Design conditions for the CIBSE Gain calculation in OpenBuildings Energy Simulator, including allowing for the introduction of fresh air or conditioned air, can be set by using the Design Data tab within the CIBSE Gain calculation.
This menu is where design conditions can be set, such as Supply Temperature:
Outdoor Conditions can be set as below. Any values can be entered manually, or select the desired day and press the Re-calculate button to update the figures:
Fresh Air Loads, can also be specified as follows:
The available Fresh Air Loads options are:
This option is for conditioning the room locally by means of fan coil units. Fresh air is not being introduced directly into the room, or at the main plant.
This option is for local conditioning via fan coils and the introduction of untreated air into the room. The untreated air could be introduced into the fan coil unit, directly into the room, or ceiling void.
This option is for local cooling in the room (fan coil units) but also have a fresh air requirement that is being managed by central plant.
The temperature of the primary fresh air must be specified. You can also set a humidity control for the primary fresh air if desired. The central plant will then be modeled based on the heating/cooling and humidify/dehumidify parameters.
When considering this option, individual room load results will be affected as the cooling on the primary fresh air will be considered. The plant results will display the fresh air conditioning loads.
This option is for all the conditioning at central plant with no local cooling. This could either be by recirculation or a full fresh air system. The illustration shows a recirculation system where primary fresh air is mixed with recirculation air then cooled to the defined supply temperature before being introduced to the room. With this option, room loads will not be affected as there is no requirement for local conditioning. The total plant loads will increase to indicate the fresh air load being handled.