Manipulating the environment within a drying chamber is essential to successful water damage restoration. Equipment is deployed to evaporate surface water and create a vapor pressure differential between saturated building materials and dry air. This vapor pressure differential causes trapped water to vaporize and move from the substrate to the air. Achieving an optimal environment for evaporation requires attention to the vapor pressure differential. The bigger the spread of vapor pressure the greater the pull of moisture from the air.
Surface Water & Trapped Moisture
Moisture consistently moves toward lower pressure whenever possible. Evaporation takes place when the vapor pressure of the liquid is greater than the vapor pressure of the air. The force that stimulates moisture movement is both defined and measured as vapor pressure. Moisture travels from higher to lower vapor pressure until an equilibrium is reached. The difference in pressures determines speed of evaporation.
Rapid air movement across wet surfaces is a critical component of efficiently removing surface water from saturated building materials. Conditions conducive to drying surface water, differ from those required to remove excess moisture trapped within structural components. Relative to vapor pressure, air movement becomes less important as the focus of removing surface moisture gives way to reducing the moisture content within structural members.
Relative Humidity &. Specific Humidity
Water damage restoration professionals consider vapor pressure, GPP (grains per pound), dew point, humidity ratio, absolute humidity and relative humidity when devising a drying strategy that will most effectively augment evaporation. Vapor pressure, GPP, dew point, humidity ratio and absolute humidity describe the actual amount of water vapor in the air. On the other hand, relative humidity relates the actual amount of water vapor to the potential amount.
The amount of moisture air can hold varies with temperature. As air is heated, its volume increases enabling the air to hold more moisture. As air is cooled, its volume decreases reducing the amount of moisture the air can hold. Relative humidity (RH) measures the amount of moisture the air is holding at a given temperature. This amount is expressed as a percentage moisture air can hold when totally saturated at the same temperature. Relative humidity measurements can be misleading as temperature determines how much water the air can hold. Warmer air has the capacity to contain more water than cooler air at the same relative humidity.
The reason RH is used in restoration is that hygroscopic materials have an equilibrium moisture content that is mainly determined by RH. In simplest terms, when RH is low, materials will generally lose moisture. When RH is high, especially above 60 percent, materials will generally gain significant moisture. When conditions exceed 60 percent RH, the structure is more likely to suffer secondary damage.
RH does not define the water content of the air unless the temperature is given. Air can hold more water vapor when the temperature of the air increases. Therefore, changes in air temperature will change the relative humidity. Relative humidity will decrease when air temperature increases. Conversely, RH will increase as air temperature is decreased.
Grains per pound (GPP) is a unit of measurement used to determine the weight of moisture in the air. The weight of moisture present in a pound of air articulates the specific humidity. GPP measurements gives water damage restoration professionals the ability to evaluate various environments on a water mitigation project.
Dew point is the temperature that air needs to be cooled to, at constant pressure, achieve a relative humidity of 100%. Dew point is important in drying because when air reaches saturation, water vapor will condense as dew on surfaces. The higher the dew point rises, the greater the amount of moisture in the air.
Vapor pressure is directly related to humidity ratio (specific humidity and dew point). As heat is applied to a material, energy is added. Raising the temperature of a wet material increases the rate of evaporation, releasing moisture from the material and changing the internal vapor pressure. The greater the difference between ambient temperature and dew point temperature, the greater the potential for faster drying.
Grains per pound
Grains per pound (GPP), dew point and vapor pressure are all directly related, specific humidity measurements that move in unison. Consequently, Grains per pound measurement are used by water mitigation technicians as a constant. Changes in GPP are directly proportional to those found in dew point and vapor pressure.
Harnessing Vapor Pressure
Vapor Pressure is a measure of a substance’s propensity to evaporate. Understanding this dynamic and harnessing vapor pressure levels within drying environments will accelerate structural drying. Accentuating the vapor pressure differential between saturated building materials and the surrounding environment hastens structural drying.
Dehumidifiers are routinely deployed to remove moisture from the air, decreasing environmental vapor pressure. This increases the vapor pressure differential between the air and the substance to be dried, accelerating drying time. Additionally, there are ancillary drying technologies that allow water damage restoration professionals to focus considerable heat directly to saturated building materials without appreciably increasing ambient temperatures. Rising vapor pressure within the building materials, ultimately boosts the vapor pressure differential between the subject and the environment.
Professional Flood Damage Restoration
Property Recovery 911 offers professional water mitigation and flood damage restoration no matter the source or scope of the water intrusion. Prompt water removal and structural drying is essential to reducing the ongoing effects of water exposure, which can wick up walls, travel under base boards, penetrate floor coverings, infiltrate sub-floors and damage adjacent rooms. If left unchecked over 48 hours, microbial growth can ensue threatening the interior environment and the health of those within.
We are prepared and on call 24 hours a day, 7 days a week to dispatch a quick response team who can be on your location within 1 hour protecting your interests. Contact Us for professional water damage restoration in Philadelphia and the surrounding suburbs at (267) 808-7200.