Results 14 to 22 of 22
06-21-2008, 09:35 PM #14
The unit may be over-sized, but when in the 90's everything seems better. Last year I had two estimates and both say 4 ton two stage recommended.
For now I'm thinking Ultra-Aire dehu till the wife can be convinced, then I'll call someone else.
06-22-2008, 12:44 AM #15
do you run your fan all the time to try and even out air temperatures, or to filter the air frequently?
If so try setting the fan back to the Auto mode
06-22-2008, 01:03 AM #16
06-22-2008, 02:48 AM #17Professional Member*
- Join Date
- Mar 2008
- Baltimore MD and Ridgebury PA
As for the estimates with 2-stage 4 ton units... this is probably because 2-stage units are generally (always?) only available in full-ton models... so if the load calc calls for a 3.5 ton then you have to use a 4 ton... well that or a 3 ton but probably not a good idea. In any case, make sure a load calc is properly performed since you have low air infiltration and very good insulation. The advantage of the 2-stage 4 ton is that in the 1st stage it will run at roughly half its rated capacity (meaning 2 tons) which is good because it will run longer and therefore actually perform dehumidification. Then, when it gets hotter out the 2nd stage will kick in for that extra-needed capacity.
For comparison, I live in Baltimore and my house was originally built in 1920. I gutted the house several years ago and installed foam insulation which seals against air infiltration and provides excellent insulation. My exterior walls however are only about R-13 because of the depth of the wall cavity that I had to work with compared to your R-20 wall insulation. My house is 1700 sq ft. I only have a 2.5 ton (single-stage) heat pump although I do have an oil furnace for my backup heat. As of late, my heatpump runs less than 50% of the time... when it was hot out 2 weeks ago it ran maybe 75% of the time. My humidity is 55% right now. It is entirely possible that 3.5 tons is simply too large for your home except when the temperature is over 100 degrees or whatever. Do yourself a favor and do your own Manual J calculation... I'd recommend HVAC-Calc.
Last edited by platchford; 06-22-2008 at 03:00 AM.
06-22-2008, 08:17 AM #18
The beauty of the dehumidfier is that adding a dehu to any sized system provides <50%RH. A one ton a/c is unable to provide <50%RH when the outdoor temps are <75^F. I have not run may a/c to date. MY basement is 68^F,<50%RH. Cracked window and 90 pint dehu operating. $15/mo. electrical. Regards TBBear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
Use +Merv 10 air filter. -Don't forget the "Golden Rule"
06-22-2008, 12:18 PM #19
If Auto fan and a reduced blower speed do not work, then odds are your home leaks like swiss cheese, you have some sort of steady exhaust fan running like a humidex or an attic ventilator, you have some leaking ducts in unconditioned space etc and unles you can adress these issues, your only bandaid fix is a dehumidifier
06-22-2008, 11:56 PM #20
This is an uninformed question, but, since a dehu is used to bypass the AC unit (intake from return - dehu output to supply), could a "one" ton complete AC unit be used as a bypass of the bigger unit ??
Why ? Well, if a one ton could provide the kind of dehumidification that a regular whole house dehu can perform it may help keep electric costs down. Would this not also be a desirable auxiliary AC unit to be used when temps are not great enough to run bigger unit ??
Guess I'm feeling frustrated at the moment. My AC is down right now the condenser fan is not running. Called the service company who sent a guy out and replaced a capacitor. Unit ran for 1 1/2 hours then fan quit again. Called back they told me thursday is earliest they can come back.
Thought maybe a one ton unit (used in a bypass) could be an emergency AC for minimum comfort as well as a dehu.
06-23-2008, 07:57 AM #21
You really are thinking outside the box! Would it not perform rather like a 2-stage AC where the 1st stage is 1.0 ton? No added sensible load like a dehu contributes.
06-23-2008, 08:17 AM #22