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Weekly Updatesretrofitting existing properties into sustainable, green buildings isn't an easy task, but it is one that can offer substantial payback for your properties. Simply by shifting your focus from obtaining LEED certification first and rokmost to obraining an Energy Star Certification can yield this satisfactory payback. Not only is this goal readily obtainable, but it is also an important initial step reward LEED certification. (See sidebar page 25, for definirion of these terms.)
In the competitive residential rental world, owners and managers who want to be environmentally friendly must be adept in utilizing technology that incorporates payback that makes financial sense, as well as providing a positive public relations image for your company.
Everything from installing shower head water restric tors in bathrooms to placing high-efficiency light bulbs in your multifamily properties are easy solutions you can implement quickly. However, specific focus on strategies for improving the energy efficiency of the heating ventilating and air conditioning (HVAC) systems in these buildings often represents an investment opportunity with satisfactory payback, since the systems typically account for 40 to 60 percent of the buildings energy use.
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With that in mind, the following are strategies you can look to first for improving your building's energy efficiency.
Upgrade Windows
Windows are often the most significant architectural feature offering a great opportunity for increased energy efficiency and improved living comfort. In the past, a window's energy-efficiency rating was seldom a factor in selection, which led to single-glazed windows. These still remain in many of the high-rises built more than 30 years ago. Replacing these windows with tinted double-or triple-glazed insulated windows can reduce energy consumption significantly.
However, window replacement represents a major capital cost, In addition to improved energy efficiency, the reduc tion in water and air infiltration as well as outside noise and the ability to maintain a more positively pressurized building are other factors that need to go into the replace ment decision. These things not only lead to a decrease in resident complaints, but can also mean increased resident retention.
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Window replacement should be considered when ever a major renovation of the ptoperty takes place. If a building already has energy-efficient windows or the property cannot afford new ones, make sure the window seals are maintained. As the windows age, the seals break down from ultraviolet rays and window use. By using thermal scanning technology the windows can be checked to determine the severity of energy loss through the window seals. If the loss is significant, the investment cost in seal maintenance is much less than that of window replacement.
Check Insulation
Since there is more exterior wall square footage than roof square footage in high-rises, insulating the walls has a greater impact on energy reduction than insulating the roof. This strategy requires gaining access to the exterior walls. Since high-rise buildings have masonry exterior walls, interior access is more feasible. However, interior walls also present challenges in that plaster, drywall and final finishes are expensive to restore.
Increasing the amount of exterior wall insulation should be evaluated when planning any major renovation, as minimum exterior wall insulation "R" values are now mandated by code for new buildings, as well as for building's undergoing major renovation. (R values ate measures of thermal resistance. The higher the R value, the greater the thermal resistance and the better the insulating capability.)
Flat roofs can have an insulation layer added when the roof is replaced, but replacing a good roof to add insulation does not generally result in a satisfactory payback.
Properly Ventilate
When it comes to ventilation, indoor air quality' and energy conservation often compete. Over-ventilating a space results in excessive energy consumption, but creates good indoor air quality. However, under-ventilating a space results in reduced energy con sumption but creates poor indoor air quality.
Most municipal codes require that a specific volume of air be exhausted from certain living areas. Similarly, these codes also require that a specific volume of air be supplied to replace the exhausted air to prevent contaminated or stale air from building up in an occupied space. Energy consump tion of this exhaust and make-up air ventilation comes from the energy used to operate fans and to heat and cool the ventilation air.
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Many high-rises over-ventilate by providing it continuously and at a constant rate. But by switching to a system that exhausts only when required, can save energy. This "demand response" ventilation requires an automated damper in the exhaust outlet of the room being ventilated, which can be connected to an independent switch so it opens and exhausts the room only when turned on and is closed during other times.
When the damper is closed, fan energy--as well as the more significant energy to heat and cool the exhausted air--is reduced. Experience shows that only 40 percent of dampers will be open at any given time in lieu of the 100 of percent the constant rate ventilated buildings. By reducing the volume of exhaust, the amount of make-up air can be lessened to maintain a slightly positive-pressure building, which reduces water and air infiltration.
This demand response ventilation system was implemented at a 13-story, 263-unit loft building in Chicago. Actual measurement of the building's total exhaust after installation of the demand response dampers confirmed a maximum 40 percent of total exhaust exiting the building at any given time.
Another opportunity to reduce energy consumption of exhaust and make-up air ventilation comes from the energy recovered from the exhaust air and transferred into the make-up air. We often do not think of exhaust air as having been heated or cooled; however, the exhaust air from a building is replaced by outside make-up air entering the building. This make-up air is introduced through fans or infiltration through the building's exterior. Either way, this make-up air is heated or cooled to the temperature within the building. The opportunity exists to use a heat exchanger that recovers the energy from the exhaust air and transfers this energy into the mechanically supplied make up air. Only energy is transferred, not the recirculation of the exhaust air back into the make-up air.
Reduced ventilation energy consumption also can occur through enhanced filtration to the mechanically provided make-up air. For example, similar indoor air quality can be obtained by providing a lower quantity of ventilation air when the quality of the ventilation air has been improved through enhanced filtration. The lower quantity of air results in reduced energy consumption. However, the minimum amount of make-up ait provided should always be slighrly greater than the total amount of the exhaust air to maintain a slight positive pressure within the building.
Watch Infiltration
Infiltration of outside air into high-rises is influenced by many factors, including wind, a building's natural stack effect and the building's ventilation systems. Control of these factors is another way to reduce energy consumption. Every window, door and opening is a potential suspect for conditioned air loss. By using thermal scanning technology, these openings can be checked to determine the severity of energy loss through the opening's seals. This testing is more accurately performed when there is a significant difference between the indoor building temperature and the outside ambient temperature. If the loss is significant, the investment in seal maintenance again offers an excellent payback.
Examine Controls & Metering
For energy reduction, the best place to start is by asking: Can the item be turned off? For example, pumps, fans or lights that serve an area occupied for only a portion of the time can be turned off when not in use, as with model apartments, offices and storage areas. You can also invest in automated controls that turn devices off. These are more consistent than manual controls and offer one of the simplest and quickest paybacks avail able in energy reduction.
There are two levels of automated controls to consider--building-level or individual living-unit level controls. A building-level control is a microprocessor-based direct digital control (DDC) system that monitors various sensors located within and at the exterior of the building. The DDC system is programmed to ensure that your building's central systems are operating efficiently.
An individual living-unit level control is a thermostat located within the living-unit that maintains the living unit temperature. Both levels of control systems provide comfort and efficiency when a building is both zoned properly and have the ability to provide heating or cooling to each zone when required.
Building orientation and solar effects cause different areas of a building to heat at different times of the day. In the afternoon, the southern and western exposures of a building generally require more cooling than the northern and eastern exposures. In buildings with inadequate zoning--sometimes the whole building is one zone--overcooling, overheating and. excess energy consumption results.
In the absence of proper zoning, a building-level DDC system can offer better control by polling strategically placed temperature sensors and using this information to better control the zone's heating and/or cooling. This strategy is even effective in residential buildings that have steam hear.
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