In regards to the recent posting I saw about running the a/c or opening the
windows, I would like to list several statements that people have made to
me about air conditioning. The location is Texas, where the temperature
is about 75 F at night and 100 F at the hottest part of the day.

1. Keeping the a/c cooling the house all day uses less electricity than
turning it off and then back on in the evening or when you return from
a vacation.

2. Running the a/c a few degrees colder at night cools the big cement slab
that the house is built on, and thus saves electricity during the day
(the a/c is set back to normal living temperature during the day).

2b. If the temperature inside the house reaches 78 F at 10 AM on both days
with the a/c set colder the previous night, and also when it was just
set normally the previous night, then that proves setting it colder made
no difference.

3. The a/c uses less current at night ( you measure it with an ammeter as
it is running ).

4. The a/c uses less current if you spray the outside unit with the garden
hose and then measure it with the ammeter.

5. Shading the outside unit (compressor and condenser) does not reduce
electricity costs [Assume shade does not block air flow].

6. If you have high ceilings and ceiling fans, it is more energy efficient
to leave the fans running at low speed all the time to pull down hot air
and get it to circulate through the a/c system.

7. It isn't worthwhile to check on the amount of Freon (or whatever) that is
in the system -- all that matters is measuring the temperature of the
cold air coming out (say 62 F) and the outside temperature or maybe the
attic temperature.

--Jeff

In sci.physics J Jensen wrote:
In regards to the recent posting I saw about running the a/c or opening the
windows, I would like to list several statements that people have made to
me about air conditioning. The location is Texas, where the temperature
is about 75 F at night and 100 F at the hottest part of the day.

snip

3. The a/c uses less current at night ( you measure it with an ammeter as
it is running ).

Hmmm, if the air going into the heat exchanger is 25 degrees cooler (100-75),
what happens to compressor efficiency and compressor hp requirements?

4. The a/c uses less current if you spray the outside unit with the garden
hose and then measure it with the ammeter.

Essentially ditto for #3.

There are companies selling swamp cooler precoolers for AC heat exchangers.

Easy enough to prove or disprove. Just watch your meter spin and spray
down the AC.

snip

--
Jim Pennino

Remove -spam-sux to reply.

1 no How dumb, you are saying cooling it when you are on vacation is
cheaper than not cooling it
2 no Dumb again
2b exact exterior temp , solar load, wind, humidity have been
maintained in a lab or your dumb again
3 no , unless voltage is higher at night, which it often is.
4 Hard water , mineral buildup
6 Question is openended
7 Hacks do a lot of stupid things, just ask Daves Heating or I can
listen to you.

J Jensen wrote:
In regards to the recent posting I saw about running the a/c or
opening the windows, I would like to list several statements that
people have made to me about air conditioning. The location is
Texas, where the temperature
is about 75 F at night and 100 F at the hottest part of the day.

1. Keeping the a/c cooling the house all day uses less electricity
than turning it off and then back on in the evening or when you
return from a vacation.

Maybe, it really depends on many many factors. It would be best to
measure the specific application.


2. Running the a/c a few degrees colder at night cools the big cement
slab that the house is built on, and thus saves electricity during
the day (the a/c is set back to normal living temperature during
the day).

See above, it might.


2b. If the temperature inside the house reaches 78 F at 10 AM on both
days with the a/c set colder the previous night, and also when it
was just set normally the previous night, then that proves
setting it colder made no difference.

Big if. If it does it really means your measurements/test is not valid.
College Physics 101 will tell you that if your test is accurate and all
factors are considered, there must be a difference, even if it is small.
Soft of the butterfly effect.


3. The a/c uses less current at night ( you measure it with an
ammeter as it is running ).

I believe that is generally true, assuming it is cooler at night.


4. The a/c uses less current if you spray the outside unit with the
garden hose and then measure it with the ammeter.

Same as above, but you may end up damaging your condenser unit.


5. Shading the outside unit (compressor and condenser) does not reduce
electricity costs [Assume shade does not block air flow].

This is an example of inadequate measurement. There is a difference but
it is so small that it is difficult to measure. See 2b.


6. If you have high ceilings and ceiling fans, it is more energy
efficient to leave the fans running at low speed all the time to
pull down hot air and get it to circulate through the a/c system.

Only if it is you goal to cool the ceiling.


7. It isn't worthwhile to check on the amount of Freon (or whatever)
that is in the system -- all that matters is measuring the
temperature of the cold air coming out (say 62 F) and the outside
temperature or maybe the attic temperature.

Worthwhile for what?


--Jeff

--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math

J Jensen wrote:
1. Keeping the a/c cooling the house all day uses less electricity
than turning it off and then back on in the evening or when you
return from a vacation.
False.
http://www.ontario-sea.org/34kyoto/ac.html

2. Running the a/c a few degrees colder at night cools the big cement
slab that the house is built on, and thus saves electricity during
the day (the a/c is set back to normal living temperature during
the day).
False.
http://www.ontario-sea.org/34kyoto/ac.html

2b. If the temperature inside the house reaches 78 F at 10 AM on both
days with the a/c set colder the previous night, and also when it
was just set normally the previous night, then that proves
setting it colder made no difference.
False.
Many, many variables in this equation.

3. The a/c uses less current at night ( you measure it with an
ammeter as it is running ).
Depends. Compressor current consumption can vary with the load.

4. The a/c uses less current if you spray the outside unit with the
garden hose and then measure it with the ammeter.
See above.

5. Shading the outside unit (compressor and condenser) does not reduce
electricity costs [Assume shade does not block air flow].
It depends.
http://homeenergy.org/archive/hem.di...95/951102.html

6. If you have high ceilings and ceiling fans, it is more energy
efficient to leave the fans running at low speed all the time to
pull down hot air and get it to circulate through the a/c system.
Fans don't cool rooms, they cool people (due to the evaporative cooling
effect on skin). To save energy, turn fans off when you leave the room.

7. It isn't worthwhile to check on the amount of Freon (or whatever)
that is in the system -- all that matters is measuring the
temperature of the cold air coming out (say 62 F) and the outside
temperature or maybe the attic temperature.
False.
There are many factors that influene the measured temperatures besides
the refrigerant charge..

"J Jensen" wrote in message
om...
In regards to the recent posting I saw about running the a/c or opening the
windows, I would like to list several statements that people have made to
me about air conditioning. The location is Texas, where the temperature
is about 75 F at night and 100 F at the hottest part of the day.

1. Keeping the a/c cooling the house all day uses less electricity than
turning it off and then back on in the evening or when you return from
a vacation.

2. Running the a/c a few degrees colder at night cools the big cement slab
that the house is built on, and thus saves electricity during the day
(the a/c is set back to normal living temperature during the day).

2b. If the temperature inside the house reaches 78 F at 10 AM on both days
with the a/c set colder the previous night, and also when it was just
set normally the previous night, then that proves setting it colder made
no difference.

3. The a/c uses less current at night ( you measure it with an ammeter as
it is running ).

4. The a/c uses less current if you spray the outside unit with the garden
hose and then measure it with the ammeter.

5. Shading the outside unit (compressor and condenser) does not reduce
electricity costs [Assume shade does not block air flow].

6. If you have high ceilings and ceiling fans, it is more energy efficient
to leave the fans running at low speed all the time to pull down hot air
and get it to circulate through the a/c system.

7. It isn't worthwhile to check on the amount of Freon (or whatever) that is
in the system -- all that matters is measuring the temperature of the
cold air coming out (say 62 F) and the outside temperature or maybe the
attic temperature.

--Jeff

This is Turtle.

You got too many Question here and I will answer just the first 2 .

