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Make Your Buildings Cool with These 3 Technologies

Key Points
  • High-efficiency rooftop units use variable-speed controls and waste heat recovery.
  • Magnetic bearing centrifugal chillers can reduce chiller energy consumption by 42 percent.
  • Geothermal (ground source) heat pump (GSHP) systems have lower maintenance costs.

If your building's cooling system is ready for a retrofit or you have some new construction in the works and you're not sure what to do, the Federal Energy Management Program (FEMP) may have some answers through its list of promising technologies. The list was created using an analytical tool—which helps identify and prioritize available energy-efficiency measures—developed by the U.S. Department of Energy's Building Technologies Office (BTO). Here are three cooling technologies making the list:

Get high with efficiency

Packaged rooftop unit

For low-rise buildings, high-efficiency rooftop units (RTUs) are applicable to just about any location, although energy savings will vary by climate. To increase efficiency, these units incorporate variable-speed controls to minimize fan and compressor energy, while capturing and reusing heat, cold and humidity from a building’s exhaust air. For a typical 90,000 Btu/hour unit, a high-efficiency RTU has an energy efficiency ratio (EER) of at least 12.2 and an integrated energy efficiency ratio (IEER) of at least 14.0.

After the U.S. Navy completed 11 RTU retrofits, total annual savings was 100 MWh. The BTO also is actively deploying this technology through the Advanced RTU Campaign. If you need help deciding if high-efficiency RTUs will work for you, check out this replacement guide, which evaluates a range of economic and non-economic factors for optimizing energy and cost performance.

Go frictionless

For large commercial buildings, magnetic bearing centrifugal chillers equipped with variable frequency drives (VFDs) can reduce chiller energy consumption by 42 percent compared to a standard rotary screw chiller. This reduction is possible because magnetic bearings eliminate friction losses and VFDs improve efficiency at partial loads. Because the magnetic bearing don't require lubrication, maintenance costs also are reduced.

A field assessment by the General Services Administration showed that a rotary-screw chiller operated with a full-load efficiency of 0.655 kW/ton and a non-standard part-load value (NPLV)efficiency of 0.704 kW/ton. In contrast, the magnet bearing variable-speed centrifugal chiller operated with a full-load efficiency of 0.562 kW/ton and an NPLV efficiency of 0.519 kW/ton. In general, the magnetic bearing chillers have higher operating efficiency than most positive displacement chillers—including reciprocating, rotary-screw and scroll—as well as many alternative centrifugal chillers (up to mid-range capacities).

However, equipment costs may be twice that of a conventional chiller of equivalent capacity. Another estimate puts the cost at 30 to 35 percent higher than an equivalent capacity rotary-screw chiller.

Pump up the savings

Geothermal heat pumps

Geothermal (ground source) heat pump (GSHP) systems are most cost effective for replace-at-end-of-life and new construction installations. These systems take advantage of the ground's constant temperature to provide highly efficient heating and cooling. During warm weather, a GSHP uses the ground as a heat sink, removing the hot air from the building.

GHPs use up to 50 percent less energy than conventional systems, while requiring less maintenance. However they're expensive to install and can have extremely long payback periods. To improve operational efficiency, variable-speed pumps and outdoor air ventilation control may be required.

Langley Research Center's new Integrated Engineering Services Building, a 138,000-square-foot multi-use facility, installed a hybrid geothermal system with a 60-ton supplementary fluid cooler to meet the cooling demand in the summer. The new building is 31.5 percent more energy efficient than a baseline building, and its energy intensity is projected to be 60 percent better than average multi-use buildings at the Center. Combined with other energy saving features, the geothermal system is helping to save $3.6 million per year in operations and maintenance costs.

Oak Ridge National Laboratory offers a guide on purchasing an energy-efficient GSHP.

Images, iStock, DOE