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issue: July 2006 APPLIANCE Magazine

Sensors and MCUs
Controlling the Cool, by Day and by Night

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by David Simpson, Contributing Editor

Ice Energy offers what it describes as the industry’s first ice storage module developed to reduce air-conditioning costs for small- to medium-sized commercial businesses.

The Ice Bear, from Ice Energy (Windsor, Colorado, U.S.), is an ice storage module designed for use with commercial businesses’ refrigerant air-conditioning systems. The module creates ice overnight, when demand and rates are low, and uses the ice for cooling during the day. An Analog Devices, Inc. (Norwood, Massachusetts, U.S.) Blackfin processor with LabVIEW Embedded has reportedly cut the effort needed to design the latest controls.

At the heart of the Ice Bear system is a 500-gallon storage tank. Most of the system’s energy is used to turn water into ice during the night, taking advantage of off-peak electric rates. The ice is used to cool the building during the day, when demand and electricity rates are high. In places like California, U.S. by using mostly off-peak electricity, the system can achieve cost savings of up to 90 percent.
The Ice Bear is the result of more than 10 years of technological refinement and field tests in commercial applications. The module is designed to work seamlessly with a new or existing refrigerant-based compressor/condenser, air handler, evaporator coil, thermostats, and utility demand meter. The system delivers five tons of cooling for 8 hours during the day, when the refrigerant circulation pump and controls draw only about 300 W.
Sophisticated controls are required to manage the tank module and its interaction with other components. Controls will determine when to operate (store energy or release energy) to maximize energy savings. More than 20 sensors are engineered into the system.
For its latest controls, Ice Energy plans to incorporate an Analog Devices, Inc. Blackfin processor, the ADSP-BF537. Key features are peripheral integration (Ethernet, CAN, multiple serial interfaces), high performance and low cost. Creative Control Solutions (Windsor, Colorado, U.S.) is working with Ice Energy to develop the custom controller using LabVIEW Embedded graphical programming on the Blackfin.
Ice Energy was familiar with the LabVIEW technology, and requested its use. “It was chosen for the ease of porting the existing control algorithm, simplified software maintenance, and the ability to drop in advanced analysis and signal processing blocks for rapid development of factory test programs,” says Dean Wiersma, product engineer, Ice Energy.
LabVIEW, from National Instruments (Austin, Texas, U.S.) has a long history as a measurement instrument programming tool. By embedding the system in Blackfin, ADI and NI aimed to cut the amount of effort and expertise required for programming, compared to that required using assembly, C or C++ programming languages. The embedded technology allows for rapid implementation of complex functions such as FFTs and digital filters that would normally take a significant amount of time for an embedded programmer. “By having the capability of dropping these functions in as completed blocks, we can spend more time focusing on the core functionality of the system instead of getting caught up in unnecessary details,” says Matt Whitlock, vice president at CCS. “Additionally, code written in LabVIEW Embedded is much easier to read, debug and maintain than code written in a lower-level language.”
CCS began working on the Ice Energy application in late 2005, with completion planned for July or August 2006. “LabVIEW Embedded gives us the flexibility to provide robust, easy-to-maintain firmware while shortening our design cycle,” says Whitlock. “Our customers use LabView for its ease of use, maintainability and extensive library of high-performance processing algorithms. This allows them to focus on the differentiating technology rather than low-level code development. Because of the programming ease, our man-hours expenditure is cut to about 60 percent compared to using a lower-level language. Ice Energy, too, has significantly reduced man-hours. This all translates to a huge time and cost savings.”
Blackfin is a 16/32 bit embedded processor designed to meet the computational needs of audio, video and communications applications. ADI reports it delivers breakthrough signal-processing performance and power efficiency while offering a full 32-bit RISC MCU programming model on an SIMD architecture. Blackfin processors present high performance, homogeneous software targets, which allow flexible resource allocation between hard real-time signal processing tasks and real-time control tasks. System control tasks can often run in the shadow of demanding signal processing and multimedia tasks.
ADI and National Instruments started developing LabVIEW Embedded for Blackfin about 2 years ago. “It was looking like embedded was becoming ubiquitous,” says Derek Leadbetter, director of DSP development tools, ADI. “With this in mind, we decided to work with National Instruments to extend and embed its graphical design capability into 16-bit versions of Blackfin. We chose LabVIEW because it is highly regarded as a standard in test instruments, and engineers are very comfortable using it to measure anything in a plant.”
CCS’s Whitlock points out that, compared to an ARM7/MCU or other solutions, the Blackfin devices are at the same price point when peripherals are factored in. “Having a bit of processor head room also gives us a buffer to accommodate for feature creep.”
He notes that, to conserve resources, LabVIEW Embedded only adds the libraries that a project actually uses. Also, “Although LabVIEW Embedded code can be around 1.8 times larger than hand-optimized C, one must think in terms of the overall application. LabVIEW Blackfin includes hundreds of hand-optimized code modules that are much more efficient than those of even the best embedded designer. With these highly optimized modules, you offset any penalties in code size from general LabVIEW constructs. One must look at the code size from the overall application perspective.
“Embedded applications continue to grow in complexity and require more software abstraction,” he observes. “Embedded designs of the future can be compared to today’s PC applications. Can you imagine writing even a simple Windows application in raw assembly?”

Suppliers mentioned in this article:
Analog Devices Inc.

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