Answer to 1 ) If you turn a hvac system off less than 8 hours. It will cost
you more money to recool the house from a very high temperature to the lower
temperature than just moving up to a higher temperature on the thermostat. If
your going to be gone more than 8 hours move the thermostat to about 85ºF or so
and turn it back down when you get back home. If your going to be gone for 24
hours or more like on vacation. move the thermostat to the highest setting of
about 95ºF and keep the house below 95ºF because refrigerator , Freezers, and
Wine Coolers are not designed to run in temperatures above 95ºF. Most or a lot
of Refrigerator & Freezers will stop working at 100ºF or above. If you read the
installation instruction when you bought the refrigerator or freezer it tells
you to not run the appliance in ambiant above 95ºF. Also do not run it in
Ambiants of below 40ºF.

Answer to 2) and 2B) .

2) Hog wash.

2B) You found the Hog wash answer was the answer.

TURTLE


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.725 / Virus Database: 480 - Release Date: 7/19/2004

(J Jensen) wrote in message . com...
In regards to the recent posting I saw about running the a/c or opening the
windows, I would like to list several statements that people have made to
me about air conditioning. The location is Texas, where the temperature
is about 75 F at night and 100 F at the hottest part of the day.

1. Keeping the a/c cooling the house all day uses less electricity than
turning it off and then back on in the evening or when you return from
a vacation.

Part of the answer this has to do with where in Texas you live. If you
live in the Houston area, you would probably want to leave it on at
all times, if nothing else to prevent a build up of humidity in your
home. If you live in a less humid part of the state, this is not as
much of a consideration.

2. Running the a/c a few degrees colder at night cools the big cement slab
that the house is built on, and thus saves electricity during the day
(the a/c is set back to normal living temperature during the day).

Realistically, you have little hope of cooling down a large cement
slab, except if you maintain a constant temperature in your home.

2b. If the temperature inside the house reaches 78 F at 10 AM on both days
with the a/c set colder the previous night, and also when it was just
set normally the previous night, then that proves setting it colder made
no difference.

It anything, this simply reveals you need a larger air conditioner
unit since your current one is unable to maintain the temperature
within acceptable tollerances.

3. The a/c uses less current at night ( you measure it with an ammeter as
it is running ).

I personally have not found this to be the case, either in upstate New
York or here in New England. The current drawn by the compressor in an
air conditioner barely reflect changes in temperature conditions.


4. The a/c uses less current if you spray the outside unit with the garden
hose and then measure it with the ammeter.

I'd assume that you are joking here.

5. Shading the outside unit (compressor and condenser) does not reduce
electricity costs [Assume shade does not block air flow].

Shading the condensor unit will improve air conditining performance,
but will have only small impact on electricity costs.

6. If you have high ceilings and ceiling fans, it is more energy efficient
to leave the fans running at low speed all the time to pull down hot air
and get it to circulate through the a/c system.

This depend on how interested you are in air conditioning your
ceilings. Most people couldn't give a hoot.


7. It isn't worthwhile to check on the amount of Freon (or whatever) that is
in the system -- all that matters is measuring the temperature of the
cold air coming out (say 62 F) and the outside temperature or maybe the
attic temperature.

If the temperature differential between the intake air and the outlet
air temperature are operating within specificationd, there is no need
to measure the freon pressures.

Harry C.

"J Jensen" wrote in message
om...

7. It isn't worthwhile to check on the amount of Freon (or whatever) that
is
in the system -- all that matters is measuring the temperature of the
cold air coming out (say 62 F) and the outside temperature or maybe the
attic temperature.
--Jeff

This has to be some of the purist BS I have read lately.

~kjpro~

"Harry Conover" wrote in message
om...
(J Jensen) wrote in message
. com...

7. It isn't worthwhile to check on the amount of Freon (or whatever)
that is
in the system -- all that matters is measuring the temperature of the
cold air coming out (say 62 F) and the outside temperature or maybe
the
attic temperature.

If the temperature differential between the intake air and the outlet
air temperature are operating within specificationd, there is no need
to measure the freon pressures.

Harry C.

And your comment to his #7 is just as asinine!!

#1 It shows you know little about refrigeration.

#2 That you are a HACK, if you really are in the trade.

#3 That you need to learn more about HVAC systems.

~kjpro~

In sci.physics, Travis Jordan

wrote
on Thu, 22 Jul 2004 23:11:19 GMT
:
J Jensen wrote:
1. Keeping the a/c cooling the house all day uses less electricity
than turning it off and then back on in the evening or when you
return from a vacation.
False.
http://www.ontario-sea.org/34kyoto/ac.html

2. Running the a/c a few degrees colder at night cools the big cement
slab that the house is built on, and thus saves electricity during
the day (the a/c is set back to normal living temperature during
the day).
False.
http://www.ontario-sea.org/34kyoto/ac.html

There are admittedly some interesting issues here. I'll admit,
I'm wondering how much heat the contents and the surrounding
walls of a room actually have, compared to the air.

A 3m x 3m x 3m room doesn't have that much air; the mass of
air in the room is readily computable by Guy-Lussac:

n = PV/(RT) = 101350 pascals * 27 m^3 / (8.314472 J/(mol K) * 300K)
= 1097 moles = 31.8 kg (assuming air is about 29 grams/mole).

This is one reason why liquid oxygen is so darned effective
at vaporizing barbeques. :-) (Cf George Goble's experiments
therein, which are perambulating around the Net; a Google
search points to

http://web.archive.org/web/200210032...rdue.edu/~ghg/

Kids, don't try this at home unless one knows what one is doing. :-) )

Of course, lucky me: I'm on a second floor condo and the only
slab is the floor. As it is, I suspect the slab doesn't get
all that hot anyway; it is, after all, sitting on the ground,
which after one goes a certain depth is a nice, constant
temperature. (However, there are a number of issues here, too,
such as crawl space.)


2b. If the temperature inside the house reaches 78 F at 10 AM on both
days with the a/c set colder the previous night, and also when it
was just set normally the previous night, then that proves
setting it colder made no difference.
False.
Many, many variables in this equation.

3. The a/c uses less current at night ( you measure it with an
ammeter as it is running ).
Depends. Compressor current consumption can vary with the load.

Well, a theoretical Carnot heat engine would of course be more
efficient if the delta-T is lower; in the night it's generally
cooler. (Of course running A/C when it's cold outside is
mostly pointless, unless it's reversible and one wants to
*heat* the house [a heat pump].)

Real A/C, of course, depends on many things, such as the
compressor's ability to compress, the amount of refrigerant
in the system (one A/C unit where I used to work we had to
overcharge in the winter to keep it from freezing up, then
remove some of the coolant in the summer so that it would
actually cool more efficiently; unfortunately around here
it can get cold in the summer which means it occasionally
had problems anyway), and of course whether things are
blocking up the ductwork, keeping the cooling coils from
warming up or the hot coils from cooling down.


4. The a/c uses less current if you spray the outside unit with the
garden hose and then measure it with the ammeter.
See above.

I'll admit I'm not sure about this, but perhaps it's because
my unit is getting on the old side; spraying the hot
coils may affect the compressor pressure, to the point
where the unit simply can't do its job since the pressure's
too low.


5. Shading the outside unit (compressor and condenser) does not reduce
electricity costs [Assume shade does not block air flow].
It depends.
http://homeenergy.org/archive/hem.di...95/951102.html

There are probably a lot of issues here. If one shades the
entire wall, for instance, the cooling load is lighter,
presumably. (Raw insolation = 1,350 W/m^2, approximately.)

Of course, shading the A/C might work until the unit shading
the A/C warms up from the sun and the A/C heating it. Ideally
one would install a highly reflective mirror system to reflect
the sunlight back at the Sun, but that would probably annoy the
neighbors... :-) (Not to mention low-flying planes.) And then
there's the "greenhouse effect", where gasses (water vapor?)
in the atmosphere simply reflect the infrared; reflecting the
infrared using a mirror simply distributes the problem, making
everyone else's domicile in the area a very small amount hotter.
So if everyone installed a mirror over their A/C units (or the
entire house!), would we be better off? An interesting question.


