Ice Water Cooling Below 2°C

Plate heat exchangers, or PHEs, have become the standard solution for industrial process cooling. The reason is largely economic: they cool process water at comparatively low capital cost, in a compact footprint, and with a well-established supplier market. But once a process requires a water outlet temperature of 1°C or 0.5°C, it leaves that comfort zone. At that point, the PHE becomes a control-intensive risk technology, one that is costly when it fails. This is exactly where HTT AG comes in, with systems engineered for this temperature range from the ground up rather than retrofitted with safeguards.

The PHE is not a bad system. It's a system optimized for a specific temperature range, and it hits its design limits outside that range. Its popularity is owed mainly to price: at water outlet temperatures of 2 to 3°C, it delivers acceptable heat transfer coefficients at an acquisition cost that specialized systems in this segment cannot initially match. It also benefits from a well-developed service network and the availability of standardized spare parts.

For processes that can operate with a 2 to 3°C outlet temperature, the PHE is therefore an economically sound choice. The question is whether the solution that looks cheaper on paper is actually the more economical one over the full lifetime of the system, and whether that holds true once required process temperatures drop below the 2°C mark.

That statement sounds obvious. Its consequences for plant operation are not. When the required water outlet temperature drops to 1°C or 0.5°C, the refrigerant on the other side of the transfer plates inevitably has to run below 0°C. Localized ice formation on the plate surface is then not an edge case, it's a physical inevitability.

What does this mean in practice?

• A layer of ice on the heat transfer surface significantly lowers the overall heat transfer coefficient. The system loses efficiency without this being immediately apparent.
• Freezing water expands. The resulting mechanical stress puts a strain on the plate geometry and the gaskets.
• In a failure scenario, the plates crack. Refrigerant and process medium mix. The system becomes economically irreparable.

That's exactly why PHE manufacturer specifications mandate that water temperature on the plate side must never fall below 0.5°C. The design temperature is typically set at 1°C, and suction pressure control must operate with an accuracy of 0.25°C. That requires a complete control loop: temperature control, hot gas defrosting, flow control on the water side, control valves, pilot valves, solenoid valves, and additional shut-off valves, depending on capacity. On top of that come design, installation, wiring, and programming costs that never appear on any list price.

What was budgeted as a lean solution grows, over the course of engineering, into a system with complex control requirements. The cost advantage over a specialized technology melts away with every additional control component.

A direct price comparison between a PHE and the BUCOdelot falling film chiller usually stops at the purchase price, and there the PHE looks cheaper. The full cost accounting tells a different story.

Controls and investment. For a PHE including a complete control system, total costs break down as follows depending on cooling capacity:

In every one of these cases, the control system accounts for a significant share of the total cost, in some capacity classes almost as much as the evaporator itself. The BUCOdelot falling film chiller comes in demonstrably lower across every capacity class from 100 kW to 1,800 kW, because it essentially only needs shut-off valves on the suction line and liquid feed.

Pump power and operating costs. A PHE requires a water pump with more than 5 m of head. The BUCOdelot needs less than 2.5 m of head. That allows for significantly smaller pumps, lowers power consumption in continuous operation, and noticeably reduces system complexity. Then there's pressure drop on the water side: PHEs reach 0.5 to 1.0 bar, while the BUCOdelot reaches only about 0.3 bar.

Gaskets and their weak points. Gaskets for large PHE units cost around €7,500 and need to be replaced on a regular basis. What's less well known: rubber gaskets are sensitive to ozone, of the kind generated by electric motors and arc welding. Organic solvents, acids, heat, and UV radiation attack the material and cause it to crack. In production environments where these influences can't be fully ruled out, that's an inherent risk that rarely gets factored into the total cost picture during planning. The BUCOdelot operates without gaskets.

Maintenance. PHEs require regular cleaning. The BUCOdelot is an open, unpressurized system that's accessible from both sides at any time, with no pressure relief and no involved disassembly. The effort required for inspection and cleaning is significantly lower. Every unplanned inspection on a PHE means a production stoppage.

On request, HTT AG designs both options, the PHE with a complete protection system and the specialized alternative, and puts the numbers side by side. The decision belongs to the customer, not to whichever list price happens to be lower.

HTT AG develops heat transfer systems that are structurally designed for operation near the freezing point, rather than being retrofitted with controls for safety.

BUCOdelot Falling Film Chiller

The BUCOdelot was developed for water outlet temperatures ranging from 0.5 °C to 1 °C. The process water flows as a thin, uniform film over cooled stainless steel surfaces. A controlled thin layer of ice – which would jeopardize operation in a plate heat exchanger (PHE) – actually improves heat transfer here instead of blocking it. The system works with physics, not against it.

