The 90% Efficiency Gap: Your RTU’s efficiency rating applies to less than 10% of real operating hours.
The APR Control® helps optimize the other 90%.
When evaluating Rooftop HVAC Units (RTU or Split), AHRI efficiency metrics such as EER, IEER, IPLV, and SEER/SEER2 are often among the first numbers considered when evaluating HVAC system performance, but these published ratings do not always reflect how the system will operate in the field. These ratings provide an important baseline for comparing equipment under controlled laboratory conditions.
The challenge is that most HVAC systems do not operate at full load for the majority of the year.
In fact, most commercial DX systems operate at part load nearly 90% of the time, where indoor conditions — not laboratory assumptions — drive actual system demand.
The Problem: Laboratory Ratings vs. Real-World Performance
Most commercial DX systems are evaluated using AHRI performance standards, which provide a consistent basis for comparing equipment under controlled laboratory conditions. These standards primarily measure full-load, steady-state operation, making them valuable for equipment comparison, but they also have important blind spots when it comes to how systems actually behave in the field.
While some AHRI standards include part-load test points, these conditions are generally based on changes in outdoor ambient temperature, rather than the continuously changing indoor load at the evaporator coil caused by occupancy, humidity, ventilation, solar gain, and thermostat settings.
That distinction is where real-world energy use begins to diverge from published ratings.
For standard fixed-capacity RTUs, this often results in:
- Frequent compressor cycling
- Unnecessary fan energy consumption
- Inconsistent humidity control
- Increased compressor wear
- Higher-than-expected utility costs
This is exactly where the APR Control®, paired with an evaporator fan VFD, delivers value.
By allowing the system to modulate compressor capacity and fan speed under part-load conditions, the APR Control helps reduce unnecessary power draw, improve humidity control, and optimize system performance during the operating hours that matter most.
Simply put:
Rated efficiency does not always equal actual operating efficiency.
The Solution: APR Control & VFD Retrofit
You don’t need to replace your entire HVAC inventory to bridge this efficiency gap. By retrofitting your existing RTU with an APR Control and an Evaporator Fan Variable Frequency Drive (VFD), you transform a standard unit into a load-matching system. This allows the system to operate like a Single Zone VAV unit, modulating both compressor capacity and fan speed.
How the Performance Compares
Condition | Standard RTU | APR + VFD System |
Full Load | Efficient | Efficient (Full Capacity Available) |
Part Load | Inefficient cycling | Continuous modulation |
Humidity | Poor control | Consistent & Improved |
Fan Energy | 100% Constant | Reduced (Cube Law savings) |
Compressor Energy | 100% Constant | Decreased Power Consumption up to 20% |
Equipment Life | High wear/tear | Extended (Reduced cycling) |
The Real Metric: Annual Energy Cost
In any HVAC system, the primary energy consumers are the compressor(s) and fan(s). By pairing the APR Control® with an Evaporator Fan VFD, both can operate more efficiently under part-load conditions, reducing unnecessary power draw and delivering conservative energy savings of up to 50%.
Our engineering team is currently working on a simple ROI calculator that facility managers and engineers can use in live conversations to see these impacts in real-time. Typical results show as much as 50% HVAC energy savings with a 2–3 year payback with the APR Control and an Evaporator Fan VFD.
Low Risk, High Impact
The beauty of the APR + VFD solution is that it requires no equipment replacement. You aren’t changing the AHRI-rated system; you are simply optimizing how it handles the 90% of the year that the controlled lab test ignores.
AHRI performance standards tell you how your unit performs in a lab. The APR Control optimizes how it performs in your building.
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Proven Energy Savings with Real Manufacturer Testing
See how independent manufacturer testing confirmed measurable part-load energy savings with the APR Control.
Traditional efficiency ratings often fail to reflect how HVAC systems actually perform in the field. See how manufacturer testing revealed a 16% reduction in first-stage compressor power consumption at part load with the APR Control installed. Explore the real data and results behind the performance claims.
