From Feasibility to Market-Ready: Designing a Robust Controller for 12 kW Water Heating

When it comes to high-power heating systems, achieving accuracy, safety, and cost-efficiency simultaneously is no small feat. We were approached by a leading heating systems manufacturer looking to move beyond the limitations of off-the-shelf solutions.

For years, the client had been integrating a commercial temperature control module into their products. While functional, the module was expensive and lacked the flexibility needed for their evolving product line. Developing an in-house solution seemed like a logical step – but their internal R&D team didn’t have the bandwidth, or the specific expertise required for such a complex solution. That’s where we came in.

Our task was to develop a temperature controller for a 12 kW three-phase instantaneous water heater – an advanced system that demanded both accurate thermal control and robust safety features.

We began with a thorough feasibility study, analyzing both technical and economic viability. The main question was: Would developing a custom controller offer a return on investment, given the client’s production volume?

Our study addressed:

  • Development costs vs. long-term savings on unit price
  • Projected production volumes
  • Unit price in production and total development costs
  • Technical complexity and development risks

Engineering the Core

We designed a temperature controller for a 12 kW three-phase instantaneous water heater, based on a Cortex-M0+ microcontroller. The system provides accurate water temperature control using a PT100 external probe, with built-in overtemperature protection through internal sensors.

A refined PID control algorithm ensures stable thermal performance. The heaters operate using 2-leg switching in a delta configuration, managed through TRIACs and zero-cross detection for efficient and reliable AC switching.

Built for Safety, Designed for Usability 

Safety and usability were key drivers in the design. The device includes:

    • Zero-Cross Detection: Opto-isolated AC inputs for reliable phase detection and reduced switching noise.
    • Multi-Level Safety Architecture:
      • Internal temperature monitoring
      • Load disconnect relay
      • Alarm relay output
      • External flow switch input
      • Bimetal sensor for additional safety cut-off
    • User Interface:
      • Seven-segment display
      • Seven-segment display

Meeting Real-World Challenges

One of the major engineering challenges was environmental: the controller needed to operate reliably in a closed cabinet exposed to high ambient temperatures. To address this, we implemented an active cooling system and optimized the heater switching behavior to reduce internal heat buildup.

These measures, combined with thermal safeguards and carefully managed power cycling, ensured long-term reliability – even in demanding operating conditions.

In the summary our team did the following:

    • Feasibility study
    • Hardware design (Concept, schematics, PCB)
    • Firmware development
    • Mechanical design (selecting and customizing COTS enclosure)
    • Supplier evaluation, component sourcing
    • Prototype assembly
    • Prototype testing and verification
    • Environmental tests in the climate chamber
    • Field testing support

From cost-efficiency analysis to system optimization, this project showcased how expertise can transform a technical concept into a reliable, market-ready solution. It wasn’t just about building a controller – it was about empowering our client to gain ownership of their technology and take control of their product roadmap while reducing costs and increasing flexibility.

Need Expert Support for Your Next Project?

We’ve got the expertise to back you up. Whether you’re exploring custom embedded solutions for heating systems or other industrial applications, we’d be glad to help deliver high-quality, tailored solution.

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