By Grant Laidlaw
Many people ask for assistance in the understanding of theoretical and practical aspects of the industry. I will endeavour to enlighten. Many people ask for assistance in the understanding of theoretical and practical aspects of the industry. I will endeavour to enlighten.
Chris asks: Grant,we are beginning to see a lot of R290 in the commercial refrigeration space and in particular the cold drink type fridges. We were wondering, what changes to tooling and basic procedures do we need to make as this is a problem for us. Any advice would be appreciated. Also, are we allowed to transport these new flammable refrigerants in our vehicles? Again, what additional procedures do we need to implement a professional driving permit (PDP)? As equipment may only use 150g of hydrocarbons is this really viable for air conditioning systems or only for larger refrigeration systems?
Chris, I addressed the first part of your question in the previous issue, let us look at the types of equipment that can utilise R290 as the refrigerant. Again, I am using international standards as South Africa is in the process of developing and amending the applicable standards.
When we look at the maximum flammable gas charge size, we find that the amount of flammable refrigerant which can be used in systems is restricted and depends on various factors:
- Location of equipment, e.g. below or above ground level;
- Occupancy of area being cooled, e.g. unrestricted access by the public, or authorised access only;
- Type of system, e.g. direct expansion or secondary / refrigeration or air conditioning.
The limits are different for comfort cooling / heating and non-comfort cooling / heating applications. Systems with less than 500g flammable refrigerant charge can be located anywhere, though it should be noted that the potentially flammable zone should still be assessed.
Comfort cooling / heating applications
For comfort cooling / heating applications the maximum charge is based on the Lower Flammability Limit or LFL of the refrigerant, the floor area and the height of the indoor unit:
Non comfort cooling / heating applications
There are practical limits. Chris, as I have said previously, South Africa is in the process of updating the relevant standards. Looking at the European standard EN378-1 specifies practical limits for all the refrigerants covered. I am reasonably sure our standards will be very similar.
To determine the maximum charge imposed by the practical limit (PL), the room volume is multiplied by PL. Examples of maximum charge determined by PL:
Cold room size 4m x 5m x 2.5m high, cooled by a direct expansion system using R290.
- Cold room volume = 8m x 5m x 2.5m = 100m3. R290 PL = 0.008kg/m3.
- Max charge = 100 x 0.008kg = 0.8kg.
Then, as above, but using R1234yf:
- Cold room volume = 8m x 5m x 2.5m = 100m3. R1234yf PL = 0.06kg/m3.
- Max charge = 100 x 0.06kg = 6kg.
The practical limit can be exceeded in machine rooms, but if this is the case, the design of the machine room must comply with EN378 and it will be designated a special machine room.
In addition to the limits above, EN378 also specifies overall maximum charges – whichever is lowest applies.
Overall maximum charge sizes:
So Chris, if for example, in the case when the whole of system is to be placed at ground level or above and in an unoccupied machine room or open air you face no restrictions with regards to the amount R290 refrigerant one can use. This is easy to achieve when utilising an indirect system.
We are therefore not necessarily limited to the 500 grams you mentioned.
I have seen many scenarios outside of our borders where large industrial R290 plants have been installed successfully. We have all the fundamental knowledge required to design, install and operate R290 equipment. With a relatively small amount of training, predominantly around the safety issues, people at all levels will easily adapt to R290.
Chris, I hope that this assists you with the use of flammable refrigerants. As I said in the previous issue, they have arrived and are certainly here to stay.