FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups 
 ProfileProfile   PreferencesPreferences   Log in to check your private messagesLog in to check your private messages   Log inLog in 
Forum index » Science and Technology » Engineering » Mechanics
Air Conditioner Question
Post new topic   Reply to topic Page 1 of 3 [37 Posts] View previous topic :: View next topic
Goto page:  1, 2, 3 Next
Author Message
operator jay
science forum Guru Wannabe


Joined: 29 Apr 2005
Posts: 142

PostPosted: Thu May 18, 2006 11:44 am    Post subject: Re: Air Conditioner Question Reply with quote

too expensive to run in that mode.

"Chris W" <1qazse4@cox.net> wrote in message
news:7PUag.33237$9c6.31207@dukeread11...
Quote:
Why aren't home air conditioner units designed to run continuously to keep
the air at what ever temperature instead of intermittently? I guess the
same could be asked of heaters too.


--
Chris W
KE5GIX

Gift Giving Made Easy
Get the gifts you want &
give the gifts they want
One stop wish list for any gift,
from anywhere, for any occasion!
http://thewishzone.com
Back to top
N:dlzc D:aol T:com (dlzc)
science forum Guru


Joined: 25 Mar 2005
Posts: 2835

PostPosted: Thu May 18, 2006 1:13 pm    Post subject: Re: Air Conditioner Question Reply with quote

Dear Chris W:

"Chris W" <1qazse4@cox.net> wrote in message
news:7PUag.33237$9c6.31207@dukeread11...
Quote:
Why aren't home air conditioner units designed
to run continuously to keep the air at what ever
temperature instead of intermittently? I guess
the same could be asked of heaters too.


As "ms" said it is too expensive to run this way. But they do
run this way as the temperature difference gets larger, or the
refrigerant charge is lost over time.

David A. Smith
Back to top
eromlignod
science forum addict


Joined: 02 May 2005
Posts: 68

PostPosted: Thu May 18, 2006 3:35 pm    Post subject: Re: Air Conditioner Question Reply with quote

Chris W wrote:
Quote:
Why aren't home air conditioner units designed to run continuously to
keep the air at what ever temperature instead of intermittently? I
guess the same could be asked of heaters too.

You can do that by controlling the throttling of the expansion valve
based on temperature feedback, or even on suction pressure. This
affects the amount of torque required from the compressor motor, which
would draw less power when not cooling as much. But the amount of
energy saved from the lower torque would not make up for running the
compressor and fan all the time and the system would not be very
efficient.

Don
Kansas City
Back to top
SQLit
science forum beginner


Joined: 04 Aug 2005
Posts: 39

PostPosted: Fri May 19, 2006 12:16 am    Post subject: Re: Air Conditioner Question Reply with quote

"Chris W" <1qazse4@cox.net> wrote in message
news:7PUag.33237$9c6.31207@dukeread11...
Quote:
Why aren't home air conditioner units designed to run continuously to
keep the air at what ever temperature instead of intermittently? I
guess the same could be asked of heaters too.


--
Chris W
KE5GIX

Some of the new dual stage systems do exactly that. Two compressors, little
one runs most of the time big one kicks in as needed. $$$$$$$ They sure
are not your track home units.
Back to top
Chris W
science forum beginner


Joined: 19 Jun 2005
Posts: 20

PostPosted: Fri May 19, 2006 6:24 am    Post subject: Re: Air Conditioner Question Reply with quote

SQLit wrote:
Quote:

Some of the new dual stage systems do exactly that. Two compressors, little
one runs most of the time big one kicks in as needed. $$$$$$$ They sure
are not your track home units.


From that and other posts, it sounds to me like the real answer to my
question is, it is too expensive to make an air conditioner that can run
efficiently at a wide range of outputs. An air conditioner that ran
continuously would need to efficiently put out a little cold are, a lot
of cold air, or anywhere in between. I'm guessing to do that you would
need a variable displacement compressor pump, variable speed fan on both
the condenser and evaporator. That would certainly raise the cost a
lot. If I'm not mistaken, reducing the speed a fan spins, effects it's
efficacy too. so you might even need a fan with a variable pitch. Maybe
just multiple fans to cover the surface of the condenser and evaporator
and turn on as many as needed.

Anyway, I think I would have the same problem on really hot days. I
hate having the cold air blow on me. I guess the only solution is to
somehow diffuse the air, by having bigger or more vents, so it doesn't
move so fast.

