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How Does Ventilation Affect the SAP Calculation?

The first type of ventilation to know about is controlled ventilation, which is always deliberately installed. It is used to ensure that the air quality of the dwelling is kept at an acceptable standard and ensure that moisture is removed as well. This type of ventilation can be achieved in two ways: it can either be natural or it can be achieved through a mechanical system.

The other type of ventilation is known as uncontrolled ventilation, and this is basically the air leakage that occurs through the fabric of the building. This is measured using a leakage test and the result of this test is known as the “air permeability” of the building. When you see the results for this, the lower to the number, the less warm air is being lost through uncontrolled ventilation; this means that the dwelling is therefore more energy efficient, which is always a good thing!

When you are looking to install a ventilation system in the dwelling under construction, you will find that there is a clear link between the air permeability of the dwelling and the type of ventilation that is going to have to be used. This is because, if the air permeability is less than 5, the amount of controlled ventilation that is provided will have to increase – this is to ensure that the home is ventilated to a sufficient standard. Although this can be done through natural means, it will sometimes be the case that mechanical systems need to be used.

There are two types of mechanical systems that could be used in a dwelling, and these are:

• Continuous extract system. This constantly works to remove air from the property, therefore ensuring that the air is always kept fresh and moisture is removed.

• Whole house ventilation system. This both supplies air to the house and extracts air. It also uses a heat recovery element to ensure that heat is retained and that it is therefore energy efficient.

What’s the Impact on SAP from Ventilation?

It is generally the case that both continuous extract ventilation and whole house ventilation can actually represent an improvement in the SAP calculations. You must exercise some caution though, as there are a number of variables that can have an effect on this. The two main factors are:

• The size and overall heat demand of the dwelling.

• The make/model of the ventilation system (the energy efficiency of different models can vary enormously).

As a general rule, it is prudent to assume that the larger the property, the less impact any ventilation system will have on the overall SAP calculation. This is for the simple reason that larger ventilation systems consume more energy than smaller ones.

It is worth noting at the end of this article that it is incredibly important to ensure that you balance the requirements of Part L with those laid out in Part F. This is so that you can ensure that you are able to provide a dwelling that is energy efficient, while also being comfortable to live in and operate.  

Jon Ponting

Author: Jon Ponting

This article was published by Jon Ponting on 26.11.2012.