Summary

PDF

Item ID: 166

Demand-Controlled Ventilation

Ventilation: Condition Only As Much Outside/Ventilation Air Needed (Demand-Controlled) vs. Prescriptive Code Minimum Based on 100% Occupancy 100% of the Time

Ventilation in commercial buildings controlled by occupancy sensors – usually CO2 monitors – to provide just the required amount of outside air and to avoid over- or under-ventilating a space.

Synopsis:

Demand-controlled ventilation (DCV) measures carbon dioxide (CO₂) concentrations to determine ventilation needs and then matches the ventilation air delivered to demand. Ventilation is thus reduced when spaces are vacant or operating at lower than peak capacity. Energy savings result from reducing the need to heat, cool, or dehumidify outside air (FEMP, 2014).

Designers have been specifying DCV for over a decade in the more obvious applications – spaces with high but varied occupant density, such as gymnasiums, auditoriums, and large conference rooms. However, for much of that time, the CO₂ sensors that were used were unreliable, difficult to calibrate, and required frequent calibration. Now, more reliable and robust CO₂ sensors are available, and this strategy is being included in more codes for many spaces. As the technology and experience with it improves, it should be routine in spaces with high-but-varied occupancy, and it may be considered for other spaces that are not as large, dense, or varied in their occupancy, such as classrooms, smaller conference rooms, restaurants, and large open office areas. There are many opportunities to include this technology when retrofitting varied-occupancy spaces and in new construction of the secondary spaces.

The most common method to incorporate DCV into the design of an HVAC system is to adjust the amount of outdoor ventilation based on the level of CO₂ in the building air. The CO₂ level can be monitored by a sensor located in the occupied zone or in the return airstream. If not already available, an enthalpy-based economizer should be included in any retrofit project (Lawrence, 2004).

DCV energy savings vary considerably, depending on baseline ventilation rate and the use and occupancy patterns of the building. Lawrence Berkeley National Lab shows that, for office buildings in California climate zones, adopting DCV practices can provide savings of 1% to 7% of total building energy use (not HVAC energy use) (Hong, 2009). Savings are much greater for a building with a more variable occupancy pattern (such as a restaurant).

Energy Savings: 10%

Energy Savings Rating: Comprehensive Analysis What's this?

Level	Status	Description
1	Concept not validated	Claims of energy savings may not be credible due to lack of documentation or validation by unbiased experts.
2	Concept validated:	An unbiased expert has validated efficiency concepts through technical review and calculations based on engineering principles.
3	Limited assessment	An unbiased expert has measured technology characteristics and factors of energy use through one or more tests in typical applications with a clear baseline.
4	Extensive assessment	Additional testing in relevant applications and environments has increased knowledge of performance across a broad range of products, applications, and system conditions.
5	Comprehensive analysis	Results of lab and field tests have been used to develop methods for reliable prediction of performance across the range of intended applications.
6	Approved measure	Protocols for technology application are established and approved.

Details

PDF

Demand-Controlled Ventilation

Ventilation: Condition Only As Much Outside/Ventilation Air Needed (Demand-Controlled) vs. Prescriptive Code Minimum Based on 100% Occupancy 100% of the Time

Ventilation in commercial buildings controlled by occupancy sensors – usually CO2 monitors – to provide just the required amount of outside air and to avoid over- or under-ventilating a space.

Item ID: 166

Sector: Commercial

Energy System: HVAC--Sensors & Controls

Technical Advisory Group: 2010 HVAC TAG (#3)

Technical Advisory Group: 2009 HVAC TAG (#2)

Technical Advisory Group: 2015-1 Commercial HVAC TAG (#11)
Average TAG Rating: 3.3 out of 5
TAG Ranking Date: 03/10/2015
TAG Rating Commentary:

This does not seem like emerging technology to me.
This is required by code in several applications, and if the heat is gas, the savings will be gas.
It's commercial, if not ubiquitous. I think the issues are installation complexity, and maybe reliability, but matching ventilation rate to occupancy (and use intensity) seems like a great way to reduce energy waste.
Needs to have automated controls. I do not think it will perform well with manual controls.
There are a number of demos in CA showing significant savings
To achieve cost-effective energy savings, much care has to be taken to choose the correct application.
BPA should investigate current adoption trends; it might not have to be incentivized to achieve reasonable adoption.

