22 // Opinion
How to Determine the Efficiency of Your Refrigeration System A simple EER calculation will enable you, in real time, to measure a system's energy efficiency – By Ed Estberg
T
here are many reasons to understand the efficiency of the refrigeration systems installed in supermarkets.
and this affects air-cooled condensers and evaporative condensers, along with store conditions. The air-conditioning system must also be included in this calculation.
First, operators need to understand the energy consequences of their compressor and condenser selections. In addition, government agencies and utilities that incentivize energy efficiency need an accurate way to rate built-up installed systems.
Getting information from fixture manufacturers is difficult. They had to pick a set of conditions for testing, and those exact conditions are almost never present in the store. The same holds true for the compressor and condenser manufacturers.
Refrigeration systems will vary by store, and operators should be free to choose store size, equipment type, and refrigeration load per store or per square foot. Each owner has a different style of store operation, and should be allowed to merchandise as they wish.
EER formula
Once operators have chosen a floor plan, the selection of a refrigeration system should be based on efficiency, cost, maintenance, and other factors. Incentives should be based on actual efficiency and not an estimated rating, but it can be difficult to get real energy numbers for a mechanical refrigeration system. My definition of refrigeration efficiency is a very simple: EER (energy efficiency ratio), which is the number of evaporator BTUs rejected by the compressor/condensers to the atmosphere per kilowatt-hour of electricity purchased. These should be real numbers, and can only be achieved on-site and after start-up. It sounds simple! Unfortunately, there are many variables in a supermarket, so getting the correct values to use in a formula is almost impossible. First, the evaporator loads vary during a typical 24-hour operating day because of customer activity, defrost schedules and store conditions, which can have a major effect on loads. The ambient temperature and humidity are also always changing,
During my investigation of an ammonia/CO 2 all-natural solution, I came upon the idea of rating the refrigeration systems. I felt we needed to know the EER of ammonia /CO 2 vs. transcritical CO 2 , for exampIe, but I could not find any real numbers that would meet my very simple EER requirement. To calculate a very simple EER, you need to know the amount of electricity (watts) consumed at a given time, and the exact total evaporator BTU load at that same time. Here is my solution, based on the type of system I am proposing to be our “SRS� (Sustainable Refrigeration System), our name for an all-natural system. (Tentatively, that will be a DX ammonia system over a CO 2 liquid-overfeed system for both medium- and low-temperature.) Submeter the wattage for the following equipment as a group: Refrigeration compressors Air-conditioning air-handler motors and compressors Condensing water pumps Tower fans Main air-fluid cooler fans De-super heater air-fluid cooler fans Heat-reclaim water pumps
Accelerate America // June -July 2018