ViperCertified Home Inspector
join:2012-03-22
Toronto
1 edit | reply to chmod
Re: Another a/c issue. I have been doing home inspection and thermal imaging for insulation related issues for a long time.
A/C's main purpose is not to cool the air but to remove the humidity from the warm air inside the building. I cant really tell what could be the problem with your system there. But it should not be running continuously, it should cycle.
Right now, in Toronto its about 32 degrees which is approx 89 F and my thermostats is holding at 77 degrees and I feel very comfortable in my house (actually more than comfortable). And the reason is my system is doing good in terms of removing humidity from the house.
Just because you are setting your stat at 73F does not mean that you will be feel comfortable.
Not sure what your long terms plans are with the house but I always recommend an infrared scan of the house once every 5 years.
See the infrared images of the house that I did - air leak from the recessed light on the 2nd floor.
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Certified Home Inspector
Certified Level 1 Thermographer |
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 cdruGo ColtsPremium,MVM
join:2003-05-14
Fort Wayne, IN
kudos:7 | said by Viper:But it should not be running continuously, it should cycle. It's been mid 90s where the OP lives the last several days which is approaching the extreme highs (95-103) that area sees. Normal highs are mid 80s. A properly sized system will run almost continuously on the hottest days of the year.
Given that it's several years old, I'm going to bet that it's not operating at it's absolute peak efficiency it was designed for when it was brand new. If it was slightly low on refrigerant, had dirty coils, or duct work went through hot unconditioned space, performance would suffer.
As Jack said above, it may be operating at more or less what it's designed to run at. |
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ViperCertified Home Inspector
join:2012-03-22
Toronto | said by cdru:said by Viper:But it should not be running continuously, it should cycle. It's been mid 90s where the OP lives the last several days which is approaching the extreme highs (95-103) that area sees. Normal highs are mid 80s. A properly sized system will run almost continuously on the hottest days of the year. Given that it's several years old, I'm going to bet that it's not operating at it's absolute peak efficiency it was designed for when it was brand new. If it was slightly low on refrigerant, had dirty coils, or duct work went through hot unconditioned space, performance would suffer. As Jack said above, it may be operating at more or less what it's designed to run at. I am not too sure if that is true.
There is another thread on this forum about someone who had question about his AC system. The problem there is very simple but people have written pages and pages of argument and are trying to prove each other wrong.
I have been trained to simplify things and look at stuff from a practical stand point.
House inside temp is 85F, you turn on the system and set the stat to 75F (e.g). Stat calls for cool air, system kicks in and it continuously runs until it reaches 75F. At this point the system shuts down (i mean stop operating). When the temp raises because of cool air loss (for any reason), the temp of the house rises and stat calls for cool air again and system turn on. The cycles repeats itself, so I dont understand why you said that the system should or does run continuously.
As far as the age of the system, my AC unit is 12 years old and still works like a charm. It cycles and my electric (hydro in Canada) bill is very very reasonable.
The OP's system is 5 year old so it should be still very efficient.
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Certified Home Inspector
Certified Level 1 Thermographer |
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| said by Viper:House inside temp is 85F, you turn on the system and set the stat to 75F (e.g). Stat calls for cool air, system kicks in and it continuously runs until it reaches 75F. At this point the system shuts down (i mean stop operating). I think this is where the confusion is. cdru's point is that on the hottest days of the year, a properly sized system will never reach the set point (75F in your example) and thus not shut off/cycle or barely hit it and only cycle minimally. This is because if the system was big enough to cycle normally on the hottest days of the year, it would short cycle on the milder days and not dehumidify properly.
