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A pharmaceutical manufacturer needed to keep space temperatures in a warehouse between 68 °F and 78 °F to maximize the shelf lives of their products. The building’s HVAC control system was designed to issue an alert to plant operating personnel whenever temperatures in the space fell outside a +/- 3.5 °F limit from setpoint. Eichleay Engineers Inc. of California designed the air handling system for the warehouse. Although the system could maintain the tight temperature tolerances, there was very little margin for safety, especially in the vicinity of the 25-foot ceiling. Eichleay hired Flomerics Inc. consultants to simulate airflow and temperature in the warehouse using software specifically designed for simulating heating and cooling of building interiors. The simulation matched physical measurements that showed that the air handling system alone was just able to hold the customer’s tight temperature requirements.

Eichleay requested the evaluation of several design alternatives, which included the addition of fans to increase air circulation within the warehouse. A fan configuration was identified that met the customer’s requirements for both temperature variation and air velocity.

TOUGH REQUIREMENTS FOR PHARMACEUTICAL WAREHOUSE
The building has 49,200 square feet of warehouse storage space with a roof height that varies from 25 to 28 feet. In order to maximize the life of the pharmaceuticals stored in the facility, the client established a requirement that the temperature throughout the entire interior space be held to 70 °F with an allowable variation of only +/- 3.5 °F. In addition, the client required that the building be maintained at less than 50% relative humidity. The outside design conditions varied from 95 °F at 90% relative humidity in the summer and -20 °F at 20% relative humidity in the winter.

The project was begun using standard computer calculations to design an HVAC system that was capable of keeping the temperature in the building at the required level, including a 100-ton DX air conditioning system and duct-mounted zone reheat coils for tight temperature control. This system can maintain the right average temperature but leaves very little safety margin. The difficulty was increased by the fact that the client wanted the ability to place pallets in any rack location in the building and stack them up to 19 feet. The major challenge was to ensure that the temperature at any position and any level in the building was within the required tolerances.

AIR HANDLING SYSTEM ALONE COULD JUST MEET SPECIFICATIONS
Construction personnel installed the equipment and performed field adjustments that brought the HVAC performance within specifications. They bled air from the HHW piping system, replaced faulty HHW valves, and adjusted the air handler controls for supply air temperature to match setpoint requirements. They replaced thermostats with less sensitive thermostats, relocated them to higher elevations and modified temperature setpoints. They modified the HVAC automation control system to lower the supply air temperature. This fine tuning substantially reduced the temperature variations but physical measurements still showed variation in the building from 68 °F to 74 °F.

The building was noted to require additional air handling equipment to narrow the temperature variations within the space. However, the cost of purchasing and installing stratification fans was too substantial to simply put them in and see if they would work, and hand calculations would not be nearly accurate enough because they could not account for the unique geometry of the building and its contents. So the decision was made to seek the assistance of a consultant to simulate the airflow and heat transfer within the building with computational fluid dynamics (CFD).

SIMULATING HVAC SYSTEM PERFORMANCE
While construction was continuing, the consultant was supplied with 2D drawings of the building, rack configuration, and HVAC layout. Construction of a 3D model, representing the building and boxes to represent the product pallets, was begun. The most important specification needed was to model the air distribution system. This included the supply air volume, velocity, and temperature, as well as the physical locations of the supply diffusers and return registers. The ambient air temperature outside the plant and insulating properties of the building were also entered. A steady-state solution on the computer was performed. The results looking at temperature were mapped as color contour charts across horizontal sections at various levels above the floor (Figure 1).

Next, the full power of a CFD model was utilized by modifying it to account for several alternatives that were being considered to reduce the temperature stratification in the building. The first option was to install eight 24-inch diameter Greenheck model MCY-24 fans and the second option was to install 50 smaller Airius destrati-fication fans. The Greenheck fans, because of their large size, require fewer fans for enhanced destratification over pallets but also generate more noise and higher air velocities. The Airius fans are smaller, quieter, and more difficult to see as they are the same color as the ceiling, more energy-efficient, easy to install, and generate a lower air velocity but require the installation of more fans. The purpose of simulation was to determine, in advance, exactly what results would be provided by each type of fan.

EVALUATING DESIGN ALTERNATIVES
Two new modified versions of the model were created. The software would have been capable of modeling the actual geometry of the fans and this would have been required if their performance was not known. However, the manufacturers of each of the fans provided detailed performance specifications, including fan curves that provided airflow as a function of pressure. The software was used to simulate fan performance to a high degree of accuracy while using far fewer computational resources. The parameters of the software were modified to match the specifics of the two fans under consideration.

The simulation was rerun for each of the new models and the contour maps showed temperatures at key levels of the warehouse. The results showed that each type of fan reduced the temperature stratification within the building to +/- 1 °F. Additional simulation results showed air velocities within the building (Figure 2). The results indicated that the larger Greenheck fans generated air velocities at a level that would cause the user’s paperwork to be blown about, making it difficult for warehouse personal to do their jobs. On the other hand, the smaller Airius fans provided much lower air velocities that would not interfere with people working in the warehouse.

SIMULATION HELPS MEETS CUSTOMER REQUIREMENTS
These results were shown to the client who agreed to purchase the Airius fans despite the fact that they represented a higher cost solution. The simulation results were crucial for the determination of what equipment would work best and for providing graphical evidence that this equipment was needed to provide a tighter temperature control.

Next, 50 Airius fans were installed in the building. Validation of the warehouse space was accomplished by monitoring 54 temperature sensors evenly distributed throughout the space at three different levels. The validation protocol first tested the system without the destratification fans and then again with the destratification fans. The first validation test passed within the +/- 3.5 °F criteria. The second validation test passed within +/- 1 °F as predicted by both of software program runs. The new HVAC system has been operational for about 18 months and the temperature alarms have not shown any excursions; the customer is extremely pleased that the building has met their requirements.

Christopher Wark is the Flovent Technical Sales Manager for Flomerics,Inc.Christopher has over twenty years of increasingly responsible technical experience in the areas of laser and engine research and advanced architectural engineering.He holds Bachelor’s and Master’s of Science degrees in Mechanical Engineering from Washington State University,Pull-man where his graduate research was in the area of combustion and mass heat transfer.