can anyone confirm ac is working properly?

[univac]

they did a lot of work to make me happy. they assure me that the equipment is doing better than what most folks have around here. i just wanted to make sure.

it was 106 outside. 48% humidity. there are three top of the line systems three years old. the best it could manage was 77 inside and 21% rh. i would like it colder. finally the hvac guys who are my friends told me i am asking more than anything can provide. they said 38 foot ceiling does not help at all. i just wanted to make sure that is true. i do apologize if they are correct and i am an idiot.

thank you

[second opinion]

they did a lot of work to make me happy. they assure me that the equipment is doing better than what most folks have around here. i just wanted to make sure.

it was 106 outside. 48% humidity. there are three top of the line systems three years old. the best it could manage was 77 inside and 21% rh. i would like it colder. finally the hvac guys who are my friends told me i am asking more than anything can provide. they said 38 foot ceiling does not help at all. i just wanted to make sure that is true. i do apologize if they are correct and i am an idiot.

thank you

A lot more info would be needed, but 30 degree delta inside to out and 21% rh its no slouch.

[hcong]

More information is needed, but assuming the units, the ducts, and the thermostats are working correctly. Also assuming your house isn't super leaky... I would say the units are undersized... but I can't tell for sure until we get more info.

[univac]

i kind of figured that. most places promise 20 degree drop. i want colder but they said it really cannot be done. now that it is 94 outside i can get it down to 68. the system is too complex that i do not even know what everything is to tell you. it was not by any means hot in here i just like an ice box. i guess i do want what is not possible. they told me if you get a 45 degree drop things will stat freezing and i will have other problems.

"no slouch" is a good enough answer. i figured they were telling me the truth but i just wanted to check with you guys. i did not mistrust my friends i just wondered if colder was actually possible. apparently not.

thank you

[univac]

oh, wait. i just read your post hcong. it is automated control. i think they are 6 ton units. 3 of them. the home is insanely tight but it has air exchange. everything is that variable speed communication stuff they have now. i don't know a lot about it so i dont know if you guys will be able to help.

[carmon]

18 tons..... how big is this house ......

[Shophound]

If your house requires 18 tons of cooling, it must be huge! And for the temperatures you like to run at indoors, I'd go with a chilled water system.

That said, I always must ask when I hear of folks wanting their house "cold" if the humidity is being controlled properly in the house. If your house has an air exchange system, depending on where you live it may be bringing too much moisture into the house, and the a/c system is struggling to deal with it, forcing you to dialing the thermostat down to feel comfortable.

[univac]

thank you guys for the answers. i was originally told to go for a commercial chiller instead of split a/c. too late now. i think i am just asking too much from split ac. people come over here with jackets so that might tell me something. i used to live in a much smaller home with window ac and that is where i got hooked on the cold. i used to sit right in front of that thing. the plus side is i like it 60 in the winter.

[hcong]

18 tons and 38 ft ceilings... did the people who installed your system do a load calculation? I am also assuming you don't have 38 ft ceilings everywhere in the house. +7200 sf home?

[univac]

these guys are good. they did all kinds of calculations and that j thing.it's about 9000 sf. the foyer and living room are three stories of ceiling. plus the living room is all glass. with the sun blazing on it but they are good windows. the thing is this is by chicago. we hardly ever see heat like this with our humidity. it will keep it at 70 degrees up to 98 outside.

i have to tell you something really weird though. i decided to put up to 77 at the pleading of my wife. at 77 it is actually more comfortable to me than 70. i mean like it actually feels colder. strange but i am sure you guys can explain that. so given that i guess my problem is solved. it should keep 77 for anything we get. unless something is coming i dont know about. i hope not. there may be a problem though. at 77 and 91 out now it seems like they are short cycling. they are on like 10 minutes in an hour. i hope that is not an issue. they decided to talk me into removing the air cleaners and that solved last years problem. which was the ducts sweating. they told me i might consider higher horse power blowers than the stock ones too. it is lennox best stuff from three years ago. i think 20.5 seer.

i really appreciate that you pros help people like me that dont know anything about this stuff.

[hcong]

these guys are good. they did all kinds of calculations and that j thing.it's about 9000 sf. the foyer and living room are three stories of ceiling. plus the living room is all glass. with the sun blazing on it but they are good windows. the thing is this is by chicago. we hardly ever see heat like this with our humidity. it will keep it at 70 degrees up to 98 outside.

i have to tell you something really weird though. i decided to put up to 77 at the pleading of my wife. at 77 it is actually more comfortable to me than 70. i mean like it actually feels colder. strange but i am sure you guys can explain that. so given that i guess my problem is solved. it should keep 77 for anything we get. unless something is coming i dont know about. i hope not. there may be a problem though. at 77 and 91 out now it seems like they are short cycling. they are on like 10 minutes in an hour. i hope that is not an issue. they decided to talk me into removing the air cleaners and that solved last years problem. which was the ducts sweating. they told me i might consider higher horse power blowers than the stock ones too. it is lennox best stuff from three years ago. i think 20.5 seer.

i really appreciate that you pros help people like me that dont know anything about this stuff.

Ducts sweating is because your ducts are not insulated enough and when the hot humid air touches the cold duct surface it forms condensation.

Your ACs can quickly cool your space down to 77 F; and once it does your ACs will cycle off. The biggest problem with short cycling will be humidity. But from what you are said, maybe the humidity and temperature level at 77 F is more comfortable to you.

Your living room is such a big space and with all those windows, it probably isn't getting enough airflow to bring the temperature down anymore. But I looked up the design temperature of Chicago and it is around 91 F Dry Bulb and 77 Wet Bulb; so your friends are right, your system is probably sized correctly, it is just too hot right now. I would try pulling blinds during the day if possible.

[univac]

thank you. i am guessing it is simply too hot this year. i hope this is not a trend. i always heard the problem here is the humidity. the ducts stopped sweating when they increased airflow by removing the air cleaners. the humidity hardly went up when i moved it from 70 to 77. i think like everyone else tells me 70 degrees and 20rh is too cold. i prefer not to close the blinds but i guess i have to. the windows are smoking hot to the touch. there are a lot of supplies and huge returns in the living room. i was just trying to get the entire home too cold i take it. like i said up to 98 it is fine. we just dont see this heat here. it hit 107 yesterday. that my reading. weather.com said it was 101.

anyways, i suppose i can rest assured it works properly. thank you.

[univac]

i just realized something. it is the amount of glass in this home. it is really cool at 77 here at 3:30am. come noon i bet 77 will be too hot for me. i know these guys designed the hvac properly. this is the architects fault i figure. i realized this because the master bath is also all glass. that room was always hot no matter what during the day. at night it is cool. i think the answer is going to be some type of better window treatments. of course this was not a problem until it got this hot. i could just wait it out too.

i think i have this figured out. it is not the ac at all in fact i think.

[motoguy128]

You need ot check your indoor hygrometer. 21%RH at 77F, is a 34F dewpoint. I'm not sure that's possible without a dessicant dehumidifier with those outdoor conditions or your short on airflow and really, really close to freezing the coil.

At that humidity, 77F shold be reasonably comfortable. I keep our downstairs at 77F and it stays between about 32-38%RH in hot weather and cool it to 76F at 8PM.

What I said above should explain why 77F freels better than 70F. Humans feel humidity as much or more than they sense temperature. That's because we cool out bodies by evaporation. So the lower the humidity, the more effective we cool ourselves, so the rate of heat loss on you skin's surface is greater. The aboslute humidity level in a home will be set by ow cold the surfae of your AC's evaporator coil is. So if you set the temperature to 77 vs. 70F, the evaporator will get nearly as cold in both conditions, so the dewpoint will be similar (if it's sized right and has long rung times regardless) But at 77F, the relative humidity is much lower, so sweat will evaporate much more quickly, than at 70F and the same dewpoint. However, your AC systm will be significantly more efficient at 77F and you rate of heat loss will be much lower since the indoor and outdoor tmerpature will be closer to each other.

[udarrell]

Univac: at 77 and 91 outside now it seems like they are short cycling. they are on like 10 minutes in an hour. i hope that is not an issue.
That is an issue when it comes to lowering the humidity sufficiently in your home. Actually at 91 outdoors & 77-F indoors the equipment is oversized for the humidity level in the Chicago area.

Ten minutes in an hour indicates that the home appears to be relatively energy efficient at design temps...

That's around 45% Relative Humidity; however at 91F that is a lot of grains of moisture.

Outdoor Temps & Humidity - U.S summer & winter;Chicago 95F summer design; 7:30 am 78% RH; 1:30 pm 51% RH; 7:30 pm 55% RH.

At those high outdoor temps that is a very high grain of moisture per lb of dry air that the A/Cs have to deal with, for which they normally need a lot of runtime.

Your home needs humidity control, have the air infiltration rate checked using Blower Door Test; get humidity at or below 50% in your home. Shophound warned you...

Also, leave the warm air at those ultra high ceilings alone; do not mix it with the diffuser throw patterns with the lower level air or draw it into returns that are too high on the walls or on the ceiling! That hotter air should not be conditioned; it acts as an insulator slowing conduction rates into your home...

[motoguy128]

i just realized something. it is the amount of glass in this home. it is really cool at 77 here at 3:30am. come noon i bet 77 will be too hot for me. i know these guys designed the hvac properly. this is the architects fault i figure. i realized this because the master bath is also all glass. that room was always hot no matter what during the day. at night it is cool. i think the answer is going to be some type of better window treatments. of course this was not a problem until it got this hot. i could just wait it out too.

i think i have this figured out. it is not the ac at all in fact i think.


