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4 - Design Description
ME4054 – Cooler Group
4.1 Summary of the Design
The refrigerated storage facility that has been designed will utilize multiple different
methods for temperature management; together they will create the required environment
to preserve the desired produce for sufficient lengths of time. The major tactics employed in
this design are absorption refrigeration, urethane insulation, efficient building design,
interior airflow generation, and interior air exchange.
The major method of interior temperature management will be absorption
refrigeration. This method of refrigeration uses an external heat source to power a thermal
pump rather than using a traditional compressor-driven air conditioning system. By
eliminating the compressor from the refrigeration system, the dependence on electricity
was eliminated.
The next method of temperature management employed in the storage facility
design was to use urethane refrigeration panels to manage the heat flow between the
environment and the interior of the building. Used urethane refrigeration panels can be
obtained from disassembled coolers at reduced costs that have close to the same insulating
properties as new panels. The panels that will be used to insulate the walls of the
warehouse have locking mechanisms built into the sides so close-fitting installation is easy
and fast. The panels also yield a seal that prevents moisture ingression, which can lower the
effectiveness of the insulation.
The floor plan of the warehouse was designed to create spaces that are conducive to
maintaining their required temperatures. The natural temperature of the ground is not
subjected to a large temperature variance; it is also near to the required temperature of the
lowest room in the structure. The basement room is also split between squash storage and
squash curing during the fall harvest; as soon as the curing is completed, the heated space
can be converted to more storage quickly and easily. The cabbage cooling room is
strategically planned to be the top room in the warehouse. Placing the coolest room in the
warehouse seven feet into the ground with the remainder being built above ground will
allow the room to be maintained with the natural exterior cold air of winter. Figure 1 shows
the recommended building layout as previously described.
Figure 1: Warehouse Floor Plan
Lack of sufficient airflow within the warehouse is the second largest cause of
produce spoilage. To prevent spoilage due to low airflow, fans will be installed within the
warehouse to create sufficient air movement. Since electricity is not available for use,
mechanical linkages attached directly to water turbines will power the fans. These fans will
be designed to run whenever there is produce stored in the warehouse, but in the event that
the water turbines cannot provide sufficient power, natural convection from the evaporator
coil will provide some air movement. In addition to the designed natural convection, all
produce crates will be stored on racking to promote increased airflow between the levels of
crates.
Another method of increasing produce storage life is to have the interior air
exchanged at least once every 24 hours. To efficiently exchange air without putting too
much stress on the refrigeration system, fresh air inflow will be directed across the
evaporator coil. In the warmer months when the evaporator is cool, the warm fresh air will
provide both; new air and will help maintain a defrosted evaporator coil. In cooler months,
interior air exchange across the evaporator coil will heat the air before it comes in contact
with the produce, as the reversed absorption refrigeration system will heat the evaporator
coil and cool the condenser coil. Air exchange is planned to happen for five minutes every
hour to ensure adequate fresh air in the warehouse, as well as maintain a frost-free
evaporator coil in warmer months.
4.2 Detailed Description
The warehouse design that will be used to preserve produce for long periods of time
without electricity is a complex design that utilizes many different tactics to achieve the
final goal. All of these individual systems work in unison to provide the necessary
temperature and airflow regulation, to maximize the storage life of cabbage and winter
squash. As described above, the systems used in the design are absorption refrigeration,
urethane insulation, efficient building design, interior airflow generation, and interior air
exchange.
Absorption refrigeration can be used without the use of electricity to cool the
desired space. Its main method of cooling replaces the compressor that is used in traditional
refrigeration with a system of a generator and absorber that act as a thermal refrigeration
pump. The absorption refrigeration system is recommended for the electricity-free
application is one that uses a lithium bromide salt and water in tandem to provide cooling
and drive the system. A diagram of the refrigeration cycle is shown in Figure 2.
Figure 2: Absorption Refrigeration Cycle
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The cycle shown in Figure 2 very closely resembles a traditional refrigeration
system with the lack of a compressor to drive the system. This is where the generator and
absorber come into play. Heat is added to the generator to boil off the water which then
travels to the condenser, through the expansion valve, and finally to the evaporator where
the water absorbs heat from the environment. The water is then returned to the absorber
where the lithium bromide salt absorbs the water. Figure 2 shows a pump that would drive
the lithium bromide/water combination back to the generator, but this can be done without
a pump by using gravity. The expansion valve in the thermal compressor portion of the
system allows the lithium bromide salt to return to the absorber once the majority of the
water has been boiled from the mixture. When the lithium bromide salt returns to the
absorber, it helps to drive the system by absorbing the water re-entering the thermal
compressor from the evaporator. The heat needed to drive the system is added from solar
panels designed to create heat from sunlight. Solar panels will not provide the necessary
heat during times of low sunlight or darkness, so a reserve system is put in place to provide
the necessary heat when the sunlight is not adequate. This backup system consists of a
kerosene flame that is placed directly under the generator. Kerosene heat will only be used
in warm months where there is a high demand on the refrigeration system and an extended
period of time without refrigeration would be detrimental to the stored produce. While this
system is not considered to be as efficient as modern compressor-driven refrigeration
systems, it is currently the most efficient method of refrigeration that does not use any
electricity.
