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Safety During the Holidays
Objective -The objective of any dehumidification procedure is to reduce the moisture content - of the building air in order to draw excess water from the structure and contents and return the environment to pre-loss conditions. Key questions such as: HOW? HOW DRY? HOW MUCH? should be addressed to determine the most expeditious and cost effective solution for each situation.
There are two major methods of dehumidification - desiccant and refrigeration. In either case, a number of air movers are stationed inside the building to circulate the dry air from the dehumidifier into all areas and to speed the drying process. As much of the water saturated debris as possible (fallen ceiling tiles, boxes, ruined sheet rock, etc.) should be removed to minimize the water load on the dehumidification process.
Contrary to popular belief, a building cannot be dried too quickly. The least damage is caused when the building contents are dried as quickly as possible. The drying process is monitored by measuring the humidity ratio daily and by plotting the results on a chart. Individual items’ moisture content should be measured with appropriate instruments to evaluate the effectiveness of the process.
Desiccant - Desiccant units pull moist air through a rotary honeycombed desiccant wheel made of a substance such as silica gel or lithium chloride which absorbs the moisture. The resulting dry air is then blown into the building space. As the moisture is removed from the air, the desiccant material in the wheel becomes saturated. The wheel surface area is divided into two parts by a divider wall. One half of the area is used for absorption of moisture and the other half passes through the reactivation chamber where heated air is blown through the wheel material to dry (reactivate) it. Once dry it then rotates back into the air dryer chamber to once again absorb moisture.
Desiccant dehumidifiers generate much drier air than refrigeration units and operate in a much wider temperature I humidity range. This method is more effective in unheated facilities, such as large warehouses or open office space, where dehumidification is more economical than air conditioning or heating the facility.
The major drawback to desiccant drying is that the reactivation air stream (warm moist air) must be exhausted outside the building being dried. The butane fired reactivation may also be a problem if the unit is to be used inside the building. Therefore, the usual application of this unit is external to the building. The warm dry air is introduced through light plastic ductwork, which is custom designed for each application, or may be introduced into the HVAC system through a mixer box. These desiccant units are indispensable for large open areas such as gymnasiums and warehouses.
Refrigeration - A refrigeration unit contains a closed cycle of refrigerant that is allowed to evaporate inside copper coils. The evaporation process cools these coils. The gaseous refrigerant is then compressed to a liquid and passed through the condenser coils where the heat removed from the evaporator coils is exhausted. Refrigeration dehumidifiers operate efficiently in warm moist conditions. The warm moisture laden air is passed over the cold refrigerant coils (the evaporator) which are below the dew point temperature of the building air. As the air passes, moisture condenses on the coils so the air exhausted contains less water than the incident air. Before leaving the unit the dried air is blown across the condenser coils where it is heated and exits the unit with a net heat gain. The condensed water is collected in a pan and pumped to a drain as required. The advantage of the refrigerated unit is that it is self-contained and can be operated inside small office spaces. It does not require an external exhaust.
Tags: Dehumidification, Drying, Refrigeration, Water Damage
