One key point of Integrated Design is the acknowledgement that the various aspects of a building and its HVAC system interact. This is especially true with efforts to reduce energy consumption in a building, as these changes in building operation can adversely impact the amount of ventilation provided.
As an example I can point to a lighting retrofit project in a building served by a variable air volume (VAV) system. Since improved lighting technologies produce less waste heat, their implementation reduces the cooling load on the building. This in turn means that less cooling air will be provided to maintain thermal comfort. With no change in the percent of outdoor air in the supply air, the amount of ventilation will be reduced as well.
From a financial standpoint, this situation can be penny wise and dollar foolish. This is because on a square foot basis, people costs far exceed those of energy. I find that people costs in commercial buildings are around $300/SF, while energy costs are around $3/SF. This situation can illustrate how an energy saving effort can end up costing more money than it saves due to losses in productivity.
Let’s say a lighting retrofit saves 5% of a building’s energy use, or 15 cents/SF in this building with a VAV system, while the reduction in ventilation reduces the value of the worker productivity by just 1%. At around $300/SF for people costs, this 1% loss in productivity has a value of $3/SF. Pennies saved, dollars lost! So just focusing on energy, while ignoring healthfulness, can end up moving away from optimizing 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 it still would be revenue neutral.
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
Another relevant fact about the people in a building is that they emit carbon dioxide (CO 2) at a concentration of about 40,000 parts per million (ppm). Therefore monitoring CO2 levels through the day can provide a dynamic assessment of the relationship between these people, their numbers, their activity levels, their duration of occupancy and the ability of the ventilation component of the HVAC system to dilute and remove their bioeffluents.
Achieving a noticeable reduction in absenteeism by rapidly diluting and removing these air contaminants requires providing ventilation rates in excess of those listed in ASHRAE Standard 62.1. The ventilation rates listed in this Standard are merely intended to achieve “ACCEPTABLE” IAQ where at least 80% of those exposed are not dissatisfied. Or looked at another way, up to 20% CAN BE dissatisfied. Like the Building Code that defines the worst building you can legally build, ASHRAE 62.1 defines the lowest level of ventilation you can get away with. In both cases, quality increases when these Standards are exceeded. This fact also points out a limitation with the LEED™ approach to IEQ, which is merely based on achieving the ASHRAE Standard 62.1 listed minimums, which is not enough ventilation to actually provide a healthy indoor environment.
The operational challenge becomes one where you not only need to provide more ventilation than listed by ASHRAE 62.1, but you need to accurately know how much ventilation is actually provided to a building’s occupants. The key questions become: What are the most important things to know about building operations? And what is the best way to get that information?
The most accurate way to determine how much ventilation is actually being provided is to use 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. In Figure 1, there is data from one example where room-to-room variations in the amount of ventilation provided is shown. The underventilation events are occurring in Conference Rooms where the VAV systems are failing to open promptly as the controls wait for a rise in local temperature to provide the signal for more ventilation. In this example, the highest CO2 reading of 1,182 ppm, occurring when the outdoor air value was 426 ppm, implies that the ventilation rate provided could be no greater than 14 cfm/person, well below the ASHRAE listed minimum of 20 cfm/person. The CO2 data presented in this figure was collected by one of the shared sensor, so that all measurements for this parameter were measured with the same laboratory grade device. Using this monitoring approach makes it easy to measure absolute humidity as well so that moisture management performance, as well as ventilation performance can be assessed too. Remember, you can’t manage what you don’t measure. And similarly, the better something is measured, the better it can be managed.
David W. Bearg, P.E. at Life Energy Associates
