Indirect systems; Natural refrigerants past, present but future.
Natural refrigerants in the agribusiness are becoming popular, now that we have to respect the environment more and more. In the refrigeration technology natural refrigerants have been introduced recently. Ammonia, Propane and CO2 has been used in the past, as an active refrigerant. Due to safety problems and high pressures other refrigerants became more popular. Since some years the natural refrigerants are coming back. The main reason for this is the environment, which suffers from the present refrigerants. No reason to explain this here in detail. In the present situation there are several ways to reduce damage from refrigeration systems to the environment:
- indirect systems; using only small quantities of refrigerant and a glycol solution for the distribution of the cold.
- using natural refrigerants.
Indirect refrigeration systems using traditional refrigerants and glycol.
Indirect systems use only a small quantity of refrigerant. The advantage is a smaller chance of leakage of refrigerant, direct emission, to the environment and the smaller quantity that can blow off. Note that a leakage of 1 kg R404a is equivalent to an emission of 3750kg CO2. Traditional systems leak approx. 5% of their content per year. The disadvantage of indirect systems however is the somewhat lower energy efficiency, which increases the emission of CO2, indirect emission.
In general one can say that an indirect system tends to use some more electric power, leading to more indirect emission, and to less leakage of refrigerant, leading to less direct emission. The total emission of CO2, direct plus indirect, can be less, provided the indirect system is designed properly. It can be concluded that indirect systems with traditional refrigerants are better for the environment, use a bit more energy and will cost a bit more. Support of the local government is needed to get these systems off the ground.
How to improve indirect systems.
Ammonia, CO2 and Propane are natural refrigerants, causing hardly problems to the environment when leaking, so almost no direct emission. Indirect systems get better efficiency when replacing traditional refrigerants. The increase of efficiency can eliminate the increase of energy consumption caused by the indirect part. For the high temperatures, -10 °C and above, Ammonia and Propane are favorite, but CO2 is coming too. It can be concluded that indirect systems, using these natural refrigerants use equal or less energy, compared to the traditional refrigerants in DX-mode. The investment however is a bit higher; approx. 5 to 10%. For these systems also support of the local government is needed to get these systems off the ground.
In stead of glycol new solutions appeared, such as Temper, Pekasol and Freezium. These solutions offer better thermal properties, reducing the energy efficiency and less energy for the pumps, but they all are rather aggressive, causing corrosion. Plastic piping has been introduced to lower the investments and maintenance. There still is a lot to develop at this stage.
Recently CO2 has been used as an indirect media, replacing glycol and others. Applications can be found in supermarkets and in the agribusiness. The advantage of CO2 is that it evaporates, resulting in small sized piping and low pumping energy. The disadvantage is the high pressure. In practice much have to be experienced as far as energy consumption and reliability are concerned. Theoretically these systems are very energy effective and cost a bit more, compared to traditional systems. In practice some difficulties have been encountered, especially where energy efficiency is investigated.
Future developments.
One can expect that indirect cooling systems, using Ammonia or Propane as active refrigerant and CO2 as indirect media will make a chance in the future of the agribusiness. There still are problems to overcome. Support of the local government is needed to get these systems further developed. It will be necessary to have a good consultant that can make the right choices, preventing disappointing results.