Since AC became common about 30 years ago, architects quite paying any attenton ot shading, building orentation and glazing in general. The focus was on funciton, not form. Hence the hidous neoecclectic deisng lacking any symmetry, character or uniformed sytle. I've seen some with as many as 5 different styles combined together.

CLoseing your blind, could cut your cooling by by as mcuh as maybe 20-30% on a really hot day.

Radiant heat fom the sun hitting the floors and interior of yoru home will make you feel hotter even if the air temperature is the same. Thsi is why radiant floor heat and even old cast iron radiators give such a niec even warmth. I'f tryign to convince a friend of mine to upgrade his boiler rather than remove it a go with a forced air furnace as most have done in this area.

[motoguy128]

IN chicago area when it's 91F outside and a outdoor dewpoint in the 70's, the system shold be running closer to 20-25 minutes, twice an hour even at 77F indoors depending on how many blinds you have closed or open.

IF it's only runing for 10 minutes, 3 times per hour, then its' at 50% capacity, and is probably oversized by at least 1/3. So if its' a 3 ton, you only need a 2 ton. IF a 4 ton, you might only need as little as 2.5 tons.

[univac]

thank you guys. i think my friends were right. i was just asking too much from it. my thermometer is reading 102. msn weather says 99. it is keeping it at 77 degrees and 31 rh no problem. it is running nearly non stop on all three though. i think asking it to do 70 in this weather is unrealistic. on the other hand i am lucky that i discovered 77 is just as comfortable 70. that might be due in part to the fact that i cranked the ceiling fans. they are cheaper to operate than compressors obviously.

[hcong]

by air cleaners, you don't mean the filters do you?

[univac]

no, i meant the lennox hepa scrubber systems. they told me they restrict the air and freeze the coils. that is the least of my problems tonight!

anyways guys i am dumbfounded at what happened today. i will call for service in the morning and let you guys know what they did.

it was keeping it at 77 all day between 99 and 103. it got down tonight to 87 and they are still set on 77. they are going nonstop and it is 81 in here. it makes no sense to me that everything would fail at once at a lower temperature. if i put it down to 72 they start cycling again and keep it there. it must be the darn home automation garbage again i am guessing. these honeywell sensors have failed about 5 times already. if it was not for bad luck i would not have any!

i am sorry i added to this post but this was very unexpected.

[Shophound]

IN chicago area when it's 91F outside and a outdoor dewpoint in the 70's, the system shold be running closer to 20-25 minutes, twice an hour even at 77F indoors depending on how many blinds you have closed or open.

IF it's only runing for 10 minutes, 3 times per hour, then its' at 50% capacity, and is probably oversized by at least 1/3. So if its' a 3 ton, you only need a 2 ton. IF a 4 ton, you might only need as little as 2.5 tons.

That would depend on what the indoor summer design temp was for this house. Manual J standard is 75 degrees F. So if OP is now running the system at 77, he has more capacity than needed for that setpoint, on a design day.

[univac]

i told you guys i would give you an update. a fan quit on a condenser and the compressor was overloaded with heat. they replaced the fan no charge of course. works today but it only hit 87. the thing is the last few days were not at all "design" days. i was attempting to run 70 degrees while it was 106 outside. they explained to me if i keep doing that the equipment is going to fail on me. 77 is fine though. i just hope we do not get hit hard in august. the thing is chicagoland does not have this design temp because it does not normally get this hot here.

thank you guys again.

[udarrell]

i told you guys i would give you an update. a fan quit on a condenser and the compressor was overloaded with heat. they replaced the fan no charge of course. works today but it only hit 87. the thing is the last few days were not at all "design" days. i was attempting to run 70 degrees while it was 106 outside. they explained to me if i keep doing that the equipment is going to fail on me. 77 is fine though.

i just hope we do not get hit hard in august. the thing is Chicago-land does not have this design temp because it does not normally get this hot here. thank you guys again.
As long as the system is setup properly with an accurate charge, the fact that you set the T-stat well below the systems design puts no more strain on it whatever, it will run to its capacity & achieve a steady state all day & into the night.

That is a lot easier on the equipment than a system that is over capacity & short cycling all the time. It's better that it runs steady with NO starting & stopping in very hot weather that is above its summer design.

A Tech should not have that opinion of what constitutes equipment abuse...though it is easy to think that way...

[univac]

thank you guys.

udarell you just made me understand something important that i did not know. that explains a lot. of course if it is set outside of the design limit it is not going to maintain x temp. we leave mainframes on 24/7 for this very reason!

[motoguy128]

Running it at 70F when it's 106F outside just uses a lot of energy, and in Chicago, mean your system is a little oversized. But A udarrell said, it doesn't really impact equipment life. IT will actually lower suction pressures for what it matters and the system will be transferring less heat when running. Run times will be longer. Actually, there's an argument that running it colder indoor might increase equipment life.

What makes the biggest difference is keeping the condenser clean. And as mentioned, starts and stop are harder on equipment than just running. Most equipment fails from poor maintenance, or getting a leak that introduces moisture in the system.