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eHam Forums => RFI / EMI => Topic started by: N3WXI on July 05, 2018, 08:29:35 AM



Title: New furnace RFI?
Post by: N3WXI on July 05, 2018, 08:29:35 AM
I am looking to install a new high efficiency furnace and air conditioner in my home and am concerned about RFI.  I am looking at the Trane S9X2 furnace and XR16 air conditioning unit.  This is NOT the infamous XV90 discussed at great length in these forums.  Another unit originally considered was a Bryant model 926T but it is a variable speed unit and that seems to contribute to the RFI problem.  Bryant does not make a unit that is not variable speed.  I had four companies out to give me estimates and asked each of them about RFI and all I got was a slack jawed stare from each of them.  I would like to respectfully ask on this forum if anyone has installed this Trane unit and if so what was your experience Re: RFI.  I'm thinking that even if there IS RFI from this unit their experience with the XV90, which now has a fix, could make fixing this one easier.

Thanks in advance for your help,
George


Title: RE: New furnace RFI?
Post by: KD0REQ on July 05, 2018, 11:22:55 AM
nope, but have the contractors bid their furnaces with the OEM suppression kit included. this ought to weed out the guys who just knock tin off your list.


Title: RE: New furnace RFI?
Post by: NK7Z on July 05, 2018, 01:33:25 PM
Borrow a FT-817ND and ask to visit a working install!  I also have a set of RFI snapshots done using SDR at:

https://www.nk7z.net/rfi-snapshots/

A variable speed motor is normally a lot RFI louder than a fixed speed motor...  I had them remove the variable speed motor, and replace it with a fixed speed motor.  I have no RFI.


Title: RE: New furnace RFI?
Post by: AA4PB on July 05, 2018, 02:16:23 PM
I had a new Trane heat pump installed last year. It has an outdoor unit with a single speed compressor (similar to the XR16). The blower fan in the indoor unit has a variable speed fan. It's hard to find a modern unit that doesn't have a variable speed fan. Anyway, I don't have any RFI issues with it - BUT - my antenna is located 100-feet from the house with all feed lines underground.

My Son had the same unit installed in his house the year before so I went over there with a hand-held Icom HF receiver to check out the noise before I purchased one. I didn't find any noise on any HF band unless I placed the receiver within about a foot of the unit. I was very concerned about the digital control system (a bunch of PC boards with flashing LEDs and all), but didn't find a problem.

The variable speed fan is kind if nice because it starts slow and gradually comes up to speed, unlike my old one which used to make noise each time it started.




Title: RE: New furnace RFI?
Post by: SOFAR on July 05, 2018, 02:27:39 PM
Furnaces have used multi-speed blower motors for decades. Medium range speed for heat, higher speed for A/C.


Title: RE: New furnace RFI?
Post by: N3WXI on July 05, 2018, 03:12:16 PM
Thanks for the reply's.  I'm aware that the main blower is multispeed, higher speed to move the denser cold air from the A/C, but my research tells me that the variable speed advertised is problematic as far as RFI is concerned, i.e. the furnaces with variable speed seem to be more likely to have RFI.  I don't know what this has to do  with the blower motor since it is the inducer motor that is the culprit.


Title: RE: New furnace RFI?
Post by: AA4PB on July 05, 2018, 04:24:04 PM
Furnaces have used multi-speed blower motors for decades. Medium range speed for heat, higher speed for A/C.

That's true but they were two speed motors that had taps on the windings. It was either high speed or low speed depending on which wires you applied the voltage to. The new systems have "variable speed" which is continuously variable and uses an electronic control circuit to send current pulses to the motor. That's what causes the RFI.

Some units now also have a "variable speed" compressor. The old way was to turn the compressor on until the desired temp. was reached and then turn it off. The new way is to run the compressor all the time and adjust it's speed to supply just the amount of heat or cooling needed to maintain the desired temperature. The result is better efficiency and a steady temperature.


