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Mini split output

Does anybody else feel like the actual output of mini split units is less than the rating, or the output of a conventional AC is higher than the rating? No matter how many times I dig into it, the result is always the same: a 2 ton conventional will always cool better than a 2 ton mini split in the same space. Is there a way to measure actual output? For example, I put a 3 ton Panasonic split HP in my 40x40x14 shop with a 19k cooling and 31k heating load, and the cooling SUCKS. It can run 24/7 and will never pull indoor temp more than 20 degrees below outdoor temp but 15 is more realistic when it's hot. The charge is correct, lines are insulated, it seems to be working properly just doesn't cool well. In comparison, my house has a 29k calculated cooling load and the 2 ton conventional (I installed it when I was 19 and didn't know how to size equipment) will keep it 67 degrees even when it's 105 outside. This just doesn't make sense to me.

Comments

  • Matt_67
    Matt_67 Member Posts: 220
    It seems to me the mini splits have less sensible capacity then conventional a/c units. We did some industrial cooling where we pulled out 4 three ton Mitsubishi p series units and installed 2 five ton conventional systems with low ambient cooling. The original setup wasn’t keeping up but with the new equipment the second five ton unit cycles. We struggled to keep the evaporators on the p series units clean so that probably was a factor as well. But if you look at the mini split air flow they are almost always below the standard 400 CFM per ton. I wonder if air recirculation is a factor as well.
    GroundUp
  • GroundUp
    GroundUp Member Posts: 1,406
    Bump?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 12,024
    Mini splits don't have the air circulation capacity,

    There like window ACs the cabinet is small do they use less air flow and cool a smaller volume of air at a greater TD
  • HVAC590
    HVAC590 Member Posts: 1
    Given the CFM requirement, would the smaller minis, 9000 BTU/12000 BTU, be more in line? It looks like some minis get really big and complex; many are not really ductless, too. The smaller ones are easier to handle for install and with lots of them vs one or a few large ones, as well as the inverter technology making sizing and ops more flexible, seems like it gets around the one point of failure problem, too--just open some doors. I'm no tech, just a constantly learning property owner who has installed and helped install and maintain many systems over my 70 years, from boilers, to central HVAC, to minis.
  • ChrisJ
    ChrisJ Member Posts: 12,882
    GroundUp said:

    Does anybody else feel like the actual output of mini split units is less than the rating, or the output of a conventional AC is higher than the rating? No matter how many times I dig into it, the result is always the same: a 2 ton conventional will always cool better than a 2 ton mini split in the same space. Is there a way to measure actual output? For example, I put a 3 ton Panasonic split HP in my 40x40x14 shop with a 19k cooling and 31k heating load, and the cooling SUCKS. It can run 24/7 and will never pull indoor temp more than 20 degrees below outdoor temp but 15 is more realistic when it's hot. The charge is correct, lines are insulated, it seems to be working properly just doesn't cool well. In comparison, my house has a 29k calculated cooling load and the 2 ton conventional (I installed it when I was 19 and didn't know how to size equipment) will keep it 67 degrees even when it's 105 outside. This just doesn't make sense to me.


    There's a few things that confuse me.

    Your house has a 29K calculated load, and yet a 24K system can keep it 67 when it's 105 outside?
    That in it self sounds really really wrong. A 38 degree drop, on a system that's undersized according to your heat gain calculation?
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
    Robert O'Brien
  • wmgeorge
    wmgeorge Member Posts: 222
    On my Mitsubishi even as I kept the supplied air filter, such as it is clean. The fan wheel got so packed with dirt after 2 1/2 years next to zero air flow. Cleaned and back to normal and it will be an every two year job from now one.
    Old retired Commercial HVAC/R guy in Iowa. Master electrician.