6. If you have high ceilings and ceiling fans, it is more energy
efficient to leave the fans running at low speed all the time to
pull down hot air and get it to circulate through the a/c system.
Fans don't cool rooms, they cool people (due to the evaporative cooling
effect on skin). To save energy, turn fans off when you leave the room.

Unless they are attic fans, pulling air *through* the attic, or
pulling air through the house during the evening or morning
hours, before the outside air gets warmer than the inside.

As for cooling people -- that works until the humidity gets so
high that the sweat doesn't evaporate. Shower time, or maybe
time for some swimming.


7. It isn't worthwhile to check on the amount of Freon (or whatever)
that is in the system -- all that matters is measuring the
temperature of the cold air coming out (say 62 F) and the outside
temperature or maybe the attic temperature.
False.
There are many factors that influene the measured temperatures besides
the refrigerant charge..


The target I've heard is 20 degrees cooler than outside.

--
#191,
It's still legal to go .sigless.

"~KJPRO~" KJPRO @ STARBAND.NET wrote in message
...
"J Jensen" wrote in message
om...

7. It isn't worthwhile to check on the amount of Freon (or whatever)
that
is
in the system -- all that matters is measuring the temperature of the
cold air coming out (say 62 F) and the outside temperature or maybe
the
attic temperature.
--Jeff

This has to be some of the purist BS I have read lately.

~kjpro~


Dave probably sent that information to him....you know Dave....full of ****
and thinks hes correct....
But...But...its beercan cold doncha know?

"Travis Jordan" wrote in message ...
J Jensen wrote:
1. Keeping the a/c cooling the house all day uses less electricity
than turning it off and then back on in the evening or when you
return from a vacation.
False.
http://www.ontario-sea.org/34kyoto/ac.html


Thanks for your reply. I especially appreciate the references.


[snip]
3. The a/c uses less current at night ( you measure it with an
ammeter as it is running ).
Depends. Compressor current consumption can vary with the load.


I have always had the opinion that #3 can't be true because it is an
electric motor and it should take the same amount of current whenever it
runs. It should run for a shorter period of time each time it comes on
at night, due to the greater efficiency of having cooler outside air...
right?

[snip]
--Jeff

The Ghost In The Machine wrote in message ...
[snip]
Of course, lucky me: I'm on a second floor condo and the only
slab is the floor. As it is, I suspect the slab doesn't get
all that hot anyway; it is, after all, sitting on the ground,
which after one goes a certain depth is a nice, constant
temperature. (However, there are a number of issues here, too,
such as crawl space.)


That is about what I thought -- the slab really doesn't change
temerature appreciably unless you really made the house really cold and held it
that way for a long time, which would cetainly not be saving electricity!
And if the a/c kicks on at the same time in the morning with or without
"cooling" the slab all night, then the rest of the day it is going to run
just the same as always.


2b. If the temperature inside the house reaches 78 F at 10 AM on both
days with the a/c set colder the previous night, and also when it
was just set normally the previous night, then that proves
setting it colder made no difference.

[snip]
--Jeff

"TURTLE" wrote in message ...
[snip]
Answer to 1 ) If you turn a hvac system off less than 8 hours. It will cost
you more money to recool the house from a very high temperature to the lower
temperature than just moving up to a higher temperature on the thermostat. If
your going to be gone more than 8 hours move the thermostat to about 85ºF or so
and turn it back down when you get back home. If your going to be gone for 24
hours or more like on vacation. move the thermostat to the highest setting of
about 95ºF and keep the house below 95ºF because refrigerator , Freezers, and
Wine Coolers are not designed to run in temperatures above 95ºF. Most or a lot
of Refrigerator & Freezers will stop working at 100ºF or above. If you read the
installation instruction when you bought the refrigerator or freezer it tells
you to not run the appliance in ambiant above 95ºF. Also do not run it in
Ambiants of below 40ºF.


I never do turn it entirely off, but that is probably a good point about
the effect on other applicances...

[snip]

(Harry Conover) wrote in message . com...
[snip]

3. The a/c uses less current at night ( you measure it with an ammeter as
it is running ).

I personally have not found this to be the case, either in upstate New
York or here in New England. The current drawn by the compressor in an
air conditioner barely reflect changes in temperature conditions.


Yeah, as I said in another reply, I think the electric motor would
always
take the same current when running, but just run for a shorter period
of
time at night.




4. The a/c uses less current if you spray the outside unit with the garden
hose and then measure it with the ammeter.

I'd assume that you are joking here.

No joke. The same person said this as #3 about the current at night
and
#2 about cooling the slab.



5. Shading the outside unit (compressor and condenser) does not reduce
electricity costs [Assume shade does not block air flow].

Shading the condensor unit will improve air conditining performance,
but will have only small impact on electricity costs.

It runs multiple times per hour here (especially the afternoon) and
the metal gets very hot in the sun. I tend to think that the savings
in shading it must be significant over the length of the summer.

--Jeff

[snip]

J Jensen wrote:
"Travis Jordan" wrote in message
...
J Jensen wrote:
.......
Thanks for your reply. I especially appreciate the references.

You are welcome.

3. The a/c uses less current at night ( you measure it with an
ammeter as it is running ).
Depends. Compressor current consumption can vary with the load.


I have always had the opinion that #3 can't be true because it is an
electric motor and it should take the same amount of current whenever
it runs. It should run for a shorter period of time each time it
comes on
at night, due to the greater efficiency of having cooler outside
air... right?

The reason the condenser motors (compressor motor + fan motor) typically
run less at night is because the system load is lighter (less sensible
heat to be removed from inside the home due to reduced heat gain from
the outside). It is true that the fan motor generally uses the same
amount of current whenever it runs due to it's design and the constant
load of the fan. In normal operation the compressor motor will draw
somewhere between RLA (rated load amps) and FLA (full load amps)
depending upon the load.

"~KJPRO~" KJPRO @ STARBAND.NET wrote in message ...
"J Jensen" wrote in message
om...

7. It isn't worthwhile to check on the amount of Freon (or whatever) that
is
in the system -- all that matters is measuring the temperature of the
cold air coming out (say 62 F) and the outside temperature or maybe the
attic temperature.
--Jeff

This has to be some of the purist BS I have read lately.

~kjpro~

This was what an a/c technician told me when I called him out to the
house
with the specific request to check if any Freon had leaked out of the
system over the years, or if it was still operating at 100%. He would
not do it,
although he did check some other things. On the bright side, he did
encourage
me to sign up for yearly maintenance by his company...
--Jeff

"Joseph Meehan" wrote in message ...
J Jensen wrote:

1. Keeping the a/c cooling the house all day uses less electricity
than turning it off and then back on in the evening or when you
return from a vacation.

Maybe, it really depends on many many factors. It would be best to
measure the specific application.


It seems to me that it would clearly be best to let it get hot in the
house if no one is there during the day and just run the a/c hard to cool
it down in the early evening. The only issue is that the a/c is then doing
a lot of work when the outside temperature is still near its hottest. I
am told by someone that this caused the unit to run and run for hours
continuously, but my suspicion is that that was due to a lack of freon or
some other malfunction (it was a small house!).


[snip]

6. If you have high ceilings and ceiling fans, it is more energy
efficient to leave the fans running at low speed all the time to
pull down hot air and get it to circulate through the a/c system.

Only if it is you goal to cool the ceiling.


I am glad that everyone seems to agree that running all the fans and cooling
all the air in the house is a bad idea, but, believe it or not, it was
proposed by a home efficiency expert to came out to the house several years
ago. (I wasn't home at the time so I didn't question him on why he said that).

