One of the projects that I was requested to initiate at GeoSystems was to minimize excessive noise and vibration of their heat pump systems.
One of the points that most heat pump manufacturers don't like to discuss is noise and vibration in the winter months. While the technology is amazing, it does require the use of a scroll compressor to be used inside the home. This is the same type of compressor that is used in central air conditioners. One difference. The compressor is now inside the home and typically runs about 80 % of the time. Many customers had been complaining about this low frequency "hum" disrupting their home environments.
Noise is an abstract problem to pin down with most consumers. One person's noise may not bother another person in the least.
Study revealed that the compressor was a major contributor to the ambient noise and vibration issue. The compressor had two known noise sources. The first was the movement of compressed gas charges through the internal HVAC circuit. This was addressed with the use of less radical pipe bends.
The second noise source was insufficient damping of the compressor mounting feet. Reviewing the foot design, I noted that the design had been used with limited success for over 40 years. The feet also used neoprene as the vibration absorbing material . Neoprene, you know the same material in wet suits and was invented in the 1920's. It's ability to damp vibration is extremely limited.
Inspiration for an alternate damping material came from athletic shoes. I had been using an insole with a material called Sorbothane for many years with great success in preventing injury. Sorbothane is in a class of materials know as viscoelastic polymers. These materials convert vibration into mild heat. If it works in running shoes, why not Heat Pumps?
Several weeks and prototypes later, I was able to damp vibration from the compressor by a range of between 64 and 92 percent.
Now, if I could only beat a 12 minute mile . . . . . .