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Sustainable technology · Sustainability and design

Bioclimatic architecture and energy savings

Before you start, make sure you know: Energy and its consumption (Secondary Year 2)

In Hermosillo, in May, a classroom without air conditioning can climb past 35 °C (95 °F) in the middle of the afternoon. In Mérida or Tijuana the problem is different, and in the mountains, in winter, it is the cold that sneaks in. Can a house or a classroom stay cool without spending on electricity? Yes: the cheapest energy is the energy you don't need to use, and bioclimatic architecture achieves a good part of that through orientation, materials, and air. At the end of the page you'll come back to this problem.

Orientation and sun exposure

South facade with an overhang: the low winter sun reaches the back of the house and the high summer sun is blocked by the overhang. house overhang winter sun summer sun S (south facade, gets low winter sun) N

What about north-facing?

A north-facing facade gets no direct sun all year. That doesn't make it "bad": it has an advantage and a cost.

  • Advantage: it provides diffuse, constant natural light, with no glare and almost no heating. That is why it is welcome in workshops, computer labs, laboratories, libraries, and drawing rooms, where direct sunlight is a nuisance on screens and paper, and where the afternoon heat is also avoided.

  • Cost: in winter it gets no heat from the sun and is the coldest facade. It calls for good insulation (walls and double-pane windows), moderately sized windows, and, if needed, gaining heat elsewhere (south-facing windows in other rooms, walls with thermal mass).

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Explain what bioclimatic architecture is and name two of its characteristic strategies, stating what each one achieves.

Explain what bioclimatic architecture is and name two of its characteristic strategies, stating what each one achieves.

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In Mexico, why is it beneficial to face the large windows of a house toward the south? Explain what this achieves in winter and what problem may arise in summer.

In Mexico, why is it beneficial to face the large windows of a house toward the south? Explain what this achieves in winter and what problem may arise in summer.

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The figure shows the cross-section of a bioclimatic house, with a wall feature marked with ?. State what this feature is, what function it serves, and explain why the…

The figure shows the cross-section of a bioclimatic house, with a wall feature marked with ?. State what this feature is, what function it serves, and explain why the winter sun enters through the window while the summer sun does not.

? summer sun winter sun N S
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A north-facing classroom receives no direct sunlight all year. Is it a bad orientation? Qualify your answer: what advantage does it have for natural light without…

A north-facing classroom receives no direct sunlight all year. Is it a bad orientation? Qualify your answer: what advantage does it have for natural light without heating, what uses benefit from it, and what insulation strategy does it require in winter?

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Solar protection for windows

When the sun hits glass directly, the radiation passes through and heats the interior; once inside, the heat gets trapped. That is why it matters where the sun is stopped.

Solution Approximate cost Effectiveness
Reflective interior film Low Medium: the sun has already passed through the glass and part of the heat stays inside
Interior blind or curtain Low-medium Medium-low: again, the heat has already come in
Exterior awning, louvers, or tree Medium High: the sun is stopped before it reaches the glass
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An apartment gets very hot in summer due to a west-facing window that receives the afternoon sun. Propose three solutions (exterior awning, blind, interior reflective…

An apartment gets very hot in summer due to a west-facing window that receives the afternoon sun. Propose three solutions (exterior awning, blind, interior reflective film) and analyze the cost and effectiveness of each, explaining why exterior shading works better.

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Thermal insulation

In a home, insulation matters most in two places:

  • The roof: in Mexico it is the surface that gets the most sun during the day, and hot air rises. It is the priority in hot climates.

  • The windows: single-pane glass lets a lot of heat through. A double-pane window has an air gap between two sheets of glass; that still air conducts heat poorly and the window insulates much better.

Exposed walls count too, especially those facing west and east.

Cross-section of a wall with a layer of insulation between two layers of brick: little heat passes through the insulated part; at the concrete column, which interrupts the insulation, much more passes. interior (cool) exterior (hot) column little heat a lot of heat insulation (green layer)

How to compare insulating materials with a fair test

To find out which material insulates better, it isn't enough to give an opinion: you have to measure. A comparison is fair when only one thing changes and everything else stays the same.

  • Variable you change (independent): the insulating material (for example cork, wool, and polystyrene).

  • Variable you measure (dependent): the temperature of the water or of the inside of the box after some time, measured with a thermometer.

  • Variables you control (the same in all tests): boxes of the same size and material, same thickness of insulation, same amount of water at the same starting temperature, same time, same place (no direct sun or drafts).

