PSI VALUES | DYNAMIC SIMULATION MODELLING
CONDENSATION RISK ANALYSIS | THERMAL MASS
2D/3D Steady State
PSI-Values are used to determine the overall heat loss at a specific junction (those at non-repeating thermal bridges such as wall to floor junctions).
Bespoke PSI-Value calculations can improve your results in SAP & SBEM assessments as it negates the need to select the default thermal bridging options meaning you can either save money on other areas or can exceed minimum compliance standards to achieve an even better-performing building and EPC.
SAP10 is due in 2020 to coincide with an update to Part L of the Building Regulations. The thermal bridging section of the calculation is seeing some big changes as detailed below:
ACDs are being removed
This means that where thermal bridging has not been included in the design, the default option will now have to be used. Signing the ACD documents pack will no longer be an option. In SAP10 this default will be changed from 0.15 w/m2k to 0.20 w/m2k. It is still possible to use established sets of construction details such as those from the Concrete Association or Energy Saving Trust however a huge emphasis is being placed in SAP10 on accurately modelled and specific PSI value calculations.
Room in the Roof junctions are being increased
It will now be even harder to pass dwellings with rooms in the roof (junctions R1-9) due to the increase in their default PSI value. SAP10 also sees the addition of a new junction R10 to cover any junctions not covered by R1-9.
Including thermal bridging in the design process will eliminate the above changes. Where the specification is being used on multiple plots or planned on future developments, then it will be cost-effective to model each PSI value for the build-up being used thus saving money elsewhere in the SAP calculation.
Dynamic Simulation Modelling
Analysing the energy performance of a building is a key part of the design process. It determines occupant comfort throughout the year.
Dynamic Simulation Modelling (or DSM) allows us to develop a highly detailed thermal model of a proposed building to accurately assess how heating, cooling and ventilation systems will actually perform and any issues that may possibly arise.
DSM is a requirement for gaining an EPC for highly complex buildings such as those with:
ventilation with enhanced thermal coupling to the structure
automatic blind control
DSM can also gain you an additional BREAAM credit.
Condensation Risk Analysis
The build-up of construction elements is often specified with little thought to the behaviour or interstitial condensation.
Interstitial Condensation commonly occurs when moist air permeates through elements of the building fabric, across which there is a temperature difference. This typically happens when warm, moist internal air moves towards the cooler outer parts of external walls and roofs, driven by a pressure difference. If the temperature drops sufficiently, the dew point may be reached within the fabric and condensation will occur.
Condensation can significantly reduce the performance of insulation and can affect the integrity of the building.
We can run a Condensation Risk Analysis on any U-Value Calculation, or designed construction element, to determine the level of risk associated within the construction element.
Our Condensation Risk Analysis Calculations are performed in accordance with BS 5250: 2006 and BS EN ISO 13788: 2002
Thermal Mass Calculations
Most SAP Calculations are carried out using default values for the dwellings Thermal Mass Parameter. Results can be greatly improved by carrying out a full Thermal Mass Calculation. This can allow for better results and potential savings in other areas of the SAP Calculation.
Using the information provided for the construction materials for all floors, walls, ceilings and roofs (internal and external), we can calculate the buildings thermal mass by multiplying the surface area for each element by its k value. The total figure is then divided by the floor area of the building to determine it's Thermal Mass Parameter.