Designing A Projector Enclosure

A proper enclosure for your projector will take some careful design, but it is not a task only for a rocket scientist. In order to succeed, you must first be familiar with what a projector needs from its surrounding environment.

Heat Exchange

The key to any enclosure design starts with heat exchange. In simple terms, your goal is to remove the heat generated by the projector. The unit of measure of heat generation is BTU (British Thermal Units). Often, the projectors BTU value will be included on the spec sheet. If not, use this simple formula to determine the BTU output of a projector: Wattage X 3.42 = BTU

If you are dedicating an air conditioning unit to the projector enclosure, you should rate your conditioner at 120% of the projector BTU rating. As an example, an air conditioner that exchanges 5000 BTU would satisfy a projector that is rated at 4000 BTU.

Note: Do not rely on an HVAC system that is intended to support a particular area of a venue to provide cooling for the projector enclosure. The problem with this approach is that the thermostat for that HVAC system is located in the room, not in the enclosure that houses the projector. Therefore, the projector environment will not receive adequate cooling. Another risk with this approach occurs in the winter, when the thermostat is set to output heat. In that instance, the projector enclosure would be receiving heat, as opposed to cooling.

Flow

Flow is measured as cubic feet per minute (CFM), or in similar metric terms. Some projector spec sheets provide the requirements for airflow. If not, contact the manufacturer's technical support to obtain this information. The key to enclosure airflow design is to ensure a reserve of air is present at the projector inlet, and that you are creating a draw at the projector outlet. This is also known as positive pressure (at the inlet), and negative pressure (at the outlet). A simple rule of thumb is to provide 120% of the projector's rated CFM at the inlet, and to draw 120% of the same value at the outlet. Example: A projector's CFM rating is 100 CFM. The inlet and outlet fans should be rated at no less than 120 CFM.

Note: It is not always necessary to have both an inlet and exhaust fan. The more important function of the two fan systems is the removal of hot air, as mentioned in the heat exchange section. So if you only have the means to use a single fan, design that as a draw, or outlet, fan.

Temperature

Blowing very cold air into a projector enclosure is not always a good idea. Very cold air can cause as many problems as hot air. Large temperature differentials in electronics or lamp systems can result in undue thermal stress. As an example, it would be perfectly acceptable to have inlet air to the projector that ranges between 70 – 76 Farenheit. Most projectors are designed to operate with inlet temperatures well above this value, usually up to about 90F. However, it is not good practice to design a system at its limits. You always want a safety margin in your engineering.

Pressure

Projector specifications will sometimes advise of a maximum operating distance above sea level. This information is based on air pressure. A maximum operating altitude of one mile above sea level is a normal specification, and covers about 95% of installations. Since most projectors are specified to support this altitude rating, you do not need to pay much attention to air pressure, other than as stated above regarding inlet and outlet loading with fan CFM's. Even if you are a couple of hundred feet beyond the operating altitude specification for the projector you are employing, following the 120% CFM guidelines and the temperature rules will keep you in a safe design zone.

Isolation

Far more mistakes in enclosure design are made in the area of input/output air isolation than any other parameter. It is very important that your inlet fan is not pressurizing your projector exhaust, and your draw fan is not pulling fresh air away from the projector intake. In addition, you do not want your inlet fan pulling the projector exhaust back into the projector! The critical place to start here is to ensure that your draw fan is sealed and isolated such that it exclusively draws from the projector's exhaust. This ensures there is only one path out of the enclosure and there is no possibility of hot air being pulled back into the projector. Make sure you know the intake and exhaust layout of the projector you are using, as each chassis will have different isolation requirements.

One must also assure a safe area is created around the projector. In other words, how much bigger does the enclosure need to be than the projector? In reality, it does not need to be much bigger to support efficient cooling, perhaps just 3-4 inches per side, as long as the parameters above are followed. Projectors tend to be designed to funnel heat out of certain openings, and ingest fresh air in the same controlled way. Rarely do the bulk of the BTU's generated radiate equally out of the total square area of a projector. Therefore, you can base your clearance on other factors like service access or general mechanical clearance and other guidelines.

General

Always take advantage of any application support you can get from the manufacturer, to help guide the design of your projector's enclosure.

Remember that projector's specifications are based on proper heat exchange, so a lot of the work is already done. You simply need to obtain the BTU, CFM, pressure rating, and mechanical layout of the product's air intakes and exhausts. Be realistic, if not conservative, regarding the ambient temperature of the environment, and make sure you are not using a room HVAC system to cool the projector enclosure. If it is a new enclosure/projector design and you have the facilities to execute a test, there is great value in verifying the enclosure airflow efficiency and internal operating temperature under thermal load, in advance of your final installation.