The development of new refrigerants blends
There are advantages to refrigerants that possess high saturation pressure such as opportunities for compact designs and higher efficiency. However, currently available refrigerants, such as R410A suffer from negative characteristics such as high GWP and low critical temperature. There is no single-component refrigerant with low GWP and high critical temperature and most mixtures that may achieve these criteria are zeotropes with high temperature glide.
It was therefore concluded that azeotropes with thermodynamic characteristics similar to R410A would be commercially attractive. A development project was undertaken to identify such blends. Three new refrigerants have arisen from this work, all formed from natural refrigerants or synthetic chemicals with a global warming potential (GWP) of less than 150:
ECP410A
The pressure-temperature characteristics and refrigeration capacity are close to that of R410A, but the critical temperature is significantly higher, improving performance, particularly at higher ambient temperatures. The blend is considered to be best suited to domestic and commercial air conditioning and heat pumps.
System performance evaluations conducted around European rating conditions reveal:
- Evaporating capacity greater than the theoretical results, being about 85% of R410A.
- Cooling COP was between 6 – 10% higher than R410A, whilst heating COP was at least 15% higher.
- Evaporating temperature was up to 4 K higher than R410A, condensing temperature is about 1 K lower and discharge temperature around 2 – 4 K lower than R410A.
ECP717
This mixture possesses advantages over pure ammonia, which has a relatively high NBP, low specific heat, low evaporating temperatures leading to sub-atmospheric operation which allows leakage of air into the system, and high compressor discharge temperatures. ECP717 overcomes these drawbacks by significantly reducing the NBP and allowing much lower discharge temperatures. Single-stage compression may be used instead of two-stage with an additional compressor. In comparison to R744, the problem of high triple point is overcome. Lastly, problems with refrigeration oil miscibility with R717 are overcome.
The following findings were made:
- COP is similar to pure R717.
- Volumetric refrigerating effect (VRE) exhibits a synergetic behaviour and gives considerably higher values of VRE than the pure components.
- Discharge temperature is significantly lower than R717, which favours system reliability.
- Improved heat transfer, particularly in the evaporator, resulting in higher evaporating temperatures.
- The degradation in COP and refrigerating capacity with increasing temperature lifts in a single stage cycle is reduced relative to pure ammonia.
This azeotropic blend is optimised for below -33˚C applications. It has particular utility for industrial process, food and blast freezing applications and will displace liquid nitrogen as well as two stage ammonia systems.
ECP744
ECP744 has advantages relative to R744, specifically, higher critical temperature and lower triple point. For R744 these introduce hindrances which result in super-critical operation at ambient temperatures above 25 C and solid formations when it undergoes rapid reduction of pressure.
Performance evaluations were carried out and it was found that the refrigerating capacity and pressure was significantly greater than that of R410A, but less than R744. The cooling COP was found to be about 6% higher than R744. The higher critical temperature, lower triple point and more efficient refrigeration cycle are all significant benefits, but the commercial benefit arises from the reduction in condensing pressure, allowing the leak tight use of silver soldered joints.
Using a combination of novel property modelling, safety analyses and comprehensive system simulation, a number of previously unidentified azeotropic and near-azeotropic blends have been identified for use in certain applications where existing refrigerant options are subject to a variety of hindrances.
These new blends offer notable advantages over existing refrigerants, in particular:
- Zero ODP and low GWP, below 150, and mainly “naturally” occurring
- Improved thermodynamic properties (such as critical temperature and minimal temperature glide) over similar existing refrigerants Good solubility with oils
- Low toxicity, and reduced flammability
- Known and understood chemical and material compatibility
Earthcare now controls patents which could achieve more than a 13% reduction in global warming, by introducing disruptive technologies to the global refrigerant market of 132 Ktonnes / annum, worth over £660 million / annum at UK prices.
Table 1: Characteristics of new blends
| Name | ECP410A | ECP717 | ECP744 |
|---|---|---|---|
| Molar Mass | 43.6 | 22.9 | 39.0 |
| NBP (°C) | -49.2 | -89.0 | -84.5 |
| Critical temp (°C) | 94.9 | 41.9 | 37.9 |
| LFL (% vol) | 2.7 – 2.9 | 4.0 – 4.2 | non-flammable |
| Likely safety class | A3 | A2 | A1 |
| ODP | 0 | 0 | 0 |
| GWP (100) | 7 | 2 | 46 |
Earthcare’s R&D Team:
