RECOMMENDATIONS (WEEK 8)

Recommendations

The most fundamental barrier to changes in mini-fridge use in residence is the attitude of students. Many students recognize their mini-fridge as a necessity and not a luxury. Parents commonly purchase min-fridges as graduation gifts from high school and whether or not a student really wants a mini-fridge, they tend to have one when arriving at university. The recommendations proposed by this research group are based on the opinion of students living in residence at Dalhousie University and upon suggestions from actors such as residence life managers and facilities management. The successful implementation of these recommendations depends on the cost to the university and more so the attitudes of students towards improving energy efficiency in residence.

This research group recommends that mini-fridges should not be allowed in residence rooms at Dalhousie University. This policy has been implemented successfully at other universities such as Mount Saint Vincent. The application of this policy would likely be more successful if combined with other changes such as secure communal fridges and longer cafeteria hours. Students surveyed for this study indicated that there would be opposition to a mini-fridge ban but this opposition may only be short-lived. Since many students were open to using communal fridges and having longer cafeteria hours, those changes may mitigate the opposition to a mini fridge ban. Resident life managers felt negatively about a mini-fridge ban as they anticipated opposition from students. Due to the attitude among students that fridges are a necessity, the resident life managers presupposed that a mini-fridge ban would be unsuccessful without considering its utility objectively of student opinion.

If a residence-wide mini-fridge ban is not implemented then there is still room to improve the efficiency of mini-fridges used on campus. Just over half of students reported that their fridges were either empty or 1/4 full for the school year. To improve the efficiency of mini-fridge use, it is necessary to reduce the number of students that have fridges but don’t use them. Many of those students with empty fridges indicated that they were indifferent to a mini-fridge ban on campus. We recommend that Dalhousie University implement an application process whereby students who want a mini-fridge must apply for a permit through the university. The object of this application would not be to exclude any students from using fridges; in fact there would be no restrictions as to who would be awarded a permit. Those students who use mini-fridges could still apply and get a fridge but those students who now have empty fridges may be less likely to go through the application process. It would be an obstacle that would reduce the number of students having empty fridges, which are needlessly consuming electricity. The application process may create incentive for students to share mini-fridges and could be the initial step towards changing mini-fridges from a necessity to a luxury. For this system to work, Dalhousie would need to provide the mini-fridges to students or use an exclusive provider. Many students only have mini-fridges because their parents purchased them prior to attending school. If students arrive at Dalhousie with mini-fridges, as many do now, then they would probably go through the application process anyway, thereby defeating its purpose. But if they had to apply and then rent fridges then the application process may be successful. This application process would allow the University to monitor the quality and efficiency of mini-fridges on campus thereby decreasing electricity use and possibly creating savings.

The results from the student survey indicated that medium and large fridges were more likely to be empty or ¼ full than small fridges. If the university allowed only small fridges in residence, then the efficiency of mini-fridges may be improved. If this were the case, it would be important to be sure that prohibiting larger fridges doesn’t cause students to stop sharing fridges with other students. Theoretically, few large fridges would use less energy than more numerous small fridges. This change could be complemented by a limit of one fridge per double room. This change would certainly help, but its utility is limited as only 5 of the 170 students surveyed indicated that they were in a double room with two mini-fridges and two of those students were in the same room.

As mentioned earlier, many students were interested in extended cafeteria hours. Longer meal hours would increase flexibility for students and possibly reduce the need for mini-fridges in residence. Relatively few students indicated that they store food in their mini-fridges. Most just like to have cold drinks, ice and snacks in their rooms. Alternatives to having the cafeteria open longer, perhaps a drink and snack counter could be open at night and during morning and afternoon hours. Students could then have access to drinks during most of the day. The commercial coolers used at these drink counters would be much more energy-efficient than the status quo where most students have their own personal fridge. Along with this change, the installation of communal fridges in residences may reduce the use of mini-fridges. Most students surveyed indicated that theft and cleanliness are the main drawbacks of communal fridge use in residence. If the communal fridges were cleaned regularly then the cleanliness

