What is the difference between the APR Control and traditional hot gas bypass?

The APR Control provides continuous capacity modulation on direct expansion air conditioning and refrigeration systems. Contractors, Distributors, and Engineers referred to the APR Control as hot gas bypass because it was the easiest way to remember and explain application use. However, the APR Control is NOT hot gas bypass! The APR Control unloads the compressor and hot gas bypass loads the evaporator.

For more information read our recent blog post on how the APR Control is better than Hot Gas Bypass: https://www.rawal.com/2022/07/26/the-apr-control-is-better-than-hot-gas-bypass/

Can the APR Control be installed on units with lead-lag controls?

If lead-lag must be used, then an APR must be installed on each circuit to maintain modulation during low load conditions.

Will my unit need multiple APR Controls?

In most applications the installation of the APR on the lead circuit is enough. When both stages are operating, a drop in suction pressure will modulate the lead circuit. When the second stage shuts off, the APR Control will continue to modulate. In some applications the use of an APR on all circuits may be beneficial, please consult our Technical Support Team for assistance.

How do I select an APR Control for multi-stage/multi-circuit systems?

You will need to know total tonnage of the unit. Then the tonnage of the circuit and in particular the lead circuit (referred to as: First On/Last Off circuit). Then we need to know the tonnage of the lead compressor stage. Only one APR Control can be installed per circuit. In most cases, only one APR is needed per system. However, there are cases where an APR Control on each circuit might be beneficial…split face evaporator coils, MUA, VAV, for example.

What is the importance of the suction line size?

The suction line size and more importantly is the riser size will determine if the oil will return. ANYTIME the suction line creates a trap or has a vertical rise (in direction of gas flow) there needs to be both velocity and volume to carry the oil up. WE ENSURE THIS IS ADDRESSED WITH PROPER SELECTION AND SIZING.

What is the meaning of the model number on an APR Control?

The APR Controls are classified by refrigerant and the maximum amount of modulation. Thus an APR-410-1 gives 1.5 tons of modulation on an R-410A system. Please note that the capacity listed on the APR is the modulation capacity and should NEVER match the total system capacity. 100% modulation is NEVER acceptable.

Example: a 3.5 ton system could not use the APR-410-3 (3.5 tons of modulation).

Why is Selection So Important?

We specifically size and select APR Controls to provide the maximum modulation at the evaporator while ensuring proper oil return to the compressor. All forms of modulation that change the velocity of the suction gas have this concern. We ensure this is not an issue by sizing our APR control to maintain above the minimum velocity in the suction lines necessary for proper oil return.

How do I select the proper APR Control for my system?

Each APR Control needs to be sized and selected by Rawal Devices’ Engineers based on your specific system and application.

The APR Control is not a one size fits all solution. We select and size each individual APR Control that leave our factory.

In order for our team to properly size and select the APR Control(s) that is best for your system, we will need to know the following information:

· Refrigerant Type
· Total Systems capacity in tons
· Capacity of the lead stage in tons
  • The compressor and circuiting configuration Example: Dual stage/dual circuit (two independently controlled circuits) Example: Dual stage/single circuit (two independently controlled stages on a single circuit)
· Is there a lead-lag control (does first stage on rotate between compressors/circuits)?
· Evaporator Coil Configuration
  • Single circuit
  • Dual circuit intertwined
  • Dual circuit split face
  • Or Other Configuration
· Split or Package System
· Split systems will require additional information, including:
  • Suction line size (inches OD)
  • Line size of ANY AND ALL suction risers (inches OD)
  • Total suction line length
  • Total length of ALL suction risers