How EVI Technology Helps Cold-Climate Heat Pumps Perform in Subzero Conditions

Cold winters put pressure on heating systems. Many ordinary heat pumps struggle when temperatures drop below freezing. But with Air Source Heat Pump for Cold Climate systems equipped with EVI (Enhanced Vapor Injection) technology, efficient heating even in subzero conditions becomes real. Let’s see how it works and why it matters.

What is EVI (Enhanced Vapor Injection)?

EVI means adding a second vapor injection into the compressor midway. This extra injection reheats refrigerant and increases compression efficiency. In simple terms, it boosts the system’s ability to produce heat when it’s very cold.

Arctic Heat Pumps use Panasonic EVI DC inverter compressors to deliver reliable performance in cold weather. 

How EVI boosts performance in subzero weather

• Raises the compression ratio safely — The extra vapor helps maintain pressure and heat output even when outside air is very cold.

• Improves heating capacity at low ambient temps — With EVI, a heater that might drop in output at –20 °C can retain useful heating.

• Better COP — The coefficient of performance (energy output per unit of electricity) stays higher with EVI than without it in freezing weather.

• Faster recovery after defrost cycles — In cold weather, outdoor units must remove frost. EVI helps the compressor recover heat output more quickly after each defrost period.

Putting it all together: Air Source Heat Pump for Cold Climate

If you specify the design properly, an Air Source Heat Pump for Cold Climate with EVI can:

• Heat your home or building with hydronic radiant floors, fan coils, low-temp radiators, or air handlers. Arctic systems support all those modes. 

• Provide domestic hot water via a built-in or optional internal heat exchanger in the buffer tank. 

• Run backup heating only when needed. The system monitors what it can handle and turns on backup when EVI mode cannot keep up. 

• Be scaled: You can link multiple units using a controller (MX controller), so a bigger building can share the load. 

Questions you should ask your installer

• Up to what outdoor temperature has the unit been tested with EVI?

• Can the system handle full heating loads at –15 °C, –20 °C, or lower?

• How often will defrost cycles occur, and can EVI reduce lost time?

• What backup heating is integrated or required?

• Is the indoor side (radiators, hydronic loops) sized for lower supply water temps?

Possible limitations & what to watch for

• If the emitter (radiator, baseboard) requires high water temperature (above ~60 °C), EVI may not fully meet the load in severe cold.

• If defrosts happen too often, efficiency drops. Proper design and site placement matter.

• Electricity cost in deep cold might reduce savings — the EVI system delays the drop, but it’s not immune to physics.

• Poor insulation or an undersized system causes heat loss that even EVI cannot overcome.

EVI technology is a key reason modern Air Source Heat Pumps for Cold Climate systems can work reliably in freezing weather. By injecting vapor mid-cycle, the system holds heating capacity and efficiency much better. If you are choosing a cold climate heat pump, insist on EVI capability and test data. Arctic Heat Pumps offers such systems and supports cold weather zones.