Here’s a comparison that clearly illustrates this: In BUCOdelot operation, an ice layer of about 6 mm forms. In conventional coil-in-tank systems, the ice thickness grows to 30 mm or more, which reduces the effective transfer area to one-fifth and continuously degrades the defrosting performance, especially with irregular return flow from the process side. With the BUCOdelot, the ice surface remains about five times larger and thus maintains consistent performance.

At the same time, the evaporation temperature is only −3 °C instead of −10 °C in the conventional ice bank process—a difference of 7 K that directly translates to lower energy costs over the entire operating period.

An important point to clarify: The heat transfer coefficient – the U-value – is comparable for PHE and BUCOdelot. Both systems deliver high heat transfer performance. The differences lie not in thermal quality, but in operating costs, control complexity, maintainability, and total cost. Those who choose the BUCOdelot do not sacrifice heat transfer performance to gain these advantages.

The system is made entirely of stainless steel, operates without pressure, is accessible from both sides at all times, and does not require disassembly for cleaning or inspection. The total refrigerant charge is only 25% of the amount in a comparable coil-in-tank system, which reduces costs, potential hazards, and operational risk.

Ice Bank / Ice Storage

The ice storage system stores cooling energy as ice and releases it as ice water at temperatures ranging from 0 to 1 °C during peak demand periods. This is the standard design specification, not an edge case. Typical applications: dough cooling in large bakeries, raw milk cooling in dairies, process cooling in the pharmaceutical industry, and peak load coverage in air conditioning systems.

An economic advantage that is often underestimated in direct comparison with the PHE: The ice storage system decouples refrigeration generation from cooling demand. The chiller charges the storage system during off-peak hours when electricity demand is lower and energy rates are more favorable. Peak loads are covered by the storage system without the need to oversize the chiller. In practice, this means: a smaller chiller, lower operating costs, and more stable process temperatures even with fluctuating load profiles.

Pillow Plate Heat Transfer Systems

Pillow plates are structured double plates with integrated refrigerant channels, installed as tank jackets, built-in ceilings, or suspended heat exchangers directly inside the tank. They precisely cool products and process media to temperatures near 0 °C without the risk of freezing that would require maintenance on a PHE in this temperature range.

At HTT AG, pillow plates are custom-designed to match the customer’s vessel geometry and process requirements. Size, wall thickness, refrigerant flow path, and pressure drop are calculated, not estimated. This enables temperature control that is significantly more precise than standardized PHE solutions, which is critical wherever tight temperature tolerances directly affect product quality and shelf life.

The need for process water temperatures below 2°C is not a niche concern. It affects a range of industries where product quality and process safety depend directly on cooling temperature.

Baked goods production: Dough heats up through friction during kneading. To preserve gluten structure and keep the yeast from activating prematurely, dough temperature has to be tightly controlled. That's only achievable with process water near 0°C.

Dairy and milk processing: After intake, raw milk must be cooled to below 4°C, and in some processes below 2°C, within a defined time window to prevent bacterial growth and ensure shelf life. Ice water cooling here isn't a premium feature, it's a process requirement. BUCOdelot systems have been in use on dairy farms and in processing plants for decades.

Fish and seafood processing: Fresh product spoils quickly. Cooling temperatures near 0°C are required by law or by quality standards at many process steps. Ice storage systems that continuously supply ice water at 0 to 1°C are well established in this industry. One relevant point: conventional coil-in-tank systems often use galvanized material, which is not permitted under European food-safety regulations. BUCOdelot systems are made entirely of stainless steel.

Pharmaceutical industry: Reaction cooling, crystallization processes, and temperature control for sensitive active ingredients require precise process water temperatures that a standard PHE cannot reliably deliver over the long term without substantial control overhead.

The technology decision doesn't start with a system comparison. It starts with a single question: what water outlet temperature does your process actually require?

If you need 3°C and a PHE already serves you well economically, an honest conversation with HTT AG will tell you exactly that. If you need 1°C or 0.5°C, you should run the full cost picture: capital cost plus control system plus gasket maintenance plus pump energy plus operating risk, over the system's full lifetime. A technology engineered for precisely this temperature range, one that delivers thermally equivalent performance at significantly lower effort, is the more economical and more reliable choice over the system's total operating life.

Tell us about your process requirements. We'll tell you which system offers the demonstrably better design for your temperature range.