BlueSeal air curtains cut infiltration rate by 90% in 13.6 metre semi-trailer

When the doors of a refrigerated vehicle are opened during deliveries, refrigerated air escapes and warm, humid outside air enters the cargo space. The problem becomes compounded over multiple stops, which is especially prevalent in last-mile delivery and urban distribution. BlueSeal air curtains have helped solve this problem for thousands of temperature-controlled vehicle operators worldwide.

According to research by CENEX UK, the air infiltration through open doors accounts for about 70% of a refrigeration unit’s total thermal load. As doors open, heavy cold air cascades out of the bottom of the doorway like a waterfall, and warm and humid air rushes in through the top of the doorway.

 In collaboration with a French semi-trailer manufacturer, we tested how effectively BlueSeal manages this exchange and the time it takes for this process to occur once a door has opened.

 The results delivered an impressive 90% reduction in infiltration rate in a 13.6 metre semi-trailer.

 

The test method: using CO₂ as an accurate tracer

Because the walls of the vehicle and the cargo it’s transporting have significant thermal mass and influence on the measurable air temperature, we used carbon dioxide (CO₂) as a tracer gas to directly and objectively capture the true dynamics of air exchange.

The cargo space of a refrigerated trailer was injected with CO₂ to an initial concentration of approximately 5000 ppm, which served as the 100% baseline, with the gas spreading homogeneously throughout the cargo space. At time t = 0, the rear doors were fully opened and the decay of the concentration was recorded every 15 seconds for over 13 minutes.

Testing was conducted inside a production hall at 23°C to eliminate external wind interference and establish a clean, controlled baseline of pure thermal buoyancy exchange. The test compared two distinct setups:

1. Chilled (+3 °C) without BlueSeal (open doorway, unprotected)
2. Chilled (+3 °C) with BlueSeal air curtain (open doorway, protected by BlueSeal)

 

The results: free fall versus controlled retention

As we can see, there is a strikingly large difference between an unprotected doorway and one fitted with a BlueSeal air curtain.

• Without BlueSeal (+3 °C): Empty within two minutes
  Without a barrier, conditioned air plummets immediately. Half of the conditioned air is lost in just 40 seconds (t50% = 0.67 minutes). After 1 minute, only 24.2% remains, and after 2 minutes, 94.7% has been replaced by ambient outdoor air. Infiltration settles at a decay rate constant of k = 1.5 to 1.6 min-1 (over 90 Air Changes per Hour (ACH)).
• With BlueSeal (+3 °C): Up to 90% reduction in air infiltration
  With the BlueSeal air curtain running, air loss slows to a crawl: infiltration drops to a stable rate constant of k = 0.15 to 0.16 min-1 (only about 9 Air Changes per Hour (ACH)), representing a 90% cut in peak infiltration rate. After 1 minute, 86.0% of the conditioned air is preserved; after 2 minutes, 75.6% remains; and after 5 minutes, nearly half is still retained. The half-life is extended from 40 seconds to 4.40 minutes – a 6.6-fold increase in retention time.

 

How vehicle size affects infiltration rates

While this test was conducted on a 13.6-metre semi-trailer, the risk of rapid temperature loss is even higher in rigid trucks and delivery vans. This is due to the door-to-volume ratio: the rate of incoming warm air depends on the doorway dimensions (predominantly on the height) and temperature difference, not on vehicle length. A shorter vehicle has nearly the same door opening, but a fraction of the internal air cushion to dilute the incoming draft.

 

Rigid trucks: Double the exchange rate

A rigid truck has a rear doorway nearly as large as a semi-trailer, but only 40% to 50% of the cargo volume. Because the incoming draft flushes a much smaller space, the Air Changes per Hour (ACH) are approximately twice as high. Without a BlueSeal air curtain, a rigid truck loses half of its conditioned air in just 20 seconds, and completely flushes its interior within a minute.

Delivery vans (LCVs): Up to 2.5 times faster air loss

While a delivery van has a smaller door opening (admitting roughly 25% to 30% of a trailer’s influx), its cargo volume is disproportionately smaller, typically only 10% to 14% of a trailer. Consequently, air turnover can be up to 2.5 times higher than in a semi-trailer. Without protection, a delivery van loses half its cold air in 12 to 15 seconds, and virtually all conditioned air within 45 seconds.

Given that a typical urban delivery stop lasts between 1 and 3 minutes, an unprotected vehicle faces complete air turnover on nearly every stop. Extending thermal retention beyond this operational window is therefore essential to preserving cold-chain integrity and preventing continuous refrigeration overload. 

 

What this means in practice

 For transport operators and fleet managers, these results demonstrate a clear operational advantage to installing BlueSeal in their vehicles.

• Strict temperature control (GDP & HACCP)
  Every door opening puts cargo temperatures at risk. BlueSeal drastically restricts the volume of warm ambient air entering the cargo space, regardless of stop frequency. By dampening thermal fluctuations inside the vehicle, it protects perishable goods from cumulative warming and ensures strict regulatory compliance from departure to final delivery
  

• Reduced refrigeration load and energy savings
  Because the cooling unit of the vehicle (TRU) no longer has to continuously recover a full cargo space of warm, humid ambient air, less energy is required to achieve this. This means that your TRU consumes less fuel (or draws less battery power in electric vehicles) and the lifespan of your TRU is extended through a reduction in mechanical wear. To explore the broader impact on energy efficiency, read how the Centre for Sustainable Energy Use in Food Chains (Brunel University) measured a 30% reduction in cooling energy for small delivery vehicles and modeled savings of up to 45% in an 18-tonne truck. 

• Minimised evaporator icing
  A byproduct of outside air entering the cargo space is the significant amount of moisture it carries in. By reducing this infiltration by up to 90%, ice build up on the evaporator coil is drastically curtailed, resulting in fewer necessary defrost cycles and sustained cooling performance.

The impact that BlueSeal air curtains have on the ability of a temperature-controlled vehicle to maintain product temperature cannot be overstated. By dramatically reducing infiltration, goods are considerably better preserved over multiple delivery stops and the energy required for a vehicle to recover cargo temperature is dramatically reduced.

And in addition to its ability to protect cargo from temperature fluctuation, BlueSeal manages to achieve this in a way that is far more convenient for drivers making deliveries, by offering an invisible and effective barrier for them to enter and exit the cargo space without obstruction.

While these controlled test-hall results provide a benchmark of pure doorway exchange, real-world conditions on the road naturally introduce external factors like ambient crosswinds. Even with these environmental variables, fleet operators consistently see the vast majority of their conditioned climate preserved drop after drop. So if you’re still on the fence about enhanced climate control in your vehicles, why not ask one of our customers how their operation has been improved since installing this technology?