Koja Oy is a family-owned company offering customers intelligent and energy efficient HVAC systems, air handling systems and industrial fan solutions. Labrys Oy presented the new InfiniSpring® solution to Koja Oy R&D Management. At the time Antti Häyrynen was planning a MSc thesis for a HVAC system fan unit. The HVAC system is shown in Figure 1 below.

Figure 1. Koja Oy heating, ventilating and air conditioning (HVAC) system.

Antti saw the potential in the InfiniSpring® integration and the new fan unit design was targeted to utilize InfiniSpring®-springs. Antti designated Miska Karttunen, an excellent candidate from Tampere University of Technology for the job.

MSc Thesis Main Targets

  • Designing new fan unit frame with integrated springs
  • Optimizing fan unit frame stiffness and mass
  • Minimizing structure borne noise (SBN) from fan unit
  • Ensuring the ease of fan unit manufacturing and assembly
  • Enabling easy maintenance for fan unit

New Fan Unit with Integrated Springs

The most important factor in vibration isolation is to ensure high vibration isolation performance. This means that structure borne noise (SBN) from the fan unit to surroundings is minimized by making the vibration isolation very soft. The high flexibility of InfiniSpring®-springs enables this.

In the project new side beams were designed utilizing the 4HS35 integrated InfiniSpring®-springs. The beam is shown below in Figure 2.

Figure 2. Koja Oy fan unit side beam with integrated 4HS35 InfiniSpring®.

The developed fan unit with integrated springs has flexible spring installation natural frequencies below 10 Hz. Vibration attenuation percentage is above 85 % in whole operating frequency range. Meaning that high vibration isolation efficiency is achieved as a result of this.

With soft InfiniSpring®-springs, the fan frame required structural modifications. Koja Oy made the modifications with the help of finite element analyses and the fan design was modified to optimize fan structural resonance modes (fan elastic body modes) above operational frequencies. This led to improved overall vibration performance of the fan.

Koja Oy Benefits 

With soft springs high vibration isolation performance is achieved. Soft springs eliminate noise and vibration issues as fan loads are not transmitted through the soft springs to surroundings. Spring integration enables simplification of fan frame and separate vibration isolation elements are avoided. Also, the support structures for the vibration isolation elements can be avoided making the design simpler.

Remember this while Designing

It is important to manage the structural resonance modes of the actual product. In this case the fan elastic body modes. Critical elastic body resonance modes are preferably designed outside of the operational frequency range. Today, with the help of finite element analyses, structural designs can be optimized for soft springs, structural resonances avoided and top level vibrational performance guaranteed safely already during the design phase.

Here is a video introducing available InfiniSpring®-spring sizes.


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