Carrier heat pump: severe/extreme weather cycle?

AllElectric

I live in the northeast in an upper floor apartment in a concrete tower. My 38QRR heat pump is installed on my terrace adjacent to the living area. The unit is mounted on a vibration-deadening pad and is normally very quiet, and I am very accustomed to the normal wintertime sounds generated by the unit because of its proximity - we hear the defrost cycle every 90 minutes along with the associated noises. But occasionally something else happens:

I need to know if there is what I describe as a severe or extreme weather cycle, that kicks-on if the sensor detects specific temperature/humidity conditions. On five separate occasions over the past two years since its installation I've noticed the heat pump go into high-noise cycles lasting 12,24 or 36 hours straight. I can confirm that each noise cycle coincided with heavy snowfall/blizzard conditions. Each time the noise cycle started mid-afternoon and continued in 12 hour increments (typically 24 hours but most recent was 36 hours), during which time the system was fully responsive to the programmable thermostat and continued to provide heat and go into its routine 90-minute defrost cycles. During these loud 12-36 hour periods, the noise is continuous whenever the heat pump is running: a low pitch sound that emanates through the base platform to the concrete floor. It sounds like a vibration, but not one caused by any apparent physical or mechanical issue with the fan; more like the sound it briefly makes during defrost. Standing next to the unit the sound is moderately audible, but it transmits to the rebar in the concrete floor in a way that causes a persistent louder noise to travel throughout my home and most of my building’s twelfth and eleventh floor apartments (my floor = their ceiling). My first carrier heat pump never made such noises except during defrost.

99% of customers have these installed in a yard or rooftop where noise goes unnoticed. Mine is adjacent to a living area and installed on a pad that was to absorb vibration that nevertheless passes right through to the concrete floor that transmits the sound to a good part of my building (ie. at least 20 apartments may notice the ambient nuisance – and the sound resonates down the stairwells of this all-concrete tower).


There’s little information available online:

1. Is this an extreme weather cycle intentionally designed to kick-in when the unit detects it might be buried in snow or coated in ice?
a. If yes, can this cycle be deleted or duration of it or other functions altered (ie. instead of 12-24 hours it is only 1 hour) – my heat pump is protected from weather by a roof overhang, and we live in NY, not Fargo.
b. If no, why is it happening and what needs to be fixed?

2. How can the noise/vibration be further mitigated/isolated?

Thanks in advance. This is a great forum.

JUGHNE

Best guess would be ice on the fan blades putting it out of balance and causing vibration or even ice on the blade rubbing the fan shroud.

Or reversing valve stuck between positions with hot gas bypassing into suction line. Giving that high pressure by-pass valve sound. Power off for 5 minutes and back on might unstick that if it is the issue.

What do you have for back up heat?

EBEBRATT-Ed

Don't know what that pad is made of but I would get some rubbery commercial roofing "walkway pads" and set the unit on that

Jamie Hall

EBEBRATT-Ed said:

Don't know what that pad is made of but I would get some rubbery commercial roofing "walkway pads" and set the unit on that

Perfect. Looking at the picture, I'd say that the material may have enough compliance and damping for high frequencies, but is much too stiff to do much for lows. Low frequencies are really tough to isolate.

John Mills_5

Could be since you say it happens in extreme weather, that defrost water is freezing in the bottom of the unit causing the compressor vibration to be amplified by the ice. OR possibly the coil is frosting up so fast that the fan is starved for air til the next defrost. Timers should be banned for defrosts and all unit have demand defrost IMO.

JUGHNE

These heat pumps are usually raised off the grade by various means. I usually raise the standard HP up 12 to 16" for our weather in NE.
The idea is that when it goes into defrost the melted ice water will run to the ground away from the unit and it's coil.
Here we can end up with a small glacier under the unit sometimes almost reaching the bottom of the heat pump.
I would always try to locate the unit so it would see the sun to get a chance for the ice pack to melt down a little.

AllElectric

Thanks for the tips. I'll need to wait for the next blizzard to test these theories about ice .....

AllElectric

JUGHNE said:

What do you have for back up heat?

Great question. There is the auxiliary heating coil built-into the FV4 blower unit, which unwittingly became a primary heat source for several weeks a few years back when an old condenser unknowingly failed on me. Is that satisfactory? I also have radiant floor heat in one room, but if I lose HVAC or electricity, there's no additional backup. Happy for any recommendations for heating (or cooling) at least some portion of this 1800 sq ft space.

Hint - I'm in an all electric high-rise apartment; my city bans kerosene and propane for heating.

ChrisJ

Examples of heat pump risers.

http://www.supplyhouse.com/DiversiTech-HPR-3-2P-3-Two-Piece-Heat-Pump-Riser?gclid=COyx0e2_iNMCFcEIvAodg6MF5Q


http://www.supplyhouse.com/DiversiTech-HPR-6-6-Heat-Pump-Riser?gclid=CPWXtIDAiNMCFYRjvAod0YgLOw


You can add these to the risers as well to help with vibration

http://www.supplyhouse.com/DiversiTech-MP-4E-EVA-Anti-Vibration-Pad-4-x-4-x-7-8