Dehumidification in Australian Buildings

Health and comfort

Humidity control is one of the problems that originally spurred the need for air conditioning. Lack of humidity control in hot, humid climates can lead to mould growth and other moisture-related problems that can lead to health and comfort problems.

Modern air conditioners dehumidify as they cool, but this dehumidification is incidental to their main job of controlling temperature. They cannot independently control both temperature and humidity.

In hot, humid climates the incidental dehumidification that occurs may not always be enough to keep the indoor humidity conditions acceptable. (ASHRAE recommends roughly a 60% relative humidity maximum at 25C.) Dehumidification occurs not just at the hot times of the year—when the air conditioner is running a lot—but also at mild times of the year when the air conditioner runs very little.

TABs, Chilled beams and Radiant Heating / Cooling

Thermally Active Building Systems (TABS) take advantage of the building design and mass of construction materials to reduce energy consumption in heating and cooling through thermal storage. Radiant heating and cooling systems are also extremely efficient and in general use these principals but in both cases there will be a need for supplementary dehumidification in many climate zones within Australia. Chilled beam designs are becoming increasingly used in commercial office buildings but require supplementary air treatment in many cases, including dehumidification.

Air conditioning, Free Cooling and Natural Ventilation

Many buildings use a HVAC unit to control their thermal environment and many now incorporate an element of free cooling as part of the designers strategy to gain Green Star points. Other buildings are naturally ventilated and do not rely on such mechanical systems to provide thermal comfort. Depending on the climate, this can drastically reduce energy consumption. It is sometimes seen as a risk, though, since indoor temperatures can be too extreme if the building is poorly designed. Properly designed naturally ventilated buildings keep indoor conditions within the range where opening windows and using fans in the summer and wearing extra clothing in the winter can keep people thermally comfortable. Again, in naturally ventilated building there may be a need for supplementary dehumidification in many climate zones within Australia

Although there are some leading edge air conditioning systems that promise to independently control humidity, conventional systems may not be able to sufficiently control the problem and can cause comfort or mould problems in certain situations. So while conventional air conditioning systems may provide some dehumidification, a dedicated dehumidifier can provide the required level of comfort.

Dehumidifier Types

Dehumidifiers work by condensing the moisture in the air and collecting it in a container or constantly draining to waste. Small residential dehumidifiers typically collect 4 to 8 liters per day with a room temperature of 20C and relative humidity of 60% to 70%.

Desiccant rotor dehumidifiers are becoming more readily available for residential use and can be purchased from many appliance retailers. These models use a slowly rotating disc or belt of material which absorbs moisture from the air; the damp section then moves through a drying process (typically a heating element), which evaporates the water and collects it in the tank. But desiccant models rarely exceed a rated extraction rate of 10L/day, while you can find refrigeration models rated up to 30L/day or more. So for heavy-duty dehumidification, a refrigeration model would be the best option.

Most commercial dehumidifiers, work by refrigeration. They draw air in, filter it, cool it to condense the moisture, then reheat it and push the warmer, dryer air back into the room. This warms the room somewhat, but not as much as an actual heater. Refrigeration models operate best in hot, humid conditions. The hotter the air, the easier it is to cool it by a large amount and extract moisture from it. Commercial dehumidifiers have a larger capacity than residential units and can be installed into the buildings existing ducted air distribution system. They range from 24 to 600L per day capacity.

Adiabatic Dehumidification in Commercial Buildings

As mentioned above, conventional humidifiers have the potential to add heat to the indoor space, obviously quite undesirable on hot days both from a comfort and energy use perspective. Heat added to a room as a by-product of the dehumidification process has to be removed by the building cooling system requiring more energy usage.

To solve this problem, Radiant Heating and Cooling offer the RNW range of Adiabatic dehumidifiers to control relative humidity in radiant heating/cooling systems.(An adiabatic process is one in which no heat is gained or lost by the system). Each machine is a cooling unit equipped with 2 additional heat exchangers that exploit the availability of chilled water (mixed to 15-18 °C) used by the building HVAC system.

The pre-treatment coil, located under the evaporator, reduces the temperature of the air, lessening the sensible load on the evaporating coil. The post-treatment coil, located after the condenser, reduces the temperature of the air before sending it back to the room. This treatment produces dehumidified air with the same temperature as the air inside the room.

Basically, RNW dehumidifiers control the “latent load”; this increases the efficiency of the building cooling system, which can operateat higher temperatures than the temperature usually required for dehumidifying.

Installation of Commercial Dehumidifiers

This is an essential element for the correct working operations of the HVAC system.

The design of the system should always ensure that:

1 Each RNW dehumidifier is equipped with 2 attachments (inlet and outlet) for the cooling water circuit: this requires 2 pipes to be fitted and normally connected to the chilled water circuit via a mixing valve.

2 There is a suitable power supply (230V-50Hz, single phase), with humidity control.

3 There is a collecting pipe to discharge condensation at each RNW dehumidification point.

4 Dehumidifiers must always be placed in a position in which they can be inspected.