Gains data model Option

Gains data

There are three levels of gains model detail:

Lumped - all internal gains including occupancy, computer, office equipment, miscellaneous, catering process and lighting gains are lumped together into a single value. Solar gains are still calculated in the usual way. Note that with Lumped gains you cannot generate Temperature distribution and Comfort simulation output data.

Note: When using the Lumped Gains model option, Comfort data is not generated because in EnergyPlus the request for comfort calculations is made in the People statement and this is not generated by DesignBuilder when Lumped gains is set.

Early - gains can be defined separately under various categories. This is the default and is normally the preferred option for design and energy assessment work.
Detailed - gains are specified by defining each individual item of equipment in each zone on the Equipment tab. If you select this option then DesignBuilder will automatically set the Timing model option to Schedules . Note that this option was developed for creating very detailed models of existing buildings based on survey data. Entering this data for a large building is very time-consuming and in most cases you will be better served by the Early gains option above.

Important Note: The Detailed gains option is included for legacy models only and may be discontinued in future versions of the software.

Gain definition level

This option allows you to choose whether the gain definition methods are defined globally here on the model options dialog or zone by zone in model data. Select from:

1-Globally in model options where a single set of settings is applied globally across the model. In this case the settings below for Occupancy method, Occupancy latent gains, Equipment gain units and Lighting gain units can be selected on the model options dialog as described below.
2-Zone by zone in model data where the definition methods for Occupancy method, Occupancy latent gains, Equipment gain units and Lighting gain units are set in model data and can be different for each zone.

Occupancy method

When the Gain definition level option is set to 1-Globally in model options, select the occupancy definition method from the following options:

1-People/area - the default option where occupancy is defined as occupancy density (in people / m2 or people / ft2).
2-Area per person - is sometimes preferred as an inverse occupancy density. Note that when switching between this option and occupancy density the definitions on the Activity tab zone level are translated accordingly. This is not the case when the number of people option below is selected.
3-Number of people - used when detailed zone by zone survey or design data is available. Unless you need to enter specific known occupancy gains zone by zone, this option is best avoided as it increases the amount of work involved

Note: When using the 3-Number of people option, the number of people in each room is entered zone by zone as values inherited from building and block levels will typically not be correct.

Occupancy latent gains

When the Gain definition level option is set to 1-Globally in model options, select the Occupancy latent gains method. There are 2 ways for the sensible-latent split of occupancy gains to be defined:

1-Dynamic calculation - where the latent fraction of occupancy gains is calculated within EnergyPlus at runtime based on internal temperatures and metabolic rate. In this case the ratio of sensible to total occupancy gain will reduce as the internal temperature in the zone increases and at temperatures much above 30°C all of the occupancy gain will be latent (occupants sweating).
2-Fixed fraction - where the latent fraction of occupancy gains is constant regardless of internal conditions and defined on the Activity tab under the Occupancy header.

Note: The total occupancy gain (sensible + latent) is not affected by this option, only the split of sensible vs latent gain.

Equipment gain units

When the Gain definition level option is set to 1-Globally in model options, set the Equipment gain units. This option provides control over the method used to enter Internal gains such as computers, office equipment, miscellaneous, catering, process.

1-Power density where zone equipment gains are entered as a power density, i.e. as a power per zone floor area in W/m2 or W/ft2. This option is usually the most convenient method for most general purpose modelling as the data is normalised by area and so can be inherited from levels above in the model hierarchy and can be effectively loaded from Activity template.
2-Absolute zone power where zone equipment gains are entered as a power value in W. This option is usually used when detailed zone by zone survey or design data is available. Unless you need to enter specific known lighting equipment gains zone by zone, this option is best avoided as it increases the amount of work involved due to the inheritance mechanism not working effectively for gains that are not normalised by floor area.

Note: When using the 2-Absolute zone power option, the equipment gains data is normally entered individually for each zone because values inherited from building and block levels will typically not be correct.

Lighting gain units

When the Gain definition level option is set to 1-Globally in model options, select the Light gain units. There are 3 ways to define General lighting gains in DesignBuilder:

1-Power density - where the General lighting gains are defined per floor area. This method has the advantage that the level of gains can clearly be understood by looking at W/m2 values and floor area. However it can cause problems when loading data from lighting templates in that if the activity is changed subsequently with a different illuminance requirement, the lighting power density is not updated. This issue has led to the introduction of the second option.
2-Normalised power density - Although the units for Normalised power density (W/m2-100 lux or W/ft2-fc) may seem quite obscure, this method of defining lighting gains has advantages over using simple Power density. Namely that the actual lighting level is associated with the lighting system type without the need to refer to the zone activity and hence illuminance requirement. So if a particular lighting system type is installed throughout a building, but the building has a range of activities each with different illuminance requirements, it will usually be possible to enter the lighting Normalised power density value once only at building level, set the activity for each zone and obtain realistic lighting gains. See General lighting gains for details on the calculation of lighting gains from Normalised power density, floor area and illuminance requirements.
3-Absolute zone power - where the lighting gains are defined as W without reference to the zone floor area. This option is used when the actual absolute lighting gains levels are known in W. Unless you need to enter specific known lighting equipment gains zone by zone, this option is best avoided as it increases the amount of work involved due to the inheritance mechanism not working effectively for gains that are not normalised by floor area.

Note: When using the 3-Absolute zone power option, the lighting gains data is normally entered individually for each zone because values inherited from building and block levels will typically not be correct.