Trial / Demo
On the 30th November 2021 the UK Government's Department for Education (DfE) released the Construction Framework 2021. The requirements of the framework apply to all school schemes unless otherwise agreed by DfE framework team. The construction framework may also be used by other contracting authorities for the purposes of delivering their requirements in terms of wider publicly funded non-education buildings in England.
What is the DfE Construction Framework 2021
The DfE Construction Framework 2021 has a Generic Design Brief (GDB) which is supported by Technical Annexes that detail the technical requirements for the design and construction of schools. Along with the School-specific Brief (SSB) and its Annexes, these form the Output Specification (OS), also known as 'School Output Specifications' (SOS), 'Facilities Output Specifications' (FOS), or 'Spec 21' (S21). These documents set the minimum technical performance standards for both new and refurbished educational buildings, covering stringent requirements for various environmental performance parameters, including operational energy performance, resilience to overheating, indoor air quality, and daylight quality.
Dynamic Thermal Modelling (DTM) is necessary to complete these tasks, specifically;
o Technical Annex 2J: Sustainability (Nov 2022).
o Technical Annex 2E: Daylight and Electric Lighting (Nov 2022).
o Technical Annex 2F: Mechanical Services and Public Health Engineering (Nov 2022).
o Technical Annex 2G: Electrical Services, Communications, Fire and Security Systems (Nov 2022).
o Technical Annex 2H: Energy (Dec 2023).
IES Consulting Dynamic Thermal Modelling Process
As specialists in Dynamic Thermal Modelling (DTM), IES Consulting can assist you in meeting the requirements of the Department for Education (DfE) Generic Design Brief (GDB) and its associated Technical Annexes.
Our team leverages detailed HVAC modelling and IES’ proprietary software tools to support accurate energy and indoor environmental quality (IEQ) calculations for DfE projects. Helping to limit risk and minimise the performance gap between design and operation.
Our process aligns with the RIBA Plan of Works Stages, to fully address all requirements of the School Output Specification, as outlined below.
RIBA Stage 2:
o Technical Annex 2H – Energy. 4.2 Concept Energy Model (CIBSE TM54 methodology Base Case + 5Nr off-axis scenarios).
o Technical Annex 2G Electrical Services Communications Fire And Security Systems - requires PV calculations to be dynamically assessed and reported monthly.
RIBA Stage 3:
o CIBSE Loads based on concept energy model.
o Technical Annex 2E – 3 Daylighting. Climate-based daylight modelling.
o Technical Annex 2H –4.3 Developed Energy Model including detailed HVAC modelling using IES ApacheHVAC.
o Technical Annex 2F - 11.5 Overheating risk assessments under current and 2080 project climate change scenarios.
o Technical Annex 2F - 10.5.4.1 Evaluation of asymmetric internal surface temperatures.
o Technical Annex 2F – 5.1 Evaluation of indoor air quality adopting detailed HVAC modelling using IES ApacheHVAC.
o Dynamically calculated HVAC loads adopting detailed HVAC modelling using IES ApacheHVAC.
o Building Regulations Part L (2021) ‘as-designed’ compliance assessment.
o Detailed Dynamic simulation CIBSE TM54 Operational Energy modelling for new facilities to ensure they meet the Energy Use Intensity (EUI) Targets defined in Technical Annex 2H
RIBA Stage 4:
o Technical Annex 2E – 3 Daylighting. Climate-based daylight modelling -update.
o Building Regulations Part L (2021) ‘as-designed’ compliance assessment -update.
o Optional simulation updates (as required).
RIBA Stage 5:
o Optional updates to all assessments.
RIBA Stage 6:
o 'As-built’ Building Regulations Part L BRUKL assessment and officially lodged Energy Performance Certification (EPC).
RIBA Stage 7:
o Annex 2H: Energy in-use monitoring.
Why are accurate energy and IEQ calculations important for DfE projects?
The SOS Technical Annex documents establish minimum technical performance standards for new education buildings. These minimum requirements include hard limits to the Energy Use Intensity (EUI) of the project, as outlined in the following table:
5.1.3 Annex 2H (Energy) requires that;
The Contractor is required to establish feedback mechanisms which are used to inform building managers whether the energy consumption is in line with the expectation set out at design stage. The information collated from the energy meters shall allow continuous monitoring, benchmarking, and post occupancy Building Performance Evaluation against operational targets.
