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  1. #1
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    Comprehensive Heat Pump Noise Reduction Thread

    Comprehensive Heat Pump Noise Reduction

    The topic is a recurring one, so much so that I'm surprised there isn't a sticky thread on it. There are bits and pieces of wisdom and anecdotal advice scattered throughout the forum, but nothing that pulls it together. Perhaps (wishful thinking?) I can draw out a comprehensive set of recommendations and/or explanations as to what causes Heatpump defrost noises and what you can reasonably ask your contractor to do about them.

    Let's try to keep this thread just to what causes and can be done about air-to-air heat pump defrost noise and not digress into whether people should use ground source or other non air-to-air HP solutions. Assume the person reading this has a heat pump, can't reasonably replace it right now, and is looking to understand whether the situation is hopeless or whether they should pursue their contractor to help find some relief.

    Based on what I've seen other people ask, many scroll compressor heat pumps make a lot of noise when they go into the defrost cycle that removes ice buildup. Some do it based on a clock cycle, others have a smarter demand based algorithm that only defrosts when actually needed. But nearly all have the noises to one degree or another.

    These noises are different than normal operational noises (Thrum, thrum of the compressor or fan noises). The defrost noises fall into three categories:

    1: The Flush - sounds like a toilet flushing or a valve opening - usually not too loud.
    2: The Moose Call - One long, low pitched mooing sound, or for my system, something like a semi-truck slamming on its brakes and skidding on a wet surface.
    3: The Jackhammer - This may go on for 2 to 20 seconds after the Moose call. It may taper off until it goes away. For my system it sounds like the 20 gallon compressor I use to run my air tools.


    (There is often also a second flush when the defrost is over, and a bit of a groan as the heat pump starts back into heat mode, but it is generally pretty quite and few people seem to complain about it.)


    So the first question for the HVAC experts on this site:
    What causes each of these sounds?
    Yes, I know each situation is different and your mileage may vary, but what is most common?
    I've seen all sorts of causes given:
    - Refrigerant backs up into the compressor diluting the oil in the compressor.
    - The reversing valve gets stuck and pressurized refrigerant pounds in the line until it opens up.
    - The reversing valve gets caught halfway and jackhammers open and closed.

    (note - to me a lot of the sounds seem like sheet metal vibration set off by something in the unit, but generally I can't see where it would be coming from)

    If I understood what was causing each I could better discuss them with my contractor.

    And the second question: What can be done about each?
    More specifically, what can I ask my contractor about having them investigate and install?

    It is interesting that some high end brands like the Lennox X-21 seem to go through cycles without a peep - what must be different about them (they all use the same scroll compressors don't they?) and can any of those features be added aftermarket to someone's existing heatpump?

    So far I have seen the following solutions recommended, but I have little idea about what each really addresses:

    Compressor noise blanket: OK, so I guess I understand that one
    Crankcase heater: What does this do and why would it help?
    Muffler: Again - what does it do an why would it help?
    Replace the reversing valve (are some better than others?)
    Defrost Delay: Some compressors have a delay between shutdown and defrost to give the reverse valve time to equalize?
    Oil additives?
    Others?


    I know these are all questions that have been running through my mind for the last few months since the weather turned cool, and I'd be willing to bet dollars to donuts that a lot of other visitors are trying to figure out the same things. It's hard to get any kind of feel for which direction to go on the topic with so many bits and pieces in threads here and there - I hope putting it all in one thread will be helpful to others too.

  2. #2
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    Thanks, Tom, for very useful post. Am looking forward to hearing from the pros on this issue. I've had a crankcase heater installed on my Amana ASZ16. This has reduced some of the sound related to slugging, but some start up and defrost noise remains. Am VERY interested to know more about why some HPs can be so much quieter than others. The Amana board update to lower defrost sound also seems promising.

  3. #3
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    1: The Flush - sounds like a toilet flushing or a valve opening - usually not too loud.
    easy one, system pressures being re-espablished as reversing valve operates

    2: The Moose Call - One long, low pitched mooing sound, or for my system, something like a semi-truck slamming on its brakes and skidding on a wet surface.
    I have never heard this as described, interested in other's comments also (caveat - have only done a few residential systems for relatives and a couple of good friends (brands used - Rheem or Goodman), so do not know what kind of poor installation problems other may face - moisture in the system, poor line slope, characteristics of other brands, etc ?
    3: The Jackhammer - This may go on for 2 to 20 seconds after the Moose call. It may taper off until it goes away. For my system it sounds like the 20 gallon compressor I use to run my air tools.
    Never have heard this either - only defrost noises I've ever heard are the 'whooshing' during reverse valve operation.

  4. #4
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    The flush is the transfer of pressure mostly in the reversing valve.

