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Unico airflow question

Sorry that I haven’t been here in quite awhile, I am a licensed contractor since 82. Recently I have a customer wanting some Unico’s. These are single speed psc m3036bl1/m3036cl1-e (6row coil) with single stage 3ton condenser. AHRI rates this match at 2.5 tons or less. Heatpumps need 225-275 cfm’s/ton and AHRI says 800 cfm or 266cfm/ ton. If I use the rating of 2.5ton I could use 700cfm or 280cfm/ton which imo should be good. This would lessen holes and lessen amps. Any opinions would be greatly appreciated. 
PC7060

Comments

  • Lance
    Lance Member Posts: 270
    I own two systems. Be advised a Unico system can be noisy if and only if there are not enough outlets. The velocity at the outlet is critical. In the beginning they allowed so many outlets per ton and found they had to increase the quantity per ton to fix noise complaints. Trunk sizing is also critical. Do not size like traditional. Follow Unico sizing. Also WRIGHTSOFT has a manual J program with Unico in its sizing system. The return system is sized like any normal system. Tip, internal ducts are usually 2" but they now have 3". Think central vacuum pipe if you want have 2" ridged pipe runs. Never undersize duct! Its better to have more, especially with high merv filters.
    PC7060
  • McGee
    McGee Member Posts: 14
    Thanks, I appreciate the tips. Yes there will be a manual j, properly sized plenum, and amount of supplies but just wondering if a 3 ton condenser which only actually has a 2.5 ton compressor would be ok to set airflow slide to the 675-700cfm which would be 270-280cfm/ton on a 2.5 ton? That would be equal to about 7 vents/ton at about 40cfm/vent. According to Unico that although at the upper end of airflow, with 3’-6’ attenuating duct would be fine. Since a 3 ton condenser is rated using 45* sst and running closer to freezing would lower that number and having a 2.5ton compressor which at a lower sst would even be less than that. I would think adj the airflow/amps to a 2.5ton would be fine but not sure. I will be attempting this and make sure I can add more vents and up airflow/amps if necessary. There will be a mild temp kit as well.  Just trying to learn from others that may have some experience with this.