I would start asking around about finding a good HVAC COMPANY and get it looked at

 

Lower air flow will cause the indoor coil to become colder which will remove more humidity during cooling operation. However, depending on the type of blower you have, just lowering the amount of air can also cause other problems that are even worse then high humidity.

Call a couple of HVAC contractors. Insist on talking to the service manager to explain exactly what you are looking to do (lower humidity) and make an appontment with the first one who sounds like they understand what you are talking about.

 

Lower air flow will cause the indoor coil to become colder which will remove more humidity during cooling operation. However, depending on the type of blower you have, just lowering the amount of air can also cause other problems that are even worse then high humidity.

With all due respect, what are the other problems that can occur.

Thanks,
Jim

 

Have them check static pressures, before they adjust the fan speed.

 

Thanks for the replies... I was hoping it would be an easy "Yes, slowing the fan speed will decrease the humidity at little cost", but I guess nothing is ever that quick and simple. I'll start calling around to see if I can find someone to come out and check out my system.

Thanks

 

Ask if they can bring the fan data chart for your brand and test the ESP to set the cfms at around 350 per ton,If not keep dialing.They might do along with a annual check and clean,for a small charge.

What brand,and you're located in which city?

 

Try,

Suma A/C
Address: 15519 W. U.S. Hwy 441
Eustis, FL 32726


Phone: (352) 357-4162
Fax: (352) 357-4168

 

If your %RH meter is ok, check the temperature of the air and %RH coming out of the supply ducts closest to the a/c. If you have a 20-25^F temperature drop, slowing the fan may not be an option. At the end of 2-3 hour a/c run, the %RH should be <50%RH. Excess duct leakage has potiential for raising the moisture level. Your heat pump should be able to maintain ,50%RH during high cooling load conditions. During cool damp weathe with low/no cooling loads and adequate fresh air, you will need supplemental dehumidification. Regards TB

 

At the end of 2-3 hour a/c run, the %RH should be <50%RH.

I pretty much never get a 2-3 hour run. If I set the thermostat back to 85 and it actually makes it to 85 (often it'll only get up to 82 or 83 without the heat pump coming on at all during the day) then I might have a 2 hour run, but most of the time, going from 82 to 78 is only an hour to an hour and a half. If I leave the system running during the day I'll get 10 to 15 minute runs with 6-10 minutes off even during the hottest part of the day.

Excess duct leakage has potiential for raising the moisture level.

Like I said before, It's a brand new house and the ducts I can see seem to be sealed pretty well, so I don't think there's too much leakage, but I haven't had the system tested, so I don't know for sure.

Your heat pump should be able to maintain ,50%RH during high cooling load conditions. During cool damp weathe with low/no cooling loads and adequate fresh air, you will need supplemental dehumidification. Regards TB

Maybe that's the problem... it's summer in florida, but I don't think I ever have a really have a high cooling load. I live in a townhouse in a middle unit, so two of my walls 'exterior walls' are connected to other units (that are hopefully air conditioned). I have an east and a west wall, but I keep the blinds closed when the sun is coming in. The attic is reasonably well insulated. As I said above, I suspect that the units may just be oversized.

I guess I should ask the tech about installing a dehumidifier too.

Thanks again,
Brett

 

Larger coils don't remove more moisture.

If the system is set up right, then you won't have problems with the compressor being damaged.
The system should be checked when they slow the blower.

 

um..are you sure? i always found that a larger coil surface equals more moisture removal. of course it needs to be set up correctly.

 

New homes often have duct leakage.

Take a couple of supply grilles down from the ceiling,if there is a gap between the drywall,and the metal of the "box" above the grille,testing has shown up to 15% of total cfm leakage just from this.

Ducts in the attic often get damaged by,insulators,Larry the cable guy,etc.,etc..

Look for leaks,have the static tested and the fan set for max of 350 per ton,maybe a blower door test,if the humidity is still an issue,then think about a dhumidifier,very few homes have one,nicwe to have,but be sure you want/need it first.

 

New homes often have duct leakage.

Take a couple of supply grilles down from the ceiling,if there is a gap between the drywall,and the metal of the "box" above the grille,testing has shown up to 15% of total cfm leakage just from this.

I suppose up to 15%. I'd have guessed more like 3% at the most, unless it was a crappy cut out of the sheetrock before ductwork install. Ya never know, tho.

 

Oversized systems will cause poor humidity control like you are experiencing. This is mainly due to the system short-cycling so that it isn't running long enought to handle the latent load. The only way to know for sure is to have a manual J load cal performed.

If they turn out to be the correct size, then you very well may be able to just slow the fan speed. As has been stated before, you really need to know how well the current blower is performing before making any changes.

Honestly though, it just sounds like you are jacking the t-stat up while gone during the day, allowing moisture to penetrate your house, then trying to solve the problem when you get home at night. In humid areas this practice can certainly cause the issue you are having. I know you tried it the other way for a day, but I don't think thats necessarily long enough to evaulate the results, since moisture will get into wood, carpets etc. and can take awhile to be removed.

 

Your system may have been sized (a long shot, I know, that someone actually put a little design thought into a residential a/c install) for a 75 degree thermostat setpoint vs. 78 or 85. At 78, your system may not run long enough to properly dehumidify, but at 75 it might.

Duct leakage has been mentioned; I would also follow through on dash's advice to pull a few vent grills and check for that infamous gap between drywall and duct sheet metal. If I lived in Florida I'd go crazy trying to make my home more airtight...infiltration is probably the largest portion of humidity problems in humid climates, followed by a/c design and performance.

 

Your cheap little hardware store hygrometer is probably totally inaccurate. Don't make major decisions based on it.
You can get a good hygrometer with accuracy of 2 or 3% for about $100.
Laura

 

I collected some data on a 14 SEER 2 ton new a/c. It shows the importance of good set-up. Look at the supply air temperatue. This is a tight home without fresh air ventilation. The a/c is able to control humidity on <90^F day. The critical issure is the air flow over the coil. Any coil will remove moisture if allowed to get cold enough and run long enough. Unfortunately only on the warmer days does the a/c run long enough to remove enougn moisture. Regards TB

 

What is the brand and model number of your OD unit, and ID unit(coil and blower).
2300 sq ft, thats the main floor and basement combined, correct?