Modelling individual zones to find optimum improvements

Related articles:

Lighting Controls

Applying global improvements to a model may result in little overall improvement to building performance. This will likely be because there are some zones in which the changes do make a significant improvement and some in which that change has the opposite effect. This article looks at how DesignBuilder can help you target cost effective improvements to reduce the rating or help pass the BRUKL.

The SBEM concept along with the DesignBuilder interface make it easy to test 'improvements' zone by zone.

SBEM

The SBEM Thermal Model assesses each zone individually and then sums these results to generate the overall building performance. SBEM does not know the location of a zone within the building, which zone is adjacent to which other zone, and models fabric heat loss/gain purely on the nature of the type of adjacency (external, underground, conditioned, unconditioned etc). Thus we can examine heating, cooling and lighting energy on a zone by zone basis to establish useful improvements. Note that Auxiliary Energy can also be assessed in this way provided the HVAC System does not provide conditioned air and there is no secondary circulation system for hot water. 

Note

    • DHW systems are generally best assessed as a complete system.

    • Renewable Systems are independent of the zones and are best removed from the Zone level analysis

    • Changing Fuel Types may have an impact on the Notional Building and are best to assess at the Building Level if the assessment is for Building Regulations.

DesignBuilder

You can include & exclude the Building/Blocks/Zones:

By default, this is always set to TRUE.

If You untick this at Building Level

And then tick it for the zone you wish to look at. In this case a top-floor office.

The calculation will now only use the data assigned for this zone.

Run the calculation for the zone: You can export the data (and input to a spreadsheet) so you have results data you can compare:

Lighting is generally something that can be improved as the technology has improved a good deal in recent years. 

Don't use generic 'unknown' LED as this is not representative of a new systems performance. Use 'Chosen' and a Benchmark value such as Building Regs:

Check the results:

The lighting energy has reduced by more than 37kWh/m2. However the heating energy has increased by almost 30kWh/m2. This is because the lighting is heating the space, reducing the heat demand. Worse still the BER has increased from 26.36kgCO2/m2 to 27.43kgCO2/m2. The reasons for this are that the CO2 factor for Gas (heating) is higher than that for electricity, plus the inefficiency of the heating system.

Lighting improvements will be more effective in unheated, cooled or internal zones adjacent to other heated zones:

The office space below this one has no external adjacencies though the floor is adjacent to the ground.

The T8 spec generates the same lighting but has a much lower heating demand:

With the proposed change in lighting there is a lower increase in heating and a clear reduction in the BER:

Continuing this analysis to other services and in other zones and will help you identify where particular measures are most effective in reducing ratings.