The principle of a clean room is that you fill up a room with clean air and keeps the air-pressure conscientiously higher than the outside.

Two types of air flow
There are two types of air flow that you can use, you have the turbinate flow and the laminar flow. With a turbinate flow the clean air is blown into the space on an few spots. This causes turbulence in the room which makes particles flowing around.

With a laminar flow air system the air is blown in from a surface that covers the entire sealing and ideally the air then leaves the space on the opposite side of the room, in this case the floor. This way the clean air takes all the dirty particles down in the flour and limits the risk of contamination.

How clean is clean
To know how clean the air really is, we have to count the amount and the size of particles that are in a given space. A classification has been developed called ISO. It works as followed: You count the particles bigger then 0,1µm in a square meter, this amount of particles determines the class. For example a ISO 3 classified clean room may have not more then 10^3 = 1000 particles of 0.1µm per square meter.

How big should my clean room be
Make sure you keep the clean room as small as possible, the bigger it gets the more expensive it gets. This is because of the large amount of clean air you'll have to blow in to the space and this takes more expensive filters and blowers.

What you can do is make a clean area on a table by covering the table with a (transparent) hood and make this airtight. Leave a opening at the bottom to enter the space with your hands to be able to work in it.

Or an other option, when you only want to store or grow things in a clean environment , you could also make something called a sterile box. You can make this box as big or as small as you want.

How to calculate the needed airflow

You can calculate this as follows:
Take the area of the sealing (or a side wall) in square meter and multiply this by 0,5m/s (this is the airspeed required to prevent the dirty particles from flowing into the space). This outcome is your required airflow in cubic meter per second. Multiply this by 3600 and you got the cubic meter per hour.

In short: Needed airflow = surface * minimum airspeed (0,5m/s)

How to choose your filter
You choose your filter according to the cleanness you want in your space and the amount of air you need to process.

A clean room where you want to work with substrate for mushrooms (like we wanted) should use H14 filters. This filter filters out 99.995% of all the particles bigger that 0,5µm. What you also need to protect your H14 HEPA filter is a pre filter, this filter will filter out all the bigger particles and prevent it form clogging your more expensive H14 filter.

When you look for filters make sure you ask how much cubic meter of air it can let trough in one hour and what the pressure drop is of the filter. You'll need this later when choosing your blower.

How to choose your blower
For this you want to make sure your blower can produce enough air pressure at the needed airflow. And keep in mind that overtime your filters will fill up with particles and need more pressure to keep up with the needed airflow. To regulate your blower its good to have a big (6Amp) knob to do this, best to order this with your blower.

Each blower comes with a diagram that shows the given air pressure at a given airflow.

Materials to use
We used wood to build a frame and PVC foil (0.3mm) to make the walls. To make the corners airtight we used a silicon kit.

Building the structure
It's best to first sketch your construction on a peace of paper to get an idea of what you want. If this is done make a front and side view with exact dimensions, this you can use a guideline for your construction. In this drawing you can see what the size of the panels, beams and all the other parts are and how they relate to each other.

You can also choose to make your parts in a 3D rendering program, this way of working especially comes in handy when you want to see if your parts fit into an already existing structure (this was the case with our clean room).

Using the clean room
First you have to clean the clean room. Clean it with water and soap and then clean it again with a alcohol solution.

Make sure you wear proper clothing then present in the clean room. If you build a clean room where you are going to walk and work in make sure you also make a 'gray room'. This is the space there you put on your special clean room suit, gloves, hairnet and shoes. It is also directly connected to the clean room.