Refrigerant Considerations
Refrigerant Considerations

The choice of the refrigerant impacts the performance and behavior of any heat pump system.
The most interesting refrigerants for heat pump applications presently are R-410A and R-407C.

When comparing compressors for R-410A and R-407C and looking at their respective COPs (Coefficients of Performance), R-410A does not seem to be the best solution.

As soon as we extend the scope of the analysis and consider the complete heat pump system immediate advantages are highlighted.

Focusing first on the condenser, where the hot water is produced, we can see, as shown in the temperature profile figure, that due to the fact that R-410A has no glide the dew condensing temperature is lower than with R-407C by an average of 2K, leading to higher system efficiency.

Typical temperature profile in a brazed heat exchanger condenser

Lower condensing temperatures for a given water temperature are advantageous. Due to the absence of glide in R-410A it is easier to achieve a lower condensing temperature. For R-407C due to its glide it is almost mandatory to use a liquid receiver to keep the lowest condensing temperature possible. Here the sub-cooling effect plays an important role. R-410A with zero glide is able to maintain a constant sub-cooling of 3.5K without a liquid receiver. R-407C systems need a liquid receiver to keep a stable sub-cooling of 1.5K.

In the air coil the same evaporating temperature is used for R-410A and R-407C. One additional effect of the absence of glide is that the unit will need less defrost cycles but this effect has not been taken into account because it strongly depends on the fin and air flow design.

In the next steps to evaluate further the effect of the different refrigerants on the complete heat pump system five different compressors for the modeling of the heat pump system have been used and different COPs result at different conditions. 

  • ZP42KSE – Air conditioning R-410A
  • ZH12K1P – Heating optimized R-410A
  • ZHI11K1P – Heating optimized R-410A with Enhanced Vapor Injection
  • ZH38K4E – Heating optimized R-407C
  • ZH13KVE – Heating optimized R-407C with Enhanced Vapor Injection

It has to be noted that only enhanced vapor injection models can reach the conditions of Air -7°C and Water +55°C, thanks to the extended envelope. The ZP42 (typical air conditioning compressor) is clearly not suitable for high temperature application in general, but has been chosen as benchmark model in this analysis and is a suitable model for lower water temperatures.

The prEN14825 has been used as reference to calculate the Seasonal Coefficient of Performance (SCOP) and to show annual running cost. This norm also divides Europe in three different climatic zones: warm, average and cold.

Domestic hot water production is included calculated at a base of 20% of total annual heating requirement.

Based on the assessment we summarize the following R-410A advantages:

  • Higher system efficiency at all climate conditions
  • Lower system cost
  • Significant end user savings on electricity bills

In any case Copeland Scroll™ Heating (ZH) R-407C and R-410A compressors provide important improvements for cold and average climates for underfloor and radiator applications as well as domestic hot water production. Enhanced vapor injection further increases the efficiency and operating envelope and therefore it is particularly indicated for cold climates and high water temperature heat pumps.

Standard air conditioning compressors might be interesting for the warmer climate and lower water temperature, but more restrictive working condition limitations might lead to an excessive use of the electrical heater.

Read the full study: R410A - R407C, A Refrigerant Analysis for Air to Water Heat Pump Applications.