By Neil Cameron, area general manager, Johnson Controls Building Efficiency Africa
The heating, ventilation and air conditioning (HVAC) systems in any facility contribute significantly to energy consumption. This makes the central plant – the boilers, airside equipment and especially chillers — a prime target for optimisation. However, a reality check is in order if organisations want to achieve more than quick one-off energy efficiency wins. A holistic whole-building approach to central plant optimisation that can deliver sustained energy savings of up to 60% requires commitment to a process.
It’s an approach that is garnering industry attention with the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) developing new energy targets based on the performance of a building as a whole. In South Africa, the majority of organisations have looked at achieving quick wins, but have not yet implemented an intelligent central plant system. While there are many service providers promising sustained wins, few can fully assess, design, and deliver holistic optimisation solutions that incorporate all related building systems and ensure they are configured to the specific needs of the organisation and optimised to achieve sustained performance.
The business case for a holistic building approach is driven by two important factors; first, the industry is quickly approaching the theoretical limit of how much efficiency can be expected from individual components; and second, today’s high-efficiency components are designed to work optimally as part of a networked, interrelated system. Central plant equipment has become more intelligent and sophisticated, making the traditional set it and forget it mind-set obsolete. A more encompassing approach to central plant optimisation can deliver energy savings that were previously unattainable. But this approach implies a process.
Central plant optimisation encompasses seven main steps:
- Design of system infrastructure: In new construction, design with operational flexibility in mind; in existing buildings, correct design deficiencies by upgrading system configurations, adding variable speed drives (VSDs) and automating. This will enable a plant to run at a higher level of efficiency over its entire lifecycle.
- Selection of components: The primary objective is to choose components that will perform efficiently in real-world operating conditions. Components sized for the worst-case scenario (e.g., a chiller that will work efficiently on the hottest day in summer) may not run efficiently in everyday conditions. It is also important to ensure that the chillers are pre-equipped with VSD’s on the compressor which will allow the chiller to operate efficiently at part-load conditions.
- Application of components: You can use a screwdriver to pound nails, but it’s hardly as efficient as a hammer. The same holds true for energy-efficient components. To achieve peak performance, the equipment must be applied and operated properly.
- Automation of the system: Building automation is a prerequisite to optimisation. A building automation system (BAS) doesn’t merely start and stop equipment to maintain set points, it starts the right equipment at the right time to maximise efficiency based on run history and efficiency profiles. It is essential for the BAS system to incorporate a central plant optimisation (CPO) algorithm to schedule the optimal number of chillers to operate under different load conditions.
- Networked optimisation software: This is the brain behind the operation that ties in with the BAS. It is the intelligent logic that holistically operates the plant in the most efficient manner.
- Maintenance: With today’s ultra-efficient components and optimised central plants, maintenance is predictive. Performance data can be regularly measured, verified and managed over the plant’s entire life cycle.
- Measurement, verification and management: This is the pinnacle of the optimisation pyramid. With real-time data available anytime, anywhere, performance drift can be identified and operators can quickly detect, diagnose and resolve system faults.
Central plant optimisation is today’s opportunity; it may be tomorrow’s mandate. Building managers, design engineers, and organisations concerned with future energy efficiency and competitiveness would do well to assess the potential of this approach and make the commitment to undertake this journey.