For those who have central air conditioning, do you set the fan to on
or auto? Seems like it might be more comfortable to keep the air
moving even when the compressor is off, but maybe that will burn out
the fan?


--


I do not feel obliged to believe that the same God
who has endowed us with sense, reason, and intellect,
has intended us to forgo their use.

....Galileo Galilei

Bill wrote:
For those who have central air conditioning, do you set the fan to on
or auto? Seems like it might be more comfortable to keep the air
moving even when the compressor is off, but maybe that will burn out
the fan?


--


I do not feel obliged to believe that the same God
who has endowed us with sense, reason, and intellect,
has intended us to forgo their use.

...Galileo Galilei

I turn mine one as soon as it becomes a bit uncomfortable. I know from
experience that if I don't have it "on", then the compressor runs
significantly more. The house stays more in the comfort zone with the
fan running. Is the cost of running a fractional horse fan full time
less than a multi horse compressor running intermittently? Don't know,
don't care.

Harry K

On Sat, 22 Jul 2006 20:20:57 -0700, Bill wrote:

For those who have central air conditioning, do you set the fan to on
or auto? Seems like it might be more comfortable to keep the air
moving even when the compressor is off, but maybe that will burn out
the fan?


I'm for auto myself. If I wanted to hear noise al the time I'd buy a
window unit. Also, in this climate what I'm really after is
dehumidification, running the fan doesn't help that.

Bill wrote:
For those who have central air conditioning, do you set the fan to on
or auto? Seems like it might be more comfortable to keep the air
moving even when the compressor is off, but maybe that will burn out

You don't have to worry so much about burn out as you do humidty.
Running the fan continuously will pick up moisture from the evaporator
coil and drain pan area and raise the humidy significantly compared to
leaving it in the auto position.

"Travis Jordan" wrote:
For those who have central air conditioning, do you set the fan to on
or auto? Seems like it might be more comfortable to keep the air
moving even when the compressor is off, but maybe that will burn out

You don't have to worry so much about burn out as you do humidty.
Running the fan continuously will pick up moisture from the evaporator
coil and drain pan area and raise the humidy significantly compared to
leaving it in the auto position.

Interesting, never woulda thought of that, thx.


--


I do not feel obliged to believe that the same God
who has endowed us with sense, reason, and intellect,
has intended us to forgo their use.

....Galileo Galilei

"Travis Jordan" wrote:

You don't have to worry so much about burn out as you do humidty.
Running the fan continuously will pick up moisture from the evaporator
coil and drain pan area and raise the humidy significantly compared to
leaving it in the auto position.

What????? If you have standing water in the coil, you have far more than
humidity problems. That's why they have drains...

Clark W. Griswold, Jr. wrote:
"Travis Jordan" wrote:

You don't have to worry so much about burn out as you do humidty.
Running the fan continuously will pick up moisture from the evaporator
coil and drain pan area and raise the humidy significantly compared to
leaving it in the auto position.

What????? If you have standing water in the coil, you have far more than
humidity problems. That's why they have drains...

Same here. Even if there is water standing there, it only accumulates
while the compressor is running so the total picked up by full on fan
will still be the same as in "auto".

Harry K

Harry K wrote:
Same here. Even if there is water standing there, it only accumulates
while the compressor is running so the total picked up by full on fan
will still be the same as in "auto".

http://www.fsec.ucf.edu/bldg/pubs/dp_air/Abstract.pdf

Travis Jordan wrote:
Harry K wrote:
Same here. Even if there is water standing there, it only
accumulates while the compressor is running so the total picked up
by full on fan will still be the same as in "auto".

http://www.fsec.ucf.edu/bldg/pubs/dp_air/Abstract.pdf

For the full article:
http://www.fsec.ucf.edu/bldg/pubs/pf118/index.htm

Conclusions
The above discussion and experimental results lead to one major
conclusion. For better dehumidification and reduced fluctuations in the
indoor humidity, cycle compressor and fan together in unitary
air-conditioning systems. To increase air movement for thermal comfort,
use local ceiling or paddle fans. Also, the air conditioner
dehumidification fraction in the field is lower than what is expected
from steady-state tests due to compressor cycling.