Synopsis:

Baseline Example:

Baseline Description: Outside Air/Ventilation Air Set to Levels Required to Meet 100% Occupancy, 100% of the Time
Baseline Energy Use: 10.5 kWh per year per square foot

Comments:

The 2009 Commercial Building Stock Assessment gives the actual electrical building energy use index (EUI) for various types of heating and cooling systems (NEEA, 2009 Pg (Table) D-EA5). Office buildings with electric heating and cooling have an EUI of 20.1 kWh/sf/year. Office buildings with no electric heating or cooling use only 8.2 kWh/sf/year (non-HVAC end uses such as lighting and plug load), indicating that the combined HVAC heating and cooling energy use is 11.9 kWh/sf/year. For all commercial buildings, the corresponding EUI values are 19.9 and 9.4 kWh/sf/year, respectively, for a heating and cooling use of 10.5 kWh/sf/year.

Manufacturer's Energy Savings Claims:

Comments:

This is a strategy; therefore, there is not a manufacturer.

Best Estimate of Energy Savings:

"Typical" Savings: 10%
Low and High Energy Savings: 2% to 40%
Energy Savings Reliability: 5 - Comprehensive Analysis

Comments:

Calculating energy savings from this measure is challenging because most studies implement DCV along with other HVAC measures. Heating and cooling account for about 53% of the total annual energy use in a commercial building. If the use of DCV results in an assumed 6% reduction in total building energy use (as suggested by Hong), then the savings are approximately 6% x 20.1 kWh/sf/year = 1.2 kWh/sf/year. This is equivalent to a reduction in the heating and cooling energy use of: 1.2 /11.9 = 10%. (Office building savings are taken as representative of the entire commercial building stock.) FEMP claims that DCV has been shown to reduce energy costs by up to 38% of HVAC energy use in an office building. Lawrence Berkeley National Lab shows that, for office buildings in California climate zones, adoption of DCV practices can provide savings of 1% to 7% of total building energy use (Hong, 2009).

DCV energy savings depend on many factors, including:

• The baseline condition of the HVAC system

• Whether or not the building meets code

• Whether or not the building is over- or under-ventilated

• The code ventilation requirements in effect when the building was permitted

• Occupancy patterns and densities, and how they have changed over time

• Weather conditions (affect the amount of time the system is in economizer mode for temperature control versus at minimum outside air for ventilation control)

• Commissioning, calibration, and maintenance of CO₂ sensors (affect the persistence and amount of energy savings because designers may adopt conservative C0₂ setpoints and failure modes to account for sensor calibration and maintenance issues)

• Selected CO₂ setpoints and failure modes

Energy Use of Emerging Technology:

9.5 kWh per square foot per year What's this?

Energy Use of an Emerging Technology is based upon the following algorithm.

Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))

Technical Potential:
Units: square foot
Potential number of units replaced by this technology: 1,860,294,000
Comments:

Calculations for the areas where this technology may be applied are shown in the table below. These are taken from the preliminary data for the 2013 update to the Northwest Commercial Building Space Assessment (NEEA, 2014). The percentages of the floor area of each type of building to which this technology may apply are rough estimates.

