Design Critique and Design Showcase: Non-electric Refrigeration System
A Request for Proposal seeks a solution to addressing the issue of the Meat Vendor community participating in the annual farmers market in the Greater Toronto Area.
Problem Statement (Abstract)
The Bolton Farmers’ Market hosts local producers from Caledon. It promotes organic and environmentally beneficial products, and the traditional farming heritage. The market does not have access to the city’s power grid [1].
In this proposal, chicken, beef, lamb, pork are all classified as meat products. Upon slaughtering of the meat, bacteria cultures start to colonize the exposed tissues. Bacteria grow at the fastest rate in an optimal range of 4 to 15ºC [2]. Therefore, it is recommended to refrigerate the meat between 0 and 4ºC [3]. In these conditions, bacterial growth is minimized [3]. Due to the lack of electricity at the market, maintaining that temperature becomes increasingly difficult without electricity, and sacrifices the sanitation and safety of the products [4]. As a result, the participation of meat vendors has diminished over the past years [1].
The objective of this proposal is to develop a sustainable and reliable solution for meat refrigeration. This solution must meet the constraints of the proposal, and the design should revolve around the philosophy and the values of the Bolton Farmers’ Market. Bolton’s farmers have identified the refrigeration problem as an impediment in their participation in the market [1]. Therefore, an improved solution to this problem would increase the reliability and practicality of meat vending, and local vendors would be encouraged to participate in the market.
Problem Statement (Abstract)
The Bolton Farmers’ Market hosts local producers from Caledon. It promotes organic and environmentally beneficial products, and the traditional farming heritage. The market does not have access to the city’s power grid [1].
In this proposal, chicken, beef, lamb, pork are all classified as meat products. Upon slaughtering of the meat, bacteria cultures start to colonize the exposed tissues. Bacteria grow at the fastest rate in an optimal range of 4 to 15ºC [2]. Therefore, it is recommended to refrigerate the meat between 0 and 4ºC [3]. In these conditions, bacterial growth is minimized [3]. Due to the lack of electricity at the market, maintaining that temperature becomes increasingly difficult without electricity, and sacrifices the sanitation and safety of the products [4]. As a result, the participation of meat vendors has diminished over the past years [1].
The objective of this proposal is to develop a sustainable and reliable solution for meat refrigeration. This solution must meet the constraints of the proposal, and the design should revolve around the philosophy and the values of the Bolton Farmers’ Market. Bolton’s farmers have identified the refrigeration problem as an impediment in their participation in the market [1]. Therefore, an improved solution to this problem would increase the reliability and practicality of meat vending, and local vendors would be encouraged to participate in the market.
Design Process
Problem Identification and Initial Design
In order to solve the issue at hand, the Request for Proposal was, as it had to be, strategically broken down. This allowed for the team to obtain a thorough understanding of the community, stakeholders, and problem. Additionally, the requirements proposed by the RFP team were critiqued as we, the team, measured the feasibility of the requirements - the "realness". As such, the problem statement was boiled down to "effect a design which implements usable, non-electric refrigeration on a hot summer day."
The initial design process required a plethora of research from the design team amidst all the chaos, if I must say, EngSci put its students through. First and foremost, the problem statement was broken into its components with respect to the research required: research on endothermic materials, research on meat, research on refrigerants, and research on existing cooling systems. The group distributed these cases among its members from which we all took partial responsibility. After undergoing some research, the group(s) solving the specified RFP came to realize that the constraints imposed by the RFP team were too pedantic thus making the problem difficult to solve by first year engineering students. After reaffirming with professor Foster (teaching praxis) we, the design teams, were able to relax the constraints.
In addition to performing research and loosening constraints, over time, the team developed design values which they implement in the following processes.
Stakeholder Interaction
Eight design teams have been tasked to solve the RFP referred to on this page: non-electric refrigeration. Since there exist so many teams and the available stakeholders are scant, a point person responsible for contacting stakeholders organized an event in which all the teams can meet the stakeholders of the RFP. And thus the team went to Wychwood Barns to find out more of the community experience. More to come soon!
Conceptual Design
The team and I came up with diverse solutions (some unrealistic I must confess):
- Space Delivery (since space is a natural vacuum)
- Liquid Cooling (used in electronics)
- Pressure Pumps (derived from paintball guns)
- Channeling Air (fanning)
- Dry Ice on Top (convection systems)
- Evaporative Cooling (pot-in-pot coolers)
- Peltier Cooling
After performing convergence techniques - namely the pugh chart - the chosen design was of the Air Channeling system. (refer to the document below)
In order to solve the issue at hand, the Request for Proposal was, as it had to be, strategically broken down. This allowed for the team to obtain a thorough understanding of the community, stakeholders, and problem. Additionally, the requirements proposed by the RFP team were critiqued as we, the team, measured the feasibility of the requirements - the "realness". As such, the problem statement was boiled down to "effect a design which implements usable, non-electric refrigeration on a hot summer day."
