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Posts Tagged ‘HVAC mitsubishi zoning ductless split’

A/C System, Manual J and sizing zoned systems

The only thing that is holding up submitting the plans is the ‘Manual J’ calculation which is the A/C heating and cooling loads. The A/C system I specified is the Mitsubishi City Multi Series S which I zoned into 6 zones (it can take a maximum of 8 indoor units, I plan 6). Instead of a central air handler and air ducts around the house there’s refrigerant pipes from unit to unit, and each unit is separately controllable via a iPhone or iPad app called MeZo from anywhere in the world with a connection.

You can have to up 130% indoor unit loads on the single external 4-ton (48,000 BTU/hr) outdoor unit which is infinitely variable in speed. ie a 4 ton unit can have up to 5.2 tons of internal loads. I have 129% of the outdoor unit loads in indoor units planned. Which means I can’t cool everywhere to 75 degrees F in the middle of the day in the middle of summer all at the same time. Instead I can direct it where I am.

Just got a call from the A/C guy. He is panicking. “The total A/C load is at least 4.8 tons, maybe over 5 tons! This isn’t big enough!”. Well….yes…….That is the whole point. It is zoneable. Maybe you can’t have the living area, the bedrooms and the workshop all cooled to 75 F  at noon in the middle of summer. But why would you want the bedrooms cooled in the middle of the day? The whole point is that you only cool the bits you use. That is the point of zoning!

And this guy is supposed to be an expert on eco-friendly HVAC solutions.