Controls for high outside air ventilation applications

Published: February 6, 2014


Save energy while maintaining high air quality

Some commercial buildings require a continuous exchange of fresh outside air to ensure high levels of air quality and reduce potential contamination. These buildings, such as hospitals, laboratories and life science buildings, typically have high energy loads related to ventilation. Other commercial building types, such as schools and office buildings, employ outside air systems for the benefit of the building's occupants. Buildings with outside air systems have unique energy challenges. Not only does the air need to be continually circulated throughout the HVAC system, but outside air also needs to be conditioned before being distributed into the space increasing heating and cooling loads in comparison to buildings that do not require 100% outside air. Until recently, building codes required a one-size-fits-all ventilation system for these buildings. Now, however, more and more building professionals are employing controls to maximize both safety in the building as well as reduce energy consumption.

Operating room

Modulating ventilation in high outside air ventilation applications requires controls that can determine whether the air change rate can be lowered when a space is unoccupied or increased when contaminants are found in the air. These controls can be simple, such as a switch or occupancy sensor, or complex, such as sensors that centrally and continually sample the air to ensure there are no contaminants. While these control systems can have significant up-front costs, they are being used in more and more buildings because those costs are paid back in a short time as a result of reduced ventilation loads and subsequent lower operating costs.

Key components

Economizer or air makeup unit

These components control the amount of outside air brought into the building.

Control sensors

These devices measure occupancy to determine how much fresh air is needed. Occupancy can be measured by carbon dioxide sensors or occupancy sensors.Ventilation can also be scheduled according to set times of occupancy (as in school classrooms).

Direct digital control

A control system using digital processors to directly control the HVAC equipment. If the building has multiple zones, then the DDC system communicates information from each zone to a central control panel.



Implementation costs

Aircuity systems - $4-5 per square foot for advanced measurements
Aircuity systems - $2-$3 per square foot for humidity and CO2 control

Potential energy savings

DCV - 30-50% of buildings energy costs

Market barrier(s)

lack of technical knowledge
technological barriers

Controls for high outdoor air systems have the most impact in commercial buildings where occupancy is intermittent and/or there is a need for high levels of fresh air changes. These applications include:


Hospitals typically have stringent rules about ventilation rates to ensure the highest level of protection and safety for patients and staff. For example, operating rooms need to have a positive pressure with respect to adjoining spaces to ensure that particulate transfer is kept to a minimum. State and federal code requires a minimum of 20 air change per hour (ACH) total and 4 ACH of outdoor air when the room is occupied and being used (ANSI/ASHRAE/ASHE Standard 170-2008: Ventilation of Health Care). Using advanced ventilation strategies, when the room is unoccupied, the ventilation rates are allowed to decrease given that the pressure and humidity requirements are being met. This potential reduction in ACH can offer savings in operating rooms that are intermittently being used. The control strategies that are used for this may include a time schedule program, occupancy sensor or a manual switch that is activated when the room is occupied. Each type of control mechanism should be considered in light of the users’ needs and preferences.


Laboratory energy use is typically the highest among commercial building energy use and one fume hood in a lab can use 3 times more energy than a typical home if constantly ventilating fresh air (PGE). To control potential contaminants, high amounts of airflow is required to circulate throughout the labs, typically exhausted through fume hoods that maintain high airflow rates. Lab users are protected from hazardous gases by working under fume hoods which induce contaminant air out of the room, but at the high cost of conditioning large amounts of air. Fume hoods can benefit from controls such as occupancy sensors and sash controllers that lower the sash when unoccupied, thereby reducing the velocity of air moving out of the room ( These systems function with variable-air-volume fume hoods and can see savings of over 50%, although the savings are only seen when the sash is in the closed position. (PGE study)

Schools and Offices

Smaller commercial buildings may also have high outdoor air ventilation systems, although this is more typical in newer buildings. There are still control mechanisms that may help reduce ventilation energy load, such as demand control ventilation and more advanced systems like Aircuity.

The building types above can also reduce ventilation rates by measuring contaminants in the air and changing the ventilation rates to meet the demand -- or lack of demand -- for clean fresh air. Demand control ventilation (DCV) is the simplest version of this concept which uses carbon dioxide sensors to modulate ventilation. A newer technology called Aircuity moves beyond a one-point measurement and allows for a multi-parameter DCV, taking measurement of various potential pollutants and adjusting ventilation rates when the levels become too high. The parameters may include total volatile organic compounds (TVOC), fine particles, carbon monoxide, formaldehyde, and relative humidity. The sensors are calibrated regularly to ensure that they measure the pollutants accurately.

