What are Net Zero Energy Buildings?

Most Net Zero Energy Buildings (NZEB) are still connected to the electric grid, allowing for the electricity produced from traditional energy sources (natural gas, electric, etc.) to be used when renewable energy generation cannot meet the building’s energy load.  Conversely, when on-site energy generation exceeds the building energy requirements, the surplus energy should be exported back to the utility grid, where allowed by law. The excess energy production offsets later periods of excess demand, resulting in a net energy consumption of zero.

Most Net Zero Energy Buildings (NZEB) are still connected to the electric grid, allowing for the electricity produced from traditional energy sources (natural gas, electric, etc.) to be used when renewable energy generation cannot meet the building’s energy load.  Conversely, when on-site energy generation exceeds the building energy requirements, the surplus energy should be exported back to the utility grid, where allowed by law. The excess energy production offsets later periods of excess demand, resulting in a net energy consumption of zero.

Energy Efficiency and Net Zero Energy Buildings

Energy efficiency is generally the most cost-effective strategy with the highest return on investment, and maximizing efficiency opportunities before developing renewable energy plans will minimize the cost of the renewable energy projects needed. Using advanced energy analysis tools, design teams can optimize efficient designs and technologies.

Energy efficiency measures include design strategies and features that reduce the demand-side loads such as:

• High-performance Envelope: The building envelope is made up of many different components: roof, walls, windows, doors, etc. The building envelope acts as a thermal barrier, playing an important role in regulating interior temperatures and determining the amount of energy required for optimal thermal comfort. Creating a high-performance building envelope means each piece is designed to minimize the transfer of thermal energy in both directions. This decreases cooling loads during summer and heating loads during New constructions provide the best opportunity to deploy a high-performance building envelope, since it can be built into the project.
• Air Barrier Systems: The basic function of an air barrier system is to prevent uncontrolled air leakage through the building enclosure. An air barrier must be a complete system of materials and components that work together to truly provide a continuous barrier to air flow
• Daylighting: Daylighting is the practice of placing windows, skylights, other openings, and reflective surfaces so that sunlight can provide effective internal lighting, reducing the amount of energy needed for heating and cooling. The process of daylighting also includes controlling how much natural light(both diffuse and direct) enters a building and is generally accompanied by lighting control systems that are responsive to the amount of daylight entering the building.
• Passive Solar Heating:  These systems  collect heat as the sun shines through south-facing windows and retains it in materials that store heat. For example, greenhouses and sunrooms are examples of passive designs. The sun’s rays pass through the windows, and the structure’s interior absorbs and retains the heat.

Once building loads are reduced, the loads should be met with efficient equipment and systems. This may include:

• Energy efficient lighting:  Energy-efficient CFL or LED lighting fixtures offer some substantial advantages over traditional lighting. Not only do these lights use less energy to light the same area as incandescent or traditional fluorescent lights, but in most cases they give off less heat. This reduces the need to cool the building in the warmer months. No matter how energy efficient a lighting system is, the energy is being wasted if no one needs it. Consider occupancy sensors which can help prevent light and energy from being wasted.
• Cooling Optimization: Chilled water can account for up to 35% of HVAC energy costs. Optimization solutions very in their approach but work to produce this chilled water more efficiently. tekWorx Xpress® solutions continuously adjust equipment sequences and key setpoints based on parameters related to process requirements and outdoor air temperature. This ensures maximum system efficiency in real‐time while maintaining cooling requirements at the lowest total kW per ton.
• Geothermal Heat Pumps:  Also known as the ground source heat pump, this technology relies on the fact that the earth (beneath the surface) remains at a relatively constant temperature throughout the year, warmer than the air above it during the winter and cooler in the summer. The geothermal heat pump takes advantage of this by transferring heat stored in the earth or in ground water into a building during the winter and transferring it out of the building and back into the ground during the summer.

With more than 40% of CO2 emissions coming from buildings, and an average of 30% of  building’s energy being wasted annually,  focus needs to shift to the way buildings are being designed, built, operated and maintained. New advancements in technology, however, are making it easier to create net zero energy buildings which are not only more energy efficient and sustainable but can also produce renewable energy.

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.

Short Term, No Cost Energy Efficiency Solutions for Reducing Campus Energy Costs

Many facilities have tight facility budgets and can utilize low- or no-cost ways to reduce energy expenditures.

Plug Load: Computers and other electronic equipment are everywhere in campus buildings and dorms, contributing dramatically to energy consumption and cost per square foot. For equipment that enables a low-power sleep mode after a period of inactivity, using these energy-saving modes can produce significant energy savings. Using smart power strips to shut off plugged-in devices such as printers, monitors, and kitchen electronics when not in use can also have a huge impact on reducing campus energy costs.

Student-led Awareness:  Several colleges and universities are successfully using no-cost and low-cost public awareness campaigns to reduce energy use on campus by reminding people to turn off the lights. People tend to take energy for granted and many are unaware of the opportunities they have to reduce energy use. These programs can help students and staff modify their behaviors and in turn see sizable campus energy consumption reductions.

Longer-Term Energy Efficiency Solutions for Reducing Campus Energy Costs

Longer-term energy-saving solutions may require slightly more extensive implementation and greater expenditures than the no-cost solutions above, but they can significantly cut annual energy costs and in a more consistent manner than the manual no- and low-cost solutions.

Lighting Upgrades: Supplemental to supporting improved energy-conscious behavior on campus, lighting systems upgrades can achieve dynamic energy savings. By installing energy-efficient LED lighting technology, campuses can lower energy consumption, decrease maintenance costs, and ultimately lessen wear and tear on heating and cooling systems. With a return on investment of less than two years in many cases, LED lighting also allows universities to implement upgrade projects in phases by building, campus or specialty.

Demand-Controlled Ventilation: Many large campus sites like auditoriums, gyms and lecture classrooms, and cafeterias are ventilated as if they are at full capacity. Ventilating such spaces based on actual occupancy greatly reduces energy consumption. Demand-controlled ventilation systems can be installed that will use carbon dioxide sensors to control the amount of outside air being supplied to a space based on occupancy. Less energy is consumed because the fans only run when outside air is needed.

Commissioning:  Investigating a building to ensure that its systems are operating appropriately and efficiently can yield significant energy savings. Over time, as campuses expand and equipment and systems change, buildings require tune-ups to maintain optimal performance. Studies have shown that continuously monitoring a building’s energy systems can lead to reductions of 25% in annual energy bills.  Savings primarily come from resetting existing controls to reduce HVAC waste while maintaining or even increasing comfort levels for occupants.

Efficient Water Use:  Low-flow faucets and shower heads as well as sink and shower controllers that automatically shut off after a certain length of time can help conserve water and energy used to heat hot water in recreation buildings.

Chilled Water Optimization: Campus cooling systems are notoriously inefficient but often go undetected as a source of savings. Most existing facilities have dialed-in operational setpoints and procedures meant to fulfill worst-case cooling requirements. This wastes significant amounts of energy.  Minimizing energy and water use can make a major contribution to reaching sustainability goals,  reducing campus energy costs and even qualifying for large utility rebates.

One such optimization platform is tekWorx Xpress®. A combination of adaptive control algorithms and Tridium Niagara N4 hardware, Xpress® algorithms continuously adjust chilled water plant 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 campus comfort cooling needs. Xpress® allows campus facilities to use less water to meet cooling and comfort needs.