may not be a problem. This is interesting because we know from experience that most students do not keep their personal fridges particularly clean but they have a problem with unclean communal fridges. This tragedy of the commons may improve as students become accustomed to sharing communal fridges. To resolve the issue of theft from communal fridges we hypothesized that secure personal compartments for each student was a potential solution. The resident life managers dismissed this idea as they presupposed that fridges with smaller compartments are not available or easily implemented. Our group is not so sure that this is truly the case but we didn’t have the scope or time to investigate such fridge modifications. A compartmentalized fridge is commonly used for commercial coin vending purposes. These machines have a number of rotating carousels that have individual compartments with different snacks. The consumer simply inserts a coin and can then open which ever particular compartment he/she wants. It’s not hard to imagine a similar machine in residence with key or combination locks instead of a coin operated system. While this may seem slightly unorthodox, it is the sort of proximate change that is needed to improve energy efficiency in residence.

Some houses in Howe hall have communal fridges and students indicated that they are not widely used. This is likely due to the fact that most students use mini-fridges in their rooms. We recommend that the university make a decision to ban mini-fridges and use communal fridges or remove the communal fridges that are present but not be used currently.

OBJECTIVES (WEEK 7)

OBJECTIVES

Ò  To design a new system that is robust and user friendly.

Ò  To develop a mini fridge based on the temperature value.

Ò  To makes it easier for consumer to bring the mini fridge anywhere.

Ò  To make it easier for consumer to get the cold beverage during they do their holiday

BENEFITS/ CONTRIBUTIONS

Ò  To provides facilities for people who love outdoor activities

Ò  To implement it as a backup for house refrigerator

Ò  To build mini fridge that could possibly be easily placed under desk in any other area

Ò  To use transportations mini fridge for children some favorite beverages 

PROBLEM STATEMENT (WEEK 6)

Comparison between traditional refrigeration system and portable mini fridge using TEC

Design Criteria

The idea was to build a portable mini fridge and to provide facilities for a person. The project aims to design and build a miniature prototype of portable mini fridge using thermal electric cooler. The system was targeted as a personal cooler and temperature of the cooled air should be lowered 7 to 8 degree Celsius from ambient temperature. Secondary objective of the project includes to make our life easier and to reduce their bill cost. This proposal and designation is to reduce the energy consumption with engineering techniques and calculation method.

Experimental Design

In this project heat sinks (hot side and cold side) operate by conducting heat or coldness from the TEC to the heat sink and then radiating to air. A better the transfer of coldness between the two surfaces, the better the cooling will be. When the heat sinks were attached the TECs, there will be uneven surfaces or gaps. The gap will cause for poor heat transfer, even if it is negligible. To improve the thermal connection between the TECs and the heat sinks a chemical compound was used. The heat sink compound, typically a white paste made form zinc oxide in a silicone base ensures a good transfer of heat between the modules and the heat sinks.

TEMPERATURE CONTROLLER (WEEK 5)

Temperature controller

To accurately control process temperature without extensive operator involvement, a temperature control system relies upon a controller, which accepts a temperature sensor such as a thermocouple or thermal electric cooler as input. It compares the actual temperature to the desired control temperature, or set point, and provides an output to a control element. The controller is one part of the entire control system, and the whole system should be analyzed in selecting the proper controller.

This circuit can cool your heat generating electronic devices by operating a DC fan when the temperature in its vicinity increases above the preset level. Its operation is fully automatic and turns off when the temperature returns normal. It uses a small 12V DC brush fewer fans used in computers

When the temperature increases the base current of Q1 (BC 547) increases which in turn decreases the collector voltage of the same transistor. Since the collector of Q1 is coupled to the base of Q2 (BD 140), the decrease in collector voltage of Q1 forward biases the Q2 more and so do the speed of the motor of fan. Also, the brightness of the LED will be proportional to the speed of the fan.

1.3 On/Off Control

An on-off controller is the simplest form of temperature control device. The output from the device is either on or off, with no middle state. An on-off controller will switch the output only when the temperature crosses the set point. For heating control, the output is on when the temperature is below the set point, and off above set point. Since the temperature crosses the set point to change the output state, the process temperature will be cycling continually, going from below set point to above, and back below. In cases where this cycling occurs rapidly, and to prevent damage to contactors and valves, an on-off differential, or “hysteresis,” is added to the controller operations. This differential requires that the temperature exceed set point by a certain amount before the output will turn off or on again. On-off differential prevents the output from “chattering” or making fast, continual switches if the cycling above and below the set point occurs very rapidly. On-off control is usually used where a precise control is not necessary, in systems which cannot handle having the energy turned on and off frequently, where the mass of the system is so great that temperatures change extremely slowly, or for a temperature alarm. One special type of on-off control used for alarm is a limit controller. This controller uses a latching relay, which must be manually reset, and is used to shut down a process when a certain temperature is reached.

