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
45
Renewable Energy Systems Findings
After having performed all necessary steps towards lowering building´s energy demand,
the last step to be carried out is the integration of renewable systems for energy
generation. Since the objective is to reach a net zero energy performance, the lower the
energy demand the lower the strive for energy generation. Given the residential buildings
specific energy needs, renewable energy systems should either provide the heating and
cooling or the fuel necessary to run the space heating and cooling systems together with
lighting and other occupant’s related uses. With this respect, the most common
strategies make use of photovoltaic systems for electricity generation and solar thermal
collectors for DHW production (only
Écoterra
,
Plus Energy Settlement
and
Plus Energy
Houses
are not equipped with solar thermal collectors). For space heating and cooling
and DHW, geothermal (
Écoterra
,
EnergyFlexHouse
,
Leafhouse
and
Riehen
) and
biomass (
Lighthouse
) energy sources may also be used depending on the feasibility and
the development cost involved. Air source heat pumps used to transfer ambient heat to a
useful temperature level is also possible if they meet certain energy-efficiency rating
(
Lima
,
Riverdale
and
Plus Energy Houses
). In addition to this, a wide range of mixing
strategies can also be employed: a building integrated photovoltaic thermal system
BIPV/T system is able to harvest a large amount of heat (
Écoterra
); geothermal and
solar thermal may be combined with low exergy systems (radiant heating) for space
heating (
Leafhouse
and
Riehen
); buildings equipped with transfer stations (hot water
storage tanks) which are connected to a district heating grid fed by a combined heat and
power plant fired by wood chips and natural gas (
Plus Energy Settlement
).
Matrix of design solutions
The main design strategies used in NZEB design have been addressed in the preceding
sections in a systematic and goal directed way. Although the role played by each
individual strategy remains to be demonstrated, the representation of the set of PA, EES
and RES measures applied in each case under the form of a matrix offers a more
general perspective with several advantages (Fig. 6). Firstly, for each building under
analysis it is possible to identify, for each class of challenge (heating, cooling,
lighting/appliances/equipment - 1
st
column from the left of figure 6) and each key
component of the energy balance (PA, EES and RES) all sets of strategies applied.
Taking
Écoterra
building as example, one can observe that heating challenges have
been addressed with PA (high thermal insulation, passive solar gain, thermal mass and
thermal storage - 2
nd
from the left) combined with EES (heat recovery - 2
nd
column from
the right). The RES applied to answer the same heating challenges are photovoltaic
systems (heat recovered from building-in integrated photovoltaics) and a geothermal
heat pump (represented in figure by the two light coloured boxes overlapping heating
challenges). Secondly, it allows extracting useful insights about design issues which are
more likely to succeed in achieving a true net zero-energy performance in heating and
heating and cooling dominated climates. In the perspective of lowering buildings energy
demand through the implementation of PA and EES, the inspection of figure 6 reveals
that most frequent strategies rely on high thermal insulation and passive solar gains
combined with radiant heating and air heat recovery in the case of heating, and on
sunshading and natural cross ventilation combined with radiant cooling and
displacement ventilation in the case of “cooling”. An interesting feature to observe is the
energy performance of the buildings on the account of the adoption energy efficiency
measures (PA and EES only) (Fig. 1). As it can be seen from figure 1, although neither
ÉcoTerra
nor
Lima
have reached net-zero energy performance, they´re both
characterised by very low and medium-low annual primary energy consumptions,
respectively. At the same time,
Lighthouse
, which can be considered a successful
project from the point of view of NZEB performance, exhibits the highest annual primary
energy consumption.
