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Originally Posted by Control Freek
I don't know the specifics about your suction pressure but suspect you would use that to load/unload the compressor when in dehumidification mode. As far as the dehumidification your option would be to decrease the discharge temperature of the unit and slow the fan speed down in order to not subcool the space. As you slow the fan down your DX load would decrease so your suction presssure would drop. You would then unload the compressor to keep the coil from frosting up.
I've used the fan routine before on chilled water unit but not DX. I would control the actual airflow stpt of the unit via space temp. The units chilled water valve would be controlled via DA reset or humidity worst case/highest signal. The fan would slow down as space temp decreased. In my application it worked well. I would let the units go down to 40% air flow and more or less idle there keep the humidity down without using reheat. My AHUs where in the core areas of a school where the load would change drasticly as kids would enter and exit the hall ways, cafateria and auditorium. Hard to dehumidify when there isn't much cooling load without using reheat. This school was also at about 10% capacity of what the equipment was sized for. It was set up as a special needs school but equipment was designed that it could be used as a regular high school if it's purpose changed.
Since you have DX I would control the DX leaving DA stpt instead of just letting the compressor go faster. I would then also let the suction pressure limit how much the compressor would load up when slowing the fan down. With the chilled water coil I didn't have to worry about tearing up compressors so I would just let the humidity drive it directly.