--
Chris W
KE5GIX

Gift Giving Made Easy
Get the gifts you want &
give the gifts they want
One stop wish list for any gift,
from anywhere, for any occasion!
http://thewishzone.com
Back to top
N:dlzc D:aol T:com (dlzc)
science forum Guru


Joined: 25 Mar 2005
Posts: 2835

PostPosted: Fri May 19, 2006 1:20 pm    Post subject: Re: Air Conditioner Question Reply with quote

Dear Chris W:

"Chris W" <1qazse4@cox.net> wrote in message
news:Hwdbg.33280$9c6.21170@dukeread11...
....
Quote:
Anyway, I think I would have the same problem on
really hot days. I hate having the cold air blow on
me. I guess the only solution is to somehow diffuse
the air, by having bigger or more vents, so it doesn't move so
fast.

Insulate the walls, and run chilled water along the inside of the
walls. Then there is no air blowing.

David A. Smith
Back to top
eromlignod
science forum addict


Joined: 02 May 2005
Posts: 68

PostPosted: Fri May 19, 2006 2:22 pm    Post subject: Re: Air Conditioner Question Reply with quote

N:dlzc D:aol T:com (dlzc) wrote:
Quote:
Insulate the walls, and run chilled water along the inside of the
walls. Then there is no air blowing.


Probably wouldn't cool very quickly without any forced convection to
help. You would have to rely on the natural convection of the falling
cold air along the wall to eventually bring the room to equilibrium.

Don
Kansas City
Back to top
eromlignod
science forum addict


Joined: 02 May 2005
Posts: 68

PostPosted: Fri May 19, 2006 2:28 pm    Post subject: Re: Air Conditioner Question Reply with quote

Chris W wrote:
Quote:
From that and other posts, it sounds to me like the real answer to my
question is, it is too expensive to make an air conditioner that can run
efficiently at a wide range of outputs. An air conditioner that ran
continuously would need to efficiently put out a little cold are, a lot
of cold air, or anywhere in between. I'm guessing to do that you would
need a variable displacement compressor pump, variable speed fan on both
the condenser and evaporator. That would certainly raise the cost a
lot. If I'm not mistaken, reducing the speed a fan spins, effects it's
efficacy too. so you might even need a fan with a variable pitch. Maybe
just multiple fans to cover the surface of the condenser and evaporator
and turn on as many as needed.


I wouldn't really need to be that fancy. You can control the
temperature of the evaporator coil by varying the amount of throttling.
The compressor still chugs along merrily and the fan still runs at the
same speed. There are all sorts of controllable expansion valves
available.

Don
Kansas City
Back to top
Paul O
science forum beginner


Joined: 01 Feb 2006
Posts: 11

PostPosted: Fri May 19, 2006 2:44 pm    Post subject: Re: Air Conditioner Question Reply with quote

N:dlzc D:aol T:com (dlzc) wrote:

<snip>
Quote:

Insulate the walls, and run chilled water along the inside of the
walls. Then there is no air blowing.

David A. Smith




Bad idea! Water would condense on the walls and then run down on to the
floor. You would end up a damp, moldy room.


Sorry,
Paul D Oosterhout
I work for SAIC
Back to top
Harry Andreas
science forum beginner


Joined: 17 Aug 2005
Posts: 22

PostPosted: Fri May 19, 2006 4:20 pm    Post subject: Re: Air Conditioner Question Reply with quote

In article <VCjbg.3779$AB3.2895@fed1read02>, "N:dlzc D:aol T:com \(dlzc\)"
<N: dlzc1 D:cox T:net@nospam.com> wrote:

Quote:
Dear Chris W:

"Chris W" <1qazse4@cox.net> wrote in message
news:Hwdbg.33280$9c6.21170@dukeread11...
...
Anyway, I think I would have the same problem on
really hot days. I hate having the cold air blow on
me. I guess the only solution is to somehow diffuse
the air, by having bigger or more vents, so it doesn't move so
fast.

Insulate the walls, and run chilled water along the inside of the
walls. Then there is no air blowing.

No, there is just condensation all over the walls, inside and out.
What follows quickly thereafter is mold inside and outside the
walls, follwed by sickness and maybe death

--
Harry Andreas
Engineering raconteur
Back to top
hob
science forum addict


Joined: 03 Aug 2005
Posts: 50

PostPosted: Fri May 19, 2006 4:51 pm    Post subject: Re: Air Conditioner Question Reply with quote

"Chris W" <1qazse4@cox.net> wrote in message
news:Hwdbg.33280$9c6.21170@dukeread11...
Quote:
SQLit wrote:

Some of the new dual stage systems do exactly that. Two compressors,
little
one runs most of the time big one kicks in as needed. $$$$$$$ They
sure
are not your track home units.