--JEff

J Jensen wrote:
"Joseph Meehan" wrote in message
...
J Jensen wrote:

1. Keeping the a/c cooling the house all day uses less electricity
than turning it off and then back on in the evening or when you
return from a vacation.

Maybe, it really depends on many many factors. It would be best
to measure the specific application.


It seems to me that it would clearly be best to let it get hot in the
house if no one is there during the day and just run the a/c hard to
cool
it down in the early evening. The only issue is that the a/c is then
doing
a lot of work when the outside temperature is still near its hottest.
I
am told by someone that this caused the unit to run and run for hours
continuously, but my suspicion is that that was due to a lack of
freon or
some other malfunction (it was a small house!).


[snip]

6. If you have high ceilings and ceiling fans, it is more energy
efficient to leave the fans running at low speed all the time to
pull down hot air and get it to circulate through the a/c system.

Only if it is you goal to cool the ceiling.


I am glad that everyone seems to agree that running all the fans and
cooling
all the air in the house is a bad idea, but, believe it or not, it was
proposed by a home efficiency expert to came out to the house several
years
ago. (I wasn't home at the time so I didn't question him on why he
said that).

--JEff

If designed properly, an AC system WILL run continuously on the hottest
(outdoor design temperature) days in order to maintain the desired
indoor (design temperature). Obviously, if the home has heated up
beyond the indoor design temperature then it will take the system a
while to cool it back down.

J Jensen wrote:
"Joseph Meehan" wrote in message
...
J Jensen wrote:

1. Keeping the a/c cooling the house all day uses less electricity
than turning it off and then back on in the evening or when you
return from a vacation.

Maybe, it really depends on many many factors. It would be best
to measure the specific application.


It seems to me that it would clearly be best to let it get hot in the
house if no one is there during the day and just run the a/c hard to
cool
it down in the early evening. The only issue is that the a/c is then
doing
a lot of work when the outside temperature is still near its hottest.
I
am told by someone that this caused the unit to run and run for hours
continuously, but my suspicion is that that was due to a lack of
freon or
some other malfunction (it was a small house!).


When the equipment is in good condition and properly sized it may run
for long times under this situation. That is normal. A larger system would
run for less time, but not be as efficient under most situations. I used a
lot of conditional statements because there are so many variables that just
measuring the results are usually the easiest way to answer the question.


[snip]

6. If you have high ceilings and ceiling fans, it is more energy
efficient to leave the fans running at low speed all the time to
pull down hot air and get it to circulate through the a/c system.

Only if it is you goal to cool the ceiling.


I am glad that everyone seems to agree that running all the fans and
cooling
all the air in the house is a bad idea, but, believe it or not, it was
proposed by a home efficiency expert to came out to the house several
years
ago. (I wasn't home at the time so I didn't question him on why he
said that).

--JEff

--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math

wrote in message
...

Easy enough to prove or disprove. Just watch your meter spin
and spray
down the AC.

Would the current go down, or the cold being delivered go up?

Bob

On Thu, 22 Jul 2004 19:38:04 +0000 (UTC), wrote:

Just watch your meter spin and spray
down the AC.


Spin?

Unless you live in the sticks, KWh meters are rapidly going digital. ;-)


--
-john
wide-open at throttle dot info

~~~~~~~~
"The first step in intelligent tinkering is to
save all the parts." - Aldo Leopold
~~~~~~~~

In article ,
~^Johnny^~ wrote:

On Thu, 22 Jul 2004 19:38:04 +0000 (UTC), wrote:

Just watch your meter spin and spray
down the AC.


Spin?

Unless you live in the sticks, KWh meters are rapidly going digital. ;-)


--
-john
wide-open at throttle dot info

~~~~~~~~
"The first step in intelligent tinkering is to
save all the parts." - Aldo Leopold
~~~~~~~~

Rapidly doesn't mean completely

All the ones I've seen spin? is there some other way of measuring
actual usage?

~^Johnny^~ wrote:

On Thu, 22 Jul 2004 19:38:04 +0000 (UTC), wrote:

Just watch your meter spin and spray
down the AC.

Spin?

Unless you live in the sticks, KWh meters are rapidly going digital. ;-)

--
-john
wide-open at throttle dot info

~~~~~~~~
"The first step in intelligent tinkering is to
save all the parts." - Aldo Leopold
~~~~~~~~

In sci.physics, Robert Morein

wrote
on Sat, 31 Jul 2004 14:32:50 -0700
:
In article ,
~^Johnny^~ wrote:

On Thu, 22 Jul 2004 19:38:04 +0000 (UTC), wrote:

Just watch your meter spin and spray
down the AC.


Spin?

Unless you live in the sticks, KWh meters are rapidly going digital. ;-)


--
-john
wide-open at throttle dot info

~~~~~~~~
"The first step in intelligent tinkering is to
save all the parts." - Aldo Leopold
~~~~~~~~

Rapidly doesn't mean completely

I would be surprised if meters are replaced just because the
readers want digital. Most likely the meters are replaced
when the building is rewired, and that's fairly rare. New
buildings, of course, will get the new meters.

I see the same problem here as with highway signs: how many
metric highway signs have you seen lately? :-) Probably
not many. I'm not sure if new highway signs are even required
to be metric -- certainly the roadwork projects here aren't
using km yet.

In any event, kWh already *is* generally metric, although
one might make a (weak) case that they should be reading
either joules, kilojoules, or megajoules. (1 kWh = 3.6 MJ.
The nearest Imperial unit might be a BTU.)

--
#191,
It's still legal to go .sigless.

TURTLE wrote:

"J Jensen" wrote in message

In regards to the recent posting I saw about running the a/c or opening the
windows, I would like to list several statements that people have made to
me about air conditioning. The location is Texas, where the temperature
is about 75 F at night and 100 F at the hottest part of the day.

About 88 average over 24 hours, and about 82 at night...

1. Keeping the a/c cooling the house all day uses less electricity than
turning it off and then back on in the evening or when you return from
a vacation.

Newton said the rate of heatflow into a building is proportional to
the indoor-outdoor temperature difference. IMO, turning the AC off
will save energy, even if only for a few minutes.

2. Running the a/c a few degrees colder at night cools the big cement slab
that the house is built on, and thus saves electricity during the day
(the a/c is set back to normal living temperature during the day).

This wouldn't help, with a constant COP that doesn't fall with a higher
indoor-outdoor temp diff. But it might, if the AC can move more heat energy
with the same electrical energy at night, given a smaller night temp diff, eg
if the COP were 3.3 at night and 3.0 during the day, or with lower off-peak
electric rates.

A 4" floorslab can store about 8 Btu/F-ft^2 with a 4-hour time constant. It
might cool from 75 to 70+(75-70)e^(-16/4) = 70.1 F after 16 hours in 70 F
air. With R20 insulation outside, RC = 20F-h/Btux8Btu/F = 160 hours, so it
might only warm from 70.1 to 94+(70.1-94)e^(-8/160) = 71.3 in 8 hours when
it's 94 F outdoors. Or less, with little air movement in the house. A slab
or a basement might be a efficient place to store coolth during a daytime
setback, since cool air falls. We might only bring coolth up into the living
space with a ceiling fan and a thermostat and an occupancy sensor as needed.

2b. If the temperature inside the house reaches 78 F at 10 AM on both days
with the a/c set colder the previous night, and also when it was just
set normally the previous night, then that proves setting it colder made
no difference.

That would say it's a small difference.

3. The a/c uses less current at night ( you measure it with an ammeter as
it is running ).

I imagine so. How much less? How does the COP depend on the temp diff?

4. The a/c uses less current if you spray the outside unit with the garden
hose and then measure it with the ammeter.

Definitely. But I'd use rainwater, with no minerals.

5. Shading the outside unit (compressor and condenser) does not reduce
electricity costs [Assume shade does not block air flow].

Shading should help, but as others say, the improvement may be small.

