Bosch Heat Pump Electrical Noise

When my Bosch Bova 36 heat pump is ON, my X10 lights flicker badly. There are several postings on line that "My lights flicker when the Heat Pump is on". Some of these are with Bosch heat pumps with variable speed motors. Most of the lights are LED lights with various dimmers. I have a Bosch heat pump, and decided to investigate.

My dimmers are old crusty X10. In addition, when the heat pump is ON, X10 in the house pretty much does not work. At all. I get around this by putting all X10 on a single outlet.

Sure enough there is about 3 volts p-p of common mode and even more differential mode 20KHz noise on the line when the heat pump is on. The pattern of bursts repeats at 8.3mS, or 120Hz. This is the voltage on my Neutral, far from the heat pump and Electrical distribution,  when the heat pump is ON.  Don't need a fancy spectrum analyzer to measure this one. Ideally this measurement would be made with a LISN (Line I,,, Network).



Turns out that technically, Bosch isn't doing anything wrong. The CISPR-11 limits for conducted emissions are below. The limits only apply  to frequencies of 150KHz and above. A product can put as much 20KHz crap on the lines as they want. Here is the CISPR-11 limits for conducted noise. Note that they don't go below 150KHz.


So what regulatory spec covers 20KHz crud on the line? None that I can find. Line Current Harmonics only cover odd harmonics up to the 39th harmonic of the 60Hz line frequency, or 2,340 Hz.

And line filters on products generally only affect higher frequencies. I looked at a 30A separate line filter and you can buy one filter that cuts 20KHz by about 20dB. 20db may be enough. I may install one of these. In addition to the $80 filter, it requires adding a box in series with the 240V line.

Conclusions

• Bosch BOVA variable speed heat pumps generate lots of 20KHz interference.
• This is most likely what interferes with LED bulbs, particularly with dimmers, causing flickering.
• X10 dimmers are particularly susceptible to this type of interference. 
  
• Other heat pumps with variable speed may have similar interference.
  
• A serious line filter (30A) may help. This is not trivial to wire into household wiring.
  
• Bosch heat pumps and X10 dimmers are a bad combination