Commercial Building Space in the Northwest where DCV may be Applied

Space Type	Total Area (sf)	Approx. % could be DCV	Target Area (sf)
Large Office	283,240,000	80%	226,592,000
Medium Office	127,610,000	80%	102,088,000
Small Office	149,740,000	80%	119,792,000
Big Box-Retail	134,190,000	80%	107,352,000
Small Box-Retail	247,840,000	80%	198,272,000
High End-Retail	61,960,000	80%	49,568,000
Anchor-Retail	119,630,000	80%	95,704,000
K-12	251,050,000	80%	200,840,000
University	128,170,000	80%	102,536,000
Warehouse	381,740,000	80%	305,392,000
Supermarket	60,820,000	90%	54,738,000
Restaurant	59,040,000	100%	59,040,000
Assembly	238,380,000	100%	238,380,000
Total	2,243,410,000		1,860,294,000

Regional Technical Potential:
1.95 TWh per year
223 aMW
What's this?

Regional Technical Potential of an Emerging Technology is calculated as follows:

Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)

First Cost:

Installed first cost per: square foot

Comments:

According to several sources, system costs can vary between $1,500 and $5,000, including installation, to retrofit a packaged HVAC system with one of the DCV strategies. Costs for large, built-up systems will vary depending on the required number and location of CO2 sensors.

Cost Effectiveness:

Simple payback, new construction (years): N/A

Simple payback, retrofit (years): N/A

What's this?

Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.

Comments:

Because savings are going to vary widely, it is difficult to quantify simple payback. The potential for savings is large, so this technology is expected to be highly cost-effective in buildings with occupancies of over 25 per 1,000 sf.

Detailed Description:

Ventilation can be one of the top energy uses in a high-occupancy building. Spaces designed for large numbers of people are required by code to have HVAC systems that can provide large amounts of outside air. However, these spaces are frequently only partially occupied or are unoccupied. A table developed by the American Society of Heating, Refrigerating & Air-Conditioning Engineers (ASHRAE) shows typical diversity of occupancy throughout the day (Washington State Building Code Council, 2012 Pg AE-34). Demand-controlled ventilation (DCV) represents an untapped potential source of energy savings for existing buildings and an excellent investment in new buildings.

CO₂ sensors are used to optimize the amount of ventilation air provided via the HVAC system. With a CO₂ sensor in the return air plenum, ventilation air will typically not need to be supplied until sometime after the room has been occupied. For HVAC systems serving multiple separate spaces, it is better to locate the CO₂ sensors in each space, three feet above the floor, and provide ventilation air whenever excessive CO₂is detected in any space. If the control system includes a motion sensor, the supply can be shut off the moment the room becomes unoccupied, regardless of CO₂ levels, but this may not be a cost-effective strategy.

DCV strategies typically include:

• Integrated fan cycling to meet ASHRAE 90.1 requirements.
• Variable frequency drive or two-speed fan motors for additional fan energy savings.
• Fleet ventilation systems for large retail applications. Fleet ventilation is a strategy for areas served by more than one system, which allows selected system(s) to provide all of the space ventilation needs and the remaining system(s) to cycle on and off to maintain temperatures.
• Carbon monoxide monitoring systems for parking garages.
• Motorized damper on outside air to modulate based on CO₂ levels.

This strategy is used routinely, and may not be considered emerging for new construction of large, variable-occupant-density spaces such as auditoriums, gymnasiums, conference rooms, and performing arts centers. This strategy should be considered for retrofitting these types of spaces, and for other spaces where occupancy fluctuates, such as large open office areas and classrooms.

Standard Practice:

The standard practice for HVAC ventilation is to provide the code-required minimum outside air, which typically specifies minimum ventilation for the maximum design occupancy at all times. However, it has been documented that many buildings do not meet this code baseline, and other buildings provide many times the required ventilation, especially when not fully occupied, and regularly ventilate unoccupied spaces.

Some corporate chains are already adopting DCV as standard practice, in advance of code requirements.

The option for CO₂ control has been included in ASHRAE 62.1 since 1999, and some codes require DCV for larger spaces with high occupant densities. Most codes refer to ASHRAE standards 62.1 and 90.1, which define both the minimum outside air requirements and how DCV can be applied. ASHRAE requirements have changed with every version.