6. If you have high ceilings and ceiling fans, it is more energy efficient
to leave the fans running at low speed all the time to pull down hot air
and get it to circulate through the a/c system.

Maybe not, if you are seated :-) You might look up "displacement ventilation."

This is Turtle.

You got too many Question here and I will answer just the first 2 .

Answer to 1 ) If you turn a hvac system off less than 8 hours. It will cost
you more money to recool the house from a very high temperature to the lower
temperature than just moving up to a higher temperature on the thermostat.

Why on earth would you say that? Do you work for Turtle Power and Light? :-)

...If your going to be gone for 24 hours or more like on vacation. move
the thermostat to the highest setting of about 95ºF and keep the house
below 95ºF because refrigerator , Freezers, and Wine Coolers are not
designed to run in temperatures above 95ºF. Most or a lot of Refrigerator
& Freezers will stop working at 100ºF or above. If you read the
installation instruction when you bought the refrigerator or freezer it tells
you to not run the appliance in ambiant above 95ºF.

I wonder what goes wrong. It can't keep up with the cooling load? At any
rate, just putting the fridge inside a house with some thermal mass and
shaded windows and little internal heat gain may be enough. Very few places
in the US have a 24-hour daily average temp over 95, and fewer still have
average night temps above 95. A house on vacation might keep itself cool
with night air, using an exhaust fan and a differential thermostat that
turns the fan off when outdoor air is a few degrees warmer than indoor air
(to account for internal heat gain.) Brand Electronics may soon be selling
a controller like this.

Also do not run it in Ambiants of below 40ºF.

In wintertime, I unplug the barn fridge and keep the apples and carrots
from freezing with a 100 W bulb in a trouble light in a lower bin, using
an EH38 "Easy Heat thermostatically controlled device" ($10.99 at Lowe's)
that turns the light on at 38 F.

Nick

wrote in message
...
TURTLE wrote:

"J Jensen" wrote in message

In regards to the recent posting I saw about running the a/c or opening the
windows, I would like to list several statements that people have made to
me about air conditioning. The location is Texas, where the temperature
is about 75 F at night and 100 F at the hottest part of the day.

About 88 average over 24 hours, and about 82 at night...

1. Keeping the a/c cooling the house all day uses less electricity than
turning it off and then back on in the evening or when you return from
a vacation.

Newton said the rate of heatflow into a building is proportional to
the indoor-outdoor temperature difference. IMO, turning the AC off
will save energy, even if only for a few minutes.

2. Running the a/c a few degrees colder at night cools the big cement slab
that the house is built on, and thus saves electricity during the day
(the a/c is set back to normal living temperature during the day).

This wouldn't help, with a constant COP that doesn't fall with a higher
indoor-outdoor temp diff. But it might, if the AC can move more heat energy
with the same electrical energy at night, given a smaller night temp diff, eg
if the COP were 3.3 at night and 3.0 during the day, or with lower off-peak
electric rates.

A 4" floorslab can store about 8 Btu/F-ft^2 with a 4-hour time constant. It
might cool from 75 to 70+(75-70)e^(-16/4) = 70.1 F after 16 hours in 70 F
air. With R20 insulation outside, RC = 20F-h/Btux8Btu/F = 160 hours, so it
might only warm from 70.1 to 94+(70.1-94)e^(-8/160) = 71.3 in 8 hours when
it's 94 F outdoors. Or less, with little air movement in the house. A slab
or a basement might be a efficient place to store coolth during a daytime
setback, since cool air falls. We might only bring coolth up into the living
space with a ceiling fan and a thermostat and an occupancy sensor as needed.

2b. If the temperature inside the house reaches 78 F at 10 AM on both days
with the a/c set colder the previous night, and also when it was just
set normally the previous night, then that proves setting it colder
made
no difference.

That would say it's a small difference.

3. The a/c uses less current at night ( you measure it with an ammeter as
it is running ).

I imagine so. How much less? How does the COP depend on the temp diff?

4. The a/c uses less current if you spray the outside unit with the garden
hose and then measure it with the ammeter.

Definitely. But I'd use rainwater, with no minerals.

5. Shading the outside unit (compressor and condenser) does not reduce
electricity costs [Assume shade does not block air flow].

Shading should help, but as others say, the improvement may be small.

6. If you have high ceilings and ceiling fans, it is more energy efficient
to leave the fans running at low speed all the time to pull down hot air
and get it to circulate through the a/c system.

Maybe not, if you are seated :-) You might look up "displacement ventilation."

This is Turtle.

You got too many Question here and I will answer just the first 2 .

Answer to 1 ) If you turn a hvac system off less than 8 hours. It will cost
you more money to recool the house from a very high temperature to the lower
temperature than just moving up to a higher temperature on the thermostat.

Why on earth would you say that? Do you work for Turtle Power and Light? :-)


This is Turtle.

Well first I see you don't work on hvac system and know what the run times are
for a properly sized hvac system verses a cool down time for a indoor temp. of
about 105ºf down to 70ºF to 75ºF . 8 hours you may save a little but at 4 to 6
hours of down time will cost you 4 to 6 hours of run time at 105ºF to get it
back to the regular temp. inside. Also your going to waiting about 1 to 2 hour
before you can stay in there when you come home.

Now if you have oversized hvac system like 5 tons on 1,500 sq. ft. house. Your
answer would be ok, but a properly sized system would cost you big time on a 4
hour down time.

TURTLE


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TURTLE wrote:

wrote:

In regards to the recent posting I saw about running the a/c or opening
the windows, I would like to list several statements that people have
made to me about air conditioning. The location is Texas, where the
temperature is about 75 F at night and 100 F at the hottest part of
the day.

About 88 average over 24 hours, and about 82 at night...

1. Keeping the a/c cooling the house all day uses less electricity than
turning it off and then back on in the evening...

Newton said the rate of heatflow into a building is proportional to
the indoor-outdoor temperature difference. IMO, turning the AC off
will save energy, even if only for a few minutes.

2. Running the a/c a few degrees colder at night cools the big cement
slab that the house is built on...

A 4" floorslab can store about 8 Btu/F-ft^2 with a 4-hour time constant. It
might cool from 75 to 70+(75-70)e^(-16/4) = 70.1 F after 16 hours in 70 F
air. With R20 insulation outside, RC = 20F-h/Btux8Btu/F = 160 hours, so it
might only warm from 70.1 to 94+(70.1-94)e^(-8/160) = 71.3 in 8 hours when
it's 94 F outdoors. Or less, with little air movement in the house. A slab
or a basement might be a efficient place to store coolth during a daytime
setback, since cool air falls. We might only bring coolth up into the living
space with a ceiling fan and a thermostat and an occupancy sensor as needed.

This is Turtle.

...If you turn a hvac system off less than 8 hours. It will cost you
more money to recool the house from a very high temperature to the
lower temperature than just moving up to a higher temperature on the
thermostat.

Why on earth would you say that? Do you work for Turtle Power and Light? :-)

This is basic 300 year-old physics, Turtle. Turning
an AC off for even 1 minute saves cooling energy :-)

...8 hours you may save a little but at 4 to 6 hours of down time will
cost you 4 to 6 hours of run time at 105ºF to get it back to the
regular temp. inside. Also your going to waiting about 1 to 2 hour
before you can stay in there when you come home.

But the AC setback still saves energy.

Nick

Hi Harry, hope you are having a nice day

On 04-Aug-04 At About 22:09:36, Harry Conover wrote to All
Subject: more fun with air conditioning

HC From: (Harry Conover)


HC Your technician was correct. He would determine if it was operating
HC at 100% though use his gauge set for pressure measurements,
HC and the temperatures measured on the evaporator and condensor
HC coil surfaces to approximate this determination.

Not on coil surfaces but Line temps as in superheat and sub cooling.