/M |
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ViperCertified Home Inspector
join:2012-03-22
Toronto | said by mackey:said by Viper:House inside temp is 85F, you turn on the system and set the stat to 75F (e.g). Stat calls for cool air, system kicks in and it continuously runs until it reaches 75F. At this point the system shuts down (i mean stop operating). I think this is where the confusion is. cdru's point is that on the hottest days of the year, a properly sized system will never reach the set point (75F in your example) and thus not shut off/cycle or barely hit it and only cycle minimally. This is because if the system was big enough to cycle normally on the hottest days of the year, it would short cycle on the milder days and not dehumidify properly. /M Ok - my question is:
Why "on the hottest days of the year, a properly sized system will never reach the set point and thus not shut off/cycle or barely hit it and only cycle minimally"?
A properly sized system is supposed to cycle unless you are constantly leaking air to the outdoors from your house as shown in my attached pictures above.
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Certified Home Inspector
Certified Level 1 Thermographer |
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| said by Viper:Ok - my question is:
Why "on the hottest days of the year, a properly sized system will never reach the set point and thus not shut off/cycle or barely hit it and only cycle minimally"?
A properly sized system is supposed to cycle unless you are constantly leaking air to the outdoors from your house as shown in my attached pictures above.
said by mackey:This is because if the system was big enough to cycle normally on the hottest days of the year, it would short cycle on the milder days and not dehumidify properly. /M |
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ViperCertified Home Inspector
join:2012-03-22
Toronto | said by mackey:said by Viper:Ok - my question is:
Why "on the hottest days of the year, a properly sized system will never reach the set point and thus not shut off/cycle or barely hit it and only cycle minimally"?
A properly sized system is supposed to cycle unless you are constantly leaking air to the outdoors from your house as shown in my attached pictures above.
said by mackey:This is because if the system was big enough to cycle normally on the hottest days of the year, it would short cycle on the milder days and not dehumidify properly. /M Ok then you should upgrade your system to one of those system where the stat controls the unit based on the humidity in the house and not 'entirely' based on the ambient temperature of the house.
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Certified Home Inspector
Certified Level 1 Thermographer |
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 Jack_in_VAPremium
join:2007-11-26
Mathews, VA
kudos:1 | reply to mackey
said by mackey:said by Viper:House inside temp is 85F, you turn on the system and set the stat to 75F (e.g). Stat calls for cool air, system kicks in and it continuously runs until it reaches 75F. At this point the system shuts down (i mean stop operating). I think this is where the confusion is. cdru's point is that on the hottest days of the year, a properly sized system will never reach the set point (75F in your example) and thus not shut off/cycle or barely hit it and only cycle minimally. This is because if the system was big enough to cycle normally on the hottest days of the year, it would short cycle on the milder days and not dehumidify properly. /M +1 you understand it. The OP is trying to reach a set point of 73 which makes it worse. |
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cdruGo ColtsPremium,MVM
join:2003-05-14
Fort Wayne, IN
kudos:7 | reply to Viper
said by Viper:Why "on the hottest days of the year, a properly sized system will never reach the set point and thus not shut off/cycle or barely hit it and only cycle minimally"? The most efficient system is the one who's cooling capacity just slightly exceeds the maximum required cooling load.
If the system is sized too small, it may be able to keep up on warm days, but not on the hottest days. If the system is sized too large, it will quickly cool some air, but won't dehumidify it. It can also result in hot and cold pockets throughout the house where air near the return and vents gets cooled quicker then what areas that are outside the natural flow of air remain hotter. Plus you're paying for larger capacity then what you ultimately need. |
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arobertiSarcastic? Me? NeverPremium
join:2000-12-21
Norwalk, CT | reply to Viper
said by Viper:Ok then you should upgrade your system to one of those system where the stat controls the unit based on the humidity in the house and not 'entirely' based on the ambient temperature of the house.
But then you'll just end up over-shooting your temperature setpoint. Why would you want a system so oversized that it couldn't control the humidity correctly to begin with?
