"Mark Schofield" wrote in message
.. .
After having a contractor do manual J to determine the tonnage for AC in
two bedrooms and a large family room, I would like to know the problems
and
issues if the system is to be zoned with individual stats and motorized
dampers to control the bedrooms and/or the large family room, either
individually or together. The tonnage was calculated for the entire load.
If
only part is being cooled, would a multi or variable fan be called for?
Not necessarly

Would the higher or lower air flow affect the refrigerant pressures?
To a point

Would
the capacity for the whole system be too much for only one zone thus
affecting the dehumidification capabilities.
Yes probably would cycle to fast and not dehumidify well
Dehumidification works best with a cold interior coil, a 25 degree split or
more. Slowing the fan will help dehumidification but a colder coil works
better.

Hopefully someone from alt.hvac
will have some input. This will be a split system for cooling only. Heat
is
oil fired hot water. Thanks for any thoughts. Mark S.

You do not mention the sqft/cubic feet involved. Zoning a/c is done in my
area for only the extreme rich. It adds a level of complexity for the
project that a lot of installers are not accustomed to.

Are your walls between the zones insulated? If not then there is little
reason to add a lot of complexity. Do you have supply and return ducts in
for the zones?

Listen to your installers and choose the one that makes the most sense. I
think your trying to trip over a penny and will end up will dollars flying
out the window. According to the link supplied your looking at ~400 hours
annually for cooling. Where I live it is more like 2000 hours.
A high seer unit installed by a good contractor with some performance
numbers after the install and you will be money ahead. IMO
http://198.147.238.24/ac_calc/default.asp