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Cooling a large commercial building is not just about meeting its peak cooling demand. Office towers, hospitals, shopping centers, hotels, and industrial facilities often operate under changing conditions throughout the year. Occupancy fluctuates, outdoor temperatures rise and fall, and equipment loads vary between daytime operation and quieter periods.

These changes make chiller selection more complicated than comparing nominal cooling capacities. A unit that performs well at full load may spend much of its service life operating at partial load. Maintenance requirements, installation space, water availability, and long-term electricity consumption also influence the total cost of ownership.

Oil-free magnetic bearing chillers offer a different approach to these challenges. By using magnetic bearings to support the compressor shaft without conventional mechanical contact, this technology removes the need for traditional compressor lubrication oil. For projects with substantial cooling demand and long operating hours, it can be an attractive alternative to conventional chiller designs.

Why Part-Load Performance Matters More Than Many Buyers Expect

Chillers are commonly compared using their rated cooling capacity and efficiency at specified test conditions. These figures are useful, but they do not always represent how a building operates throughout the year.

Consider an office building during a mild spring day. Most occupants may be present, yet the cooling demand is considerably lower than it would be during a hot summer afternoon. A hotel may experience changing loads as guest rooms, kitchens, meeting facilities, and public areas follow different operating schedules.

When a chiller spends many hours at reduced capacity, its ability to respond efficiently to changing demand becomes an important selection factor.

Magnetic bearing compressor technology can support efficient operation across a range of loads, depending on the compressor design, controls, and operating conditions. Variable-speed operation can help the compressor adjust its output as cooling demand changes.

For buyers, the important figure is not simply the highest efficiency value in a brochure. It is how the complete chiller performs across the expected operating range.

How Magnetic Bearings Change Compressor Design

Conventional compressor designs commonly rely on mechanical bearings and lubrication systems to support moving components and manage friction. An oil-free magnetic bearing compressor uses a magnetic field to support the rotating shaft, allowing it to operate without conventional bearing contact during normal operation.

This changes several aspects of compressor operation.

Removing compressor oil from the refrigeration circuit eliminates oil-related issues associated with conventional oil-lubricated compressor arrangements. The system does not need to manage the same oil-return and oil-separation requirements, although other refrigeration components and maintenance procedures remain necessary.

Reduced mechanical contact can also contribute to lower friction-related losses. Combined with appropriate compressor controls, this design can support efficient operation over a wide range of cooling loads.

However, oil-free technology should not be treated as a guarantee of lower energy consumption under every condition. Actual performance depends on the refrigerant, outdoor temperature, chilled-water settings, condenser design, system controls, and the building's operating profile.

A proper comparison should use certified performance data and realistic project conditions.

Why Air-Cooled Chillers Can Simplify Project Planning

Cooling towers are a familiar part of many large water-cooled chiller installations. They can be an effective choice for suitable projects, but they also require additional equipment, water management, piping, and maintenance.

An air-cooled chiller rejects heat directly to the outdoor air, removing the need for a separate cooling tower and its associated condenser-water circuit.

That can be particularly useful where a building has limited space, restricted water availability, or a preference for a simpler plant arrangement. Rooftops, commercial developments, and facilities undergoing refurbishment may benefit from avoiding the structural and plumbing requirements associated with a cooling tower.

The trade-off is that air-cooled performance is closely tied to outdoor conditions. During hot weather, the temperature difference between the refrigerant and ambient air may increase, affecting compressor power consumption.

Designers should therefore compare air-cooled and water-cooled options using local weather data, annual operating hours, water costs, plant-space limitations, and maintenance requirements rather than assuming one configuration is always superior.

Refrigerant Selection Is Becoming a Bigger Procurement Decision

Refrigerant choice affects more than the chiller's cooling performance. Environmental regulations, future servicing arrangements, refrigerant availability, and the equipment's expected operating life all deserve attention.

The Dunham-Bush ACM-AE Athena series is offered with different refrigerant options, including HFC-134a and HFO-513A, as well as HFO-R1234ze configurations. The available cooling capacity varies by refrigerant and model configuration.

These refrigerants do not have identical environmental characteristics or operating requirements. Buyers should review the applicable global warming potential, local regulatory position, service availability, and manufacturer-approved operating conditions for the specific unit being considered.

