July 17, 2018

Efficient Comfort: How to Design Energy-Conscious HVAC Systems: Part 1

This is the first part of a two-part article about manufacturing HVAC…

This is the first part of a two-part article about manufacturing HVAC systems to be more energy efficient and better for the environment. Stay tuned for the second part of this article where we discuss transforming design iterations and transforming target definition in the manufacturing process.  

As engine and powertrain efficiencies improve, OEMs are searching for new ways to reduce the energy used by climate control systems. But efforts to improve efficiency can’t compromise comfort, a high priority for consumers, or key safety features like defrost/demist, a top regulatory requirement worldwide. More OEMs are turning to digital simulation to transform the HVAC system design process, helping them achieve these goals while overcoming the budgetary and timeline challenges introduced by traditional prototype development and testing.

The power required to run a compressor and cool vehicle occupants can have a significant impact on fuel economy and range. In the United States alone, the increase in fuel consumption from air conditioning is estimated at 30 gallons per vehicle per year, reaching up to 70 gallons in extremely hot states like Texas and Florida. This can add up to over a hundred dollars or more per year out of OEMs’ customers’ pockets. The impact of climate can be even more severe for electrified powertrains: studies show that air conditioning can reduce battery range by up to 40%.

Where you live impacts fuel use! Extreme climates that rely on air conditioning for more months of the year use more fuel per vehicle – and that’s just in the US. (https://blog-assets.3ds.com/uploads/2023/03/69047.pdf)

With such fierce competition among OEMs to improve both vehicle efficiency and comfort, manufacturers that can manage to reduce energy consumption without compromising HVAC system performance will gain a distinct advantage in the marketplace. Digital simulation helps OEMs predict system performance while maintaining or even lowering development costs. Let’s look at three ways this works:

Transforming Prototype Testing

At an average price of $750,000 per prototype vehicle, reducing the number of prototypes can amount to dramatic cost-savings. Digital simulation is accurate and fast, helping OEMs reduce the risk of product failure at release – and the costly recalls that can result – while improving their chances of meeting vehicle performance targets even before a physical prototype is available.

When a solution can predict performance digitally, prototypes are no longer used for the costly process of discovering problems that need further redesign and rework – and more prototypes to test. Instead, they are transformed into a means to validate predictions, reducing the need for additional prototyping and re-testing to help keep development on-time and on-budget.

Digital simulation with PowerFLOW reduces physical prototypes by providing complete, digital validation of fully integrated 3D designs. By applying real-world conditions to 3D geometry, simulation can accurately re-create the HVAC system and blowers starting up and making passengers comfortable. In the real world, this process starts long before passengers get in the vehicle – and so does simulation. For example, digital simulation can re-create a condition known as “solar soak”: when a vehicle sits for hours in the hot sun.

Simulation can capture the complex temperature stratification anywhere throughout the cabin at any time during a long, highly transient solar soak as it develops over a span of hours. But unlike a physical test, it can help engineers understand what characteristics of the flow and HVAC system led to these temperatures. Interpreting temperature and flow data that cannot be captured in any other way offers distinct advantages over physical testing, including the means to discover root causes and previously unknown conditions, test novel solutions with less risk, and understand the impact on human occupants in ways no physical test can. PowerFLOW offers the capability to measure the real-world human comfort response – including a range of human physiologies and configurations – during these conditions. PowerFLOW accomplishes this complete simulation in less than a week’s turnaround time.

Using SIMULIA PowerFLOW to understand what will happen in the real world, design decisions are far better informed than physical testing allows. Simulation replaces the typical trial-and-error approach by informing design decisions informed with real-world performance data from thermal and flow analyses. This helps engineers to quickly iterate on different design options and even uncover and introduce novel approaches to challenges like system efficiency. They can re-simulate and confidently understand the outcomes of design changes without the costly rework, and re-testing of additional prototypes, that is typically required with late-stage changes. Options like the energy impact of different glass properties, or the energy lost or gained from different panel insulation options, can save gallons of fuel or tens of miles of range in the final production vehicle.

Simulating the effects of different glass options (left) and various insulation options (right) on vehicle energy efficiency helps designers balance cabin comfort and energy consumption targets.

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