Defrosting heat pumps
I am going to try to explain why you need to disconnect the fan when thawing a heat pump. again, unless you know what you are doing this is not something to try on your own. with the fan running you are drawing cold air across the coil which is going to of course cooling the hot gas down. it may work for a bit but as the coil defrosts it is going to cool the gas down more and more. and as I said before common sense says a cooler hot gas temp is not going to defrost the coil. -= HvacTech2 =- ... "While you ponder this analogy, I'm going outside." -- Calvin ___ TagDude 0.92á+[DM] ++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++++++ spam protection measure, Please remove the 33 to send e-mail |
Hi PrecisionMachinisT, hope you are having a nice day On 22-Jul-12 At About 12:00:19, PrecisionMachinisT wrote to PrecisionMachinisT Subject: Defrosting heat pumps P From: "PrecisionMachinisT" P And no, Im not gonna apologize for defrosting my heat pump with the P fan running--all I can say is it has always worked just fine for me P when the need has arisen to defrost in a pinch Lets just say you do it your way and abuse the system and I will do it my way and save wear and tear on the compressor. I have defrosted it both ways and my way works much better and faster. as I said I have seen and worked on WAAAAAAYYYYY more heat pump systems than you have ever seen. I actually prefer a garden hose when it isn't below freezing out. -= HvacTech2 =- ... "After they make styrofoam, what do they ship it in?" - s.w. ___ TagDude 0.92á+[DM] ++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++++++ spam protection measure, Please remove the 33 to send e-mail |
Hi PrecisionMachinisT, hope you are having a nice day On 22-Jul-12 At About 14:21:23, PrecisionMachinisT wrote to PrecisionMachinisT Subject: Defrosting heat pumps P From: "PrecisionMachinisT" P "HvacTech2" wrote in message P Now back to the original post--I still think he needs to have the P jumper checked and reset the timer to 30 or 60 minutes if its P currently set at 90.......this being somethning I do on a routine P basis when the weather changes to the point where frosting of the P outdoor unit becomes problematic. Again, experience comes in. different brands use different defrost methods. Trane uses demand defrost and some use pressure or the standard time/temp. one would have to know what brand/model he has to be able to even start to form an opinion. even then it is too hard to make a diagnosis over the net. you really need to be there to check pressures airflows etc... -= HvacTech2 =- ... "On the other hand you have different fingers." - s.w. ___ TagDude 0.92á+[DM] ++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++++++ spam protection measure, Please remove the 33 to send e-mail |
"HvacTech2" wrote in message ... I am going to try to explain why you need to disconnect the fan when thawing a heat pump. again, unless you know what you are doing this is not something to try on your own. with the fan running you are drawing cold air across the coil which is going to of course cooling the hot gas down. it may work for a bit but as the coil defrosts it is going to cool the gas down more and more. and as I said before common sense says a cooler hot gas temp is not going to defrost the coil. Ive done it a fairly large number of times, and on several different makes of heat pump, always worked fine for me is all Im saying. At first, having the fan running isnt even a factor at all--like I say, the fan is pulling from a vaccuum so there is no airflow at all........ Liquid water just runs off the coils and onto the ground......... Later, when the blockage is cleared to the point where air starts to flow through the coils, yes there is some loss of efficiency--but its not near as much as you seem to think, and at that point the total btu required to vaporize the remaining liquid is not terribly substantial. On the other hand, and what I find amusing is that you have taken such a rigid position, up to and including maintaining that it won't work at all, and you continue to present this as factual.......when apparently you have never even attempted defrosting a heat pump in this manner. I have, and it has always worked for me--hey maybe Im just lucky or something then, I dunno......so you are free to do / say / think as you please--but just realize in doing so you are basically calling me a liar over something I have done / seen with my own eyes on numerous occasions. So suggest at least *try* it sometime *then* get back to me afterwards. And no, Im not gonna apologize for defrosting my heat pump with the fan running--all I can say is it has always worked just fine for me when the need has arisen to defrost in a pinch -- SVL |
