Retrofit vs. Replace

The Problem with Oversized HVAC Systems

The Problem with Oversized HVAC Systems
Air Duct Industrial


HVAC systems are typically sized for full load conditions, which only occur for a small percentage of the year. The rest of the time that system is oversized, which can lead to many operational issues.

Oversizing HVAC systems is a common industry practice to create safety margins when conditions are extreme or unknown. Unfortunately, there are costs to this oversizing that are often not conveyed to the end user:

  • Increased up front cost for larger equipment
  • Increased short cycling, which can result in:
    • Poor humidity control, affecting occupant comfort
    • Additional wear and tear on the equipment, resulting in decreased lifespan and increased service and maintenance costs
    • Increased energy usage

The graph below, from a 2011 study “Oversizing of HVAC system: Signatures and penalties” by Ery Djunaedy et. al., depicts Building A which has an oversized air conditioning system that cycled on and off 11 times in an 8-hour span from 12pm-8pm. Building F, with a right-sized system, cycled on and off once during that same time span. All of this occurred under “design day” conditions (100+ degrees ambient, as indicated by the red line).  

Each time a compressor cycles it introduces the risk of electrical and mechanical failures. Additionally, the compressor is only rated for a limited number of starts throughout its lifespan. 


The APR Control is an add-on device that is installed in the condensing section, becoming an integral part of the system’s operation to right-size your equipment based on the load at a given time.

How the APR Control changes your air conditioning system’s operation:

The APR Control will modulate the system capacity to match the load going across your evaporator coil. It will extend the compressor runtime, thereby reducing the number of starts, and allowing for:

  • Enhanced dehumidification capabilities
  • Evaporator coil freeze protection
  • Compressor protection from liquid slugging, excessive cycling, and overheating
  • Improved indoor air quality (IAQ) by better maintaining proper humidity and temperature levels

Full Operational Description

Direct Energy Savings

Case Studies

How Rawal Devices' APR Control Improved Run Times to Eliminate Short Cycling and Prevent Lockouts

A restaurant's oversized chiller was short cycling, leading to frequent lockouts. The APR Control kept the system running and the customers and staff happy!

Learn from Rawal Experts

Get exceptional live technical support for installation and service – call Rawal Devices today!

The Rawal APR Control is a variable capacity enhancement to DX HVAC systems.