Page 14 - Water-energy_2020

F. Calise, et al. Energy Conversion and Management 220 (2020) 113043

Eth,AH) Table 8
Annual results: Proposed System 2 (PS2).
+ E el,PV E el,RO E el,District& E el,HPheat E el,HPdhw E el,HPcool E el,self / E el,self /
Eth,MED/(Eth,MED 25 MWh/y 123 4395 201 388 184 % 64
E el,prod
E el,demand
plant&RO
2820
41

Annual energy, environmental and economic results: PS1 and PS2.
Eth,ECH) Table 9 PS2 PS1 PS2 PS1 PS2 PS1 PS2
PS1
+ PE RS [MWh/y] PES [%] 64.4 ΔC[k€/y] 1265 FW PROD /FW demand [%]
Eth,TKcool/(Eth,TKcool the ACH for the chilled water production. Due to the high cooling de-
15,575
59
490
32.2
68
13,600
ΔCO 2 [%]
SPB [years]
J tot [M€]
PI [−]
–
0.5
7.84
13.8
28.2
63.9
27.8
6.2
mand of the district, T topTK1 significantly decreases from 86 °C to 75 °C.
56
T topTK1 increases again up to 85 °C when the cooling demand decreases
Eth,AH) around 18:00. As it can be seen, in the early morning and afternoon
hours the freshwater is obtained only by the auxiliary heater without
+ any solar energy support.
The production of freshwater has a constant trend (Fig. 10) of al-
Eth,TKdhw/(Eth,TKdhw production, especially in the morning and evening hours. The stable
3
most 15 m /h, but the summer freshwater demand is higher than the
water production is due to the constant supply water temperature of the
MED unit. In particular, the plant is equipped with a biomass auxiliary
heater AH (switching on only when the radiation is not null, from 06:00
75
to 18:00) that allows constant activation temperature of 75 °C of the
MED unit, when the top temperature TK2 is lower than 75 °C. The
Eth,AH) graphs also show that during the selected day, AH is always activated.
Note that during summer, freshwater demand is high due to the large
+ number of tourists on the island of Favignana and, as it occurs in the
Eth,TKheat/(Eth,TKheat freshwater demand of the users. Therefore, it is necessary to purchase
day represented in this figure, the system is not able to cover the
3
freshwater from the mainland (by ships) at high cost (7 €/m ). This
result affects the profitability of the plant in a negative manner. The
cooling demand is almost covered for all hours of the day by the chilled
water produced by the ACH (driven with solar thermal energy) and
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stored into TKcool. It is thus possible to take advantage of the thermal
inertia of the tank until 20:30, while, after this time, the activation of
Eth,TKcool the auxiliary electric chiller is needed. Nevertheless, this only occurs for
577
a small number of hours and for covering a small amount of the cooling
demand due to the considerably decreasing of the ambient temperature
Eth,TKdhw 1080 in the evening hours.
When the ambient temperature T amb decreases, the heating demand
(Fig. 11) of the district is significant. This occurs during the first hours
of the day, when the top temperature of storage tank TKheat is lower
Eth,TKheat 168 than the set point temperature of the water in the direction of the
district buildings (equal to 55 °C). At that point, the auxiliary burner
P th,AH is switched on to cover the heating demand. Around midday, T amb
increases up to about 20 °C, the heating demand decreases and the
(PS1). Eth,MED storage tank TKheat covers the demand until it is discharged. This oc-
1 1100 curs from 09:00 to 20:00, when the AH gets reactivated. Regarding the
DHW demand, it is possible to note that in a typical spring day, when
System % both heating and cooling demand are null, the storage tank TKdhw
covers all of the user demand.
Proposed Eth,CPVT 3180 summer day during the operation of PS2 are presented.
In Fig. 12 the trends of power generation and demand for a typical
During the night hours, when the radiation is null, because no
results: MWh/y electric storage system is included in the proposed layout, the electric
demand of the users is matched by the local pre-existing grid of the
7 Eel,CPVT district of Santa Marina Salina (at 0.18 €/kWh e ). PV production reaches
Table Annual 1240 a peak value of 1.1 MW at midday. Between 09.00 and 15:00, the
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