"HvacTech2" wrote in message ... Hi PrecisionMachinisT, hope you are having a nice day On 22-Jul-12 At About 12:00:19, PrecisionMachinisT wrote to PrecisionMachinisT Subject: Defrosting heat pumps P From: "PrecisionMachinisT" P And no, Im not gonna apologize for defrosting my heat pump with the P fan running--all I can say is it has always worked just fine for me P when the need has arisen to defrost in a pinch Lets just say you do it your way and abuse the system and I will do it my way and save wear and tear on the compressor. I have defrosted it both ways and my way works much better and faster. as I said I have seen and worked on WAAAAAAYYYYY more heat pump systems than you have ever seen. I actually prefer a garden hose when it isn't below freezing out. Okay, fair enough..... And if the temp in the house has dropped so low to where there is insufficient heat to be picked up by the evap then yes, I spose it can be hard on the system.. FWIW, I also prefer to use a garden hose if one happens to be handy and I have the time to stand there with it...this even if its well below freezing. And your right about my experience--I do have 4 heat pumps here, each are from a different manufacturer, and no, I dont work hvac for a living, nor do I even work on other folks systems. Now back to the original post--I still think he needs to have the jumper checked and reset the timer to 30 or 60 minutes if its currently set at 90.......this being somethning I do on a routine basis when the weather changes to the point where frosting of the outdoor unit becomes problematic. -- SVL |
Hi PrecisionMachinisT, hope you are having a nice day On 30-Jan-05 At About 00:51:02, PrecisionMachinisT wrote to PrecisionMachinisT Subject: Defrosting heat pumps P From: "PrecisionMachinisT" P Just to get to the basics......IF the coil is frosted and the airflow P blocked, then the system isnt able to pick up much at all in the P way of heat--and so it *needs* to be defrosted...the sensing method P and most other system specifics becoming pretty much moot at this P juncture. That depends. what caused the icing? was it a bad sensor or board, maybe an undercharge, maybe a bad reversing valve etc.. That is why it is necessary for a tech to be there to check all of this. there is no way to direct someone over the internet to check this for you. there are just too many needed expensive tools. -= HvacTech2 =- ... !WARNING(101): blue eyes, cute smile : warrenty not included ___ TagDude 0.92á+[DM] ++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++++++ spam protection measure, Please remove the 33 to send e-mail |
"HvacTech2" wrote in message ... Hi PrecisionMachinisT, hope you are having a nice day On 22-Jul-12 At About 14:21:23, PrecisionMachinisT wrote to PrecisionMachinisT Subject: Defrosting heat pumps P From: "PrecisionMachinisT" P "HvacTech2" wrote in message P Now back to the original post--I still think he needs to have the P jumper checked and reset the timer to 30 or 60 minutes if its P currently set at 90.......this being somethning I do on a routine P basis when the weather changes to the point where frosting of the P outdoor unit becomes problematic. Again, experience comes in. different brands use different defrost methods. Trane uses demand defrost and some use pressure or the standard time/temp. one would have to know what brand/model he has to be able to even start to form an opinion. even then it is too hard to make a diagnosis over the net. you really need to be there to check pressures airflows etc... Just to get to the basics......IF the coil is frosted and the airflow blocked, then the system isnt able to pick up much at all in the way of heat--and so it *needs* to be defrosted...the sensing method and most other system specifics becoming pretty much moot at this juncture. -- SVL |
Hi PrecisionMachinisT, hope you are having a nice day On 30-Jan-05 At About 09:13:24, PrecisionMachinisT wrote to PrecisionMachinisT Subject: Defrosting heat pumps P From: "PrecisionMachinisT" P Generally around here it's simply caused from a change in the weather P and having the timer set for too long of a time span--your other P choice being frequent defrosts taking place when there isnt even P any frost formed on the coils...basically a nuisance situation where P your damned if you do and your damned if you dont, too... This sounds like a case for demand defrost. demand defrost which trane uses self adjusts due to the fact that it senses the temp difference between the air in and out of the coil and goes into defrost when the delta T is about 25 degrees. of course you don't want to go changing them all now but it is something to consider when you need to change one down the road. -= HvacTech2 =- ... "The ice cream truck in my neighborhood plays `Helter, Skelter.'"- s.w. ___ TagDude 0.92á+[DM] ++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++++++ spam protection measure, Please remove the 33 to send e-mail |