The State of Oregon building codes allow DCV. A proposed code change would require DCV for larger spaces with high occupant densities.

The State of Washington building codes allow DCV via the use of "alternate methods" utilizing ASHRAE 62.1.

The State of Idaho adopted the International Building Code, which permits reduced ventilation during reduced occupancy.

The State of Montana adopted ASHRAE 90.1 for commercial spaces, which allows ventilation to be adjusted for variable occupancy.

Development Status:

CO2 sensors are commercially available, but accuracy and long-term calibration concerns, as well as application and integration issues have prevented widespread adoption. Programming of energy management systems has not been standardized and is a critical element of system operation.

End User Drawbacks:

Potential obstacles include difficulties integrating with an existing energy management system or economizer controller, and determining the appropriate location for the CO₂ sensor(s). An effective DCV system requires more careful design than a standard system. For instance, each space being served should have some form of occupant sensing. In some cases, multiple sensors may be needed. For example, a large variable air volume (VAV) system serving multiple spaces would require multiple sensors.

If operators are concerned with the accuracy and tolerance of CO₂ sensors, they may adopt conservative set points and failure modes, reducing the effectiveness of the strategy.

Other factors may govern the ventilation system design and operation, such as pressurization between spaces (e.g., between kitchens and dining rooms), release of contaminants that are a health hazard to occupants, and changes to the return and exhaust air controls. Some applications, such as movie theaters or performing arts centers, cannot tolerate fan cycling.

Public schools may be reluctant to implement this technology because it may raise concerns about indoor air quality (IAQ) among parents who are convinced that poor IAQ may be contributing to their child’s poor performance or rashes. This obstacle may be overcome by letting parents know that the school will take extra steps to ensure that the children have a constant supply of adequate ventilation air by monitoring each space 24 hours per day and adjusting the ventilation air supply as needed.

Operations and Maintenance Costs:

No information available.

Effective Life:

Comments:

A 15 year service life based on typical control systems, assuming sensor calibration or replacement at regular maintenance intervals.

Competing Technologies:

If variable frequency drives, energy-efficient motors, duty-cycling of fans, dedicated outdoor air systems (DOAS) and performance-tested HVAC are already in place, the energy savings of DCV systems will be less. However, these technologies can be combined with DCV systems to maximize savings.

Reference and Citations:

J. Zhang, et. al., 01/01/2013. Energy Savings for Occupancy-Based Control (OBC) of Variable-Air-Volume (VAV) Systems
PNNL
Special Notes: Report on increased savings achievable in offices with advanced occupancy sensors that can determine how many people are in the occupied space.

ASHRAE, 10/01/2009. Standard Benchmark Energy Utilization Index
ASHRAE

Marty Stipe, 06/01/2003. Demand-Controlled Ventilation: A Design Guide
Oregon Office of Energy for the Northwest Energy Efficiency Alliance

NEEA, 01/01/2014. Total Pacific Northwest Building Stock Based on Preliminary Numbers from the 2013 Update to the CBSA
Northwest Energy Efficiency Alliance

CADMUS, 12/21/2009. Northwest Commercial Building Stock Assessment (CBSA): Final Report
Prepared by the CADMUS Group for the Northwest Energy Efficiency Alliance

Mike Schell, 03/25/2003. Demand Control Ventilation Using CO2
ASHRAE Journal

Oregon DOE, 02/10/2014. Demand-Controlled Ventilation Case Study
Oregon Department of Energy

Bill McConnell, 08/05/2007. Demand-controlled ventilation
Modern Building Services

Carrier, 11/09/2005. Demand Controlled Ventilation System Design
Carrier

Manitoba Hydro, 02/11/2014. Carbon Dioxide (CO2) Sensors
Manitoba Hydro

Green Business, 01/15/2009. California Investor-Owned Utilities Partnering for Energy Efficiency Rebates
www.greenbizsbc.org