It can also be concluded that certain duty-cycling devices, which cycle
the compressor off and let the fan operate in order to pick up cooling
from the thermal inertia of the cooling coil, would raise indoor
humidity. While it is not contested that letting the fan operate will
extract the stored cooling in the coil, it will be at the expense of
increased indoor humidity.

Clark W. Griswold, Jr. wrote:
What????? If you have standing water in the coil, you have far more
than humidity problems. That's why they have drains...

It is the water evaporating from the coil (and yes, the drain area) that
causes the increased humidity. Read the linked article below for more
information.
http://www.fsec.ucf.edu/bldg/pubs/pf118/index.htm

Bill wrote:
"Travis Jordan" wrote:
For those who have central air conditioning, do you set the fan
to on or auto? Seems like it might be more comfortable to keep
the air moving even when the compressor is off, but maybe that
will burn out

You don't have to worry so much about burn out as you do humidty.
Running the fan continuously will pick up moisture from the
evaporator coil and drain pan area and raise the humidy
significantly compared to leaving it in the auto position.

Interesting, never woulda thought of that, thx.

And I forgot to mention that with conventional (not variable-speed) fan
motors you are adding between 500 and 1000 watts of heat into the air
stream - which later must be removed.

Travis Jordan wrote:
Travis Jordan wrote:
Harry K wrote:
Same here. Even if there is water standing there, it only
accumulates while the compressor is running so the total picked up
by full on fan will still be the same as in "auto".

http://www.fsec.ucf.edu/bldg/pubs/dp_air/Abstract.pdf

For the full article:
http://www.fsec.ucf.edu/bldg/pubs/pf118/index.htm

Conclusions
The above discussion and experimental results lead to one major
conclusion. For better dehumidification and reduced fluctuations in the
indoor humidity, cycle compressor and fan together in unitary
air-conditioning systems. To increase air movement for thermal comfort,
use local ceiling or paddle fans. Also, the air conditioner
dehumidification fraction in the field is lower than what is expected
from steady-state tests due to compressor cycling.

It can also be concluded that certain duty-cycling devices, which cycle
the compressor off and let the fan operate in order to pick up cooling
from the thermal inertia of the cooling coil, would raise indoor
humidity. While it is not contested that letting the fan operate will
extract the stored cooling in the coil, it will be at the expense of
increased indoor humidity.



I would not leave the blower on for these reasons:

1 - It uses a significant amount of energy, generates heat and doesn't
do a whole lot. A couple ceiling fans use far less power and do a lot
more

2 - If the air handler and/or ducting pass through areas like a hot
attic, you are going to have significant cooling loss.


As for the humidity argument, it's hard to imagine that a unit with a
proper drain is going to have enough water left in it after the
compressor shuts off to worry about.

Travis Jordan wrote:

wrote:
As for the humidity argument, it's hard to imagine that a unit with a
proper drain is going to have enough water left in it after the
compressor shuts off to worry about.

I hear you, but empirical studies (see the link) done by the Florida
Solar Energy Center show otherwise.

From the link (http://www.fsec.ucf.edu/bldg/pubs/pf118/index.htm):

"The location of the drain pipe on the drain pan of most air
conditioners is such that it drains water only if the water level is
above a certain level, say 1/4" or 3/8".

Like the man said, "it's hard to imagine that a unit with a proper
drain" ...

wrote:
Travis Jordan wrote:

wrote:
As for the humidity argument, it's hard to imagine that a unit
with a proper drain is going to have enough water left in it
after the compressor shuts off to worry about.

I hear you, but empirical studies (see the link) done by the Florida
Solar Energy Center show otherwise.

