CCAT cold box 2017: Difference between revisions

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Background

The Campus Center for Appropriate Technology (CCAT) of Humboldt State University (HSU) is known as a place where students, faculty, and volunteers can collaborate, innovate, and create projects that reduces, reuses, and recycles waste. CCAT build a cold box several years ago, and it has not been maintained since 2014. In this Spring 2017 project, Katelyn P. and Winessa N-S. will restore and maintain CCAT’s cold box.

According to CCAT [1], by using Humboldt’s natural cool weather, its cold air is captured by allowing it to flow through the vents into the box, hence “cold box.” The cold air circulates in the box, dropping the temperatures of the produce and other items as well as ridding of smelly odors. In this project, students hope to renovate or possibly create a new “cold box” for better efficiency. The design behind the chill box is to have an insulated "box" that has 2 holes connecting to the outside. These holes can be put wherever the designer chooses, but ideally they would be on the top or the back of it. The holes allow cool air to flow through one tube and then the hot air to rise inside of it and flow out of the box. This then leaves the box cool and dry allowing for a better way to store your foods.

Problem statement

The objective of this project is to restore, possibly create, and maintain a space to store fresh fruits and vegetables and other items at temperatures natural to the Humboldt environment. By applying methods like these, we are able to reduce the use of electricity and also save money at specific times of the year.

Literature Review

This is a review of the available literature pertinent to refrigeration.

Refrigeration basics

Refrigeration is the science and practice of controlling temperature conditions, to slow down the growth of bacteria in food, drinks, and other items ^[1] What a refrigeration system typically consist of is a compressor which circulates the refrigerant and raises the pressure of the refrigerant forming vapor from. ^[2]. It is the art of maintaining a body of temperatures below its surroundings or alternatively as the removal of heat from a place in which it is undesirable to a place in which it is not. ^[3]

On the other hand, for this project, a cold box does not need a compressor. Instead, a cold box will need to consist of five characteristics. It needs to have water resistance, the ability to withstand continual use, the ability to maintain a temperature not exceeding at around 5°C for a week, affordability and simplicity. Developing countries should be able to use these “cold boxes.” The temperature of this cold box is low because it is used for vaccines. The temperatures for cold box in this project will vary depending on the season. ^[4]

Refrigeration concerns

In industrialized countries, people use refrigerators which has refrigerants. A refrigerant is a substance that absorbs heat by evaporating at low temperatures and pressures and gives up heat by condensing at high temperatures and pressures.” ^[5] Many refrigerants have been banned because these have been known to deplete the Earth’s ozone layer, which is necessary to help protect biological life from the sun’s harmful UV rays. These refrigerants are called chlorofluorocarbons or simply known as CFCs. ^[6]

In addition, where one part of the world uses refrigerators, another part of the world with millions of people have no refrigerators due to the lack of energy and electricity. According to the Food and Agriculture Organizations of the United Nations (FAO), more than one third of the food produced today is lost or wasted. ^[7] The lack of refrigeration impacts the well-being of people as well as the health of the environment. The total costs of food waste amount globally are about $2.6 trillion, which includes the environmental costs at $700 billion and the social costs at $900 billion. ^[8]

To help solve this problem, the implementation of refrigeration can help decrease these global costs. Sustainable methods of refrigeration can also increase the well-being of people who live in impoverished areas and protect their environments.

Types of Refrigeration

There are three methods of cooling: passive or evaporative, sorption heat driven, and mechanical compression ^[2]. In industrialized countries, the use of grid electricity is the main method of refrigeration. On the other hand, in developing countries, refrigeration is used without a reliable source of electricity.

Type 1

Passive and evaporative refrigeration is a system that utilizes temperatures at 10 to 25°C. ^[9] In this type, traditional methods are used with wet sack coverings or porous jars in which the heat is evaporated from the water into a dry atmosphere. The best utilization of this refrigeration method is during the night or in the shade. The only disadvantage is that this method cannot be used in wet weathers. ^[10].

Type 2

Sorption heat driven coolers is a type of refrigeration that utilizes both liquid absorption and solid adsorption. ^[2]. This method has several advantages. It does not need any moving parts, therefore, there would be less need for replacing components and skilled maintenance personnel. The next advantage that these are simple to manufacture. It will only need local maintenance. The third advantage is that these adapt to locally available fuels like solar energy and biomass. The last advantage is that this method does not need the use of CFCs. ^[2].

Type 3

Mechanical compression refrigeration is a system that utilizes power. It ranges from the use of the grid electricity, solar photovoltaic systems, and to water turbine driven coolers. The advantage of having this type of method is having food and other items cool for a long period of time; however, to maintain these types of mechanical compression refrigeration and to replace its parts will be costly. ^[2].

Vacuum Basics

A vacuum, the "space in which there is no matter or in which the pressure is so low that any particles in the space do not affect any processes being carried on there. It is a condition well below normal atmospheric pressure and is measured in units of pressure (the pascal). A vacuum can be created by removing air from a space using a vacuum pump or by reducing the pressure using a fast flow of fluid, as in Bernoulli’s principle." ^[11]. In modern particle physics, the vacuum state is considered the ground state of matter. ^[12]. For this project the idea that 'The warm wet air is forced up and over the cold air. When the warm air is forced up, it causes surface air pressure to drop, sort of like having a small vacuum develop'. ^[13] In our chill box the cold air flowing in will create a change of pressure in the box sucking the hot air, that has risen to the top, out the window and these will create the cool temperature in the box allowing for food storage.

Designing interpretive materials

According to the FAO, the most realistic method of refrigeration used in developing countries is evaporative cooling. It typically consists of an outer pot and an inner pot. ^[14]Between the two pots consists of an evaporative medium like sand. The food is placed into the inner pot. To create the cooling effect, water is added into the sand, and it draws heat from the inner chamber pot. This cause and effect cools the food and other items down to 20°C. ^[15]

Project Evaluation Criteria

Tentative Timeline

Budget

Introduction for the budget: The materials used for the cold box will be donated by CCAT, materials used from a friend, gathered from our environment (beachgrass), or bought from ArcataSCRAP, Scrapyard in Arcata and Ace. We have thought on refurbishing the existing cold box at CCAT, but it was too bulky for the current residents; therefore, we will use materials to accommodate their needs. The following table is a draft of our budget, approximating estimates of purchasing materials.

Acknowledgements