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  1. #14
    Join Date
    Sep 2005
    Location
    Atlanta GA area
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    42,433
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    High and low returns gather the cooler air at lower levels and the warmer air at higher levels...
    Mix it, and then condition (cool, dehum, heat, etc) the air before distributing it.

    High/low returns work great with higher than 8 ft ceilings!
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

    GA's basic rules of home heating and AC upgrades:
    *Installation is more important than the brand of equipment
    *The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
    *Cheap is not good, good is not cheap; however expensive is not a guarantee of quality!
    Choose your contractor wisely!

  2. #15
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    3,068
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    Quote Originally Posted by bugman-74 View Post
    I like this concept.

    Spiral ducting is exposed, correct?

    Why returns high and low? I'd suspect the low returns to be extremely susceptible to debris
    Yes, exposed. With the right registers and air flow they can blow air a good distance.

    Low returns to pull cool air off the floor (where you're working) when it's in heating mode. High returns to pull the heat off the ceiling when air conditioning. Together they work together in both heating and cooling. When heating and the fan is blowing the lower one is pulling cool air off the floor, mixing it with warm air (doing you no good) near the ceiling, adding some heat from the furnace and blowing it back into the space. Basically the same in cooling, but the high one raises pulls the warmer air off of the ceiling and basically works to better average the temperature from floor to ceiling.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  3. #16
    Join Date
    Sep 2007
    Location
    State College, PA
    Posts
    2,904
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    Ductless systems in my opinion will not produce a fast pull down. They are designed for constant/consistent run with low power consumption.
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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  4. #17
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    25,680
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    Fast pull down means over sized and little if any humidity control.

    Minis in a garage or kitchen is a BAD idea!

    What's the Code in your area concerning Flammable Material and HVAC in garages?

  5. #18
    Join Date
    Jan 2012
    Location
    Broomall, PA
    Posts
    2,887
    Post Likes
    Quote Originally Posted by firecontrol View Post
    Ducted furnace connected to spiral duct. GOOD filtration with returns located both high and low. I'd suggest a two stage split system AC. First stage for de-humidification and second stage for fast cool down.
    Is dehumidification a primary concern in Arizona?
    If I do a job in 30 minutes it's because I spent 30 years learning how to do that in 30 minutes. You owe me for the years, not the minutes.

  6. #19
    Join Date
    Nov 2019
    Location
    Tucson, AZ
    Posts
    9
    Post Likes
    Thread Starter
    What's the Code in your area concerning Flammable Material and HVAC in garages?
    Great question. I believe they require a separate system for the garage vs living area (my shop is a detached structure and will have a separate system). As far as any other restrictions, I will have to dig up the code.

    Is dehumidification a primary concern in Arizona?
    Some dehumidification is needed, but no its not as big of a concern as say somewhere like FL or LA

  7. #20
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    42,433
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    The flammable materials part would concern me...
    Many decades ago... saw a situation in a shop... where an open flame ignited a parts washer (yeah, it probably had gasoline rather than varsol in it)...
    Anyhow... they were lucky, they got it out before the whole shop went up...

    If you will be working with flammable materials regularly... might consider a furnace with a sealed firebox (condensing), with fresh combustion air being piped in (dual pipe install).

    Regardless... I would mount the furnace up in the air... as most flammable gases are heavier than air and settle to the ground.
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

    GA's basic rules of home heating and AC upgrades:
    *Installation is more important than the brand of equipment
    *The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
    *Cheap is not good, good is not cheap; however expensive is not a guarantee of quality!
    Choose your contractor wisely!

  8. #21
    Join Date
    Nov 2019
    Location
    Tucson, AZ
    Posts
    9
    Post Likes
    Thread Starter
    The flammable materials part would concern me
    The solvent I use is similar to Safety Kleen. It is in a dedicated parts washing cabinet with a cover that has a fusible link. Spray paints and whatnot are stored in a flam cabinet.

    The majority of my work in the shop is "wrenching" and not focused on flammable materials.

    Code does require the furnace to be elevated from floor.

  9. #22
    Join Date
    Apr 2007
    Location
    Tucson, Arizona
    Posts
    1,280
    Post Likes
    Hello fellow Tucsonian, I’ve built and conditioned over 20 garage-mahal types all over the area. A mini split will not make you happy or comfortable. Ducted unitary systems are much better. I have had the best results with 2 stage or inverter systems for shops. The problems are exaggerated in a shop, opening a door in the summer would overwhelm a mini. My current garage is ~2000 sq. foot, with a 2 stage, 3 ton, dual compressor Trane system with exposed spiral duct. In the summer it’ll hum along on first stage 1-1/2 ton compressor (think 4 barrel carb). Pull a car in and the radiant heat is crazy how hot it’ll feel, even though the air temp hasn’t changed. I do paint and bodywork on stuff and frequently spray in the same shop. I have 3- 24x24x12” deep pocket filters that last a few years with pre-filters. Garage doors don’t seal very well and leak quite a bit.
    I’d recommend reconsidering those skylights, in southern Arizona. They’re basically west facing windows all day. We could power 67 incandescent bulbs with the same energy we use from the heat gained in a standard skylight. The amount of “free” light we get from skylights isn’t worth it at all. Upgrading to double or triple pane is a must if skylights are a requirement. I’ll dig up some pics of some garages from the past, and post them here.
    There are two ways to do things, Right and Again.

  10. #23
    Join Date
    Apr 2007
    Location
    Tucson, Arizona
    Posts
    1,280
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    These are in a 5000 sq. foot, the duct systems were mirrored on each half with 2 4 ton 2 stage gas packs. This one was for one of the most fastidious individuals, and is the second or third garage-mahal we did for him. I think this one was ~2010.
    There are two ways to do things, Right and Again.

  11. #24
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    9,727
    Post Likes
    Quote Originally Posted by bugman-74 View Post
    I like this concept.

    Spiral ducting is exposed, correct?

    Why returns high and low? I'd suspect the low returns to be extremely susceptible to debris
    LOW RETURN with a proper Filter grille set-up
    would Not have more than normal issues
    with the duct interior.

    ___
    RE: Post # 7

    SPRAY PAINT / Welding ROOM with PROPER VENTILATION
    should be pursued.


    REF: INDUSTRIAL VENTILATION by ACGIH
    https://www.acgih.org/forms/store/Pr...uctNumber=2097
    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

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