Where is the water coming from?
A friend called and gave me the following information concerning his basement. I do not have an answer for the accumulation of water in the supply ducts other than possibly condensation.
Water has accumulated in supply ducts (flex duct). Holes were poked in supply ducts and “water poured out of them”.
Ducts run through basement for first floor. Basement tied into main system. System tonnage increased with new system a year ago to accomodate additional area of basement.
Mold/mildew above drop ceiling and on drywall in basement.
In the process of drying basement with dehumidifiers.
Third party will probably to called to do mold clean up.
Suggestions/answers are needed.
Replies
Please supply more information. Where is this house located? How is the basement constructed? What was the relative humidity of the space before dehumidification was begun? What is it now? How was the duct system sealed at the connections? Give as many details as possible. What type of system is it? Is the water in the airstream or in the insulation layer of the duct?
Water collecting in duct insulation at lowest points nearest metal supply ducts. Duct membrane is taped to metal boot and insulation is pulled up around boot with jacket.
RH was 50.3 and 72.3F when I visited today.
Split system with gas heat.
Mold/mildew noted at floor joists and rim joist. Around windows at bottom corners (areas of air leakage?)
Metal boots/grills installed at drop ceiling rusting. No water in these supply ducts. These ducts connect at tops of boots.
This is my take:
1. Basement should not be conditioned simply by cutting into the first floor system.
2. System was replaced in past two years. Friend says system was increased in size to accomodate additional area in basement. Worst thing to do. System super cools but does not sufficiently dehumidify.
3. Lack of dehumidification in basement leads to increase in humidity above 50%. Drop ceiling insulates/isolates floor joist cavity from remainder of basement. Rim joist is poorly insulated/sealed allowing heat and warm possibly moist air in. Metal boots near exterior walls (rim joist) are chilled when conditioned air circulates through them. Warm moist air at condenses on metal and gravity takes it to the lowest point in the duct. Any moisture in pressure membrane probably evaporates into circulated air.
4. Solution: Remediate mold/mildew. Replace all duct work. Separate system with properly sized AC and possibly system dehumidifier for basement. Insulate rim joist and ventilate space above ceiling. Identify all exterior moisture penetration issues and correct.
I'm not sure about your diagnosis but just because I don't fully understand your description. The wet insulation indicates a break in the vapor barrier of the duct insulation. The mold and mildew seems to indicate infiltration of humid outdoor air into the cooled space.
Your prognosis sounds correct but how will you ventilate the space above the ceiling? The metal boots need to be insulated with a proper vapor barrier to protect the insulation or insulated with an armaflex or imcoa sheet type insulation.
I would drop in grills in place of ceiling panels to allow air to circulate above.
One per separated space should do nicely. Let us know how it works out.
Nothing has been mentioned about return air in the basement.
Since the system was upsized to include the basement load (sq. ft?), and "super cools, but doesn't dehumidify", it sounds like a ROT calculation was made, and ad hoc distribution installed. The presents of mold, in addition to moist air infiltration, may also indicate a lack of proper circulation via adequate return air.
Dave
You are right. Return via staircase to first floor. HVAC contractor did not do these folks any favors!
To make an informed suggestion to remedy the situation, the following is a minimum of details required:
Details of the residence, wall construction, insulation values, basement foundation construction and finishes, square footage of everything, geographical location, siting details (like the presence of large shade trees, general lot description, etc) and the details on the HVAC system(s) including all equipment capacities, and supply and return duct specifics.
What you have described, significant amounts of liquid in the supply ducts, falls outside the list of problems associated with "simple" poor equipment sizing/selection and poor installations details.
Inside of an AC system, working anywhere close to properly, the only place that liquid water should be present is at the evaporator coil and the drainage for that coil. In systems that have horizontal or downflow coil orientations, some carry-over is possible if poorly done.
Outside of an AC system, especially during a transient, condensation on the outside of uninsulated ducts is not unexpected or uncommon. In a concealed space, unsealed and uninsualted ducts will stain the ceiling in most cases, so avoid this situation.
Basements are difficult to treat properly; typically are below grade with little or no cooling load and lots of cool (or at least below dewpoint temperatures of "normal" inside air conditions, ie 75 degF, 50% relative humidity) surfaces.
Rules of thumb are useful primarily in budgeting so I will not go there.
My suggestions:
1) find an experienced HVAC professional (preferably a competent design engineer with a PE license) and have a detailed analysis performed of the residence - i.e. a room-by-room load calculation, block load calculation and a design-day dehumidifcation load performed. With all of the pertinent and accurate information provided up-front, this should be a 4 or 5 hour task. A reasonable fee would be in the $500-600 range.
2) based on the analysis, compare the loads to the existing equipment, make changes/adjustments as necessary - again, a competent professional should be involved, a manufacturer's technical service advisor or a real sharp NATE certified technician.
3) remove the flex duct, replace with galvanized steel, seal the joints and insulate with 1-1/2" foil-face fiberglass duct wrap, staple and tape the seams, AFTER the distribution has been verified as adequate. Include/add returns in the basement near the floor.
Some of the necessary actions to remedy this situation will be expensive. I suspect that previous "cost saving measures" are more to blame than incompetence here. If your friend balks at paying to do it right, do your best to encourage them otherwise.
Also see 62168.9 for some additional ideas/comments.
Edited 9/9/2005 9:32 am ET by Tim
Great information Tim. We often get what we pay for. Ignorance is our worst enemy. A copy of your post is going to my friend.
Thanx