The APR Control provides (air conditioning circuit) modulation for humidity control, the benefit of extended runtimes, and the ability to maintain a system in a dehumidifying mode all serving Comfort and Indoor Air Quality. These factors allow simple single-stage/multi-stage DX systems to respond to a wide variety of operating conditions that all benefit space comfort.
By using the APR Control to extend system runtime, you are essentially keeping thermostatic controls from being satisfied as quickly as usual (when operating with minimal part-load control). In addition, because the APR Control keeps a portion of the evaporator coil in a dehumidifying mode during part-load operations, humidity control is dramatically improved. The Rawal device will also maintain the average temperature of the discharge air.
A 5-ton package direct expansion (DX) air conditioning system is required to provide space cooling for a classroom. The occupancy of the space requires that 30% (or more) of the system’s capacity be dedicated to conditioning the fresh air necessary to satisfy ventilation codes. The high percentage of outside air will cause large fluctuations in load that will keep standard on/off thermostatic controls from responding accurately or maintaining proper space humidity levels.
The 5-ton unit can be modified with an APR-410-3 Control (3.5 tons capacity control). This will provide 70% capacity control, allowing the system to modulate capacity to match changing load conditions from 5 tons down to about 1.5 tons and all points in between. Because the APR Control allows the system to operate down to around 35% of the total capacity, and permits the evaporator coil to stay below the dew point in a dehumidifying mode, the system will keep the humidity levels low without the addition of electric or other sources of reheat.
Additional component solutions can be added in the rare occasion when the APR Control alone is not sufficient for the challenges of the space. These solutions are typically simple and always cost-effective when compared to prepackaged products and their many limitations. They include:
- Reheat (less than usually necessary) with de-humidistat control to extend runtime and force a system run
- Thermostatic controls that allow setpoint flexibility
- Reduced air flow to improve cycling and latent capacity
As a result of correcting many installed systems, Rawal Devices technical support staff have been called on to assist the system service mechanics and designers with the flexibility to accommodate the calculated peak load/demand, but also provide the system with the necessary capacity modulation to meet a wide variety of load conditions.
To learn more about humidity control at part load, Click Here.