In addition;
The minimum environmental data required for occupied spaces is internal space temperature, carbon dioxide and outside temperature for each occupied space. This enables energy and building systems performance to be evaluated in order that further insights into the effectiveness of the Building Services HVAC systems can be provided to the School and Contractor and to inform systems commissioning and balancing. Correlating the internal conditions with energy consumption enables the identification of avoidable energy use, building performance issues and sensors or meters that are likely to be out of calibration. This is a powerful means of remote system diagnosis.
If design stage calculations are inaccurate, this can and does leave developers in contractually difficult situations whereby they cannot justify the reasons for the underperformance concerning operational energy demand and indoor environmental quality. Such situations may incur additional post-completion costs and impact contractor selection choices for future DfE work.
Setting the Right Trajectory
The new IES VE Parametric tool, due to be released as part of the VE 2024, offers an ideal concept design stage analysis tool to set DfE projects on the right trajectory before undertaking the DfE Concept Stage Energy Model.
The tool allows the impact of high-level parameters such as site orientation, shading and façade strategy, glazed area, and construction fabric specifications, to be evaluated at the concept design stage. Watch this space for further details.
Limiting Risk and Liability
IES Consulting encourages the adoption of detailed HVAC modelling from an early stage in the design process to fully leverage the value that dynamic simulation modelling can offer. We suggest introducing detailed HVAC modelling at RIBA Stage 3. We also use the same detailed HVAC model to accurately evaluate indoor air quality and overheating risk metrics. This allows us to close the ‘performance gap’ between design theory and practice with respect to IEQ and operational energy demand.
Following practical completion, the application of IES iSCAN software allows us to generate a digital twin of the school, which further enables any performance gap to be closed, as required by Annex 2H: Energy - in-use monitoring.
This combination provides contractors with the tools necessary to remove any risk of underperformance on their part. Any post-practical completion disputes concerning operational energy demand and IEQ can be quickly resolved through the presentation of supporting data.
Where this does not occur (i.e. ‘ApacheSim’ HVAC modelling is used), contractors may be exposing themselves to unforeseen risks.
The Importance of Detailed HVAC Modelling
The use case for detailed HVAC modelling is made clear when modelling heat pumps. When modelling the operational energy demand of a heat pump using IES ApacheSim, a single Coefficient of Performance (CoP) is entered to account for the operational energy efficiency of the heat pump.
In practice, the efficiency of a heat pump is in constant flux, owing to variables including the ambient temperature, the desired flow temperature, and the system load.
The CoP for a heat pump when providing space heating functionality is typically given based on a flow temperature of 35°C, and based on an ambient temperature of 7°C. A Seasonal CoP can also be used which takes into account the varying temperatures throughout a season, providing an average efficiency rating that is more representative of actual usage conditions than a single-point measurement. However, the use of SCoP data is often far removed from system behaviour in reality. More often than not, the use of SCoP data results in the underestimation of operational energy demand, and by extension, carbon emissions. This is because in practice, space heating systems frequently operate at higher flow temperatures than the 35°C assumption used in the SCoP calculation. Furthermore, depending on the thermal efficiency of the building, space heating can be largely constrained to external conditions cooler than 7°C.
Excel spreadsheet showing ASHP COP curve modelling based on manufacturer’s data, accounting for system load and outdoor dry-bulb temperature
When the modelling of systems that include variable speed pumps and fans (such as heat pumps) does not account for these details, simulations can result in output information that significantly deviates from operational performance in practice. This can ultimately result in customer dissatisfaction if a building does not perform as efficiently or effectively as they were led to believe.
To close the Performance Gap and ensure that DfE projects perform as intended, we always advocate the use of IES ApacheHVAC to ensure that the performance gap is minimised.
For further information on how IES Consulting can assist you in meeting the requirements of the Department for Education (DfE) Generic Design Brief (GDB) and its associated Technical Annexes, visit our dedicated webpage.