The initial design process required a plethora of research from the design team amidst all the chaos, if I must say, EngSci put its students through. First and foremost, the problem statement was broken into its components with respect to the research required: research on endothermic materials, research on meat, research on refrigerants, and research on existing cooling systems. The group distributed these cases among its members from which we all took partial responsibility. After undergoing some research, the group(s) solving the specified RFP came to realize that the constraints imposed by the RFP team were too pedantic thus making the problem difficult to solve by first year engineering students. After reaffirming with professor Foster (teaching praxis) we, the design teams, were able to relax the constraints.
In addition to performing research and loosening constraints, over time, the team developed design values which they implement in the following processes.
- Design for Maintainability (a modular design will enable easy to replace parts)
- Design for Cost Effectiveness (the components are not expensive and easy to manufacture)
- Design for Usability (the stakeholders i.e the meat vendors must be able to effectively complete their task without hindrances in the design)
Stakeholder Interaction
Eight design teams have been tasked to solve the RFP referred to on this page: non-electric refrigeration. Since there exist so many teams and the available stakeholders are scant, a point person responsible for contacting stakeholders organized an event in which all the teams can meet the stakeholders of the RFP. And thus the team went to Wychwood Barns to find out more of the community experience. More to come soon!
Conceptual Design
The team and I came up with diverse solutions (some unrealistic I must confess):
- Space Delivery (since space is a natural vacuum)
- Liquid Cooling (used in electronics)
- Pressure Pumps (derived from paintball guns)
- Channeling Air (fanning)
- Dry Ice on Top (convection systems)
- Evaporative Cooling (pot-in-pot coolers)
- Peltier Cooling
After performing convergence techniques - namely the pugh chart - the chosen design was of the Air Channeling system. (refer to the document below)
After much deliberation, discussions, and debates, the team was able to reiterate the Air Channeling solution to a sufficient degree. In order to reiterate, sufficient justification was required. For instance, the team was in disagreement for a long with respect to which cooling agent to be used in the design. According to the RFP's failed reference designs, ice encouraged bacterial growth, dry ice is not so accessible, and gas is potentially hazardous. Our design team chose to temporarily move on with ice since solving the issue of preventing bacterial growth was as simple as creating a barrier between the ice and the meat. Upon the finalization for the critique the design characteristics of the components of the solution were established such that a prototype could be created.
Modelling
Multi-team Prototyping
After many multi-group discussions wherein the design team pooled resources, information, and ideas, three of the eight groups, ours included, decided to build a pre-prototype that will serve for only experience purposes. In this model, the decided upon refrigeration system used evaporative cooling. In this cooling technique, a wet cloth is draped over an opening to an otherwise insulated cooler. This wet cloth evaporates causing the air inside the cooler to cool down. This was done using more affordable materials as the detailed design was not yet accomplished. One fact that was realized afterwards is that the evaporative cooling technique is effective in conditions below 30% humidity. However, hot Torontonian weathers can reach up to 70% humidity rendering the aforementioned model ineffective. This experience led us (the design team) to perform excessive research on the topic of refrigerants (leading me to thermodynamics discussed in the mathematical modelling).
Prototyping
Upon finalizing the solution design characteristics and justifying general components and their functionality, the team set out to find prototyping material. The following will outline the justification to the use of materials/components in design:
- to be used to provide ventilation to lift cold air that has dropped due to convection
2. The flap covering at the opening of the cooler is to be made of retracting insulative material - preferably rubber. The rubber first is inherently insulative and will thus block out most heat. Second the rubber is self retractive and so what gap is created to remove or put in meat is only exposed to the outside during meat removal and insertion.
After many multi-group discussions wherein the design team pooled resources, information, and ideas, three of the eight groups, ours included, decided to build a pre-prototype that will serve for only experience purposes. In this model, the decided upon refrigeration system used evaporative cooling. In this cooling technique, a wet cloth is draped over an opening to an otherwise insulated cooler. This wet cloth evaporates causing the air inside the cooler to cool down. This was done using more affordable materials as the detailed design was not yet accomplished. One fact that was realized afterwards is that the evaporative cooling technique is effective in conditions below 30% humidity. However, hot Torontonian weathers can reach up to 70% humidity rendering the aforementioned model ineffective. This experience led us (the design team) to perform excessive research on the topic of refrigerants (leading me to thermodynamics discussed in the mathematical modelling).
Prototyping
Upon finalizing the solution design characteristics and justifying general components and their functionality, the team set out to find prototyping material. The following will outline the justification to the use of materials/components in design:
- The first category of components outline the insulation providing building material.
