Why HVAC Systems Won't Cut it for Humidity Control

Moisture at a construction site warrants serious attention, particularly because most building materials absorb moisture. As a result, a common construction drying solution includes the use of an on-site HVAC system in an attempt to maintain ideal relative humidity levels. The problem with this approach is that HVAC units are meant to condition air so the occupants inside feel comfortable. Using an HVAC system for a different reason increases the appliance’s load, causing unnecessary wear and tear. It’s simply the wrong tool for the task.

What Happens When You Use an HVAC System for Construction Drying

An HVAC unit is capable of removing humidity from indoor air, particularly when the air conditioner runs. But, engineers design these systems to control temperatures (i.e., thermal loads), not remove moisture. For an A/C to cool the air, it must remove excess humidity first. For this reason, the most energy-efficient units become less efficient in regards to removing humidity because the cold coil doesn’t get cold enough for humidity control purposes. The result is a system that reaches the temperature set point quickly but doesn’t remove much humidity due to its short cycling. The moisture that the unit acquires ends up re-evaporating into a space.

Air conditioner manufactures attempted to give their units the ability to eliminate excess moisture by slowing the fan, which allows the cold coil to get cold enough to remove humidity. Incidentally, A/C units produce very cold air, which cools some of the system’s components as well, such as ducts and discharge registers. Condensation then forms on the cooling components and drips water into the unit. A/C over-cooling also produces temperatures that are not conducive to the drying or installation of construction materials, such as paint, concrete, wallboards, flooring, fireproofing, and lumber.

Heating systems generally do not have components that remove moisture or reduce vapor pressure. They create drier conditions because humidity levels to lower relative to the increased temperatures. In the end, the hotter temperatures do not remove water in the air. Additionally, temperatures that are too warm may cause materials to dry too quickly, leading to premature failure in the future.

Better Construction Drying Solutions

Using an HVAC system to dry a building under construction might void its warranty. As a result, building owners may not allow the use of the unit during construction. The best way to create and maintain the ideal conditions at a construction site is with an independent desiccant dehumidification system. These systems do not condense moisture. Instead, they use desiccant materials that attract and trap moisture in the air, lowering the airstream’s vapor pressure. The moisture and contaminants that pass through the system vent it into an exhaust-air stream via independent, portable ductwork.

The best desiccant dehumidifier for a construction site is one that’s designed for space’s size, envelope tightness, outside weather conditions, and other variables. Pair the construction drying solutions with a coordinating heating and cooling system that allows you to create the ideal environmental conditions for worker comfort and appropriate material drying. Get in touch with a Polygon representative today about how desiccant dehumidifiers will improve your construction site’s productivity and keep you within budget. 

[Photo from Michael Casey via CC License 2.0]