| Topic: |
Science > Physics |
| User: |
"" |
| Date: |
09 Jul 2005 10:45:09 PM |
| Object: |
difference between "cooling" & "heat rejection"? |
comes now
http://www.engineeringtoolbox.com/unit-converter-19_185.html
to tell us that a "ton of air conditioning is 12,000 BTU/hour of
cooling, or 15,000 BTU/hour of heat rejection"
what is the difference between the two units?
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| User: "daestrom" |
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| Title: Re: difference between "cooling" & "heat rejection"? |
10 Jul 2005 11:08:54 AM |
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<alanh_27@yahoo.com> wrote in message
news:1120967109.577238.99460@g49g2000cwa.googlegroups.com...
comes now
http://www.engineeringtoolbox.com/unit-converter-19_185.html
to tell us that a "ton of air conditioning is 12,000 BTU/hour of
cooling, or 15,000 BTU/hour of heat rejection"
what is the difference between the two units?
This goes into the age-old question of what you're interested in. The COP
of an A/C unit is how much heat is removed from the cold spot (same for
refers and freezers). The COP of a heat pump is how much heat is dumped
into the warm spot. The difference is how much energy it takes to move the
heat from cold to hot.
A one tone A/C unit can remove 12,000 BTU/hour from the 'cold spot'. If it
has a COP of 4.0, it uses about 3000 BTU/hour of electrical energy to move
that heat from the 'cold spot'. The heat dumped out ('rejected') out the
outside condenser is the sum of all the heat removed from the house, *plus*
all the electrical energy it took to run the unit (12,000 BTU/hr + 3000
BTU/hr) = 15,000 BTU/hr. This is part of why a heat pump has a different
HSPF than SEER.
But the exact amount of energy needed to move 12,000 BTU/hr from the 'cold
spot' varies with a lot of things. Design, environment, maintenance... So
the 3,000 BTU/hr is not a simple, hard-and-fast number. The definition of
one ton of A/C is 12,000 BTU/hr, period, stop, end of statement.
But for sizing the outdoor condenser unit, yes they must reject about 1.25
times the A/C cooling provided by the evaporator inside.
daestrom
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| User: "N:dlzc D:aol T:com \dlzc\ N: dlzc1 D:cox" |
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| Title: Re: difference between "cooling" & "heat rejection"? |
10 Jul 2005 02:08:47 PM |
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Dear daestrom:
"daestrom" <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote in message
news:qKbAe.21400$e%5.14610@twister.nyroc.rr.com...
<alanh_27@yahoo.com> wrote in message
news:1120967109.577238.99460@g49g2000cwa.googlegroups.com...
comes now
http://www.engineeringtoolbox.com/unit-converter-19_185.html
to tell us that a "ton of air conditioning is 12,000 BTU/hour
of
cooling, or 15,000 BTU/hour of heat
rejection"
what is the difference between the two units?
This goes into the age-old question of what you're interested
in. The COP of an A/C unit is how much heat is removed
from the cold spot (same for refers and freezers). The
COP of a heat pump is how much heat is dumped into the
warm spot. The difference is how much energy it takes to
move the heat from cold to hot.
So you feel that the difference presented on the website is NOT a
conversion factor (as presented), but instead assumes certain
things about efficiency, and heat sink temperature?
the 3,000 BTU/hr is not a simple, hard-and-fast number. The
definition of one ton of A/C is 12,000 BTU/hr, period, stop,
end of statement.
David A. Smith
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| User: "daestrom" |
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| Title: Re: difference between "cooling" & "heat rejection"? |
11 Jul 2005 05:49:40 PM |
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"N:dlzc D:aol T:com (dlzc)" <N: dlzc1 D:cox T:net@nospam.com> wrote in
message news:2neAe.25763$Qo.22689@fed1read01...
Dear daestrom:
"daestrom" <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote in message
news:qKbAe.21400$e%5.14610@twister.nyroc.rr.com...
<alanh_27@yahoo.com> wrote in message
news:1120967109.577238.99460@g49g2000cwa.googlegroups.com...
comes now
http://www.engineeringtoolbox.com/unit-converter-19_185.html
to tell us that a "ton of air conditioning is 12,000 BTU/hour of
cooling, or 15,000 BTU/hour of heat rejection"
what is the difference between the two units?
