4 FM quick reads on HVAC
1. How to limit contamination on cooling-tower performance
One common issue with cooling tower operation is contamination. The environment in which cooling towers operate exposes them to a range of contaminants. Inorganic solids such as dust, dirt, sand, and silt are introduced into the tower from the atmosphere and the tower's water supply. These solids collect in the tower basin, erode circulation-pump impellers, clog spray nozzles, and form scale on heat-transfer surfaces.
Another common contaminant in cooling towers are organic solids, such as leaves, grass clippings, pollen, algae, and bacteria. As with inorganic solids, organic solids tend to collect in basins, nozzles, and heat-transfer surfaces. But unlike inorganic solids, organic solids can pose a health risk to personnel.
Managers have several options for limiting the impact of contamination on cooling-tower performance. Water-treatment programs can help keep the contaminants suspended in the water, limiting their ability to form scale. Programs also can help minimize the growth of organic contaminants.
Even with a well-designed water treatment program, the quantity of solids in a cooling tower's circulating water tends to increase, so most tower manufacturers recommend a blowdown system that bleeds off a portion of the circulating water and replaces it with fresh circulating water. Technicians need to set the concentration of solids in the circulating water, as well as the rate at which water is replaced, in order to keep the tower operating within the manufacturer's guidelines for suspended solids.
To limit the accumulation of living organisms, manufacturers use two methods of water treatment — biocides in circulating water and exposing the water to ultraviolet (UV) light. Biocide programs must be designed for the specific environment in which the tower operates and be regularly monitored to be effective.
UV systems use chambers installed that expose the circulating water to a moderate level of UV light. The light is intensive enough to disrupt the DNA material within most organisms, either killing them or preventing them from reproducing.
HVAC Efficiency Should Be Part Of A Broad Strategy
Today's tip from Building Operating Management comes from Daniel H. Nall of Flack + Kurtz. For facility managers interested in efficiency, the HVAC system offers a significant opportunity. But the opportunity to boost HVAC efficiency should not be addressed in isolation. To be most effective, HVAC efficiency tactics should be part of a broad strategy to reduce energy use.
The pursuit of energy efficient buildings involves the integration of multiple strategies and systems. These systems include architectural enclosure, lighting, domestic water heating, vertical transportation and HVAC.
For HVAC systems, the loads come primarily from five sources: the building envelope (heating and cooling), lighting (cooling), occupancy (cooling), equipment for programmed use (cooling) and ventilation (heating and cooling).
Ventilation load is a function of either the number of persons occupying the space or of the mechanisms necessary to control contaminant concentration and introduction to the space. In most climates of the eastern and southwestern regions of the United States, minimization of outside airflow is an effective energy conservation strategy for some portion of the year, when the outside air is either warm and humid or very cold. Control of ventilation rate determined by occupancy, referred to as demand-control ventilation, is a common energy conservation strategy, especially for spaces with intermittent dense occupancy. Conventional practice would require continuous provision of the maximum calculated ventilation rate, allowing the peak occupancy to be averaged over several hours. Demand-control ventilation would provide the exact flow rate required for actual occupancy at a point, but would allow ventilation to be reduced to a minimum when the space is "in use," but unoccupied. Procedures for implementing demand-control ventilation are described in detail in ASHRAE Standard 62.1, the ventilation standard for acceptable indoor air quality.
With heating and cooling loads reduced to a minimum, utilizing a high-performance building envelope, high-performance lighting with daylight-responsive lighting controls and occupancy sensors, Energy Star office equipment and demand-controlled ventilation, the energy efficiency of the HVAC systems themselves can be addressed.
Fault Detection And Diagnostics (FDD) Is Attracting Industry Interest
Today's tip from Building Operating Management comes from Jim Sinopoli of Smart Buildings LLC. Fault detection and diagnostics is attracting industry interest.
If you are buying books or music from an online site, it's likely that the e-commerce company analyzes your purchases, creates a profile of what type of books or music, authors or performers you like, and then proactively sends you email regarding other items you may be interested in purchasing. Those firms regularly mine data to improve their business performance. Generally facility managers haven't fully embraced such data analytics. However, that is changing.
Today, a new generation of analytics is becoming available to facility managers. The most prominent of these new analytics tools is fault detection and diagnostics. Fault detection and diagnostics finds problems within building systems that are causing the HVAC system to waste energy.
The idea of fault detection and diagnostics for HVAC systems is not new. Research, development and testing of fault detection approaches have been around for about 20 years or so. What is new is the increased interest in and actual use of fault detection. For example, Microsoft has seen promising results with fault detection and diagnostics. Another example of industry approval of data analytics and fault detection and diagnostics came in October 2011, when the U.S. Green Building Council announced a technology agreement that would allow building owners to use an automated fault detection tool with the LEED Online platform, thus supporting the commissioning of buildings. USGBC's interest is that the tool generates reports for LEED Online, including diagnostic functions and faults during the building's performance period.
Another sign of industry interest comes from a Lawrence Berkeley National Laboratory study on monitoring-based commissioning, which uses building diagnostics. Lawrence Berkeley established an average energy savings of 10 percent through the use of monitoring-based commissioning, with as much as 25 percent in some cases.
Repair Or Replace The Boiler: Four Questions To Answer
Today's tip from Building Operating Management comes from James Piper, a contributing editor for Building Operating Management and Maintenance Solutions magazines: When deciding whether to repair or replace a boiler, facility managers should answer these four questions.
Boilers and water heaters have finite service lives and eventually require replacement, even with comprehensive maintenance. But even though a unit's age is a key consideration, it is not the only factor facility managers must consider. While no rules exist for this decision, facility managers must address several important questions.
- What is the age of the equipment? Maintenance costs rise as boilers age. Replacement costs will always exceed maintenance costs, unless something major goes wrong. But watching the trend in maintenance costs is more important. If these costs remain relatively flat, the better option is repairing the boiler or water heater. Costs that rise consistently and rapidly indicate replacement, as does difficulty in getting replacement parts.
- What is the equipment's operating history? Identical boilers that operate in similar facilities often have much different operating histories, depending on set-up, operating practices, and maintenance. Operators and managers need to review the equipment's history to determine if any findings suggest that replacement is the better option.
- Is the equipment efficient? New boilers offer substantial increases in annual operating efficiency compared to boilers only 10 years old. So when evaluating options, managers need to consider the annual savings from installing a new, higher-efficiency unit.
- What is the configuration of the equipment? Older installations of central boilers and water heaters tend to feature one or two large units. That set-up often forced operators to cycle one boiler to match part-load operating conditions.