Calculating the annual cost of energy to heat and cool a gas pad in your cleanroom or fab.

There are several ways to do this, but in all cases the site weather is the most important factor affecting the cost.

For buildings or areas within buildings that draw in quantities of outdoor air and exhaust it through equipment and are not significantly affected by solar heat gains or losses, the annual energy cost can either be determined manually using “BIN data” for the city of interest and applying thermodynamic and fluid flow equations for the fresh air and exhaust flow rates, air cooling and heating processes, and air conditioning system efficiency.  “BIN data” is a form of weather data that lists the number of hours annually vs. temperature and dewpoint or wetbulb temperature.  The US Air Force has been a source of this data but more current data is available from ASHRAE.

One can also use proprietary software such as Trane “Trace” or ISMI Sematech CleanCalcII that were designed to perform these calculations.

From the CleanCalcII web-site, it is described as follows:

The ISMI CleanCalc II Fab Energy Simulation tool is a computer program that estimates annual and peak energy for cleanrooms and fabs based on hourly, world-wide weather data and 46 other variables including size, location, room temperature and relative humidity, recirculation and makeup air handler flow rates and other operating parameters, humidification method, heat source, chiller efficiency, fan efficiency, boiler efficiency, tool energy, tool heat removal, and heat burden.
Outputs include total annual and peak energy consumption values for cooling, heating, humidification, chiller, boiler, electrical, and fossil fuel. The model can analyze five scenarios side by side with graphing capability for each scenario, including weather bin data graphically overlaid onto psychrometric charts for each scenario. This energy analysis tool has the capability to quickly show the impact of cleanroom design changes on energy consumption.

This software can do much more than calculate annual energy consumption for the gas pad, but it is a convenient tool with ample worldwide, hourly weather data embedded and is preferred for this problem by this author (who was a co-developer).  For more information, see:  This software is also available from ASHRAE.

Another program that would be suitable is HDMakeupAir by Hands Down Software, the co-developer for ISMI CleanCalc II.  It has more features related to calculating makeup air but has no capability for addressing fab utilities.  For more information, see:

Ralph Cohen, P.E., who provided this information, is an engineering consultant to customers for gas systems components and HVAC, specializing in semi-conductor and other industrial manufacturing facilities.   He has over 30 years in the field, and continues problem solving for clients through his consultancy.    More information on Ralph’s project work, publications, etc. can be found here RalphCohenConsultancy or call 971-227-8989.


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