KITCHEN EXHAUST HOOD TESTING & BALANCING

The kitchen hood captures smoke, grease, and other particles, mixed with air, above the kitchen appliance. An exhaust fan pulls the air from the hood through an exhaust duct. The amount of air exhausted must be replaced by air brought into the building from a make-up air unit, or through the air conditioning or heating system.

There are also diffusers, filters, and controls that complete the system. The purpose of these components is to move proper and equal amounts of exhaust and makeup air in and out of the building, to carry out unwanted heat, grease, smoke, and steam.

When all these systems and components operate properly, the “typical problems” listed above are replaced with comfort, reduced operating cost, good food, and prosperity.

Have the system cleaned; If the hood and grease ducts have been in use, require the system cleaned before you begin testing. A greasy system is very unpleasant to work on, and your odds of a successful balance are reduced. The system should be balanced with the appliances below the hood turned on, so the temperature of the air is near what it will be under actual operating conditions.

Gather and record nameplate data; Record design information from the plans, and then collect equipment and motor information from the field to be sure the proper equipment was installed. Be sure to measure and record the hood size, grease filter size, and the exhaust duct dimensions. List all required airflows. Make a sketch of the floor plan, hoods, grease filters, registers, grilles, and equipment locations.

Visual inspection and start-up; Check that all ductwork is connected, filters and controls are installed, and that all grilles and registers are in place with dampers open. The system should have been previously started up and checked out. Drill static pressure and temperature test holes. Start-up the exhaust and makeup air systems.

Initial testing; Before measuring airflow through the equipment, measure building pressures. Be sure all systems; kitchen exhaust, makeup air, heating, cooling, and bathroom exhaust fans are operating when this test is performed. Attach a 7.5 meters length of tubing to a low-pressure manometer and place the tube in a protected area outside of the restaurant. Be sure not to pinch off the tubing. The open port will read the pressure in the restaurant. Read the difference between the indoor pressure and outdoor pressure on the manometer.

Building pressure reveals the sum of all the airflows. A positive pressure means the total makeup air exceeds the total exhaust air.

Measure make-up airflow; If the air is delivered through registers and the airflow is within the capacity of your air balancing hood, measure each of the registers and add them together to find the total airflow for the makeup air. Often, the air is delivered through the kitchen hood or through a high-capacity registers. These must be measured using an airflow traverse at the register, or, better yet, in the duct delivering airflow to the register.

Part of measuring makeup air is documenting the amount of fresh or outside air entering the air conditioning and heating systems. This can be done by traversing fresh air inlets or by using temperature calculations.

Measure the exhaust hood airflow; Exhaust hood airflow measurement requires practice and a touch of art. You need to compare the measurements you’ll take here to other system values that you’ll take during final testing to verify that your airflow reading is correct.

Final equipment testing; Once you’ve achieved required airflow through the exhaust and makeup air systems, you must measure pressure, electrical, and rpm values at each piece of equipment. This is done to verify the equipment is operating properly and within specifications.

Pressure is taken by drilling test holes in ductwork and fan housings. Remember, the grease duct can’t be penetrated for a pressure test. Try a 18-in. piece of stainless steel or copper tubing slid between the exhaust fan and the curb attached to your manometer. This method works especially well if the fan is hinged.

Measure electrical values on each motor including voltage and amperage. Compare the amp reading with motor nameplate to verify the motor isn’t running over full load amps.

Measure motor and fan speeds; Use this information with horsepower and the static pressure readings to plot airflow on the manufacturer’s fan performance chart to verify your airflow readings. Record pulley and belt sizes and model numbers.

Complete the balancing; There are a few final tests you can perform that will make a big difference in system performance.

Air balancing and diagnosing kitchen exhaust and other HVAC systems assures you and your customer that the system is performing as it should. Both of you can know the job has been done right. Air is invisible. Measurement is the only way to verify that a system is working.