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One winter a newly acquired Hupmobile 1929 four-door saloon, bought in Pennsylvania, USA, was being stored in a garage. The owner Jan Olander found that the newly chromium-plated parts started disintegrating and for the rest of the winter he tried to wipe the car regularly to keep it dry.
The dehumidifier works by air passing through a specially impregnated rotor. The rotor material is extremely hygroscopic (humidity-absorbing) and is therefore able to absorb a large quantity of water from the passing air stream – the process air.
The process air is led through the rotor and leaves the discharge side of the dehumidifier as dry air with a very low relative humidity of 15-25% RH. The rotor turns slowly, and another smaller air stream makes sure that the rotor is continuously dried of the absorbed water – regeneration. This air stream, is taken from the outside, heated and blown through the rotor so the absorbed water is discharged outside as wet air. This means there is no need to empty a water tray.
The desiccant dehumidifier is controlled by a hygrostat that keeps a constant relative air humidity of 55% RH, and the operating expenses for the dehumidifier are 65-260 Euro, depending on the size, building materials, level of sealing, etc. of the garage. It should be stressed that, strictly speaking, there is no need for insulation but the garage should be as airtight as possible in order to reduce the operating time of the dehumidifier.
In Jan's 45m2 garage he spent 260 Euro per year in electricity but with improved sealing of the doors and the new electronic hygrostat that accompanies the dehumidifier, he would see reduced power consumption.
General considerations on humidity
The lowest RH values are found April to July where values of 50-60% are common, whilst the RH value for the rest of the year reaches 70-100%. With a RH value below 55%, no corrosion occurs, and with a RH value below 70% there is no risk of mould on fabric, leather trims and wood. With low RH values no creeping air currents or bad contacts occur on power cords and many problems with starting are avoided – such as humidity in the ignition system. When you keep your garage dry you can prevent all sorts of deterioration of the car, and inconveniences caused by humidity. A further advantage is that the car will quickly dry out when it goes into the garage wet after a journey. The comfort zone for a human being is 40-60% RH, and the climate in a dehumidified garage will be much more pleasant, as dry air feels warmer than moist air at the same temperature.
Jan Olander contacted Munters in Farum and bought an MG 90, then sealed his garage doors as this has a major influence on the energy consumption of the dehumidifier. The dehumidifier ran for 2-3 weeks continuously in order to extract the humidity from the walls, floor and ceiling. Then the operation time fell to a few hours per day (controlled by the hygrostat). The dehumidifier keeps the level of relative air moisture at 55% RH.