 chmodPremium
join:2000-12-12
Lockport, IL | Another a/c issue. Roughly 1800sqft with basement I think. I know insulation is an issue on the first floor as its lath and plaster. Second floor is drywall with insulation with batt insulation over top in the attic. Nothing over top of the first floor attic space (just the kitchen). Central air/forced air heat throughout. Two 10" round to the second floor which is quite small, I think the master is 16x16 and the other room is 8x10 not including the hallway. One return at the top of the second floor at the top of the stairs on the wall, the other on the bottom of the stairs on an adjoining wall between kitchen and living room. A/c is an american standard I'm not sure of the tonage about 5years old, the inside unit is a goodman about 4years old. When it gets about 90+ with decent humidity my ac runs all day until it starts to cool off at night (I keep it at 73) it wil sometimes reach 76. I seem to get much better air flow in some vents vs others. Any idea where to start diagnosis?
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Some people are like Slinkies. Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs. |
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 Jack_in_VAPremium
join:2007-11-26
Mathews, VA
kudos:1 | said by chmod: When it gets about 90+ with decent humidity my ac runs all day until it starts to cool off at night (I keep it at 73) it wil sometimes reach 76. I seem to get much better air flow in some vents vs others. Any idea where to start diagnosis?
The average AC installation is sized for a 15 degree differential from outside air temperature.
90 - 15 = 75
My guess would be Your units are probably doing all they are capable of doing. You are trying for 73 deg but can't reach it until the heat load goes down at night. |
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ViperCertified Home Inspector
join:2012-03-22
Toronto
1 edit | reply to chmod
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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 MsradellP.E.Premium
join:2008-12-25
Louisville, KY
 ·AT&T U-Verse
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An air conditioner should be able to return here about 20° cooler than the air it takes in, not than the outside temperature. If you don't think it's true just go to Las Vegas in the heat of the summer. It's 110°+ outside yet inside is extremely cool 70° in many cases.
You need to check the temperature of the air and a return and compare it to the temperature of the air coming into the house from the unit. You should see at least 15° and more likely 20° temperature differential between the to. While the outside temperature has some affect it's not huge. If you have the correct temperature differential look elsewhere for your problems, I'd certainly start with insulation and air leaks! It could also be a sizing issue for the AC unit. Are you sure the outside unit is matched correctly for the inside unit? Being different suppliers would lead me to believe they may not be. |
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 alkizmo
join:2007-06-25
Pierrefonds, QC
kudos:1 | reply to chmod
Have you cleaned the heatsink of your A/C? Considering the A/C seems to have been installed before you bought the place, I'm betting you don't know last time someone did some cleaning.
If the A/C can't cool down its coils on the outdoor unit because of grime blocking air flow in the heatsink fins, then it won't perform very much.
After I cleaned up mine, it manages to drop the house temperature by 15F in less than 30 minutes. Before it would take it hours, if even it reached it. |
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Jack_in_VAPremium
join:2007-11-26
Mathews, VA
kudos:1 | reply to Msradell
= Msradell  An air conditioner should be able to return here about 20° cooler than the air it takes in, not than the outside temperature.
If you don't think it's true just go to Las Vegas in the heat of the summer. It's 110°+ outside yet inside is extremely cool
quote:
Absorption chillers use heat to drive the refrigeration cycle, they produce chilled water while consuming just a small amount of electricity to run the pumps on the unit. Absorption chillers generally use steam or hot water to drive the lithium bromide refrigeration cycle but can also use other heat sources.
Most likely Direct-fired absorption chillers that offer customers a choice in how they consume energy to produce chilled water. The chiller uses natural gas or other fuels to fire the absorption refrigeration cycle.
A direct-fired absorption chiller can be used as a primary component for hybrid plants or other applications where electrical demand and consumption are expensive or in short supply.
The efficiency of the double-effect cycle used in these chillers makes them competitive with electric chillers in many regions of the world where electricity prices have risen dramatically over the last decade. All sizes also can act as a chiller/heater to supply chilled or hot water for conditioning the building during the summer or winter. |
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 cdruGo ColtsPremium,MVM
join:2003-05-14
Fort Wayne, IN
kudos:7 | reply to Viper
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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| reply to Msradell
Here in Vegas most houses use freon based mechanical air with supplemental evaporative cooling (swamp cooler). Electricity here is expensive most houses keep at 76 to 78 degrees f. Large businesses use chillers and keep temps in the high 60's to low 70's. I have a 4 ton heat pump without a (swamp cooler) in a 1500 sq. ft. two level town house. It cycles normally and keeps us at a comfortable 76 degrees f. in 110+ temps. Plus in the spring to summer we only have 5 to 10% humidity. |
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| reply to Viper
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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chmodPremium
join:2000-12-12
Lockport, IL | reply to chmod
Thanks for the replies. I guess a set point of 73degrees is asking to much on these really hot days. As cdru mentioned its been in the mid to upper 90's the past few.