From the link (http://www.fsec.ucf.edu/bldg/pubs/pf118/index.htm):

"The location of the drain pipe on the drain pan of most air
conditioners is such that it drains water only if the water level is
above a certain level, say 1/4" or 3/8".

Like the man said, "it's hard to imagine that a unit with a proper
drain" ...

I hear you too, but every air handler I've worked on in the past decade
has had drains that exit from the side of the pan. This includes Trane,
Carrier, Bryant, Lennox, and yes, even Goodman. If you can name an air
handler where this isn't this case we'll have a notable exception.

"Travis Jordan" wrote:


http://www.fsec.ucf.edu/bldg/pubs/dp_air/Abstract.pdf

It would be interesting to read the complete paper to see what the actual
numbers are. A couple of points jumped out:

The effect they are seeing is most prevalent when the AC is oversized and thus
does not run for max dehumidification effect. In that situation it's almost
intuitive that the little moisture that does condense on the coils won't drain
off and thus will get blown back into the building.

One could also infer that they were looking at a ultra high humidity location
(Florida); seeing the results for other locations would also be interesting.

Clark W. Griswold, Jr. wrote:
It would be interesting to read the complete paper to see what the
actual numbers are.

Here's a related article:
http://www.fsec.ucf.edu/bldg/pubs/pf118/index.htm

"Travis Jordan" wrote:

Here's a related article:
http://www.fsec.ucf.edu/bldg/pubs/pf118/index.htm

Thank you... Will read in detail after a cup of coffee. Was interesting to see
they were seeing that much water in the drain pan. That strikes me as a really
poor drain design.

Clark W. Griswold, Jr. wrote:
"Travis Jordan" wrote:

Here's a related article:
http://www.fsec.ucf.edu/bldg/pubs/pf118/index.htm

Thank you... Will read in detail after a cup of coffee. Was
interesting to see they were seeing that much water in the drain pan.
That strikes me as a really poor drain design.

I think the problem with evaporator drain pans is that the drain comes
off the side rather than the bottom. Because of the way the connector
terminates this means that there is usually 1/4" or so of water in the
bottom of the pan. I don't know why HVAC manufacturers haven't dealt
with this issue - maybe it just hasn't been important to them?

Travis Jordan wrote:

I think the problem with evaporator drain pans is that the drain comes
off the side rather than the bottom. Because of the way the connector
terminates this means that there is usually 1/4" or so of water in the
bottom of the pan. I don't know why HVAC manufacturers haven't dealt
with this issue - maybe it just hasn't been important to them?

The drain pans in my house (the ac is in the attic) are tilted, so that
the outlet is in a low corner. This minimizes the water collection.

Leaving the fan running when it's not actually cooling would be stupid.
The attic is 140 degrees, and all I'd be doing is pumping the heat
from poorly insulated ducts back into the house. Whoever designed this
type of installation was trying to get the homeowner to consume as much
energy as possible, but hey, it installed real cheaply.
grrrrr....

Travis Jordan wrote:
wrote:
As for the humidity argument, it's hard to imagine that a unit with a
proper drain is going to have enough water left in it after the
compressor shuts off to worry about.

I hear you, but empirical studies (see the link) done by the Florida
Solar Energy Center show otherwise.

But it doesn't show what you think. It is addressing letting the fan
continue running _after_ the compressor has shut off. If the
compressor never comes on at all, the study is off the point. Again.
With the fan running full time and the compressor not running, there
will be no increase in humidity due to the air flow picking up moisture
off of the A coil.

As to use of ceiling fans - that is also part of the way I use it.
Furnace fan on, ceiling fan on and that circulates all the air in the
house. On a warm day, it will operate that way all day without ever
firing up the compressor. Shut off the fan and the compressor will be
running within the hour.

