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06-09-2011, 02:31 PM #14Professional Member*
- Join Date
- Mar 2011
- Galveston Texas
to take the temp put a thermometer in the return grill and put on in the closest supply grill.
Yes duct work that is too small will also cause condensation, as well as other problems. The reason to have the stat set for auto is so after the cooling cycle it has a chance to dump all remaining condensation off of the coil and allow it to also drain out of the drain pan. if water is allowed to stay on the coil or in the pan it will put humidity back INTO the house.
Again if the ducts are not insulated and the humidity is high in the basement they will sweat. open up some of the grills in the basement to help it move some air around and allow air from the basement to get to a return (if there isn't one in the basement) so that it can help pull the humidity out.
06-09-2011, 02:38 PM #15Regular Guest
- Join Date
- Mar 2011
OK, so allowing the fan to continue on slow when the AC is not running as apposed to having the fan turn off while the AC is not running, causes a situation where the system is not able to
"dump all remaining condensation off of the coil and allow it to also drain out of the drain pan?"
06-09-2011, 04:12 PM #16
06-09-2011, 09:36 PM #17Regular Guest
- Join Date
- Jun 2011
Humidity in basement is to high. Comfort level is 30-50. Most duct has about an R4 insulation value which is not much. Open all the supply and return vents. Run fan in auto.
Ask tech to chack Delta-T.
06-25-2011, 12:27 PM #18Regular Guest
- Join Date
- Mar 2011
Update After Visit From Technician
A little history for those of you that might be starting fresh with this one:
I’ve somewhat recently “upgraded” from a 20 year old 2 ton, split system Heil that was never quite able to bring the temp down to 72 when it got past 82 degrees outside to a 2.5 ton Lennox which is able to get down to temp with no problem so far. I was going to say “without a sweat” but you’ll soon see that that isn’t the case.
I have a small cape cod with virtually no insulation that is like a little brick oven in the summer time.
The old and new systems are/were split systems with the furnace and coil in the basement. The basement is half unfinished. This is where the system is located. The other half is finished but it is a very rare occasion that we ever use it. For the past 20 years, I would rarely condition the basement in the summer and only a little in the winter.
Problems with the new unit consist of major sweating on the two supply trunks that come off of the system and it doesn’t appear to be dehumidifying as well as I would have hoped.
The tech from the company that installed the unit came out about two weeks ago. He checked a few computer settings and then measured the supply and return temps, which were 58/74 for a difference of 16. He said that the difference should be more like 20 and also that the system had been set up as if it were a 3-ton unit as apposed to a 2.5 ton. He also said that the unit outside was charged too much.
He changed the fan speed from 1270 CFM to 1105 CFM, took some of the charge out of the unit outside and then got temps of 56.7/75.7, which he seemed to be pleased with. He said that the unit was now set up exactly as it should be. While he was here, he also called the salesman who sold me the unit, who also doubles as a supervisor. The salesman/supervisor said that in a few weeks, he would set up an appointment to have the supply ducts insulated and a small return cut into the unit itself. This last part has not taken place yet.
What the tech did made the run cycles a little bit longer but has had absolutely no effect on the sweating problem and very little effect on the humidity problem.
As per suggestions from this thread, a little more than a week ago, I changed the thermostat from the fan being on all the time, to Auto. This DID have a slight effect on the dehumidification of the main floor. It went from hangin’ around 51-53% to 49-51%. Not much but at least headed in the right direction. Obviously the changed fan setting had no effect the condensation problem.
As of yesterday, I started experimenting with another suggestion from this thread, which was to open the supply vents in the basement to condition the air down there. This had a fairly dramatic effect on the sweating. Unfortunately, at the same time, it pretty much turned the unfinished part of the basement into a freakin’ MEAT LOCKER!
Here is a link to some photos of my situation. It’s the sweating at it’s worst when I don’t have any supply vents open down there. It will also show you the different shapes and sizes of surfaces that might need to be insulated.
OK, question time. Please keep in mind my goals of controlling the condensation hopefully without using the supply vents and making it so cold down there. Also I would LOVE it if I could get the RH on the main floor down to at least 45% and hopefully between 40-45%. I really don’t think that this is too much to ask after paying seven grand for the furnace and AC, do you?
1.Not knowing much about this stuff, I’m afraid of having the supply ducts insulated. I have this vision that it will only hide the problem as apposed to correcting it. I have thoughts of a wet gooey mess behind the exterior foil where all kinds of nasty mold and crap will develop. Also, in order to insulate, there would be 2 or 3 damper levers covered up. Should I let them insulate the supply ducts?
2.As you can see from the photos, there are round supply ducts and the older rectangular supply ducts and there is even quite a bit of condensation where they joined the new unit to the main supply duct. If I let them insulate all of those areas, how should it be done and what would be the best materials to use.