- Reflective Barrier prevents heat transfer in the form of radiation. Primarily, tin or aluminum foil prevents infrared radiation which contributes most to heat. The prototype held a mix of aluminum foil and aluminum tape. We presume that the final product will uphold a more sustainable implementation of a reflective barrier.
- Thick insulation prevents heat transfer via conduction. We chose to use Extruded Polystyrene foam (XPS) to provide insulation to the meat. This is preferred above Expanded Polystyrene foam as it does no create a mess upon its disintegration and is consequently far more usable.
- The outer layer bucket consists of insulative, removable, sturdy material. This material will hold ice and water and provide a uniform cooling condition to the meat.
- The inner bucket(s) are of conductive, sturdy material so as to cool down and allow for the meat to be cooled as well.
- The second category will outline the maintaining the cold temperature component
- The fan to be fitted into the final product is to be battery run and therefore have low power consumption. The fan is to be used for one of two reasons (to be determined after empirical observation)
- to be used to provide ventilation to lift cold air that has dropped due to convection
2. The flap covering at the opening of the cooler is to be made of retracting insulative material - preferably rubber. The rubber first is inherently insulative and will thus block out most heat. Second the rubber is self retractive and so what gap is created to remove or put in meat is only exposed to the outside during meat removal and insertion.
Critique
There were to analyzers or critics present at the critique: Giorgio, a Teaching Assistant graduated from Engineering Science and Professor Irish, the instructor of our engineering design course. All team members were asked questions during the critique regarding our solution and prototype. During this critique, the team and I realized considerable amounts of improvements and alternatives to implement in to the design which will be further discussed.
Suggested Improvements:
The final motivating factor, which the critics argued, is that the design must be effective. The primary question posed by the critics is why this cooler is better than the rest. The obvious answer is because it works. However, the suggestions is that there must be or we must show quantitative proof of the effectiveness of our design. For this purpose, this prototype will undergo mathematical modelling and physical testing.
Suggested Improvements:
- The fan used as an inducer of a semi vacuum draws in residual hot air from defected areas. To effect a solution to this problem, the design team considered implementing a mechanical contraption that will block the fan's suction when the lid of the cooler is lifted.
- The design team avoided considering refrigerants other than ice since they posed either safety concerns. However, Giorgio was not convinced is a maintainable refrigerant and recommended safely sealed nitrogen gas to act as a coolant.
- The third aspect of design which needed to be reframed is the retracting flap or opening. The critic argued (quite pedantic of him I must add) that the flap can get dirty easily and also spread the dirt onto the hands and clothes of the meat vendors.
The final motivating factor, which the critics argued, is that the design must be effective. The primary question posed by the critics is why this cooler is better than the rest. The obvious answer is because it works. However, the suggestions is that there must be or we must show quantitative proof of the effectiveness of our design. For this purpose, this prototype will undergo mathematical modelling and physical testing.
Pre-Showcase Development
Detailed Design
The following are some of the details to be done on the existing prototype to enhance the design and will prove to be fundamental to the implementation:
- The way the lid opens
- Dimensions (maximizing volume within constraints)
- Space between two buckets for ice (maximizing volume while maintaining temperature)
- Exterior Form (for usability and aesthetics)
- The Inner Retraction Flap Material and Design (redesign for usability)
- Scaffolding material and structure
The details are discussed as well as identified in the design handbook for the Meat Cubby below.
Testing
Preliminary Testing (Stage 1)
In the first stage of testing, the design team decided to test the internal temperature fluctuation using the prototype. This can be done as the prototype is functional high fidelity prototype. In this stage, the internal ambient temperature of the cooler was tested against an external ambient temperature of 23 degrees Celsius. The insides of the cooler were first filled with ice and temperature was recorded. Thereafter, the temperature was recorded at half hour intervals. This increased error in the ideal test as the lid had to be constantly opened in order to measure temperature. However, this can account for the frequency of openings the user would do on the final implementation. Despite the margin for error, the internal temperature was maintained at 0 - 3 degrees Celsius for an astounding 29 hours! The first stage of testing has been completed successfully and we hope to add additional features to improve the design. The second stage of testing will consist of testing, not the internal ambient temperature, but the temperature of meat, both full and single in the cooler.
Stage 2 Testing
The second stage of testing consisted of the lid being opened and closed at every 5 minute intervals. The testing lasted for a total of nine hours and was completed successfully. The temperature inside fluctuated within the constraints of 0 degrees to 4 degrees Celsius.
Behavior Modeling
To model behaviour theoretically, it was required that the design team conduct enough research in order to understand the mathematical and theoretical basis of the actual Solution. The equations relating to heat transfer help model heat transfer in the design of this product. This is because of the simplicity of design. as most components are of uniform. The equation used, models the rate of heat transfer between the aluminum foil and foam insulation. Hence, the model is only of conductive heat transfer.
