High indoor humidity

[PatrickD]

Bought 28 year old house. Replaced windows, wiring, HVAC ( including duct work )and insulation. Converted screened in porch into 4 seasons room with separate gas pack HVAC. Air tight crawl space ( double 6 mill vinyl dirt floor covering, foam insulation outer walls ) underneath with duct supply and return.After 1 month occupation, humidity 68-71% throughout house. What options for correcting do I ( and installer ) have? Thanks, guys---------Patrick

[coolwhip]

Make sure the duct in the crawl space is ceiled and insulated. Did you have a load calc. done on the home? If not , the a/c may be oversized. It may be cooling the temp. down but not removing the humidity like it should. Does the ac short cycle? What size home? what tonnage is the ac? Model and serial? Outdoor temp? indoor temp-wet bulb? Suction temp? subcooling?

[espock]

Your options could be:
1) Buy a dehumidifier, probably least expensive option.
2) Have your installer install a TXV (Thermostatic Expansion Valve) at your evaporator to improve latent heat removal (might slow down the blower speed a little bit as well if possible).
3) Install a "whole-house" dehumidifier. This is probably most expensive option.

Read these articles for info http://www.contractingbusiness.com/news/article.cfm/newsarticleid/550

or look at the Q/A for hunidity control from this site
http://www.centralcityair.com

[dash]

Sounds like all the thermal improvements you made,reduced the size A/C system needed,if you replaced with the original size ,now you are likely oversized.

If your contrator knew of all the improvements,maybe he can help you now.Oversized systemed= high humidity indoors.

[PatrickD]

Thanks,fellas, for your prompt response.
The current indoor readings: 72.3 degrees, 71% humidity. Outdoor readings: 84% humidity, 77 degrees.
If its oversized, who has responsibility for corrections?
Do you replace the current HVAC for lesser ton units?
If a whloe house dehumidifier is preferred, who foots the bill?
Can I insist the units be relaced for smaller ones (or is that being too much of an a$$ hole )? .
The installer thinks the units are short cycling ( I've not noticed ) and adjusting the fan speed will do the trick. Is that reasonable ?
By the way, fans set on continuous, no moisture on walls or windows yet.
Thanks again--------Patrick

[dash]

Fan should be set on auto,fan on ,will add humidity,from the wet coil and pan,on the off cycle.

Who should pay?Depends, as I said,did they know about all the thermal improvements or not?If they did,then they should have some part in correcting the problem.

Many of the ideas already stated ,will help,hard to say from here if that will be enough.

Another trick is run a 4" duct ,with a damper, from the supply to the return duct(near the grille),this will improve dehumidification,just as a bypass damper does in a zoning system.

[PatrickD]

Thanks, Dash. FYI- About 2000 sq. ft. house. Three ton Split system for most of house ( one story ) and 2 ton gas pak for 4 seasons room and portion of kitchen.

[espock]

If the AC is slightly oversized, you can use the extra BTU to remove latent heat i.e. moisture. Ask the installer to move the blower to the lower speed tab possible (to get lower evap. temp for better moisture removal but still above freezing temp), then adjust the Freon charge to get proper supperheat (i.e. guarantee gas returning to the compressor). This would lower your total system's SEER but better in humidity removal. If you can afford, install the TXV since this regulates the freon flow to the evap. best under various heat loads (day vs. night) and prolongs the life of the compressor (well worth it long term).

Other thought, 72F @ 71 RF, the dew point is about 62F, the evap. should be able to remove a bit of moisture. If your evap drain line puts out decent amount of water, it is doing its job, maybe your house is not well insulated from moisture infiltration from outside or there are moisture generation sources within the house (bath room not ventilated ...). If there is not much water dripping from the AC drain line, then take those suggested measures.

[Edited by espock on 06-22-2004 at 02:57 PM]

[airman1]

if you fail to get it lower...downsize the coil to a 2 ton with a 3 ton txv...smaller coil will remove 50% more humidity and still give you three tons of cooling...been downsizing in houston for 18 years so i know this will work

[PatrickD]

You guys are the best! Thanks---------------Patrick

[PatrickD]

One other question and I'll quit aggravating you folks. What's a TXV?

