About the authorWhat is the limit on energy reduction?
If you are like a lot of other ammonia refrigeration system end-users you are trying to reduce your costs associated with energy usage. You may be exposed to a constant barrage of ideas or methods of what to do. One of the more popular concepts is: decrease the discharge pressure.
OK, now what? Someone said I need to do this and everyone talks about it, but what should I do?
The recommendation of lowering the discharge pressure is based on a broad premise of; lowering the discharge pressure reduces the amount of work (re: energy) that the compressor requires to meet that operating condition. Therefore, a primary task is to find out how much the discharge pressure can be decreased and what the resulting savings will be. Seems fairly simple.
One thing to consider before doing this though is to understand if there will be any implications when you begin the process of trying to lower the discharge pressure of the refrigeration system. Do you change the pressure control settings gradually or take a leap of faith and try to lower it drastically? Regardless of which method you might select it would be helpful to know how low can you go?
Unfortunately, in a lot of refrigeration systems certain barriers exist. These limitations are a function of the system design and the requirements of your process. You could start with the following question: What else in your system needs hot gas to operate?
After all, anything else that uses hot gas may be impacted if we try to lower the discharge pressure. You might have hot gas defrost or gas-powered pumped recirculation systems. If you reduce the discharge pressure it can affect these. Therefore it is important to recognize this impact before you begin making adjustments.
If you try to lower the discharge pressure too much the hot gas defrost cycle may produce unintended consequences. The defrosts may be inadequate or take too long. Similarly if you have gas-powered recirculation systems you may not be able to “pump or transfer” sufficient liquid.
What you will find is these two requirements are competing with your desire to lower the discharge pressure. The end result is, it is important to understand what these limits are and how to minimize their impact so that you can maximize your savings.
