ASHRAE Journal - April 2021 - 44

TECHNICAL FEATURE

Power (W)

Temperature (°C)

work time is similar for 0° and 45°. Sloping
TABLE 8 Impact of PV panels and slope of PV panels.
the PV panels on the trailer roof is hard from a
ELECTRICITY
DIESEL CONSUMED (L) DIESEL-GENERATOR WORK TIME (H)
mechanical point of view, increases the initial
PRODUCED (KWH)
cost and decreases the stability of the MMEU.
Without PV
0
416
-
1,054
-
The impact of the PV panels in the spring is
WINTER
PV 0°
132
378
-9%
955
-9%
higher because of more sunny days and higher
PV 45°
314
337
-19%
856
-19%
outdoor temperatures.
Without PV
0
241
-
632
-
To demonstrate the dynamic change of paramSPRING
PV 0°
797
70
-71%
193
-69%
eters, two consecutive days with the highest solar
PV 45°
950
67
-72%
185
-71%
radiation during winter are chosen (Figure 5) in
Without PV
0
205
-
506
-
the case of PV panels with 0° slope (Case A).
AUTUMN
PV 0°
286
119
-42%
298
-41%
The average outside temperature for the twoPV 45°
403
114
-44%
285
-44%
days is 1.1°C (34°F), and the average electricity
consumption is 6.76 kWh per day. The MMEU
FIGURE 5 Simulation results from Feb. 20 at 12 a.m. to Feb. 22 at 12 a.m.
works for 13.7 hours, and the diesel generator
Inside Air
20
works for 10.7 hours during the 48-hours.
Temp.
10
Inside Operative Temp.
At night, one full heating cycle lasts around
0
Ground Temp.
8 min (≈ 3 min of MMEU work). The PV panels'
Outside Air Temp.
-10
max power is about 950 W. The diesel genera12a
4a
8a 12p 4p
8p
12a
4a
8a 12p
4p
8p 12a
tor works from 6 a.m. until 10:00 a.m. and
Time
again from 6 p.m. until 10 p.m.
2,400
PV Panels
Diesel Generator PV Panels
1,800
When battery power is negative, the batter1,200
ies provide electricity. Positive battery power
0
-600
means the battery is charging. The operative
Battery
-1,200
temperature during occupancy is 2°C (3.8°F)
12a
4a
8a
12p 4p
8p
12a
4a
8a
12p 4p
8p 12a
lower than the inside air temperature.
Time

Discussion and Conclusion

TABLE 9 Summary of the annual MMEU operation in different climatic conditions.

ENERGY (KWH)
TIME (H)
ELECTRICITY (KWH)
The MMEU (Case A) reduces tent
DIESEL
TOWN
electricity consumption by 76% to
TOTAL
PV ADDITIONAL
HEAT
HEAT COOLING
HEATING COOLING
GENERATOR
REQUIRED PRODUCED REQUIRED RECOVERED SUPPLIED SUPPLIED
81% and diesel consumption by 79%
TOTAL
to 93% compared to using only a
Stockholm
1,968
2,313
1,639
5,585
3,669
392
1,626
115
1,369
diesel generator for electric heatOttawa
2,446
3,236
1,568
6,328
3,998
879
1,649
286
1,189
ing. The supply of the electricity
Riga
1,989
2,268
1,674
5,571
3,616
457
1,600
134
1,460
produced annually (Table 9) by PV
Chicago
1,973
3,335
919
3,876
2,399
2,082
1,056
601
725
panels is higher than the demand.
London
944
2,169
577
1,895
1,152
559
609
165
412
Therefore, the optimal heating and
Seattle
1,030
2,853
394
1784
1,075
851
563
281
272
cooling algorithms should be furNew York
1,658
3,394
573
2,467
1,437
2,526
674
719
485
ther investigated for various scope
of applications-different shelter types, sizes, thermal
described MMEU model are using dynamic airflow rate
properties, occupancy and equipment schedules,
and air recirculation, especially during winter. A diesel
required inside temperatures and airflow rates coupled
generator exhaust tube economizer can also be applied.
by different regions and climate conditions. Defining
It is also possible to integrate a smart electricity grid
needs will make it possible to produce different models
and an improved electricity consumption schedule
according to specific heating, ventilation and electricity
according to the available battery power capacity and the
consumption demands.
PV produced power, using weather forecasts and definSome possibilities to improve the efficiency of the
ing optimum battery size and amount depending on the
44

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ASHRAE Journal - April 2021

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