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Need a VERY Small A/C System

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Eugene Silberstein 3
Eugene Silberstein 3 Member Posts: 1,380
in A-C, Heat Pumps & Refrigeration
Mike is searching for the smallest possible conventional split system. Ductless splits will not work for what he needs.

Mike, I'm still searching for you...

If you locate something that will work, let me know.

:)

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  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
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    6,500 btu/hr.

    Serves three rooms: two bedrooms and one fully internal bath.

    Supply ductwork is run, but it's not absolutely necessary that it be used.

    Have plenty of room above good-sized back-to-back closets. 9' ceilings with 6' x 9' of gross area. Bath is easily accessed from the closets.

    Having a really hard time finding a traditional air handler/condensing unit anywhere near this small. Suggestions?

    Perhaps some sort of mini-split system than can be "rigged" for flow (and hopefully return) to two rooms? Gain is nearly a perfect 50-50 split between the two main rooms with an itsy-bitsy requirement for the bath.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
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    Forgot to Say

    In the current use, these rooms are typically unused.

    Installed ductwork is arranged such that I can easily add a modulating damper to allow somewhat different setpoints in both major rooms. One of those rooms is the "master" however.

    Due to internal stacked staircases and framing it was truly impossible to supply and return these rooms via the unit on the other side of the central stair hall without dropping ceilings (NOT an option anywhere except a bath or closet).
  • Eugene Silberstein 3
    Eugene Silberstein 3 Member Posts: 1,380
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    Tough one, Mike

    You would be hard pressed to locate a split air conditioning system in the 6500 btuh range. You mentioned using a ductless split, but you would not be able to guarantee the proper operation of the system. This is primarily due to the fact that the blowers used on the air handlers of ductelss split systems are not designed to push air against an opposing pressure. The minute you connect ductwork to the supply side of the unit, your air velocity and volumes will plummet and likely result in the freezing of the evaporator coil.

    There is one alternative, though. You mentioned that, due to the stacked staircases, you are unable to run ductowrk to these three rooms. Depending on the layout of the home, you may be able to install an air handler above these rooms that will provide cooling for not only these rooms, but a portion of the main area as well. See if this will work...

    Let's say you are able to get hold of a 1.5 ton split system. The areas you are trying to cool require about 0.5 tons. You now have an "extra" ton of air conditioning capacity. If you are able to run a supply duct from the 1.5 ton unit and have a takeoff that will terminate in the wall of the staircase, you will now be "dumping" the excess air into the main portion of the structure. This will allow you to undersize the other system.

    Since these additional rooms are not utilized all of the time, you can consider this to be a unique method of capacity control. Considering the fact that most air conditioning systems are, by design, twice as large as they need to be on an 85 degree day, reducing the capacity of the system by one ton will still allow the system to satisfy the cooling load on the home.

    Consider the following: Air conditioning systems are designed to provide the rated cooling capacity at the design outdoor temperature of 95 degrees. As the outdoor temperature drops below 95 degrees, the capacity of the system increases and the heat gain of the structure decreases. At an outdoor ambient temperature of about 85 degrees, the cooling capacity of the air conditioning system is about twice the heat gain of the structure.

  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
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    Thanks!

    Regarding the mini-splits: One mfgr. told me the exact same thing (back pressure) when I questioned the use of the knockouts for "additional" supplies. Would be fine for just to supply that internal bath, but not half the flow...

    In that regard, is there any "split" mini-split? e.g. single condensing unit operating multiple evap/fan units?

    "Dumping" is a possibility as I could (with some trouble) run a duct to the stair hall. I currently have no A/C supplies to the upper stair hall under the assumption that cold air falls anyway. The stair hall is warmer, but it really doesn't bother me or anyone else. Besides, all of the rooms opening to the upper stair hall have operable transoms and I've found that opening them results in lower hall temp at the expense of higher run-time of the A/C unit already installed upstairs.

    Suggestion for the smallest capacity traditional condensing unit/air handler??? DO NOT want a super-efficient model unless it utterly EXCELLS under a VERY HIGH latent load! Latent load is so high here that it's not uncommon for A/C systems to run more at night than during the day! Seriously!

    p.s. Single Unico system for the ground floor--ductwork laid, but air handler not yet installed. Planned t-stat location is in the downstairs stair hall... "Dumping" into the upstairs stair hall may well interfere. Do have one possible alternate t-stat location, but the system was honestly engineered for the t-stat in the hall. Were I not so ignorant and were the project so long-running I would have used high-velocity for the upstairs as well. WAY too late now.
  • Marty
    Marty Member Posts: 109
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    mitsubushi

    They make several different styles of multi evap to a single condensing unit. http://www.mrslim.com/
  • jwade55_3
    jwade55_3 Member Posts: 166
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    Here is something I did once.

    Same type of situation, kinda, anyways. Small watersource heat pump, coupled to a indirect hw tank. Use the tank as "cooling tower" of sorts, the heat pump will run till about 100 deg h20 temp, but with such a small load, depending on the size of tank you use, could take up to 10 hours to bring to that temp, based on incoming h20 temp, etc. Then send water from this tank to primry tank to preheat incoming cw from street. I think I still have a piping diagram somewhere...

    J
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
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    Thanks Again for the Effort!

    The dual evap mini-split does look like a possibility if I abandon the ductwork, but it's still greatly oversized at 18,000 btu.

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