Updated: November 8, 2021
Shortly after traditional HVAC units were introduced in Japan around the 1950s, it was realized that the bulky and loud systems needed a redesign to meet the needs of smaller homes built close together. Developed as an alternative, mini-split systems were created as heating and cooling systems that allow the temperature of individual rooms or zones to be controlled. Today there are a variety of mini-split systems on the market, before purchasing one it is important to understand the capacity of these units.
As advancements in technology continue, the popularity of mini-splits continues to grow. The latest systems are more energy-efficient and run quieter than previous models. There are even units with a dry mode that claims to pull moisture without cooling a room. However, many mini-split manuals actually suggest that when in dry mode, the temperature should be set slightly lower than the room temperature to lower humidity. In theory, these systems seem to be a great fit to simplify installation for cooling, heating, and dehumidifying but do they have the track record to prove their efficiency in all categories?
One product | One installation | One contractor…Wouldn’t it be nice?
Myth: Mini-Split systems control indoor humidity levels with dehumidification.
Truth: Yes & No…
Mini-split systems dry the air but do they adequately dehumidify indoor living spaces below 60% Relative Humidity?
These systems only dry the air, which limits the capabilities of multi-split systems removing moisture from the air. Unfortunately, there are too many variables to consider, after in-depth research, the following questions were not fully answered.
How many pints will be removed an hour/ per day?
An average family of four produces 25 pints of moisture a day, through cooking, cleaning, laundry, showers, perspiration, even breathing, and more. These units “dry” 4 pints of water an hour on average (some less), and would have to run for over 6 hours non-stop to compensate for the added moisture. Mini-splits were not designed to run 6 hours non-stop. The main function is to cool – not dehumidify. Integrating an escape route for the added moisture is key.
Is dehumidifying the space left to the tenant to oversee and manage?
Unfortunately, residents are likely to choose personal comfort over property protection. Mini-split systems relinquish total control of the unit to the tenants. This allows the residents to regulate relative humidity settings, runtime of unit, mode (cool, dry, heat), even control if the unit is used at all. These choices ultimately determine the amount of moisture removed from the air.
How long will the unit run in dry mode?
In theory, it sounds great to have dry mode, to remove humidity with only a small decrease to temperatures through heating air supplementary. Are tenants aware when the relative humidity is too high? Tenants often don’t understand the negative side effects associated with excess moisture and more often than not can’t be relied upon to run their units accordingly. Will tenants run dry mode continuously? The parameters of dry mode, intervals/ continuous, are undefined.
What are the controls for humidity setting?
Settings are basic, offering “HIGH”, “LOW” and “STANDARD”. An important feature of supplemental dehumidification is removing moisture, a dehumidifier should help keep indoor relative humidity levels below 60 percent year-round. Mini-split systems are capable of drying some of the added moisture during warmer months. Unfortunately, they are not designed to dehumidify in cold weather and will not pull moisture in the winter months. Dehumidification should run independently of cooling systems to ensure proper moisture removal. Mini-splits do not determine relative humidity without an additional accessory therefore control is extremely limited.
What is the operating temperature range of units?
These systems have indoor and outdoor units; the outdoor compressor will not work in temperatures below 50°. Humidity levels will vary through the year depending on the season. During the winter, people are home more frequently producing even more moisture. It is common to find condensation forming on the windows during colder months. Signs of potentially dangerous levels of moisture are not always visual and “humid weather provides excellent conditions for mold to grow”1 according to the University of Florida. Yet, mini-split systems do not provide dehumidification in heating mode.
What does the installation process entail?
One product, one installation, with one contractor, sounds ideal and appealing, especially for new construction apartments. However, if mini-splits are not pulling enough moisture daily, humidity will increase potentially causing property damage, remediation, the risk of litigation, and more. Mini-splits cannot be relied upon to sufficiently maintain moisture levels and lower high humidity. Due to so many unanswered variables installing a supplemental in wall dehumidifier is advantageous to remove moisture generated and trapped inside. Contrary to popular belief an in or on wall dehumidifier can be easily installed in 30-45 minutes and doesn’t require a separate contractor.
As suggested by the Environmental Protection Agency (EPA), indoor relative humidity RH should be kept below 60 percent — ideally between 30 percent and 50 percent, if possible.2
Key Factors of Effective Dehumidification to Consider:
- Easy installation
- Size of room or space in square feet
- Pints per day removed; Coefficient of Performance, measured in L/kWh
- Setting to control relative humidity levels
- Draining of collected condensate
- Placement of unit
- Energy efficiency of unit effectively running
- Residential behavior
The need for dehumidification in rental properties is often exemplified, for instance, seniors become more sensitive to cold temperatures with age. Tenants will often leave thermostats at higher temperatures and a handful even refuse to run their units, mini-split systems are unable to pull moisture from the air if they are not running. Limited income is also a factor for many renters, who would rather leave the unit off to save on their electric bill.
Supplemental Dehumidification Independent of HVAC System is a Necessity to Remove Moisture Trapped Indoors
The purpose of supplemental dehumidification is to remove moisture from the air and help lower relative humidity (RH) below 60%. Supplemental dehumidification will adjust RH levels indoors to compliment the capabilities of cooling systems.
As the demand for efficient housing increases, sufficient ventilation is limited due to tighter envelopes. Since moisture is continuously added to the air indoors, supplemental dehumidification is essential to condense and remove moisture trapped in your property. Innovative Dehumidifier Systems is available to guide you through the entire process and put the control back in your hands. Learn more about the IW25-4 In Wall / ON Wall Dehumidifier with Bi-Polar Ion Generator.
What are multi-family developers/ general contractors/ owners using to provide supplemental dehumidification and Why?
1. Lee, H-J and Peart V. (January 2007). Basic Mold Prevention University of Florida IFAS Extension, 2007.
2. United States Environmental Protection Agency, Mold Course Chapter 2, July 2021, accessed October 14, 2021 <https://www.epa.gov/mold/mold-course-chapter-2>