MAragorn
Mechanical
- Jun 26, 2006
- 33
I am looking at a project that was not my design but is now mine to resolve.
Without having access to the early design decisions, it appears that the rooftop units are about 2 x as big as necessary. When the thermostat calls for cooling, it is satisfied pretty quickly, thus the compressor does not run all that long, so there is not a whole lot of dehumidification going on. Additionally, this is on the coast, so all the time the compressors are NOT running, the system is dumping a fairly humid mixture of outside air and un-cooled return air.
As I said, these are DX units, with 2 stage electric heat. To my advantage, they are 2 compressor units, so 2 stages of cooling.
Now in the good old days, I would have used a chilled water system with hot water reheat, cooled all the air down to 55F then reheated for comfort, thus yielding the sweetest, dry-est system in town. But not in these energy conscious days.
To obtain a dry space, I COULD replicate the good old days, driving the air cold then using those honking big EHCs to reheat. Not a good plan.
I COULD re-sheave, driving the cfm low, and the air cold to have the compressor run much more of the time...except...I believe I am going to be told by the manufacturer that the minimum acceptable cfm for the unit won't be low enough to match load/cfm/humidity to give a comfortable space and not damage the compressor. It will be better, but better probably won't be good enough.
So do you long-time DX guys have a magic bullet to shoot and put this high humidity problem down?
Without having access to the early design decisions, it appears that the rooftop units are about 2 x as big as necessary. When the thermostat calls for cooling, it is satisfied pretty quickly, thus the compressor does not run all that long, so there is not a whole lot of dehumidification going on. Additionally, this is on the coast, so all the time the compressors are NOT running, the system is dumping a fairly humid mixture of outside air and un-cooled return air.
As I said, these are DX units, with 2 stage electric heat. To my advantage, they are 2 compressor units, so 2 stages of cooling.
Now in the good old days, I would have used a chilled water system with hot water reheat, cooled all the air down to 55F then reheated for comfort, thus yielding the sweetest, dry-est system in town. But not in these energy conscious days.
To obtain a dry space, I COULD replicate the good old days, driving the air cold then using those honking big EHCs to reheat. Not a good plan.
I COULD re-sheave, driving the cfm low, and the air cold to have the compressor run much more of the time...except...I believe I am going to be told by the manufacturer that the minimum acceptable cfm for the unit won't be low enough to match load/cfm/humidity to give a comfortable space and not damage the compressor. It will be better, but better probably won't be good enough.
So do you long-time DX guys have a magic bullet to shoot and put this high humidity problem down?