Harry K

wrote:
Travis Jordan wrote:

I think the problem with evaporator drain pans is that the drain comes
off the side rather than the bottom. Because of the way the connector
terminates this means that there is usually 1/4" or so of water in the
bottom of the pan. I don't know why HVAC manufacturers haven't dealt
with this issue - maybe it just hasn't been important to them?

The drain pans in my house (the ac is in the attic) are tilted, so that
the outlet is in a low corner. This minimizes the water collection.

Leaving the fan running when it's not actually cooling would be stupid.
The attic is 140 degrees, and all I'd be doing is pumping the heat
from poorly insulated ducts back into the house. Whoever designed this
type of installation was trying to get the homeowner to consume as much
energy as possible, but hey, it installed real cheaply.
grrrrr....

True, but my installation is in the basement and has no ducts above the
ground floor. I actually gain a small (very) amount of cooling from
the basement. I have debated opening an air return vent from the
basement directly into the plenum so it would suck all that nice cool
air out.

Harry K

wrote:

Leaving the fan running when it's not actually cooling would be stupid.
The attic is 140 degrees, and all I'd be doing is pumping the heat
from poorly insulated ducts back into the house. Whoever designed this
type of installation was trying to get the homeowner to consume as much
energy as possible, but hey, it installed real cheaply.

You might want to look into blowing some cellulose in the attic high enough to
cover the vents. It's reasonably cheap, Lowes will loan you the blower and as
long as you don't plug any soffit vents, could save you a few bucks each month
on your heating & cooling bill.

"Harry K" wrote:

But it doesn't show what you think. It is addressing letting the fan
continue running _after_ the compressor has shut off. If the
compressor never comes on at all, the study is off the point. Again.
With the fan running full time and the compressor not running, there
will be no increase in humidity due to the air flow picking up moisture
off of the A coil.

And by definition, you won't be putting more humidity into the air, just
removing less. As they say, its a tradeoff. The additional cooling would be
minimal. But is the comfort gained from continuous moving air worth the higher
humidity?

"Harry K" wrote:

I have debated opening an air return vent from the
basement directly into the plenum so it would suck all that nice cool
air out.

Speaking from personal experience, it doesn't work.

Actually, someone did an analysis on why that doesn't provide any cooling to
speak of. On top of that, the air tends to be quite humid in the basement.

wrote:
Travis Jordan wrote:
Travis Jordan wrote:
Harry K wrote:
Same here. Even if there is water standing there, it only
accumulates while the compressor is running so the total picked up
by full on fan will still be the same as in "auto".

http://www.fsec.ucf.edu/bldg/pubs/dp_air/Abstract.pdf

For the full article:
http://www.fsec.ucf.edu/bldg/pubs/pf118/index.htm

Conclusions
The above discussion and experimental results lead to one major
conclusion. For better dehumidification and reduced fluctuations in the
indoor humidity, cycle compressor and fan together in unitary
air-conditioning systems. To increase air movement for thermal comfort,
use local ceiling or paddle fans. Also, the air conditioner
dehumidification fraction in the field is lower than what is expected
from steady-state tests due to compressor cycling.

It can also be concluded that certain duty-cycling devices, which cycle
the compressor off and let the fan operate in order to pick up cooling
from the thermal inertia of the cooling coil, would raise indoor
humidity. While it is not contested that letting the fan operate will
extract the stored cooling in the coil, it will be at the expense of
increased indoor humidity.



I would not leave the blower on for these reasons:

1 - It uses a significant amount of energy, generates heat and doesn't
do a whole lot. A couple ceiling fans use far less power and do a lot
more


If you mean 'measureable' amount yes, 'significant' no. A fractional
hp electric motor doesn't use much. It also doesn't put out much heat.
The fan plus my ceiling fan keeps the compressor from running as often
so which does use a significant amount of power.

2 - If the air handler and/or ducting pass through areas like a hot
attic, you are going to have significant cooling loss.

Yep, it would be a losing proposition in that case.