HC So long as the freon in the system is at a sufficent level to
HC continuously provide bubble free liquid in the high pressure line, it
HC makes little difference in the operating characteristics of the air
HC conditioning system.

wrong again. in some systems you want bubbles in the liquid column such as in
a piston type metering device.

HC In fact, larger industrial systems always include a view port in the
HC liquid freon line to check for excess bubbles. Too many bubbles
HC may also reflect a need for the addition of freon to the system
HC or the installation of the system was faulty and contains trapped
HC air.

actually the sight glass is only supposed to be used only for moisture
indication. the only proper way to check is gauges using superheat and/or
subcooling depending on metering device.

HC A refrigeration gauge set is incapable of revealing this information,
HC and indicates only that the pressures in the low and high pressure
HC sides of the system are consistent with the particular variety
HC of freon in use for the measured surface termperature on both the
HC condensor and evaporator coils. It reveals very little helpful
HC information about the adequacy of the freon charge in the system.
HC Usually a pocket sized card for the freon in use (typically
HC Freon-22 in small to medium size -- 3 to 30 tons -- central A/C
HC systems).

HC On smaller home systems which lack a view port, most competent
HC refrigeration techs will, after checking the operating pressures,
HC charge the system up to the point where frost begins to appear on the
HC evaporator low pressure tube fitting. This is the point of optimal
HC cooling and presumably optimal system efficience.

wrong again. as I said before. the only way to properly charge a system is by
superheat or subcooling. this "frost back" method is sure early death for a
system.

HC I'm not a refrigeration engineer

It's quite obvious to anyone in the trade.


-= HvacTech2 =-


... Fault lies with systems not the technologies involved.

___ TagDude 0.92á+[DM]
++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++++++
spam protection measure, Please remove the 33 to send e-mail

TURTLE wrote:

The location is Texas, where the temperature is about 75 F at night
a nd 100 F at the hottest part of the day.

About 88 average over 24 hours, and about 82 at night...

If you turn a hvac system off less than 8 hours. It will cost you more
money to recool the house from a very high temperature to the lower
temperature than just moving up to a higher temperature on the thermostat.

Well first I see you don't work on hvac system and know what the run times are
for a properly sized hvac system verses a cool down time for a indoor temp. of
about 105ºf down to 70ºF to 75ºF.

How would the house get from 70 F to 105 F in 8 hours on a 100 F day?
Assuming it could (which would save lots of AC energy), and assuming
it had resonable insulation, it would have very little thermal mass,
so the AC could cool it back to 70 F very quickly.

Now if you have oversized hvac system like 5 tons on 1,500 sq. ft. house.
Your answer would be ok, but a properly sized system would cost you big
time on a 4 hour down time.

The setback would still save energy, unless the AC becomes a lot less
efficient (has a lower COP) with a higher indoor-outdoor temp diff.

A 1500 ft^2 house with 300 Btu/h-F of thermal conductance could warm from
70 F to 105 F in 8 hours on a 110 F day if RC = -8/(ln((105-110)/(70-105)
= 4.1 hours, which makes C = 4.1x300 = 1200 Btu/F, not much. A 36K Btu/h
AC might cool the house from 105 to 70 F in (105-70)1200/36K = 1.2 hours.
Keeping the house 70 F for 8 hours would require 8(110-70)300/36K = 2.7
hours of AC operation... 1.2/2.7 is a 55% energy savings.

Nick

(J Jensen) wrote in message om...
"~KJPRO~" KJPRO @ STARBAND.NET wrote in message ...
"J Jensen" wrote in message
om...

7. It isn't worthwhile to check on the amount of Freon (or whatever) that
is
in the system -- all that matters is measuring the temperature of the
cold air coming out (say 62 F) and the outside temperature or maybe the
attic temperature.
--Jeff

This has to be some of the purist BS I have read lately.

~kjpro~

This was what an a/c technician told me when I called him out to the
house
with the specific request to check if any Freon had leaked out of the
system over the years, or if it was still operating at 100%. He would
not do it,
although he did check some other things. On the bright side, he did
encourage
me to sign up for yearly maintenance by his company...
--Jeff

Your technician was correct. He would determine if it was operating at
100% though use his gauge set for pressure measurements, and the
temperatures measured on the evaporator and condensor coil surfaces to
approximate this determination. If these are within the prescribed
ranges, there likely is little need to top off the refrigerant charge
in the system.

So long as the freon in the system is at a sufficent level to
continuously provide bubble free liquid in the high pressure line, it
makes little difference in the operating characteristics of the air
conditioning system.

In fact, larger industrial systems always include a view port in the
liquid freon line to check for excess bubbles. Too many bubbles may
also reflect a need for the addition of freon to the system or the
installation of the system was faulty and contains trapped air.

A refrigeration gauge set is incapable of revealing this information,
and indicates only that the pressures in the low and high pressure
sides of the system are consistent with the particular variety of
freon in use for the measured surface termperature on both the
condensor and evaporator coils. It reveals very little helpful
information about the adequacy of the freon charge in the system.
Usually a pocket sized card for the freon in use (typically Freon-22
in small to medium size -- 3 to 30 tons -- central A/C systems).

On smaller home systems which lack a view port, most competent
refrigeration techs will, after checking the operating pressures,
charge the system up to the point where frost begins to appear on the
evaporator low pressure tube fitting. This is the point of optimal
cooling and presumably optimal system efficience.

I'm not a refrigeration engineer (although I am a physicist/engineer),
but over the years (at least 30) I've maintained or installed some
reasonable large refrigeration systems and air conditioners (some of
which were two-stage special purpose systems capable of reaching test
chamber temperature of below -80-degrees F), sever 30-60 ton air
conditioning systems, and installed 3 central systems in homes that
I've owned.

During these years, out of necessity I learned how to replace
compressors, braze joints, pull a vacuum and "dry" the systes, employ
leak detectors and repair leaks, all basic to the HVAC trade,
consequently I'm pretty sure of the correctness of the info I post,
and I would challenge any A/C or HVAC tech to specifically cite and
correct any error. In fact, over 30 years I never had to employ an
HVAC tech to correct any of my work. (In fact, it was the inadequance
of the HVAC techs that I encountered that first cause me to get my
hands dirty!)

Harry C.

p.s., Never SMOKE when you're working with freon. Any competent
refrigeration engineer can explain to you why this precaution is
needed, but your average HVAC tech is little more than a glorified
plumber and likely hasn't a clue (unless of course his supervisor has
informed him)!

"CBHVAC" wrote in message ...
"~KJPRO~" KJPRO @ STARBAND.NET wrote in message
...
"J Jensen" wrote in message
om...

7. It isn't worthwhile to check on the amount of Freon (or whatever)
that
is
in the system -- all that matters is measuring the temperature of the
cold air coming out (say 62 F) and the outside temperature or maybe
the
attic temperature.
--Jeff

This has to be some of the purist BS I have read lately.

~kjpro~


Dave probably sent that information to him....you know Dave....full of ****
and thinks hes correct....
But...But...its beercan cold doncha know?

Damn, you trade guys are good on arm waving pontification, but short
on details.

Could it possibly be that all you know about the subject is what you
were told in trade-schools, and not by a competetent, degreed
engineer?

Why the reluctance to attempt and correct the specific errors you
found?
Lemme guess!

Harry C.

wrote in message
...
TURTLE wrote:

The location is Texas, where the temperature is about 75 F at night
a nd 100 F at the hottest part of the day.

About 88 average over 24 hours, and about 82 at night...

If you turn a hvac system off less than 8 hours. It will cost you more
money to recool the house from a very high temperature to the lower
temperature than just moving up to a higher temperature on the thermostat.

Well first I see you don't work on hvac system and know what the run times
are
for a properly sized hvac system verses a cool down time for a indoor temp.
of
about 105ºf down to 70ºF to 75ºF.

