April 2004

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Productivity and Health vs. Energy Penalties - the Outdoor Air Riddle
We can have our outdoor air - and energy efficiency too. 

Leonard A. Damiano, 
V.P. Sales & Marketing


Contributing Editor

The objectives of business and governments must include the health, safety and comfort of their employees and visitors. Employee productivity improvement is often viewed as a "nice" byproduct from satisfying these obligations, principally due to the difficulty in measurement and the lack of specific and directly applicable studies. Thus, the issue providing the largest potential investment return is consigned to a much-diminished level of priority.

Building operators are generally motivated to minimize their operating budgets and are not involved in general policy discussions. The overall priority is often subverted by operational imperatives. Facilities engineers tend to act on those issues that cut cost or reduce complaints, and not those can improve productivity or health of their buildings' occupants.

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Productivity improvement and efficient energy management are not mutually exclusive objectives. To support and underscore this conclusion, I have selected for summary two fairly recent studies that point to the expectation that we can simultaneously reach both goals, without sacrificing either one.

The first involves school buildings, which generally have fewer dollars to spend on their operation per sq. ft., than do for-profit organizations. Pinching facility operation's pennies is more of a way of existence, than it is an irregular budgetary tactic. The second is a newer and broader study commissioned by the U.S. EPA on the impacts of increasing ventilation rates, primarily directed at the large U.S. stock of commercial buildings. The conclusions that are reached relative to building design and energy usage are just as valid today as they were in the late '90's.

Both studies were performed by independent governmental agencies or by scientific research contracted by governmental agencies. All contributors are highly qualified and well respected.

School Buildings

The Energy Solutions Division of Scientific Applications International Corp. (SAIC) completed evaluations of four state schools between July 1995 to November 1996. In four schools studied by SAIC for the New York State Energy Research and Development Authority (NYSERDA) 1, the energy penalty did not preclude increasing outdoor air ventilation rates to meet ASHRAE Standard requirements of 15 cfm per occupant in classrooms. The summary also illustrates that implementing energy conservation measures (ECMs) could offset any increase in energy consumption resulting from higher ventilation rates. In fact, energy cost savings are possible through implementing ECMs and increasing ventilation. Depending on baseline ventilation rates and the type of ventilation measures, the NYSERDA studies illustrate the following:

In one case, the ECMs planned by the school could easily offset the rise in energy consumption caused by increased ventilation rates. "In fact, net future facility cost energy savings of 9.1% (15.1% - 24.2%) are possible with the ECMs and increased ventilation." 1 This equates to $6.48 per occupant per year.

Technical research has provided us with many references that conclude increased ventilation rates do not necessarily need to result in increased energy costs. In new designs, with the proper attention and intelligent selections of control components and building materials, a balance can be struck between the seemingly conflicting objectives.

Office Buildings

"Energy Cost and IAQ Performance of Ventilation Systems and Controls" was published by the EPA in 19992. Although this study was primarily concerned with the increases in ventilation required by ASHRAE Standard 62-1989 vs the 1981 version (20 vs, 5 cfm/person), the analysis is still applicable, as are their conclusions. Some of their key findings included the following:

VAV Systems Save Energy: Variable air volume systems provided $0.10 - $0.20 energy savings per square foot over constant volume systems.

VAV with Fixed Outdoor Air Fractions Caused Outdoor Air Flow Problems: VAV systems may require a different outdoor air control strategy at the air handler to maintain adequate outside air for indoor air quality than the constant volume predecessor. If the fixed outdoor damper strategy of the CV system, which is commonly used in the VAV systems, results in a fixed outdoor air fraction, the outdoor air delivery rate at the air handler will be cut to about one half to two thirds the design level during most of the year.

Core Zones Received Significantly Less Air than Perimeter Zones and space temperatures tended to be higher: Both CV and VAV systems provided an unequal distribution of supply air and outdoor air to zones. The south zone received the highest and the core zone received the least outdoor air. The core zone received only about two thirds of the building average outdoor air flow and had higher space temperatures.

Core Zones in VAV Systems with a Fixed Outdoor Air Fraction Received Very Little Outdoor Air: The VAV system with fixed outdoor air fraction diminished the outdoor air delivery to the core zone to only about one third of the design level. With a design level of 20 cfm of outdoor air per occupant, the core zone received only 6-8 cfm per occupant, and only 2-3 cfm per occupant with a design level of 5 cfm per occupant. Along with higher temperatures in the core zone, this shortfall could contribute to higher indoor air quality complaint rates in the core relative to the perimeter zones.

VAV with Constant Outdoor Air Control Displayed Improved Indoor Air Performance without any Meaningful Energy Penalty. A VAV system with an outdoor air control strategy that maintains the design outdoor air flow at the air handler all year round had slightly lower energy cost in the cold climate, and slightly more energy cost in the hot and humid climate. It is therefore comparable in energy cost, but preferred for indoor air quality.

