HUMIDITY CONTROL
Drying success: getting dehumidification right
Dave Marshall-George, UK & Ireland sales director at Condair, examines what contractors ought to consider when undertaking dehumidifier projects
www.heatingandventilating.net
additional heat. Desiccant systems typically add more heat due to the regeneration process, so installing cooling coils after the dehumidifier can help manage temperature. If this heat gain is not managed, the area being dried can experience a significant rise in temperature. End-users can often try to counteract heat gain by venting the room, but introducing outside air can bring in more moisture, making humidity control less efficient. Some condensing units, such as the Condair DC-N, address this issue by incorporating a secondary external condenser, similar to a split air conditioning system. This setup allows heat to be exhausted remotely, maintaining precise temperature and humidity in the room. The placement of the dehumidifier within the
Above: Dave Marshall- George, UK & Ireland sales director at Condair
project space is an important consideration. Installing the unit inside the area to be dried can simplify the process and reduce the need for extensive ductwork. Using internal air for intake ensures more consistent conditions and can improve the accuracy of humidity control. In some cases, drawing supply air from outside can be used to over-pressurize the area and prevent unwanted air ingress. For pressure-neutral setups with desiccant
D
elivering a successful dehumidifier project requires HVAC contractors to navigate a range of technical and practical
challenges. Lowering humidity in a room is not simply a matter of installing a dehumidifier. It involves understanding the psychrometrics behind air drying, the impact on temperature and the installation requirements of different technologies. Approaching projects with an understanding of these topics will help deliver successful humidity control and client satisfaction. The first major decision in any dehumidification
project is choosing the right technology. There are two principal types of dehumidifiers: condensing and desiccant. Condensing systems work by cooling air so that moisture condenses on a cold surface and is then drained away. These systems are most effective in environments where the temperature is above 20°C, and they are typically used to reduce humidity to around 45–50% relative humidity (%RH). Their installation is straightforward, requiring only connections for power and drainage. Alternatively, desiccant dehumidifiers operate by passing air through a rotor coated with a moisture- adsorbing material. This technology is not affected by ambient temperature, making it suitable for cold environments and for achieving humidity levels below 45%RH. However, desiccant systems require ducting to vent hot, moist air outside and a secondary airstream to regenerate the desiccant material, which can mean a more complex installation.
Dehumidifier installation planning is critical, especially for desiccant systems. These units have two separate airflows - one for the process air and another for rotor regeneration. Managing
14 January 2026
systems, the regeneration airstream can be managed externally, while process air circulates within the treated space. Understanding the client’s requirements for internal conditions will help contractors work with suppliers to determine the best location and airflow configuration. Sizing the dehumidifier correctly is essential for
project success. Contractors must gather detailed information about the desired room conditions, the volume of air in the space and the rate of air exchange. Ventilation could be through doors, windows or via an air handling unit. In naturally ventilated areas, estimating air exchange is critical, including the number and size of doors and their usage patterns. The number of occupants, their activities and any open sources of water also influence the required size of dehumidifier. Providing this data to the supplier enables
accurate psychrometric calculations, ensuring the selected unit meets the project’s needs. A reputable supplier will offer guidance on sizing and address all relevant installation and technology selection considerations. Ultimately, addressing these considerations
pressure within the system, across these airflows, is essential. Incorrect pressurisation can reduce efficiency or cause moisture problems. To maintain proper pressure and prevent crossflow through the rotor, contractors ought to install short ducts with dampers on both intakes. This allows for more precise set-up during commissioning and helps avoid operational issues that could subsequently compromise the system’s effectiveness. Temperature management is another key
consideration. The process of drying air generates heat - about 680W for every kilo of moisture extracted. Mechanical components in both condensing and desiccant systems contribute
early in the project lifecycle helps avoid common pitfalls and ensures a smooth delivery. By understanding the technologies, managing airflow and temperature, strategically placing units and accurately sizing equipment, HVAC contractors can deliver dehumidifier projects that meet client expectations and maintain the desired humidity. The Condair Group is the world’s leading specialist in humidity control and evaporative cooling, with energy efficient, hygienic and innovative technologies for commercial, industrial and heritage applications. Condair is represented in the UK by Condair Ltd, which offers system design, manufacture, supply, installation, commissioning, maintenance and spares.
DOWNLOAD THE HVR APP NOW
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32
