I just had a new HVAC system installed in a new house and have not paid for it yet. Today the temperature is 100 outside. I have my thermostat set to
77 and the actual temperature is 81. (This is upstairs, downstairs a separate system is maintaining the selected temperature.)I am getting about a 20 degree drop. Is that acceptable or should the system be doing better?
Thanks for any help!
How long has it been running? What was the temp when you begin to cool it down?
It could take many, many, many hours to drop a 100 degree space, with all it's 100 degree furnishings, the full 23 degrees.
If you realy have the question if the upstairs unit has been properly charge is have a heat load done to your home.
Also have your system checked to make sure ther is no problems.
Its set to 77 and its 81 , maybe the thermostat is not calibrated if its cycling, turn it to 70, how hot was everything when you started it, wait a few days and let it run continously, keep the thermostat temp set low so it runs. My installer gave a guarnteed temp drop in writing.
In addition, if everything in the home is loaded with the latent heat of humidity it will take many times longer to pull the sensible temp reading down. Also, the upstairs area usually has a greater heat-gain than the lower floor area.
Higher ambient (outdoor Temps) can considerably lower the capacity of an
82-F outdoor temp Rated Ultra High SEER Rated unit. In very hot & especially humid climate zones, I would go primarily by the higher outdoor 95-F "EER Ratings & BTUH performance at those very high application load conditions." I also hope your new unit has a Scroll compressor & a TXV metering device ahead of the E-Coil. - udarrell
Stick a thermometer in the vent. The A/C should be putting out air about 20 degrees cooler than the air that goes into the system (ambient). If you're getting a 20-degree drop, it's as good as it gets.
If you have not paid, you must return your 81 degree air and get hotter air in return. I'm sure they have an air exchange place nearby.
Your cool air will be sold to defray your debt.
20 degrees is about as good as you'll get.
On Wed, 08 Aug 2007 15:03:21 -0700, ransley wrote Re Re: Is this acceptable HVAC performance?:
Here's a way to measure performance:
1) With the house warm, turn the thermostat down so the a/c will turn on and run for at least 10 minutes. 2) After running for ten minutes, and while still running, measure the temp of warm air going into the a/c unit as close as you can get to it. At the same time, measure the cool air coming out of the vent nearest to the a/c unit. 3) A 20 - 25F temp drop is very good. More than 30F and you may have an over sized unit.
It should be doing better. We had the same problem for years with our unit and could never get below 80 if it was 100+ outside. Other houses in the area could reach 70 if they wanted. We eventually sold the house and the new owner's inspection showed up that the unit was not big enough for the house. We put some money in escrow for them so the whole thing would just go away.
BTW, we had for years been trying to get A/C people to find out what was wrong but we would have been better employing retarded chimps. ALL of them were useless cretins. Not one of them (7 or 8 different people) said the unit was too small and it was just fine - but it wasn't.
What temperature is in the manual J calculations?
Bullshit, without all the required data, everything is a WAG (wild ass guess).
Now, if you want to talk about:
TESP, CFM SP, ST, SH LP, LT, SC DB, WB AT, CT, CDT ST, RT, EDT CA, CRLA FA, FRLA Etc.. we can get somewhere.
You're assuming that a lot of things are correct.
20-degree drop doesn't mean jack shit.
It's not as bad as all that. It's not a definitive indicator of system health, but it is in line with typical performance of typical healthy systems.
In other words, you wouldn't expect to see a 5 degree difference or a
50 degree difference -- those would likely be an indication of something not quite right, or some exceptional circumstance.All rules of thumb are imperfect.
20+/- degrees from the inlet to the outlet is typical. That says nothing about the difference between the indoor and outdoor temperatures. Clearly you can condition down to 65 degrees indoors even if it's 110 outside (but it will cost you $$) with a big enough system. Just go to any shopping mall for a demonstration.
wrote in news:42efe$46ba921b$9440c41e$21621 @STARBAND.NET:
Oh bullshit. What's the superheat?