  • Control box: a box with no insulation, to know how much the temperature changes when there is no protection.

  • Repeat the test and take the average, so that a measurement error doesn't decide the result.

If the hot water cools less in one box, that material did a better job of slowing the flow of heat. The same idea works with ice: the one that melts the least wins.

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Explain what the thermal insulation of a building is and name the two elements of a home where it is usually most important (roof, facades, windows), justifying your…

Explain what the thermal insulation of a building is and name the two elements of a home where it is usually most important (roof, facades, windows), justifying your choice.

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Explain why a double-glazed window insulates better than a single-glazed one: what role the air gap between the two panes of glass plays.

Explain why a double-glazed window insulates better than a single-glazed one: what role the air gap between the two panes of glass plays.

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Explain what thermal insulation in a building is and reason the meaning behind the phrase "insulation is the first form of heating", relating it to energy demand.

Explain what thermal insulation in a building is and reason the meaning behind the phrase "insulation is the first form of heating", relating it to energy demand.

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Design a school experiment to compare the insulating properties of three materials (cork, wool and polystyrene): setup with identical boxes and hot water or ice, which…

Design a school experiment to compare the insulating properties of three materials (cork, wool and polystyrene): setup with identical boxes and hot water or ice, which variable is measured, and how to ensure the test is fair.

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Thermal mass and cross ventilation

Floor plan of a house with thick walls and open windows on opposite facades: cool air enters on one side, crosses the house, and leaves on the opposite side. air crosses the whole house inlet outlet thick walls: thermal mass
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A classroom gets very hot in the afternoons during June. Propose three bioclimatic solutions (without air conditioning), order them from lowest to highest cost, and…

A classroom gets very hot in the afternoons during June. Propose three bioclimatic solutions (without air conditioning), order them from lowest to highest cost, and explain how each one works.

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Explain what cross ventilation is, how it is achieved in a home, and why it cools down a space without using electricity.

Explain what cross ventilation is, how it is achieved in a home, and why it cools down a space without using electricity.

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Explain what the "thermal mass" of thick walls is and how traditional houses in northern Mexico take advantage of it to stay cool during the day and warm at night.

Explain what the "thermal mass" of thick walls is and how traditional houses in northern Mexico take advantage of it to stay cool during the day and warm at night.

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Design according to Mexico's climate

Mexico has several climates and each one calls for different strategies:

Climate Examples Priority
Hot dry Hermosillo, Mexicali, Monterrey Shade, thick walls (adobe, brick), insulated or light-colored roof, courtyards, night ventilation
Hot humid Mérida, Cancún, Veracruz Constant cross ventilation, high and lightweight roofs, shade, large windows with protection
Temperate Mexico City, Puebla, Querétaro Take advantage of south-facing sun in winter, overhang for summer, good roof insulation
Cold mountain Sierra, Toluca Gain south-facing sun, insulate roof and walls very well, double-pane windows

Local materials help: adobe and brick provide thermal mass; a green roof (plants on the rooftop) provides shade and cools; bamboo or lightweight wood work well in humid climates.

House with a green roof, an overhang over a south-facing window, and a shaded interior courtyard: strategies for a hot climate. green roof overhang courtyard shade, plants, and cool air without electricity
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Design the bioclimatic strategy for a new classroom in your local area: orientation of windows, overhangs or awnings, insulation and ventilation. Justify each decision…

Design the bioclimatic strategy for a new classroom in your local area: orientation of windows, overhangs or awnings, insulation and ventilation. Justify each decision based on the climate of your area.

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Design the bioclimatic strategy for a public library in Monterrey, where summers are very hot: orientation, solar shading of facades, ventilation and materials. Justify…

Design the bioclimatic strategy for a public library in Monterrey, where summers are very hot: orientation, solar shading of facades, ventilation and materials. Justify each decision based on the climate.

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A contemporary house built in a dry Mediterranean climate zone features large unprotected west-facing windows and lightweight partition walls. In summer, the interior…

A contemporary house built in a dry Mediterranean climate zone features large unprotected west-facing windows and lightweight partition walls. In summer, the interior becomes uninhabitable after 16:00 and the air conditioning units must run at maximum capacity continuously.\na) Identify the two main physical design errors regarding evening solar radiation and the thermal inertia of the building envelope.\nb) Design a renovation proposal inspired by two solutions from traditional vernacular architecture (such as shaded interior courtyards, latticework, or thick walls such as rammed earth). Explain for each one the passive physical principle it harnesses (evaporative cooling, radiation interception with ventilation, or thermal wave lag and damping).

