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

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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.

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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.

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"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

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"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.

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"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%