Title: RE: New furnace RFI?
Post by: N3WXI on July 08, 2018, 10:47:54 AM
Agreed.  Actually in the variable speed furnaces the main blower runs all the time.  When the thermostat is not calling for heat or cooling the blower runs at a very low speed, this accomplishes two things.  Ordinarily as a house cools in the winter it cools more quickly in certain areas like around windows and doors.  The circulating air tends to eliminate this effect keeping the house more comfortable.  Second the home's air is constantly circulated through the air filter keeping the air cleaner.  Or so they say.  I don't know what all this has to do with RFI however as we know from the XV90 episode that the RFI comes from the inducer motor (actually it's drive circuits) and that motor only runs when the burner is running, at least I think so.  I'm thinking I should call one of the companies I got an estimate from and clarify some of this.   I'm just hoping that the RFI has been fixed in this later generation of Trane funace (S9X2) and air conditioning (XR16).


Title: RE: New furnace RFI?
Post by: K7JQ on July 08, 2018, 12:59:47 PM
I just had two Lennox Merit series HVAC systems installed here in "hot" Arizona. I specified no two-stage compressor, and no variable speed blower motor. They do a wonderful job, and no trace of RFI from either unit. You get some great perks/discounts if you buy it through a kiosk in Costco.


Title: RE: New furnace RFI?
Post by: K7JQ on July 08, 2018, 01:06:41 PM
Forgot to mention...they are 16 SEER systems. You mentioned wanting to buy a high efficiency system. Probably the more expensive 20+ SEER units will all have two-stage compressors and variable speed motors. Comes with the territory. 16 SEER will still give you beneficial energy savings.


Title: RE: New furnace RFI?
Post by: N3WXI on July 08, 2018, 08:45:04 PM
Ok.  I'm looking specifically at a Trane S9X2 two stage non variable speed furnace (S9V2 would be variable speed) and a XR16 single stage 16 SEER A/C.  I was hoping that someone reading this forum would have some experience with that model but so far no luck although the responses so far have been encouraging.  One of the factors in favor of Trane, I think, is the mess that was their model XV90 in the early 2000s.  They eventually found a fix for the RFI and if the newer units do have issues they should be able to fix it easier.


Title: RE: New furnace RFI?
Post by: WB4SPT on July 11, 2018, 11:09:19 AM
Just curious.  Why a furnace and not a heat pump?   No furnace = no induction motor. 

Yes, I have had some "quality EMC time" with my Trane XV90.   :o


Title: RE: New furnace RFI?
Post by: N3WXI on July 11, 2018, 11:50:56 AM
Heat pumps aren't recommended for my area, western Pennsylvania.  Did you resolve you're XV90 issues?


Title: RE: New furnace RFI?
Post by: WB4SPT on July 11, 2018, 03:04:37 PM
Heat pumps aren't recommended for my area, western Pennsylvania.  Did you resolve you're XV90 issues?


Yes,   my XV90 quiet as can be.   Much better than stock.  My direct neighbor has a heat pump and he raves about it.   We are in Rochester, NY, and have very cheap electrical rate.  Am considering the switch myself.   Tired of feeding the 100,000 BTU propane beast! 


Title: RE: New furnace RFI?
Post by: N3WXI on July 11, 2018, 06:22:21 PM
Care to share what you did to quiet your XV90 or did it come like that out of the box?  As I said before they eventually found a fix for it's RFI troubles.


Title: RE: New furnace RFI?
Post by: WB4SPT on July 12, 2018, 08:58:08 AM
Care to share what you did to quiet your XV90 or did it come like that out of the box?  As I said before they eventually found a fix for it's RFI troubles.