Your argument seems to be that outside temperature shouldn't affect how well the system cools? I've never seen a house that was 100% air-tight -- and even if it were, that would present a whole new set of challenges... |
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scross
join:2002-09-13
Cordova, TN | reply to Viper
Concerning that recessed light fixture, aren't these supposed to be left relatively uninsulated, in order to allow the fixture to dissipate its own heat? Everything I've read says to allow several inches of clearance between these fixtures and any insulation, but it looks like maybe they got a bit carried away here. |
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ViperCertified Home Inspector
join:2012-03-22
Toronto | said by scross:Concerning that recessed light fixture, aren't these supposed to be left relatively uninsulated, in order to allow the fixture to dissipate its own heat? Everything I've read says to allow several inches of clearance between these fixtures and any insulation, but it looks like maybe they got a bit carried away here.
Yes, they should have 3 inches of clearance from insulation or any combustible material.
OR
They can be in contact with insulation but these fixtures should have double shell and should be IC rated.
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Certified Home Inspector
Certified Level 1 Thermographer |
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iknowPremium
join:2012-03-25 | reply to cdru
said by cdru:said by Viper:Why "on the hottest days of the year, a properly sized system will never reach the set point and thus not shut off/cycle or barely hit it and only cycle minimally"? The most efficient system is the one who's cooling capacity just slightly exceeds the maximum required cooling load. If the system is sized too small, it may be able to keep up on warm days, but not on the hottest days. If the system is sized too large, it will quickly cool some air, but won't dehumidify it. It can also result in hot and cold pockets throughout the house where air near the return and vents gets cooled quicker then what areas that are outside the natural flow of air remain hotter. Plus you're paying for larger capacity then what you ultimately need. that's a bit modified depending on the area you live, in las Vegas, and similar areas, you DON'T want to remove ANY humidity, so you can size it for the max heatload. also, in most areas, a 2 speed compressor, a variable speed blower, and a thermostatic expansion valve allows the AC to compensate for widely varying temperatures and humidity, so can be sized larger on max cooling setting. |
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It was 109* F here yesterday.
My upstairs unit could only keep it down to 76.
Texas!
Dave |
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iknowPremium
join:2012-03-25 | said by workablob:It was 109* F here yesterday.
My upstairs unit could only keep it down to 76.
Texas!
Dave
R50 in the attic, and a radiant barrier is the answer. unless you want to add a window AC for the hottest days. the expensive way is to change out your central AC for one with a thermostatic expansion valve, a variable speed blower, and at least a 2 speed compressor, a stepper motor compressor would be ideal. and have the unit oversized to handle those hot days. |
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 chambercPremium
join:2008-08-05
Irving, TX
 ·Time Warner Cable
| said by iknow:said by workablob:It was 109* F here yesterday.
My upstairs unit could only keep it down to 76.
Texas!
Dave
R50 in the attic, and a radiant barrier is the answer. unless you want to add a window AC for the hottest days. the expensive way is to change out your central AC for one with a thermostatic expansion valve, a variable speed blower, and at least a 2 speed compressor, a stepper motor compressor would be ideal. and have the unit oversized to handle those hot days. 109 here in Irving too. Our upstairs stays 74 and downstairs 72 during even those days. |
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 SwedishRiderRider on the StormPremium
join:2006-01-11
Connecticut
kudos:1 | reply to aroberti
said by aroberti:I've never seen a house that was 100% air-tight -- and even if it were, that would present a whole new set of challenges...
When building his house, a neighbor down the street went with Icynene insulation, and it's about as air tight as you can get without going closed cell. The downside is that it's expensive (about 3.5X the cost of fiberglass) and you are supposed to install air handlers to exchange the outside air because the home is sealed so well (or so said the salesman when quoting me a price).
I decided to go with traditional fiberglass with 2x6 exterior walls and a higher total R-value over the second floor. I just didn't want to get into additional equipment and I had heard of some buildings with interior problems because the house was sealed too well (mold, sickness, etc.) And I just thought it was simply too expensive. I don't think my heating and cooling bills are ridiculous either... 2x6 with vapor barrier has been great at maintaining interior heat and cooling.
My neighbor does like Icynene though... he recommended it and said he would use it again if he built again. |
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