Multiple internal partitions on a single plane: issues and solutions

Modified on Fri, 5 Jan at 7:42 PM

DesignBuilder cannot assign more than one partition construction to a single internal wall plane. This behaviour can cause issues for cases when there is more than one partition type on a single plane.

This could for example be a "heavy partition" at the ground floor level aligned with a "light partition" on the first floor.

This Knowledgebase article looks at the issue and how to circumvent it using practical examples (though with same geometry)

1. A double height workshop or warehouse space with an office in a corner with a store room above.

Note that these types of geometry are best drawn using Boolean or Add Surface tools rather than using merging tools. Some of potential issues with merging:

1. There will be a wall-floor bridge between the two blocks

2. Vehicle Access doors or windows that cross the the junction between the zones must be drawn as two separate doors / windows: introducing additional bridging.

3. Daylighting based on windows in the child zone may not be modelled correctly.

It is not unusual that the partition between the office and warehouse is different to that between the store and warehouse and thus it will be expected that separate assignments should be made. However, the partition construction is only relevant in how it affects the thermal calculations between and within zones. These calculations are dependent on the partition U-Value and thermal mass. There is no heat demand in the spaces in this example apart from that for the Heated Office. Thus, the partition construction used between the unheated warehouse and unheated store is not relevant and is only required to divide the spaces. The specification for the partition between heated and unheated spaces will need to be correct however. Thus it is not an issue that a single partition assignment is made here, provided the specification used is that for the partition between heated and unheated spaces.

Note that to ensure that such a construction is not used elsewhere in the building (even if other insulated partitions have the same specification) it will be best to create this as a separate construction and assign it only for this situation.

2. Looking at the reverse situation: A heated warehouse with heated office and unheated store we need to consider how SBEM models this situation.

For this you need to have some understanding of the SBEM thermal model:

Each zone in SBEM is completely independent of other zones. This may be surprising when using DesignBuilder, where you have drawn up the model clearly showing the exact adjacencies of different zones. Each zone consists of construction elements with thermal properties and an adjacency (exterior, underground, unheated adjoining space, conditioned adjoining space & strongly ventilated space). Different activities have different heating setpoints but even when 'adjacent' spaces have different setpoints there is no heat transfer between them. Where you have two zones with a 'conditioned adjacency' between them (eg heated warehouse and heated office) then despite these activities having different heating setpoints there will be no heat transfer through the partition between them. Thus the U-value for partitions between heated spaces is not relevant (though the thermal mass will have a small effect) to the calculation. In this situation, if the partition constructions are similar (eg using stud wall but with different levels of insulation - or none) then it is safe to assign the construction between unheated and heated space also for the partition between heated spaces.

Thus, only where the partition separates at least two heated spaces AND the thermal masses of upper and lower partitions are significantly different is it necessary to model these partitions differently.

If this is the case then the blocks must be drawn separately and merged as described below:

Important notes:
1. For partitions which arise at the junction of blocks it is best to make the assignment at the surface level.

2. Resetting of a partition which is shared by two blocks may not be automatically assigned to the other block as these are at the same hierarchical level. Thus it is always advisable to refresh the geometry afterwards using the Rebuild command.

To prevent any potential issues in the case where different partition constructions need to be applied to surfaces that are adjacent to a single larger surface, we suggest the following approach:

Represent building using two horizontal storey blocks

- Create two "storey" high blocks to represent the building

- Draw a "Hole" in the floor between the bottom and upper warehouse parts

- Merge warehouse zones using the "Merge" command

Ground Floor:

First Floor:

Building level:

Since the warehouse is now created using two separate blocks, each part of the partition between the workshop and office/store is treated independently.

The “Lightweight” partition can therefore be applied only to the upper “Store” zone without having any impact on the bottom part of the construction.