As for the humidity argument, it's hard to imagine that a unit with a
proper drain is going to have enough water left in it after the
compressor shuts off to worry about.

Right.

Harry K

Clark W. Griswold, Jr. wrote:
wrote:

Leaving the fan running when it's not actually cooling would be stupid.
The attic is 140 degrees, and all I'd be doing is pumping the heat
from poorly insulated ducts back into the house. Whoever designed this
type of installation was trying to get the homeowner to consume as much
energy as possible, but hey, it installed real cheaply.

You might want to look into blowing some cellulose in the attic high enough to
cover the vents. It's reasonably cheap, Lowes will loan you the blower and as
long as you don't plug any soffit vents, could save you a few bucks each month
on your heating & cooling bill.

Holy criminy cripes! That would be about 4 feet or more of blown
cellulose. And you could forget about ever going up there to work on
the AC system, or the wiring, or anything else.

It's the DUCTS that are in the attic, not just the vents. Actually,
the entire system should be removed from the attic in super-hot
climates such as PHX or most of the south.

There is one insulation system I've seen, but not used (yet), so I
can't recommend it personally. It's Icynene; they put this foam on the
underside of the roof, and pretty much seal the attic. Vapor isn't a
problem because of the type of foam. This renders the entire attic
essentially another highly insulated space, and the heat gain is
severly reduced. Mileage may vary.

wrote:

There is one insulation system I've seen, but not used (yet), so I
can't recommend it personally. It's Icynene; they put this foam on the
underside of the roof, and pretty much seal the attic. Vapor isn't a
problem because of the type of foam. This renders the entire attic
essentially another highly insulated space, and the heat gain is
severly reduced. Mileage may vary.

Yep. Considered it for a new 3000 sq ft house I'm building. Then we got the
bids. They wanted $18K over what fiberglass bats would cost. Even if I saw 25%
reduction in heating and cooling, the payback on that was over 50 years.

Decided to go with dense cellulose in the walls and blown in the attic. Install
for either is critical, but the cellulose is almost as good as foam and only
marginally more expensive than fiberglass.

wrote:

Holy criminy cripes! That would be about 4 feet or more of blown
cellulose. And you could forget about ever going up there to work on
the AC system, or the wiring, or anything else.


Sorry - thought you only had ducts up there - not the whole system.

Clark W. Griswold, Jr. wrote:
wrote:

Holy criminy cripes! That would be about 4 feet or more of blown
cellulose. And you could forget about ever going up there to work on
the AC system, or the wiring, or anything else.


Sorry - thought you only had ducts up there - not the whole system.

Around here, most builders put the evaporators and air handlers up
there as well. Then you get an 18" x18" access to work on it. Useless
piece of garbage....

Geez, it isn't even real ducting. It's that flexible plastic stuff. I
wonder how few years that'll last in 140 degree attics?????

wrote in message ups.com...

I would not leave the blower on for these reasons:

1 - It uses a significant amount of energy, generates heat and doesn't
do a whole lot. A couple ceiling fans use far less power and do a lot
more

I agree if you're talking about a single story house. But in my two-story
house the difference between upstairs and downstairs will be about
5 degrees with the blower running constantly, and up to 10 degrees
if the blower runs only intermittently. So the blower has an air mixing
or equalizing effect with multiple stories.

--
John Richards

"Clark W. Griswold, Jr." wrote in message ...
"Harry K" wrote:

But it doesn't show what you think. It is addressing letting the fan
continue running _after_ the compressor has shut off. If the
compressor never comes on at all, the study is off the point. Again.
With the fan running full time and the compressor not running, there
will be no increase in humidity due to the air flow picking up moisture
off of the A coil.

And by definition, you won't be putting more humidity into the air, just
removing less. As they say, its a tradeoff. The additional cooling would be
minimal. But is the comfort gained from continuous moving air worth the higher
humidity?

It depends on what the ambient humidity level is. Could be a
problem in Florida, but no problem here in California.

--
John Richards