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more fun with air conditioning
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 |
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#2
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more fun with air conditioning
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. |
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#3
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more fun with air conditioning
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 |
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#4
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more fun with air conditioning
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 ~~~~~~~~ |
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#5
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more fun with air conditioning
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 |
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#6
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more fun with air conditioning
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. |
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#7
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more fun with air conditioning
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 ~~~~~~~~ |
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#8
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more fun with air conditioning
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. |
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#9
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more fun with air conditioning
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 |
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#10
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more fun with air conditioning
"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 |
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#11
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more fun with air conditioning
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. |
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#12
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more fun with air conditioning
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 |
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#13
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more fun with air conditioning
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.. |
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#14
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more fun with air conditioning
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. |
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#15
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more fun with air conditioning
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 |
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#16
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more fun with air conditioning
"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 |
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#17
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more fun with air conditioning
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. |
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#18
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more fun with air conditioning
"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 |
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more fun with air conditioning
"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] |
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#20
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more fun with air conditioning
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 |
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more fun with air conditioning
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 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.732 / Virus Database: 486 - Release Date: 7/30/2004 |
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more fun with air conditioning
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 |
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more fun with air conditioning
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 |
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more fun with air conditioning
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 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.732 / Virus Database: 486 - Release Date: 7/29/2004 |
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more fun with air conditioning
"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~ |
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more fun with air conditioning
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more fun with air conditioning
"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~ |
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more fun with air conditioning
"~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? |
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more fun with air conditioning
"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. |
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more fun with air conditioning
"~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 |
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more fun with air conditioning
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more fun with air conditioning
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