[RFI] Weather related RFI - New Heat Pump Comments

Steve Dyer w1srd at yahoo.com
Tue Sep 24 12:17:20 EDT 2013

One additional comment on air source heat pumps. I just had a Bryant 
Evolution Extreme (same as Carrier Infinity) installed which has a VFD 
compressor. I was concerned about RFI of course. They offer an RFI kit 
that goes between the unit and the A/C line which I had installed as 
part of the deal.

The installer was a home energy performance guy, not your typical slam 
and run HVAC dealer, so he was interested enough to take the time and do 
some testing with me. His grandfather was a ham :-).
Even without the RFI kit, I did not hear any noise from the unit but we 
installed it anyway since he got the distributor to throw it in. None of 
the ECM fan motors make any noise either. Overall a great unit RFI wise 
and performance wise. It's amazingly quiet in the audible range too.

A couple additional "just in case" measures during install:
1. Pulled shielded, twisted pair control cable between the T-stat, air 
handler and outside unit. These new systems are "communicating" and only 
use two wires and a proprietary serial protocol. I can dig up the Belden 
part number if anyone is interested.
2. Put all electrical in metal conduit.

Reduced our cooling bill to ~$100/month during 2 of the hottest months 
on record in the foothills of the Sierra.

No, I don't work for Carrier/Bryant. Just very impressed with this 
technology. Not your fathers HVAC. Do find a dealer that understands 
these systems. We had some teething pains as I was the first install in 
this area, but it all got done right in the end.


> This is just a total shot in the dark but do they have an air source
> heat pump which was installed within the last few years?  Sometimes
> these are called ductless AC units.  The newer models use PWM to drive
> the compressor.  The variable speed drive which PWM allows makes the
> units much more efficient (they can run more or less continuously
> instead of all on or all off) but PWM is, of course, full of
> harmonics.  The unit I had recently installed is below the noise floor
> at my antennas but I can see poorly filtered models being a real
> problem for radio amateurs.  If they had an air source heat pump
> installed, you should see the compressor on the exterior of the house.
>   It will look something like this:
> https://www.goductless.com/hvac/images/mitsubishi/PC19508-d.jpg
> If you live in a climate where you get more than a few inches of snow
> in one storm, the compressor will likely be wall hung 4'-8' off the
> ground.  Otherwise, it will be on a plastic or concrete pad.
> Again, just a shot in the dark.  Seems like a possibility considering
> it's more or less continuous during cold weather.
> -Jeff
> On Mon, Sep 23, 2013 at 9:58 AM, Gary Tuck <gtuck at mac.com> wrote:
>> Last winter I had almost steady RFI most every day, most hours of the day.  It seemed to begin when new neighbors moved in next door.  As the weather warmed in the spring, the RFI disappeared.  Then the neighbors moved and I had hope they took the noise source with them.  They are gone but the weather cooled yesterday and the noise is back.  The house is vacant.   So, now I have to get serious.  The only sources I've had in the past are power line noise and defective lights.  I've tried turning off every circuit in the house last winter and I'm convinced it isn't within our home.  It's steady, raspy but not sputtering. I was assuming that it is a portable heater of some kind but what common sources are there related to cold weather?  What might I be looking for?
>> Thank you!
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