Results 1 to 10 of 10
  1. #1
    Join Date
    Oct 2006
    Posts
    7

    Mini split math perplexity

    I have not been able to find an answer to this question. I am in Mexico and all the homes are 8 inch thick concret walls so mini splits are the AC of choice for retro-fitting older houses here.

    I understand the negatives about over-sizing....so, If I have 3 rooms requiring 8,000 btu of cooling and have a single 24,ooo btu compressor to run 3 mini splits what happens when I run just one mini split? Am I now way over-sized? Or are the new units smart enough and capable to run the compressor as an 8,000 unit (I forget the technical term, but understand comercial units are able to do this)?

    Great forum!

    Thanks in advance,

    Scott

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,358
    Daikin and others have multiple mini-split systems known as variable refrigerant flow, or VRF. Daikin markets this technology under their trade term VRV, for variable refrigerant velocity.

    For this VRF to work the compressor is inverter driven, along with the condenser fan. This allows the system to vary its capacity according to demand. In essense, if you have three 8,000 btuh coils and only one calls for cooling, the compressor and condenser fan will run at the optimum speed for this load. If another coil calls while the first is still running, the comp and fan will ramp up to compensate. It is "cool" stuff.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  3. #3
    Join Date
    Dec 2006
    Location
    Fayetteville,Arkansas
    Posts
    1,427
    Quote Originally Posted by shophound View Post
    Daikin and others have multiple mini-split systems known as variable refrigerant flow, or VRF. Daikin markets this technology under their trade term VRV, for variable refrigerant velocity.

    For this VRF to work the compressor is inverter driven, along with the condenser fan. This allows the system to vary its capacity according to demand. In essense, if you have three 8,000 btuh coils and only one calls for cooling, the compressor and condenser fan will run at the optimum speed for this load. If another coil calls while the first is still running, the comp and fan will ramp up to compensate. It is "cool" stuff.
    I was thinking Daikin also. Just went to one of their little dealer workshops and was very impressed. It does everything mentioned above plus provides heat.
    If you choose not to decide you still have made a choice.

  4. #4
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,358
    Quote Originally Posted by hvaclogic View Post
    I was thinking Daikin also. Just went to one of their little dealer workshops and was very impressed. It does everything mentioned above plus provides heat.
    A Daikin rep came to our last RSES chapter meeting and had about everyone in the room very impressed. I don't even work with resi all that much these days, but it sure piqued my interest! Add to that the Nordyne IQ Drive system I got to play with last night...I've seen the future, and the future is VARIABLE.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  5. #5
    Join Date
    Apr 2005
    Location
    Tampa, Florida
    Posts
    1,634
    Quote Originally Posted by shophound View Post
    .I've seen the future, and the future is VARIABLE.
    By the time this hits the markets, it'll have only taken the US about 10 years to catch up to the rest of the world on this.

  6. #6
    Join Date
    Oct 2006
    Posts
    7
    So, Can I assume most/all mini splits: Carrier, York, Mitsubisi, Sanyo, Mirage is what we have here, have some sort of variable device in them?

    Or is that a big mistake assumption to make?

    Are there any other ways or mechanisms to achive this also?

    Should I ask the AC dealers how they're units do this?

    Thanks.

    Scott

  7. #7
    Join Date
    Mar 2006
    Location
    Delaware
    Posts
    448
    Nearly all of the modern minisplit manufacturers offer inverter models, which means they are variable capacity. It's tough to go oversize and have a problem with these, unless you go WAY oversize.
    Right now, Fujitsu has the best efficiency, but Mitsubishi, Sanyo, LG, Daikin, Hitachi, Panasonic, and others all offer these inverter units.
    If you go with the multisplits, which it seems you're doing, they do this also. When running just one unit, the compressor slows way down, and the microcontroller figures it all out. The expansion valves will adjust accordingly, the room blower will also, etc. Nice systems, actually. Just don't go too small! And do the math first.
    The only real downside of having a way oversize indoor unit is potentially there may be a noise issue. The bigger ones, of course do make more noise. Fortunately, the manufacturers all have specs on this too.

    Quote Originally Posted by procare View Post
    I have not been able to find an answer to this question. I am in Mexico and all the homes are 8 inch thick concret walls so mini splits are the AC of choice for retro-fitting older houses here.

    I understand the negatives about over-sizing....so, If I have 3 rooms requiring 8,000 btu of cooling and have a single 24,ooo btu compressor to run 3 mini splits what happens when I run just one mini split? Am I now way over-sized? Or are the new units smart enough and capable to run the compressor as an 8,000 unit (I forget the technical term, but understand comercial units are able to do this)?

    Great forum!

    Thanks in advance,

    Scott

  8. #8
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,358
    Quote Originally Posted by procare View Post
    So, Can I assume most/all mini splits: Carrier, York, Mitsubisi, Sanyo, Mirage is what we have here, have some sort of variable device in them?

    Or is that a big mistake assumption to make?

    Are there any other ways or mechanisms to achive this also?

    Should I ask the AC dealers how they're units do this?

    Thanks.

    Scott
    Your best bet would be to get some product data from the manufacturers you are considering and carefully read them, then evaluate if what is offered is a good match for your proposed application.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  9. #9
    Join Date
    Oct 2006
    Posts
    7
    wilco...and thank you very much guys.

  10. #10
    Join Date
    Oct 2005
    Location
    MN
    Posts
    133
    The little Fujitsu single units that offer SEER 21 look VERY interesting for use in Mexico, since electric rates appear about double what they are here in Minnesota.

    Frank

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event