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Energy sources and saving habits

At home and in the community, renewables are used with simple technologies: a solar water heater on the roof, a fuel-saving wood stove that uses less fuel, photovoltaic panels for part of the consumption. In Mexico, electricity consumption is measured in kWh and appears on the CFE bill.

Saving habits and the efficiency label

Some habits that save energy: turning off lights and unused devices, using LED bulbs, unplugging chargers, drying clothes in the sun, showering with a solar water heater, ventilating instead of using air conditioning. The ones that save the most are usually those involving devices that use the most energy for the most hours: refrigeration and water heating.

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Name three renewable energy sources and three non-renewable ones, and explain the fundamental difference between the two groups in one sentence.

Name three renewable energy sources and three non-renewable ones, and explain the fundamental difference between the two groups in one sentence.

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What is the energy label on household appliances? Explain what its letter indicates and why it is worth looking at it (and at the annual consumption figure) before…

What is the energy label on household appliances? Explain what its letter indicates and why it is worth looking at it (and at the annual consumption figure) before buying.

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Name three energy-saving habits at home, estimate which one saves the most energy over a year, and justify your estimate.

Name three energy-saving habits at home, estimate which one saves the most energy over a year, and justify your estimate.

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Savings, the rebound effect, and payback

Calculating the savings from an improvement uses the relationship energy = power × time: $E = P \cdot t$. If $P$ is in kW and $t$ is in hours, $E$ comes out in kWh.

If the prices in a payback problem are in another currency, the method is the same: annual savings = energy saved × price per kWh, and payback = investment ÷ annual savings. Just make sure everything is in the same currency (in Mexico, pesos and the CFE rate).

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A $9\ \text{W}$ LED bulb replaces a $60\ \text{W}$ incandescent bulb that gave the same amount of light. If it is turned on for 4 hours a day, calculate how much energy,…

A $9\ \text{W}$ LED bulb replaces a $60\ \text{W}$ incandescent bulb that gave the same amount of light. If it is turned on for 4 hours a day, calculate how much energy, in $\text{kWh}$, is saved in a year (365 days).

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A school replaces $100$ $60\ \text{W}$ fluorescent luminaires (which operated for $6\ \text{h/day}$) with $20\ \text{W}$ LED panels. An energy saving of $66.7\ \%$ was…

A school replaces $100$ $60\ \text{W}$ fluorescent luminaires (which operated for $6\ \text{h/day}$) with $20\ \text{W}$ LED panels. An energy saving of $66.7\ \%$ was projected. However, after the renovation, lighting electricity consumption was only reduced by $33.3\ \%$ because the staff, perceiving that "LEDs consume nothing", leave the lights on for an average of $12\ \text{h/day}$.\na) Calculate the original daily consumption in $\text{kWh}$, the projected consumption after installing the LEDs, and the resulting actual consumption. What percentage of the theoretical savings has been lost?\nb) Explain using these data what the "rebound effect" (or Jevons paradox) is and how it distorts energy efficiency forecasts.\nc) Design two automated technical measures (sensors, timers, or control systems) that prevent this rebound effect without relying on the will or behavior of the users.

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On a sustainability forum, a user states: "A heat pump with a $\text{COP} = 4$ generates $4\ \text{kWh}$ of heat for every $1\ \text{kWh}$ of electricity consumed. This…

On a sustainability forum, a user states: "A heat pump with a $\text{COP} = 4$ generates $4\ \text{kWh}$ of heat for every $1\ \text{kWh}$ of electricity consumed. This violates the principle of conservation of energy, as it implies an efficiency of $400\ \%$, which is physically impossible."\na) Technically refute this statement: explain where the remaining energy comes from and why transferring heat is not the same as generating it through the Joule effect.\nb) If a single-family home requires $7,000\ \text{kWh}$ of thermal energy per year for heating, calculate the electricity consumption and the annual bill (at $0.20\ \text{\$/kWh}$) using electric radiators compared to a heat pump with $\text{SCOP} = 3.5$.\nc) Predict what will happen to the instantaneous $\text{COP}$ and the power consumed by the heat pump during a cold snap where the outdoor temperature drops from $10\ ^\circ\text{C}$ to $-5\ ^\circ\text{C}$. Justify your prediction.

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Summary

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