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Views: 263 Author: Capital Technology Publish Time: 2026-10-09 Origin: Site
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● San Ace Counter Rotating Fan vs Two Conventional Fans in Series: Quick Comparison
● How a San Ace Counter Rotating Fan Works
>> Two Rotors, One Airflow Direction
>> Why the Two Rotor Speeds May Differ
● How Two Conventional Fans in Series Work
>> Series Installation Primarily Targets Pressure
>> Why the Installed Pair Needs Testing
● Static Pressure and Airflow: Compare Curves, Not Endpoints
>> Maximum Airflow Is Not Delivered Cooling Airflow
>> A Published Comparison: San Ace 172 CR vs Two Series Fans
● Power Consumption and Noise: Compare Equivalent Cooling Duty
>> Higher Performance Does Not Automatically Mean Lower Energy Use
>> Noise Needs an Installed Assessment
● Installation Space, Controls, and Maintenance
>> Compare Total Installed Depth
>> Verify PWM and Speed-Monitoring Details
>> Two Motors Do Not Establish Redundancy
● Recent San Ace Data: What a Modern Specification Shows
● A Practical Six-Step Fan Selection Procedure
>> 1. Define the Thermal Requirement
>> 2. Characterize the Airflow Path
>> 3. Obtain Comparable Fan Curves
>> 4. Locate the Operating Points
>> 5. Test in the Actual Enclosure
>> 6. Validate Fault and Service Conditions
● Which Fan Arrangement Should You Choose?
>> Favor a San Ace Counter Rotating Fan When
>> Consider Two Conventional Fans in Series When
● Request a Model-Specific Cooling Comparison from CAPITAL
>> 1. Is a San Ace counter rotating fan always better than two conventional fans in series?
>> 2. Do two fans in series double airflow?
>> 3. Do counter rotating fans move air in opposite directions?
>> 4. Can PWM control reduce noise and power consumption?
>> 5. Are two conventional fans in series a redundant cooling system?
>> 6. What information is most important before selecting either option?
Choosing between a San Ace counter rotating fan and two conventional fans in series is not simply a question of adding more airflow. It is a decision about pressure capability, aerodynamic compatibility, power consumption, installation space, and cooling reliability.
For dense servers, telecommunications equipment, and industrial electronics, the stronger solution is the one that delivers sufficient airflow through the actual enclosure—not the one with the highest free-air airflow rating.
At Capital Technology Co., Limited, our selection approach centers on the operating point: where the fan's pressure–airflow curve intersects the equipment's resistance curve. A purpose-designed San Ace counter rotating fan can outperform a conventional series arrangement, but the advantage must be verified for the specific models and installation. SANYO DENKI has documented such an advantage in a direct comparison, rather than establishing a universal rule for every fan combination.
| Comparison factor | San Ace counter rotating fan | Two conventional fans in series |
|---|---|---|
| Basic arrangement | Two oppositely rotating impellers in a purpose-designed assembly | Two separate fans positioned sequentially along one airflow path |
| Aerodynamic design | Impellers and surrounding geometry developed as a coordinated system | Performance depends on how the individual fans interact |
| Pressure capability | Designed for demanding, high-resistance cooling applications | Can increase pressure capability, but installed results require verification |
| Airflow selection | Use the complete assembly's pressure–airflow curve | Use a validated combined curve, not added airflow ratings |
| Installation | Defined assembly dimensions | Requires allowance for both fans, mounting, and any spacing |
| Speed control | PWM available on compatible models | Depends on both fans and the controller arrangement |
| Maintenance | Replacement depends on assembly construction | Individual replacement may be possible |
| Best evaluation method | Test against the actual system resistance | Test the complete installed pair |
SANYO DENKI positions its counter rotating fan range specifically for equipment with high mounting density and limited cooling space. Its product descriptions emphasize coordinated impeller, frame, motor, and drive-circuit design.
A counter rotating fan has an inlet-side impeller and an outlet-side impeller rotating in opposite directions. Both stages contribute to moving air through the same intended airflow path.
The distinction is important: opposite rotor rotation does not mean opposite airflow.
The downstream rotor operates in the flow produced by the upstream rotor. Designing the two stages together allows the manufacturer to address their aerodynamic interaction rather than treating the second fan as an unrelated component.
This makes a San Ace counter rotating fan more than two ordinary fans attached together. The assembly's performance depends on its impeller geometry, frame design, motor characteristics, and operating speeds.
Matched stages do not necessarily run at identical speeds.
