Shop Products
Houzz Logo Print
adamdoc_gw

Geothermal and humidity upstairs...

Adam F
9 years ago

Hi all - thanks in advance for reading... To say this has been a saga would be an understatement...

We have two 3 ton Bosch Geothermal units installed in our new construction sprayfoam insulated home almost exactly 12 months ago. Shortly after that time, I noticed that humidity seemed high, so our installer recommended activating the "Dehumidification" setting on our Honeywell Prestige HD 2.0 T-stats. Downstairs went from the 50% range to 42-44% almost immediately, and it has remained there since. Upstairs didn't perform as well, but we soon switched into heat mode, and the problem went away...

Fast forward to this spring... Humidity downstairs stayed fine, but upstairs was regularly above 60%, and we've had dozens of visits from our installer, and now several from Bosch, after I contacted them via Twitter. Bosch has been EXTREMELY responsive, but we're all a bit at a loss still, though it seems we're headed in the right direction. Here's what we've done (not necc in order)...

1. Put the fan speed on slow. No help.

2. Forced stage 1 for 60 minutes, and then eventually even disconnected stage 2 activation. No help.

3. We changed the drainage trap on the air handler to prevent airflow from sucking in water. No help.

4. We re-leveled the air handler to be sure there was no overflow... No help.

5. We adjusted the back loop re-circulation circuit to be higher and lower pressures... No help. (This is a loop form the main output back to the return to prevent overpressurization if only one small zone is calling).

6. We tried a variety of dehumidification settings on the T-Stats, though there is no dehumidifier on the system, so this just runs the temp down a bit intermittently. Didn't do anything upstairs, though it does seem to help downstairs...for some reason. Last night, for example, the humidity down there got to 48% for the first time ever, after I turned off the dehumidification setting for 5 days... I was about to be happy about how it wasn't needed, and then turning it back on fixed the issue.

7. Opened all three upstairs zones to be 20% open even when not calling, to improve circulation. Not much help.

8.Replaced a temp control valve that was faulty. No effect on humidity, but cooling was faster.

9. The copper line-set was undersized for the run, so it was changed. After doing that and charging the compressor and water loop within half a hair of perfect, the BTU calculations went far beyond ideal... Humidity went down a little, but not consistently.

10. I put a hygrometer in the upstairs master, and monitored it. I finally got a standalone dehumidifier, which got us to around 56% on a good day. Better than 65%. Still not ideal.

11. Most recently, we tested the humidity in the attic, and it was 62%. So, we added a return in the attic, which is totally sealed with foam (open cell under the roof, closed in the walls). The attic already had a register, but no return. We also made the register larger. At the same time, we moved the dehumidifier into the attic, and have it on a continuous drain into the air handler drain line...

THIS DID THE MOST so far. As of now, we can regularly get down to 50%, but still occasionally get up to 58% like we did last night...and therein lies the mystery. Last night, our bedroom got up to 58%, which was easy to notice because I woke up sweaty for the first time since step 11.

I went into the attic, and all was well. No leaks, no sweating, and the dehumidifier was running. Temp was 70, and humidity was 42%!

So, my question is...WHAT GIVES?!

Does the attic just still need to dry out?

ONE variable from last night that really got me thinking is that we just got a puppy, and she sleeps in our mudroom, which has an exhaust fan. I turned it on overnight to give some white noise - not a permanent plan, but we wanted to see if it would cut down on whining. Well, with that on, the downstairs humidity went to 48% for the first time since we moved in...

Well, that got me thinking. We also have a bathroom upstairs with a kitty litter box in it, and we run that fan (110CFM Panasonic - fairly silent) ALWAYS.

So, we passed our blow-test with flying colors, and we have replacement air with powered baffles for our 1200CFM vent hood...

So...is it possible that running our vent fans (appropriately sized, as opposed to contractor grade) is pulling humidity/outside air BACKWARDS through the other vent fans in the house? This am I turned off the fan in the cat room, and the humidity is 51% as I remotely monitor from work while typing this... We'll see if it gets lower.

I am kicking myself that I didn't think of that earlier, since I knew that our 1200CFM hood needed replacement air for risk of backdrafting out pilot lights, but never considered a 110CFM fan to be worthy of consideration... Anyway, if anyone has any thoughts, I'd appreciate it.

For reference, we are in Atlanta, and it's been hot with 75-90% humidity over the majority of this period, with rare exceptions... We have two 3 ton units, and the upstairs is a split. The upstairs in minimally oversized, but several opinions have agreed that the sizing is appropriate.

One other item - the Bosch reps think that the open cell foam in the attic could be wet from prolonged humidity and may just need time to dry out, but if the attic humidity is already at 42% is that still a consideration? Dicuss...

Thank you in advance. I'll send my wife's amazing baked goods from our DCS setup (that got me into this forum in the first place) to anyone who solves the mystery.

Comments (11)

  • sktn77a
    9 years ago
    last modified: 9 years ago

    I'm thinking a combination of air infiltration and oversized upstairs unit (although deactivating the second stage should have helped there). How big is upstairs, downstairs and the attic and does the second floor system serve the attic also?

  • sktn77a
    9 years ago
    last modified: 9 years ago

    Is your washer/dryer on the second floor?

  • fsq4cw
    9 years ago
    last modified: 9 years ago

    Have you considered an HRV or ERV? Probably an ERV in your location.