The following are some of the details to be done on the existing prototype to enhance the design and will prove to be fundamental to the implementation:
- The way the lid opens
- Dimensions (maximizing volume within constraints)
- Space between two buckets for ice (maximizing volume while maintaining temperature)
- Exterior Form (for usability and aesthetics)
- The Inner Retraction Flap Material and Design (redesign for usability)
- Scaffolding material and structure
The details are discussed as well as identified in the design handbook for the Meat Cubby below.
Testing
Preliminary Testing (Stage 1)
In the first stage of testing, the design team decided to test the internal temperature fluctuation using the prototype. This can be done as the prototype is functional high fidelity prototype. In this stage, the internal ambient temperature of the cooler was tested against an external ambient temperature of 23 degrees Celsius. The insides of the cooler were first filled with ice and temperature was recorded. Thereafter, the temperature was recorded at half hour intervals. This increased error in the ideal test as the lid had to be constantly opened in order to measure temperature. However, this can account for the frequency of openings the user would do on the final implementation. Despite the margin for error, the internal temperature was maintained at 0 - 3 degrees Celsius for an astounding 29 hours! The first stage of testing has been completed successfully and we hope to add additional features to improve the design. The second stage of testing will consist of testing, not the internal ambient temperature, but the temperature of meat, both full and single in the cooler.
Stage 2 Testing
The second stage of testing consisted of the lid being opened and closed at every 5 minute intervals. The testing lasted for a total of nine hours and was completed successfully. The temperature inside fluctuated within the constraints of 0 degrees to 4 degrees Celsius.
Behavior Modeling
To model behaviour theoretically, it was required that the design team conduct enough research in order to understand the mathematical and theoretical basis of the actual Solution. The equations relating to heat transfer help model heat transfer in the design of this product. This is because of the simplicity of design. as most components are of uniform. The equation used, models the rate of heat transfer between the aluminum foil and foam insulation. Hence, the model is only of conductive heat transfer.
Final Stage of Prototyping
Before the showcase, the design team and I decided to create a medium fidelity prototype. This prototype would demonstrate the exact proportions, dimensions, and aesthetics of the final design. In order to achieve this magnitude of fidelity, the ideal available resource was the Solidworks software on the school computers. This responsibility was tasked to me. By considering stakeholder interaction with the device, I was able to determine a range of optimal dimensions for the final design.
Note To the Assessors: For the sake of this portfolio, I was unable to upload the final virtual prototype made on solid works due to the inability to install exporter to the school computers on which the model was built. To improvise, below is the attached documentation for the final poster which contain a cross sectional cut picture of the final solution.
Determining Dimensions
According to the criteria proposed in the RFP, the design should hold a considerable amount of meat, as well as be operational by one person. However, the constraint of operational by one person did not coalesce with coning considerable amount of meat less than 150lb. Therefore, the design was concentrated towards storing considerable amount of meat. In order to calculate the safe load that one individual can carry, we used the NIOSH lifting equation which resulted to about 9.68 kg. Due to this, we determined that the individual handling is not a viable constraint and we re-framed that to one person can handle it with the assistance of other accessories used in lifting.
Before the showcase, the design team and I decided to create a medium fidelity prototype. This prototype would demonstrate the exact proportions, dimensions, and aesthetics of the final design. In order to achieve this magnitude of fidelity, the ideal available resource was the Solidworks software on the school computers. This responsibility was tasked to me. By considering stakeholder interaction with the device, I was able to determine a range of optimal dimensions for the final design.
Note To the Assessors: For the sake of this portfolio, I was unable to upload the final virtual prototype made on solid works due to the inability to install exporter to the school computers on which the model was built. To improvise, below is the attached documentation for the final poster which contain a cross sectional cut picture of the final solution.
Determining Dimensions
According to the criteria proposed in the RFP, the design should hold a considerable amount of meat, as well as be operational by one person. However, the constraint of operational by one person did not coalesce with coning considerable amount of meat less than 150lb. Therefore, the design was concentrated towards storing considerable amount of meat. In order to calculate the safe load that one individual can carry, we used the NIOSH lifting equation which resulted to about 9.68 kg. Due to this, we determined that the individual handling is not a viable constraint and we re-framed that to one person can handle it with the assistance of other accessories used in lifting.
Design Showcase
The design showcase consisted of the team "pitching" our design in the Great Hall on the UofT campus. The audience consisted of the general public, stakeholders, as well as investors. In order to increase the success of the pitch, the team decided to print out distributable flyers which summarized the design of the Meat Cubby. During the showcase, the team was confronted by multiple individuals including investors. We were subject to much questioning and critique. This, in turn, helped the team prepare for the evaluation. The assessors consisted of one instructor (Patricia) and one stakeholder. Together, the watched the demonstration, after which we were subject, once again, to questioning. This time, we were thoroughly prepared.