I separated out the induction motor drive wires (3) from the rest of the wiring harness.   I pulled the contacts out of the plug-in PCB connector.   Then, two wraps of the individual wires around 3x mix 31 cylinders.   Braided the 3 conductors from chokes to motor.   re-inserted the contacts.   
The 120V mains in was fed thru a metal cased Corcom line filter.   The thermostat cable received a split core mix 31.  I recall a second LV wire out of the cabinet getting a 2nd split core, but forgot its function.  Perhaps the control voltage to a remote electrostatic air filter, or maybe the control cable to the outside compressor unit.   
All told, the RFI at 75 to 20m was reduced about 20dB, as viewed on the Rx S meter.  To about S2/ish.   


Title: RE: New furnace RFI?
Post by: K7JQ on July 12, 2018, 10:27:12 AM
If it were me, I wouldn't want ANY RFI"ish" noise from my HVAC system :D. An S2 noise level will block out an S1 signal. Pre-purchase of an HVAC system, I would buy one with no RF hash, guaranteed by the dealer.


Title: RE: New furnace RFI?
Post by: KC1BMD on July 12, 2018, 11:29:04 AM
… I would buy one with no RF hash, guaranteed by the dealer.

I'd like to see someone try to get that in writing. :)


Title: RE: New furnace RFI?
Post by: K7JQ on July 12, 2018, 12:48:25 PM
… I would buy one with no RF hash, guaranteed by the dealer.

I'd like to see someone try to get that in writing. :)

I and a friend of mine specified that in the contracts of our new HVAC systems. Basically, it stated that eliminating any RFI to our amateur radio receivers was solely the responsibility of the dealer/installer. They were confident of steps needed, if necessary, to mitigate any problems. Of course, both of us specified no 2-stage compressors, and no variable speed motors. We were fairly confident that there would not be an issue in the first place, but covered our butts anyway. We weren't about to start messing and experimenting with the electronics of brand new units ;).


Title: RE: New furnace RFI?
Post by: N3WXI on July 12, 2018, 01:43:51 PM
The system I plan to order (probably tomorrow) has no 2 stage compressor in the A/C and no variable speed motor in the furnace.  I also am confident in the new equipment (It is NOT an XV90).  I'm intending to discuss at length the RFI situation before I "pull the trigger".  I'm curious about what you had specified in your contract.  What was specified as a remedy if they could NOT eliminate any RFI to your satisfaction?  I don't imagine they could reinstall your old unit.
What brand was the new equipment you installed?  Was there any RFI at install?  Thanks?


Title: RE: New furnace RFI?
Post by: K7JQ on July 12, 2018, 04:50:18 PM
The salesman was familiar with possible RFI generation, especially with variable speed motors and two stage compressors. He was confident there would be no problem with the systems I picked, but inserted "If any radio frequency interference, factory technician will come back out to filter it" into the contract. Nothing was mentioned if elimination was not possible. Sufficient language for me, as I wasn't going to mess with it. No way would I have them reinstall the 16 year old tired units ::). I used a reputable company that I had employment dealings with in the past, so I was confident I would be taken care of.

As per a previous post to this thread, I purchased two Lennox split systems. The compressor/condenser is a ML14XC1, and the natural gas-fired furnace/blower is a ML180UH, 16 SEER systems. No RFI at all at install.

73,   Bob K7JQ   


Title: RE: New furnace RFI?
Post by: N3WXI on July 12, 2018, 05:18:37 PM
Thanks for that info.  I'm fairly confident that the newer systems won't have RFI problems and the responses I am getting seem to bear that out.  I am going to have a long discussion about it with the salesman before I agree to anything and am going with one of the largest and most well known companies in my area.  I have decided on a Trane system partially because they should be very familiar with RFI due to their problems with their XV90 in the early 2000s.


Title: RE: New furnace RFI?
Post by: N0GRV on July 27, 2018, 08:06:59 PM
here is a lot of good info on ecm motor noise and how to resolve it.

file:///C:/Users/LATITU~1/AppData/Local/Temp/Solving%20Furnace%20and%20AC_RFI_KM4LHZ_v9.pdf