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Last edited 24 May 2022
Form factor, it could be said in general is a mathematical way to compare two different variables of an object by ratios. It is commonly used in the electronic hardware industry ascwell as the design and construction industry.
In electronics form factor might be used in different ways to describe the size, shape, and specification of various pieces of hardware or components such as motherboards, USB and disc drives or memory cards.
In the design and construction of buildings, form factor is a simplified way of measuring the efficiency of a buildings' shape, by means of a ratio between the external surface area (SA) and the internal treated floor area (TFA). This is specifically useful when it comes to heating, because the TFA is the floor area to be heated and the SA is the surface through which the heat will gradually be lost. The lower the ratio between the two the slower will be the heat loss for the same level of fabric performance.
Lower heat loss factors ( or ratios) of between 0.7 and 2.0 will be found with simple medium to high rise buildings whilst higher factors from 2.0 up to 5.0 will be found wih lower rise and single detatched dwellings as these have a greater surface area that is exposed to the outside.
Form factor has gained interest, partly because it is a fundamental element of the internationally recognised passivhaus standard. This is a design and construction standard for passive buildings which targets achieving thermal comfort only by the heat generated by the occupants ( or minimal heating) , it does so though super insulation, minimising thermal bridges, airtightness, triple glazed openings, and ventilation systems with heat recovery.
Form factor is a simplification tool and designers should be aware that there are some complexities in the different ways certain variables are calculated when it comes to the detail. For example in the passivhaus air tightness test (n50) the treated floor area used to calculate the internal volume excludes any internal walls and floors. In the infiltration air change rate used for ATTMA & Buildings Regulations, it is the number of cubic meters of air leakage per hour per metre 2 of the envelope that is of concern. As such intermal walls and floors are included as within the total internal volume as the variable considered. ith Passive hoause being measured as ≤ 0.6 [email protected] 50 Pa. and ATTMA as m3/hr/[email protected] (q50).
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