Civil Engineering Reference
In-Depth Information
DHW demand. The consumption of natural gas for the conventional boiler is
2,690 kWh/y.
Starting from the monitored data on electricity generation and loads, the fol-
lowing balance equation is applied to the building case study:
E
net
;
LH
¼
E
PV
j
j
E
GRID
j
j
ð
1
Þ
where
• E
PV
is the on-site photovoltaic annual generation of electricity (kWh/y);
• E
GRID
is the end use energy for electric needs of the LH (kWh/y).
Based on the monitoring outcomes, the annual balance was calculated
according the Eq. (
1
), as one year is a proper time span to cover all the building
operation settings, with respect to the climatic variables and the season succession
(Sartori et al.
2012
).
Table
3
shows the outcomes of the annual LH balance calculated by means of
the Eq. (
1
), where both generation and load are computed in terms of end-use
energy. Energy generation results lower than energy load, with a deficit of
0.9 MWh, that is, 7.7 % of the overall electricity load. This involves that the LH is
a nearly Net ZEB, when considering the encountered energy flows at the final use
level.
On the basis of the above results for the annual energy balance of the LH, the
authors propose a set of retrofit actions for the assessed building, in order to shift
the assessed building toward the Net ZEB target. In detail, the following options
are undertaken:
• to install more efficient PV panels, with a 19 % efficiency model;
• to install more efficient GHP equipment (nominal COP = 4.6);
• to directly connect the GHP to the storage tank and to the manifold, without the
GHP heat exchanger;
• to improve thermal insulation of the roof, by means of proper rock wool boards,
10 cm thickness, taking the U-value from 0.25 W/(m
2
C) of the existing
building to 0.15 W/(m
2
C);
• to optimize the volume of the main storage tank in order to reduce the GHP
consumption;
• to integrate a night setback on the proportional integrative derivative (PID)
temperatures setup;
• to add mobile blinds, on the south-oriented windows, working in the hottest
hours during summer season, if occupancy schedules are set to 0.
The reduction in energy load for each end use, due to the above options, is
calculated through TRNSYS simulations (TRNSYS
2003
). The foreseen PV
energy yield (about 38.3 MWh/y) would allow a complete covering of the total
building load (E
net, LH
= 0). The other retrofit options would induce an overall
electricity saving of 2.8 MWh/y, thus further reducing the electricity consumption
to 22.8 MWh/y.
