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 forboth 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 humidityin 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 buildingwas 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 fromthe 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 showedvariation 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 (Figure1).