THERMOELECTRIC COOLING (WEEK 4)

Thermoelectric Cooling

Thermoelectric cooling uses the Peltier effect to create a heat flux between the junctions of two different types of materials. A Peltier cooler, heater, or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other, with consumption of electrical, depending on the direction of the current. Such an instrument is also called a Peltier device, Peltier heat pump, solid state refrigerator, or thermoelectric cooler (TEC). They can be used either for heating or for cooling (refrigeration), although in practice the main application is cooling. It can also be used as a temperature controller that either heats or cools.^[1]

This technology is far less commonly applied to refrigeration than vapor-compression refrigeration is. The main advantages of a Peltier cooler (compared to a vapor-compression refrigerator) are its lack of moving parts or circulating liquid, and its small size and flexible shape (form factor). Its main disadvantage is that it cannot simultaneously have low cost and high power efficiency. Many researchers and companies are trying to develop Peltier coolers that are both cheap and efficient.

A Peltier cooler can also be used as a thermoelectric generator. When operated as a cooler, a voltage is applied across the device, and as a result, a difference in temperature will build up between the two sides.^[2] When operated as a generator, one side of the device is heated to a temperature greater than the other side, and as a result, a difference in voltage will build up between the two sides. However, a well-designed Peltier cooler will be a mediocre thermoelectric generator and vice-versa, due to different design and packaging requirements.

Thermoelectric junctions are generally only around 5–10% as efficient as the ideal refrigerator compared with 40–60% achieved by conventional compression cycle systems. Due to the relatively low efficiency, thermoelectric cooling is generally only used in environments where the solid state nature Peltier (thermoelectric) cooler performance is a function of ambient temperature, hot and cold side heat exchanger (heat sink) performance, thermal load, Peltier module (thermopile) geometry, and Peltier electrical parameters.

LITERATURE REVIEW (WEEK 3)

In 1834 Jean Peltier noted that when an electrical current is applied across the junction of two dissimilar metals, heat is removed from one of the metals and transferred to the other. This is the basis of thermoelectric refrigeration. Thermoelectric modules are constructed from a series of tiny metal cubes of dissimilar exotic metals which are physically bonded together and connected electrically. When electrical current passes through the cube junctions, heat is transferred from one metal to the other. Solid-state thermoelectric modules are capable of transferring large quantities of heat when connected to a heat absorbing device on one side and a heat dissipating device on the other. The Koolatron's internal aluminium cold plate fins absorb heat from the contents, (food and beverages), and the thermoelectric modules transfer it to heat dissipating fins under the control panel. Here, a small fan helps to disperse the heat into the air. The system is totally environmentally friendly and contains no hazardous gases, nor pipes nor coils and no compressor. The only moving part is the small 12-volt fan. Thermoelectric modules are too expensive for normal domestic and commercial applications which run only on regular household current. They are ideally suited to recreational applications because they are lightweight, compact, and insensitive to motion or tilting, have no moving parts, and can operate directly from 12-volt batteries.

Jean Peltier

Tom Mancini 

If want to do is heat or cool, using solar energy this way is probably more efficient and certainly cheaper than converting it first into electricity. "That approach ought to be comparable to photovoltaics, or a little better. Traditionally solar-powered refrigerators and vaccine coolers use a combination of solar panels and lead batteries to store energy for cloudy days and at night in the absence of sunlight to keep their contents cool. These fridges are expensive and require heavy lead-acid batteries which tend to deteriorate, especially in hot climates, or are misused for other purposes.[3][4] In addition, the batteries require maintenance, must be replaced approximately every three years, and must be disposed of as hazardous wastes possibly resulting in lead pollution.[3] These problems and the resulting higher costs have been an obstacle for the use of solar powered refrigerators in developing areas.

The use of solar energy to power refrigeration strives to minimize the negative impacts refrigerators have on the environment.^[1][2] Fishermen in the village of Maruata, which is located on the Mexican Pacific coast, have no electricity. But for the past 16 years they have been able to store their fish on ice: Seven ice makers, powered by nothing but the scorching sun, churn out a half ton of ice every day.

