Our company did an install a few years ago that had similar humidity problems. Home owner was the engineer( for real ). We performed a Man J and Man D, heat load calcs called for 4 tons cooling. We did installed, set up and startup. Heat pump/ 2 speed/ variable speed ahu with an ERV and electric back up heat. Sometime after load and duct calcs the owner switched to very energy effiecent insulation, SIPS panel roof and very tight construction. We were never consulated about any negative effects of these changes. Winter the house heated great, summer they kept complaining about high humidity. The ERV was suspect but set up checked out. Owner had an energy evalaution and found that he only needed 2 ton of cooling due to the insulation that was used. System was in second year of use and we were prepared to install a smaller unit at our expense. Luckily the 2 speed unit will perform perfectly on low speed with proper fan settings. We have not had another complaint. Little E.O. changes can have dramatic effects.
Okay, new question. We are getting ready to downsize the units - probably to two 3-ton units from the present pair of 5-ton units. The present units are 13 SEER. Contractor has presented quotes for 13 SEER and 16 SEER replacements, with a fairly significant price difference.
Is it worth it? Seems like I heard somewhere that in hot/humid climates, the SEER rating wasn't as big a deal as [memory gives out]. I don't want to spend an extra 70% if it isn't going to buy me anything.
By the way, thanks to all of you for your input. It's been eye-opening...
A few things to look at before it all gets blamed on oversizing.
I usually find that dropping the blower speed down and running the fans in Auto mode can get places here sized for a ton for every 400 sqaure feet to hold under 60%.
Now with the aprilaires one of the install methods they recommend is the bypass method and this means it draws in air from the return air duct and blows it back into the supply duct. The only problem is you have to run the air handler blowers all the time.
So running an air handler blower all the time, especially a pair of 5 tonners is going to put your bill up.
the setting on the Aprliaires is a little misleading also as the controller is for "so many bars", with "one bar" meaning it is trying to maintain a 65F dewpoint and "seven bars" meaning it is going to try and maintain a 40F dewpoint. I would recommend "three bars"
Now if the air handler fans are running all the time, they are going to revaporate a couple pounds of water back into your house everytime the compressor cycles off.
If you have any kind of fresh air intake to the return, running the air handler fans all the time is going to draw in unconditioned outdoor air.
I would first verify the operation of the air conditioning and have it documented how it is performing, drop the blower speed down so you have perhaps 1700 or so CFM moving per system, and then only run the air handlers when the compressors run.
I would also make sure that the dehumidifers had their own return air grilles and did not rely on having to run the air handler fans all the time. By all the time, I mean when ever there is a call to dehumidify. You make it sound like you can never get it down below 60% in there so I assume the dehumidifiers are running steady and the blowers of the air handlers are running steady.
10 minutes per hour and you got the system set up to 82 degrees all day while you are at work will just tend to pump a little bit of moisture into the home. You have both air handlers set up like this? 10% outside air on the two systems right now is 400 CFM.
Originally Posted by adt2
that will overwhelm a pair of aprilaire 1700s, they just start to catch up then you ventialte for another 10 minutes!!!!!!!
You are not their breathing all day, I would disbale the fan cycler until december
The dehumidifiers - as I understand it - are set such that they do not run more than about 10 minutes out of every hour. The air handler does not run constantly. I have observed this in the early spring / late fall, when there is no heating or cooling load on the system; the air handler still kicks on for about 10 minutes at the end of every hour.
As far as I know, I do not have variable speed equipment at this time. Not sure if the fan speed can be turned down.
I believe the dehumidifiers are set up to pull air out of the return air system; they don't have their own intakes.
standard rule of thumb down here I am afraid, more humid than houston, but less insulation on walls
Originally Posted by beenthere
Before you spend any money changing anything, you need to get another company in there to just verify that the systems are properly functioning for what they were designed to do.
