LBNL research investigates both the IAQ and energy performance of ventilation systems. ASHRAE has has partially integrated these performance principles into the current 62.2-2016 ventilation standard in the United States and Canada. Some state building regulations, such as the California’s Title 24 energy-performance regulation, require compliance with this standard.
The ASHRAE Standard
ASHRAE standard 62.2-2016 gives a method to calculate the minimum constant airflows for residential buildings. It also allows the use of variable volume mechanical ventilation, which could be any of the following.
- Ventilation averaged over short periods.
- Scheduled ventilation.
- Ventilation continuously controlled in real time.
The first strategy requires total airflow rate over any three-hour period to comply with the 62.2 standard. This allows for switching the ventilation system off during short periods, if high airflow rates can happen later.
All three cases require the equivalent ventilation principle. This means that the annual exposure to pollutants must be no higher than constant-airflow ventilation systems will achieve.
LBL scientists Sherman, Walker, and their colleagues have pioneered the ideas of “ventilation equivalence” and “IAQ equivalence”. Ventilation equivalence is based energy metrics, while IAQ equivalence is based on health-related metrics. Other scientists propose a method that uses available data expressed in the disability-adjusted life years (DALYs) metric.
Based on disease incidence models, researchers calculated the DALYs lost as a result of long-term exposure to indoor pollutants in residences. They published values of the DALYs lost per incidence of disease. To explain this concept, they used the unit damage estimate (UDE) value for each contaminants of concern (COC).
The “IAQ equivalence” principle also proposed use of these unit-damage estimate (UDEi values in order to set a DALY limit value and then proposes checking that the combination of contaminant concentrations stays below this limit. LBNL estimated this limit as 8200 mDALY per person per year for the established COCs.
Limits to IAQ Equivalence
The IAQ equivalence approach assumes that indoor COCs are clearly identified and prioritized, which they currently aren’t. This equivalence methodology also must eventually include acute exposure issues. Nevertheless, it could eventually be integrated into evaluation methods for innovative smart ventilation systems, and even directly into the control systems with real-time sensors. This background will lead to a “smart IAQ” approach that goes beyond just ventilation and into energy efficiency.
Smart Ventilation’s Energy Performance
The fundamental goal of smart ventilation is to reduce ventilation energy use and cost while maintaining acceptable IAQ. Smart-ventilation controls use the principle of equivalent ventilation to calculate IAQ for ventilation systems whose airflows aren’t continuous. Smart ventilation also allows real-time control by calculating instantaneous and long-term pollutant exposures and doses, relative to a continuously operating ventilation system. Those controls reduce the pollutant levels compared to a non-smart, non-controlled ventilation system.
Current smart-ventilation systems save energy and reduce pollutant levels slightly compared to continuous ventilation with these strategies.
- Using timers or temperature sensors to determine when ventilation occurs so that the energy impact is smallest. For example, shifting ventilation from times of high temperature difference to times of low temperature difference. This ability is particularly valuable as a peak-demand-reduction strategy.
- Accounting for operation of other ventilation systems, such as kitchen and bathroom exhaust fans and clothes dryers. For example, if the close dryer operates for an hour, the ventilation systems controls reduce its operating time to compensate for the clothes dryer’s air exchange.
- Reducing ventilation during times when the building is unoccupied.
- Ventilating more at some times to compensate for other times when ventilation is reduced. For example, ventilating more when the outdoor air is cleaner and less when the outdoor air is dirtier.
Assessment of Indoor Air Quality Benefits and Energy Costs of Mechanical Ventilation.” In Proceedings of the 2011 32nd AIVC Conference and 1st Tightvent Conference, Toward Optimal Airtightness Performance. Brussels, Belgium, 2011. “