William Goetzler. et. al., 09/30/2012. Energy Savings Potential and Research, Development, & Demonstration Opportunities for Residential Building Heating, Ventilation, and Air Conditioning Systems
Prepared by Navigant Consulting for U.S. DOE Building Technologies Office

Tianzhen Hong, 07/08/2009. Assessment of Energy Savings Potential from the Use of Demand Control Ventilation Systems in General Office Spaces in California
Lawrence Berkeley National Laboratory

Tom Lawrence, 12/01/2004. Demand-Controlled Ventilation and Sustainability
ASHRAE

Washington State Building Code Council, 1/1/2012. 2012 Washington State Energy Code
Washington State

FEMP, 1/1/2014. Promising Technologies List
U.S. DOE Federal Energy Management Program

Rank & Scores

PDF

Demand-Controlled Ventilation

2015-1 Commercial HVAC TAG (#11)

Technical Advisory Group: 2015-1 Commercial HVAC TAG (#11)
TAG Ranking: 8 out of 29
Average TAG Rating: 3.3 out of 5
TAG Ranking Date: 03/10/2015
TAG Rating Commentary:

This does not seem like emerging technology to me.
This is required by code in several applications, and if the heat is gas, the savings will be gas.
It's commercial, if not ubiquitous. I think the issues are installation complexity, and maybe reliability, but matching ventilation rate to occupancy (and use intensity) seems like a great way to reduce energy waste.
Needs to have automated controls. I do not think it will perform well with manual controls.
There are a number of demos in CA showing significant savings
To achieve cost-effective energy savings, much care has to be taken to choose the correct application.
BPA should investigate current adoption trends; it might not have to be incentivized to achieve reasonable adoption.

2010 HVAC TAG (#3)

Technical Advisory Group: 2010 HVAC TAG (#3)
TAG Ranking:
Average TAG Rating:
TAG Ranking Date:
TAG Rating Commentary:

2009 HVAC TAG (#2)

Technical Advisory Group: 2009 HVAC TAG (#2)
TAG Ranking:
Average TAG Rating:
TAG Ranking Date:
TAG Rating Commentary:

Technical Score Details

TAG Technical Score: 3.2 out of 5

How significant and reliable are the energy savings?
Energy Savings Score: 3.3 Comments:
Jan 2010 Comments: 1. Energy savings should be good. 2. Difficult to quantify daily and seasonal energy savings because of varying occupancies -mostly heating savings. Some strategies allow greater fan savings. 3. DCV is one of the most promising energy efficiency technologies. 4. New construction: Several codes require DCV in high potential applications; therefore savings will be limited. Retrofit: More savings potential, simply because there are fewer existing facilities that are using DCV, even in areas with high savings potential. How great are the non-energy advantages for adopting this technology?
Non-Energy Benefits Score: 3.1
Comments:
Jan 2010 Comments: 1. It's become pretty common in Seattle. Required by code for high density occupancy. 2. Good potential for energy savings. 3. Can provide better IAQ, but not always 4. Provides a way to meet ASHRAE 62.1 requirements, other than withfixed high percent of outside air or savings energy but not providing adeqaute ventilation air quantities. 5. Essentially there are no non-energy benefits. 6. Depends on particular zone/ space type. Some spaces (e.g. gym, auditorium) are no-brainers. Others such as office areas probably have less potential savings. How ready are product and provider to scale up for widespread use in the Pacific Northwest?
Technology Readiness Score: 4.9
Comments:
Jan 2010 Comments: 1. Lots of good products are available, with good competition. 2. Not "plug and play" technology yet 3. Some contractors are better and more knowledgable than others. See earlier comments on whether this is an "emerging technology." How easy is it to change to the proposed technology?
Ease of Adoption Score: 2.3
Comments:
Jan 2010 Comments: 1. It requires some maintenance competency. 2. Simple concept, but can be complicated to install -especially in VAV (location of CO2 sensor, sequence and strategies that meet ventilation code, while minimizing energy use) and interoperability with economizers 3. Simple for users. 4. DCV is not a simple sequence to re-engineer if it is ever lost or altered. 5. I have seen very few contractors proposing a sequence of operation that would control air to the zone before modulating the OSA damper. It would be good to include a "best DCV practices guide" for customers and contractors. And provide a verification protocol which will be used after installation, something which the installer and owner will see ahead of the project. Considering all costs and all benefits, how good a purchase is this technology for the owner?
Value Score: 2.4
Comments:
Jan 2010 Comments: 1. Depends on application 2. Just a guess.... 3. Paybacks will vary; need application guideline for best paybacks 4. Depends on application/occupancy 5. Electric fan-only payback is not so great. Good with electric heat, but these systems are not so common. 6. Payback is highly dependent on occupancy of space served. In densly occupied spaces, payback is extremely fast (~3 years). In standard commercial spaces, payback would be over 5 years. 7. Depends on size of zone.