Solar refrigeration can also be inexpensive and it would give the electric grid much-needed relief. Electricity demand peaks on hot summer days—150 gigawatts more in summer than winter in the U.S. (A gigawatt equals on billion watts.) That's almost 1.5 times the generating capacity of all the coal-fired power plants west of the Mississippi River. Further, solar is plentiful. The solar energy hitting 54 square feet (five square meters) of land each year is the equivalent of all the electricity used by one American household, according to data from the National Renewable Energy Laboratory and Energy Information Administration, both part of the U.S. Department of Energy.

 Adam Grosser

More than a billion people lack access to electricity and refrigeration, which means they also lack access to important vaccines that need to be kept cool. Nonprofits are pouring millions into developing vaccines that don't need refrigeration, but tech venture capitalist Adam Grosser has a different idea: change the fridge.

Working with a thermodynamics team at Stanford, Grosser built a thermos-sized device that contains a refrigerant that's triggered when the device is heated and left to cool. It then acts like a powerful cold pack, turning anything from a jug to a hole in the ground into a twenty-four-hour minifridge. At roughly fifty dollars apiece, Grosser's device could potentially bring people in the developing world high-maintenance medicines -- and the simple pleasure of a cold drink on a hot day.

INTRODUCTION (WEEK 2)

Refrigerator

A refrigerator (colloquially fridge) is a common household appliance that consists of a thermally insulated compartment and a heat pump (mechanical, electronic, or chemical) that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room. Cooling is a popular food storage technique in developed countries and works by decreasing or even arresting the reproduction rate of bacteria. The device is thus used to reduce the rate of spoilage of foodstuffs.

A refrigerator maintains a temperature a few degrees above the freezing point of water. Optimum temperature range for perishable food storage is 3 to 5 °C (37 to 41 °F).[1] A similar device which maintains a temperature below the freezing point of water is called a freezer. The refrigerator is a relatively modern invention among kitchen appliances. It replaced the icebox, which had been a common household appliance for almost a century and a half prior. For this reason, a refrigerator is sometimes referred to as an icebox.

Freezer units are used in households and in industry and commerce. Most household freezers maintain temperatures from -10 to 0 °F (-23 to -18 °C), although some freezer-only units can achieve −30 °F (−34 °C), and lower. Refrigerators generally do not achieve lower than -10 °F (-23 °C), since the same coolant loop serves both compartments: Lowering the freezer compartment temperature excessively causes difficulties in maintaining above-freezing temperature in the refrigerator compartment. Domestic freezers can be included as a separate compartment in a refrigerator, or can be a separate appliance. Domestic freezers are generally upright units resembling refrigerators, or chests (resembling upright units laid on their backs). Many upright modern freezers come with an ice dispenser built into their door

Some refrigerators are now divided into four zones to store different types of food:

−18 °C (−0 °F)	Freezer
0 °C (32 °F)	Meats
5 °C (41 °F)	Refrigerator
10 °C (50 °F)	Vegetables

Table 1: Temperature

The capacity of a refrigerator is measured in either litres or cubic feet. Typically the volume of a combined refrigerator-freezer is split to 100 litres (3.53 cubic feet) for the freezer and 140 liters (4.94 cubic feet) for the refrigerator, although these values are highly variable.

Temperature settings for refrigerator and freezer compartments are often given arbitrary numbers by manufacturers (for example, 1 through 9, warmest to coldest), but generally 3 to 5 °C (37 to 41 °F)[1] is ideal for the refrigerator compartment and −18 °C (−0 °F) for the freezer. Some refrigerators are required to be within certain external temperature parameters to run properly. This can be an issue when placing units in an unfinished area such as a garage.

European freezers, and refrigerators with a freezer compartment, have a four star rating system to grade freezers.

Temperature	Time Storage
min temperature = −6 °C (21 °F).	Maximum storage time for (pre frozen) food is 1 week
min temperature = −12 °C (10 °F).	Maximum storage time for (pre frozen) food is 1 month
min temperature = −18 °C (−0 °F).	Maximum storage time for (pre frozen) food is between 3 and 12 months depending on type (meat, vegetables, fish, etc

Table 2: Temperature And Time