July 26, 2018

Efficient Comfort: How to Design Energy-Conscious HVAC Systems: Part 2

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

This is the second part of a two-part article about manufacturing HVAC systems to be more energy efficient and better for the environment. Read the first part, here.

Transforming Design Iterations

While time-intensive simulations offer a great deal of accuracy, design iterations might require greater speed – but not rely on accuracy as much. Several development approaches require the ability to iterate quickly through a lot of different design options. For example, simulation can support the process of tuning HVAC controllers for fan speed, blower speed, compressor power and engine operation during cool down. It can also support hardware-in-the loop processes, where physical controller hardware is tested together with virtual models of the cabin. Simulation can even support  novel control system approaches such as overcooling the cabin during regenerative braking to reduce overall AC power consumption. Each of these complex, time-consuming, and rigorous product development and testing processes can all be evaluated with less time and risk than studying real-world prototypes would introduce.

When development has to wait for physical models to test these solutions, it is more risky to introduce novel approaches – because it’s hard to tell if they’ll work or not before spending a lot of money to build them. But with digital simulation, engineers can introduce – or even discover — novel approaches faster and with less risk, to advance competitive product development innovations more quickly and at lower cost. Simulation takes just hours or days, vs weeks or months spent physically testing these same options, and simulation offers more detailed analyses, insights, and design freedom than any test environment can.

How does simulation do it? Traditional methods to tackle these challenges use a system models-based solution alone. Systems models must be calibrated against accurate flow and temperature information. With PowerFLOW, the vehicle’s system model can be combined with a three-dimensional model of the HVAC system, including complete cabin geometry. The co-simulation approach leverages the accuracy of real-world geometry and flow-physics with the speed of a systems modeling approach, dramatically reducing turnaround times.

Co-simulations can be used to quickly and easily test a wide range of characteristics, including the interaction of the car with the exterior (sun, wind or vehicle speed), or the changes in HVAC system operating modes from foot to face or from low to high air flow rate, along with their corresponding toll on overall vehicle energy efficiency. With this method, system models – which are commonly used to support 1D  drive cycle simulations – can now leverage the 3D  model, including the performance results of real-world simulations– to fully evaluate cabin comfort during drive cycles, reducing the need for repetitive physical tests usually run in grueling climate and weather conditions.

Simulation accurately predicts thermal transients to evaluate temperature anywhere throughout the cabin.

Transforming Target Definition

A complete digital model of the vehicle’s cabin can benefit design even earlier on in the concept design phase by helping engineers to determine the right performance targets for a vehicle under development. For example, the cabin design of a previous model can be repurposed – quickly morphed to the target dimensions – and an AC system 1D model can be used to estimate the cooling power needed to achieve a rough temperature target in the cabin, allowing engineers to choose between a 3kW or 4kW system or to decide what type of glass should be used to improve energy savings. This enables informed decisions even earlier on during vehicle development, minimizing the risk of over-engineering the system to the detriment of the battery range or fuel economy. Plus, it offers the chance to explore novel design approaches that are nearly impossible to test with physical prototypes.

By calculating airflow (L), acoustics, thermal transients, and their impact on human comfort (R), Exa’s PowerFLOW solution offers a complete digital cabin for climate system and controller design.

SIMULIA solutions support a complete, end-to-end digital process to enable faster, more innovative, more efficient, and more cost-effective vehicle development programs. The range of available solutions offers fast turnaround times to ensure quick design iterations, highly dynamic drive cycle and controls tuning processes, reliable and accurate human comfort predictions to pass critical design gates, and complete digital sign-off solutions to ensure failure-free late-stage prototypes. By combining climate control solutions with robust airflow and acoustic solutions, SIMULIA powers af complete digital cabin.

For more information on climate system design with PowerFLOW, read the Exa whitepaper, Beyond Comfort: Exploring Simulation-Driven Design for Climate Systems.

Reference: A Simulation Based Process for Designing Energy Efficient Climate Control, C.-W. Chang, E. Tate, J. Juszkiewicz, K. Bhambare, A. Mann, SAE TMSS 2017, Plymouth, MI, October 10th-12th

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