How Do Buildings Keep Cool in Hot Climates?

Rooftop HVAC

Controlling the temperature of a building is essential, mainly when the building is in a hot climate. Care must be taken when designing to ensure the building will be cooled effectively and adequately.

Buildings keep cool in hot climates with air conditioner alternatives, like hydronic or evaporative cooling. Materials appropriate for the climate are used in construction — same for roofing and insulation. Airflow, window location, shading, and energy-efficient appliances also keep a building cool.

While most people assume that an air conditioning unit is the only answer to cooling a building in a hot climate, they couldn’t be further from the truth. There are methods beyond conventional air conditioning to cool a building. Read on for more detailed information about these cooling methods.

Alternatives to Air Conditioning in Hot Climates

Air conditioning systems are not always practical in hot climates — they have to work harder, thus energy bills are higher.

As a result, people are looking for more efficient ways to cool down buildings. While there are many innovative designs in the works, the following are already used in different areas of the world:

Hydronic Cooling

Hydronic cooling is the process of removing heat from a space with chilled water as the medium for heat exchange. It may seem odd to use water as a medium. However, water can absorb significantly more heat energy than the same volume of air, approximately 3000 times more.

Hydronic cooling works by first cooling the water with a chiller, dry cooler, or cooling tower. The water is then pumped through the system into heat exchanger units. Air handlers use fans to pull warm air in.

As warm air and humidity are pulled from the room, it is replaced with cool, dry air. The pump works nonstop, and the now warm water leaves the heat exchanger to be chilled. The water only needs to be slightly cooler than the ideal indoor temperature.

Hydronic cooling is an efficient cooling system. Zone control installation is an option, allowing different temperatures in different areas or only cooling your chosen locations. Hydronic systems can be a trench system or an underfloor pipe system. These systems produce even temperature distribution.

Hydronic cooling systems work distinctively opposite of evaporative cooling as it introduces humidity into the space but have many benefits. Hydronic cooling is an efficient cooling system.

Evaporative Cooling

Evaporative cooling is another term for adiabatic cooling. Similar to hydronic cooling, it uses water but with a different method. Evaporative cooling uses water vapor to cool the air.

Evaporative cooling is not new. It dates back to early human civilization. This system forces hot air through wet cooling pads by a fan. The cooling pads remain moistened continuously by a water pump. The pump delivers water to the cooling pads. The now cool air is blown into the building.

More compelling, evaporative cooling is sustainable and energy efficient. It uses 90% less energy than conventional air conditioning yet delivers comparable temperatures. Further comparing, conventional air conditioning recirculates warm indoor air, but evaporative cooling circulates freshly filtered air into a building, improving air quality.

Proper Materials Keep Buildings Cool

Material selection is imperative when your building’s location is in a hot climate. Some building materials are more conductive of heat than others. The right professionals can ensure your building has the best materials for the hot climate.

Thermal Mass Materials

Concrete and stone buildings have a high thermal mass. Simply, thermal mass materials both absorb and release heat gradually. They absorb heat from the sun during the day. That heat radiates out in the afternoon. These materials, when used properly, help maintain comfortable temperatures inside your building.

Phase Change Material

Phase change material, or PCM, is actually latent heat storage. PCM is a substance capable of releasing and absorbing energy at the phase transition, resulting in cooling effects. The transition is primarily between solid and liquid states. While the material changes from liquid to solid and vice versa, heat is absorbed or released.

Due to the nature of PCM, it contributes to a reduction in energy consumption.

PCM demand is growing in the construction industry. It is expected to boom in both volume and value in North America, particularly between 2020 and 2025. One factor pushing the demand for PCM is the construction of green buildings.

Insulation Helps Regulate Temperature

Spray foam insulation is a commonly used material. Spray foam is unique in its installation. It expands after it is sprayed and seals as it expands.

It regulates temperature because it resists heat transfer. There are various types of spray foam. Each serves a unique purpose based on the location of the foam. High-density foam is generally used at the highest level of a structure.

Different Roof Designs Can Dispel Heat

One location that is paramount to cooling a building in a hot climate is the roof. The hotter the roof of your building is, the harder it is to keep the interior cool.

The color of your roof makes a difference. Dark roofs absorb sunlight, which heats the building. At noon, a flat dark roof can receive the equivalent of 100 light bulbs per square foot (0.09 sqm). Even more alarming, these dark roofs can warm the air flowing over the roof, contributing to global warming via radiating heat.

Ideally, a roof will have high solar reflectance and high thermal emittance. Solar reflectance is a surface’s ability to reflect solar energy from it and back into the atmosphere. On the other hand, thermal emittance is a surface’s ability to radiate any solar energy it absorbs.

Best materials for cool roofs:

  • Green roof. A vegetative layer on a roof provides shade and removes heat, reducing temperatures. Compared to conventional roofs, the temperature of a green roof is 30 to 40 degrees cooler.
  • Asphalt Shingles. Asphalt shingles have small reflective granulates. The lighter colored, the better. This roof type is most often used for residential homes.
  • Metal roofs. Metal roofs have a solar reflectance of more than 70%.

Reflective coatings:

  • Aluminum roof coatings. These coatings contain aluminum flakes and look like an aluminum sheet. Most have 50% solar reflectance although some are 70% or more.
  • Terra-Cotta tiles. Tiles are used in warm climates because they are high in both solar reflectance and thermal emittance.
  • White roof coatings. White roof coatings reflect  70% to 80%. Multiple layers are the most reflective.

