TOPCon Workshops Require Both Heating and Cooling: Why Conventional HVAC Designs Cannot Simply Be Replicated

In the mass production of n-type TOPCon (tunnel oxide passivated contact) solar cells, photovoltaic manufacturing has entered an era of extreme competition defined by micrometer-scale structural control and incremental conversion-efficiency gains of 0.1 percentage points. When building or expanding TOPCon workshops, many cell manufacturers habitually adopt comfort-air-conditioning or standard central-HVAC schemes used in general industrial buildings, expecting one system to handle both workshop cooling and equipment heat rejection.

In actual production, however, this approach often creates a series of engineering risks. In summer, excessive workshop humidity can degrade screen-printing pastes; temperature drift in wet-cleaning baths can cause nonuniform etching; and in winter, residual heat from high-temperature diffusion and firing areas may not be removed effectively, causing frequent chiller overload alarms.

TOPCon cell production is far more complex than simply supplying cool air in summer and warm air in winter. Stable, high-yield continuous production requires a fundamental distinction between workshop environmental loads and process-cooling demand, followed by a temperature-control architecture matched to process-section characteristics and seasonal transitions.

I. Core Decoupling: Workshop Environmental Loads (HVAC) vs. Process Cooling Demand (PCW)

The central mistake in copying a conventional air-conditioning design is attempting to use a single system to address both indoor environmental conditions and precision heat removal from high-power equipment. In a TOPCon workshop, these two load categories have fundamentally different physical characteristics and control logic.

1. Workshop Environmental Loads (HVAC System)

The HVAC system primarily manages airflow distribution in the cleanroom, heat released by personnel, heat transfer through the building envelope, and makeup air required after large-volume exhaust. Its core objective is to maintain workshop temperature (for example, 22°C ± 1°C), relative humidity (for example, 45% ± 5%), and cleanliness within specified ranges, thereby preventing particle deposition and condensation in the workshop.

2. Process Cooling Demand (PCW System)

The process cooling water system primarily serves high-temperature equipment and chemical process baths on TOPCon production lines, including tube diffusion furnaces, PECVD systems, ALD (atomic layer deposition) equipment, laser-doping systems, and wet-cleaning equipment. The substantial heat generated by this equipment is not released directly into workshop air; it must be removed through direct heat exchange in internal equipment heat exchangers using high-precision process cooling water.

If these functions are confused and workshop recirculation airflow is increased in an attempt to cool diffusion furnaces or PECVD equipment, the result is not only excessive fan energy consumption but also disruption of cleanroom positive pressure and airflow organization, creating serious quality risks and energy waste.

II. Multiple Variables: Effects of Process Sections, Temperature and Humidity, and Seasonal Change

TOPCon workshops impose demanding requirements on temperature-control systems because they integrate complex chemical, thermal, and optical processes and are strongly affected by outdoor conditions and exhaust-air volumes.

1. Differentiated Temperature-Control Requirements Across Process Sections

Wet texturing and cleaning: These sections require temperature control of large volumes of acid and alkaline process solutions. Even a small bath-temperature fluctuation of 0.5°C can directly alter chemical reaction rates and produce nonuniform pyramid-texture morphology on silicon wafers. The section therefore requires rapid thermal response while also accommodating the substantial sensible and latent loads removed by corrosive exhaust systems.

High-temperature diffusion and PECVD/ALD: These are typical high-heat-load, continuous-operation applications. Furnace bodies and high-frequency power supplies generate sustained, substantial heat, requiring the process chilled-water system to maintain very high stability during 24-hour continuous operation, without cooling-water temperature drift or interruption.

Screen printing: This process is highly sensitive to ambient relative humidity (RH). The viscosity of electrode materials such as silver paste can vary significantly with humidity. If workshop humidity is too high, the paste may absorb moisture, leading to screen-mesh blockage or line-width deviation and directly reducing cell conversion efficiency.

2. Seasonal Conflict Between High Exhaust Rates and Makeup-Air Heat and Moisture Treatment

Because wet-process and chemical-use areas in TOPCon workshops require extensive corrosive exhaust, large volumes of outdoor makeup air must be introduced through makeup air units (MAUs). This creates pronounced seasonal load variations:

Hot and humid summer conditions: Outdoor makeup air has a high moisture content, so MAUs require substantial cooling capacity for deep dehumidification and cooling. The cooling-source system must therefore handle simultaneous peaks in sensible and latent loads.

Cold and dry winter conditions: Although outdoor air is cold, high-temperature process equipment inside the workshop continues to release large quantities of heat. Outdoor makeup air must be heated and humidified, while the process cooling water system (PCW) still operates at full cooling duty. The facility therefore experiences the complex condition of a cold exterior, a hot interior, and simultaneous heating and cooling demand.

III. A Practical Path Forward: Cascaded Cooling and Free Cooling

To address the complex requirements of TOPCon workshops, modern photovoltaic temperature-control architectures are evolving toward staged supply, precise temperature control, and dynamic energy optimization:

Cascaded water supply and temperature-zone separation: PCW supply-temperature requirements vary by equipment. Laser equipment and high-precision sensors, for example, may require high-accuracy chilled water at 18°C to 20°C, whereas PECVD equipment and the external surfaces of diffusion furnaces can use medium-temperature water at 22°C to 25°C. Cascaded cooling with separate temperature zones avoids wasting high-grade cooling capacity by supplying unnecessarily cold water to medium-temperature equipment.

Reducing energy consumption through free cooling: Because TOPCon workshops require process cooling throughout the year, lower outdoor temperatures during transitional seasons and winter can be used to produce process water through plate heat exchangers in free-cooling mode. This allows chiller compressors to shut down partially or completely and can significantly reduce manufacturing cost per watt of cell output.

IV. Industrial Temperature-Control Implementation: KAYDELI Photovoltaic-Specific Equipment and Customized PCW Solutions

In the construction and retrofit of temperature-control systems for TOPCon cell workshops, standard general-purpose chillers often cannot accommodate the combined requirements of wet-process bath temperature control, high-load PECVD heat rejection, and high-precision cooling water for laser equipment. To address these industry challenges, KAYDELI provides customized cascaded PCW supply and multi-loop constant-temperature solutions designed around TOPCon processes.

For project implementation, KAYDELI develops application-specific models based on the actual heat-load characteristics and piping-network topology of each TOPCon process section. Separate water distribution is configured for the different heat-rejection requirements of PECVD equipment, diffusion furnaces, wet-cleaning baths, and other systems, with high-head variable-frequency pump sets and high-accuracy temperature-control modules matched accordingly. This approach helps prevent localized overheating caused by hydraulic imbalance and enables flexible switching to free-cooling mode during seasonal transitions, supporting low-energy operation while maintaining high cell yield.

Heating, cooling, temperature, and humidity control in a TOPCon workshop cannot be solved by simply adding conventional comfort-air-conditioning systems. Only by fully decoupling workshop HVAC from process-equipment PCW, and by applying cascaded cooling and precise temperature control according to the physical characteristics of wet processing, diffusion, screen printing, and other sections, can stable mass production of high-efficiency cells be supported.