3.Should I let them “cut a small return” in the unit itself? Again, not knowing much, this “feels” like hacking up a brand new system.
4.Keeping my goals in mind, please explain in layman’s terms, the exact steps that YOU would take next if you were me?
If you could answer my numbered questions as asked I would REALLY appreciate it. Please feel free to add whatever else you think is necessary for me to know but I just know that I will personally understand things better if you answer what I’ve asked.
If you’re still with me, GOD BLESS YOU and thank you very much for your help!!!
06-25-2011, 06:30 PM #19
1. The condensation is not coming from the duct itself, it is coming from humid basement air condensing on the cold duct. Insulation will prevent the air from reaching the duct, so insulation will fix the problem, not cover it.
2. We would use 2" foil backed insulation with foil taped joints.
3. It's perfectly normal to add a return in the side of a furnace, but not the back.
4. Frankly, it's too late for a "next step" other than insulating ducts and adding return if needed. The first step to control humidity is improvement of the structure since most of the humidity is coming from humid outdoor air infiltrating the structure. Add a vapor barrier, seal penetrations, add insulation. Then have a load analysis done to find out what size A/C is needed for the improved structure; it will be noticeably smaller than the size needed for an unimproved structure. The reason the A/C should be calculated carefully is that it should be just big enough. Just big enough means that it will run almost continously when the outdoor temperature is at the normal maximum high. It needs to run continuously because air conditioners are not dehumidifiers per se. They remove humidity but to effectively control humidity the air must be reheated after being cooled and dehumidified. In an actual dehumidifier the unit does the reheat function. An air conditioner doesn't have a reheat function, heat load from outside and inside is the source of reheat. So, dehumidification will be most effective when the heat load from outside and inside matches the amount of cooling being done by the A/C which will cause the A/C to run more. Since the normal maximum high occurs infrequently, most of the time the A/C will be too large to work well as a dehumidifier. Current state of the art dehumidification control of A/C units will not actively control humidity, having no reheat function for times when there is insufficient heat load to make the unit run continuously. Premium units may have two stages of cooling or even variable cooling that will enhance dehumidification by more closely matching the unit's cooling capacity to the load on the structure, causing the unit to run more. A premium thermostat with humidity control will not actively control humidity, it's function is to slow down the fan to enhance dehumidification and also to offset the cooling setpoint so that the apparent temperature is more stable. The actual humidity may not change or may even go up with a humidity controlling thermostat. Normal comfort range for humidity is 40-60%. I work in a climate where if indoor humidity is 50% we consider the equipment to be working very well. When a customer is concerned with actual comfort versus an arbitrary humidity target and humidity is less than 60% we don't have humidity control complaints when a properly sized premium system has fan slow down control and cooling setpoint offset.
In your case, if you want to further control humidity buy a dehumidifier.
06-25-2011, 09:08 PM #20Regular Guest
- Join Date
- Mar 2011
Thank you very much for taking the time to help me out. I appreciate it.
06-25-2011, 09:16 PM #21
Seal and insulate.
Hopefully the coil is not to wet/COLD. 57F is not a bad temp as far as having a wet coil goes.If common sense is so common how come so few of us have it!
06-25-2011, 10:48 PM #22
What part of the country wouldn't insulate ac duct?
06-26-2011, 12:47 AM #23Regular Guest
- Join Date
- Mar 2011
About an hour west of Philly.
06-26-2011, 06:30 AM #24
we just have so much humidity down here and use the ac so much we have to insulate well. I have no knowledge of your local codes and install practices.
06-26-2011, 09:20 AM #25
I run into this all the time, near Pittsburgh. Almost none of our basement ducts are insulated. We install a shiny new variable speed furnace and a/c, and get sweaty ducts.
I have insulated many systems. It usually looks like crap when I do it. Best is to get a dehumidifier, piped to a floor drain. The dehumidifier takes away moisture and makes heat in the basement, which is too cold anyway. The new a/c takes away heat, everyone is happy. You still might need to insulate the supply trunk nearest the furnace, we usually wrap the plenum and first elbow.
Just remember, the better the a/c dehumidifies, the greater the temperature drop, which causes more sweating on the ducts. Your old system didn't dry out the air as well, so didn't sweat as much. I expect 18-21 degrees temperature drop.
Get a dehumidifier! One customer last summer was mad that I suggested she spend more on a dehumidifier after spending 10 grand on an Infinity system that dehumidifies. When I came back a few weeks later, she was mad that she waited all those years to get a dehumidifier! That basement was a night and day difference. No damp walls, it smelled better, the whole house was more comfortable.Jason
06-26-2011, 09:32 AM #26
I still say, seal and insulate.
Insulation will also increase efficiency, by decreasing heat gain through the ductwork walls. seal those gores on the elbows and insulate.
BJA105 lives in Randy's climate, I do not. A dehumidifier will remove water that's for sure.If common sense is so common how come so few of us have it!