The evolution of ventilation systems and controls began with demand-controlled ventilation (DCV), then moved to occupant-controlled ventilation (OCV) and finally to smart ventilation.
Demand-Controlled Ventilation (DCV)
HVAC designers have employed Demand-Controlled Ventilation (DCV) for many years. DCV controls ventilation in response to occupancy. DCV responds to demand rather than delivering a prescribed ventilation rate. Here’s how.
- DCV systems, quantify demand by measuring or RH or CO2,which rises and falls according to occupancy.
- Or, the DCV system simply responds to occupancy sensors, with or without help from RH and CO2 controls.
How Occupancy-Controlled Ventilation (OCV) is different from DCV
OCV is slightly different from DCV. OCV assumes that occupants aren’t responsible for all of a building’s pollution. Residences have a lower occupant density than commercial buildings where DCV systems are common. In dwellings, building materials, furnishings, household chemicals, and attached garages create a greater percent of indoor air pollutants than in commercial buildings. These pollutants occur regardless of occupancy. Therefore, halting ventilation during unoccupied periods may expose occupants to high levels of these pollutants when they return. Here are some alternatives that prevent this pollutant accumulation.
- Pre-occupancy flushing by the ventilator to remove accumulated pollutants
- Allowing the ventilation system to operate at a lower rate during unoccupied periods
- Using an economizer to flush the dwelling before occupancy
How Smart Ventilation incorporates DCV and OCV
Smart Ventilation integrates information from many sources in order to make an informed and intelligent decision about how best to ventilate. These sources of information may include the following:
- Outdoor conditions such as temperature, humidity, pollutant concentrations, wind speed, and wind direction
- Indoor information sources include occupancy, humidity, pollutant concentrations, and building-pressure changes that indicate the operation of exhaust fans or the opening of windows
- Whole-house conditions such as predefined schedules and operation of the HVAC-system, exhaust fans, and clothes dryers, which may exchange air with outdoors
- Global inputs such as community- or regional-scale electricity demand or price of electricity
With this information, a smart ventilation controller isn’t limited to decisions based on one or two inputs. The smart controller considers many inputs and control strategies. These sophisticated control strategies depend on financial, energy, air quality, and social benefit. Smart ventilation controls can shift operation from times of high thermal loads, high electricity peaks, or high daily outdoor-air pollution to times when thermal loads, electric peaks and outdoor air pollution are lower.