D e s i g n I s s u e s f o r N e t Z e r o – E n e r g y B u i l d i n g s
43
As for the g-values, all buildings with the exception of
Lima
and
EnergyFlexHouse
are
characterised by values higher than 50% used as reference. With consideration of U-
value and g-value of windows, it is well known that they must be balanced according with
the climate building challenge. Low U-values in conjunction with high g-values, for
instance, are appropriate for a cold climate given that in this way is promoted heating
performance. Bearing this in mind, it is no surprise that U-values and g-values of Lima
that face heating and cooling challenges are, respectively, higher and lower, than the
rest.
Figure 4: U-values and g-values of windows of the case studies
An important role in the buildings heat modulation and distribution is played by thermal
heat loss surface area of envelope (A) - heated volume (V) ratio or, in other words,
compactness. Typically, a high compactness (for small residential buildings A/V ≤ 0.7
m
2
/m
3
) is recommended for heating dominated climates due to the fact that a low
exposed surface area is limiting the heat losses, whereas medium-high compactness is
more adequate for heating and cooling dominated climates because the cooling demand
will be reduced (Wimmers 2012). A high compactness could be sacrificed sometimes in
in favour of higher surface oriented to the South (Passive On 2007). According to table 2
and figure 5, the A/V ratio values of buildings varies between 0.41 and 1.07 m
2
/m
3
, a fact
which suggests high to medium-high compactness. As it can be seen from figure 5, with
the exception of
Lima
(which is a very small, single story building dealing with heating &