    The Moose is the compressor working while the load is transfering

    The jackhammer is the oscillating scroll slapping the sides of the compressor due to high refrigerant pressure (possibly liquid refrigerant slugging; some scrolls do not use accumulators), it is not the reversing valve.

    Compressor sound blanket = obvious answer

    Crankcase heater = keeps refrigerant from settling under the oil in the compressor on shutdown. If liquid ref. migrates under the oil, it will force the oil out of the compressor on start up and cause damage. It has nothing to do with defrost.

    Mufflers are used on Reciprocating compressors. It is a small expansion tank to balance the flow of gas between strokes of the recip compressor.

    Defrost delay timers = The timers allow refrigerant to balance, instead of slamming the refrigerant into the opposite direction. Remember, the refrigerant is flowing in the opposite direction with opposing force.

    Oil additives = NEVER add oil additives unless manufacturer allows!
    Last edited by mgenius33; 01-08-2011 at 12:24 AM.
    "The only true wisdom is in knowing you know nothing" Socrates

  5. #5
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    Oct 2010
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    Anderson, South Carolina, United States
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    Where is the hp located? right beside your bed? I would suggest looking at possible problems with the equipment if it really is that loud compared to other equal efficiency/age hps but if it is just normal defrost sounds then i would suggest moving the hp to another location on the outside of your home if it bothers you that much. It may be undercharged(defrosting more than it shoud) or overcharged (greater pressure differential making louder noise than usual)
    As for your questions:
    Compressor blanket would help with normal operation sounds of compressor and some noise of defrost cycle but i don't believe it would make too big a difference in your case but it would be the cheapest and easiest solution to try.
    Defrost delay would help your problem because there wouldn't be near the pressure difference in they refrigerant cycle

  6. #6
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    Kingston Ontario Canada
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    They frost delay timer (if equipped) will make the transfer quieter as I have it on my Carrier 38YZA heat pump. I used it for the first few years, however, I disabled it as I don't like all the extra start and stops the compressor has to make. Nevertheless, it does make the whole process quieter.

    thorton
    ________________________
    In fact, air at 0.4 F contains about 85 percent of the heat it contained at 70 F

  7. #7
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    Monroe County, PA
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    OK, to summarize some of the responses and to give the HVAC experts here a chance to debate some of the suggestions made so far:

    The most bothersome noises - the Moose Call and the Jackhammer - are both coming from the compressor itself.

    - The Moose Call is because the compressor is working extremely hard (although I wish there was a better explanation of this part - is it because there is too much pressure in the return line because the reversing valve hasn't opened yet / opened fully?)

    - The Jackhammer is because the scroll is slapping the inside of the compressor (again - because it is under too much load? - Or perhaps for the opposite reason - there is a vacuum on the output side of the compressor creating negative pressure between the scroll's vanes and compressor walls?)

    Overall - assuming the compressor is isolated from the housing (it is on mine and all the other designs I've seen), defrost noises should not be originating with the housing or the coils or the copper linesets. Except for unusual cases, attempts to monkey with the housing or secure the refrigerant coils, or anything of that like is a waste of time. It's all coming from the compressor itself.

    So based on some of the solutions above, the following can and cannot make a difference:

    Line Mufflers - Not Applicable - this is a scroll compressor issue, not a reciprocating compressor issue (or do they make a difference on Scroll compressors too?)

    Crankcase Heater - Not Applicable - Refrigerant getting into the compressor shouldn't be an issue in defrost cycle (unless the reversing valve isn't working properly maybe?)

    Correct Refrigerant levels - This one is a hard one to discuss with a contractor because it can come across as questioning their skills, but how often / to what degree is overcharging a contributor, and is mostly reflected in the Moose Call or the Jackahmmer?

    Defrost Delay Timers - Might make a difference. Some say the 15-30 seconds lets the lines equalize (so would this help with the Moose Call, the Jackahmmer, or both?) while other say it wouldn't make any difference at all.

    Compressor Sound Blanket - would not prevent the noises from being created, but should lessen how loud they are.

    Oil Additives - Are there any manufacturers who actually do have a recommended additive? Put another way, if a contractor says his company rep recommended a specific additive to reduce defrost noise creation, and said it would not void the warranty, should he be looked at with great skepticism, or might he be telling the truth?

    Problematic Reversing Valves - no-one had much comment on this issue, although in other threads it is often pointed to as the underlying cause in some way? Are there different designs, better quality levels, etc.? Since some brands and models seem to be so much quieter than others, and the compressors themselves are all made by the same company, is it not the RV itself that differentiates between quieter and noisier systems?

    From what I've read in the posts above,
    the only things that MIGHT make a difference are extra noise blanketing on the compressor and possibly adding a delay between shutting down and restarting the compressor as the reversing valve cycles. Is that ALL there is?

