Real-time data improves aircon efficiency

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Faced with the challenge of reducing energy consumption of large-scale air-conditioning systems in tropical climates, Chiller Energy Management System (CEMS) Engineering is using Compact FieldPoint and LabVIEW Real-Time from National Instruments to acquire and analyse real-time data for more efficient cooling. Thirumalaichelvam Subramaniam
 of CEMS Engineering explains

Real-time data improves aircon efficiencyIn the last three years, CEMS Engineering developed a breakthrough approach for improving the quality and energy efficiency of commercial air conditioning systems in the tropics including those located in office buildings, factories, and hospitals.

To cool a large area, commercial and industrial centralised air-conditioning systems traditionally consist of multiple machines — chillers — that control air temperature by removing heat from a coolant liquid through vapor-compression or an absorption-refrigeration cycle. The typical approach to cooling a building is to determine how much energy is required to cool a particular building to a desired temperature and then set each chiller to produce chilled water at the same setpoint.

But these calculations are usually based on the worst-case condition — the one or two hottest days of the year — which leads to inefficient energy use and hard-to-control building temperatures.

CEMS Engineering pioneered technology to lower the energy usage of these chillers while still maintaining the same, cooled temperature of the building. CEMS Engineering uses the National Instruments Compact FieldPoint programmable automation controller (PAC), and LabVIEW running on an industrial PC to acquire real-time input data directly from sensors on the chillers. This data is used to determine and send new operating instructions to the chillers.

These operating instructions are determined through a series of variance calculations of the real-time input data, PID control loops, principles of thermodynamics, heat transfer and advanced mathematical optimisation and other proprietary equations in a LabVIEW Real-Time application. CEMS has saved clients up to 30 per cent of their air conditioning energy costs in tropical countries where cooling costs typically consume 45 to 60 per cent of building energy expenses.

Optimising operating parameters

CEMS Engineering systems use a novel approach in determining optimised operating parameters of chillers. Users acquire real-time input data directly from sensors outside, on the chillers, and in the buildings. CEMS Engineering conducts a series of variance calculations of the real-time input data with proportional-integral-derivative (PID) control loops and then uses this data to determine and send new operating instructions to the chillers using small electrical signals.

There are no moving parts and the operating instructions are determined using a series of genetic algorithms that combine heat transfer principles, thermodynamics and mathematical predication to operate the chillers in the most energy efficient manner, while maintaining industry standards and without compromising the comfort level of occupants in a commercial or industrial building.

With the support of National Instruments LabVIEW and Compact FieldPoint hardware, implementation of the CEMS Engineering system was completed within six months of commencement and is now installed and running at customer sites.

CEMS Engineering reduced time to market with the integration inherent between NI LabVIEW software and Compact FieldPoint hardware. With LabVIEW, CEMS Engineering could fully use the power of graphical system design, progressing from a design to a prototype, to working deployment in astounding speed. The system relied on Compact FieldPoint for data acquisition, analysis, decision making and solid state controls.

See the heat

With the graphical interface, users can literally see the heat flow coming into and out of each building. Another benefit of this graphical real-time monitoring approach is that his firm can cost-effectively handle its clients’ energy management remotely. After the systems are installed, CEMS engineers implement real-time monitoring from their offices to monitor and control systems anywhere in the world.

CEMS modulates the chillers according to the change of internal and external load at ten-second intervals, automatically controlling the chiller loads. By benchmarking the average consumption of the chillers for each day, the plant managers can see drastic changes in consumption when CEMS is in savings mode. All necessary data is recorded and reported to plant managers to verify the amount of savings made in chiller consumption.

In the event of a mechanical problem, CEMS engineers can alert the facilities manager or the plant manager to switch over to their standby system while they make arrangements to make on-site repairs. CEMS monitors the number of hours each chiller has been running, and schedules preventive maintenance based on the manufacturers’ specifications for each chiller type and condition.

05 August 2009

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