As Spring approaches, and along with it the humidity season, it's a perfect time for a refresher course in Indoor Humidity Control.

This is also an issue in the Southern states all through the winter, and also in commercial and industrial settings.

When considering indoor air quality, on top of the list is humidity control.

Two main things to remember, sensible is the temperature (energy or heat) that can be measured with a thermometer, latent is the (energy or heat) tied up in humidity.  It means hidden heat, and when it comes to condensing moisture from air, it takes lots of energy no matter which method is used.

Learn more about "Psychrometrics" here

Humidity out-of-control can result in structural damage, mold and mildew issues, and product loss or quality issues in manufacturing.

In the summer months especially, because of warmer outdoor temperatures, we concentrate our efforts on removing excess heat.

The reason being warmer air holds more moisture than cool air, more moisture in the air can result in condensing on cool surfaces.  You will see this in the interior of your refrigerator in humid climates, you will see outdoor hot humid air condense on the outside of windows in a COOL air conditioned house, you will see this inside your walls in the winter if interior moisture (from bathrooms and kitchens for example) gets into the wall and interacts with the cold drafts of winter.

As far as indoor air quality, and removing the moisture, there are three basic ways to do it.  One easy way (sort of) and two better ways - although the two better ways are rarely seen in the residential and light commercial markets (they are not simple).

Most of the time, moisture is removed by condensing it on a cooling coil either in a residential furnace, or in a rooftop or air handler of a commercial application.  The refrigeration system makes the evaporator coil cold, the moisture is condensed on the coil, and then drips off and runs to a drain.

Graphic Source, with more details

The unique and somewhat disadvantageous part of this method is the cooling coil / refrigeration system is also the method of temperature control.  When its warm in the space, the system runs, the water is removed, the air is cooled, the temperature is brought down to the desired level.

Then the refrigeration shuts off, either by way of a control valve or the compressor cycles off all together - varying degrees of both depending on load.

The problem is if the space temperature is cool enough such that the system doesn't run, the coil is thus warmed up to the air stream temperature and not cool enough to condense any moisture from the air.  NO dehumidifying.

There may well be times when the temp is OK, but yet the humidity is elevated - but the system will be ineffective at this condition.

Think in terms of a commercial laundry with steam and water driven processes (although also a warm situation), consider an indoor swimming pool, or any other application with a high indoor humidity load.  Also consider an application with any appreciable outdoor ventilation air requirement, during which case humid outdoor air (normally warm) is brought into the cooler indoor environment.

Another, better method of removing moisture is the dry desiccant wheel.  Although complicated from a mechanical system, psychrometrics, and control standpoint, they are actually fairly simple devices.

Think in terms of the little desiccant pack you find in a new box of shoes, basically a chemical pellet or other form of media absorbs moisture via a chemical interaction with the moist air.

A chemical embedded wheel rotates in and out of the air stream, moisture is absorbed from the air and captured in the "desiccant material", and as the wheel rotates to a second exhaust air stream, the wheel is heated which in turn evaporates the moisture from the wheel and then blown out the exhaust stack to the outside.  Simple.  But energy intensive.

Graphic Source, with more details

Read more from Munters / CargoCaire

A third and less common, but also more interesting system is the liquid desiccant system.  Nearly identical in method as the above wheel, the difference is the moisture absorbing material is actually a water / mineral salt fluid.  Yes, mineral water will absorb moisture when sprayed into the air stream.  As long as the mineral is Lithium Chloride at about a 40% solution.

The solution is sprayed in the air stream in the "conditioner" section, captured in a basin, then pumped to the "regenerater" section where it is heated and the moisture driven off and out via an exhaust fan (out the roof).

Simple, but also complicated.  These systems will be found in extreme industrial applications like candy factories, pharmaceutical and other demanding applications.  History note, they have their roots back in the Manhattan Project.

Why does this all matter?

When it comes to climate change, warmer outdoor temperatures mean higher humidity loads on mechanical systems - we have to remember the humidity is removed first before any cooling can happen.  NO COOLING if the system is overloaded because of elevated temperature and humidity.

The air conditioning load from millions of residential commercial and industrial buildings is a major load on the electric grid, which means power plants, which means CO2 emissions.

Are you ready to go without your air condition?  Are you ecologically minded, but what about during a heat wave?

Should we shut down offices and factories?

In California the new "Demand Response" laws will require customers on the grid to "willingly submit" to controlled air conditioning outages if the grid gets overloaded or unstable - this a stop gap measure to prevent rolling black outs.

Now with the new CO2 / Sustainable measures in California, the day may come where air conditioning is considered a luxury and your government might say no more?

That's the basic intro, questions or comments please open a discussion in the Forum?