Service shops and garages

Automotive service shops and garages oftentimes have high levels of pollutants from the vehicles being worked on in the shop. Sensors that measure indoor air pollutants such carbon monoxide and NOx (nitric oxide and nitrogen dioxide) can be tied to a ventilation system to ensure that mechanics and employees are breathing fresh air. This greatly increases the health of building occupants.


Lower ventilation energy translates to lower energy costs: in highly ventilated buildings, like hospitals, ventilation energy costs can comprise of nearly 40% of total energy costs. With demand control ventilation, ventilation rates can be reduced, translating into significant energy savings.

Air quality improvements in commercial buildings: bringing in fresh outdoor air has been shown to improve indoor air quality, making the indoor space more comfortable and healthy for its occupants.

Challenges and market barriers

Difficulty with Environmental Health and Safety codes: convincing Environmental Health and Safety officials to lower the ventilation rate may pose a challenge for hospitals and laboratories. While much of the research shows that lowering ventilation rates during unoccupied times is safe, there is a long institutional history of over-ventilating to ensure safety. This challenge can be overcome with transparency and communication between designers and code officials.

Retrofits for Demand Control Ventilation must include VAV controls: unless the building already has direct-digital controls, variable-air volume and manifolded exhaust fans, a retrofit to DCV may be too cost-prohibitive in existing buildings.

Sensor maintenance: in multi-parameter DCV, the sensors often need frequent calibration and maintenance, oftentimes every six months. While this maintenance is typically included in contracts with sensor and control manufacturers, it is still an added level of maintenance that building manager will need to address.

Statewide energy savings

We took a high-level look at the potential energy savings in Wisconsin from controls for high outside air ventilation applications. The estimate is meant to provide a sense of scale showing the impact these control technologies might have on Wisconsin energy customers. While demand control ventilation is gaining popularity in certain commercial sectors in Wisconsin, adoption of advanced controls for high outside air applications is low.

To estimate statewide impacts, we assumed that controls for high outside air applications would be a retrofit opportunity in the following sectors: education, food service, health care, office, public assembly and service (according to the principal building types of the Commercial Energy Consumption Survey). We applied a technical savings rate of 30% of HVAC energy in these sectors. We assumed an applicability rate of 25%.

All data used for these estimates are from the Wisconsin Energy Statistics (2012) and Department of Energy's Commercial Energy Consumption Survey data (2003).

Financial incentives

There are not currently financial incentives available for these controls specifically. However, Focus on Energy offers custom incentives for Business customers and Large Energy User.

Custom incentives until end of 2014:
- $0.04/kWh
- $125/peak kW
- $0.40/Therm + $0.

Contact Focus on Energy to find out more.

Wisconsin Institutes for Discovery

The showcase laboratory building in the center of UW-Madison's campus demonstrates a number of cutting edge energy efficiency technologies. The building was designed to be one of the most energy efficient laboratories in the country and one of the ways it achieves those efficiencies is through variable air volume (VAV) controls in their fume hoods. When not in use, ventilation rates go down by 50%, which translates into high savings. MORE

Aircuity case studies

In Fort Dodge, Iowa, the Central Community College serves 6,000 students. The campus recently expanded to include a new Bioscience and Health Sciences Building to address the workplace needs of biotechnology and healthcare sectors. To help meet the building's sustainability goals, the design team decided to include a centralized demand control ventilation system for the lab space of the building. Aircuity's system continually monitors the air quality in approximately 5,000 square feet of lab space. When sensors detect contaminants above a certain threshold, the ventilation is increased to ensure that the contaminants are removed. As the air becomes cleaner, the sensors automatically reduce the ventilation to save energy. MORE

Operating room case study

In Providence St. Peter Hospital in Olympia Washington, the operating rooms are configured with a nighttime setback that reduces the ventilation rates to 15 air changes per hour (ACH), employing sensor controls to determine when the rooms become occupied. These sensors include both infrared (movement) and ultrasonic (sound) sensors. They estimated the payback for this system to be 8.6 years. MORE

Operating Room HVAC Setback Strategies

summary This paper, written by the American Society for Healthcare Engineering, provides a detailed background on opportunities and considerations for operating room HVAC setback strategies. Types of setbacks strategies are discussed, with focus on factors to consider when deciding if a setback strategies is right for a particular space.
citation The American Society for Healthcare Engineering (ASHE). (2011) Operating Room HVAC Setback Strategies. American Hospital Association, Chicago, IL. LINK

