At the time of writing, hopefully throughout Europe most of the R22 conversions have already taken place, and I have already helped several existing customers already navigate this course of action.
As R22 is being phased out across the world, people are unsurprisingly looking to natural refrigerants as a replacement.
Although other Freon gases are available to replace R22 and perhaps may offer an easier short term option, most of these on the market today will soon be phased out due to high global warming potentials (GWP), even though they don’t have any ozone depletion potential (ODP) like R22 has.
Of the two major natural refrigerants that have proven to work in industrial plate freezer systems, Ammonia and CO2; Ammonia is a perfect choice, offering excellent thermodynamic properties, low power consumption, and it is already a common refrigerant that almost every industrial refrigeration engineer is familiar with. It also benefits from having a less complicated installation than CO2, and does not require as many component replacements either, due to CO2’s high pressure rating.
This guide is not intended to be a full guide on how to perform a complete R22 / Ammonia conversion, but instead however, it is intended to make the reader aware of what is required to convert purely the plate freezers.
The key matter with both refrigerants is understanding the chemistry behind them.
Many older R22 plate freezers where fitted with Copper hose gaskets & plate connector gaskets. These will need replacing with Alloy ones in the case of a like-for-like replacement, or better yet, upgrading to a newer sealing concept we offer such as O-ring fittings & screw in adaptors.
Although pure anhydrous Ammonia does not react with copper, it will do in the presence of moisture.
Cu2+(aq) + 4 NH3(aq) = Cu(NH3)42+
Plate Freezer systems typically run below atmospheric pressure on Ammonia, and even if they don’t, it is still possible to get moisture in the system over time regardless (or even from new Ammonia).
Since on a pumped Ammonia system, the low pressure receiver acts as a big still, the water collects here and gets pumped around the system.
Hence over time, the Ammonia will corrode the old copper gaskets and cause leaks.
The second thing to be aware of, is the chemistry between Ammonia and R22 itself.
R22 + R717 = Ammonium Cyanide + Ammonium Chloride + Ammonium Fluoride
CHClF2 + 5NH3 = NH4CN + NH4Cl + 2NH4F
The products of the reaction then go onto react further with the R22, Ammonia and Iron in the system to form more chemical compounds.
It is recommended when doing a changeover to leave the plate freezer open to the air for a long time, and follow up by steam cleaning inside all the freezer components to help remove any existing oil residue.
Since PTFE inside the hoses is actually permeable to a certain extent, it is normally recommended to change all the hoses for new ones (especially considering, that normally the hoses would be past their recommended maximum service life anyway). Otherwise again, careful cleaning procedures must be established to ensure no R22 is left.
This document is only intended to be an outlined overview of this process, and when carrying out such a task it is essential it is done by a trained engineer who is familiar with all necessary procedures required and consult any local safety authorities.
The last change when converting to Ammonia is to ensure the plate freezers work efficiently.
Since Ammonia has favourable thermodynamic transport properties, it can be run perfectly fine on the existing designs & header sizes, however taking the opportunity to change the orifice size whilst the freezer is apart can add valuable efficiency.
Since the latent heat of vaporisation is considerably higher in Ammonia than R22, the mass flow is considerably lower.
In order to balance the flow to the plates, smaller orifices need fitting. On older freezers especially, the orifices are oversized to begin with compared to modern practices, so they would benefit more again.
As plate freezers can vary wildly in size and product loads, we recommend getting in contact with us for assistance in calculating the orifice size correctly – otherwise trial and error is usually necessary which is time consuming and expensive in refrigeration systems.