The urethane insulation used in the building design is a rather simple concept that
yields impressive results from a relatively low investment. Insulation panels that are
specified for use are constructed of a combination of metal exteriors with urethane foam
sandwiched between. These panels are very common in modern refrigerated facilities so
used panels are readily available from vendors who disassemble refrigeration systems.
Used panels provide sufficient insulating properties at a fraction of the cost and are
accepted by the Amish community as a method of insulating. Installation of the panels is
made simple by cam lock mechanisms built into the sides of the panels that allow panels to
lock together with a moisture blocking seal. The main enemy to urethane insulation panels
is moisture. The metal exterior of the panel helps to block moisture and maintain dry panels
that provide the intended insulating properties.
The floor plan of the warehouse is another passive system that makes the building
as efficient as possible. The two main rooms of the building are designed to be stacked on
each other to take advantage of environmental conditions that will help to maintain interior
temperatures. The top room will be constructed with the majority of the room above the
grade. Maintaining the temperature of the room during the warm months will be done with
the absorption refrigeration system, but once the ambient air temperature becomes low
enough, the refrigeration system will no longer be needed to cool the room. When the
exterior air becomes too cold, heat from the refrigeration system will be used to help heat
the room to prevent freezing of the produce. The bottom room of the warehouse will be
situated approximately seven feet below grade. At this depth, the average ground
temperature is approximately 48 degrees Fahrenheit and fluctuates by approximately 2.5
degrees Fahrenheit throughout the year. The bottom room of the warehouse needs to be
maintained at 50 degrees Fahrenheit for squash storage, so very little heat will be required
to raise the temperature of the room. When squash curing is required, the bottom room of
the warehouse will be partitioned to allow a heated portion for curing, as well as a portion
for storage. Once the curing process is completed for the season, the portion of the bottom
room used for curing will be converted to storage for the remainder of the storage season.
Interior airflow is the primary concern for the squash storage portion of the
warehouse. In previous years, approximately 50% of the stored crop of squash was lost due
to a lack of sufficient airflow within the storage facility. In order to provide electricity-free
airflow, fans will be powered using water turbines and mechanical power transmission to
the fans themselves. Since airflow is required from August through March, the water
turbines will be fed with a closed loop system that allows an anti-freeze/water mixture to
be used that will prevent freezing of the system. This system requires two tanks: one at high
elevation and one at low elevation. The high elevation tank will be placed at approximately
50 feet above the second tank. This height differential will allow for the necessary head
pressure to turn the water turbines. The flow rate of water from the top tank to the bottom
tank will be approximately 30 gallons per minute, which is sufficient to turn the water
turbines. The water tanks will be capable of holding 100,000 gallons of the antifreeze/water mixture to ensure a constant supply of flowing fluid.
In order to maintain a constant flow of water, the high elevation tank must be
refilled when possible. To accomplish this, wind and water powered pumps will be utilized.
A water turbine placed in the nearby river will provide relatively constant mechanical
pumping power while the river is not frozen. In the event that the river becomes completely
frozen or the flow of water is not sufficient due to environmental conditions, a wind turbine
will provide pumping capacity. Wind is not nearly as consistent as the flow in a river, but
the large size of the storage tanks will ensure that the fans will be capable of running for
approximately one day even if the pumping systems used to refill the tank are not
operational.
Since sufficient airflow is so critical to produce preservation, racking will be used
within the warehouse to promote more airflow. The racking will provide more space
between the storage crates than the current method of stacking the crates directly on each
other. The current method of crate stacking has yielded much higher spoilage rates within
bottom crates compared to crates stacked on the top level. The racking will simulate having
all crates on the top of a stack to promote the airflow between all levels of crates.
The final supplemental method of air movement within the warehouse will be
employed in the cabbage storage room by using natural convection from the evaporator
coil. The evaporator coil placement near the top of the storage room will take advantage of
the natural flow of warm air to the top of the room and cooler air falling to the bottom of the
room. A high placement of the evaporator coil will also reduce the temperature differential
between the floor and ceiling of the warehouse. If the coil were placed too close to the floor
of the room, the cool air would rest at the bottom of the room and warm air would stay near
the ceiling if the fans were to stop running.
Interior air exchange is another very important aspect of maintaining a favorable
environment for produce storage. In the case of the electricity-free warehouse, efficiency is
very important because wasted energy is an unnecessary load that can be reduced. In the
warmer months, the exterior air is warmer than the desired interior temperature of the
warehouse. To help cool the exterior air as it is exchanged with interior air, it will be
directed over the evaporator coil as it enters the building. This will not only help to cool the
air as it initially enters the warehouse, but it will also serve as a means to defrost the
evaporator coil. The efficiency of the evaporator coil is greatly increased by reducing the
frost that can build up on the coil due to humidity in the controlled environment. Exterior
air will be drawn into the building every hour for approximately five minutes. This will
allow for sufficient air to be exchanged, to have full air exchange in any 24-hour period, and
will also maintain a nearly frost-free evaporator coil.
