Moisture Removal Rate (MRR) Calculator
Calculation Results:
Pints Per Day (PPD): 0
Gallons Per Day: 0
Pounds Per Hour: 0
Grain Depression: 0 Grains
Understanding Moisture Removal Rate (MRR)
The Moisture Removal Rate (MRR) is a critical metric used by HVAC engineers, restoration professionals, and indoor environmental specialists to quantify the performance of dehumidification equipment. It measures the volume of water vapor extracted from the air stream as it passes through a cooling coil or desiccant medium.
The Science of Grains and Airflow
In psychrometrics, moisture is often measured in Grains per Pound (GPP) of dry air. There are 7,000 grains in a single pound of water. To calculate how much water is being removed, we must look at the "Grain Depression"—the difference between the inlet moisture level and the outlet moisture level—multiplied by the volume of air moving through the system.
The Formula
To calculate the Pints Per Day (PPD) removal rate, the following physics-based formula is used:
Where:
- CFM: Cubic Feet per Minute of airflow.
- Grain Depression: Inlet Grains/lb minus Outlet Grains/lb.
- 71.4: A constant derived from air density (0.075 lbs/cu.ft) and time conversion factors.
Why This Matters
In water damage restoration, calculating MRR allows technicians to verify if their dehumidifiers are operating at peak efficiency. If the grain depression is too low, the equipment may be failing, or the ambient temperature may be outside the machine's optimal operating range. For industrial applications, such as pharmaceutical manufacturing or indoor agriculture, precise MRR calculations ensure that humidity remains within tight tolerances to protect product integrity.
Practical Example
Imagine a high-capacity dehumidifier processing 400 CFM. The air entering the unit is at 90 Grains/lb, and the air exiting the unit is at 50 Grains/lb.
- Grain Depression: 90 – 50 = 40 Grains.
- Calculation: (400 × 40) / 71.4 = 224.09.
- Result: The unit is removing approximately 224 Pints Per Day.