4 FM quick reads on HVAC
1. With HVAC Upgrades, Look Beyond Like-Kind Replacement
Today's tip from Building Operating Management magazine: When replacing elements of the HVAC system, evaluate whether to replace units with a like kind or not.
Say you're replacing a chiller. Because chillers can easily last 30 years or more, the odds are good that the needs of the building and its occupants have changed since it was installed. In that case, it probably isn't a good idea to replace units with like kind.
For one thing, chillers with older technology are not as energy efficient as units made today. What's more, you might find out that the size of the existing unit may not meet the needs of current and future occupants. There's also the question of how much redundancy you have and need. Questions like those are why bringing in an outside engineer, while an added expense, is probably a good idea.
The result of not replacing in kind can be significant. Two Shell Plaza in Houston was formerly outfitted with four 500-ton chillers. As a result of an upgrade by Hines, two of those chillers remain, but only in a backup role. The cooling is now provided by a pair of 680-ton chillers with variable frequency drives. That approach not only allows for more efficiency, but also gives more flexibility when it comes to providing cool air during off-peak hours when only a limited number of tenants need it. Changes like that can only come about if a project is properly evaluated beforehand and the building's use is carefully examined.
In some cases it might be preferable to replace with similar units. Kirk Beaudoin, territory facilities manager, North American retail operations, Nike, says that tracking service calls, breakdowns and temperature complaints helps his company identify problems that would prevent the organization from being able to replace old units with similar new units. "Our assumption is that our stores were properly designed when built. So unless we have identified ongoing comfort issues that are related to sizing of equipment, or if there have been any modifications to the store which would require a review of the systems, we generally replace with the same tonnage," he says.
This has been a Building Operating Management Tip of the Day. Thanks for listening.
LEED-CI: Greening Leased Space
Today's tip is about how to use LEED for Commercial Interiors to save energy in tenant space. After a slow start in the marketplace, tenants are using LEED CI much more frequently these days to implement sustainable strategies in leased space. Conventional wisdom had been that tenants have very little control over their energy spend when they lease space, and therefore there was no reason to implement a systemized energy or sustainability strategy, outside of putting out a few recycling bins. But LEED-CI offers a framework for tenants who wish to be energy efficient and green.
LEED-CI offers 37 points (out of 100) for energy efficiency strategies. The area with the most potential impact for tenants is, believe it or not, HVAC. LEED-CI offers up to 10 points for optimizing HVAC performance. Because building-level HVAC is one thing tenants don't have control over, LEED-CI rewards tenants for implementing zoning and controls for their own space. There are several options available for achieve these points, including simply "demonstrating that HVAC system component performance is 15 or 30 percent better than ASHRAE 90.1- 2007."
LEED-CI offers up to seven points for reducing lighting power density up to 35 percent below the standard set in ASHRAE 90.1 - 2007. This can be done by using efficient fixtures, like T5s, or, as LEED CI suggests, using daylight responsive controls in spaces within 15 feet of windows and under skylight.
A third area for which LEED CI rewards tenants for energy efficiency measures is plug loads, like appliances. Four points are available for using 90 percent Energy Star-rated appliances, office equipment, electronics and commercial food service equipment. The credit excludes HVAC, lighting and building envelope products.
Finally, five points can be earned for enhanced commissioning.
LEED CI also offers 14 points for various materials and resources strategies, like recycling, and 17 points for indoor environmental quality strategies like selecting low-emitting materials. Sustainable sites strategies can get you 21 points and water efficiency strategies round out LEED CI with 11 possible points.
Variable Frequency Drive Technology Has Improved For HVAC Applications
Today's tip comes from James Piper, contributing editor for Building Operating Management magazine: Improved variable frequency drive technology makes them worth considering for many HVAC applications.
The variable frequency drive (VFD) is one of the most successful energy management tools that facility managers have applied to HVAC systems. Those who have used the drives have realized energy savings ranging from 35 to 50 percent over conventional constant speed applications, resulting in a return on their investment of six months to two years.
While the number of applications suitable for early generation drives was somewhat limited based on the horsepower of the motor, today's drives can be installed in practically any HVAC application found in commercial and institutional buildings. Today, systems can be operated at higher voltages than those used by early generation systems, resulting in off the shelf systems that are available for motors up to 500 horsepower.
Early generation systems also suffered from low power factor. Low power factor robs the facility of electrical distribution capacity and can result in cost penalties imposed by electrical utility companies. Today's systems operate at nearly constant power factor over the entire speed range of the motor.
Another problem that has been corrected by today's systems is operational noise. As the output frequency of the drives decreased in response to the decreasing load, vibrations induced in the motor laminations generated noise that was easily transmitted through the motor mounts to the building interior. Today's drives operate at higher frequencies, resulting in the associated noise being above the audible range.
Most of the latest generation systems use what is known as pulse-width modulation. In pulse-width modulation systems, the output of the VFD is a quasi-sine wave that consists of a number of narrow voltage pulses that vary in both duration and voltage.
Three Boiler Control Upgrades Can Improve Energy Efficiency
Today's tip comes from James Piper, contributing editor for Building Operating Management and Maintenance Solutions magazines:
When specifying boiler controls it is important to understand that operating efficiency is only one consideration. The boiler control system must be able to meet the facility's peak heating load while operating efficiently under part-load conditions. Typical controls that facility managers should consider when upgrading existing boilers include the following:
1. Flue-gas trim. One of the best indicators of a boiler's combustion efficiency is the flue-gas composition. Trim controls constantly monitor the temperature and the chemical composition of the flue gas, making changes to the combustion controls to limit the quantity of excess air brought into the boiler. While all boilers require some excess air for complete combustion, natural-gas-fired boilers can operate effectively with as little as 3 percent excess air. Boiler efficiency increases approximately 1 percent for each 15 percent decrease in excess air provided to the boiler. With most boilers operating at 10 percent or more excess air, the annual energy savings from flue-gas trim controls is significant.
2. Automatic blowdown. To limit the quantity of deposits that can accumulate in a steam boiler, technicians can bleed off part of the boiler's water, typically on a continuous basis. The boiler wastes energy if the blowdown rate is too high, and the concentration of solids in the water becomes too high if the blowdown rate is too low. Automatic blowdown controls regulate the quantity of water that technicians bleed from the system based on the actual level of contaminants.
3. Sequencing. Many facilities operate more than one boiler at a time, depending on the load. This frequently results in more boiler capacity than is actually needed. Since the operating efficiency of a boiler is highest when it is operating at or near full load, this practice can waste a significant amount of energy. Automatic sequencing controls examine the load conditions and determine the boiler or combination of boilers that will meet that load most efficiently.