Facility managers are in a bind. HVAC systems often use more energy than any other equipment or system in a building. According to the EPA, at least 45% of energy costs in commercial buildings are due to heating and cooling expenses. There’s even a tax rebate available, based on energy savings per square foot. And yet, if you reduce ventilation or turn the system off on weekends to save money, indoor air quality (IAQ) will worsen.
“I work in all kinds of buildings,” says Mike Klingler, service manager for Farber Corporation in Columbus, Ohio, “and I am often asked to reduce the energy costs of the HVAC systems. One of the areas we check is ventilation rates for the building.
Decreasing ventilation rates may reduce overall energy consumption and reduce operating costs but at the same time we have to maintain good indoor air quality standards too. There’s usually a very tight ventilation standard that the service provider has to control in order to reduce energy costs and maintain quality indoor air conditions. Considering the dynamic changes in a building and a functioning HVAC system, in many cases, it’s not real easy.”
Demystifying ASHRAE Standards and Indoor Air Comfort
Creating guidelines for “comfortable indoor conditions” has proven difficult due to the sheer number of variables—personal and environmental—that play a role in determining how people experience comfort. Similarly, good indoor air quality can be equally difficult to define as it largely depends upon the level of outdoor pollution, the number of occupants in any given space, or even an individual’s susceptibility to allergen or odor.
ASHRAE has developed two standards that address the subject of thermal comfort and ventilation: ASHRAE Standards 55 and 62.
ASHRAE 55 “Thermal Environmental Conditions for Human Occupancy” specifies the combination of environmental and personal factors that create a comfortable, productive environment for 80 percent of the occupants in any given space. The standard describes six primary factors that must be addressed when defining thermal comfort conditions: metabolic rate, clothing insulation, air temperature, radiant temperature, air speed, and humidity. These factors are considered in defining a range of operative temperatures that provide acceptable thermal conditions.
ASHRAE 62 “Ventilation for Acceptable Indoor Air Quality” defines the role that ventilation plays in the control of contaminants in the air. The standard specifies minimum ventilation rates and IAQ that would be acceptable to building occupants. Largely applicable to the design of new buildings, the standard is also intended for use as a guidance document to improve IAQ in existing buildings. A key consideration in the latest version of the standard (62.1-2004) is outdoor air quality, which is no longer ignored or assumed to be acceptable. These two standards actually suggest thresholds for all of the key parameters mentioned above. That makes ASHRAE a good source for optimizing HVAC systems to promote occupant comfort and, surprisingly, to manage energy costs.
How to Balance Your System
Once you know your thresholds, here are some tips for optimizing your HVAC system.
Proper Airflow—Conduct duct traverses to measure air pressure, velocity and flow. If pressure is too high and/or airflow too low, it could mean your system is working too hard to push too little air through. It’s probably time to replace dirty coils, fans and filters, which have probably been adding mold to the system, too.
Check Ventilation—Many buildings are either over-ventilated—needlessly spending energy on blowers—or under-ventilated, particularly airtight buildings built during the 1970s with underpowered ventilation systems. Under-ventilation leads to bad IAQ in a hurry. Use ASHRAE guidelines to get your balance just right.
Add Variable Frequency Drives (VFDs)—The EPA recommends demand-based variable air volume systems, using VFDs to more efficiently regulate HVAC motors, pumps and so forth. That’s money up front for the installation but significant long-term savings in energy costs.