How would the house get from 70 F to 105 F in 8 hours on a 100 F day?
Assuming it could (which would save lots of AC energy), and assuming
it had resonable insulation, it would have very little thermal mass,
so the AC could cool it back to 70 F very quickly.

Now if you have oversized hvac system like 5 tons on 1,500 sq. ft. house.
Your answer would be ok, but a properly sized system would cost you big
time on a 4 hour down time.

The setback would still save energy, unless the AC becomes a lot less
efficient (has a lower COP) with a higher indoor-outdoor temp diff.

A 1500 ft^2 house with 300 Btu/h-F of thermal conductance could warm from
70 F to 105 F in 8 hours on a 110 F day if RC = -8/(ln((105-110)/(70-105)
= 4.1 hours, which makes C = 4.1x300 = 1200 Btu/F, not much. A 36K Btu/h
AC might cool the house from 105 to 70 F in (105-70)1200/36K = 1.2 hours.
Keeping the house 70 F for 8 hours would require 8(110-70)300/36K = 2.7
hours of AC operation... 1.2/2.7 is a 55% energy savings.

Nick


This is Turtle.

This all looks good on paper but in the real world with a over sized hvac system
as you say a 3 ton on 1,200 sq. ft. house. A properly sized hvac system will
have a 1.5 or maybe 2 ton at most on the 1,200 sq, ft. house. 3 ton 36K btu
rating system when properly sized will never be on a 1,200 sq. ft. house.

Now you say the 3 ton 36K btu rating is used in your calculation here. All hvac
system are rated at 95ºOutdoor temperature and when the ambiant goes above the
95ºF level your BTU rating falls a good bit to maybe 31K or 33K btu's at 105ºF
outdoor temperature.

Now with all your calculations that the hvac system is perfectly tuned and all
coil are clean and serviced regularly. There was some research done in
California on systems being properly charged with freon, Clean coils, and
running at what they should be putting out. More than half was not operating at
what they should have been and was not putting out the BTU rating stated by the
manufactor. A lot of the system checked was running at about 70% of what they
should be putting out.

Now to you have a big ass 3 ton hvac system on 1,200 sq. ft. house. I personally
have a 2,250 sq. ft. home and cool it with a 3.5 ton 14 seer system. I have let
my cooling system be off for being gone for about 8 to 10 hours and on a 105ºF
day. My house inside went up to about 98ºf inside and when i turn on my
perfectly tuned system on. It took 3.5 hours to pull the house back to 72 ºF.
The first 2 hours you can not stay in there for it being too hot. Now if i would
install a over sized hvac system and have a 5 ton or so. It would not be but a
hour or so to get back down to 72ºF inside but I would have to deal with high
humitity in the house and will have to run my system at lower temperature than
72ºF or maybe down to 65ºF to get the water vapor out of the house. With a 90%RH
a house at 60ºF will feel very warm inside. With a 10%RH and 95ºF inside the
house will feel very cold. If you don't properly size the system you will have a
nitemare with %RH to deal with.

Now here is one that will never fit with your calculation on the cooling of the
house. All properly designed and sized hvac systems are designed and installed
to have a 90% run time which are designed to be run all the time and not turn
them off. On a properly sized / designed hvac system if you started at 100ºF
inside temperature could easily have a 8 hour run time to get it cool enough to
be called cool enough to live in it. So if it is designed correctly your theory
is out the window. If you have a oversized system you could maybe somewhere near
the recovery time needed to get the house back down in temperature, but with no
humitity removial like it should be.

Now you had said a house inside with no air on will not go up to 100ºF+ with in
8 hours -- out in the direct sun light, 105ºF outdoors, Roof area temperatures
running about 190ºF with the direct sun light on it, house with the average R-19
rating on it, and most all houses are not air tight. In 8 hour, I would be
surprized to not see it 100ºF.

Now one last point here. Your calculation will be for the air inside the house
and not for the metal , cloth couches , Rugs / carpet, and furniture which will
hold and release heat over the next 4 to 8 hours and you will have to remove
this extra heat held by these items as the next 8 hours of operation time goes.

Nick i live in the real world and you must live in the Paper world.

TURTLE


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TURTLE wrote:

If you turn a hvac system off less than 8 hours. It will cost you more
money to recool the house from a very high temperature to the lower
temperature than just moving up to a higher temperature on the thermostat.

Newton died in 1727. These days, few people argue with his Law of Cooling.

How would the house get from 70 F to 105 F in 8 hours on a 100 F day?
Assuming it could (which would save lots of AC energy), and assuming
it had reasonable insulation, it would have very little thermal mass,
so the AC could cool it back to 70 F very quickly.

Now if you have oversized hvac system like 5 tons on 1,500 sq. ft. house.
Your answer would be ok, but a properly sized system would cost you big
time on a 4 hour down time.

The setback would still save energy, unless the AC becomes a lot less
efficient (has a lower COP) with a higher indoor-outdoor temp diff.

A 1500 ft^2 house with 300 Btu/h-F of thermal conductance could warm from
70 F to 105 F in 8 hours on a 110 F day if RC = -8/(ln((105-110)/(70-105)
= 4.1 hours, which makes C = 4.1x300 = 1200 Btu/F, not much. A 36K Btu/h
AC might cool the house from 105 to 70 F in (105-70)1200/36K = 1.2 hours.
Keeping the house 70 F for 8 hours would require 8(110-70)300/36K = 2.7
hours of AC operation... 1.2/2.7 is a 55% energy savings.

This all looks good on paper but in the real world with a over sized hvac
system as you say a 3 ton on 1,200 sq. ft. house. A properly sized hvac
system will have a 1.5 or maybe 2 ton at most on the 1,200 sq, ft. house.

OK. Let's try 1.5... An 18K Btu/h AC might cool the house from 105 to 70 F
in (105-70)1200/18K = 2.4 hours. Keeping the house 70 F for 8 hours would
require 8(110-70)300/18K = 5.4 hours of AC operation... 2.4/5.4 is a 55%
energy savings, not unlike the previous 55% savings.

Now you say the 3 ton 36K btu rating is used in your calculation here.
All hvac system are rated at 95ºOutdoor temperature and when the
ambiant goes above the 95ºF level your BTU rating falls a good bit
to maybe 31K or 33K btu's at 105ºF outdoor temperature.

Good info. While using the same electrical power? What happens to the COP?

How is latent heat rated? I sometimes wonder if a house would cool quicker
after a setback if the owner sprayed some of the inside surfaces with water.
The cold side of the AC would transfer heat better with condensation than
without, and the house surfaces would cool more quickly with evaporation
than without, and 400 cfm of moist return air carries a lot more heat than
dry air. The water wouldn't add to the net cooling load, since it requires
heat to evaporate. It might act as a catalyst, speeding heat transfer.

Now with all your calculations that the hvac system is perfectly tuned and all
coil are clean and serviced regularly...

Of course. By certified HVAC criminals. ("That'll be $8764.32, Mr. Sneedley.
I knocked off $10 for the blowjob.")

There was some research done in California on systems being properly charged
with freon, Clean coils, and running at what they should be putting out. More
than half was not operating at what they should have been and was not putting
out the BTU rating stated by the manufactor. A lot of the system checked was
running at about 70% of what they should be putting out.

This criminal negligence may not have much to do with
whether AC setbacks save energy.

...I personally have a 2,250 sq. ft. home and cool it with a 3.5 ton
14 seer system.

Well-maintained, no doubt.

I have let my cooling system be off for being gone for about 8 to 10 hours
and on a 105ºF day. My house inside went up to about 98ºf inside and
when i turn on my perfectly tuned system on. It took 3.5 hours to pull the
house back to 72 ºF.

Maybe you have some unshaded windows and lots of insulation
and lots of pet rabbits or PCs.