For example, the San Ace 172 CR model 9CR5748P9G001 has published rated speeds of 7,300 rpm on the inlet side and 6,400 rpm on the outlet side. These different speeds belong to the design of that particular assembly. They are not a general setting that should be copied when constructing a conventional series pair.
Two conventional fans in series sit along the same airflow path. Ideally, their pressure contributions combine at a common flow rate.
Their airflow ratings do not simply add.
For example, placing two fans individually rated at 100 CFM in series does not establish a 200 CFM installed airflow. The resulting airflow depends on the combined fan characteristic and the resistance of the equipment.
This differs from a parallel arrangement, where fans serve adjacent airflow paths.
The second fan receives the flow delivered by the first, rather than necessarily receiving the inlet conditions used for its individual catalog rating.
Consequently, a series arrangement needs evaluation as a complete assembly. Fan spacing, intervening structures, inlet restrictions, and downstream obstructions should be included in that assessment.
The engineering question is not whether each fan performs well independently. It is whether the pair performs well together inside the intended product.
Maximum airflow and maximum static pressure describe different ends of a fan curve.
Maximum airflow occurs near the low-resistance end. Maximum static pressure occurs at approximately zero airflow. A fan does not deliver both maximum values simultaneously.
Real equipment operates between those endpoints. Filters, heat sinks, circuit boards, grilles, and narrow passages establish a resistance curve. Its intersection with the fan curve determines the operating airflow.
This is why a high static pressure cooling fan can be valuable in a restrictive chassis, while its advantage may be less relevant in an open, low-resistance installation.
SANYO DENKI's technical report compares the San Ace 172 CR model 9CR5748P9G001 against two conventional 9SG5748P9G001 fans in series.
At the report's expected system impedance, the counter rotating assembly achieved:
- 22% higher airflow.
- 50% higher static pressure.
- Approximately 17% lower power consumption.
The reported operating power was 238 W for the counter rotating assembly and 285 W for the conventional pair. These figures apply to the identified models and comparison conditions—not to every San Ace product or series installation.
The practical lesson is to request a comparison at a defined system resistance. A percentage advantage without model numbers and test conditions is not enough for procurement.
A counter rotating fan may provide more pressure capability, but that alone does not establish lower power consumption.
There are two useful comparisons:
1. Maximum-performance comparison: Which solution delivers more airflow at full command?
2. Equal-duty comparison: Which solution uses less power while meeting the same cooling requirement?
The second is often more useful for product development. If an assembly has sufficient performance margin, speed control may allow it to satisfy the requirement without continuous full-speed operation.
SANYO DENKI states that compatible PWM models can operate at the minimum necessary speed to reduce power consumption and noise. The actual benefit depends on the selected model and control strategy.
Do not assume a counter rotating fan is quieter merely because it is aerodynamically optimized. Also, do not arithmetically add the decibel ratings of two conventional fans.
Compare both arrangements at the same thermal duty, microphone position, enclosure configuration, and background conditions.
Catalog noise figures are useful for screening, but the enclosure can affect the final acoustic result. For noise-sensitive equipment, include both overall sound level and objectionable tones in the acceptance criteria.
A single assembly is not automatically thinner than two separate fans.
The published San Ace 172 CR example is 102 mm thick. Two 51 mm fans also total 102 mm before considering installation hardware or additional spacing.
Compare:
- Overall depth and mounting footprint.
- Connector and cable-clearance requirements.
- Guard and grille arrangements.
- Required spacing or duct transitions.
- Access for replacement.
A complete dimensional drawing is more useful than a generic "space-saving" claim.
Before specifying either solution, check the exact electrical documentation:
- Supply voltage and permitted operating range.
- Rated and startup current requirements.
- PWM input requirements.
- Tachometer or pulse-sensor outputs.
- Behavior at minimum duty cycle.
- Fault-detection and shutdown strategy.
Do not assume that every counter rotating model exposes identical control signals or permits independent control of both stages.
Neither architecture should be classified as redundant solely because it contains two motors.
A failed stage may restrict the remaining airflow. Shared power or control circuitry can also create common failure paths.
If continued operation after a failure is required, test that condition explicitly. Define acceptable temperatures, alarm timing, derating behavior, and replacement procedures before approval.
A more recent example is the 80 × 80 × 80 mm San Ace 80 9CRHA family, released in May 2025 for applications including GPU servers, network devices, and power supplies.
The 12 V model 9CRHA0812P8J001 lists:
| Published specification | Value |
|---|---|
| Maximum airflow | 199 CFM |
| Maximum static pressure | 2,700 Pa |
| Rated input | 144 W |
| Inlet/outlet rated speeds | 18,500 / 19,300 rpm |
| Sound pressure level | 85 dB(A) |
| Expected life | 40,000 hours under stated conditions |
The life specification is an L10 value: 90% survival under the manufacturer's specified continuous-operation conditions, including free air, 60°C, and rated voltage. It is not an unconditional service-life guarantee.
