Ventilation of Mechanical Rooms with Refrigeration Equipment in Excel

Ventilation of mechanical rooms with refrigeration equipment is a process of providing adequate air flow and temperature control to ensure the safe and efficient operation of the refrigeration system. Mechanical rooms are enclosed spaces that house compressors, condensing units, piping, valves, and other components of the refrigeration system.

There are two main purposes of ventilation for mechanical rooms: normal ventilation and emergency ventilation. Normal ventilation is required whenever the mechanical room is occupied, and it aims to prevent excessive heat build-up and provide fresh air for the occupants. Emergency ventilation is activated when a refrigerant leak is detected, and it aims to dilute the refrigerant concentration, trigger alarms, and shut down any combustion sources in or near the mechanical room.

The design and installation of ventilation systems for mechanical rooms must follow the requirements of ASHRAE Standard 15-2007 and applicable local building codes. Some of the general requirements are:

• The ventilation system must have separate ducts and fans for exhaust and make-up air, and they must serve only the mechanical room.
• The exhaust fan must discharge upward at a minimum velocity of 2,500 feet per minute (fpm) at the required emergency ventilation flow rate.
• The exhaust fan must have nonsparking blades and the motor must be totally enclosed if it is located in the air stream or inside the mechanical room.
• The ventilation system must not cause negative pressure in the room to exceed 0.25 inches of water column.
• The ventilation system must have a clearly identified control switch for emergency ventilation with a tamper-resistant cover, located outside the mechanical room and adjacent to the designated principal door.
• The ventilation system must have a detector for refrigerant leaks, located where the leak would concentrate, and it must trigger audible and visual alarms both inside and outside the mechanical room, actuate mechanical ventilation, and shut down any combustion sources in or near the mechanical room.
• The ventilation system must provide a self-contained breathing apparatus (SCBA) for emergency use.

The ventilation rates for mechanical rooms depend on the size of the room, the heat load of the equipment, the type and amount of refrigerant, and the occupancy of the room. The following are some of the general guidelines for ventilation rates:

• Normal ventilation: The minimum ventilation rate is 0.5 cubic feet per minute (cfm) per square foot of mechanical room area or 20 cfm per occupant, whichever is greater. The ventilation rate can be reduced if external means of cooling or electrical wiring rated for higher temperatures are used. The normal ventilation must be continuous or activated by a thermostat and a manual control switch.
• Emergency ventilation: The minimum ventilation rate is 30 air changes per hour based on the gross mechanical room volume, unless analysis indicates that a release of the entire system charge will not result in the room concentration exceeding 40,000 parts per million (ppm) or 25% of the lower flammability limit (LFL) of the refrigerant. The emergency ventilation must be activated by the refrigerant detector and the manual control switch.

        # Step 2: Calculate Ventilation Rate in CFM
        = A1 / (C1 * B1)

        # Step 3: Convert to CMS (assuming 1 CFM = 0.000471947 CMS)
        = A2 * 0.000471947
      

        % MATLAB Calculation
        heatOutput = 50000; % BTU/hr
        temperatureDifference = 20; % °F
        airHeatCapacity = 0.24; % BTU/(lb°F)

        ventilationRate_CFM = heatOutput / (airHeatCapacity * temperatureDifference);
        ventilationRate_CMS = ventilationRate_CFM * 0.000471947;

        ventilationRate_CMS