Protecting Indoor Air Quality with Demand Control Ventilation

Lights, camera, air quality

How movie theaters can keep audiences of every size comfortable

In a large theater it can be a major production to keep moviegoers comfortable. Ventilation needs are changing constantly, depending on whether the movie showing is a blockbuster or a bomb, playing during a matinee or opening night. The more people in the theater, the bigger the problem of providing acceptable indoor air quality (IAQ). People — and the CO2 they breathe out — have a real impact on IAQ; the bigger the audience, the more fresh air needed to fix the problem. Too much fresh air, driving the cost of heating and cooling, can cause energy bills to skyrocket.

Fresh air needs vs. energy spending

Today, many major theater chains, large retail chains and other businesses are keeping customers comfortable with Demand Control Ventilation (DCV), which controls the amount of fresh air introduced according to the number of occupants. Lennox has developed a unique, advanced DCV system in partnership with Novar®, a building control manufacturer focused on energy management controls. In the past two years, Lennox has used the system in more than 20 projects, including auditoriums and hotel lobbies. L Series® and S-Class™ packaged rooftop units from Lennox are the industry's only rooftop units that can automatically control outside air dampers without the addition of a DDC system. This full measure of control is also available with T-Class™ packaged rooftop units from Lennox that have the modulating economizer option installed.

Controlling fresh air based on carbon dioxide levels

Demand control ventilation estimates the number of people in the building based on current carbon dioxide levels (using a CO2 sensor) and then signals the rooftop unit controller. To minimize the need for mechanical cooling, a gear-driven economizer modulates according to outside air temperature. The unit controller overrides the outside air damper according to CO2 levels, forcing it to the appropriate position based on occupancy. (The damper will stay wide open to accommodate blockbuster crowds, but it would remain in the minimum position for a nearly empty matinee.)

Overriding the outside air damper is possible only with a modulating economizer damper; otherwise, someone would have to be sent to the roof every time the CO2 measurement changed.

A simple and efficient system

The integrated controls make Lennox' DCV system efficient and simple to use. The CO2 measurement is read by Lennox' factory-mounted Integrated Modular Controller (IMC) or the Novar® ETM-2051 unit controller. A signal is sent based on the CO2 measurement, overriding the damper position to minimize energy use and ensure a comfortable, healthy environment. The user-friendly design allows theater or store managers to monitor CO2 levels and other information, including alarms, on-site or from a remote location.

All Lennox economizers are gear-driven without linkages. Gear-driven economizers mean less maintenance, because they eliminate binding and reduce the need for adjustment. This helps ensure the correct amount of fresh outside air is always available to maintain comfort and minimize energy usage.

Businesses feel the benefits of improved IAQ

Theaters aren't the only businesses that get tangible benefits from improving indoor air quality. Poor IAQ can lead to a range of problems, from undesirable odors to sick building syndrome. It can not only make people uncomfortable, it can also make them sick. The preeminent standard for maintaining air quality through ventilation is ASHRAE (American Society of Refrigeration and Air Conditioning Engineers) Standard 62-2001.

Meeting ASHRAE needs

ASHRAE's "Ventilation for Acceptable Indoor Air Quality" prescribes ventilation rates necessary to maximize comfort while minimizing energy use and liability concerns. The standard is continually evolving as knowledge of how best to address air quality concerns increase. This standard is taken into consideration and incorporated into many local building codes to promote best practices with respect to ventilation for maintaining air quality. ASHRAE standards define acceptable IAQ as "...air in which there are no known contaminants at harmful concentrations...and with which a substantial majority (80% or more) of the people exposed do not express dissatisfaction."

According to ASHRAE studies, about 15 CFM of ventilation air per person is adequate to dilute body odor to an acceptable degree. Per ASHRAE's standard, CO2 is not considered a "specifiable contaminant," but is only an indicator of level of occupancy. CO2 can be measured easily, cheaply and accurately. Many other contaminants cannot. Demand control ventilation is only one of the ways Lennox is helping companies to protect the health of their customers and employees.