    From my perspective, the Flush, and even the Moose call are tolerable. But the Jackhammer is just ridiculous. Sometimes it only lasts 5 seconds, other times it can go on for nearly 30 seconds. If there is one thing I wish I understood the options about, it would be how to stop the jackhammer. Looking through posts here and Youtube clips online, that seems to be the thing that bothers people the most.

  8. #8
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    Is that ALL there is?

    You could have 2 separate systems, GSHP for heating (no defrost needed) and air-air for AC or separate ground source for AC. (actually what I have in own home as AC seldom used anyway - different sizes)

  9. #9
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    Removed. 1st Tone it done. be respectful.
    2nd. Read the 1st.
    Last edited by Stamas; 09-21-2011 at 03:46 PM. Reason: Rude
    "The only true wisdom is in knowing you know nothing" Socrates

  10. #10
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    Quote Originally Posted by mgenius33 View Post
    Removed Quote
    Thanks.

    I've been asking questions HERE so that I don't pester my contractor with unrealistic expectations and demands - trying to vet the rumors and crackpot ideas found across the internet with the experts here at HVAC-Talk before I waste my contractor's time asking about them. So far he's been out to replace 2 failed boards that had nothing to do with defrost noise - but that's all. I respect his time and his expertise and wanted to have my ducks in a row before I posed any defrost noise questions.

    Getting a solution to my circumstance was never my purpose in creating this thread - I had been hoping that this thread would give the experts here a chance to put their knowledge about Defrost Noise management into one thread so other laypeople after me wouldn't follow the same dance I've done for the last 2 months trying to understand their options well enough to make a good decision. Having one really comprehensive thread about defrost that you all could point newbies to - and tell them to read that before posing any further questions - would have been so much easier than re-answering all the same questions each week. Mgenius33's entry at http://hvac-talk.com/vbb/showpost.ph...71&postcount=4 is one of the best I've seen anywhere - I was hoping others would add to it. And while I've obviously ticked off at least one person, I hope other pros here might fill in some additional tips or clarifications that will help others in the future.

    BTW - I'm not looking to solve "my" problem anymore - I'm convinced that any remedy will be just as expensive as moving the units so I'm just going to pay my contractor to move both units (a pair of 3 ton systems) to the far side of my house. They'll still be noisy as heck, but it will be my neighbor's problem now (thankfully, his bedrooms are on the far side of his house too).
    Last edited by Stamas; 09-21-2011 at 03:46 PM. Reason: Same.

  11. #11
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    Well Tom, first let me apologize for the unprofessional manner in which I handled myself.
    It seems I didn't take some of my very own advice that I've posted myself many times on threads. "this is not personal, simply a debate"

    My attitude was a derivative of some of the assumptions you were making. Especially, the text in one thread being inverted and questioned in another. The fact is, many of us take pride in our work and our research in this trade. There are those who don't. Those are the dirty clothes wearing high school drop outs that, hang ducting their whole lives, and call themselves HVAC tradesman.

    You see, it's perception. When a person such as yourself continued to make statements about our contradictions, and then specifically made some about mine, out of context, this gives me the appearance of being blooter.
    We are simply trying to give advice. We cannot give any definitive answers, being that we cannot truly diagnose the physical machinery.

    So, with that said, I hope your local technician can cure what ails your HVAC problems. Good luck!
    "The only true wisdom is in knowing you know nothing" Socrates

  12. #12
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    Tom, Another newbie here. I was amazed at the effort you went to to try to gather all the issues into one thread for those of us who will encounter them in the future... good job!

    Out of this comes the impression that Heat Pumps generically are noisier than A/C compressor units.

    This raises a red flag for me.

    I live in So Cal (San Diego) in a wood frame condominium complex where all the A/C compressor housings are on the roof (ie directly above the ceiling of the top units).

    Recently we had to install some more aggressive isolation blocks under the corners of each housing to attempt to decouple vibration from the structure. Prior to that some residents were bothered by the noise in their units. After, the noise was still there but it was more tolerable.

    I currently am getting bids on either a Trane or Rheem Heat Pump to replace the existing Trane A/C - Gas Furnace system.

    So, two questions arise for the experts here:

    1) Does the 'defrost' cycle only occur in cold climates? (our min temps in winter are in the 50s and occasionally the low 40s)

    2) Would the normal noise/vibration level of even the quietest Heat Pump roof unit be expected to be higher than that of a quiet A/C compressor?

    I'm basically trying to head off 10 years of misery dealing with complaints from my neighbors if Heat Pumps are really not a good idea in this situation.

    Thanks for having this discussion!

    -rb-


    Quote Originally Posted by Tom Campbell View Post
    OK, to summarize some of the responses and to give the HVAC experts here a chance to debate some of the suggestions made so far:

  13. #13
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    Mr. Campbell if you would be willing to post you Email in your profile I will be glad to help you or call you.

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