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Some people are like Slinkies. Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs. |
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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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| reply to chmod
My car said it was 100 degrees yesterday. Normally my set points are this (Fan on 24/7):
Honeywell VisionPro 8000 w Adaptive Recovery 2H/1C M-F schedule:
WAKE: 6AM - 7AM : Cool to 72 Heat to 68
LEAVE: 7AM - 3:30PM: Cool to 78 Heat to 62
RETURN: 3:30PM-12:30AM: Cool to 72 Heat to 68
SLEEP: 12:30AM to 6AM: Cool to 78 Heat to 62
Yesterday when I got home around 5:30 it was at 77. It took 2 hours to move 1 degree? I went to bed around midnight and it was 73.
So we put it on 72 and into "permanent hold". When I left for work today its 72 and when I get home hopefully its still 72.
I'm wondering if permanent hold is more cost effective when the temperature swings are that dramatic. Then it can cycle and maintain 72 rather than run for hours trying to bring 78 down to 72.
Goodman SSX16 condenser outside.
Goodman 70k btu forced air furnace, variable speed fan.
Approx 15 SEER with coil, return and blower speeds.
Could not get 16 SEER without redoing the whole return and getting the 90k btu furnace with a larger air handler. |
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cdruGo ColtsPremium,MVM
join:2003-05-14
Fort Wayne, IN
kudos:7 | said by cypherstream:Honeywell VisionPro 8000 w Adaptive Recovery 2H/1C M-F schedule:
WAKE: 6AM - 7AM : Cool to 72 Heat to 68
LEAVE: 7AM - 3:30PM: Cool to 78 Heat to 62
RETURN: 3:30PM-12:30AM: Cool to 72 Heat to 68
SLEEP: 12:30AM to 6AM: Cool to 78 Heat to 62
Yesterday when I got home around 5:30 it was at 77. It took 2 hours to move 1 degree? I went to bed around midnight and it was 73. Where is the thermostat in relationship to vents, returns, and windows? What was the outside temperature at the time? Looking at yesterday's weather almanac, it looks like it was over 90 by 11 AM until around 7PM and was at it's high from 2-5PM. If the thermostat is in a shaded room it's possible it wasn't calling for cooling while southern facing rooms with larger windows where quite a bit hotter. If/when it did call for cooling that hotter air starts to get moved around the house and just hasn't cooled yet. |
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| said by cdru:said by cypherstream:Honeywell VisionPro 8000 w Adaptive Recovery 2H/1C M-F schedule:
WAKE: 6AM - 7AM : Cool to 72 Heat to 68
LEAVE: 7AM - 3:30PM: Cool to 78 Heat to 62
RETURN: 3:30PM-12:30AM: Cool to 72 Heat to 68
SLEEP: 12:30AM to 6AM: Cool to 78 Heat to 62
Yesterday when I got home around 5:30 it was at 77. It took 2 hours to move 1 degree? I went to bed around midnight and it was 73. Where is the thermostat in relationship to vents, returns, and windows? What was the outside temperature at the time? Looking at yesterday's weather almanac, it looks like it was over 90 by 11 AM until around 7PM and was at it's high from 2-5PM. If the thermostat is in a shaded room it's possible it wasn't calling for cooling while southern facing rooms with larger windows where quite a bit hotter. If/when it did call for cooling that hotter air starts to get moved around the house and just hasn't cooled yet. Its in our upstairs hallway.
I want to do a test this weekend and put a thermometer in the lower level and get the temperature difference. I'm in a bi-level with an open entrance foyer where it is impossible to prevent the cold air from drifting downstairs and the hot air rising upstairs. We mainly live on the upstairs floor because that is where the living room, dining room and kitchen are located as well as 3 bedrooms and a master bath.
The downstairs consists of my office, a 3/4 bath, laundry room and family room (of which I am renovating right now).
Another issue with the upstairs hallway, although its shaded and away from direct vents, the pull down attic door is in that same hallway too. I wish I had a FLIR imager to look at the IR patterns in the hallway ceiling to see the heat and cool loss in that area.
I know it used to be at LEAST a 10 degree difference in temperature between the upstairs and downstairs level. Thus we keep the fan on 24/7 since its a variable speed DC motor. This seems to help and cut that degree difference in half. |
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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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