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Lowering Dwelling Emission Rate (DER) Through Effective Ventilation

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Lowering Dwelling Emission Rate (DER) Through Effective Ventilation

By Ruth MacEachern

Product Manager

Paul Croughan, National Account Manager at EnviroVent looks at the challenge facing specifiers of how to effectively lower a property’s Dwelling Emission Rate (DER).

“Since SAP Appendix Q was incorporated into the SAP calculation, there have been various ways open to specifiers to improve their SAP ratings.

SAP Appendix Q meant that individual product performance could be assessed and taken into account as part of the property’s SAP calculations.  As a result, ventilation systems were increasingly required to reduce humidity levels in dwellings and improve their DERs.  In the past few years Mechanical Ventilation with Heat Recovery has become more popular with housebuilders, however Positive Input Ventilation (PIV) is slowly being recognised as one of the most effective and least expensive options.  

PIV systems work by drawing in fresh, filtered, clean air from outside and gently ventilating the home from a central position usually in the loft, above a landing in a house, or a central hallway in a flat or bungalow.  They operate by diluting moisture laden air, displacing it and replacing it to control humidity levels between 45 and 60 per cent.

The requirement for new dwellings to improve performance by an extra seven per cent to meet the 2013 edition of Part L1A (energy efficiency for new building), means that PIV has become even more important as it can give savings on the Dwelling Emission Rate of around 5 per cent. Progressively more stringent requirements from Part L of Building Regulations at first may appear to conflict with Approved document F because one requires a more airtight building for energy efficiency and the other stipulates a need for free flow of air.

However, this can be resolved by specifying an effective ventilation system, especially where specifiers are looking to achieve the higher code levels (4, 5 and 6). In this situation, Mechanical Ventilation with Heat Recovery (MVHR) is often used as an option in order to gain points and lower a home’s DER.  A high performing MVHR system through SAP (Standard Assessment Procedure) may give a benefit in the best case of around 7-8 per cent lowering of the DER.  Alternatively, MVHR is often used if there is an acoustic condition that prohibits the opening of windows.

With MVHR, the cost could very well be around the £2,000-£3,000 mark to install in an average dwelling.  PIV, on the other hand, can often be installed for around a quarter of that cost, but is likely to provide a lowering of up to 5-6% on the DER. In addition, as with MVHR, you don’t need background ventilation (window vents) with PIV if the air permeability is greater than three air changes per hour.  It also negates the requirement for any extract fans – providing all wet rooms are off the central hallway and landing with windows that can be opened.

There are other advantages of PIV too. PIV or Multiple Input Ventilation (MIV) systems are increasingly being specified on standard builds, where they are often incorporated with Air Source functionally or automatically alternating the source of air from either the loft space or directly from the atmosphere. This allowscooler air to be supplied directly from the atmosphere in warmer months (rather than the loft space)  to provide all year round ventilation.

When you compare PIV to other methods of meeting Part F, it is clearly a cost-effective way forward, largely because of its effect in lowering the property’s DER.

In the case of PIV, the benefit is automatically calculated by SAP without having to refer to the SAP Appendix Q database, which is used to validate individual product performances for systems 3 and 4.  This therefore allows specifiers to calculate various different options and gain an understanding of how each accrues points by way of lowering the DER.

With increasing pressure to improve energy efficiency, the new build sector is clearly reaping rewards from specifying PIV systems that offer a cost-effective option to lowering DERs.”