Completed:
4/12/2010 2:43:50 PM
Last Edited:
10/26/2010 2:11:25 PM

Market Potential

PDF

Demand-Controlled Ventilation

Last Edited:

7/3/2011 3:25:28 AM by E3TUser

Market Segment:

DCV is most applicable to commercial spaces that have significant ventilation requirements, but ventilation needs vary widely and are unpredictable. Places of assembly, such as gymnasiums, auditoriums, lecture halls, conference rooms, churches and theaters are good applications for DCV. These spaces are designed for a high occupancy and need for a large volume of outside air. See EES report for more details.

Regional Fit:

CO2 based DCV has energy savings potential in office buildings, government facilities, retail stores, shopping malls, movie theaters, auditoriums, schools, etc. This technology is for any building in the country with mechanical ventilation. The ventilation code sets a ventilation rate that is conservative with respect to how buildings are actually used. This proposal allows us to capatilize on actual building operation.

Zones:

Heating Zone 1, Heating Zone 2, Heating Zone 3, Cooling Zone 1, Cooling Zone 2, Cooling Zone 3

Performance Trajectory:

DCV is already available in wireless lasting 2-3 years between battery changes. Furthermore, sensors today are self calibrating.

Product Supply and Installation Risk:

This technology is not unlike economizers, and therefore is subject to evolve as any other mechanical system. It is already available in wireless and is self-calbrating. However, problems have occured when using a 2-position actuator instead of a modulating actuator. With the 2-position, the space temperature flucuated and the space felt drafty when the damper went to full open position. We need to use a 4-20 mA signal with a time delay between readings, ~5 minutes)

Technical Dominance:

This technology is relatively low first cost, usually less than 2 year payback, and when set up properly, has virtually no maintenance.

Market Channels:

Initially, having the utilities provide financial incentives to help with the added first cost would help bring awareness of DCV to Building Owners, Contractors and Engineers. Further, writing a white paper for the Engineering, Construction, and Building Owners would be a big boost.

Regulatory Issues:

We have not found any resistance once the technology is explained.

Other risks and barriers:

There will be some who will object to reducing the amount of outside air to the building for concerns of inability to flush toxins from inside the building. An understanding of how ventilation rates are determined usually puts this concern to rest.

Basis of Savings:

Ventilation rates are determined via the Mechanical Code and are based on the use of the space. For each usage, we can calculate the amount of energy needed per square foot to condition the ventilation air for that geographical location using degree days. We would then need to make an educated estimate of the diversity we could see. Studies show 0.4 to 2.2 year paybacks and an average savings of about ~$0.50/sf annually.

Completed:

4/19/2010 11:56:56 AM by Emily Salzberg

Your Technical Feedback

The technical feedback form may be used to submit further information about Demand-Controlled Ventilation. When possible, please list your references and sources of information.