"HvacTech2" wrote in message ... Hi PrecisionMachinisT, hope you are having a nice day On 30-Jan-05 At About 00:51:02, PrecisionMachinisT wrote to PrecisionMachinisT Subject: Defrosting heat pumps P From: "PrecisionMachinisT" P Just to get to the basics......IF the coil is frosted and the airflow P blocked, then the system isnt able to pick up much at all in the P way of heat--and so it *needs* to be defrosted...the sensing method P and most other system specifics becoming pretty much moot at this P juncture. That depends. what caused the icing? was it a bad sensor or board, maybe an undercharge, maybe a bad reversing valve etc.. That is why it is necessary for a tech to be there to check all of this. there is no way to direct someone over the internet to check this for you. there are just too many needed expensive tools. Generally around here it's simply caused from a change in the weather and having the timer set for too long of a time span--your other choice being frequent defrosts taking place when there isnt even any frost formed on the coils...basically a nuisance situation where your damned if you do and your damned if you dont, too... So far ( and in my limited experience ) Ive yet to stumble upon any system that has totally effective and reliable defrost controls, but this is not to say there might not be some out there. A good indicator of when I will need to re-set the timers to a shorter span is when the weatherman starts calling for "possible snow in the lower elevations".......its a safe bet that if I dont reset, excessive coil frosting and generally lowered overall heat output will become a problem, this is true with the Lennox unit at the residence as well as the Bard and Luxaire units in the machine shop..... === I dont run heat strips in the house at all anymore, having installed a relay within the Lennox 5 ton air handler that operates an unducted 3-1/2 ton FHP wshp that's located in the first floor rec room acting as backup heat instead.......( IIRC, with 50 degree well water, the COP of that unit is better than 4 ) but still I continue to run the air source unit during temperature swings ranging into the low teens--in that scenario ( outdoor temps in the mid teens ) there will be a ~10 minute defrost cycle that occurs once for about every 40 minutes of operation. During defrost or on a call for auxillary heat from the programmable stat, the water source unit kicks in....I also installed a second ( manual ) stat downstairs thats tied into it that allows me quickly warm up that area on an as-needed basis. -- SVL |
"HvacTech2" wrote in message ... Hi PrecisionMachinisT, hope you are having a nice day On 30-Jan-05 At About 09:13:24, PrecisionMachinisT wrote to PrecisionMachinisT Subject: Defrosting heat pumps P From: "PrecisionMachinisT" P Generally around here it's simply caused from a change in the weather P and having the timer set for too long of a time span--your other P choice being frequent defrosts taking place when there isnt even P any frost formed on the coils...basically a nuisance situation where P your damned if you do and your damned if you dont, too... This sounds like a case for demand defrost. demand defrost which trane uses self adjusts due to the fact that it senses the temp difference between the air in and out of the coil and goes into defrost when the delta T is about 25 degrees. of course you don't want to go changing them all now but it is something to consider when you need to change one down the road. Yeah, not worth the effort on a 15 year old unit... Matter of fact I have been looking into replacing that Lennox condensor with maybe a new Trane unit--but as of yet I havent found complete specifications published on the web....for me this is a *must have* in order to make any informed decisions, also I really dont wanna replace the air handler even though the evap coils at a minimum should be removed for a thorough cleaning soon. Then again, if it works, don't mess with it.........in reality, the biggest issue is that the ductwork installer hired by the previous owner was a hack, and the ducting has mostly been covered over.......and with the house being just shy of 7500sf fixing this becomes a *major* renovation...... -- SVL |
HvacTech2 wrote:
I am going to try to explain why you need to disconnect the fan when thawing a heat pump. again, unless you know what you are doing this is not something to try on your own. with the fan running you are drawing cold air across the coil which is going to of course cooling the hot gas down. it may work for a bit but as the coil defrosts it is going to cool the gas down more and more. and as I said before common sense says a cooler hot gas temp is not going to defrost the coil. I think we could all agree the moving cold air across the coil is less desirable. Maybe I missed where somebody else brought it up, but... why bother with disconnecting the outdoor unit fan for a onetime "emergency" defrost when you can just cover the thing with a big trashcan lid or something? %mod% |
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