High-Rise Building Systems
Consider the effect on the bottom line of saving a third of a building’s utility costs. Most buildings use 10% to 30% more energy than necessary and have major opportunities to save. Energy savings of 30% are attainable with a comprehensive approach to operations, maintenance, repairs.
High-rise buildings typically serve a handful of purposes: Condominiums, hotels, offices, retail spaces, parking, or a mix of these functions. With height comes energy intensive processes such as air conditioning the core of the building year round, elevatoring, and pumping potable water up the
building. In addition, each functional type has several unique energy challenges. Many typical energy cost saving upgrades for low-rise buildingscan be used on high-rises. High-rise
specific techniques are also available.
Choices made by building operators play a large role in the cost of running a building: Effective control of energy costs depends on good decisions
about the operation of existing systems as well as regular physical maintenance and repairs. A major benchmarking study in New York showed variations of 20%-30% in energy usage between physically and
functionally similar high-rises that were differently operated. (1 )
This brochure discusses the most common energy-wasters found in high-rise buildings as well as a selection of well-established and innovative ways to fix them through upgrades and repairs to mechanical systems, ventilation systems, lighting, and the building envelope. It also identifies resources to help owners and operators save money. For personalized help with your building, contact SEDAC directly. At SEDAC, we can recommend the right energy saving options for your particular building. We can assist in comparing projects for their return on investment and payback periods. Some options are so effective they can have paybacks of less than 1 year. We can also identify incentive funding to shorten the payback of other beneficial projects for your building.
Old and inefficient boilers and chillers are common culprits in building energy waste. The fans, motors, and pumps that run distribution systems are also guilty; SEDAC often finds this equipment running constantly, even when there is no need. An unscheduled or poorly programmed building automation system (BAS) can also undermine efforts to reduce energy costs.
FANS, PUMPS AND COMPRESSORS: VFDs
Motors that run fans, pumps, and compressors are found throughout your building’s HVAC systems. These motors are a common culprit in wasting energy
because they operate at a constant speed regardless of the needs of the system. Throttling devices like control valves and outlet dampers are sometimes used, but these are both expensive and wasteful.
A much better solution exists; control devices called Variable Frequency Drives are very effective at reducingmotor waste. VFDs are quite economical as well and tend to have quick paybacks for motors larger than 5-10 hp that operate 2,000 hours or more annually. VFDs can be installed in many locations in an HVAC system. Some popular choices for saving energy are:
- Chilled water pump motors
- Air handling unit (AHU) fan motors
- Cooling tower fan motors
- Hot water boiler pumps
- Exhaust fans
Before an existing boiler system reaches the end of its useful life, take the time to assess a high efficiency replacement. Incentives are available to help cover the incremental costs of high-efficiency systems - but they are only available if you are replacing a working boiler! Your options will be more limited if you wait until the boilers fail. Consider switching to a modular system if your building is currently heated by one or two very large boilers. In a modular system, a series of smaller boilers is installed. A modular system more efficiently handles heating loads in non-peak load conditions, which make up most of the heating season. This technique can save 5%-7.5% of the boiler’s annual gas usage. Upgraded boiler controls and accessories are another great way to save energy costs. Outdoor air reset controls (to reduce water temperatures); oxygen trim controls (to improve combustion efficiency); and stack economizers (to capture waste heat) are all effective at improving the impact of your energy dollars. Steam trap maintenance and regular boiler tune-ups are often ignored, but offer simple and effective cost savings. There are great incentives available for these solutions.
CHILLERS and COOLING TOWERS
Cooling accounts for a large percentage of the energy costs of tall buildings; many require cooling year round. High efficiency chillers can make a huge difference in operating costs. New chillers can range in efficiency from as low as 1.25 kW/ton to as high as 0.38 kW/ton. In other words, buying low-end equipment can lead to operating costs that are 250% higher than if you had purchased high efficiency equipment! (2) Also consider a series of modular chillers when looking at replacement of a large chiller. These small units can fit in a freight elevator and are easier to maintain and replace. Next, look for cost savings in the operation of your equipment. Similar to heating, the basics of managing cooling costs with controls and operational changes starts with turning equipment off when not needed, followed by finding optimum operating temperatures. A thorough analysis of the cooling loads, optimum chiller sequencing, and loading schedule will provide the basis for chiller plant improvements. Installing automatic chiller scheduling controls will allow the building operators to minimize chiller plant operating costs and shut down the chiller plant when there is no cooling load. Once the operating schedules are optimized, consider automatic chilled water outdoor air reset controls. These controls, like boiler controls, adjust the water temperature based outside temperature, and save energy costs during milder weather. Cooling towers are a final piece of the chiller plant that should be improved. Water conservation means energy savings, so it makes sense to look into retrofit kits.
