HUMIDITY CONTROL


An installer’s guide to dehumidifi ers


Dave Marshall-George, sales director at Condair, considers the most important aspects of installing dehumidifi ers.


L


owering indoor humidity can be complicated. The dehumidifi cation process has a signifi cant impact on air temperature and, depending on which type of


dehumidifi er is being used, there can be various installation obstacles to overcome. So, what should an installer consider before setting out on a dehumidifi cation project? Firstly, which type of dehum to use? There are two main technologies – desiccant and condensing. A condensing dehumidifi er collects water by condensing it on a cold surface, whilst desiccant units adsorb moisture by passing air through a desiccant rotor.


Condensing systems are ideal for warmer conditions, as


more condensation occurs. This technology is great in rooms of 20°C or more and for projects that need to lower humidity down to around 45-50%RH. As the room’s temperature has no impact on the ability of the desiccant to adsorb moisture, these systems can be used at any temperature, making desiccant a more fl exible technology and ideal for cold environments. Desiccant dehumidifi ers are also able to maintain a humidity below 45%RH.


Installing a condensing system is often simpler as it needs connections for just power and drain. A desiccant dehumidifi er has no drain but does need a duct to vent hot wet air away from the area being dried. To remove moisture from the desiccant rotor, a secondary hot airstream is passed through the rotor, which carries the moisture away to the outside. Pressure management must be considered whenever a dehum has ducting. Each model has a pressure rating and inadequate or excessive airfl ow through the system may reduce effi ciency or cause wetting issues. As there are two airfl ows through a desiccant system, care must also be taken to avoid crossfl ow through the desiccant rotor. Installing short ducts on both intakes will allow for dampers to be fi tted, which can help manage internal pressure and avoid crossfl ow issues. Alongside pressure, temperature management must also


be reviewed by the installer. The thermodynamic principle of drying produces heat at around 680W per kg of moisture extracted. In addition to this, the mechanical elements incorporated into both technologies produce heat. Without assessing and controlling this, the area being dried can experience signifi cant heat gain. All too frequently, the heat gain from dehumidifi cation is countered by venting an area. But opening windows or proactively bringing in outside air, can reintroduce moisture and impact humidity control. For condensing systems, if the heat gain is too great, some units, such as the Condair DC-N, have a secondary condenser that can be located outside. This is similar


16 March 2024 • www.acr-news.com


to a split air con unit and allows the heat in the refrigerant loop to be remotely exhausted and the dry air delivered to the room at a precise temperature and humidity. Heat gain in desiccant systems will be greater than condensing, as the “regeneration” portion of the desiccant wheel is heated to remove the moisture. This heat transfers to the process airfl ow as the rotor revolves, so adds signifi cant heat to the dry airfl ow. To counter this, a contractor can install a cooling coil before or after the dehumidifi er. Dehumidifi er location is another important decision to be made early in the project. If the unit is placed inside the area to be dehumidifi ed, installation can be simpler with less ducting needed to direct airfl ows. Air can be taken from the area being dried and delivered directly back to it. Using the room air rather


Installing a condensing system is


often simpler as it needs connections for just power and drain.


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