    SR

  • Adam F
    Original Author
    9 years ago
    last modified: 9 years ago

    Haven't considered ERV or HRV because all experts we've talked to from Bosch say the system should work. We DO have a clean air intake/recirc system but that just brings in fresh air intermittently as far as I know.

    Our laundry is upstairs, but we don't use it much (only two people).

    Our house is roughly 2000 ft down, 3000 up, with attic over the entire upstairs. All but 2000 ft is very low ceiling and all is spray foamed. And home today with exhausts all off, and upstairs is 53%, down is 44%. It's been lower with upstairs cat exhaust on. Not sure it made a difference.

    How do I check for infiltration sites? Blow test was phenomenal, according to the guy who did it. Is this a positive/negative pressure issue in the house? Fixable?

    Adam

  • fsq4cw
    9 years ago
    last modified: 9 years ago

    Bringing in unconditioned outdoor air may be a problem if the air is of a higher humidity than the exhausted ‘conditioned’ air. This may be a design flaw. You’re running your geo at high cost to dehumidify the air then exhausting it to be replaced by possibly more humid air. An ERV would be ‘conditioning’ the air exchange to preserve the work done by the geo units instead of just pissing it away.

    What’s this 1200cfm vent hood, a stove hood? That’s far more cfm than what’s needed for fresh air exchange every few (3) hours.

    I would suggest hiring an independent ventilation/duct specialist that does custom design work. It’s unlikely the guys you have now will admit they messed up the design/installation. If the line set was the wrong size what else is wrong? You shouldn’t need to run an expensive to operate stand-alone dehumidifier.

    Were you not home when the blower door test was run? That was the time to check for infiltration sites!

    A PROPER static pressure test should also be performed on the ductwork to determine its performance.

    IMO

    SR

  • jackfre
    9 years ago
    last modified: 9 years ago

    Not sure if it will help, but Tjernlund makes a product called the AirXchanger. It runs off a humidistat. It is worth a look. It might help the attic

  • Adam F
    Original Author
    9 years ago
    last modified: 9 years ago

    Thank you for the reply. I was home when the blow test was done, and they said the test was amazing, and the the house was extremely tight. We did find one problem, which was a window left open by a painter. When we closed it, we didn't find anything else.

    As to having an independent person check it out, our installer is essentially out of the picture. We now have some senior techs at Bosch who are on the case. They've made a few visits, and have suggested tweaks. Things are improving, so they want me to keep waiting, but soon we will have low outside humidity, and we'll have to wait another year to solve this. They have assured me that their warranty will hold, and that they will take on fixing whatever needs fixing.

    Who would I hire to do an independent check? We're in Atlanta, if you have any suggestions.

    As to the attic, it is now super dry, and I plan to turn off the dehumidifier to see if it stays that way.

    As far as the 1200CFM vent hood, I'm not sure I understand what your concern is. That's what we needed for the BTU rating of our range, and we have a dedicated Broan replacement air system that only opens when the hood is on.

    Is there a way to increase the static pressure in the house so that we are net pressure positive, so as not to pull in outside air?

    I guess out biggest problem is that we can't get anyone who thinks this is as urgent as we do...

    thanks again,

    Adam

  • Adam F
    Original Author
    9 years ago
    last modified: 9 years ago

    One more piece of info - this is the ventilation system they installed for each unit (the link won't work, but the name is below). We have one up and one down. The downstairs one doesn't seem to have any problems..

    Honeywell Y8150 Fresh Air Ventilation System

  • mike_home
    9 years ago
    last modified: 9 years ago

    How large is your house? Was a load calculation done? How was the size of the AC units determined?

    My first thought is 6 tons is over sized for a new construction with a sprayed foamed attic. The ACs might be shorting cycling.

    Does the attic have ventilation? Are there ridge and soffit vents? The fact the second floor is more humidity than the first makes me think there is a lot of moisture trapped in the attic. All the moisture that rises to the attic cannot escape if there is no ventilation.

    These would be the areas I would investigate.

  • fsq4cw
    9 years ago
    last modified: 9 years ago

    OK on the vent hood.

    Regarding the Honeywell Y8150 Fresh Air Ventilation System, the installation manual states:

    . TIPS:
    . To meet ASHRAE 62.2-2003, system must have at least a MERV 6 filter installed.
    . In cold climates, balanced ventilation is recommended. An exhaust fan or heat recovery ventilator can be used.
    . Humid climates may require additional dehumidification equipment.

    I still believe your solution lies in the direction of proper attic ventilation and HRV/ERV fresh air exchange. I doubt that Bosch has any real interest beyond the proper operation and COP of their HPs.

    IMO

    SR

  • Adam F
    Original Author
    9 years ago
    last modified: 9 years ago

    Hi all - an update... So, we had SouthFace consult (they are a green building nonprofit in Atlanta), and they basically advised adding a dehumidifier for the upstairs unit. Their thinking is that given how well insulated and air-sealed we are, the unit will only adequately dehumidify when it is extremely hot outside, and even then, it may not run long enough. They said we could tinker forever, but thought that a dehumidifier would solve everything in the fastest and cheapest way possible. Onward and upward! Thanks for the input... Also, it is a good thing we did investigate with Bosch, since they found a TON of installation errors made by our original terrible installer.

    Adam