Economizers on VAV Systems May Be Advantageous for Both Indoor Air Quality and Energy in Cold and Temperate Climates. By increasing the outdoor air flow when the outside air temperature (or enthalpy) is less than the return air temperature (or enthalpy), economizers can reduce cooling energy costs. For office buildings, economizers may operate to provide free cooling even at winter temperatures (e.g. at zero degrees Fahrenheit), provided that coils are sufficiently protected from freezing. For the office building, energy savings of about $0.05 per square foot were experienced by the VAV system economizer over the non-economizer VAV system in cold and temperate climates. The economizer on the CV system was much less advantageous due to increases in heating energy costs for this system, and was actually more expensive under some utility rate structures.

VAV with Constant Outdoor Air Control and an Economizer Offers Significant Advantages, while VAV with Fixed Outdoor Air Fraction and No Economizer offers offers Significant Disadvantages: Of all the ventilation systems and controls studied, the VAV system with constant outdoor air flow, which in cold and temperate climates is combined with an economizer and proper freeze control and humidity control, provided the good overall performance considering outdoor air flow, thermal comfort and energy efficiency. The VAV system with a fixed outdoor air fraction and no economizer provided the poor overall performance because it failed to deliver adequate outdoor air and had no energy benefit.

Raising Outdoor Air to Meet ASHRAE Standard 62-1989 in Office Buildings Resulted in Very Modest Increases in Energy Costs. Raising outdoor air flow from 5-20 cfm per occupant in office buildings typically raised HVAC energy costs by only $0.02 - $0.08 per square foot (2% - 10%) depending type of system and climate. Considering the total energy bill, this increase amounted to approximately 1% - 4%. This is much less than is commonly perceived by practitioners. The cooling cost increases in the summer months were counterbalanced by cooling cost savings during cooler weather. Cost increases were higher for economizer systems than systems without economizers because much of the cost savings from higher outdoor air flow rates during cooler weather was already captured by the economizer system. The most significant factor affecting this increase was occupant density.

Contrary to Conventional Wisdom, the Impact of Raising Outdoor Air Flow Rates in High Occupant Density Buildings may be Least in Hot Humid Climates. While raising outdoor air flow rates in the education and auditorium buildings raised cooling costs in Miami more than it did in Minneapolis and Washington, D.C., this was more than offset by the high increase in heating and fan energy these climates which was not experienced in Miami. The net result was much less relative impact in Miami.

Energy Recovery Technologies May Potentially Reduce or Eliminate the Humidity Control, Energy Cost and Sizing Problems Associated with ASHRAE Standard 62-1989 in Education Buildings, Auditoriums, and Other Buildings with Very High Occupant Density.

Control Solutions, Inc Protecting or Improving Indoor Environmental Quality During Energy Efficiency Projects May Not Hamper Energy Reduction Goals. Many energy efficiency measures with the potential to degrade indoor environmental quality appear to require only minor adjustments to protect the indoor environment. When energy efficiency retrofit measures (including lighting upgrades), which were adjusted to either enhance or not degrade indoor environmental quality, were combined with measures to meet the outdoor air requirements of ASHRAE Standard 62-1989, total energy costs were cut by 35% - 45%. Operational measures compatible with indoor environmental quality cut total energy costs by 10%-20%. Avoiding operational measures that degrade indoor environmental quality meant that total energy reductions of only 3%-5% in the office building, and 7%-10% in the education building were foregone. There appears to be demonstrable compatibility between indoor environmental goals and energy efficiency goals, when energy saving measures and retrofits are applied wisely.

This study is now 5 years old and appears to have been seldomly quoted. The drafters of our ventilation standards and codes should take note of these conclusions and not ignore them. The U.S. Green Building Council reflects these traditionally contradictory goals through the promotion of the LEED Green Building Rating Program.3 A growing number of local and state governments are using the LEED Rating System a viable tool in the promotion of energy efficiency and sustainable public building programs.

Don't let anyone make you chose between these desirable and attainable objectives. We can have our outdoor air - and energy efficiency too. We need only make them priorities in mechanical system design and not to compromise when pressured by short-term construction costs.


1 Science Applications International Corporation (SAIC), Energy Solutions Division, "Evaluation of Increased Ventilation Rates and Energy Conservation Measures at Four New York State Schools", 1997(?)
2 U.S. Environmental Protection Agency, Indoor Environments Division, "Energy Cost and IAQ Performance of Ventilation Systems and Controls", 1999. 
3 U.S. Green Building Council, LEED Rating System v2.2 (draft language for 2004), http://www.usgbc.org 

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