Thermal efficient box: description of my project

I would like to describe my group project (we have been working by 3) for my “Design of Energy-Efficient Building” class: building the most efficient box that is able to retain the highest amount of heat during a two hours experiment.

Goals

To understand deeply the environmental performance criteria within the build environment, it is important to care about the energy performance of a building. For this project, we have tried to build a box with an interior size of 3′ by 3′ by 4′ in which heat loss are minimal. The aim is to appreciate the purposes and benefits of energy modeling and to find the best solutions to design a box with the following conditions: an interesting price, and a nice aesthetic aspect, and which can retain the most heat energy during 2 hours, with a lightbulb of 150 watts on for the first hour. Before building the real box, we have made some simulations with the software IES-VE to find the best available materials to insulate it.

We intended to store energy inside the box at the same time as we avoid energy loss to the outside. To achieve this two goals, we have built a box with two layers of materials 1 and 2 with complementary properties. One of the materials must be an insulator to try to decrease heat loss. Since the duration of the experiment is two hours, the other material has to be able to store energy quickly and release once the heat power is off. To meet this objectives, the insulating materials envelop the whole box made of the other material.

Methodology

 1) Definition of the limits

The limits of the problem have been determined by the conditions in which we will test the efficiency of the box, the classroom: an inner size of 3′ by 3′ by 4′, a 150 W lightbulb heat source, an outside temperature around 72F, an experiment of 2 hours with one with the lightbulb on and the second one with the lightbulb off, a record of the temperature every 6 minutes, a turkey thermometer for measurements.

2) Research about materials

To choose efficient and relevant materials, we have been looking for the following criteria:

  • the good thickness in mm

  • the thermal conductivity in W/m.K

  • the density in kg/m3

  • the specific heat in J/kg.K

  • the cost in $/m2

  • and the grey energy in kWh/m3

 3) Research about wall assemblies

To choose efficient and relevant wall assemblies, we have been looking for the following criteria:

  • the choice of different layers of materials

  • the thermal resistance or R-value in m2.K/W

  • the thickness in m2

  • the mass in kg/m3

  • and the way to assemble the materials

4) Simulations

After deciding the different six wall assemblies, we have simulate them with IES-VE. Firstly, we have designed the geometry of the 3′ by 3′ by 4′ box. Then, in order to represent the classroom, the place of the experiment, we have created four buffer zones surrounding the box. After having integrated the physical features, it is possible to integrate the thermal conditions of the experiment.Finally, by drawing the inside temperature of the box in function of the time, we can compare the thermal degradation of the different wall assemblies and find the most performing one.

5) Construction of the model

After the simulations, we have decided to build a water and foam box. The construction materials we have chosen to build the “Water Tower Box” are:

  • for the polyurethane boards layer, 3 foam insulating sheathings of 1/2 in. 4 ft. x 8 ft.

  • and for the water layer, 936 bottles of water.

The goal will be to compare the results of the simulations and of the experiment.

Results

Here is the result of the construction of the box model:

box2

box axonometry

 Here is the comparison between the experiment and the simulation with IES-VE:

box thermal degradation

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