There are generally two types of dehumidifier. A refrigerator dehumidifier works by using a fan to draw in moist air which then passes over coolant-cooled coils. The air is warmed and dried and allowed to re-enter your home. A desiccant dehumidifier, on the other hand, uses a heated, absorbent material to draw moisture out of the air and this is collected in a water tank that needs emptying periodically. Both dehumidifiers can cool the room by reducing humidity, but they are not designed to lower the overall air temperature.
If your home is regularly heated, you may prefer to opt for a refrigerator dehumidifier, as these need the air in the room to be warmer than inside the dehumidifier. Desiccant dehumidifiers are more efficient in cooler temperatures, so if you want to tackle mold or mustiness in a cold basement, garage, or conservatory, one of these may be a better choice.