39 Recovery Analysis of Domestic Electric Storage Water Heaters
597
Design for remanufacturing can identify and prevent inefficiencies in the process
(Prendeville et al. 2016). In addition, disassembly can be considered a critical task
since it connects product returns with product recovery, and a prerequisite for some
of the tasks of the recovery process (Aksoy and Gupta 2010). Therefore, considering
the disassembly operations involved in the inspection guide suggested in Sect. 39.3.1
for a used DESWH, we provide below certain improvements in the product design
in order to facilitate them.
The recoverability of a used DESWH depends to a large extent on the condition
of the internal walls of the storage tank. The sacrificial anode plays a key role in
tank protection because it minimizes corrosion inside. Therefore, an adequate maintenance of this component extends the lifespan of the DESWH. If the anode is not
checked and replaced regularly, protection against corrosion is lost. Also, the efficiency decreases drastically as the internal surfaces begin to accumulate layers of
lime. The formation of lime depends on the hardness content and the alkalinity of
the water. Likewise, the magnesium anode is in its dissolution a source of hardness.
In general, the anode and the electrical resistance are placed together centred in
the lower part of the tank. This design reduces energy efficiency due to the formation of scale around the anode, and therefore, around the resistance. In addition, it
prevents the anode from being easily checked and replaced without performing a
maintenance to the resistance. The location of the anode is, therefore, a factor that
must be considered to improve the design of the product in view of recovery. Thus,
we suggest the following redesign recommendations for avoiding these problems.
One of them consists of placing the anode separated from the resistance. Hence, the
anode could be checked without having to perform a maintenance to the resistance
and guaranteeing the transmission of heat to the water. Another option is to place two
anodes screwed independently at the top and bottom in opposite corners of the tank
and separated from the resistance. The advantages of having two sacrificial anodes
is that it maximizes the anticorrosive protection inside the tank, thus prolonging the
lifespan of the DESWH and simplifying the revision and replacement of the anodes.
We note that the increase in manufacturing costs by incorporating another anode is at
most U$S 10, which makes it economically beneficial considering the best quality of
the future returns and therefore the lower recovery costs. We consider important to
mention that any of these design suggestions facilitate also repair and maintenance
operations.
As we mentioned above, the accumulation of lime inside the storage tank reduces
it lifespan. An alternative to reduce this negative effect is to use a water softener
that removes calcium and magnesium from the water before it flows into the tank.
However, this may be difficult to implement, so it may be more appropriate for
users to perform a frequent maintenance of the DESWH in order to prevent lime
accumulation.
Finally, we analyze the two materials used most often for the insulation of
a DESWH: polyurethane foam and glass wool. The sealant property of the
polyurethane foam simplifies the union and stability of the surfaces of the DESWH.
However, this property causes the foam to break down when it is detached from
the tank, therefore causing greater dismantling costs, and in addition the material
597
Design for remanufacturing can identify and prevent inefficiencies in the process
(Prendeville et al. 2016). In addition, disassembly can be considered a critical task
since it connects product returns with product recovery, and a prerequisite for some
of the tasks of the recovery process (Aksoy and Gupta 2010). Therefore, considering
the disassembly operations involved in the inspection guide suggested in Sect. 39.3.1
for a used DESWH, we provide below certain improvements in the product design
in order to facilitate them.
The recoverability of a used DESWH depends to a large extent on the condition
of the internal walls of the storage tank. The sacrificial anode plays a key role in
tank protection because it minimizes corrosion inside. Therefore, an adequate maintenance of this component extends the lifespan of the DESWH. If the anode is not
checked and replaced regularly, protection against corrosion is lost. Also, the efficiency decreases drastically as the internal surfaces begin to accumulate layers of
lime. The formation of lime depends on the hardness content and the alkalinity of
the water. Likewise, the magnesium anode is in its dissolution a source of hardness.
In general, the anode and the electrical resistance are placed together centred in
the lower part of the tank. This design reduces energy efficiency due to the formation of scale around the anode, and therefore, around the resistance. In addition, it
prevents the anode from being easily checked and replaced without performing a
maintenance to the resistance. The location of the anode is, therefore, a factor that
must be considered to improve the design of the product in view of recovery. Thus,
we suggest the following redesign recommendations for avoiding these problems.
One of them consists of placing the anode separated from the resistance. Hence, the
anode could be checked without having to perform a maintenance to the resistance
and guaranteeing the transmission of heat to the water. Another option is to place two
anodes screwed independently at the top and bottom in opposite corners of the tank
and separated from the resistance. The advantages of having two sacrificial anodes
is that it maximizes the anticorrosive protection inside the tank, thus prolonging the
lifespan of the DESWH and simplifying the revision and replacement of the anodes.
We note that the increase in manufacturing costs by incorporating another anode is at
most U$S 10, which makes it economically beneficial considering the best quality of
the future returns and therefore the lower recovery costs. We consider important to
mention that any of these design suggestions facilitate also repair and maintenance
operations.
As we mentioned above, the accumulation of lime inside the storage tank reduces
it lifespan. An alternative to reduce this negative effect is to use a water softener
that removes calcium and magnesium from the water before it flows into the tank.
However, this may be difficult to implement, so it may be more appropriate for
users to perform a frequent maintenance of the DESWH in order to prevent lime
accumulation.
Finally, we analyze the two materials used most often for the insulation of
a DESWH: polyurethane foam and glass wool. The sealant property of the
polyurethane foam simplifies the union and stability of the surfaces of the DESWH.
However, this property causes the foam to break down when it is detached from
the tank, therefore causing greater dismantling costs, and in addition the material