XML will not lodge due to Negative TER

When you run an EPC calculation using SBEM v6.1b, the TER may be negative in some cases, and while this doesn't prevent the XML from being generated, it will fail to lodge.


Negative TER values can be generated by the latest version of SBEM because the 2021 Notional Building now incorporates a PV System whose area is dependent on the building's Foundation Area and the proportion of heating not provided by heat pumps. From the NCM Modelling Guide 2021:


The renewable energy generated onsite is subtracted from that consumed (using carbon factors) to generate the TER.

In previous English NCMs the Notional Building had no renewable energy and so the Notional Building rating was never negative.

The NCM states that the TER is equal to the Notional Building Rating but is set to zero if the Notional Building has a negative rating.


However, currently SBEM does not correct a negative TER in the EPC calculation.

We have asked BRE to fix this problem in SBEM.

The same will apply to the TPER (Target Primary Energy Rate).

Note that the Typical Rating is calculated as 4 times the TER so that will be also be negative when the TER is negative.


Solution

To fix this problem you will need to reduce the Foundation Area.

By default, the Foundation Area is derived by DesignBuilder automatically based on the user input of Maximum Number Of Storeys:


1. Check the following article to ensure the Foundation Area has the correct data:

Foundation Area and Maximum Number Of Storeys

2. Note that the Foundation Area is displayed in the Summary Output from a BRUKL calculation: (SBEM does correct a negative TER in the BRUKL calculation)


3. The Foundation Area can be overwritten in Project Details.


Note the minimum Foundation Area permitted by SBEM is 1m². It must be accurate for the BRUKL calculation as it affects the TER but is less important for the EPC calculation (but still important) in that it affects the reported newly built and typical ratings.


In this situation, both should ideally report as zero.

Your Accreditation Scheme may be able to provide additional guidance on how to reset the Foundation Area when you encounter this issue.

See also: Foundation Area and Maximum Number Of Storeys