How to prevent condensation in enclosures

First, how does condensation happen? It occurs in one of two ways: (1) the air cools to its dew point or (2) when the air is so saturated with water vapor, it can’t contain any more water. This is what we call humidity.

If a weather report tells us that humidity is 100%, then we know the air temperature and air pressure are completely saturated with water.

What temperature does condensation occur?

Temperature and condensation are related. The temperature at which condensation forms is called dew point. Dew, or condensation dew, are the water droplets on cars and other surfaces that we wake up to in the morning.

At dew point the amount of water vapour that is condensing equals the amount of water vapour being evaporated into the air. Where does condensation occur? If the temperature falls below dew point, and the water condensing starts to exceed the amount of water being evaporated, condensation is going to form on any cool surface. To put it in simpler terms, condensation happens at any temperature – what matters is the difference in temperature between the air and surfaces.

At what relative humidity does condensation occur?

Humidity reaches 100% when the dew point and the temperature are the same. Condensation happens when the temperature falls. Generally, condensation starts to form at 65% humidity.

Condensation in electrical enclosures

Outdoor electrical enclosures tend to be installed in environments with high ambient humidity levels. Indoor cabinets, moisture can’t always evaporate. Without effective electrical-enclosure moisture control, condensation can form.

For outside electrical cabinets and electrical housings, this is especially dangerous in sub-freezing temperatures. Condensed water freezes, and then turns to frost. Frost can potentially cause malfunctions or even failure in sensitive electrical systems. Condensation in electrical panels can be especially dangerous.

How to prevent moisture in electronics is another pressing question, as you’re dealing with possible threats. For example, moisture in electrical cables can lead to shortages and even fire.

It’s not easy for your customers to solve condensation problems after installation. Those problems also include corrosion, mould, and risk of shock to workers. Preventing condensation in electrical enclosures should be the focus at design stage.

NEMA- and IP-rated cabinets

As a designer, you want to give your customers outdoor weatherproof cabinets for electronics or electrical equipment.

The most effective outdoor enclosure cabinets for preventing moisture and liquid ingress are NEMA or IP rated. The key word here is “ingress.” These enclosure types are rated according to the level of protection they provide against the entry of moisture, liquids and solid objects.

Let’s back up. NEMA (National Electrical Manufacturers Association) is the largest trade association of electrical engineers in the U.S. IP ratings were developed by the International Electrotechnical Commission (IEC) and are used in Europe and increasingly in the U.S. IP stands for Ingress Protection or International Protection. NEMA and IP ratings tell you the amount of protection against moisture, water ingress and solid objects. To learn more about the significance and meaning of these ratings, and how they compare, see our guide What are NEMA and IP Ratings?

Now let’s take a closer look at an IP65 enclosure, which is roughly the equivalent of NEMA 4/4X. This means the enclosure protects against:

• Incidental human contact with enclosed equipment
• Falling dirt
• Dripping/light splashing of liquids
• Rain, sleet, snow
• Damage by external formation of ice
• Windblown dust

Electrical cabinet parts play a key role. The enclosure needs IP65-rated components to maintain its rating – an IP65 lock, for example. Let’s say you’ve added the components needed to sell your enclosure as IP65 rated. That’s all well and good, but there is no NEMA or IP-rated enclosure that will prevent condensation, because no enclosure is completely air-tight. Remember, these enclosures protect against ingress. You can be confident that, for example, water won’t enter as rain.

The problem occurs as temperatures change once the enclosure is installed. The air inside an enclosure will draw moisture-rich air inside. This, of course, can lead to condensation accumulating and pooling at the bottom of the enclosure. This is a problem more common in higher IP-rated enclosures because it’s more difficult for water vapour to escape.

The good news is, you have many options. For example, design your IP65 enclosure with ventilation. You’ll just need to make sure your vents are IP rated, but they are available. For other components you’ll need, check out our Quick Guide: Industrial Components for Outdoor Cabinets.

How to prevent condensation

To significantly reduce condensation, these methods are often used:

1. Avoid fluctuations in temperature

Advise customers to locate the outdoor enclosure cabinet away from direct sunlight and any other heat sources that can create the conditions that cause excessive condensation.

Plastic enclosures provide better insulation than metal enclosures, with lower heating capacity.This means that when air temperature changes quickly, plastic enclosures adapt faster, which in turn means less condensation.

Also, enclosures should not be placed in damp areas, i.e., near bodies of water, where steam is likely to be an issue.

2. Ventilate

Electrical-enclosure ventilation is vital to combatting condensation. The equipment being housed will naturally give off heat, which can lead to problems if the enclosure lacks sufficient air flow. Condensation is not the only problem – the equipment can overheat.

This can be offset by electrical-panel vents. Slanted louvre vents are the most common. As to the enclosure itself, electrical-cabinet vents create passive ventilation and are typical in smaller enclosures with lower input power. Crossed ventilation regulates the internal air temperature while drawing in fresh air and expelling stale air.

A naturally ventilated electronics enclosure is certainly economical, but not as efficient as forced-air ventilation, which relies on mechanical means. These condensation-reduction systems use blower fans to circulate and cool the air within the enclosure. Large equipment with high input power typically requires forced air due to the amount of heat generated.

3. Install air conditioning

Consider this if the enclosure will be installed in an environment where temperatures of 40˚C (104˚F) are common.

4. Decrease humidity

How to protect electronic devices from humidity: use an enclosure dehumidifier. There are several different types. One is a dehumidifier that draws moist air over a refrigerated coil with a small fan. This increases the saturation of water vapour, causing it to condense on to the coils. The water drips into a pan, bucket or a pipe and exits the enclosure.

 

Another type of electrical cabinet dehumidifier is electronic. It uses a Peltier heat pump to transfers heat to a cool surface, condensing the air’s water vapor. Like the first option, a bucket or pipe will need to be installed to collect the water. Another type removes humidity without involving water through a process call electrolysis. This is the use of electricity to decompose water into oxygen and hydrogen gas.

5. Keep the temperature above dew point

Install an anti-condensation unit. This is a heater controlled by a humidistat. When the outside temperature cools down, so does the air inside the enclosure. The air becomes saturated with water. If the temperature goes below dew point inside the enclosure, the water vapour starts to condense. The humidistat detects the increase in humidity and switches on the heater, which prevents the enclosure’s temperature dropping below dew point.

6. Backfill with dry nitrogen

Dry gas purging is done during the manufacturing process to create a dry, inert environment inside the enclosure. The dry nitrogen used removes humidity within sensing systems and reduces oxidation effects.

7. Add silica gel

This is a desiccant that absorbs and holds moisture. Silica gel is a low-cost alternative, but the problem is that it needs regular attention. When saturation makes replacement necessary, labour is required to go to the site to do the work.

Condensation protection is another consideration. Applying corrosion inhibitor sprays to the enclosure and its components helps prevent corrosion, which results from condensation.

 

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Questions?

Email us at sales@essentracomponents.com or speak to one of our experts for further information on the ideal solution for your application 800-847-0486.