Ventilation and noise in quick-freezing workshops are two items that tend to be pushed to the end during equipment selection and are prone to rework after production begins. Ventilation relates to safety and workshop environment; noise relates to working conditions and compliance. Both are determined at the layout stage, so they must be reviewed together with equipment layout.
Ventilation Must Do Two Things
First, remove the low-temperature nitrogen gas produced during the quick-freezing process. After liquid nitrogen vaporizes, its volume expands greatly. If not exhausted, it will accumulate in work areas and low-lying places, diluting oxygen. This is a safety requirement. For concentration monitoring and interlock practices, see Exhaust and Oxygen Concentration Monitoring for Liquid Nitrogen Quick-Freezing Cabinets.
Second, maintain workshop temperature, humidity, and airflow organization. The equipment itself is a cold source, and the surrounding air will be cooled. Combined with moisture in food workshops, condensation easily forms on equipment and floors. Ventilation must carry away moisture and form a stable airflow direction around the equipment.
How to Estimate Exhaust Air Volume
Exhaust air volume is not given empirically based on workshop volume, but calculated from nitrogen generation:
- Based on liquid nitrogen consumption per batch (or per unit time), calculate the mass of nitrogen after vaporization;
- Convert to volumetric flow using local atmospheric pressure (volume is larger at high altitudes);
- Size the exhaust air volume according to the peak nitrogen generation flow rate, and leave margin;
- Check whether overall ventilation is sufficient based on workshop air changes per hour.
| Input | Source |
|---|---|
| Liquid nitrogen consumption per batch / per unit time | Equipment gas consumption parameters and production takt time |
| Nitrogen volume after vaporization | Converted by mass and local atmospheric pressure |
| Allowable oxygen concentration in work area | According to safety regulations |
| Workshop volume and air changes per hour | Building conditions |
At high altitudes, air density is lower and air exchange efficiency decreases, so exhaust must leave a larger margin. For related relationships, see Effects of Altitude and Atmospheric Pressure on Liquid Nitrogen Quick Freezing.
Airflow Organization and Inlet/Outlet Layout
| Principle | Practice |
|---|---|
| Inlet and exhaust form a flow direction | Air inlets on the relatively clean, low-temperature side of the workshop; exhaust outlets near above equipment and nitrogen accumulation zones |
| Avoid short-circuiting | Inlets and outlets should not face each other directly, avoiding fresh air short-circuiting straight to exhaust |
| Treatment of low-lying areas | Nitrogen is heavier than air; install exhaust or concentration monitoring points in low-lying areas |
| Separate from equipment exhaust | Workshop general ventilation and equipment local exhaust should be designed separately to avoid competing for air volume |
| Door openings and passages | Reduce open ports along convection paths, or add air curtains to reduce cold air spillage and moisture ingress |
Tunnel production lines have tail gas extraction ports at the inlet and outlet ends to reduce cold air escaping from both ends. For structure and air volume parameters, see Liquid Nitrogen Quick-Freezing Tunnel.
Noise Sources and Reduction
Noise from quick-freezing equipment mainly comes from three places:
| Noise Source | Characteristics | Noise Reduction Direction |
|---|---|---|
| Fans | Continuous noise, related to rotational speed | Select low-noise models, add vibration damping, duct silencing |
| Refrigeration units (if auxiliary refrigeration is present) | Compressors and condenser fans | Unit vibration damping, acoustic enclosures, keep away from work areas |
| Valves and airflow | Airflow noise during liquid supply and release | Layout optimization, add silencing or sound insulation |
The basic approach to noise reduction is three layers: “source—transmission—receiver”:
- Source: Select low-noise equipment, install vibration damping pads and flexible connections to reduce vibration transmission;
- Transmission: Add sound insulation or silencing to units and ducts, use vibration-isolated supports for piping;
- Receiver: Reasonable layout, keep noise sources away from work stations and office areas; add acoustic screens when necessary.
Workshop overall noise limits are implemented according to the occupational health regulations of the project location. Target values are confirmed with the customer during the proposal stage.
Why Ventilation and Noise Must Be Reviewed Together
Two reasons:
- Fans are both ventilation components and noise sources. Increasing exhaust air volume simultaneously increases fan power and noise. The two must be weighed in the same table, not adjusted separately;
- Layout is a shared constraint. Unit positions, duct routing, and sound insulation measures all affect layout. Settling them all at once is easier than revising twice.
If equipment layout, ventilation, and noise are handled separately, rework often occurs such as “the fan is installed but noise exceeds limits” or “the acoustic enclosure is installed but exhaust is insufficient.”
Common Questions
Can workshop ventilation rely only on natural ventilation?
Not recommended. Nitrogen generated by liquid nitrogen vaporization requires a reliable, continuous exhaust path. Natural ventilation is greatly affected by weather and building conditions, and is high-risk as a primary means. Mechanical exhaust is recommended as the primary method, with natural ventilation as auxiliary.
What margin should be left for exhaust air volume?
It is recommended to leave margin on top of the value calculated from peak nitrogen flow rate. The specific coefficient is determined based on workshop volume, altitude, and equipment operating conditions. For high altitudes and multiple units in the same room, the margin should be larger.
Where should noise exceedance generally be addressed first?
Look first at the source and vibration transmission: vibration damping pads, flexible connections, and fan selection are often cost-effective fixes; acoustic enclosures and silencers come next. The specific plan depends on measured noise values and dominant frequency bands.
Who issues the drawings for ventilation and noise?
Equipment interface parameters (gas consumption, equipment exhaust requirements, noise levels) are provided by the equipment supplier; workshop general ventilation and noise reduction engineering is generally the responsibility of the customer or HVAC designer. Both parties align on interfaces during the layout stage. For related division of responsibilities, see the interface table approach in Key Points for Liquid Nitrogen Storage Tank and Cryogenic Piping Design.
For workshop ventilation and noise conditions, you can send the equipment model, number of units, workshop dimensions, and location. We provide equipment-side exhaust requirements and noise parameters for HVAC design reference: Contact Kunning Cryo
The ventilation and noise reduction practices in this article are general industry engineering practices. Specific implementation follows project requirements and local regulations; equipment-side exhaust and noise parameters are cited from Kunning Cryo liquid nitrogen quick-freezing equipment technical documents. Each model is subject to its corresponding technical parameters.