Transport Refrigeration Units (TRUs), otherwise known as “Reefers”, have received great attention for some time recently in their ability to be operated solely on liquid nitrogen (LN2). European companies have been using this technology for some time now and early this year a US western cryogenic facility has successfully completed a long-haul frozen food transport test by a retrofitted 53’ insulated trailer using a LN2 reefer.
If anyone has had experience with reefers they could tell you how loud they are, how filthy they can be, and how difficult their maintenance up-keep can become. Take away the extra weight and material handling of the entire diesel engine system including fuel tanks, engine assembly, filters, exhaust, alternator, belts, fans; the TRU engine components list goes on and on. Then remove the entire refrigerant system; the A/C compressor, condenser, switches, solenoids, high and low pressure systems, etc. All maintenance components that need to be checked and maintained periodically to make sure a driver’s load won’t be lost. Replace the system with two LN2 tanks, two safety valves, a heat exchanger, four fans, two batteries, and a solar panel, what do you get? A completely zero emission, silent, fully -50 degree capable running 53’ refrigerated trailer.
Liquid Nitrogen reefers can be used in two ways: Closed System and Open System.
In a closed LN2 system, like refrigerant, it is electronically controlled by pressure through a heat exchanger with an electric fan blowing the cold air through it and into the cargo area. Return fans circulate the air inside the cargo area and the LN2 system to regulate what temperature is desired inside the van. As LN2 is used, its pressure increases and after the pressure reaches its expansion limits the LN2 is released by a valve at top of the system releasing it into the air as non-harmful nitrogen gas. This system is patented and approved for use in the US by Federal regulations.
In an open LN2 system (European use), great safety precautions are used as LN2 is released into the cargo area of an insulated van by a controlled temperature electronic device. A safety net or gate is locked and unlocked to prevent a person from entering the area before the LN2 is released into the atmosphere as that would cause harmful effects to a person’s well-being. This system, so far, is forbidden for use in the US for on-road transportation services.
The challenge for a system like this is that no driver can pull up to a fuel station and fill up their reefer with some liquid nitrogen. It is only sold and distributed by licensed retailers and consumer distribution centers. For a carrier to gain fully efficient TRUs the fleet has to be less-than-truckload and have a fully capable LN2 reservoir tank on its yard for refilling every 24 hours. With no noise, the units can run constantly abiding by city limit laws. The solar panels supply constant power to the unit and the battery supply back-up power for night applications. For every one gallon of diesel fuel burned, one hour of cooling capabilities is achieved in a traditional reefer. For every ten gallons of LN2 used, one hour of cooling capabilities is achieved in a LN2 reefer. But ten gallons of LN2 still costs 10% less than one gallon of today’s diesel fuel price and overall with maintenance, procurement, and operational costs it saves over 20% annually to a carrier’s bottom line.
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