Optimizing Laboratory Ventilation Rates

summary This best practice guide is one in a series by the program Labors for the 21st Century which works to provide information about efficient ways to safely design, construct and operate high performance laboratories. This particular best practice guide focuses on ways to optimize ventilation air flow and its associated energy costs while still maintaining the high levels of safety required for laboratories. It refutes the common rule of thumb that "more is better" when designing for ventilation rates and discusses the best practice of optimizing rather than maximizing ventilation.
citation Geoffrey Bell. (2008). Optimizing Laboratory Ventilation Rates. Lawrence Berkeley National Laboratory. LINK

Smart Laboratories Cut Energy Consumption More Than Half

summary This fact sheet provides an overview of the Smart Labs concept that University of California-Irvine spearheaded. The concept of reducing the air changes per hour of laboratories was tested in the Smart Labs Project pilot program. The program includes an integrated set of laboratory design criteria and performance standards. This information sheet also discusses how the Smart Lab concept may be incorporated into retrofit opportunities.
citation University of California, Irvine. (2013) Smart Laboratories Cut Energy Consumption More Than Half: Better Buildings Challenge Demonstration Project. University of California, Irvine. LINK

Assessment of Energy Savings Potential from the Use of Demand Controlled Ventilation in General Office Spaces in California

summary This research was conducted by Lawrence Berkeley National Laboratory and examines the energy savings derived from utilizing a demand control ventilation system in California office buildings. The researchers modeled various ventilation strategies using EnergyPlus simulations. Their results show that DCV is only cost effective for office spaces if the typical minimum ventilation rate with DCV is 38 L/s per person. While these results are specific to California, this research demonstrates that cost-effectiveness of DCV is dependent on occupancy patterns and baseline ventilation conditions.
citation Tianzhen Hong and William J. Fisk. 2010. Assessment of Energy Savings Potential from the Use of Demand Controlled Ventilation in General Office Spaces in California. Ernest Orlando Lawrence Berkeley National Laboratory. LINK

A Review of Demand Control Ventilation

summary This paper provides background and update on demand control ventilation (DCV) technology for commercial buildings, its penetration and acceptance in the market, and to identify what evidence there is that such systems are benefiting current building stakeholders in terms of energy savings, improved indoor environmental quality, and reduced complaints. The paper also provides a basis for a study design to assess the effectiveness of existing DCV systems operating under real conditions. (summary excerpted from the paper).
citation Michael G. Apte. (2006) A Review of Demand Control Ventilation. Ernest Orlando Lawrence Berkeley National Laboratory. LINK

The Impact of Demand-Controlled and Economizer Ventilation Strategies on Energy Use in Buildings

summary This article, while written in 1999, provides a good overview of the issues surrounding constant volume air systems and demand controlled ventilation. Researchers analyzed demand controlled ventilation (along with economizers) in various combinations for four typical buildings, eight ventilation strategies and twenty US climates. The ventilation strategies were modeled through a computer simulation (DOE2.1E). This research also provides information on economizer ventilation as a means to reduce energy use. The results from this study show that energy savings could be significant, and greater savings are possible in buildings with large variability in occupancy and relatively high internal gains.
citation Brandemuehl, Michael J. and James E. Braun. (1999) The impact of demand controlled and economizer ventilation strategies on energy use in buildings. ASHRAE Transactions 105(2) LINK

Demand-controlled ventilation: Control strategy and applications for energy-efficient operation

summary This report/brochure was written by Siemens, a global company that provides building systems solutions. The brochure describes the benefits of demand-controlled ventilation, how to design and commission DCV systems and examples of how systems are implemented in practice.
citation Siemens. (2010) Demand-controlled Ventilation: control strategy and applications for energy-efficient operation. Accessed April 12, 2014. LINK

Energy Efficient Building Environment Control Strategies Using Real-time Occupancy Measurements

summary This study examined occupancy of large multi-function building by installing a wireless camera sensor network. Using data collected through this sensor network, the researchers developed a model to predict user modality patterns in buildings.With this model, they were able to predict usage and thereby control HVAC systems in an adaptive manner. Their simulations predicted a 14% reduction in HVAC energy usage by optimizing according to occupancy patterns.
citation Varick Erickson, et. al. (2009) Energy Efficient Building Environment Control Strategies Using Real-time Occupancy Measurements." Proceedings of the 1st ACM Workshop On Embedded Sensing Systems For Energy-Efficiency In Buildings (BuildSys 2009) in conjunction with ACM SenSys. Berkeley, CA. LINK