This goes into the age-old question of what you're interested
in. The COP of an A/C unit is how much heat is removed
from the cold spot (same for refers and freezers). The
COP of a heat pump is how much heat is dumped into the
warm spot. The difference is how much energy it takes to
move the heat from cold to hot.
So you feel that the difference presented on the website is NOT a
conversion factor (as presented), but instead assumes certain things about
efficiency, and heat sink temperature?
I feel the proper definition of 'ton of A/C' is 12,000 BTU/hr heat removal
rate. The 'heat rejection' rate is not a well accepted definition. This is
because of those 'certain things about efficiency and temperature'. If a
definition is only valid under specific circumstances, and those
circumstances are not part of the definition, then it's a lousy definition.
But I pointed out that the heat rejected by a heat pump is different than
the heat absorbed by one. And the difference is *on the order of* a factor
of 1.25. So this is probably what the authors of said web page are trying
to describe.
One can find *many* references describing/defining one ton of A/C. The
first one I learned was, "The same cooling as melting one ton of ice in 24
hours." But over the course of many years studying/working with
thermodynamics, heat engines and heat pumps, that web site is the first one
I've run across that describes a 'ton of heat rejection' as any particular
number. I consider the web site's attempt to define such a unit as
'suspect'.
daestrom
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| User: "" |
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| Title: Re: difference between "cooling" & "heat rejection"? |
11 Jul 2005 06:02:24 PM |
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See: http://www.sizes.com/units/ton.htm
My favorite is that 1 tun = 4 hogsheads
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| User: "N:dlzc D:aol T:com \dlzc\ N: dlzc1 D:cox" |
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| Title: Re: difference between "cooling" & "heat rejection"? |
09 Jul 2005 11:35:37 PM |
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Dear alanh_27:
<alanh_27@yahoo.com> wrote in message
news:1120967109.577238.99460@g49g2000cwa.googlegroups.com...
comes now
http://www.engineeringtoolbox.com/unit-converter-19_185.html
to tell us that a "ton of air conditioning is 12,000 BTU/hour
of
cooling, or 15,000 BTU/hour of heat
rejection"
what is the difference between the two units?
A typo separates them, it would appear. A ton is a specifc
amount of heat. It doesn't matter what the "sign" is.
URL:http://www.answers.com/topic/conversion-of-units
David A. Smith
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| User: "Gregory L. Hansen" |
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| Title: Re: difference between "cooling" & "heat rejection"? |
11 Jul 2005 06:41:37 PM |
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In article <1120967109.577238.99460@g49g2000cwa.googlegroups.com>,
alanh_27@yahoo.com <alanh_27@yahoo.com> wrote:
comes now
http://www.engineeringtoolbox.com/unit-converter-19_185.html
to tell us that a "ton of air conditioning is 12,000 BTU/hour of
cooling, or 15,000 BTU/hour of heat rejection"
what is the difference between the two units?
Cooling is the amount of heat drawn from an object you want to make cold.
Heat rejection is the amount of heat transferred to the general
environment, and it must be hotter than the general environment if you
want to get rid of it. Air conditioners will generate more heat on the
outside than they remove from the inside because they're not perfectly
efficient.
--
"A good plan executed right now is far better than a perfect plan
executed next week."
-Gen. George S. Patton
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| User: "~^Johnny^~" |
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| Title: Re: difference between "cooling" & "heat rejection"? |
12 Jul 2005 11:25:57 AM |
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-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
On Mon, 11 Jul 2005 23:41:37 +0000 (UTC),
glhansen@steel.ucs.indiana.edu (Gregory L. Hansen) wrote:
Air conditioners will generate more heat on the
outside than they remove from the inside because they're not
perfectly efficient.
Perfectly efficient, in relation to maximum theoretical reverse
Carnot efficiency? :-)
Do the math
http://www.coolchips.gi/technology/ccalc.shtml
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=lShz
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--
-john
wide-open at throttle dot info
~~~~~~~~
"There are two means of refuge from the miseries
of life: music and cats." -Albert Schweitzer
~~~~~~~~
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