Beneath the Surface

04/29/2009 |

By Darren Goody

The difference between knowing that something works and knowing the details of how something works opens a world of opportunity when applied to building systems. Lighting, HVAC, and domestic hot-water systems account for roughly 50 to 80 percent of a building’s total energy consumption. Given this fact, it becomes clear that understanding the details of how your systems operate can have real impacts on efficiency and operational savings.

It’s not uncommon for facility teams in existing buildings to have only a general knowledge of their building systems. Teams are often overworked and understaffed. The prior education and experience of team members may not align with the building systems’ technology, and there may be no solid systems documentation from which to draw. But, all facility teams have the capacity to develop an in-depth understanding of their building systems, and this knowledge is paramount to efficiency improvements.

An Ounce of Prevention
Unfortunately, building systems don’t come equipped with “failure” lights to let you know when they need a check-up. Most systems are on autopilot until the damage is done. An in-depth knowledge of systems operation enables you to anticipate or avoid premature failures. Through regular inspections and proactive measures, you can address operational problems before they result in excessive equipment wear and tear, and years of additional, unnecessary energy consumption.

Another practical advantage of assessing the efficiency and energy consumption of each system is that you can more effectively plan for equipment replacement and/or upgrades. Precise information on systems’ efficiencies is necessary for a well-informed cost-benefit analysis. In today’s volatile energy market, you may be in line for an upgrade sooner than originally anticipated if you find evidence of a quick return on investment from energy savings.

Translating Knowledge into Savings
Rule No. 1: operation = energy consumption. Minimize your systems’ operational schedules to operate only when necessary. Although this seems obvious, it’s frequently not done. Dig into the details of your system based on its programming and controls to find out exactly when each component in the system is running. Be sure your systems are turned off or set back during weekends and holidays when occupancy is low. If you need to accommodate only a few people in the building, look for creative solutions rather than operating the entire system for the additional time. If systems give you trouble at start-up, don’t automatically start entire systems 2 hours before occupancy. Experiment with different start times. Better yet, look at an optimal start-up strategy with proper controls. Control strategies work well once they’re optimized.

Match the cooling and heating capacity delivered by systems as close as possible to the actual load on the system. Having variable capacity capability is essential to achieving better alignment with the load, but you can’t tap into this flexibility without the right controls. Once you understand what your equipment is doing to meet the load, you can tell if your equipment needs an upgrade or if your controls need an upgrade, or possibly both. For example, the short cycling of pumps is one key indicator that you may need a variable speed drive upgrade. Short cycling of compressors or chillers are other warning factors.

Take advantage of “free” cooling prior to occupancy. Operate your fan systems in a morning cool-down mode to pull in outside air. In a large building, the temperature differential between the outside air and building mass usually makes running the fans in the early morning more efficient than bringing the chiller plant online earlier in the day. Although it’s a common belief that you need a temperature delta of 10 to 12 degrees or greater to warrant this strategy, even a delta of 6 to 8 degrees can consume less energy than bringing the chiller plant online sooner in the morning.

During occupancy, make sure the dampers in an airside economizer package are working properly. Even on larger buildings with experienced staff, it’s not unusual to find that dampers don’t open at all, or don’t open and close as completely as they should. Water-side economizers are even more efficient than airside economizers, but they require controls that can fail undetected, resulting in mechanical cooling operation in lieu of free cooling. The facility manager should integrate inspections into the maintenance plan to verify that all valves and dampers maintain correct positioning.

Utilize additional cooling capacity available from a cooling tower to lower your condenser water temperature, which will lower your chiller’s power consumption. This is commonly known as floating head pressure control.

Look at the whole picture. Understand how each piece of equipment operates within the system. How you would expect them to operate may differ from how they actually operate once they’re affected by other equipment in a system. For example, in the Northwest, simultaneous heating and cooling occurs in large buildings to heat the perimeter and cool the interior or cool one exposure while heating another. Understanding the load diversity within your building’s zones will help you create an optimized solution for delivery of cooling and heating capacities. Recognizing significant load diversity may warrant system changes.

Three Power Tools
Three tools exist to help you assess the details of how your system is operating: observation, functional testing, and trending or data logging.

Observation. Go beyond walking through your space. Inspect your systems frequently to see how they’re operating on a day-to-day basis under real load conditions. Take full advantage of all available design and construction documentation on the building to understand the intent of each piece of equipment in each system.

Functional Testing. This procedure allows you to simulate certain variables and see how the system performs in various modes of operation under different load conditions. If done correctly, functional testing allows you to see how your system will respond under all types of situations. You can compare how the system responds with your expectations to determine how your systems actually operate when you’re not around. While observation is still necessary, functional testing will lessen the amount of observation required.

Trend analysis or data-logging analysis. Trend data analysis uses your building’s HVAC control system to collect status information from system points, such as pump status, fan status, temperatures, valve positions, damper positions, etc. These points are measured and stored in a graphical format. Data logging analysis utilizes portable data loggers as a supplement to your building’s HVAC control system. It can also be a standalone tool if you don’t have a direct digital control system capable of trend collection. By collecting data at various times of day and all seasons of the year, trend data and data logging allow you to see how your system operates over various periods of time under real load conditions.

With an in-depth understanding of how, when, and why your systems operate the way they do, you’ll be able to make informed decisions and necessary adjustments to increase your building’s efficiency and save money.

Darren Goody is the commissioning and auditing manager for the Energy Management Solutions team at Green Building Services Inc. The Energy Management Solutions team provides technical and strategic building management services to building owners and facility managers throughout the country. Darren can be reached at (866) 743-4277 or darren@ greenbuildingservices.com


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