When selecting air filters based on total cost of ownership (TCO), a science-based approach allows cleanroom and maintenance operators to decrease time-consuming and expensive cleaning and disposal costs, extend filter lifetime, reduce labour costs and count the saving as 'cost avoidance', while using personnel for other activities.
Camfil, in an industry first, recently launched CREO (cleanroom design and energy optimisation) software, aimed specifically at optimising AHU air filters, supply HEPA, exhaust HEPA and dust collection filtration selection, while optimising the most energy-efficient solution.
Increased energy costs and industry quotas for CO2 reduction are more visible than ever within the life sciences community. Protecting people, the process and the environment are essential attributes of efficient air filters, adding science to the air filters' efficiency targets while still reducing energy consumption is a requirement and not an option today.
Substantial and quantifiable energy-saving opportunities do exist by selecting the correct type and combination of air filters. The life science consulting engineers and end-users are actively investigating these opportunities by consulting Camfil as well as targeting related design considerations such as the ideal air change rate for specific process steps, studying 'ventilation on demand' and of course minimising the biggest contaminant in cleanrooms - people, all to minimise operating costs.
CREO is a modelling tool that allows designers and owners to simulate much of what has been stated above in addition to other design considerations such as recovery time simulation, room leakage factors and generation of particles from the process can be easily calculated by using this advance design software. It's interesting to note some recent studies and published papers have seen 2-3 million particles at 0.5 microns a minute generated per person versus 10,000 particles a minute depending on the garment selection. CREO helps see the recovery time impact in seconds.
In order to make an 'apples to apples' comparison between CREO and lifecycle cost green (LCC) software, we start by understanding what filter efficiency is required to protect the process, environment and people. Unfortunately, there is a paradoxical relationship between energy savings and filter efficiency; the higher the grade selected (a minimum efficiency reporting value of MERV 13 or F7) on the make-up air, the higher the energy consumption will be because the resistance will increase as efficiency increases. Do not use coarse fibre or synthetic media; select glass or fine fibres.
Once the filter grades have been established, along with the number of filtration steps and where these grades are located within the air handling unit or cleanroom, selection should be based on optimising the pressure drop across each step and establishing a change-out point to maximise life at the lowest operating cost based on scientific data.
In the 1990s, Camfil developed LCC software to optimise HVAC or pre-filtration selection. The software, which has been updated over the years, evaluates features of the system in use, such as variable frequency drives versus constant volume, and carbon dioxide emission calculations. It also evaluates the key essentials for any air filtration TCO calculation: filter unit cost, labour cost, true average pressure drop, disposal cost, energy cost and hours of operation.
Standard operating procedures or quality assurance may dictate when HEPA filters are changed, based on a specific site history or experience. This makes no technical sense from an air filtration point of view. It is more of a risk-v-benefit decision the particular site has made. While this is understandable at the time, the procedure should be reviewed periodically to take advantage of any potential savings with minimal risk. Ideally, filters should be changed on pressure drop. Often, due to the end-users' system and resources, a time-based strategy is selected based on preventive maintenance windows. Optimising lifetime and reduction in energy consumption during the filter's working life is still possible and can be shown using the CREO software.
Scientific data - not calculated data - is the key. It is easy to take the simple straight line average and quote an average pressure drop. However, a well-manufactured filter does not behave in this way; you will see a parabolic loading curve. LCC and CREO software uses data from hundreds of air filters used in many different environments taken from real-life, longterm testing globally. This data gives the user information an aid in making an informed air filter selection. Also, it takes the guesswork out of when and how to change filters in multiple environments, and find the lowest TCO.
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