Passive Cooling: Natural Ways to Cool Your Home
Created By RISC | 1 year ago
Last modified date : 1 year ago
During the summer, you may look for somewhere to escape the heat. If you prefer to stay home, there are ways to reduce the heat without relying solely on air conditioners with high power costs…
Your well-being depends on thermal comfort, air quality, visual comfort, and acoustic comfort. These are all components of human comfort. With scorching summer weather, thermal comfort is a priority. You have various ways to reduce heat in your house and make it feel more comfortable.
• Environmental factors such as air temperature, relative humidity, the average temperature of the surrounding surface, and wind speed are examples of human thermal comfort variables.
• Manmade factors
Let's look at environmental factors affecting human thermal comfort.
To begin, air temperature is defined as the temperature of dry bulb air as measured by a thermometer. The comfort temperature range is 22-27 °C, with 24-25 °C being optimal.
Relative humidity is the ratio of moisture in the air to the maximum quantity of moisture that the air can accept without condensation. The comfort range is 20-75%RH, with 55%RH being the most comfortable.
The average quantity of heat radiation influencing that environment is referred to as the mean radiant temperature (MRT). Humans feel around 1.4°C warmer or cooler if the average temperature of the surrounding surface increased or decreased by 1°C.
Finally, wind speed (air velocity), can be experienced as air movement, with an acceptable boundary range of 0.05-1.00 m/s. The wind speed should be neither too low or too high. When the wind speed increases by 1 km/h, or around 0.28 m/s, we feel 0.4 degrees Celsius cooler.
Let's now look at the sources of coolness that exist around our homes.
Here are several natural cooling sources:
Coldness from the ground has both underground and underwater sources not influenced by heat from the sun's rays. As a result, the temperature is lower than the ambient outside air temperature and remains consistent throughout the day. The typical soil temperature in Thailand is roughly 26-28 degrees Celsius at a depth of 1 meter from the soil surface, and the average water temperature from significant water sources at a depth of 1.50 meters or more is approximately 23-25 degrees Celsius.
Evaporation at the surface, both from the water source and from absorbent materials, and plant transpiration, which collects heat energy from the environment and uses it to convert water to steam. As a result, the temperature of the surrounding surroundings drops. Water evaporation requires 2.3 MJ/kg (2,200 BTU/hour) of heat energy to convert 1 liter of water to vapor.
Wind helps in the removal of heat and moisture from objects and surfaces, as well as the evaporation of sweat, which is the release of heat from the human body. However, the average wind speed in Thailand is moderate to low, rarely exceeding 4 m/s (about 1 m/s at a height of 10 m from the ground). As a result, before entering the structure, it is required to plan for wind resistance, increase wind speed, or decrease wind temperature.
Cool from the sky: Because the background temperature of the universe is as low as -270 degrees Celsius (2.735 degrees Kelvin), the temperature of the sky when not impacted by solar radiation is exceedingly low. It has a temperature range of roughly -70 degrees Celsius (203 degrees Kelvin) and rises as it gets closer to the ground. To put it simply, the sky is an excellent source of cooling.
Shade can protect from solar radiation, the most powerful generator of heat on the Earth's surface. A shadow avoid heat from the sun's beams, especially at 2pm, when the heat is at its peak. Shade can reduce heat by up to 5 times.
As we know, environmental elements play a role in natural cooling around the house. The next stage is to determine which natural cooling methods can be used in our homes in accordance with building design rules.
Earth Cooling
• Dug down 0.60 meters deep to create a hole at 26-28 degrees Celsius with shading and plant protection to limit sun exposure. Create water sources or water the area to raise soil humidity, causing evaporation and lowering soil temperature.
• Create a 1.50-meter-deep pond with a temperature of 23-25 degrees Celsius and shade. Increase evaporation through wind speed or the installation of fountains, waterfalls, or water turbines.
Evaporative Cooling
• Water source design by constructing a 32-meter-wide pond in the absence of sunshine to provide environmental cooling as an air conditioner rated at 12,000 BTU/hour.
• Choosing trees with 5.5 liters per hour transpiration (65 liters per day) can generate environmental cooling as an air conditioner with 12,000 BTU/hour.
• Exterior surface material selection: materials with high water absorption and evaporation, low thermal absorption (light color), low mass, low density, high emissivity (rough surfaces, big surface area).
Natural Ventilation
• Increase wind flow by orienting the building and designing the building shape to capture more wind from each direction.
• Increase wind speed by strategically arranging trees and soil hills, such as planting trees with wind gap proportions of roughly 1.75:1 and constructing 30-degree soil hills.
• Reduce wind temperature by creating water sources, planting trees, and choosing surface materials, such as adjusting water source into shading area, creating wind flow into building, choosing trees with spreading shapes to create shades and tall trees to increase wind movement, selecting exterior surface materials with shading and evaporative area, and getting the wind into the building.
Night Sky Radiation
To reflect heat radiation back to the sky at night, choose a roof covering with an emissivity greater than 0.9. Furthermore, the roof material should be lighter in weight to reduce heat accumulation and improve exothermic reaction. Furthermore, the roof slope angle should be 15-30 degrees for coolness accumulation in a certain region. Roofs that face the sky can maintain around 7 BTU/hour/square foot of cooling at night.
Solar Radiation Protection
• To avoid heat, use landscape design to plant trees in surrounding areas to produce shade and lessen direct heat from sun radiation. Furthermore, depending on the leaf forms, bushes, sizes, and types that coincide with these orientations, trees can absorb heat, enhance water evaporation, and raise soil surface humidity.
South: hits by sun rays from above over time.
• Spreading shape: the trunk height should be greater than the users in the region.
• Shrubs layered to generate horizontal shading from above with wind movement
• Trees that do not shed leaves in the summer
• Trees that transpire at a rate of 5.5 liters per hour
• Trees that can filter particles and toxins
West: affected by sun radiation from a low angle with extreme heat from afternoon to evening.
• Trees with column/cone or pyramid shapes to create buffers
• Vertical shading trees to prevent sunlight in low angle and promote wind flow
• Trees that do not shed leaves in the summer
• Trees that transpire at a rate of 5.5 liters per hour
• Trees that can filter particles and toxins
• Design for heat prevention by aligning roof and shade design with building location and direction by checking home sunshine direction during hottest period or 14:00 in each day and then picking shading equipment to install depending on each region.
As we can see, we may conclude that these methods are natural strategies to lower heat in our home.
• Adding shade to an outdoor area by using roofs, awnings, or trees.
• Opening the windows to allow air to circulate without introducing heat into the house. Installing fans to boost air ventilations if there are constraints about ventilation gaps.
• Planting as many trees as possible around the house, especially near doors and windows, to provide shade and cooling. Adding ponds, fountains, or waterfalls can promote coolness through water evaporation if there are more areas in the house.
Story by: Saritorn Amornjaruchit, Assistant Vice President and Research Integration & Design Solutions for Well-Being, RISC