[Shophound]

TXV = thermostatic expansion valve. It is a much more accurate metering device for the evaporator in that it maintains a consistent coil temperature over a wider range of operating conditions. A piston, also known as a fixed orifice or flow rater, meters the same amount of refrigerant regardless of conditions. Sometimes this amount is perfect, other times, such as during high or low loads, it's too much or too little, respectively.

A TXV can contribute to long compressor life, along with proper maintenance.

[54regcab]

Originally posted by airman1
if you fail to get it lower...downsize the coil to a 2 ton with a 3 ton txv...smaller coil will remove 50% more humidity and still give you three tons of cooling...been downsizing in houston for 18 years so i know this will work

Airman, does this increase or decrease DeltaT provided CFM remains constant?

[wormy]

Do you have any sources for humidity in the house?
i.e. Hot tub, water fall (artwork, decor, etc), large aquariums, clothes drier vented properly (vent disconnected behind drier may be more noticeably since the laundry room will get hot. Sometimes they are not as noticable though. Sometimes you will see an unusual accumulation of stuff get on you air filter for your air conditioner. Compare the color of what you find on your air filter with the color of the lint you get out of your drier filter. A drier vent venting under the house is not good either.
Not only do you add all the moisture from your wet clothes to under the house... but the heat rises up against your floor and cunducts the heat back into the house. Turn your drier on and check the vent outside. If its blowing alot of air, then chances are its not come undone. If you can get under your house *SAFELY* then a visual inspection is best.


Factors that contribute to an air cond system to not remove humidity properly include...
Duct leaks
High Air Flow
Oversized equipment
Low refrigerant

Just a side note:
I've seen systems with the new refrigerant (R-410 / Puron)
appear to be fully charged by the gauges, but an actual
capacity check revealed it was not right.

(For the tech's out there... 19 delta T Dry bulb 8 delta T Wet Bulb... removing plenty Sensible but not latent. This is on a Trane XL14i with the correct air flow.
No duct leaks. Capacity check revealed about 19000 btu
total but should have been closer to 38000 at the time.
Don't have all the info available right now to show you... just be warned the R410 might fool you even though the charge looks right.)

Other factors to consider...
Cheap hygrometers from wal-mart are just that... cheap.
Get you hvac guy come in and test with an accurate meter.
Does the house feel like a cave? Cold, damp, and clammy?

Is the hygrometer located near a room with sources of water? i.e. Kitchen, bathroom, laundry.
It should be located on an interior wall also.

[dan sw fl]

Originally posted by PatrickD
Thanks, Dash. FYI- About 2000 sq. ft. house. Three ton Split system for most of house ( one story ) and 2 ton gas pak for 4 seasons room and portion of kitchen.

Location __? Did I miss the city you are in?

... As Always .. Did you correlate this performance with an updated Manual J analysis?

[wormy]

Check his profile ;)

[dan sw fl]

Originally posted by PatrickD

The current indoor readings: 72.3 degrees, 71% humidity. Outdoor readings: 84% humidity, 77 degrees.

If its oversized, who has responsibility for corrections?

If a whole house dehumidifier is preferred, who foots the bill?

The installer thinks the units are short cycling and adjusting the fan speed will do the trick. Is that reasonable ?

By the way, fans set on continuous, no moisture on walls or windows yet.

dT across coil is VERY VERY Small.

Setting fan on Auto and mininum fan speed is likely to get you to < 60% R.H.

Try that for ~ 2 weeks and if not consistently < 58% R.H. request whole house dehumidifier AT Contractors Expense for not evaluating new conditions in Manual J that he should have provided to you as part of prosposal.

If a summary of Manual J was actually provided, then the owner should be responsible adding dehumidifier ( perhaps at time & materials cost with an accomodating, fair contractor ).

I WRITE the Window S.H.G.C. basis into the proposal if the builder is not absolutely clear on the degree of window and door glass tinting.

Renovations ALWAYS Require MUCH more effort to assure that the building structure variables are addressed correctly.

[dash]

This thread started about a year ago,doubt the OP is checking back still.

[wormy]

Thats too funny :D