In today’s highly competitive and dynamic markets, HVAC and appliance manufacturers must design products with more features and enhanced performance, while meeting noise and space requirements. Combined with cost considerations, time-to-market windows, agency approvals, product and component performance— including power consumption, noise and reliability—these factors force many OEMs to launch products with design compromises that often result in lost sales and profits. These factors are constraints that create an engineering environment that often results in a lengthy, iterative design process. It is only when a product-development team looks beyond solving each constraint individually that product-design innovation can occur.

Product developers confront formidable design constraints. HVAC and appliance OEMs face government mandates to improve their product’s efficiency and noise along with the ongoing challenges of operating in a competitive market. For instance, in 2002 the government mandated a 20 percent efficiency improvement in air conditioners and heat pumps, effective in 2006. In addition, quieter products have become a market differentiator as consumers become more sensitive to the rising level of ambient noise from their products.

This article illustrates work within the HVAC and appliance industry that reaches beyond an iterative design process with a disciplined engineering approach to achieve significant improvements to:

Technical issues:
• Improve OEM product performance levels and efficiency ratings.
• Use brushless DC motor technologies for efficiency and noise benefits.
• Reduce audible noise—especially for European and classroom standards.
• Integrate the fan and motor solution into the HVAC and Appliance products.
• Integrate other control requirements into the electronics of the motor driver.
• Optimize air distribution.

Business issues:
• Reduce part count, labor and supply base management issues.
• Provide user benefits to improve OEM sales.
• Reduce applied cost.

Choosing innovation

Torrington Research engineers redesigned a fan system to integrate the fan, motor, control and other end-unit elements, significantly simplifying the design. The original design, shown in top photo, required 120 parts. The redesigned assembly, shown in lower photo, uses only 24 parts. The new design also improved efficiency and fan control.

Managing an innovative product development process requires strong fundamental technologies, an eye to using these technologies to provide effective benefits to the customer, and discipline in the design activities. The process discussed here uses a five phase engineering program with reviews at the end of each phase. This enables the design team to evaluate progress against objectives and make mid-course changes as necessary to meet its goals through the design stages. Before Phase 1 starts, the design team lays out performance goals. Benchmarking competitive products and using inputs from the customer marketing groups helps the design team determine the scope of the work that has to be done to meet or exceed the product goals.

The five phases include:

• Feasibility. This phase generates the concept design including performance predictions, estimated part cost and non-recurring expenses.
• Working model. The second phase builds and tests physical models. The design team will compare results to the phase one predictions.
• Prototyping. The third phase produces prototypes of the finalized product and refines the design based on their performance.
• Tooling. Once the design is frozen, tooling can be completed— a major component of this phase.
• Manufacturing engineering/manufacturing development. This phase focus on optimizing the manufacturing and testing processes.

Applying the process

The Torrington Research design team is working on several HVAC condensing unit applications. Each program has challenges including cost constraints, performance, noise, and package space. The following describes the application of the process and how it achieves product innovation as a result.

Feasibility. The right design concept is critical to success. We must support the customer’s low-cost, high-performance condensing unit goals. Part of the design team’s challenge in this is to select from a variety of potential design outcomes. For example:

• Cost objective. The higher efficiency of an integrated brushless DC motor, coupled with an efficient aerodynamic fan design, generates cost advantages by allowing for a significant reduction in condensing coil surface area. The reduced coil increases airflow resistance. The fan, operating at higher efficiency, offsets the extra work involved in moving air through a smaller condenser. The objective is to deliver the same cooling performance while yielding significant savings in material, labor, shipping, storing and handling costs.

• Efficiency objective. The higher efficiency fan combined with an efficient, variable speed brushless DC motor substantially reduces the seasonal operating energy usage. At reduced speed, power reduces by the cube of the speed ratio. For example, a 20 percent reduction in speed equals a halving of the power. The fan and motor are often designed to perform at design operating conditions, an event that occurs very seldom, validating the variable speed requirement.

• Noise objective. Another benefit of a higher efficiency fan design is the ability to design using a lower rotational speed. The team designs the fan to run at reduced peak speed versus any alternative technology. This capability fundamentally lowers noise levels. It also increases motor torque, which the team can evaluate as a trade off. The variable speed capability of the fan motor additionally reduces noise in all off-peak conditions.

