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  1. #1
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    Jan 2020
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    Can I go ductless? I keep being told I need an ERV and those are ducted

    Hello, new member, learning the rules. Please be patient with me. I joined as I'm seeing some great information being shared on this site and I have a few questions/clarifications I'd like to get your input on.

    Background - building a new house. Chosen ICF for the walls. Will be very air tight. No gas. Only electric at the house. Flat roof. Solar panels on the roof. Trying to be energy efficient. Located in MA. The house will be built into a slope. 2 floors above ground. 2 floors mostly below ground. 1100 sqft per floor.

    My initial plan has been to use mini-split heat pumps. Leaning toward Mitsubishi or Fujitsu low temperature heating units wall mounted units. Leaning towards the ceiling cassettes for the interior units. Going all ductless as I'm thinking this would be lower maintenance and more room by room temperature control.

    Yet, I keep being told I need an ERV/HRV for fresh air. And those seem to require ductwork. And I'm trying to avoid the costs and maintenance associated with ductwork.

    The other option I'm told is to do bathroom exhaust fan on a timer. But I suspect with how airtight the house is going to be... that would take air out but there aren't places for the air to come in. So I think I need to still actively bring fresh air into the house.

    Would it be feasible to leverage the fresh air option on the ceiling cassettes? Paired with the bathroom exhaust fans?

    Thank you in advance!

  2. #2
    Join Date
    Jun 2014
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    Some cassettes have a knockout that can be used with fresh air, some have a knockout that you can use for a small supply duct for a separate room.
    Being it’s a tight house you’ll need an ERV/HRV.
    If not you’ll have moisture problems.
    Bathroom fans will not be adequate. You need air in and out.
    I havent failed. Ive just found 10,000 ways that wont work. - Thomas Edison

    Its not whether you get knocked down, its whether you get up. - Vince Lombardi

    "In this house we obey the laws of thermodynamics" - Homer Simpson

    Local 486 Instructor & Service Technician

  3. #3
    Join Date
    Nov 2006
    Location
    Athens, Ohio
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    Consider all the appliances that blow air out of the house - bathroom fans, range hood, clothes dryer, anything that burns fuel such as a water heater or furnace (if you have those). The house must be able to replace that air or the fans cannot perform.
    Tight houses are good but we want to control what air goes in and out.
    AOP Rules: Rules For Equipment Owners.

    Free online load calculator: http://www.loadcalc.net/


    There = not here. Their = possessive pronoun. They're = they are
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  4. #4
    Join Date
    Oct 2006
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    As tight as our houses are getting now are we getting in danger of not having enought oxygen while sleeping that we do not wake up in he morning? Are we going to need an alarm to warn us of the lack of oxygen for us to breath?
    Blue Fox

  5. #5
    Join Date
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    Location
    Athens, Ohio
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    Quote Originally Posted by lentz View Post
    As tight as our houses are getting now are we getting in danger of not having enought oxygen while sleeping that we do not wake up in he morning? Are we going to need an alarm to warn us of the lack of oxygen for us to breath?
    I suspect that's an exaggeration. Few houses have zero infiltration and that's an unreasonable target.
    How tight would a house have to be for NO air to infiltrate and how long would it take for the occupants to deplete the oxygen? It's not a sealed coffin.
    AOP Rules: Rules For Equipment Owners.

    Free online load calculator: http://www.loadcalc.net/


    There = not here. Their = possessive pronoun. They're = they are
    It's = contraction of it is. Its = the possessive form of it
    Too = also. To = expressing motion. Two = 2
    Then = after that, next. Than = indicates a comparison.
    Questions should end with a question mark "?" Statements end with a period "."

  6. #6
    Join Date
    Aug 2002
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    Southold, NY
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    Deadly lack of Oxygen doubtful but it is a concern.

    3 - 4 complete air changes are recommended every day.

  7. #7
    Join Date
    Jan 2020
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    Massachusetts
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    Thread Starter
    OK, it sounds like we need to actively bring in fresh air.

    So the cassette has a knock out for fresh air. Are you suggesting the ERV/HRV is the one that brings in the fresh air and supplies it to the cassette? So the ductwork is to the cassette?

    OK, that might make more sense to me than a completely different ductwork system for the ERV/HRV.

    Has anyone done this setup before? ERV/HRV ducting fresh air to a mitsubishi or fugitsu ceiling cassette? Pros and cons of this approach?

  8. #8
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    I was just asking a question. The houses are getting greal tight now. In bad weather people might not leave the house for days,
    Blue Fox

  9. #9
    Join Date
    Aug 2009
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    Beatrice, NE
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    You could duct the ERV from the attic and run oval pipe through interior walls for both exhaust and make up. Use bathrooms and kitchens as exhaust points and dump air back into halls/living areas. It is really not that difficult unless you have an issue with the floor plan where walls don't line up. You could also plan a chase in the house to run both exhaust and make up air through then come off the chase for each floor. I think if possible I would want it in a garage area or storage room where it would be easier to service than in an attic, but that's just me.

