What about humidity control? Some buildings need to control the humidity of the air they supply into the building. If the airs moisture content is below this value then we need to introduce moisture into the air using a humidifier, this is usually one of the last things in the AHU. This device will usually either add steam or spray a water mist into the air. Many standard office type building in northern Europe and north America have turned off their humidity units or uninstalled them to save energy.
If the air is too humid then this can be reduced through the cooling coil. The cooling coil can be used to further reduce the moisture content by removing more heat, but of course this will decrease the air temperature below the supply setpoint, if this occurs then the heating coil can also be turned on to bring the temperature back up, this will work although it is very energy intensive. A pump circulates water between the two. This will reduce the heating demand of the heating coil when the outside air temperature is below the supply setpoint temperature and the return air temperature is higher than the setpoint, the heat would otherwise be rejected to atmosphere.
These will be used to control the pump as well as measure the effectiveness. As the pump will consume electricity, it is only cost effective to turn on if the energy saved is more than the pump would consume. This allows some of the exhaust air to be recirculated back into the fresh air intake, to offset the heating or cooling demand. This is safe and healthy to do but you will need to ensure the exhaust air has a low Co2 count so we need some Co2 sensors to monitor that.
When in recirculation mode, the main inlet and outlet dampers will not fully close in this setup because we still need a minimum amount of fresh air to enter the building. Another variation we might come across, is the heat wheel. This uses a large rotating wheel, half of it sits within the exhaust air stream and half of it sits within the fresh air intake.
The wheel will rotate, driven by a small induction motor, as it rotates it picks up unwanted heat from the exhaust stream and absorbs this into the wheels material. The wheel then rotates into the fresh air intake stream, this air is at a lower temperature than the exhaust stream so the heat will transfer from the wheel and into the fresh air stream which obviously heats this incoming air stream up and thus reduces the demand on the heating coil. This is very effective but some air will leak from the exhaust into the fresh air stream so this can not be used in all buildings.
Another version we might come across is the air plate heat exchanger. Save my name, email, and website in this browser for the next time I comment.
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Filter Driers How do they work. Thank you for sharing this information, Its very useful for my school project. Very good presentation…i really understod and enjoyed it.. Amazing post and valuable information.
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So where do we find Air handling units?
Define static regain and calculate static regain factor for various types of duct enlargements Introduction: In air conditioning systems that use air as the fluid in the thermal distribution system, it is essential to design the Air Handling Unit AHU properly. The primary function of an AHU is to transmit processed air from the air conditioning plant to the conditioned space and distribute it properly within the conditioned space. A typical AHU consists of: 1.
Supply and return air fans which provide the necessary energy to move the air throughout the system Transmission of air: In an AHU, air is transmitted through various ducts and other components with the help of fans. Since the fan motor consumes a large amount of power, and the duct system occupies considerable building space, the design of air transmission system is an important step in the complete design of air conditioning systems. In the end the success of any air conditioning system depends on the design of individual components as well as a good matching between them under all conditions.