This phase established product development objectives to design a fan system that integrates the fan, motor, control and other end unit elements. The design would use a series of proprietary technologies to provide the following benefits versus traditional solutions:

• Higher efficiency.

• Significant reduction of axial length.

• Lower noise.

• Variable speed capability.

• Lower applied cost.

Benchmarking through dynamometer tests of standard and proprietary fans at the same flow and pressure point determines the highest efficiency fan solution. The design team’s solution, when compared to the traditional metal blade fan found in virtually all residential air conditioners, runs up to 35 percent higher efficiency.

The proposed design also incorporates a number of secondary adjustments from the modeling test results, which while individually render small improvements, result in a significant advancement in sound levels.

• Modeling. The design team makes working models of the design’s fan components—blades, scroll, housing—using various rapid prototype techniques, including an in-house SLS (Selective Laser Sintering) machine. This facilitates actual testing to validate the airflow, power and sound performance predictions quickly. The team also lays out the motor control electronics and builds a “bread board” of the design for the motor. A high performance custom motor will be used in the prototype and final manufactured product. Being able to turn working models quickly allows the design team to fine tune and test more iterations of the design—crucial to hitting design windows and validating performance predictions before prototyping and tooling the product.

• Prototyping. Prototypes are an extension of the modeling process. At this point the design team makes up prototypes incorporating the custom designed motor. Once manufactured, the team runs the prototypes under various environmental and application specific conditions and compares the results to both the benchmark and predicted performance. After a design refinement the team puts the prototypes through extensive accelerated life testing and again compares measured performance against benchmark and predicted performance.

The design team evaluates the sound signatures and resolves various trouble frequencies to lower noise levels even further. Fan noise may include a specific blade pass frequency, a natural frequency, some harmonic of fan speed or a motor generated noise. This tuning generates the final acoustic solution of the product design before design is frozen and tooling is initiated.

Design and manufacturing iterations. Successful mechanical design and engineering is environment- and process- dependent. There are many factors that affect the design. The design team’s early and clear understanding of materials selection and manufacturing process flow determines the success of their product designs. The design team involves manufacturing engineers and production line management early in this project’s design stages to facilitate concurrent engineering. Having all of these skill sets represented on the team ensures that a design optimized for the lowest cost production possible.

The design team’s efforts pay off. First, the design’s higher efficiency fan/motor integration process reduces the use of materials. The fan hub and fan shroud double to hold the motor components and eliminate the steel motor shell. Second, the team’s design for manufacturing approach greatly reduces part count and production labor. Elimination of screws, fasteners and brackets further reduce the total part count and the total cost of the fan solution.

These steps and the resulting cost reduction of the fan and motor combination make budgetary room for the cost of the motor control electronics and achieve the ultimate goal of incorporating a brushless DC motor solution.

Quantifiable benefits

Using an engineering approach to achieve innovative results the design team realizes the following significant improvements in a product’s features and benefits structure. Cost-effective integration of a brushless DC fan means that a brushless DC solution can replace a typical AC powered device. The equalization of the costs means that the design can incorporate the following benefits of the brushless solution.

• Efficiency gains averaging 23 percent. Using peak efficiency and variable-speed control allows for seasonal efficiency gains resulting in higher seasonal power reductions.

• Reduced system costs. In the preceding case, the condenser size is reduced without effecting unit performance. The higher efficiency fan module offsets the increased energy needed for the smaller coil. Reduced unit size and weight are additional benefits. Similar system cost improvements occurs in other end uses.

• The fan module is capable of multi-tasking. The motor drive electronics can incorporate various unit control functions such as electronically starting a compressor motor, eliminating start contactors for the fan, working equally well in 50 and 60 cycle environments as well as provide sensing of fan speed control and other end unit control issues.

• Improved fan control. In this case, variable speed may be based on condensing head pressure resulting in lower power consumption and lower noise levels.

For reprints of this article,
contact Jill DeVries @ 248-244-1726 or devriesJ@bnpmedia.com.

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