Is a GMP requirement to establish a differential pressure normally Pa between cleanrooms and adjacent less clean spaces to avoid product contamination. Leakages calculation is the first step we should know to calculate later the amount of required fresh air, within a complete air balance that we will explain in another post.
Once agreed on the importance of knowing the leakages to successfully design an over-pressurized cleanroom, let us see how to calculate it.
Exponent n we normally assume equal to 0. Nevertheless, this is dependant of the Reynolds number. As more turbulent is the airflow, n approaches 0. In a laminar flow, with low Reynolds, n approaches 1. As usual, we will calculate with Excel. This could be another separate sheet from the others needed to complete the calculation.
First, we will prepare a sheet that will be the base for our calculations, covering all scenarios: type or leakages and differential pressures that we will have in our facility. The final aspect should be something like this:. In the following section put the door characteristics of your project. You can select the appropriate dimensions: length, width. Also, select an air gap for each type.
Usually 2 to 4 mm. In this example, I selected 3 mm for a single and double door and 5 mm for roller doors:. And now we can calculate the leakage for each element at different pressures by applying the above formula:. This is only for my commodity when I use the match formula later. This sheet will serve as a basis for any calculation. We only must adapt this to the characteristics of the project and the gap we want to consider. The arrows show the air leakages:. With this layout our calculation sheet we write the room number, description, door size and reference, pressure:.
For each room, we will have leakage in and out by adding all of them to achieve the desired pressure. Established the leakages for each room, we can go on with the air balance for each room to know the amount of fresh air we need.
But we will explain this in another post. Save my name, email, and website in this browser for the next time I comment. Social Networks. Newsletter First name or full name. By continuing, you accept the privacy policy. Introduction It is not necessary to explain here the importance of overpressure in pharmaceutical facilities. To achieve this, we will need in our design two premises: Airtight construction. The amount depends on the total area of the cracks, the type of crack and the pressure difference across the crack.
The volume flow rate of infiltration may be calculated by:. The pressure difference in Equation 2 results from the effects due to the wind dynamic , due to the stack effect elevation and due to building pressurization or depressurization. For the purpose of this investigation, building pressurization or depressurization was only considered.
To include secondary effects would require measurements or estimates of external building wind velocity and an estimate of the stratification of the air density due to building height. To use the ACH method, the manufacturing space gross volume must first be estimated. Based on measurements performed and provided data, the estimated gross space volume for this particular manufacturing space was 2,, ft 3. Applying Equation 1 with a 0. Similarly, at the higher rate of 2.
Therefore, it is reasonable to assume the actual volume is between these two bounding conditions. To use the crack method, the building differential pressure was measured and compared under several different operating conditions of the building air conditioning units and of the production system air handling units.
The calculated air balance rates under these conditions were used to yield the following experimentally fit relationship, also shown in Figure 1. Figure 1: Building differential pressure with respect to negative airflow volume. The exponent in Equation 3 of 1. The conditions of near-operation supply rate of the air conditioning units and exhaust airflow rate of the air handling units of the production systems also provided a check of the reasonableness of these results.
With a normal net inflow of , CFM, the differential pressure between the building and the outside based on Equation 3 is a negative 0. Using published experimental data for typical building surfaces 10 , a differential pressure of 0. The difference 78, CFM between the wall and roof infiltration estimated by the crack method and the total infiltration estimate of , CFM can be attributed to window and door infiltration, which were not completely characterized in this study.
An artificially lower negative air balance condition was also created during the collection of differential pressure data. For these conditions, a 62, CFM flow rate resulted with a differential pressure of 0. At a differential pressure of 0. Under this condition, the infiltration is estimated at. This reduction in the infiltration rate estimate is illustrative of the potential benefit for maintaining control of the conditioned air space pressure, which could be realized through the adjustment of the air balance within the manufacturing space.
In summary, a technique for estimating air infiltration in a manufacturing facility was presented. A mathematical relationship was elucidated which provides the means for approximating the values for building infiltration rates of outdoor air. With specific conditional modifications, this relationship could be used to predict air filtration estimates under numerous manufacturing conditions. Burge, H. Salvatore R.
Afshari, A. Rylander, R. Brennan, T. Cummings, and Lstiburek, J. Andersson, J.
0コメント