A Bizarre Mildew (?) Puzzle --- brand new equipment

[Mizike531]

I greatly appreciate any help you can offer.

I just had a massive HVAC project completed at my home --- awesome system, Bryant Evolution variable speed, zoned --- working like an absolute champ.

I have been having a VEXING problem for the last week... I'm going to describe the symptoms, and then I will explain more about the project:

• A/C Runs all afternoon / evening (No Smell)
• At some point in the night, the A/C stops as the outdoor temperature drops (No Smell)
• We keep the furnace fan running all night and into the morning (No Smell)
• Depending on heat, the A/C kicks back on around noon. (STRONG MILDEW SMELL)
• After ~30 minutes of running, the smell dissipates (No Smell)

We keep the fan running at low speed continuously, and there is no smell at all until the A/C compressor kicks on each morning/afternoon.

More detail: when this smell starts, I can flip the system's mode to "Fan Only", and the smell will go away! I can then flip it back to "Cool", and as soon as the compressor kicks on the smell returns. I have tested this extensively and repeated the steps a half-dozen times.


Those are the symptoms... if you can help, I will be eternally grateful.


More about the project:

• Replaced all basement ductwork with sheet metal (2 story home, couldn't get to the ducts in the walls)
• Replaced previous A/C with Bryant 189BNV variable-speed A/C, 3 ton
• Replaced previous furnace with Bryant 987 variable-speed modulating furnace, 80k BTU
• Installed Honeywell ERV
• Installed Honeywell 4" furnace filter cabinets, using 3M 1550MPR filters
• Installed full zoning into 4 zones: First Floor, Living Room, Second Floor, Master Suite

Thank you very much in advance!

[lkapigian]

I'm sure one of the Green Grass States guys will be along, I am assuming you are in a high humidity area? Why do you leave the fan on, do you have fresh air make up tied to the unit or seperate?

[Mizike531]

Good question: yes, the ERV (balanced ventilation system) is tied into the main HVAC ductwork, and runs through the furnace.

I originally suspected it may have been sucking in rain or a bunch of humid air, but that only makes sense (I think) if the mildew smell persists while the fan is running but the A/C compressor is off.

[lkapigian]

Good question: yes, the ERV (balanced ventilation system) is tied into the main HVAC ductwork, and runs through the furnace.

I originally suspected it may have been sucking in rain or a bunch of humid air, but that only makes sense (I think) if the mildew smell persists while the fan is running but the A/C compressor is off.

No dehumidification with the A/C Off? What is the RH when A/C is off? Perhaps RH is climbing under low sensible load conditions-- Teddy Bear will be along soon I am sure

[Mizike531]

This is one of the more bizarre parts of the equation: I am absolutely anal about indoor humidity levels. I started this project after air-sealing our house tightly, to a point that ventilation became necessary.

I live in South/Central PA (Mechanicsburg), and we do get a lot of humid weather this time of year.

That said, indoors:
- I have four humidity/thermometer combos throughout the house, and I track them religiously. Upstairs never gets above 48%; downstairs never gets above 53%; basement never gets above 56%.
- I have a dehumidifier in the basement, and try to keep the humidity as low as possible. It is currently 49%, but on humid days I've seen crest it as high as 55-56%.
- The evolution system has built-in dehumidification, which kicks on when cooling isn't needed but humidity is up. That is generally the first thing that kicks on in the AM when we get the smell, but not always.

The climate control is great in here. Just can't understand the smell.

[lkapigian]

This is one of the more bizarre parts of the equation: I am absolutely anal about indoor humidity levels. I started this project after air-sealing our house tightly, to a point that ventilation became necessary.

I live in South/Central PA (Mechanicsburg), and we do get a lot of humid weather this time of year.

That said, indoors:
- I have four humidity/thermometer combos throughout the house, and I track them religiously. Upstairs never gets above 48%; downstairs never gets above 53%; basement never gets above 56%.
- I have a dehumidifier in the basement, and try to keep the humidity as low as possible. It is currently 49%, but on humid days I've seen crest it as high as 55-56%.
- The evolution system has built-in dehumidification, which kicks on when cooling isn't needed but humidity is up. That is generally the first thing that kicks on in the AM when we get the smell, but not always.

The climate control is great in here. Just can't understand the smell.

We do a lot of infinity which is Evolutions Step Sister--Unless there is something I am not aware of, the dehumidify only works when there is a call for cooling and just it slows the fan down-- unless you have reheat I am not sure how yours will run to dehumidify only--( I could be wrong) thinking you need a whole house dehumidifier

[Mizike531]

If the overall RH were high --- I would be on the same page.

