The Future of EER?

Most in the HVACR industry would agree that legislative practices and emergency technology have a direct impact on the established guidelines or common practices throughout the country.

With that in mind, we were curious about the impact of variable-speed drives and compressor technology on energy-efficient ratio (EER), especially when viewing it through the lens of regional differences. We decided to raise a question about this issue and were pleased to have four experts offer their opinions.

QUESTION:

"Given the growth and emergence of variable-speed drives and inverter compressor technology, in your opinion, what is the future of EER?"

Developing HVACR products that use electrical energy as efficiently as possible and consume less electricity to operate is a continuous goal of our company. From our perspective, this goal is shared by an ever increasing number of electrical utilities and state, local and federal government guidelines. Variable-speed drives and inverter compressor technology represent two viable options to enhance the energy efficiency of HVACR units. EER could easily become even more important as the quest for energy efficiency increases. As interest grows in the total power consumption of a specific air conditioner or heat pump, a measurement such as EER that relates to the steady-state efficiency of a unit, rather than just the efficiency when the unit is running at partial load, may generate renewed interest.
—Gary Clark, senior vice president marketing, Goodman Global

Despite the popularity of variable-speed drives and inverter-driven compressor technology, EER will, unfortunately, continue to be a required HVACR system measurement point. The Department of Energy and the Air-conditioning, Heating and Refrigeration Institute (AHRI) have indicated that EER is a required, certified value for all unitary systems greater than or equal to 65,000 Btu/h; AHRI has indicated that EER is a required, but not certified, value for all unitary systems less than 65,000 Btu/h.

Utility companies are comfortable with the EER value because it presents a measure of HVACR systems operating at full load. Usually when the HVACR system is operating at full load, utility companies' electrical systems are the most stressed, and they believe that regulating EER is the best way to reduce this stress.

Utility companies, however, don't fully consider two important issues:

1. Unlike inverter-driven systems, traditional single-speed HVACR systems can only operate at full capacity or full load.

2. Inverter-driven systems only operate at the level needed to match the load in the space, and many systems are designed based on the heating load so the inverter-driven system will be operating at a level much lower than full load with a much higher EER.

Instead of focusing on EER values, utility companies should realize how much energy HVACR systems with variable-speed drives and inverter compressors actually save. SEER (Seasonal Energy Efficiency Ratio), IPLV (Integrated Part Load Value) or IEER (Integrated Energy Efficiency Ratio) are better indicators of these systems' year-round efficiency. Inverter-driven systems only run at capacities needed to satisfy the cooling or heating requirements — most of the time operating at part-load capacities. It is unlikely that an inverter-driven system will ever operate at full load — contractors typically install slightly larger systems to cover the cooling load or to provide additional heating capacity. Also, as a great value for the consumer, HVACR systems with inverter-driven compressor technology have very high power factor numbers (greater than 97 percent), meaning that almost all of the power the system brings in will be efficiently used to produce cooling or heating, unlike traditional systems that have much lower power factor numbers.

Until utility companies understand the value of variable-speed drive and inverter-driven compressor technology, how systems with these components push peak loads down and don't encourage building additional power plants or necessitate utility companies purchasing expensive short-term power to satisfy loads, EER will continue to be the desired measurement.
—Paul Doppel, director of government affairs, Mitsubishi Electric Cooling & Heating Solutions

We all understand that the performance of air-conditioning equipment declines when the temperature is hotter outside. In general, both efficiency and capacity suffer as the difference between ambient and indoor temperatures increases. Since air-conditioning is the largest load that utilities face during the hottest parts of the hottest days, they can either build generating plants and a grid that are substantially oversized almost all the time (which is very costly for all customers) or seek solutions that reduce peak demand. A stringent EER⁹⁵ requirement is one approach to limiting increased demand at high temperatures. This is captured in EnergyStar specifications (EER ¡Ý 11.5 for splits; 11 for single-packaged units). The regional agreement adopts this approach for the four southwest states, with more stringent requirements than EnergyStar for split systems (capacity-dependent).

Of course, there are other ways to limit demand. Many utilities have paid customers to accept controls that override the thermostat and prevent compressor operation for 15 minutes per hour during high demand times. This on-off approach is expensive to install. Variable-speed drives and inverter compressor technology (and all their permutations) could reduce power demand (and output) without completely turning off the equipment. For example, instead of cycling a four-ton unit off 25 percent of the time (which aggregates to the equivalent demand of a three-ton unit running continuously, at most), the utility might run the four-ton unit at two tons the entire hour. This strategy would ride on the ability of the "smart grid" to enable real-time pricing, giving customers more information and control. Both manufacturers and utilities are actively looking at this kind of strategy now.