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  1. #27
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    Quote Originally Posted by teddy bear View Post
    For healthy indoor conditions, you should have a fresh air change in 4-5 hours. With high out door dew points and low/no cooling loads plus the moisture from the people in the space, expect to need a small whole house dehumidifier to maintain comfortable %RH. 3-5 lbs. per hour of dehumidification is needed with a 2-3 occupants and +60^F outdoor dew points.
    If you could stop fresh air infiltration, you would be in air polluted space with insufficient oxygen levels to be healthy.
    Add the small whole house dehumidifier like the Ulra-Aire 70H. I would include fresh air option for the calm weather ventilation.
    Regards Teddy Bear
    Thank you for the advice... Would you have an idea of the cost of that system?

  2. #28
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    Quote Originally Posted by Hammer09 View Post
    Do you have Daikin units? Just wondering if the problem is worse in my case because of my units or because of my house.
    It's with minisplits in general, or atleast what I've found.

    I have a fujitsu, and I have a Midea.

    All minisplits work off of the same principal, and are very similar.

    Personally, I would agree with Teddy Bear and the ultra air 70h.
    Although, I would tell you that with it, you are getting a very premium system, that (atleast in my market) is more of a rarity than the norm. Most people end up satisfied with the humidity levels without it, although you will be much happier with it.

    As far as costs, we can't be specific because every installation is different, but I would tell you it's in the thousands of dollars, not hundreds.


    One thing to point out, and the biggest complaint I get, is that "my normal system didn't have these problems".
    Rightfully so, but if your having issues with dehumidification during low loads, you were probably have dehumidification issues with the old system, but it kept it below a threshold of you noticing.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  3. #29
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    Jun 2001
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    How about we drop back a bit? What did the room by room load calc indicate would be the right size unit?
    Perhaps you should have read the instructions before calling.

  4. #30
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    Quote Originally Posted by jrbenny View Post
    How about we drop back a bit? What did the room by room load calc indicate would be the right size unit?
    Honestly, I'm not sure. Should I ask the installer what it was? I can provide the square footage and the BTUs for each unit, can the room load calc be determined that way?

  5. #31
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    Quote Originally Posted by hvacvegas View Post
    It's with minisplits in general, or atleast what I've found.

    I have a fujitsu, and I have a Midea.

    All minisplits work off of the same principal, and are very similar.

    Personally, I would agree with Teddy Bear and the ultra air 70h.
    Although, I would tell you that with it, you are getting a very premium system, that (atleast in my market) is more of a rarity than the norm. Most people end up satisfied with the humidity levels without it, although you will be much happier with it.

    As far as costs, we can't be specific because every installation is different, but I would tell you it's in the thousands of dollars, not hundreds.


    One thing to point out, and the biggest complaint I get, is that "my normal system didn't have these problems".
    Rightfully so, but if your having issues with dehumidification during low loads, you were probably have dehumidification issues with the old system, but it kept it below a threshold of you noticing.
    Thank you for the additional info, that is good to know. I had the same complaint, we never saw humidity and/or air quality problems with the PTAC we had before the mini-splits. That really is a sticking point for me, how could one system increase humidity while the other doesn't? I get that they are different, but shouldn't a professional installer take steps to make sure that isn't going to be an issue prior to an installation? It's very frustrating to have a new system that isn't usable for my family.

  6. Likes jrbenny liked this post.
  7. #32
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    Quote Originally Posted by jrbenny View Post
    How about we drop back a bit? What did the room by room load calc indicate would be the right size unit?
    X2. Many people think because it's an inverter system oversizing does not matter. Not true.
    Make your expertise uniquely valuable.

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  8. #33
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    Minisplits do not have the same coil depth as PTACs or central a/c. One row of cooling coil isn't a lot of surface area to drop moisture out of the air.

    If the minisplit control scheme, overlayed on this thin coil, is based on varying blower and compressor speed to manage air temperature, dehumidification will be the loser here. Coil temperature has to stay cold enough, and sufficient rows of coils be in place, to effectively remove moisture at lower air speeds.

    Short of ripping out the minisplits I think separate dehumidifiers are the solution, here.
    Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.

  9. #34
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    Minis run 200-225 cfm per ton. Cold coils and slowed airflow. So properly sized minis dehumidify just fine.
    Perhaps you should have read the instructions before calling.

  10. #35
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    Quote Originally Posted by Hammer09 View Post
    Thank you for the additional info, that is good to know. I had the same complaint, we never saw humidity and/or air quality problems with the PTAC we had before the mini-splits. That really is a sticking point for me, how could one system increase humidity while the other doesn't? I get that they are different, but shouldn't a professional installer take steps to make sure that isn't going to be an issue prior to an installation? It's very frustrating to have a new system that isn't usable for my family.
    So what size was that ptac?
    Perhaps you should have read the instructions before calling.

  11. #36
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    Minis run 200-225 cfm per ton. Cold coils and slowed airflow. So properly sized minis dehumidify just fine.
    Interesting. Looked up some specs for a Mitsubishi Halcyon minisplit rated at 12,000 BTUH nominal. At high fan speed it moves 489 CFM and removes moisture at a rate of 2.7 pints per hour. 2.7 pints = 2.81 lb/hr moisture removal capacity.

    Next time I'm around a minisplit I'll measure enthalpy going in and out of the evap so by (Hin - Hout)/(Hin - Hadp) I can see what kind of coil bypass factor these little guys run at.
    Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.

  12. #37
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    Quote Originally Posted by Hammer09 View Post
    Thank you for the advice... Would you have an idea of the cost of that system?
    For an idea of cost, search Ultra-Aire, plenty of prices out there.
    Because of the technical nature of the products, suggest getting a local a/c contractor to sell and install. It will cost a little more but well worth it.
    Your tech needs to get the a/c working correctly and doing its part of humidity control. A small whole house dehumidifier is intended to keep a home dry during low/no cooling loads and high outdoor dew points.
    Your cooling cost will not go up and your home will be much more comfortable.
    Regards Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  13. #38
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    Quote Originally Posted by Shophound View Post
    Interesting. Looked up some specs for a Mitsubishi Halcyon minisplit rated at 12,000 BTUH nominal. At high fan speed it moves 489 CFM and removes moisture at a rate of 2.7 pints per hour. 2.7 pints = 2.81 lb/hr moisture removal capacity.

    Next time I'm around a minisplit I'll measure enthalpy going in and out of the evap so by (Hin - Hout)/(Hin - Hadp) I can see what kind of coil bypass factor these little guys run at.
    Funny. All I hear in Daikin training are the numbers I posted. "Rated" test is 350-400 depending on the system. Allegedly, the systems operate lower cfm per ton during standard ops. Need to do some testing myself.
    Perhaps you should have read the instructions before calling.

  14. #39
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    Quote Originally Posted by jrbenny View Post
    Minis run 200-225 cfm per ton. Cold coils and slowed airflow. So properly sized minis dehumidify just fine.
    So, would you recommend I go back to the installer and ask them to size them down?

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