Let's review your claim:

If you turn a hvac system off less than 8 hours. It will cost you more
money to recool the house from a very high temperature to the lower
temperature than just moving up to a higher temperature on the thermostat.

You mentioned money, but you didn't mention time.

The first 2 hours you can not stay in there for it being too hot.

Maybe you need a timer to precool the house before you get home.

Now if i would install a over sized hvac system and have a 5 ton or so. It
would not be but a hour or so to get back down to 72ºF inside but I would
have to deal with high humitity in the house and will have to run my system
at lower temperature than 72ºF or maybe down to 65ºF to get the water
vapor out of the house. With a 90%RH a house at 60ºF will feel very warm
inside. With a 10%RH and 95ºF inside the house will feel very cold...

The ASHRAE 55-2004 comfort standard says most people would find 90% RH
at 60 F "very cold" (Y = -3.2, with 99.6% of people dissatisfied) and
10% RH at 95 F "very warm" (Y = +2.8, with a 97.4% PPD.) Maybe you need
a comfortstat vs thermostat. It might automatically lower the air temp
to compensate for a higher RH or Mean Radiant (wall) Temperature.

Now here is one that will never fit with your calculation on the cooling
of the house. All properly designed and sized hvac systems are designed
and installed to have a 90% run time which are designed to be run all
the time and not turn them off.

At the local summer design temp, which occurs 1% of the time?

On a properly sized / designed hvac system if you started at 100ºF
inside temperature could easily have a 8 hour run time to get it cool
enough to be called cool enough to live in it.

A house like this would likely have lots of thermal mass, so it seems
unlikely to get to 100 F during an 8 hour setback...

Now you had said a house inside with no air on will not go up to 100ºF+
with in 8 hours -- out in the direct sun light, 105ºF outdoors, Roof
area temperatures running about 190ºF with the direct sun light on it,
house with the average R-19 rating on it, and most all houses are not air
tight. In 8 hour, I would be surprized to not see it 100ºF.

With little mass, and some unshaded windows and internal heat gains. If the
owner and builder weren't crazy, the house and roof would be white, in a hot
climate, with a radiant barrier under the roof, eg Norbord's foil-faced OSB.

Now one last point here. Your calculation will be for the air inside the
house and not for the metal , cloth couches , Rugs / carpet, and furniture
which will hold and release heat over the next 4 to 8 hours and you will
have to remove this extra heat held by these items as the next 8 hours
of operation time goes.

No. My calc included the entire thermal mass of the house. A 1500 ft^2 house
has 12K ft^3 of air that weighs about 900 pounds. Its specific heat is about
0.24 Btu/F-lb, so the air only has 216 Btu/F of capacitance... 3000 ft^2 of
1/2" drywall would add another 1500 Btu/F of capacitance, and so on.

Nick

In article ,
wrote:

1/2" drywall would add another 1500 Btu/F of capacitance, and so on.

Nick

Nick if you packed more sand in your ass you wouldn't fall over as much.

Just how often do you call criminals over so you get your reaming?

bill wrote:

Nick if you packed more sand in your ass you wouldn't fall over as much.

Just how often do you call criminals over so you get your reaming?

Dear Bill,

I am not indifferent to the depravity of your cravings.

May God have mercy on your soul.

Nick

There seems to have developed an ant-intellectual movement on the hvac
newsgroups lately.

It's like the dummy's want revenge for something, poor schooling, tired of
feeling stupid, whatever, but it's a shameful thing this, all the dummy's
united behind PJM who himself doesn't seem to be ageing very well, anyway,
the poor soul.

wrote in message
...
bill wrote:

Nick if you packed more sand in your ass you wouldn't fall over as much.

Just how often do you call criminals over so you get your reaming?

Dear Bill,

I am not indifferent to the depravity of your cravings.

May God have mercy on your soul.

Nick

Here you go Nicki_Doo... Complements from S.A. village drunk! Good..O!

Marc O'Brien wrote:

There seems to have developed an ant-intellectual movement on the hvac
newsgroups lately.

It's like the dummy's want revenge for something, poor schooling, tired of
feeling stupid, whatever, but it's a shameful thing this, all the dummy's
united behind PJM who himself doesn't seem to be ageing very well, anyway,
the poor soul.

wrote in message
...

bill wrote:


Nick if you packed more sand in your ass you wouldn't fall over as much.

Just how often do you call criminals over so you get your reaming?

Dear Bill,

I am not indifferent to the depravity of your cravings.

May God have mercy on your soul.

Nick

Don, perhaps I could help you, boy. Maybe I could teach you something
slightly technical, something that you could then make your own kind of
original remarks on. Perhaps that'd make you feel a little better, being
able to participate in these technical forums appropriately applying a
little newly learned technical thought.

We should try, it might be quite therapeutic, you wouldn't feel so out of
place here needing to side with idiots just because they have numbers and
are so willing to accept you as one of their own.

"Don Ocean" wrote in message
...
Here you go Nicki_Doo... Complements from S.A. village drunk! Good..O!

Marc O'Brien wrote:

There seems to have developed an ant-intellectual movement on the hvac
newsgroups lately.

It's like the dummy's want revenge for something, poor schooling, tired
of
feeling stupid, whatever, but it's a shameful thing this, all the
dummy's
united behind PJM who himself doesn't seem to be ageing very well,
anyway,
the poor soul.

wrote in message
...

bill wrote:


Nick if you packed more sand in your ass you wouldn't fall over as
much.

Just how often do you call criminals over so you get your reaming?

Dear Bill,

I am not indifferent to the depravity of your cravings.

May God have mercy on your soul.

Nick

Marc O'Brien wrote:

There seems to have developed an ant-intellectual movement on the hvac
newsgroups lately.

Ummmm? Please point out the intellectual that the anti-intellectual
movement is against.. It certainly isn't Nicki! You do know that
Villanova isn't exactly high on the ladder of our field. And Nicki's
so-called education is not in our field... He is an arts major
working at a Liberal arts college. Might even be the Janitor!
He is a hobbyist. Hasn't the slightest idea of what it takes to
run a logical everyday business. Depends on others for a paycheck.
The educational association to which he belongs is extremely social-
istic or downright communistic. While some of our working campatriots
here may not have Engineering or higher degrees.. they do have a working
knowledge of what it takes to make a living with hard work and dealing
with the general public. He likes to call us HVAC criminals.. Well
folks.. You cannot be licensed here if your a felon. But you can teach
or whatever at Villanova with a Felony conviction. Our people are all
insured, Bonded, and licensed.. Licensed means passing rigorous tests
on technicals and codes after a solid education in this field. All of
our work must have paid for plan certification and when work is done
...have in line inspections, before final inspections. We here are career
individuals while people like Nicki are just hobbyists. We deal everyday
and many nights and Holidays etc. with real life environmental problems
plus ongoing useable research for the future. Guys like Nicki have no
responsibility tagged to their actions ...We do... And some of our very
talented people answer questions very specifically in alt.home.repair.
So when some one is sent there.. from one of our groups.. it is not an
insult and does keep our groups from being muddied up with redundant
questions. As for Paul...Well if you don't like him...Lump it!!
If you have appreciated this missive...Please send Marc O'Brien a cheap
bottle of Yellow-Tail wine. It would be a mercy to keep him from
getting the Delirium Tremens again. ;-p


It's like the dummy's want revenge for something, poor schooling, tired of
feeling stupid, whatever, but it's a shameful thing this, all the dummy's
united behind PJM who himself doesn't seem to be ageing very well, anyway,
the poor soul.

wrote in message
...

bill wrote:


Nick if you packed more sand in your ass you wouldn't fall over as much.

Just how often do you call criminals over so you get your reaming?

Dear Bill,

I am not indifferent to the depravity of your cravings.

May God have mercy on your soul.

Nick