Kitchen Demand Control Ventilation

Food service facilities have high energy consumption with equipment and commercial kitchen ventilation (CKV) being the primary energy consumers in a restaurant. Exhaust hood airflow drives HVAC energy consumption for CKV, so the first step in reducing this exhaust airflow is designing high efficiency hoods with low capture and containment (C&C) airflow rates.

The next step is using demand control ventilation (DCV) to further reduce exhaust airflow when cooking is not taking place under the hood, but when appliances are hot and ready for food preparation.

DCV has evolved from simple two-speed fan control systems to proportional control with variable frequency drives (VFDs) based on exhaust temperature. This improvement allowed for varying airflows throughout the day. Then, an optical sensor was added to the temperature-based control to detect cooking activity taking place under the exhaust hood to further enhance performance.

The latest system introduced to the market the added measurement of exhaust airflow and automated balancing of multiple exhaust hoods connected to a single fan (or a dedicated fan), as well as the modulation of replacement air for the space. The DCV system is designed to reduce fan energy consumption by slowing the exhaust and makeup air fans whenever a full speed is not needed. It modulates the speed of motors with VFDs (Variable Frequency Drives) based on input that it receives from two sources: (1) temperature sensors mounted in the exhaust duct and (2) optic sensors that span the length of the exhaust hood.

KDCV System Configuration


  • 1. System Controller:

    Receives input from the Touchpad(s) and Hood Controller(s) to control the output for the VFDs.

  • 2. Hood Controller:

    Oversees Temperature and Optic Sensors on each hood and sends sensor data to the System Controller via RS-485 communication.

  • 3. Touchpad:

    Provides switches for the operation of hood lights and fans, bypass, mornitoring LEDs, and programming.

  • 4. Optic Sensors:

    Monitor the presence of smoke and vapors inside the hood. Send a signal to the Hood Controller to increase fan speed when cooking.

  • 5. Air Purge Units:

    Miniature blowers send air into Optic sensor housings to prevent smoke and grease from collecting on lenses.

  • 6. Temperature Sensor:

    Monitors the exhaust air temperature in the duct and sends a signal to the Hood Controller to vary fan speed in proportion to heat load.

  • 7. VFDs:

    Variable Frequency Drives receive signals from the Hood Controller to control the speed of the fans based on the heat and smoke load.


Benefits


  • Fan energy consumptions(kWh) and peak load(kW) savings: up to 74% and 70%
  • Make-up air heating and cooling load reduction(Therm): up to 40%
  • Payback period: Less than 2 years overall


  • Auto On/Off capabilities and reduced noise in the kitchen hoods
  • Compliance & Sustainability
  • Compliance with ASHRAE 90.1 & California Title 24
  • LEED v4 EA credit 1 baseline requirements