Fresh outside air keeps a building and its occupants healthy.  In fact, outside air ventilation is a code requirement in many cities, states, and municipalities. However, if the air outside is humid, then the air you’re bringing into your building is also humid.

Excessive humidity indoors promotes invasive microbial growth in wall cavities, ceiling tiles, mattresses, furniture, carpeting, and tile grout.

It causes rooms to smell musty, it’s unsightly and unhealthy. In fact, hotels can lose guest loyalty because of it. Senior living facilities, because of the high number of residents with compromised immune systems, subject their population to higher risk of health problems if mold is an issue.

Mold at your property can cause both minor reactions (nasal stuffiness, throat irritation, coughing or wheezing, eye or skin irritation) and more severe reactions like lung infections, especially for those with mold allergies or lung disorders like COPD.

The cost to repair mold damage and prevent its return can be astronomical. As the National Institute of Building Sciences describes one hotel’s costly mold reparations, “only a few years after opening its doors, the hotel underwent a major overhaul. Over 40,000 square feet of gypsum wallboard was removed and replaced in the newly constructed guestrooms. Three hundred HVAC systems were replaced … Ultimately, repairs and other associated costs exceeded $6 million.”

Where is high humidity a problem?

If someone were to ask you which states have the highest humidity, would Florida and Louisiana immediately come to mind? Those southern states do have relatively high humidity.

Humidity and its resulting problems aren’t limited to Florida and Louisiana. Other states like West Virginia, Wisconsin, New York and Washington have high humidity too. In states east of the Rocky Mountains, even small amounts of moisture in the outdoor air can lead to indoor moisture and moisture-related problems during the spring, summer and fall, if the air is not properly conditioned.

High humidity presents a greater problem in these areas where high humidity levels last for an extended period of time (a month, for example) in the cooling season. That means buildings in Orlando, FL are more susceptible to humidity challenges than, say, Atlanta, GA.

Why humidity can be difficult to manage

Air Conditioners to the Rescue?

Air conditioners can reduce humidity by pulling warm air in and cycling it over cold coils, producing condensation, thereby removing moisture and reducing humidity in the air.

However, air conditioners alone are rarely the solution: they can measure temperature but they cannot measure humidity. Because of this, the air conditioner stops running when the ideal temperature is reached, NOT when the ideal relative humidity is reached.

At the point when the ideal temperature is reached, the air conditioner stops cooling, allowing humidity to rise. This can make the indoor space seem warmer than it actually is. It is possible for building humidity to never be effectively reduced!

Humidistats to the Rescue?

Your HVAC units might feature humidistats, which measure humidity but do not control humidity.

Active Dehumidification Components to the Rescue?

“Active dehumidification components” target and control humidity. HVAC units are either designed with active dehumidification components or without. HVACs that include this feature tend to be more expensive and less common than those without this feature.  Note that on PTAC’s, active dehumidification cannot be retrofitted later. Justin Lendowski, Sr. HVAC Control Technician / Product Development Engineer at Telkonet, recommends that when shopping for HVAC’s, do not skimp on options like this one. PTACs with dehumidification are worth the extra cost if you can find the funds in your budget.

Energy Management Systems to the Rescue?

Some Energy Management Systems (EMS) can be programmed to measure and control humidity using special firmware.  

Remember the outside air requirements we mentioned earlier? The amount of outside air entering a building has to be controlled. This is done using a damper, a mechanical device that opens and shuts to control the intake of that outside air. Some EMS systems have the capability to control the damper via the firmware in their smart thermostats.

Typically, EMS firmware that controls humidity is designed to work with fan coil units. There are some EMS platforms that can essentially add active dehumidification to PTAC units, depending on the design.

The best way to dehumidify is to cool slowly, using a Cool/Low Fan. It dehumidifies better than a Cool/High Fan. Less airflow over the cold coil allows more condensate (moisture in the air) to form on the coils, removing it from the supply air more effectively. When the relative humidity is above a certain threshold, smart thermostats can be programmed to allow only Cool/Low.

Fan coils with the heating coils in the re-heat position can be controlled to actively dehumidify by reheating the air coming off the cooling coil, so over-cooling does not happen.

It’s easier to dehumidify a room or living space that is unoccupied than one that is occupied. Without occupants in the space, the air conditioner can run more aggressively, until the humidity in the air reaches a defined level without disturbing anyone with an uncomfortably chilly space or the noise of a continuously running HVAC.  

Telkonet has come up with a way to dehumidify even when a room is occupied; the key is that comfort cooling takes precedence. The system can overcool in Low/Cool by a mere 1 or 2 degrees without an occupant likely noticing. Telkonet thermostats feature a “Refresh Cycle”. When the room becomes unoccupied, during each Refresh Cycle the HVAC system activates and drives the relative humidity down . The sustained cooling drives effectively dehumidify the air. Though relative humidity climbs between refresh drives, it never reaches the peak levels seen during the occupied period. The Refresh Cycle forces the HVAC system into a sustained cooling drive, which typically lasts for 10 to 15 minutes every 4 to 6 hours (this is programmable).

A Final Takeaway

Humidity is more problematic in some climates than in others, but nevertheless, there are large swathes of the U.S. that do experience periods of high humidity and its threat to damaging buildings and their contents.

Mold and mildew caused by sustained high humidity inside buildings can cause health problems ranging from mildly annoying to life threatening. In particular, hotels can lose loyal guests who are turned off by the sight and smell of mold and mildew, some of whom announce their bad experiences on TripAdvisor and other social media platforms, complete with photos.

The most effective preventative action is to install HVAC systems that feature “active dehumidification”. When HVAC budgets preclude this pricey feature, energy management systems can play an active role in dehumidification.

Select an EMS company with expertise in reducing and preventing high humidity. When researching your EMS options, do your homework. Be selective. Ask questions. If you don’t understand their answers, by all means, ask more questions.