What do the different air flow options mean in DDB?

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Introduction In the Design Database package, In the various heat gains programs, you can specify four different type of air loading for your rooms.

Method

There are four options for Fresh air loads in the various heat gain programs: These options relate to the following examples.

Option 1 - No Additional Fresh AIr Choose this option if you are conditioning the room locally by means of fan coil units and you are not introducing any fresh air into the room or at the main plant. For example:

What do the different air flow options mean in DDB?

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Option 2 Fresh Air Introduced Locally Into Rooms Use this option if you are conditioning the room locally by means of fan coil units and are also introducing untreated fresh air directly into the room. This could be directly onto the back of the fan coils or straight into the room or the ceiling void. For example:

Option 3 Conditioned Primary Fresh AIr This option should be used if you have local cooling in the room via fan coil units and where you also have a fresh air requirement that is being managed at your central plant. When you select this option you must set the supply temperature for the primary fresh air. You can also optionally set a humidity control for the primary fresh air. The central plant will then have to heat\cool and humidify\dehumidify the fresh air requirement based on the parameters you set. With this option the individual room load results will be affected, as the primary fresh air is already cooled at central plant and therefore reduces the load that local fan coils have to overcome. The plant results will show the fresh air conditioning loads required.

What do the different air flow options mean in DDB?

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Option 4 Fresh Air From Central Plant With Conditioned Air Use this option if all of your conditioning is being performed at your central plant with no local cooling in the rooms. This could either be by a recirculation or full fresh air system. The diagram below shows a recirculation system where the primary fresh air is mixed with recirculation air and then cooled to the defined supply temperature before being to the room. If this option is selected then the room loads will not be affected, as there is no requirement for conditioning of fresh air locally in the room. The total plant loads however will increase to take account of the fresh air load that is being handled.