True Analytics™ - Energy Savings, Comfort, and Operational Efficiency
| Optimizing Building Performance
for Health as well as energy use
David Bearg, PE
Life Energy Associates
Building Automation can improve the management of building operations,
including ensuring the healthfulness of the indoor environment as well
as energy use. In order to accomplish this expanded scope, start
by asking what information about operations needs to be included in the
adoption of building automation, and the best ways to acquire this
information. The two most important components of health-related
aspects of building operations are ventilation and moisture management
Ventilation, the “V” of the HVAC system, can be in direct competition with the energy use and functioning of the distribution component of the HVAC system. It may not be delivering this outdoor air, to dilute and remove indoor generated air contaminants, to where the people are located in the building. The most accurate way to measure the local ventilation performance is by comparing the in-space values for carbon dioxide (CO2) with the outdoor air concentrations, as this allows the direct calculation of per person ventilation rates. While some measurement requirements, such as from ASHRAE and LEED specify that this indoor measurement should be in the breathing zone of the occupants, this approach can lead to the collection of readings too close to the 40,000 parts per millions (ppm) concentrations in the exhaled breath and indicate ventilation deficiencies when they don’t really exist. The recommendation of the ASTM D 6245, Standard Guide for Using Indoor Carbon Dioxide to Evaluate IAQ and Ventilation, is sampling at a distance of at least two meters from where the nearest person might be standing. Experience has indicated that the sampling location should also be no more than four meters from where the nearest person might be.
Whatever the location chosen to achieve diagnostic feedback on ventilation performance, the critical aspect of this potential benefit in improving the operation of the building is the need for timely review of this monitoring data. This is because monitoring studies measuring carbon dioxide (CO2) in several buildings are showing that conference rooms are typically not even providing the ASHRAE minimums of Standard 62.1 for Achieving Acceptable Indoor Air Quality during meetings. This all too common operational condition imparts an unnecessary risk for the occupants in sharing cold and flu viruses for colds. You can’t manage what you don’t measure.
In one published retroactive study comparing multiple office spaces it was found that increased ventilation resulted in a significant reduction in short-term absentee rates. In this study, for every $1 invested in conditioning more OA, $6 in reduced absentee rates were achieved. This study compared ventilation rates well in excess of the ASHRAE minimum recommended values with those at these minimums or just slightly above. ASHRAE 62.1 defines “acceptable IAQ” as one with which a substantial majority of those exposed (at least 80%) is not dissatisfied. Under this definition, up to 20% of the people can be dissatisfied with the IAQ, and yet the definition of “acceptable IAQ” is still achieved.
In addition to potentially achieving good ventilation, there is a powerful underlying financial benefit: Achieving a healthy indoor environment yields more dividends than energy saving options. When computed on a square foot basis, people costs far exceed energy costs. People costs in commercial buildings can average around $300/SF, while energy costs in the northeast are averaging around $3/SF. Improving the value of worker productivity by just one percent can achieve a payback of $3/SF, or equal to the entire cost of the energy.
So just focusing on energy, while ignoring healthfulness, can decrease building performance, when productivity is included in the equation. Imagine if the productivity loss were 2%, how much worse this would be. Conversely, if a 1% increase in the productivity of the workforce could be achieved by increased ventilation, this added benefit could justify a doubling of energy costs and would still be revenue neutral.
Therefore, the goal of achieving automated buildings should include not only smart buildings, but smart and healthy buildings. To understand what it takes to achieve a healthy indoor environment you first need to understand both the interrelationships among the various HVAC and building components and the role that people play in indoor ecology. People emit numerous air contaminants including particulates, chemicals and viruses, as well as heat and moisture. While the particulates emitted from people’s activities have been greatly reduced since smoking has been banned from most indoor environments, people are a major source of shed skin cells. The response to people being a source of chemicals has lead to the demand for “Fragrance Free Zones”. But the biggest threat to health is the viruses that make others sick as well.
The most accurate way to determine how much ventilation is actually being provided to a building’s occupants is by using one of the shared-sensor monitoring systems that measures CO2 concentrations. In this approach, air samples are transported via tubing from multiple locations in the building to a central location and one accurate sensor. Since the same sensor is being used to measure each of the sampled locations, the error created by using multiple sensors does not enter into the calculations. This very accurate CO2 monitoring data even allows the calculation of the percent of outdoor air in the supply air by comparing the concentrations in the outdoor air, the supply air, and the return air.
While historically the %OA determination was done by comparing the mixed air temperature with the return air and outdoor air temperatures, this approach is not very accurate due to problems of poor mixing between these two air streams. The CO2 approach is far more accurate, relying on the supply air leaving the air handling unit and not just the estimate of the mixed air temperature before any heating or cooling coils, (i.e., adiabatic mixing).
While generous ventilation does not guarantee a healthy indoor environment, it is a critical requirement. Therefore, you need to accurately monitor CO2 concentrations, which would mean doing more than just putting CO2 sensors on the wall. The data also needs to be logged, trended and reviewed. In one building where CO2 sensors were installed as part of an effort to achieve Demand Controlled Ventilation (DCV), a commissioning effort determined that this DCV wasn’t working as intended until several months later in the life of the building. This is an all too frequent occurrence, as DCV requires that every component of the system, including the sensor functioning, the communication protocols and the HVAC response, all need to work together toward the intended goal of having the ventilation provided match the varying needs of the space.
Energy is, or course, still very important, as changes in buildings, more effective lighting strategies and improved thermal performance of the building envelope mean that a larger percentage of the energy consumed by the building and its systems go to conditioning outdoor air for ventilation. This is even more reason to accurately know how much ventilation is being provided
Another key aspect impacting the comfort and healthfulness of the indoor environment is its humidity. Accurately measuring dew point temperatures at numerous locations in the building provide feedback on absolute humidity levels and consequently moisture management performance.
Uncontrolled humidity levels can lead to degraded IAQ due to mold growth. Humidity levels too low can cause discomfort for contact lens wearers. Also, moisture management can involve significant energy costs. In one dew point temperature monitoring project the locally elevated absolute humidity values in a conference room were due to a coffee urn with the heat left on. Review of this absolute humidity data can also assess specific aspects of moisture management that include the operation of the HVAC system in dehumidification, as well as humidification. Absolute humidity monitoring can also identify moisture intrusions from the outdoors, and serve as an early warning system against elevated moisture levels, the precursor to mold growth.
We need to move to smarter buildings. The opposite of a smart building is a dumb one, without the ability the measure IAQ. We need to achieve not only smart buildings, but healthy ones as well where persistent commissioning includes monitoring of CO2 and absolute humidity, and provide ongoing assessments of both ventilation and moisture management as tools for effective balancing of IAQ and energy use.
About the Author
an educational background that includes both Chemical Engineering (a
B.S. from Northeastern University) and Environmental Health (an M.S.
from the Harvard School of Public Health), and over thirty years of
experience in understanding and resolving indoor air quality issues,
Mr. Bearg has an in depth understanding of what it takes to achieve a
healthy indoor environment. His definitive book, Indoor Air Quality and HVAC Systems,
was published in 1993. His current efforts focus on Integrated
Performance Assessments to determine whether the various components of
a building and its HVAC systems are achieving, or not achieving, a
healthy indoor environment.
David Bearg through his efforts with Life Energy Associates helps clients achieve healthy and productive indoor environments, either proactively or in response to IAQ concerns.
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