Beating the high cost of staying cool

Calculate seasonal energy efficiency for your HVAC system.


SEER ratings are calculated by dividing the BTU of cooling output during its normal annual usage by the total electric energy input in watt hours (W·h) during the same period. Courtesy: RittalConfusion about the application and accuracy of the Energy Efficiency Ratio (EER) and the Seasonal Energy Efficiency Ratio (SEER) leaves many plant engineers struggling to ensure their energy calculations will deliver the most value to plant operations.

Understanding the definitions, calculations, regulations, and key considerations can provide clarity on saving energy and money on cooling industrial enclosures.

The difference between EER and SEER

Introduced by the Air Conditioning & Refrigeration Institute in 1975, EER measures and compares the efficiencies of HVAC unit to another. SEER was signed into law by President George H.W. Bush in 1992. SEER is considered an improvement because it takes seasonal temperatures into account to better approximate what happens in the actual end use application for the cooling unit.

SEER is calculated by dividing the BTU of cooling output during its normal annual usage by the total electric energy input in watt hours (W·h) during the same period.

SEER = (BTU/H ÷ W)

Every air conditioning unit is assigned a SEER rating. The higher the SEER (for the climate), the more energy-efficient the cooling unit. For example, upgrading from a SEER 9 to a SEER 13 unit can reduce power consumption by 30%.

A SEER 13 standard was to take effect starting in 2006 as the standard for optimal energy efficiency. The SEER 13 standard is estimated to limit air pollution and reduce fossil fuel consumption by up to 33 million metric tons of carbon, according to the Washington, D.C.-based Environmental and Energy Study Institute. The U.S. Department of Energy estimated 4.2 quadrillion Btu would be saved between 2006 and 2030 with a SEER 13 standard. While legislation on the standard has not been approved, the concepts of SEER are being applied in the industry.

Why does SEER matter?

It's true that SEER does not apply to industrial enclosure air conditioners, as they're deployed to run year-round to cool installed equipment. However, that doesn't mean SEER shouldn't be a consideration when calculating potential savings from energy-efficient enclosure cooling systems. For example, when comparing costs and benefits of a cooling system retrofit, SEER can be useful as a variable to calculate energy savings, a critical consideration in overall plant efficiency.

Consider the following scenario to demonstrate how understanding SEER can be useful in an industrial enclosure air conditioning purchasing decision. In this example:

  • Your plant is located in the Great Lakes region.
  • You're running 23 enclosure cooling units, for three shifts a day, five days a week.
  • You switch out your enclosure cooling units with energy-efficient 2600W, wall-mounted cooling units with a SEER rating of 6.2 (adjusted for your temperate climate)
  • Your average electricity rate is $1.39/ kWh.
  • Your annual energy savings could range from $69,249.00 to $171,922.00, depending on the unit model and manufacturer (for this example, we calculated savings when switching out to Rittal's Blue e and Blue e+).

Of course, it's worth noting that SEER standards for cooling units vary widely across the globe. For example, in Europe, the ESEER (European Seasonal Energy Efficiency Ratio) does not incorporate free-cooling to any degree, as the minimum ambient temperature of 20ºC (68°F) is unrealistic for most of the continent.

Measuring energy efficiency

In the case of industrial air conditioners, another good measure of efficiency is the Cooling Coefficient, a ratio calculated by dividing the amount of cooling capacity by the amount of power consumption. This calculation is made at an internal and ambient temperature (typically 95° F internally and externally).


Another industrial energy efficiency metric that is mandated in ASHRAE 90.1 is Sensible Coefficient of Performance (SCOP).


The SCOP often is used to compare the efficiencies of different makes and models of cooling units. You can often find it in buyer's guides and brochures. A higher SCOP is better. Cooling units for computer rooms use SCOP because it better captures the conditions found in them. SCOP was chosen specifically to measure climate control in industrial settings for two reasons:

  • EER was deemed inadequate because it includes latent cooling.
  • SEER also gives credit for latent cooling but does not account for the fact that the cooling load in a typical industrial setting is not seasonable, but rather consistent year-round.

Taking steps to upgrade

Considering how critical energy costs are to most industrial operations, making the decision to upgrade enclosure cooling systems is a significant first step.

A good place to start is by evaluating your facility's energy efficiency. The Environmental Protection Agency's energy performance rating system helps facility managers assess how efficiently their buildings use energy, relative to similar buildings. You can find out your energy performance ratings through EPA's Energy Star Portfolio Manager, an interactive online tool that tracks energy and water consumption. The energy performance of a building is expressed on a scale of 1 to 100. For example, a rating of 50 indicates that the building performs better than 50% of all similar buildings over the course of a year.

When it comes to evaluating the cooling efficiency of enclosures, it's important to know how much heat energy the air-conditioning system must remove. One way to figure this out is to add up the heat loads of all electronic components as specified by their respective manufacturers. Another is to add up the power, P, that the electronics consumes and then multiply it by one minus the efficiency, E, of the system:


The number you reach will define the need for cooling capacity.

Also, several sizing software tools are available to help you figure out how enclosure air conditioners will perform. Some even walk users through the application factors and determine the need for cooling, and can calculate the internal enclosure temperature and suggest an appropriate air conditioner with the best cooling capacity relative to power consumption.

For example, consider an enclosure air conditioner with a cooling capacity and power consumption at 95/95, 60 Hz of 2,700 W and 1,500 W, respectively. Then є = 2,700/1,500 = 1.8. This energy cooling factor was arrived upon by taking the ratio between useful cooling capacity and power consumption:

є = Ѳk/Pel

(Ѳk = useful cooling capacity, W and Pel = power consumption, W)

We also know that with enclosure air conditioners, internal and external humidity affect performance. As you consider systems with the most reliable ways of discharging condensate from the enclosure, you may want to investigate advanced fan and filter units with condensate evaporators to eliminate moisture.

Making the right decisions

Now that we have established that cooling industrial enclosure with energy-efficient air conditioning units can significantly prolong the life of your equipment, save energy, and reduce downtime, it's time to address the purchasing process.

Besides EER, SEER, AND SCOP measurements, here are some other factors to consider before making your purchase.

Cooling Output – Measured in watts, this is the ability of the cooling device to remove heat from a system. Also sometimes measured in tons, as 1 ton of refrigeration is freezing 2,000 pounds of water at 32°F for 24 hours.

Internal Heat Load – This is the amount of heat energy that the electronics inside the enclosure produce. It's important to know how much heat energy (in Btu/hour or in watts/hour) is generated in the enclosure before shopping for an air conditioner that has enough capacity for your needs. ·

Mains Operating Frequency – In North America, 60 Hz is the norm (compared to 50 Hz in the rest of the world), so when an air conditioner operates at 60 Hz, its fans and compressor rotate faster and cools somewhat more efficiently. If shopping outside of North America, it's helpful to know that some units are dual-rated so they can operate at both 50 Hz and 60 Hz.

Industrial plant operators and managers are paying more attention to enclosure climate control, and the most efficient means of keeping equipment housed within them cool. This is a good thing—even if we don't yet have formal standards for testing and establishing cooling capacities in North America.

What's important is to get ahead of existing and future air conditioning unit ratings and regulations, and educate yourself on making the best decision that fits your plant's operating needs and budget.

Eric Corzine is climate control product manager at Rittal Corporation.

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