Leveraging 1D simulations to achieve low computational costs and reduce time-to-market

Taking a fresh approach to refrigeration

To reduce wasted food and energy when designing a refrigerator, It is necessary to start with simulation.

“With simulations we can test anything from the length of the compressor run time to how long the evaporator fan is on,” says Anderson Bortoletto, principal engineer of advanced product development of the Sub-Zero Group, Inc. “We don’t have to build prototypes. Then we can evaluate what the refrigerator is doing so we can understand the impact on preservation.”

Crafting crisper, cleaner customer experiences

Since its founding in 1945 in Madison, Wisconsin, Sub-Zero Group, Inc. (Sub-Zero) has been a leader in the luxury kitchen appliance market. In recent years, it has sought to expedite product development by determining the factors that minimize time-to-market without compromising product robustness and performance. Virtual prototyping allows Sub-Zero to understand how the interplay between components makes a refrigerator far more than a cold box.

The key to enhancing Sub-Zero’s appliances depends on learning how a machine’s essential parts interact. For refrigerators that means designing compressor coils and a condenser that can keep a head of lettuce fresh and green for weeks. Yet it’s imperative that Sub-Zero appliances look attractive. Customer satisfaction depends on maintaining a clean, refined design.

Refusing to sacrifice high quality for reliability involves numerous design restrictions. These restrictions include building compartments that do not obscure items, making sure different areas in the refrigerator are easy to access and using materials that are sturdy, as environmentally friendly as possible and supremely styled. Sub-Zero product developers also face the challenge of not being able to control perturbation, which in refrigerator terms is defined as how internal temperature changes when a person opens a door, adds or removes items or moves an item to a new spot.

“Traditionally, we evaluated refrigerator models experimentally,” says Bortoletto. “We put a considerable amount of investment into coming up with a prototype. Now we can do that virtually with Simcenter Amesim, which decreases the costs and the time to get those insights.”

Removing heat is still the central task

The most significant job Sub-Zero’s elite refrigerators perform is removing heat that has entered the cold box. This is accomplished by the evaporation and condensation of the refrigerant that circulates inside the refrigerating system. Evaporation cools the space, the same way alcohol coming off a person’s skin creates a chilling effect.

In simple terms, a refrigerator is a machine that pumps heat from its interior out to the kitchen, thereby cooling the items inside. Four components are key to this process: the evaporator, compressor, condenser and expansion device. In the evaporator, refrigerant changes phase from liquid to gas (evaporates) by absorbing the heat from the interior of the appliance. That heat contained in the refrigerant is pumped by the compressor to the condenser where the heat is dissipated when the refrigerant changes its phase from gas back to liquid. The expansion device lowers the pressure of the refrigerant so it is ready to evaporate when it enters the evaporator again and the cycle continuously repeats itself.

Sub-Zero created accurate representations of refrigerator components by using Simcenter™ Amesim™ software and working closely with Maya HTT, a Siemens Digital Industries Software Expert Partner in nine products. The team at Maya HTT built a library of custom Simcenter Amesim components specifically for Sub-Zero. Simcenter Amesim is part of the Siemens Xcelerator business platform of software, hardware and services.

Using Simcenter Amesim helped Sub-Zero maximize the efficiency of simulations. A five-year history of trust and familiarity with the Maya HTT team made it easy for Sub-Zero product developers to share their thoughts.

“Since Maya HTT is our long-time partner, they’ve gotten to understand what we’ve been trying to accomplish over time,” says Bortoletto. “Without them, we couldn’t have gotten closer to the ideal end state for the refrigerators.”

How 1D simulation played a part

By using Simcenter Amesim, Sub-Zero was able to conduct 1D simulations of refrigerator performance that had low computation costs and shorter time-to-market. The simulations were a robust and dependable solution for improving model design.

“Simcenter Amesim was so effective that Sub-Zero expects to have its design exploration time reduced from two months to one week, a decrease of 88 percent,” says Bortoletto. Using 1D simulations also allows sub-Zero to perform system-level and parametric analysis and rapidly and easily prepare models.

By contrast, 3D computational fluid dynamics (CFD) simulations would have had only one advantage, high fidelity design. The disadvantages of 3D CFD simulations for this kind of project include high computational costs, added work to remove irrelevant details using computer-aided design (CAD) meshing and the fact that system level simulation is usually not feasible.

“We can learn how to adjust a refrigerator to preserve a certain type of cheese or beverage while still maintaining the machine’s energy efficiency,” says Bortoletto. “That’s only achievable if we learn the dynamic behavior of the appliance. Yet it’s exorbitant to do that with a traditional 3D CFD simulation with a single simulation over time.”

Sub-Zero used Simcenter Amesim to produce 1D simulations, which are complex. The refrigerator’s four essential components need to be analyzed repeatedly as they run over periods of time in a continuous closed loop. The components must work together quietly and efficiently, using a minimum of energy and materials.

Despite Sub-Zero’s focus on the refrigerator’s core mechanical components, its product engineers are well aware that creating recognizable, customizable looks are part of supporting the company’s brand identity. Sub-Zero believes luxury is equal to substance. Retaining quintessential features like the top grill in the Classic and Pro series and introducing amenities like clear doors keep the design process dynamic.

Democratizing simulation opens new doors

Using Simcenter Amesim has enabled Sub-Zero’s product engineers to develop a greater appreciation for democratization of simulation. The concept is defined as giving individuals who are not experienced modeling analysts the ability to perform advanced simulations and use data generated from them to improve designs. Scott Wareing, Sub-Zero’s senior vice president, now defines simulation as a core competency.

“Simulation is integrated seamlessly into our development process and used as naturally as any physical product development tool is used today,” says Wareing. “Engineers will model and simulate components, subsystems and entire products prior to physically building them.”

Sub-Zero is already planning to venture beyond laminated food preservation cards into the digital realm. Its product developers hope to create smartphone apps and responsive technology within models that allow owners to change their refrigerator’s settings. The pairing will allow an owner to preserve particular types of foods in certain spots. An owner will also be able to check a model’s energy efficiency and adjust it to conserve energy further.

“We’re designing with smarter control algorithms, instructions to show how appliances will react with changes to the environment,” says Bortoletto. “Say the owner has a larger family that interacts with the refrigerator more than average. How will the control algorithm act to keep the optimal temperature and deal with more temperature fluctuation? That’s how we’ll differentiate ourselves when compared with the competition.”

In the coming years, Sub-Zero plans to continue developing thousands of tasteful, exemplary design options and improving on the durability of features like door hinges. It will also begin using Simcenter Amesim to revamp Cove, its line of dishwashers. ”Using Simcenter Amesim to generate simulations will allow Sub-Zero to better understand new avenues of conservation, including reducing water usage and energy consumption,” says Bortoletto.

Fortunately, dishwashers are easier to model than refrigerators. After gaining experience with Simcenter Amesim, Sub-Zero product developers know what they will learn. The 1D simulations will help predict the behavior of Cove dishwashers in different cycles. They will also allow engineers to reduce cycle time. “These things impact the environment in a positive way and improve performance of the product,” says Bortoletto.