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Use Variable Speed Technology to Cut Energy Usage, Ensure Code Compliance

In 2018 and 2023 the DOE will be implementing new building energy codes focused on part load efficiency for light commercial roof top units. The new energy codes will make it critical for commercial building owners and managers to stay ahead of the regulation curve on energy usage. As a result of the upcoming increase in efficiency standards the demand for more efficient heating, ventilation and air conditioning (HVAC) solutions is increasing.

Building owners/managers can achieve significant energy savings in the range of 15-25% by replacing existing or specifying new light-commercial rooftop units with new units that utilize variable-speed technology. In many cases, the use of variable-speed technology is a good way for commercial buildings to meet the forthcoming regulatory requirements for efficiency and energy usage. It can also help meet future minimum standards that are put into place after 2018 – with a short payback.

While this type of technology is not new, some manufacturers are applying it to package units in nontraditional ways. One way they are doing this is by combining indoor and outdoor fans with variable speed compressors to increase efficiency. Because manufacturers are focusing on part-load efficiency, more roof top units are available that are significantly more efficient than the technology previously available with constant volume units.

Part-Load Performance is Critical

As commercial facilities prepare for the change in efficiency standards, it’s important to use technologies that maximize part-load efficiency. Variable-speed technology is a cost-effective way to do this, typically offering a three- to five-year payback for facilities using older constant volume light-commercial rooftop units. The HVAC industry is also focused on staying ahead of the regulation changes by employing variable-speed technologies across product portfolios, to ensure that equipment works efficiently and reduces energy consumption.

Variable speed components meet the actual load required during any given time over a wide operational range, meaning their speed and output varies to reflect the conditions and demands of the space. By precisely matching output to the cooling demands of the space, compressors and fans operate at their fastest levels when demand is high, and modulate to slower levels when demand is less, for an ultra-high Integrated Energy Efficiency Ratio (IEER) a measurement of part – load efficiency. The result is lower annual energy use and typically smaller annual energy bills. This is especially true when compared to constant volume rooftop units, where the load is either on or off and controlled by a zone sensor or thermostat.

A majority of the time rooftop units don’t need to run at full load causing this method to not be as efficient as variable-speed technology. Balancing outdoor air flow, indoor air flow and the compressor to match actual load requirements helps produce the most efficient energy profile for the equipment while still meeting load demands and occupant comfort.

Variable-speed technology also provides better dehumidification control when all of the systems work together. When a system is properly sized and applied, it is able to operate indoor fans at lower speeds that provide enhanced humidity removal.

An additional benefit that many overlook is the reduction in the number of times components are turned on and off, which helps extend longevity of the components and equipment life.

Successes

Real-world results from commercial buildings that have switched from constant volume equipment to light-commercial rooftop units with variable-speed technology illustrate that it’s possible to reduce energy consumption between 15-25%.

These commercial buildings also report achieving very tight temperature and humidity control with the technology. The improved system accuracy impacts occupant satisfaction, which can result in fewer hot and cold complaint calls for facility managers.

The key to sustaining an optimized performance with variable-speed technology is periodic basic maintenance of the rooftop units. Maintenance includes changing filters, cleaning coils and verifying that operational set points are maintained. The frequency of necessary maintenance will vary based on environmental factors and geographic location. A building located in a construction zone or another environment with more debris in the air, will likely require more frequent maintenance of rooftop units because the coils and filters will clog faster.

Some HVAC equipment manufacturers offer service contracts to perform this maintenance, which is an option to consider.

Integrated Controls

Integrating a building automation system (BAS) can also further enhance the efficiency of rooftop units with variable-speed technology. A BAS can help a building owner or manager increase energy efficiency, lower utility bills and ensure the HVAC equipment is operating optimally.

Some manufacturers offer rooftop units with industry-standard communication platforms, such as BACnet® and LonTalk™. Utilizing a standardized communication platform for integrating the units with a BAS provides detailed information about how the unit is performing, which is vital to implementing advanced controls strategies that can enhance energy efficiencies.

Efficient Equipment for Increasing Demands

Integrating new rooftop equipment can help building owners and facility mangers improve building efficiency and meet the escalating industry regulations. A switch from constant volume technology to variable-speed technology is a cost-effective solution that provides significant energy savings while still delivering the comfortable space that building occupants want.

Bryan Ware is the portfolio leader for light commercial package rooftop products for Trane.

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