jdfs
Electrical
- Feb 9, 2009
- 4
Hello,
I have a cold storage facility that is implementing a new control scheme such that it can operate the compressors with floating suction pressure. What relationship exists between floating suction pressure and the additional heat added because the evaporator fans need to run more often(because the temp diff across the evap coils will be less with higher suction pressure, thus a greater airflow across the coils will be required to provide the same amount of cooling)? Specifically, are there any equations I can use to calculate the relationship? The only way I can think to resolve this is to use
heat load to be removed = 1.08 X CFM X temp diff
Since I know the heat load of the space and approximate the temp diff(required setpoint in the space - suction temperature), I can solve for the CFM required. Next, I use
fan bhp = (CFM * Static Pressure * specific gravity of air)/(6356 X Fan efficiency)
If I ignore static pressure, and since the specific gravity of air is 1, and I can approximate the fan efficiency, and I know the CFM, I can solve for the fan bhp required. Converting bhp requirement to BTU/hr using 1 HP = 2545 BTU/hr, I can get the additional heat load added to the space by running the fan motors. I can find the heat load for different suction pressures by changing the suction temperatures and solving for a diff CFM.
So is my methodology correct?
I have a cold storage facility that is implementing a new control scheme such that it can operate the compressors with floating suction pressure. What relationship exists between floating suction pressure and the additional heat added because the evaporator fans need to run more often(because the temp diff across the evap coils will be less with higher suction pressure, thus a greater airflow across the coils will be required to provide the same amount of cooling)? Specifically, are there any equations I can use to calculate the relationship? The only way I can think to resolve this is to use
heat load to be removed = 1.08 X CFM X temp diff
Since I know the heat load of the space and approximate the temp diff(required setpoint in the space - suction temperature), I can solve for the CFM required. Next, I use
fan bhp = (CFM * Static Pressure * specific gravity of air)/(6356 X Fan efficiency)
If I ignore static pressure, and since the specific gravity of air is 1, and I can approximate the fan efficiency, and I know the CFM, I can solve for the fan bhp required. Converting bhp requirement to BTU/hr using 1 HP = 2545 BTU/hr, I can get the additional heat load added to the space by running the fan motors. I can find the heat load for different suction pressures by changing the suction temperatures and solving for a diff CFM.
So is my methodology correct?