Transcritical CO2 Heat Pump Water Calculator
High-Temperature Heat Pump Engineering: Model non-isothermal supercritical gas cooler temperature glide matching, Lorenz thermodynamic COP, and domestic hot water savings.
Water Temperature Specs & Ambient Conditions
Heating COP & Operating Economics
Recommended Tools & Equipment
Tested hardware and components for high reliability
Transcritical CO2 Heat Pump Water Heating Thermodynamics
Transcritical CO2 water heaters leverage the unique non-isothermal supercritical gas cooler glide to produce domestic and commercial hot water at superior thermodynamic efficiency.
1. Lorenz Cycle Ideal Reference
Because the heat rejection occurs along a temperature glide, the theoretical benchmark is the Lorenz cycle rather than the Carnot cycle:
COP_Lorenz = T_water,lm / ( T_water,lm - T_evap )
where $T_{water,lm} = (T_{w,out} - T_{w,in}) / \ln(T_{w,out}/T_{w,in})$ is the logarithmic mean temperature of the water heat sink.
Frequently Asked Questions
Why are transcritical CO2 heat pumps (EcoCute) exceptionally efficient for water heating?
Conventional refrigerants (R410A, R134a) condense at a constant temperature, creating large temperature differences and thermodynamic irreversibilities (pinch mismatch) when heating water from 10°C to 65°C. Supercritical CO2 does not condense; it cools along a continuous temperature glide (from 105°C down to 15°C) that perfectly mirrors the temperature rise of counter-flowing water, delivering remarkable seasonal COPs ($> 4.0$).
Why must incoming water be as cold as possible for maximum CO2 heat pump efficiency?
The refrigerant leaving the gas cooler is cooled directly by incoming cold water. Cold water inlet temperatures (10°C–15°C) allow CO2 to cool down to 15°C–18°C before expansion, dramatically increasing liquid density and cooling capacity. If incoming water is already warm (e.g. 45°C recirculation loop), gas cooler exit temperature rises, crippling COP.
What is the Japanese "EcoCute" standard?
Introduced in Japan in 2001, "EcoCute" refers to domestic transcritical CO2 heat pump water heaters. Millions of units operate across Japan and Europe, producing sanitary hot water at 65°C to 90°C without supplementary electric resistance elements even at -20°C ambient temperatures.