Written by Shaun Hill

Thermal Comfort

The imminent release of the latest SAP calculation methodology (SAP 10) has given us a sneak peak at the new routes to energy compliance in the residential sector – this also allows us to speculate on the changes which may also be coming in the belated release of non-domestic PartL2A expected at some point next year.

Along with changes outlined below – the regulations are finally representing the great work the UK has done to embrace renewable power sources whilst simultaneously de-commissioning inefficient and carbon intensive methods of energy generation.

This will be a step change in how building servicing strategies are determined, placing greater emphasis on demand reduction to comply with the regulations – the balance of gas and grid electric carbon is now almost at parity and is only going one way in the future. Offsetting carbon generated by an inefficient building with PV will become less viable – driving building designers down a different path.

Here is a summary of the major changes and what they might mean to you:

Electric CO2 emissions reduce significantly

As mentioned above – the changes to the electricity related carbon emissions may be the most significant factor – reducing from 0.519 kgCO2/kWh to 0.233 kgCO2/kWh.

The carbon factor has been applied for current greener production and reduced carbon emissions associated with older method of producing electricity (coal burning).  SAP 10 recognises a greener grid and efficient energy mix for production which will give designers more options moving forward.

The assumed heating pattern has changed

Heating patterns traditionally assumed that weekend energy usage is higher than weekdays. Through study and actual data collection – this has been proven not to be the case. SAP 10 has been adapted to apply a more realistic daily pattern every day of the week. This aims to reduce energy use and cost overall.

Default distribution loss factors associated with heat networks have been increased

Decentralised network losses have been underestimated or where unknown, too much leeway has been given in the current version. Changes will marginally reduce effectiveness which could have impacts particularly on schemes where heat networks are popular and significant carbon reductions are required by Planning –  London for example. There will be a focus on calculating and proving anticipated network losses in order to claim benefits – continuing to leave losses as ‘default’ will mean that the assumption is taken that 50% of heat is lost in transmission resulting in huge carbon penalties to be offset elsewhere. This is where employing a CIBSE Accredited Heat Network Consultant can also pay real dividends to help minimise these losses through good design and implementation of the recognised best practice standard.

The calculation of lighting energy has been updated

Accurate lighting design will have a higher impact against a simpler approach to calculation in previous SAP models. This is in line with the SBEM method which credits lighting type(s) with higher efficacies

The options for entering thermal bridges have been revised

As accuracy and age of the ACD scheme (Accredited Construction Details) have come into question, SAP 10 will remove this with the introduction of alternative schemes or giving the option for bespoke heat loss values to be calculated for each junction. Not using thermally efficient construction details will have a big impact on carbon compliance.

Hot water consumption has been adjusted for shower flow rate

As opposed to a standardised usage value, SAP 10 will take actual flow rates from each shower based on fittings used. This will lead to variations between fitting types and more alignment with water energy efficiency calculations under Part G of Building Regs.

The configuration of PV systems will matter

SAP 2012 used a fixed assumption for the proportion of electrical energy generated by Photovoltaic (PV) systems to be consumed within the dwelling regardless of what is connected to an individual dwelling.

This has now been changed so formulas calculate only direct PV supply per dwelling.

PV diverters can now be included

A PV diverter prevents electricity produced from photovoltaic panels from being exported to the grid, and instead directs it to an immersion heater in the water cylinder. It will now be possible to account for these systems in SAP 10 which will provide extra design options.

MCS overshading data can now be used

An option will now exist in SAP 10 to allow the overshading factor used for the PV calculation to be taken from Microgeneration Certification Scheme data. This would overwrite the default options currently available in SAP.

In summary, these changes will provide much needed additional sophistication and accuracy to the SAP calculation enabling building designers to drill down into the carbon impact of the measures they are taking. In theory, greater accuracy at design stage will enable better prediction of performance in use and the better application of various building technology – all round a step in the right direction.

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