When dealing with high percentage outside air systems, it comes down to matching the capacity of the compressor(s) to the varied entering air conditions. The APR Control’s ability to load match will keep the compressor active despite the varied entering air conditions. This load matching ability of an APR Control enhanced system will keep discharge air temperature consistent, the discharge air below desired space dew point, as well as preventing compressor abuse from rapid cycling or floodback. These are the conditions that historically have plagued DX systems in high percentage outdoor air applications.
Whether on multiple zone VAV applications or simply where a VFD has been added to evaporator fan, the APR Control will modulate the capacity of the system to match the changing load. By responding to changes in suction pressure, the APR will reduce systems’ cooling capacity as the load on the evaporator is reduced (via zoning or simply a VFD) putting the system in to balance so risks associated with low airflow associated with VAV systems can be eliminated.
High altitude has lower air density, resulting in inadequate heat transfer at the evaporator coil. This leads to low suction pressure and improves the likelihood of coil icing. The APR Control will maintain suction pressure above a minimum psi as set on the APR Control (118 psi/40°SST).
As the APR Control can help match system capacity, it is, by extension, minimizing extremes in space temperature and relative humidity. By simply stabilizing space conditions with the APR
Control, a significant number of “nuisance calls” can be eliminated. Also, by reducing the wear and tear related to short cycling, coil frosting and liquid slugging, it is likely that adding the APR Control to the circuit will reduce downtime over the life of the system.
Liquid slugging can result in damage to the compressor! The APR Control prevents or eliminates liquid slugging or compressor floodback from occurring by varies the cooling capacity of the evaporator coil by modulating refrigerant flow. During low load or non-design day conditions, when floodback or slugging is likely to occur, the APR Control will only allow enough refrigerant into the coil that can be fully evaporated.
During mechanical failures, like a broken TXV or loose fan belt, the APR Control diverts vapor into the suction line so that liquid refrigerant never reaches the compressor!
Mismatched equipment such as improper fan size, or undersized evaporator coils can be relieved with the addition of the APR Control. Cost or job design may prohibit the ability to replace the equipment fan/evaporator. The addition of the APR Control will manage refrigerant flow to better match the output of the condenser section with the capacity of the evaporator/fan coil.
Undersized ductwork will lead to reduced airflow across the evaporator coil resulting in an extreme suction pressure drop. The APR reduces refrigerant flow to eliminate the chance of coil freezing as a result of low evaporator temperature. The APR Control will protect the refrigeration circuit from ultimately failing. In some situations, correcting the ductwork can be unfeasible even though it will provide a better/correct system. The APR Control will protect the circuit and allow the unit to function within the duct design limitations.
High humidity conditions, in spaces serviced by direct expansion equipment can result from short cycling conditions, or as a result of too much cooling capacity compared to load. Studies have found that if a short cycling condition exists, and the evaporator coil is not kept “active” for a long enough runtime period, the coil may start to load with moisture, but runtime could be too short for that moisture to fall to the drain pan and down the drain…which is officially when dehumidification is completed, all other conditions may result in the moisture re-evaporating back into the air stream and into the space!
The APR Control can protect against the problems related to clogged filters, which will likely cause airflow across the evaporator coil to be reduced causing a drop in suction pressure which will eventually result in coil frosting. The APR will maintain suction pressure by modulating refrigerant flow reducing capacity at the evaporator.
APR Control will keep the suction pressure from falling to prevent coil freezing, compressor floodback, short cycling, and low discharge air temperatures. By eliminating these symptoms, you can extend your compressor lifecycle.