The principles of LEED address the need for efficient and reduced water use in buildings. Plumbing systems, cooling towers, and landscaping are the main areas where green design can effectively minimize a building’s demand for treated water. As building owners and facility managers feel the pressure of increased energy costs and higher energy demands, chilled water systems can be an overlooked source of savings. Further, chilled water system improvements count toward LEED certification projects with low-cost steps, some of which offer relatively quick paybacks.
Chilled Water and LEED Certification Projects
Cooling systems can be optimized in several ways to directly contribute to LEED certification. First and foremost, installing water cooled chillers when replacements are necessary is a huge step toward improved efficiency. Air-cooled HVAC systems requiring higher fan power to reduce temperatures are less energy efficient. Some industry experts estimate that a building can save up to 30% percent on HVAC energy consumption when using a water-cooled chillers compared to air-cooled chillers.
Hydronic and Cooling Strategies for LEED Certification Projects
Central plant design has a tremendous impact on annual energy and life cycle costs. Consider converting Primary/Secondary systems to Variable/Primary. P/S systems often suffer from “low ΔT syndrome”, a condition wherein cold water from the chiller and warm water from the load mix before returning to the chillers. This low ΔT reduces chiller capacity and places the chiller at a less than desirable point on its efficiency curve. With this reduced chiller capacity, the only way to meet the load is to turn on additional equipment, the net effect of which is that more equipment is operating and at less than design efficiencies. Variable/Primary systems eliminate the inherent mixing and raise the ΔT to design levels.
While the Variable/Primary configuration is known to be the most efficient hydronic design, converting from a Primary/Secondary system is very capital intensive due to the significant mechanical modifications required. tekWorx Integrated Primary-Secondary® (IPS) solution mimics the functionality of the Variable/Primary system but allows all existing pumps and piping to remain in place, simply adding a few sensors and valves for controllability.
Chilled Water System Power Consumption and LEED Certification Projects
Most components within a chilled water system will benefit from Variable Frequency Drives. With Variable Frequency Drives (VFDs), compressor and fan motor speeds can be varied to better meet desired cooling and humidity levels and can significantly reduce annual energy consumption. This makes them ideal for projects focused on energy efficiency and LEED goals.
Variable frequency drives can be applied to condenser fans to reduce short cycling of compressors during lower outside air temperature conditions. This allows systems to isolate a single circuit or stage of the compressor and better maintain the fixed head pressure to avoid short cycling.
Additionally, VFDs can be added to condenser water pumps to control the speed of the cooling tower fans and reset the condenser water temperature. By lowering the condenser water temperature, the lift of the compressor is reduced thus reducing energy use.
Energy-focused Control Strategies for LEED Certification Projects
Chilled water system equipment, like fans and pumps, can benefit from a control scheme that operates more pieces of equipment at lower speeds versus allowing equipment to increase to full capacity before staging on the next unit. Chillers themselves are most efficient somewhere between 40 and 60% of peak capacity so running more equipment maximizes the heat transfer surface area at all operating points, increasing efficiency and reduces pressure drops.
Take the affinity laws, for example, wherein pumping energy is proportional to the cube of the speed pump. There are times when running 2 pumps at a lower speed may consume less power than 1 pump running alone at a higher speed, 3 pumps may be more efficient than 2 pumps, etc.
Cooling Optimization Can Be Key To LEED Certification Projects
Cooling systems can optimize building performance and contribute to Leadership in Energy and Environmental Design (LEED) certification and other sustainability programs. The LEED rating system rewards environmentally sustainable practices that conserve energy, material and water resources. Reducing water use and/or using chilled water more efficiency can drastically cut energy costs while demonstrating a more sustainable approach to cooling facilities.
tekWorx adaptive algorithms continuously adjust equipment operation and key setpoints based on such parameters as occupancy level and outdoor temperature to maximize the system efficiency in real‐time while maintaining comfort cooling needs. Xpress® considers the interaction of all chilled water plant equipment and maximizes the system holistically, using less water to meet site needs and positioning it well for LEED points and certifications.