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  1. #1

    Question Fan Coil always running & humidity control issues

    Hi,
    I bought a newer condo (2007 concrete 4 story building) last year and it has a fan-coil system above the ceiling, and uses the hot/cold water lines in the building to heat cool. There is a compressor on the roof that chills the cold line during certain conditions... I think anything over +10C and it runs.

    The fan-coil is the APHBC model listed in on this page. There is no model number on the unit but there are a couple extra bits I have been able to figure out. It has dual blowers, the plenum opening is 10 x 40 and it has 2 rows for the cold coil and two rows for the hot coil. The apartment is 1050 sq ft, so I am assuming it moves a lot of air. If you look at the tech specs on that site you can probably make some good guesses as to what it actually is. Or if there is a picture of something you need to identify, I can do that.

    I have two separate concerns.

    First if I set the thermostat to 21C the unit runs close to 100% of the time. On a cooler day it might run 80%. So something in the system is not keeping up. Possibly this is the case of the fluid type, or the ability of the heat exchange to transfer heat fast enough? Eitherway, it seems 'broken' I was of the understanding that a heating/cooling system should be running more like 30% of the time. Is this a problem if it runs almost all the time? We usually get within a degree or two of our preferred temperature. Running through filters pretty fast though with these high run times.

    Second issue is we have no in-unit humidity control. I had some problems with excess humidity a month ago as the cold pipes were puking huge amounts of condensation, since it was hot out and the system was working hard, also the drip tray wasn't draining. I insulated the cold water pipes and fixed the drain, mean while my hardwood floor is ruined, as it didn't like the humidity. The condo board may be replacing the floor as this is technically their equipment that was improperly installed causing damages to us. My concerns with lack of humidity control linger though. The building uses a positive pressure central air system for the hallways. This pushes air into our apartment continuously. This air doesn't feel like it has any sort of humidity control applied to it (very moist in summer, very dry in winter), what is likely the case here?

    In terms of in suite humidity controls, ignoring the fact the building is pushing air into our suite, what are my options with this fan-coil system installed? In winter humidity here drops down to as little as 10%, so we need a way of adding water to the air. This is critical in terms of installing hardwood. The new hardwood is very pricey and can probably handle 60% but certainly not 10%. What kind of built in humidifier options would I have with a system like this?

    Any advice would be appreciated. (o:

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,316
    The positive pressure system uses outdoor air to pressurize the building. It should be cooled and dehumidified in summer and humidified/heated in winter. Otherwise the design is essentially pumping untreated air into each apartment unit.

    This may be a large part of the problem why your HVAC system inside your condo can't keep up. I would lean hard on the condo board to have the pressurization system evaluated...if it is supposed to treat the incoming air but isn't, that must be fixed. If there never was any form of conditioning equipment installed for the pressurization protocol, that's a design flaw and goes back to who did not specify that such equipment should be in place.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

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