(206) 949-5683, Top Rated Plumber, Seattle
Results 1 to 15 of 23

Thread: PTAC and ductless air conditioning?

Hybrid View

  1. #1
    DIY Member mar3232's Avatar
    Join Date
    Oct 2011
    Location
    Indiana
    Posts
    82

    Default PTAC and ductless air conditioning?

    I have a pretty small ranch house, really just 2 "major" rooms that need cooling and I'm faced with either buying a new outdoor heatpump condensing unit (trane) OR something that may be a "smarter" ? choice.

    I'm single, so really only need to cool the parts of the house I'm in at the time -- tv room etc.

    Can someone explain the PTAC and ductless air conditioning systems? I just ran across these on the home depot site (Ramsond) and know NOTHING about them.

    I read about a simple hole through an exterior wall? high efficiency?

    I know most of guys are in the business of installing whole house units so you may knock these but please be objective.

    2000 to repair my heat pump -- but I want to make sure of other options.


    Also -- another question -- I mounted a window AC unit high on a wall (cutout the wall) in my bedroom for occasional use. Of course, I'll drain it correctly and insulate it well.

    Is there any reason why I can't vent the hot air from it into my attic? (There will be a roof vent nearby). thanks.

  2. #2
    DIY Member mar3232's Avatar
    Join Date
    Oct 2011
    Location
    Indiana
    Posts
    82

    Default

    in other words the window unit is NOT going through an exterior wall -- it's an interior wall that I'll build a "chamber" around and hopefully vent into the attic. (which is a non functional attic)

  3. #3
    DIY Member mar3232's Avatar
    Join Date
    Oct 2011
    Location
    Indiana
    Posts
    82

    Default

    looking into it further, certainly don't want PTAC but interested in the ductless mini split.

    good thing is, if I got 2 air handlers, I could turn off the one I really don't need but I wonder also about overall effieciency (electrical)? what do you guys think about these systems?

    would I go ahead and seal up my ducts if I were using one? or put the ductwork in a cycling fan only mode maybe?

    I'd get it for cooling, not heating.

  4. #4
    Plumber jimbo's Avatar
    Join Date
    Aug 2004
    Location
    San Diego
    Posts
    9,001

    Default

    Your window A/C unit with a "chamber" around it, will not likely work. It most likely will not get the air circulation needed and will be ineffective and suffer early failure.

    PTAC is a fancy word for a thru-the-wall air conditioner unit. Most are sold with heat, but can be purchased as just cooling units. The heat feature can be electric heat or a heat pump with back up electric. They will mostly require a 220 volt circuit. Some units with small btu and very small or no heat can be had on 120 volts. They are easy to install ( no ducts, no tubing) but are not as efficient as a central hvac system.

    The ductless mini spit systems have a more or less conventional condensing unit or heat pump unit outside, and the indoor unit is a wall mounted ( NO DUCT WORK) air handler ( blower unit). You can get an outdoor unit which is multi-zone, meaning it will feed two ( or 3 or 4) separate indoor air handlers.

    The only thing which has to pass thru the wall is the set of copper supply and return refrigerant lines, and a small electric wire.

    Most PTAC brands sell accessory duct kits so the cool/heat can be shared into an adjacent room.

    A single PTAC will be in the $700 to $1000 range. A two-zone ductless, $1500 to $2000 plus install ( requires an HVAC tech with vacuum pump, gauges, etc)

  5. #5
    DIY Member mar3232's Avatar
    Join Date
    Oct 2011
    Location
    Indiana
    Posts
    82

    Default

    I'm not interested in the PTAC.

    At least I could save cooling costs by shutting off my living room air handler when I'm in the TV room at night. Only 2 major rooms in this house, living room with kitchen and a "TV room".

    What have you heard about efficiency vs a wholes house (at least there isn't all that ductwork in the way (I could seal the ducts?)

    Reliability of these systems?