The evolution system explicitly shows 'dehumidifying...' on the control. Not sure how it works, but it does a solid job

I hope some other idea may come out. Thanks again.

[lkapigian]

I'm sure Teddy Bear will be along, he is one of the greats here on Humidity- I live in a dry climate so I get what I glean from them....Thinking though the low sensible load on higher humidity days and the A/C is not on and will not turn on for a call of de humidify only without dropping below set point by 3 degrees or so- No expert but thinking the solution is a whole house dehumidifier

[teddy bear]

I'm sure Teddy Bear will be along, he is one of the greats here on Humidity- I live in a dry climate so I get what I glean from them....Thinking though the low sensible load on higher humidity days and the A/C is not on and will not turn on for a call of de humidify only without dropping below set point by 3 degrees or so- No expert but thinking the solution is a whole house dehumidifier

Teddy Bear is not that good. He would suggest, start taking things apart and look for the wet moldy spot. It could be a duct that allows outside dap air to come into the home and stay wet for extended time.
Turn you nose on and start a difficult job. The a/c dehumidification over cools and make things sweat for hours on end. A couple weeks and you end up with odor producing growths.
Good luck and start digging. Any ducts in the slab or fresh air inlets into the home? Also outside walls that get wet and then sun warming the surface driving the moisture into the all assembly and condensing on the backside of the drywall.
Follow you nose.
Keep us posted.

Regards Teddy Bear

[Mizike531]

Thanks Guys. Teddy, the key symptom I can't explain: the smell only occurs as soon as the compressor kicks on. It just doesn't make any sense...

With the fan running, no smell. Compressor kicks on, bad smell. After 30 minutes with the compressor on, the smell dissipates.

I appreciate any other theories that you can throw out.


To answer your questions directly:
- No ducts in the slab (this home has a basement)
- Fresh air: we have an ERV that I noted, hooked into the main HVAC
- Water behind drywall: can't happen here... just because our basement is unfinished block, and everything else is above-ground.

[teddy bear]

Coils have wet spots, warm wet spots produce odors. Cold wet spots, not so much.
Follow your nose and keep us posted.
Regards TB

[Sleuth]

.

Can you post a picture of the furnace/coil plenum configuration?
Upflow/horizontal? Transitions?
..

[Mizike531]

Away from home until late today, but will get pics asap.

Short version: upflow: air pulls into return trunk, through filter, into furnace, blows out into coil, then in to a flange that feeds the 4 zones.

No transitions --- straight from furnace in to coil.


Interesting side note: 3 ton a/c, but 4 ton coil. I checked the model numbers against the guide (ahri I think?), and they are an approved combination.

[Mizike531]

Attaching pictures, sorry for the delay, and also sorry they are sideways --- they don't appear this way in any other editor, I'm not sure why this is happening.

[Mizike531]

We are still in the same situation.

Our contractor came out and cleaned the coil, but the smell persisted. We then had a professional duct cleaning come out and clean everything --- no change.


We are now considering putting a UV light on the coil to see if it might help... otherwise, it seems like our only option is to escalate to Bryant directly.

[teddy bear]

Wish we could help. When starting compressor, smell the different supplies for source. Wet crock?? Include the ERV in search. Fresh air 24/7 or ??? Touch areas and smell hands for odor.
This probably not health threatening.
Keep us posted. If you were a nearby could help more.
Lets see how it goes with drier weather coming up.
Regards TB

[stvc]

I really can't think of any reason that may happen. Since the ERV and fresh air intake are probably new to the equation could it be drawing something in from the outside that when the coil cools it smells?

Looks like a real nice job on the install.

[teddy bear]

I have found a fresh air inlet that have a heavy growth of mold after a summer of hot humid weather. Condensation formed in the metal duct between the fresh air inlet and the ventilation equipment. The basement was cool enough to make the moisture in the fresh damp air stream. Take the outside duct off and smell or visually inspect.
Keep us posted.
When do you operate the ERV? Try 24/7 on high for the ERV.
Also try running the a/c blower on med or high instead of low during when the a/c is off.
Regards TB

[teddy bear]

I have found a fresh air inlet that have a heavy growth of mold after a summer of hot humid weather. Condensation formed in the metal duct between the fresh air inlet and the ventilation equipment. The basement was cool enough to make the moisture in the fresh damp air stream. Take the outside duct off and smell or visually inspect.
Keep us posted.
When do you operate the ERV? Try 24/7 on high for the ERV.
Also try running the a/c blower on med or high instead of low during when the a/c is off.
After the dehumidifier fails get a heavy duty Ultra-Aire connected to the a/c ducts to help keep them drier, quicker.

Regards TB