Page 8 - Water-energy_2020

F. Calise, et al. Energy Conversion and Management 220 (2020) 113043
energy demand of the district in RS; E el,toGRID,PS and E el,fromGRID,PS are the
,
,
,
,
,
,
Δ = ⎛ E th heat RS + E th DHW RS + ⎛ E th cool RS
electric energy delivered/withdrawn to/from the local grid in PS; the CO 2 ∑ ⎜ η F · NG ⎜ ⎝ COP CH RS + E el RS
,
,
,
index i is related to the i-th time step of the simulation. i ⎝ BRS
The model includes the evaluation of the total capital cost (J tot ) for ⎞ ⎞
− E el fromGRID PS, , + E el toGRID PS, , ⎟ F · el ⎟
each proposed plant, according to the summary reported in Table 6. ⎠ ⎠i (18)
The total capital cost (J tot ) also includes the cost of the piping network
as discussed in the previous subsection. The economic savings ΔC are where, F el is the CO 2 equivalent emission factor for electricity and F NG is
evaluated by comparing the operating costs of the reference and pro- the CO 2 equivalent emission factor for natural gas,
posed systems:
4. Case studies
,
,
,
,
,
,
⎡ ⎛ E th heat RS + E th DHW RS ⎞J NG + E th cool RS + E el RS J , ⎤
η
⎢ ⎝ LHV NG AH RS ⎠ ( COP CH RS , ) el fromGRID ⎥
,
,
⎢ ⎥ This paper proposes two polygeneration systems for supplying
J
⎢ + M fw demand water ship ⎥ thermal and electric energy and fresh drinkable water to remote re-
,
,
Δ C = ∑ ⎢ ⎥ gions. The considered remote regions are Santa Maria di Salina and
i ⎢ − ⎛M SolarField + M DesalinationUnit + E el fromPS el fromGRID ⎥ Favignana (Fig. 2).
,
J ,
⎢ ⎝ ⎥
⎢ ⎥ The first part of this work deals with the characterization of the two
,
,
⎢ − E el toGRID PS el toGRID + E th AH PS J biomass ⎞ ⎥ remote regions, in order to estimate the thermal and electric energy
,
J ,
,
η
⎣ LHV biomass AH PS ⎠ ⎦ i
,
demand, as well as the drinkable freshwater demand.
(15)
2
Santa Maria di Salina is a district of 8.75 km of the Salina island,
where, J water,ship is the specific cost of the water transported by ships; located in the archipelagos called Aeolian Islands (Tyrrhenian Sea,
J el,fromGRID is the specific cost of the electric energy withdrawn from the South Italy). This district consists of 852 buildings and 903 inhabitants.
grid; J NG is the cost of natural gas; J biomass is the cost of the wood chip, Since this district is an attractive touristic zone, an increase in the
and LHV biomass and LHV NG are the low heating values of the wood chip number of inhabitants is considered during the summer season. The
and natural gas, respectively; M SolarField and M DesalinationUnit are the electric- and thermal-energy demand of this district was estimated,
maintenance costs according to values reported in Table 6. Note that modelling five kinds of representative buildings. In particular, building
2
the last term of Eqs. (1) and (2) is considered only in the proposed plant V1 is a single-family house of 93.24 m , building V2 is a two-floor
2
PS1, where the wood chip auxiliary heaters are used to cover the multi-family house, including two apartments of 93.24 m ;Off is a two-
thermal energy demand for DHW, heating and desalination when the floor office; H is a two-floor hotel, and Sch is a two-story school. SMS
solar radiation is scarce or null. and F stand for the name of the area: Santa Maria di Salina and
The simple payback period, i.e., the ratio between the total capital Favignana, respectively.
cost J tot of the proposed system and the yearly economic saving ΔC, and Table 1 displays the geometrical features of the analyzed buildings,
the profit index (PI) are calculated as follows: and Fig. 3 shows the SketchUp modes.
Considering the year of construction of the district and the geo-
J tot graphical location, it is assumed that the buildings of the island are
SPB = 2
Δ C (16) poorly insulated (U equal to 1–1.4 W/m K), Table 2. In particular,
Table 2 displays the features of the envelope and windows of each
building. The number of district inhabitants increases during the
Δ CAF· − J tot
PI = summer seasons (May-September SS), reaching 1750 people, due to the
J tot (17)
increase of the touristic activity of the island.
where, AF is the Annuity Factor [years], depending on by the discount In particular, it is assumed that only a limited number of houses are
rate a [%] and the system time horizon TH [years]. occupied during the winter season (October-April WS), whereas during
The yearly avoided equivalent carbon dioxide emissions ΔCO 2 of the the summer season all of the houses are occupied (Table 3). Moreover,
PS vs. the RS are also evaluated: the hotel occupation triplicates during the summer season. The offices
are considered open during the whole year and the schools are closed
from June to September, according to Italian regulation.
2
Favignana is an island of 19.3 km in the Egadi archipelagos of the
Fig. 2. Case studies location.
8