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,408

    Default

    The mini-splits have been around for a long time, and they just keep getting better (not that they were ever bad). The noisy part is outside, and you have some freedom on where you want the units on the wall. They work just fine when you only have one or more working, and are quite efficient. The key, like with anything HVAC releated, is to get one the proper size. Especially with a/c, you don't want one too big. They work best when running constantly on that very hot day. On/off cycles usually mean it can't dehumidify well, and comfort levels drop. Plus, those extra on/off cycles create more stress and wear on the system.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #7
    In the trades Dana's Avatar
    Join Date
    Jan 2009
    Location
    01609
    Posts
    2,720

    Default

    Quote Originally Posted by jadnashua View Post
    The mini-splits have been around for a long time, and they just keep getting better (not that they were ever bad). The noisy part is outside, and you have some freedom on where you want the units on the wall. They work just fine when you only have one or more working, and are quite efficient. The key, like with anything HVAC releated, is to get one the proper size. Especially with a/c, you don't want one too big. They work best when running constantly on that very hot day. On/off cycles usually mean it can't dehumidify well, and comfort levels drop. Plus, those extra on/off cycles create more stress and wear on the system.
    "The noisy part" is now whisper quiet with scroll compressors and inverter-drive/continuously variable speed units, which is quite a contrast to reciprocating 1 & 2 speed compressors. At low to mid-speed you can be standing right next to it and barely be aware that it's running unless you happen to be in the air flow or are looking at the fan. It's often quieter than your refrigerator by quite a bit. Listen to this 2-ton LG at low-speed- the 60hz hum is barely above ambient wind noise on the microphone.

    With inverter drive mini-splits in fact you DO want to oversize it (by ~50%, maybe slightly more) if highest efficiency is the goal, since the part-load efficiency can be 2x as efficient as when it's running flat-out. The turn-down ratios of lowest:highest speed are on the order of 1:5 to 1:3, so the duty cycles are long and nearly continuous at moderate loads, even if oversized (within reason.) This is very different from what makes sense for sizing 1-2 speed AC systems. At 50% oversizing a minisplit will spend the vast majority of it's time running at half-speed or less, where it's most efficient. The key to getting the most out of it is to not crank the setpoints up & down often or turn it off, since the lower efficiency of running at max speed on the recovery ramps will usually end up using more power than letting it run with truly phenomenal efficiency at low speed just maintaining temp. See figure 14 in this document. The COP at 87F outdoor temps at min-compressor and min to mid fan speeds blows away the (still quite decent) efficiency at max speed, and the mid-speed COP @ 95F outdoor temps is still more than 50% better than at max-speed. At ~50% oversizing and a "set & forget" control strategy they should outperform their (already outstanding) SEER numbers.

    At more than 50% oversizing the air volume requirements on the interior blower can become an issue, and at 2x oversizing it can be a bit too breezy for comfort at mid-load or higher, even if it's slightly more efficient.

  8. #8
    DIY Junior Member emarie15's Avatar
    Join Date
    Sep 2012
    Location
    Tempe
    Posts
    1

    Default

    Quote Originally Posted by mar3232 View Post
    I have a pretty small ranch house, really just 2 "major" rooms that need cooling and I'm faced with either buying a new outdoor heatpump condensing unit (trane) OR something that may be a "smarter" ? choice.
    I think that a PTAC unit might be the right choice... here is some information to help you decide better. Good luck!

Similar Threads

  1. ductless ac help
    By chaoster in forum HVAC Heating & Cooling
    Replies: 5
    Last Post: 07-08-2010, 07:22 PM
  2. Ductless bathroom exhaust fan
    By shelbyhughes@comcast.net in forum Remodel Forum & Blog
    Replies: 3
    Last Post: 06-29-2009, 05:50 PM
  3. ductless heat pump vs gas
    By pipewoe in forum HVAC Heating & Cooling
    Replies: 0
    Last Post: 04-07-2009, 10:07 AM
  4. Central air VS ductless system
    By chaoster in forum HVAC Heating & Cooling
    Replies: 1
    Last Post: 05-23-2008, 03:25 PM
  5. Ductless vent fans...
    By coach606 in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 8
    Last Post: 08-05-2006, 11:24 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •