Too Hot? Too Cold? Just Right: The 3 Crucial Keys to HVAC/R Compressor Savings

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goldilocks.jpgToo hot. Too cold. Just right. Just like all consumers, Goldilocks expected that her preferences would be met. Luckily for the three bears, she didn’t have social media and rating websites like Yelp to broadcast the fact that her first two bowls weren’t to her liking! Today, consumers do have those powerful tools, and it’s even more important to make sure that their needs are met. When it comes to customer satisfaction and guest comfort for businesses like restaurants or retail, getting everything just right can’t be done without your heating, ventilation, cooling, and refrigeration equipment (HVAC/R) performing impeccably. And the heart of this equipment is a modern wonder called the compressor. Compressors are the component of your air conditioning and refrigeration that do the real work to enable the transfer of heat from inside the building to outside.

Unfortunately, the cooling and refrigeration that compressors provide is quite expensive. For most restaurants, compressors use more than 50% of the electricity consumed over the course of a year. That could easily cost you more than $25,000 a year, making finding compressor savings key to protecting profits. These costs are a major reason that the Department of Energy last week released updated efficiency standards for refrigeration equipment. These standards will take effect in 2017 and are projected to save restaurants and supermarkets $12B over the next 30 years.

So what can you do to manage the performance and contain the total cost of ownership for the roof top units, walk-in coolers, walk-in freezers, prep tables, display cases and other equipment that relies on compressors? In addition to good preventive maintenance, HVAC/R equipment benefits from three key strategies:

  • Monitoring the energy used by the equipment: This practice can identify two key issues: runtime and compressor cycle length. In refrigeration equipment, the compressors are designed to run no more than 80% of the time. If they are running more than that, there may be a problem, such as a failed automatic door closure, dirty condenser coils, or a frozen evaporator coil. This “overload” can be seen in the chart to the left below. This walk-in freezer is running 100% of the time, other than defrost cycles. The chart on the right shows a better operating unit.

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  • Temperature Monitoring: This is particularly useful in understanding the performance of a walk-in refrigeration unit. Temp data helps to determine whether the unit is ever reaching its set point (or target temperature). If it’s not, there is clearly a problem. Temperature monitoring can also determine whether that set point is too low.
  • excessive-runtime-300x150.pngExcessive Runtime: An example to the right shows the freezer maintaining a proper temperature (in red) between about 3 and 8 degrees (aside from normal defrost cycles), indicating that the excessive runtime (in grey) is being caused by some other issue. It’s worth noting that because the freezer temperature is not affected, this rampant energy waste would not be discovered if the energy use of this piece of equipment were not being tracked individually.
  • Compressor cycle length: Compressors are designed to turn on and off thousands of times during their useful lives, but their lifetimes are bounded by a set number of expected on-off cycles. So “rapid cycling”, or many very fast on and off cycles, shortens the life of your equipment. A good rule of thumb is that if your compressor is running for extended periods with cycles of less than 3 minutes in duration, there is a problem. This can be seen in the data for two roof top units (RTUs) below – again the problem is on the left.

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With strategic use of equipment-level energy monitoring, temperature monitoring, and compressor cycle length monitoring, your energy bill won’t be a bear, your customers will feel just right, and you and your equipment will live happily ever after.