, it’s conceptually similar to “deep cooling” of water sources.)
Some advanced designs also employ desiccant or molecular dehumidification in parallel with cooling systems, allowing more flexibility in dew point control.
Regulatory, Technical, and Compliance Considerations
GMP, NAPRA, and Pharmaceutical Cleanrooms
Pharmaceutical and biotech cleanrooms must adhere to Good Manufacturing Practice (GMP) guidelines, which often demand strict control over temperature and humidity to avoid microbial proliferation, chemical degradation, or contamination. NAPRA (for pharmacy compounding in Canada) further imposes environmental controls on sterile compounding spaces. In many cases, humidity excursions constitute a deviation, so the HVAC must be validated to maintain dew point and RH within limits.
Temperature and humidity sensors must be qualified, calibrated, and validated to meet regulatory expectations. Deviations from setpoints require detection, alarm, logging, and investigation procedures.
ISO 14644 and Cleanroom Design Standards
ISO 14644 (notably Parts 1, 4, and 5) governs classification, design, and operational requirements of cleanrooms. The deep cooling and dew point control system must integrate seamlessly into the cleanroom envelope, airflow strategy, and pressure cascades.
Designers must ensure that airflow patterns do not cause cross-contamination or dead zones. Also, placement of sensors (for temperature, RH, dew point) should follow industry practice. The HVAC elements must not compromise laminar (or unidirectional) flow, differential pressures, or airflow uniformity.
Energy, Maintenance, and Validation Trade-offs
Deep cooling plus reheat is energy intensive: you cool excessively, then heat back up. Designers must balance energy cost with control precision. In certain designs, two cooling coils or bypass schemes reduce energy penalties.
Operational maintenance is critical. Condensate drains must be secure, clean, and monitored. Cooling coils must resist fouling and microbial growth. Controls must be reliable, redundant, and integrated into BMS systems.
Validation and periodic requalification of HVAC performance (temperature, humidity, deviation alarms) must align with GMP and ISO procedures. Controls should log dew point, RH, temperature continuously.
Best Practices in Deep Cooling Design
- Decouple latent and sensible loads: Use separate coils or stages so that humidity constraints don’t force overcooling of the space.
- Locate sensors wisely: Dew point, temperature, and RH sensors should be placed in return or mixed-air streams, not too close to coils or reheat zones.
- Use control logic that prioritizes humidity need: In many cases, humidity control (dew point) trumps temperature control.
- Consider partial bypass or modulation: To reduce energy penalty, include bypass dampers or modulated cooling to avoid excessive reheating.
- Plan for validation and redundancy: Include spare sensors, alarms, actuators, and calibration strategies.
- Integrate into airflow design: Avoid interference with laminar flow, recirculation loops, and pressure cascades.
Conclusion
Deep cooling is a powerful tool in the HVAC designer’s arsenal when managing dew point in cleanrooms. Its correct application ensures both thermal comfort and moisture control, which is essential for sensitive processes in pharma, biotech, and microelectronics. Yet the energy cost, control complexity, and regulatory demands require careful planning and execution.
At Cleanroom Catalyst, we specialize in EPC (Engineering, Procurement, Construction) services for critical environments. We design and deliver cleanroom HVAC systems tailored to GMP, ISO 14644, and NAPRA requirements. If you’re planning a new build or retrofit, let us help you integrate robust, validated deep cooling and dew point control systems that meet your process needs and regulatory mandates.
Contact us today to discuss how Cleanroom Catalyst can design your next cleanroom with optimized deep cooling and humidity control.