Maximizing Air Flow Helps Cool Buildings

Some buildings are designed with the buildings’ cooling needs in mind. Airflow plays a crucial role in cooling. When considering airflow to cool, there are two simple perspectives: cross ventilation (horizontal) and stack ventilation (vertical). For hot climates, cross ventilation is not recommended as it relies on external airflow to ventilate the building.

Cross Ventilation

Cross ventilation is best used when the outside temperature is cooler than the inside temperature. It utilizes wind and thermal buoyancy. Orientation of doors and windows also impacts the air flow. Cross ventilation is considered one of the most natural methods to cool.

Stack Ventilation

Stack ventilation flow is referred to as the chimney effect or vertical ventilation. Commercial and industrial buildings utilize this ventilation system.

It works to cool as cold air exerts pressure under the warm air, pushing the warm air up. The warm air rises because it is less dense than cool air. Stack ventilation requires vents or windows for the air to enter and leave. Warm air must be able to escape for this ventilation system to work and is usually released through the rooftop.

Some buildings run into issues with stack ventilation. The building may over or under ventilate. These issues can be averted with a large enough stack. However, particularly in winter, over-ventilation is possible as the colder weather may cause inadequate regulation of airflow.

Stack ventilation has several benefits, however. They cost less to operate than conventional systems. Maintenance is generally lower also. Typically, it requires less energy than conventional air conditioning systems.

Window Placement Offers Passive Cooling

Choosing the best window placement can result in passive cooling. It is estimated that almost 40% of unwanted heat enters through windows. The best placement is windows that are located opposite of each other. This placement allows for natural ventilation.

Weatherize Windows

One way in which buildings gain heat is through cracks and gaps in windows, referred to as air infiltration. Sealing windows with caulk and weatherstripping can protect an interior from heat. It keeps outside air from infiltrating interior spaces.

Window Coatings

Window coatings can reflect heat away. Window coatings serve more than one purpose. They also reduce glare and sun damage to furniture and other objects inside. Sun control films can reflect all but 10% of incoming sunlight resulting in cooler interiors.

Exterior Shading Reduces Heat Radiation

By planting trees and shrubbery and investing in outdoor window shades, you can reduce the temperature inside of a building.

Greenery

Greenery serves more than an aesthetic purpose. Strategically placed trees, plants, and shrubbery can also provide passive cooling.

Trees provide shade. Shaded areas are blocked from direct sunlight which results in a decreased temperature  of 11 to 25 degrees. However, the type of tree makes a difference. Evergreens, which are generally dense, can provide continuous shade. Deciduous trees, on the other hand, are better for locations with multiple-season weather. In the warm months, they block heat and in cold months, allowing sunlight in.

Deciduous trees with high, expansive crowns would be ideal at the south side of a structure as this would provide maximum shading in the summer. Low crown trees are best on the west of a building, providing shade from the low, late afternoon sun.

Caution should be taken when planting trees. Regardless of the intended purpose, trees planted too close to a structure could damage the foundation over time as the tree matures and root systems grow.

Plants and shrubs shade the ground. While this may seem inconsequential, there are still considerable benefits. Shading the ground reduces heat radiation and cools the air before it reaches the surface of your building. Climbing vines are another option worth considering as they shade the perimeter.

Further, plants produce evapotranspiration. Plants remove water from the soil via their roots and release water vapor through their leaves. The exchange from liquid to gas uses heat from the plants’ surroundings, cooling the air.

Window Coverings

As discussed earlier, the windows and their placements are a factor, but the coverings of the windows are as well. Blinds and curtains do little to block heat. With both blinds and curtains affixed on the inside of the window, heat gain is likely.

Some window covering options that may be suitable for a building are:

  • Sun shades. Sun shades on windows can block a significant amount of sun and heat. The sun shade absorbs the heat, and the heat either dissipates or reflects away.
  • Louvers. Some buildings have louvers. Louvers are narrow slats that slope downward and are placed over windows. They serve two purposes. They let light in and keep sunlight out.
  • Paneled shutters. Paneled shutters are less prevalent in contemporary buildings. They are present in some older buildings. Nonetheless, shutters are incredibly functional. They prevent sunlight and heat from entering a space.

All 3 of these coverings serve the same purpose. They stop sunlight and thus heat from entering a building.

Energy Efficient Appliances Reduce Heat Output

Appliances make a difference as well. Most buildings do supply refrigerators and dishwashers. Refrigerators, however, are one of the most significant energy users. Dishwashers also require a lot of energy, mostly from heating the water. All of this energy creates heat output. Using energy-efficient appliances will reduce the amount of heat that is being released into your building space.

Drawbacks of Conventional Air Conditioning

The days of relying heavily on conventional air conditioning are over. Conventional air conditioning units require a substantial amount of energy to function well. The volume of the electricity generated releases pollution, carbon dioxide specifically, into the air. This process contributes to ozone depletion. In the warmest conditions, these units can easily assume 3000 watts of electricity per hour.

For other reasons, conventional air condition units are detrimental to the environment. Newer units are made of plastics, which are non-biodegradable and harmful to the environment. Ductwork for the unit also breeds bacteria which gets released into the air when the unit is turned on. This bacteria can be toxic to humans.

These units are also costly to run. They do not cool evenly. Thus, it takes longer to reach the desired temperature. Conventional air conditioning only recirculates the interior air. The air is not cleaned.

Conclusion

Cooling a building in hot climates can be expensive. However, there are many more options available to replace conventional air conditioning or utilized alongside conventional cooling to reduce costs and protect the environment.

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