From that and other posts, it sounds to me like the real answer to my
question is, it is too expensive to make an air conditioner that can run
efficiently at a wide range of outputs. An air conditioner that ran
continuously would need to efficiently put out a little cold are, a lot
of cold air, or anywhere in between. I'm guessing to do that you would
need a variable displacement compressor pump, variable speed fan on both
the condenser and evaporator. That would certainly raise the cost a
lot. If I'm not mistaken, reducing the speed a fan spins, effects it's
efficacy too. so you might even need a fan with a variable pitch. Maybe
just multiple fans to cover the surface of the condenser and evaporator
and turn on as many as needed.

Anyway, I think I would have the same problem on really hot days. I
hate having the cold air blow on me. I guess the only solution is to
somehow diffuse the air, by having bigger or more vents, so it doesn't
move so fast.

ASHRAE has criterion for moving air when air conditioning - see the ASHRAE
manuals.

If you move air too slowly, room air will stratify, and if you move it too
rapidly, it will give you windchill :-)

15 FPM is the recommended flow rate for AC, 5 FPM for heating. (You can drop
the size of an AC unit significantly by keeping air moving over 15FPM in
rooms vs having it below 15FPM. ) Home units have AC on high speed, and
heating on low speed fan settings.

Continuous running provides more even air and fewer complaints about
comfort.

Running the fans 24/7 is the least costly, both from maintenance and
from energy use, even when not even considering the savings from raising or
lowering temperature from nominal by running 24/7.
(think starting the entire mass of air in a building moving each time you
start a fan vs just overcoming friction as it moves continuously
- in a house test moving 25,000 cu ft continuous vs on demand, one month
one way the next month the other, the difference was $20 per month lower for
24/7.
Then think of the wear on a bronze bushing starting and stopping from
dead stop dozens of times a day for years vs non-stop running wear. )

-----
And as to vents - there are roughly 5-6 types for each size, for
different applications and velocities.

If the air is moving too fast from the vents you have, get a vent that is
more diffuse or one that can direct air off the workspace.
(Normally, vents for AC are directed upward so the cold air it moves into
the room drops gently through the room's exisitng warmer air, while heating
vents are directed along the walls to warm them and directed down so the
warm air rises through the room's exiith sting cooler air. In one of my
rooms that is 25 feet long with lots of glass and wall vents, I had to
change the vent types spring -cooling type- and fall -heating type- to get
the comfort desired )

fwiw

Quote:

--
Chris W
KE5GIX

Gift Giving Made Easy
Get the gifts you want &
give the gifts they want
One stop wish list for any gift,
from anywhere, for any occasion!
http://thewishzone.com
Back to top
Bruce Durdle
science forum beginner


Joined: 01 May 2005
Posts: 17

PostPosted: Fri May 19, 2006 8:21 pm    Post subject: Re: Air Conditioner Question Reply with quote

I've just installed an inverter-driven heat pump/AC unit (~ 1 kWe/3.5 kWth)
that manages to run over a wide speed range from flat out when starting in a
cold room to ticking over when things are up to temp - check out Panasonic.
Mitsubishi and others.

Bruce.
"Chris W" <1qazse4@cox.net> wrote in message
news:Hwdbg.33280$9c6.21170@dukeread11...
Quote:
SQLit wrote:

Some of the new dual stage systems do exactly that. Two compressors,
little
one runs most of the time big one kicks in as needed. $$$$$$$ They sure
are not your track home units.


From that and other posts, it sounds to me like the real answer to my
question is, it is too expensive to make an air conditioner that can run
efficiently at a wide range of outputs. An air conditioner that ran
continuously would need to efficiently put out a little cold are, a lot of
cold air, or anywhere in between. I'm guessing to do that you would need
a variable displacement compressor pump, variable speed fan on both the
condenser and evaporator. That would certainly raise the cost a lot. If
I'm not mistaken, reducing the speed a fan spins, effects it's efficacy
too. so you might even need a fan with a variable pitch. Maybe just
multiple fans to cover the surface of the condenser and evaporator and
turn on as many as needed.

Anyway, I think I would have the same problem on really hot days. I hate
having the cold air blow on me. I guess the only solution is to somehow
diffuse the air, by having bigger or more vents, so it doesn't move so
fast.