A refrigerant that appears suitable today must also be evaluated against the expected service life of the equipment. For a major commercial project, replacing a chiller is a significant investment, so refrigerant planning should form part of the initial procurement process.

The lowest initial price is not necessarily the strongest long-term choice if future compliance or service arrangements become difficult.

Matching Chiller Capacity to the Building

Oversizing and undersizing can both create problems.

An undersized chiller may struggle to maintain the required indoor conditions during peak demand. An oversized unit may cycle more frequently or operate outside its most suitable range if its control system and configuration do not adequately accommodate low loads.

A reliable selection process begins with a cooling-load calculation. Engineers should consider building orientation, glazing, occupancy, ventilation requirements, lighting, equipment heat gains, operating schedules, and local design weather conditions.

Existing buildings require additional attention because actual operating data may reveal differences between the original design assumptions and current demand.

For multi-chiller plants, load sharing also matters. The control strategy needs to determine when individual chillers start, how cooling demand is distributed, and how the system responds when one unit is unavailable.

The best solution is therefore not necessarily the chiller with the largest capacity. It is the equipment configuration that meets the required load while operating effectively across the building's actual demand profile.

Installation Conditions Still Matter

Oil-free compressor technology does not eliminate the need for careful installation planning.

An air-cooled chiller needs sufficient airflow around its condenser coils. Installing the equipment in a confined rooftop enclosure or beside a wall that restricts discharge air can increase air recirculation and reduce performance.

Noise, vibration transmission, structural loading, maintenance access, drainage, and refrigerant-system service clearances should also be reviewed.

For rooftop projects, the supporting structure must accommodate the unit's operating weight and relevant site loads. The installation layout should allow technicians to inspect components and access service points without dismantling surrounding equipment.

Electrical supply is another important consideration. Available voltage, starting and operating current, protective devices, cable sizing, and control-system integration must be confirmed against the selected model's technical documentation.

Addressing these issues during design is generally more straightforward than correcting them after delivery.

Look Beyond the Purchase Price

Chiller procurement should account for the cost of operating the equipment over many years.

Electricity consumption is often one of the largest long-term expenses. Maintenance labor, replacement components, refrigerant servicing, downtime, and the availability of technical support can also affect the total cost.

An oil-free magnetic bearing chiller may reduce certain oil-related maintenance tasks, but it still requires scheduled inspections, condenser cleaning, electrical checks, control-system maintenance, and other procedures specified by the manufacturer.

Buyers should also examine the service network and the availability of technicians familiar with the selected compressor technology. For critical facilities, the cost of an extended cooling interruption can be more significant than a modest difference in the initial equipment quotation.

A lifecycle comparison based on realistic operating hours and electricity prices offers a more useful basis for procurement than purchase price alone.

Evaluating the Dunham-Bush ACM-AE Athena Series

The Dunham-Bush ACM-AE Athena is an air-cooled, oil-free magnetic bearing chiller series designed for larger cooling applications. Its published capacity range varies according to the selected refrigerant and configuration, with the overall product range covering substantial commercial and industrial cooling requirements.

The series features advanced controls and is certified to AHRI Standard 550/590, with published performance stated to exceed ASHRAE Standard 90.1 requirements. Buyers should confirm the relevant certification and performance data for the exact model and operating conditions specified for their project.

The technology may be worth evaluating for commercial buildings and facilities that require significant cooling capacity, want to avoid a cooling tower, and place a high value on part-load efficiency and reduced oil-related compressor maintenance.

For a more detailed review of the available configurations, see the Dunham-Bush ACM-AE Athena air-cooled magnetic bearing chiller.

Make the Selection Around Operating Conditions

An efficient chiller plant begins with a clear understanding of the building it must serve. Cooling-load calculations, local climate, annual operating hours, refrigerant considerations, installation constraints, and service requirements should all be included in the selection process.

Oil-free magnetic bearing technology provides another option for projects seeking to balance cooling performance with long-term operating requirements. When the equipment is properly sized and integrated into the wider HVAC system, it can offer practical advantages for facilities with demanding and variable cooling loads.

The final decision should be based on verified performance data and the needs of the specific project—not a single efficiency claim or compressor feature.

http://www.great-hvac.com
​China HVAC Refrigeration

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