IQF tunnel sizing is one of the few cold-chain capex decisions where the right answer changes by half an order of magnitude depending on the product. A spiral sized for premium berries (1.5 MT/hr) is almost useless for shrimp processing (4 to 5 MT/hr). A tunnel sized for shrimp would be wasted on berries.
The wrong answer is expensive in both directions. Oversize the line and you burn capital that does not earn its return, plus electricity you do not need. Undersize it and you miss the harvest window, push product into less efficient pallet blast, and lose customers to operators who can process at the speed the customer ships.
Here is the practical framework we use.
Step one: pick the product window, not the average
Most operators size IQF lines off an average throughput. The right number is the peak window throughput. A line that runs at 2 MT/hr for ten months of the year and 6 MT/hr for two months has to be sized for the 6 MT/hr peak, or those two months hand business to a competitor.
For seasonal categories (berries, sweet corn, peas) the peak is the harvest window, which might be six to ten weeks. For protein categories (shrimp, finfish) the peak is set by upstream processing capacity, which is steadier. Either way, size to the peak, not the median.
Step two: tunnel format follows the product
Spiral freezers are the right answer for products with consistent particle size that need long dwell. Berries, peas, and small fruit work well on spirals. Throughput typically lands between 1.5 and 4.5 MT/hr per spiral.
Tunnel freezers are the right answer for products with variable particle size or longer particles. Shrimp, finfish, and certain vegetables work better on tunnels. Throughput per tunnel typically lands between 3 and 9 MT/hr depending on belt width and tunnel length.
We run an IQF tunnel at Mehsana configured for prepared meals and seasonal volume, with stainless wire mesh belt for fast SKU changeover.
Step three: build for the cleaning cycle, not just the freezing cycle
This one gets missed often enough that it deserves its own step. IQF lines run dirty fast. Belt cleaning, drum cleaning, chamber cleaning, and CIP washdown between SKUs add up to one to two hours per shift. If you size a line at 4 MT/hr but you can only run 6 hours of the 8-hour shift, your real throughput is 3 MT/hr.
A 9 MT/hr tunnel pulling 300 kW continuous needs a refrigeration plant that can hold setpoint while the tunnel is at full draw.
CIP washdown is the silent throughput killer. We spec quick-disconnect CIP on the IQF line so the changeover is 20 minutes, not 60. That decision adds about 8 percent to capex and recovers it within the first season.
Step four: refrigeration plant has to keep up
The IQF line is only as fast as the refrigeration plant feeding it. A 9 MT/hr tunnel pulling 300 kW continuous needs a refrigeration plant that can hold setpoint while the tunnel is at full draw. If the plant is already running 80% of capacity on the rest of the building, adding the tunnel will starve everything else.
Scope the plant capacity before scoping the tunnel size. We have seen operators install a tunnel that runs at 60% of rated throughput because the plant cannot keep up. The capex was wasted.
Step five: SKU change frequency drives belt material
If you are running one product all season (peas all summer) you can use a standard plastic modular belt. If you are running four different protein SKUs in a single shift, you need a belt material that washes down fast and dries fast, plus a belt geometry that does not trap product. Stainless wire mesh is more expensive than plastic modular, but it pays back in change-time savings on multi-SKU operations.
This is one of those decisions that looks small in the spec discussion and shows up as a 12% throughput delta on the operations floor.
Putting it together
A practical sizing exercise looks like this.
Identify the peak window throughput by product. Layer that against the planned SKU mix. Choose spiral or tunnel based on product geometry. Layer in cleaning cycle time and refrigeration plant capacity. Pick the belt material based on changeover frequency.
The number that drops out of that exercise is the right one. The number that drops out of "what did the last operator install" is usually 25 to 40 percent wrong.
A note on partnerships
IQF is one of the categories where an operator and a customer should sometimes share the capex. If a frozen brand wants outsourced IQF and the volume is steady enough to justify a tunnel, the right answer is sometimes a tolling arrangement with a tunnel built to the customer spec, financed jointly. The operator owns the asset and the operation. The customer gets dedicated capacity at a known cost per kilogram. We have one of those arrangements live at the Mehsana facility, and it has been the most stable customer relationship in the IQF book.