Thanks for all of the replies. In answer to some of the questions: The system has been on for a couple of months. The system consists of 3 units (one downstairs and 2 up). The upstairs is the problem. The home is well insulated. I have actually paid 60% of the contract cost. The contractor has a little more work to do (load balance and a couple of other minor cosmetic things and agrees no additional payment is due until all of the work has been completed. He has been very slow completing the final items.)
The exterior temp I gave and the interior temp indicated by the thermostat are correct.
To me as home owner, I don't care about all the technical aspects. My question is simply: "I hired a company to design and install a system. They did. Is it normally considered acceptable for the interior temp to to be 81 when the exterior temp is 100 on a very sunny day."
If the answer is "Yes, any lower and your system would be oversized" then fine. If the answer is "No" then the contractor should correct the situation be it the freon charge level, unit size, duct design, airflow rate, j page calculations, or whatever.
Pssst! This is "alt.home.repair" not "alt.hvac" - you're in the wrong group.
My answer is that if 90 to 100 deg days are not unusual in your area, then I would not be satisfied. What happens as the temp drops later in the day? On a 100 deg day, when does it finally reach 77?
I'd also look at your attic venting. Is it adequate? Are the soffit vents open and not blocked with insulation? In areas with 100 deg days, I would also install a radiant barrier on the underside of the roof, which can help a lot. If you improve any of these, you will be saving energy costs as well.
Reading you latest post puts a new slant on your first post.
You are asking here, it seems, about the 20 degree drop.
But it was still confusing, I realize now. Your first paragraph says it's 100 out and 81 in. That's a 19 degree difference, so I didn't think that what you were referring to when you said a 20 degree drop.
If you meant the same thing, why did you up it from 19 to 20?
I said, perhaps negligently, but I'm not getting paid, that a 20 degree drop is the most you're going to gget, but that referred to 20 degrees from the input to the AC to the output, the air just before it goes in the AC to when it comes out**. IIRC, I think it was this thread where someone was explicit about hat.
Once the room is down to 90, say, a 20 degree drop will yield 70 degree output.
**But maybe measuring it as described where this footnote comes from, you only have a 15 degree drop. That might be acceptable also. Then you'll only get 75 degree air out, until the room is 85, when you should get 70 degree air out.If your ac is big enough for the space to be cooled, you should be able to get it down to 70, but I don't think you said either how big your AC is or how big it was calculated that you need. Or how much hot air might be leaking in, through leaks or radiation, and how much the cold might be getting out. And is the attic adequately ventilated. Or how long you had been running the AC. You have never replied to any of the questions or suggestions offered, you just seem miffed that we say technical things and you're not interested in those. But we can't answer your question if you won't answer our only slightly technical questions. "How long has the AC been running" doesn't seem very technical to me, but maybe that is because I have 3 years trade school and 10 years experience in "how long". Also, I finished a certificate program in "running".
Also you shouldn't just rely on one thermometer to know the indoor temp. It could be bad, even though it is new. Surely you have another thermmometer around the house that you have reason to believe is accurate, or you can go to the store. You don't need expensive, which is almost always based on the decoration, but it should be large enough to mark every 2 degrees and to be able to read when it is between two of the markings. Then look at all the thermomters for sale like it and pick one that reads in the middle, the mode, mean, or median of what they have. They will probalby all be very close to each other, but make you don't buy one that is not. Then see if you have 81 or something closer to 77.
Also, did you try turning the stat down to 70, as somoene suggested. This is not so that you can keep your house at 70, but to see if it will go lower than 81 if the stat is set lower. Not only might the thermometer on the stat be wrong, but it could be right and the stat could be calibrated incorrectly. That's no big deal. If it is out of warranty and cools (or heats) the room to 4 degree hotter than it is set for, then one just sets it 4 degrees lower. These numbers are just there to help. They were not given by God.
So, if you've tested everything and it's all adequate and unless they sold you the wrong AC with your consent, maybe it's not acceptable. I'd like to hear the answers to everyone's questions before I can say something stronger.
And, have you pointed this out to the ac contractor? You should do it over the phone, so that he allows time and brings whatever he needs to fix it, instead of waiting and telling him when he is there and causing him to make another trip.
Pssst! I know "HVAC" and "you don't" - so, quit handing out inaccurate information.
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