Lighting is one of the simplest places to start cutting energy costs in your building. There are two main offenders: Inefficient lamps (like T12 fluorescents) and leaving lights on unnecessarily.
CHECK LIGHTING POWER DENSITY (LPD)
While not an energy-saving measure in itself, having a lighting designer identify overlit areas in your building can help inform decisions and boost savings in a future lighting retrofit.
Two obvious cost savers: Replace both incandescents and linear fluorescents with high efficacy LEDs. A lighting retrofit starts with a survey of existing lighting; this inventory makes it possible to apply for incentives for retrofits. Then, a lighting expert can design replacements while considering lighting power density needs. Remember, 1:1 replacement can result in overlighting and is not necessarily the best solution!
Lights can be switched off by occupancy sensors, vacancy sensors, daylighting sensors, timers, BAS controls, and conscientious people. Check the back page for Behavior Change Tips. Daylighting sensors can control the perimeter spaces in a high-rise, while allowing the interior spaces to be artificially lit. Occupancy and vacancy sensors are perfect for spaces like offices, conference rooms, storage areas, and restrooms. In stairwells and hallways, consider bi-level lighting controlled by occupancy sensors that reduce light levels when nobody is around.
Constant volume ventilation and exhaust systems are an easily overlooked cause of building energy waste. Providing fresh air to people and venting stale air is a necessity - but it should be done judiciously.
DEMAND CONTROL VENTILATION
CO2 sensors tied to the ventilation system are a great way to save energy costs. When people are present and producing CO2, ventilation is provided in accordance with occupancy levels. When CO2 levels are low, ventilation levels can be lowered.
Constant volume exhaust fans from kitchens and bathrooms can waste huge volumes of conditioned air when allowed to operate regardless of need. Save
heating and cooling dollars in your residential highrise by linking exhaust dampers to the light switch or occupancy sensors in kitchens and bathrooms. VFD
drives then modulate air flow based on static pressure in the exhaust stack.
High-rise walls and windows have a few places where energy dollars often leak out. These include air leaks as well as gaps in insulation. If the doors in
your building are hard to open (or won’t stay closed), uncontrolled stack effect (hot air rising and escaping out leaks in the top of the building) may be to blame and wasting money as well.
Air sealing is a simple, effective place to save energy dollars. Focus on leaks at the bottom and top of the building to limit the stack effect, as well as air sealing vestibules, elevators, stairwells, and rooftop access. If insulation is missing behind baseboard heaters and radiators, the problem is simple to fix with a reflective insulating layer. Window replacement in a high-rise is costly, but there are low-e films, shades, and ways to add panes of glass from the inside (without removing original windows) that are worth consideration.
Changing how people use energy in a high-rise building may seem like an area building owners and operators can’t affect. However, a growing body of expertise built on social science research reveals ways to change buildings so that people are encouraged to save energy and energy dollars. Successful programs provide residential end-users with information on their energy use, with comparisons to other users. If possible, feedback as to whether their usage is improving can be a powerful motivator. Goal setting and rewards are also popular tactics. For commercial end-users, benchmarking energy usage and implementing a building energy dashboard are two ways to provide information to help change how businesses operate and maintain their energy-using equipment.
COMBINED HEAT AND POWER
Combined heat and power (CHP) is an integrated system located at or near a building or facility. It can economically generate part of a building’s electricity
needs, and provide hot water, heating, cooling, and dehumidification as well. CHP units for high-rises can be strategically located at the point of energy use, in the basement, or on the rooftop. On-site generation is fuel efficient, versatile, and can double as a stand-by generation system. Typically, the most efficient design sizes a CHP system to meet heating loads and treats the electricity generated as a by-product.
- Photo Credits: www.sxc.hu, www.delhi-industries.com/hvac-blowers.html, www.olymspan.com, www.johnsoncontrols.com