    I understand the concern over initial cost but you mentioned maintenance on the duct. Once installed there should be no maintenance, only on the equipment.

  10. #10
    Join Date
    Nov 2004
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    SW FL
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    Quote Originally Posted by Chestnut View Post
    Hello, new member, learning the rules. Please be patient with me.

    I joined as I'm seeing some great information being shared on this site and
    I have a few questions/clarifications I'd like to get your input on.

    Background - building a new house. Chosen ICF for the walls.
    Will be very air tight. No gas. Only electric at the house.
    Flat roof. Solar panels on the roof. Trying to be energy efficient.
    Located in MA. The house will be built into a slope. 2 floors above ground. 2 floors mostly below ground.
    1100 sqft per floor.

    My initial plan has been to use mini-split heat pumps.
    Leaning toward Mitsubishi or Fujitsu low temperature heating units wall mounted units.
    Leaning towards the ceiling cassettes for the interior units.
    Going all ductless as I'm thinking this would be lower maintenance and more room by room temperature control.

    Yet, I keep being told I need an ERV/HRV for fresh air.
    And those seem to require ductwork. And I'm trying to avoid the costs and maintenance associated with ductwork.

    The other option I'm told is to do bathroom exhaust fan on a timer.
    But I suspect with how airtight the house is going to be ...
    that would take air out but there aren't places for the air to come in.

    So I think I need to still actively bring fresh air into the house.

    Would it be feasible to leverage the fresh air option on the ceiling cassettes?
    Paired with the bathroom exhaust fans?

    Thank you in advance!
    Ventilation: ~ 100 to 140 CFM, continuous or intermittent
    _________ ASHRAE 62.2 - 2013, use Infiltration credit of ~ 0.14 A.C.H. Natural

    Heating Total 4 Floors: ~ 42,600 BTU/HR with HRV +/- 20%
    _____ Upper 2 Floors: ~ 31,000 BTU/HR


    Upto ~ 18 Cassette or Wall mount mini-split heads.
    + use of Straight electric in bath rooms/ small areas.

    __________________
    _ CONCEPTUAL
    ___ WALLS: ~ R-20
    __ CEILING: ~ R-40+
    __ WINDOWS: U-FACTOR < 0.20


    __ DEHUMIDIFIER(S): UltraAire 120H or other model with ventilation option
    __ Exhaust Fan: FAN TECH is an option
    __________ https://www.fantech.net/

    https://www.ultra-aire.com/dehumidif...-7c1badab-71e8

    DETAILED Room-by-Room ACCA Manual J Calculation is The Starting Point.

    ___ My gmail address: racingdan11
    Attached Images Attached Images   
    Last edited by dan sw fl; 01-18-2020 at 05:38 AM.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  11. #11
    Join Date
    Feb 2010
    Location
    Metro Atlanta, GA
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    I'm going to assume that you're planning on using either multi port outdoor units or an outdoor unit with a branch box feeding multiple heads instead of a bunch of one to one units. If that's the case, room by room sizing is critical. Outdoor units that can feed multiple indoor units always feed some amount of refrigerant to all of the heads even if they're not calling. Since the fans run continuously there will always be some degree of overheating in a satisfied space. A good document on this can be found here on Mitsubishi's publicly available site.

    The smallest cassette Mitsubishi makes is a 9,000 btu in either the one way (MLZ series) or the four way (SLZ series), so if the room it's in doesn't need that BTU load it will overheat. This can be overcome to some degree by stopping the fans when the unit satisfies - cutting jumpers on the MLZ or through function settings on the SLZ - but if the coils get too hot while idle the blower will come on to reject some of the heat. Also, you'll have to have a thermostat that can sense temperature at the wall instead of using the internal sensing at whatever head unit you're using.

    The other thing to take into consideration with ceiling cassettes is service access. The one way cassettes are serviceable from the bottom, but the four way cassettes have their control boards above the ceiling plane so they would need attic access or some sort of ceiling panel.

    I'm a huge fan of Mitsubishi but the units get misapplied so often that people blame the equipment instead of the system design.

    As far as ERV ducting is concerned, the Mitsubishi one way cassettes do not have a knockout for bringing in fresh air, only the four way cassettes have that.

  12. #12
    Join Date
    Jan 2020
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    Massachusetts
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    Thread Starter
    Hi, one more detail about the house. Flat roof. no attic. Part of the reason looking at ductless is and many zones is the house is 4 floors. Built into a slope. 2 floors are underground. I'm expecting the below ground to be naturally cooler and humid... I was thinking mini-splits are also good at dehumidifiying when on "dry" mode.

  13. #13
    Join Date
    Aug 2002
    Location
    Southold, NY
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    Quote Originally Posted by Chestnut View Post
    Hi, one more detail about the house. Flat roof. no attic. Part of the reason looking at ductless is and many zones is the house is 4 floors. Built into a slope. 2 floors are underground. I'm expecting the below ground to be naturally cooler and humid... I was thinking mini-splits are also good at dehumidifiying when on "dry" mode.
    A Manual "J" Load / Loss calculation is a MUST

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