That’s a tough one, but for simple, relatively small cleanroom projects there are a few things that you can do to help ensure everyone bidding the job is “singing from the same song sheet.” No matter how simple, it’s very important to generate a specification sheet and conceptual drawing or sketch and make sure all the prospective bidders get it and reference it in their proposal. The sketch must include the ceiling height in the cleanroom and room sizes. Ask them to separately itemize any items that they feel are needed but are not included in the spec sheet. If you do not have anyone in your organization qualified to generate this document, hire an outside consultant with the understanding that all you need is a very basic scope statement. The time you spend trying to figure out the differences between bids will cost you more time, money, and frustration than the consultant will charge. Plan on at least two bid phases, initial and final bids. As you evaluate the bids you will get a better understanding of what is needed and can make better decisions regarding what to specify in the final bid phase. The evaluation phase of the bids can almost be an education on cleanroom design for your staff. Don’t be shy about asking contractors why one proposal is different than another. Make sure you are comfortable with their explanation.

Here are some very important specifications to include in your document that are critical for a contractor to determine cost. If everyone gets a spec sheet with these variables defined, your final bids will be more accurate and should be more consistent.

1. Room Classification, either Fed Std or Iso spec should work here.
2. Temperature specification and tolerance. Example: 68 +/- 5 Deg.
3. Humidity specification and tolerance. Example: 50 +/- 10% RH. Let the bidder know if the temperature and humidity specifications are process critical or operator comfort. If humidity control does not affect your product, leave it out. It is the most costly specification to control for the HVAC system.
4. Amount of process exhaust in CFM. This is relevant since both outside air to generate room positive pressure and air removed from the cleanroom by the process has to be accounted for.
5. Process heat load in kilowatts (KW). Are there ovens, large process machines, or just operators in the cleanroom? If you are not sure about this item, list the connected electrical voltage and current draw (amps) to start with. This will ensure some A/C tonnage is dedicated to this specification.
6. Number of operators. This affects temperature and to some degree, humidity.
7. A brief definition of the manufacturing process or product in the cleanroom may also help.
8. A description of the host building is helpful since this may affect where the HVAC equipment can be placed.

You may have other critical parameters, but these values will help everyone size the mechanical system. Wide variation in A/C tonnage numbers is an indication that the contractor may not understand cleanroom design and you should ask them to explain the differences. For lower classification or more complicated cleanrooms, a professional generated specification is needed. Always check references.

Kelly Barton, is Sr. Sales Engineer with Clean Rooms West, he may be reached at kbarton@cleanroomswest.com.