This example demonstrates substantial pressure capability, but it does not establish superiority over an unspecified conventional pair. A fair comparison still requires that pair's validated performance and the equipment's operating point.
Identify heat sources, acceptable component temperatures, inlet-air conditions, and operating modes.
Include realistic worst-case conditions rather than only nominal room-temperature operation.
Measure or estimate the pressure drop through the complete cooling path.
Include filters, protective grilles, heat sinks, internal restrictions, and outlet structures. Where filter loading is relevant, assess both clean and maintenance-limit conditions.
Request curves for the proposed counter rotating assembly and the complete conventional pair.
Avoid building a decision from maximum airflow alone. Use consistent units and stated electrical conditions.
Overlay the fan characteristics and system resistance curve.
Assess whether each solution delivers the required airflow with sufficient margin across the intended operating envelope. Fan-selection literature identifies this system-curve comparison as fundamental to selection.
Record component temperatures, airflow or pressure, electrical input, speed signals, and acoustic performance.
Use representative restrictions and production-intent mounting wherever possible.
Test failed-stage behavior, obstructed airflow, supply variation, and relevant maintenance scenarios.
Approve the solution against documented acceptance criteria—not simply because one configuration looks stronger on paper.
- The enclosure has substantial airflow resistance.
- A validated model provides better operating-point performance.
- A purpose-designed assembly simplifies integration.
- Pressure capability is limiting the thermal design.
- The electrical and acoustic requirements remain acceptable.
- Existing fans already meet the requirement as a tested pair.
- The enclosure accommodates the complete installation.
- Individual replacement supports the maintenance strategy.
- Procurement standardization offers a meaningful advantage.
- Testing confirms acceptable cooling, power, and noise.
Our selection principle is straightforward: choose the arrangement that meets the documented cooling duty with the best overall integration and lifecycle trade-off.
Capital Technology Co., Limited manufactures DC fans and AC fans under its CAPITAL brand. According to the company background supplied for this article, it also serves as SANYO DENKI's chief agent and supplies customers including ZTE, HUAWEI, and HYTERA.
For a useful application review, provide your enclosure dimensions, supply voltage, heat load, existing fan model, temperature limits, noise target, and available resistance measurements.
Ask CAPITAL for a model-specific comparison of a San Ace counter rotating fan and a conventional series arrangement. The objective should be a documented recommendation covering operating airflow, electrical requirements, mounting, and validation—not simply a quotation based on fan size.
No. Published examples show advantages for specific models and system conditions. The better solution depends on the actual resistance curve, thermal requirement, electrical limits, and installation.
No. Series arrangements primarily combine pressure capability at a common flow rate. Installed airflow follows the intersection of the combined fan curve and the system curve.
No. The impellers rotate in opposite directions while contributing to the assembly's intended airflow direction.
Yes, on compatible models, reducing speed to the level needed for cooling can reduce both. Verify the selected model's control specifications and thermal performance.
Not automatically. Remaining airflow after one fan fails must be tested, and shared power or control failures must be considered.
The required cooling duty, system resistance, complete fan curves, available space, electrical specifications, acoustic limits, and fault-response requirements.
1. - SANYO DENKI, "High Air Flow and High Static Pressure Counter Rotating Fan 'San Ace 172' CR Type," Technical Report No. 35, May 2013. Primary source for the identified series-fan comparison, operating power, rotor speeds, and dimensions. [sanyodenki]
2. - SANYO DENKI, "Counter Rotating Fan," official San Ace product overview. Source for product positioning, coordinated design features, and PWM-related noise and power guidance. [products.sanyodenki]
3. - SANYO DENKI, "SANYO DENKI Develops 80 × 80 × 80 mm Counter Rotating Fan with the Highest Static Pressure in the Industry," published May 28, 2025; release date May 26, 2025. Source for the 9CRHA specifications and stated life conditions. The article does not extend its time-qualified market-ranking claim to the present. [sanyodenki]
4. - Advanced Thermal Solutions, "Fan Curves and Laws," Qpedia, February 2008. Source for fan-curve endpoints, system resistance, and operating-point selection principles. [qats]
5. - Company positioning and customer names come from the supplied brief and have not been independently verified. Before publication, confirm agency wording and permission to name customers. The selection procedure is an editorial engineering checklist, not a claim that CAPITAL performed the cited manufacturer tests.