In winter months when the exterior air is very cold, the air will still be directed
across the evaporator coil upon entry to the warehouse. With the absorption refrigeration
system set for reverse flow, the evaporator coil will become hot, so the cold exterior air will
be heated before it comes in contact with any of the produce. This will reduce the required
amount of heat necessary to maintain the required temperatures within the warehouse
while still providing adequate fresh air to the interior of the warehouse.
4.2.1 Functional Block Diagram
Figure 3: Functional Block Diagram
4.2.2.1 Insulation
Insulation used in this design consists of an outer skin constructed of stainless steel
and an inner core of urethane foam. The outside of the panel helps to protect against the
ingression of moisture that can lower the R-value of the panels. The panels used in the
design can be purchased as a used product, which helps to lower cost without losing much
efficiency of the design.
Figure 4: Insulation Panel
4.2.2.2 Absorption Refrigeration
Absorption Refrigeration is the main method of cooling utilized in the warehouse
design. The system uses an external heat source from either solar energy or a kerosene
flame to drive a thermal compressor, which pumps the refrigerant to the condenser and
evaporator in the system. The refrigeration will be run in a standard configuration to
provide cooling to the facility and can also be reversed to provide heating for the same
structure.
Figure 5: Absorption Refrigeration Cycle
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4.2.2.3 Interior Air Flow
Airflow within the facility will be provided by fans, which receive rotational energy
from water turbines through mechanical linkages. The water turbines are fed a sufficient
flow of an anti-freeze/water mixture through a closed loop system that is fully operational
through all seasonal temperatures. This system has elevated and ground level tanks which
provide the necessary head height for the specified water turbines. Water is returned to the
elevated tank using a water turbine driven pump, which is placed in the nearby river as well
as by wind powered water pumps. The wind-powered pumps provide a means of backup
pumping in the event the water flow in the river is insufficient to replenish the elevated
water tank. The water tanks are designed to provide enough water to they water turbines to
provide interior airflow for a full day without any pumping back to the elevated tank.
Figure 6: Water Storage System
Figure 7: Water Turbine to Fan Transmission
4.2.2.4 Interior Air Exchange
Fresh air must be exchanged with the interior air periodically throughout a full day
to ensure the best produce storage environment. To achieve this situation, louvers are
installed near the top of the building that can be opened to allow fresh airflow in and
interior airflow out. The exterior airflow into the facility will be directed over the
evaporator coil in both the cold and warm months. This will allow cold outdoor air to be
warmed in cold months and cooled in the warm months before it contacts the produce in
storage. Drawing the warm air over the evaporator coil in the warm months will also serve
as a means for defrosting the evaporator coil.
Figure 8: Interior Air Exchange
4.2.2.5 Efficient Building Design
The building floor plan is designed to maximize and take full advantage of favorable
environmental conditions. The top room has the most exposure to the ambient air, so it will
only need to be heated when the exterior temperature falls below freezing. The lower room
is situated below the frost line of the ground where the average temperature of the ground
is 48 degrees Fahrenheit with a 2.5 degree Fahrenheit differential throughout the year. As
a result relatively little heating or cooling is required to maintain this room at the required
50 degrees Fahrenheit. By utilizing the natural conditions of the ambient air and the
underground heat, system energy usage can be reduced.
Figure 9: Building Floor Plan
4.3 Additional Uses
While this warehouse is currently designed to fit the specifications of Amish
farmers, it would also be an efficient design for customers where electricity is not readily
available. This design can run without any supplemental electricity, so it could be placed
anywhere in the world where wind and waterpower are accessible. There is high potential
for this warehouse design in warm climates where there is high sun exposure and constant
running water sources, such as large rivers. In this environment, freezing of the
environment around the warehouse would not be a concern and fans could be directly run
from the hydrodynamic power of the flowing river; allowing for year round energy and a
more efficient system.
This facility design would also be an possible solution for maintaining a stable
environment for medical supplies in regions of the world where electricity is not as readily
available. In areas of the world where a large warehouse was not required, smaller portable
versions could be produced that would be capable of cooling smaller loads and used for
numerous different applications such as: meat storage, produce storage medical supply
storage (blood, vaccines, certain antibiotics, etc), homes, or other remote buildings such as
hospitals, built where electricity is not readily available.
There are also possible applications of this system into larger societies, which are
continually moving toward more energy efficient standards and regulations. Large buildings
could use the methods employed in this facility to maintain more efficient, temperaturecontrolled buildings. Implementing the methods into the buildings of large cities, where
pollution from electricity generation is a growing problem, could result in lower greenhouse
gas emissions along with a large reduction in energy usage. The cooling and insulation
methods could also be implemented in order to create energy self sufficient homes all over
the world.