Originally Posted by adt2
The standard air handlers have multiple speed settings and a good tech should be able to see how much air you have moving presently, and he should be able to drop the speed on the two units.
Your dehumidifers should run, whenever it is more humid than what you set them for.
The air handlers are kicking on for 10 minutes out of every hour when you are at work, you are setting the temperature up when you are not there. So it will be like the spring or fall everyday, but now it is pumping humidity and the AC is not going to kick on as you have the temperature set up. Probably 70% of the cooling you need right now to condition outdoor air in houston is to pull moisture out and only 30% is needed to cool the temperature.
This fan cycling is pumping moisture into your home.
If the dehumdifiers draw in air from the air handler return air duct and then supply dry air to the air handler supply duct then all it is doing is it is drying out the air handler. The majority of the air is flowing backwards through the air handler in a short circuit.
You are better off if the dehumidifier can draw air directly from its own intake, then supply it back to the house through a backdraft damper and then into the air handler supply air duct work.
So do you think I am better off - for the time-being - just shutting the dehumidifiers off? If all they're doing is pulling in outside air all day long, seems like the thing to do is turn 'em off and see what happens. Can't hurt, I guess.
Originally Posted by adt2
keep in mind as its relatively new the materials are off gassing in your home and if you reduce fresh air too much you may increase the indoor air polution and possibly put your family at a higher risk of health problems
Oh and what canark says too - he doesn't know allot but he does know humidity cause he sweats allot
Actually he knows alot for an engineer that is
Last edited by The Penguin; 07-14-2008 at 04:57 PM.
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The dehumidifiers are bringing in the outside air or your air handlers are? You made it sound like if the system has not run for one hour it will turn on the air handlers for 10 minutes.
Originally Posted by adt2
Try this, leave it set at 74F all day for a couple days, see if it improves.
You need to get someone over there who can figure out exactly how your system works, as I do not believe you completely have it figured out presently.
Humidity is most likely coming from the outside air, since you did not post that you have a water feature in your living room, that your wife simmers chile all day, or your wife hang dries laundry in your living room.
So if your house is as tight as the inspectors say,humid air is not infiltrating in at a high rate so I would really suspect it is mechanical. So it is either that forced fresh air intake or a constant exhaust fan causing the problem is my guess.
Forgot to mention - I did a little experiment over the weekend. My t-stats have a timer feature that tells you to the nearest hour how long the compressor has been running. I reset the timers on both units at 9am Saturday, and noted the reading on the electric meter.
Checked 'em at 9am Sunday. One ran 5 hours, the other ran 11 hours. Don't remember the exact kwh usage, but when I figured the cost, it was about $28 for a 24-hour period. Mentioned the 11-hour number to my wife, and she said she'd lowered one T-stat while the kids napped. Told her not to mess with it the next day so I could get a baseline.
Checked 'em again this morning. Five hours on one, six on the other. Total cost in the range of $18 per 24-hour period. Threatened wife if she messed with t-stats again.
we pay about 36 cents a kWh here.
17 cents is steep for the states, but you also have to try and not be the guy who just bought a hummer and then cries about 5 dollar gasoline.
A house your size here with the steady 2 hp pool pump would be paying about 1800 a month for power bills
high elec bill
first, see if you can find a reputable contractor who is an acca member. have him perform j-load's on your house. this should give you a definitive answer as to what size system or systems you need.
if they think you need just 5 tons of air maybe they can remove one system and redesign your existing duct work. your duct work will not work correctly if they were sized for a 5 ton unit, and you only need a 3 ton unit. different size ducts produce different cfm's.
as well, your RH at 60% is way to high! at 60% that is conducive to the growth of mold. a good RH is between 45-50% in my opinion.
Lastly, with a correctly designed HVAC system you should be able to remove both your dehumidifiers. there is NO need for them in a correctly designed home. your a/c unit needs to run at least 7-10 minutes before it even starts the dehumidification process. if your units are short cycling, it will never do that!