DAIKIN Rebel Heat Pump

How to Handle 100% Outside Air Without Fossil Fuels Even at -10 °F 

Designing HVAC systems for 100% outside air in cold climates has always been a challenge. When ambient temperatures drop below freezing, most DOAS heat pumps lock out around 20 to 25 °F. Without heat recovery or gas backup, the system can no longer provide heat, leaving building operators with limited and often costly options. 

For applications like laboratories, paint booths, or hospital isolation rooms where energy recovery is not allowed due to contaminated exhaust air, this issue becomes even more critical. Historically, these spaces have relied on oversized electric resistance heat or fossil fuels to keep systems operational during winter. 

The Electric Preheat Solution 

Daikin Rebel DOAS Heat Pump now has a proven way to operate in extreme winter conditions without gas or energy recovery. The Electric Preheat Kit is a bolt-on, field-installed accessory that tempers incoming outside air to protect the coil during defrost cycles. By maintaining the right entering air temperature, the system can operate in ambient conditions as low as -10 °F. 

 

How It Works 

  • The preheat kit raises the entering air temperature upstream of the coil to prevent freeze-up. 
  • The Rebel unit continues operating in full heat pump mode, even in sub-zero conditions. 
  • This eliminates the need for fossil fuels and supports electrification goals. 

 

Key Features 

  • Independent power feed with seamless integration to the MicroTech 4 controller 
  • Complete installation package with all necessary hardware and programming instructions 
  • Flexible kW sizing and cabinet configurations for a wide range of applications 
  • Cold climate design to prevent coil freeze during defrost cycles 

Where This Solution Makes Sense 

This technology is ideal for buildings that must exhaust 100% of their air and cannot use energy recovery due to health, safety, or regulatory reasons. 

  • Laboratories with fume hoods 
  • Industrial facilities using hazardous materials 
  • Healthcare isolation rooms 
  • Paint booths and finishing shops 

These facilities are common in Washington and fall under state exemptions from energy recovery requirements. 

 

Why It Matters 

As building codes and sustainability goals continue to move away from fossil fuels, many owners and design teams are looking for reliable ways to heat 100% outside air. The Electric Preheat Kit: 

  • Extends Rebel DOAS operation down to -10 °F ambient 
  • Reduces reliance on large electric reheat banks 
  • Ensures code compliance for exempt applications 
  • Supports decarbonization and energy efficiency targets 
  • Simplifies system design in challenging conditions 

 

A Practical Path Forward 

At AirReps, we help engineers and owners solve real design challenges. The Electric Preheat Kit for Rebel DOAS heat pumps provides a simple and effective way to keep 100% outside air systems running year-round in cold climates without fossil fuels. 

To learn more about how this solution can support your next project, contact your Account Executive or email [email protected].