--
Chris W
KE5GIX

Gift Giving Made Easy
Get the gifts you want &
give the gifts they want
One stop wish list for any gift,
from anywhere, for any occasion!
http://thewishzone.com
Back to top
N:dlzc D:aol T:com (dlzc)
science forum Guru


Joined: 25 Mar 2005
Posts: 2835

PostPosted: Sat May 20, 2006 1:04 am    Post subject: Re: Air Conditioner Question Reply with quote

Dear eromlignod:

"eromlignod" <eromlignod@aol.com> wrote in message
news:1148048532.299012.47030@j73g2000cwa.googlegroups.com...
Quote:
N:dlzc D:aol T:com (dlzc) wrote:
Insulate the walls, and run chilled water along the
inside of the walls. Then there is no air blowing.

Probably wouldn't cool very quickly without any
forced convection to help. You would have to rely
on the natural convection of the falling cold air
along the wall to eventually bring the room to
equilibrium.

It works well with hor water *heating*, but there is a
potentially larger temperature difference to do the driving.

David A. Smith
Back to top
N:dlzc D:aol T:com (dlzc)
science forum Guru


Joined: 25 Mar 2005
Posts: 2835

PostPosted: Sat May 20, 2006 1:06 am    Post subject: Re: Air Conditioner Question Reply with quote

Dear Paul O:

"Paul O" <first.d.last@company.com> wrote in message
news:e4klka$k53$1@boulder.noaa.gov...
Quote:
N:dlzc D:aol T:com (dlzc) wrote:

snip

Insulate the walls, and run chilled water along
the inside of the walls. Then there is no air
blowing.

Bad idea! Water would condense on the walls
and then run down on to the floor. You would end
up a damp, moldy room.

Good point. Actually the whole room wouldn't be moldy, only the
"condensor". The dew point in the room would be close to the
water temperature...

David A. Smith
Back to top
N:dlzc D:aol T:com (dlzc)
science forum Guru


Joined: 25 Mar 2005
Posts: 2835

PostPosted: Sat May 20, 2006 1:08 am    Post subject: Re: Air Conditioner Question Reply with quote

Dear Harry Andreas:

"Harry Andreas" <andreas@computer.org> wrote in message
news:andreas-1905060921250001@147.16.85.59...
Quote:
In article <VCjbg.3779$AB3.2895@fed1read02>, "N:dlzc D:aol
T:com \(dlzc\)"
N: dlzc1 D:cox T:net@nospam.com> wrote:
....
Insulate the walls, and run chilled water along
the inside of the walls. Then there is no air blowing.

No, there is just condensation all over the walls,
inside

Yep.

Quote:
and out.

Nope. See where I said to insulate the walls above?

Quote:
What follows quickly thereafter is mold inside
and outside the walls, follwed by sickness and
maybe death

Consider that the condenser coils in a refrigeration system do
exactly this. Yet "sickness and maybe death" is a rare thing.
The metals of construction probably serve to "poison" most
biogrowth.

David A. Smith
Back to top
Google

Back to top
Display posts from previous:   
Post new topic   Reply to topic Page 1 of 3 [37 Posts] Goto page:  1, 2, 3 Next
View previous topic :: View next topic
The time now is Sun Oct 22, 2017 6:29 am | All times are GMT
Forum index » Science and Technology » Engineering » Mechanics
Jump to:  

Similar Topics
Topic Author Forum Replies Last Post
No new posts Question about Life. socratus Probability 0 Sun Jan 06, 2008 10:01 pm
No new posts Probability Question dumont Probability 0 Mon Oct 23, 2006 3:38 pm
No new posts Question about exponention WingDragon@gmail.com Math 2 Fri Jul 21, 2006 8:13 am
No new posts question on solartron 1260 carrie_yao@hotmail.com Electrochem 0 Fri Jul 21, 2006 7:11 am
No new posts A Combinatorics/Graph Theory Question mathlover Undergraduate 1 Wed Jul 19, 2006 11:30 pm

Copyright © 2004-2005 DeniX Solutions SRL
Other DeniX Solutions sites: Electronics forum |  Medicine forum |  Unix/Linux blog |  Unix/Linux documentation |  Unix/Linux forums  |  send newsletters
 


Powered by phpBB © 2001, 2005 phpBB Group
[ Time: 0.0577s ][ Queries: 16 (0.0111s) ][ GZIP on - Debug on ]