integration of solid oxide fuel cells and ... - Ea Energianalyse

7.2. Economical considerations
to 6 years 8 . So before it is decided to make such a system, the installation
and maintenance costs should be established.
One disadvantage of the ABS AC unit is that when the ambient
temperature raises, so does the need for air conditioning, but at the same
time the COP of the ABS unit decreases. So during very hot periods,
this can give rise to a lack of cooling unless the ABS units is originally
overdimensioned 9 . This is however not so much a problem in the hotel
case where a supplementary electrical air conditioner is already present
since the ABS unit can only generate about 1/3 of the required cooling
due to the restricted amount of waste heat.
Just as for the SOFC the ABS unit has only been modeled as steady
state assuming that it runs at full load all the time. But since there was
only enough waste heat in the SOFC exhaust gas to generate around 1/3
of the entire cooling demand of the hotel, the ABS unit should be able to
run as base load all the time, and the supplementary ECH should be used
to regulate the total cooling production. So the steady state assumption
should not give so big an error on the ABS unit.
ABS vs Hot water production
In the economical calculations for the hotel, it has been assumed that all
the hot water production should be done by using waste heat from the
exhaust gas. This was done partly to make it easier to compare it to the
”naked” SOFC system, case B (with no ABS, so there was plenty of heat
for the hot water production), and partly because generating hot water
from the exhaust gas only takes a heat exchanger, whereas generating
cooling takes a much more expensive ABS unit.
But if the hotel is placed in a hot climate, the hot water heating
could quite inexpensively be done by solar heating panels because the
required temperature for the domestic hot water is so low - around 60 ◦ C
compared to the approximately 150 ◦ C needed for the ABS unit. And
when additional air preheating is used in the SOFC-ABS system, the ABS
unit can use almost all of the waste heat. If the ABS unit is allowed to
8 This is under the assumption that the installation and maintenance cost of the ECH
is the same regardless of whether an ABS unit is installed - after all there will be an ECH
in either case - the only difference is a 35% reduction in size of the ECH if an ABS is also
installed.
9 Or it could just be tolerated that the indoor temperature raises a couple of degrees
during heat waves (as long as there is some air conditioning, the consequences of a heat
wave should not be life threatening for anyone)
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