Computational Fluid Dynamics for Naturally Ventilated Systems
Research Question
In my research I believe that by looking and understanding ancient vernacular passive systems and working with computer aided design and cfd wind analysis, we will be able to create a system that can manipulate airflow to cool a space. This data can then inform modernized plans and sections that use these strategies in tandem with modern construction techniques such as 3d printing, to be able to create a space and skin that breathes, allowing for a cooler and healthier interior.
This can then inform future designs that allow for a cooler space without the need for large-scale Air Conditioners or a system to incorporate within existing structures to aid in the overconsumption of air conditioners.
As the earth increases in temperature due to the global climate crisis, partially caused by the emissions from and for air conditioning, there is an increasing need for the air conditioners that are causing the problem.
It is expected that by 2050 there will be a 4x increase in AC consumption worldwide which will consume 10% of global energy consumption.
This will only add the the heating of the earth, therefore adding to the problem.
In addition to being bad for the earth, Air Conditioners are also bad for our health, increasing the prevalence of Sick Building Syndrome as more and more buildings are being sealed from the environment to run HVAC systems. This Increases the concentration of pollutants from the building materials, as well as circulating stale air.
Air conditioners themselves also pull moisture from the room to give the sensation of cool, but if you stay in the room long enough it will pull moisture from your skin as well, affecting the first layers of your skin and leaving it dry and stretched. This can enhance skin conditions and contribute to dry and itchy skin.
Also going from a cold environment inside, to an extreme hot environment outside and then back to the cold, as we run from one place to another can place extreme stress on your whole body, not just your skin.
This brings the question of “what is cool”? And How do humans feel temperature?
A lot of temperature is determined by feel. Humans do not usually feel the dry bulb temperature, but go by a feel-like temperature, which is a mix of the dry bulb and the wet bulb temperature. This is because humans have extraordinarily moist skin, and so when air is blown across it, it picks up this moisture and removes it, making us feel a cooler sensation. This is evaporative cooling and it is what contributes to wind chill and temperature perception.
Most of temperature is perception, which is why on sunny days it feels warmer than cloudy days of the same temperature, because out skin feels the radiation of the sun.
Therefore, changing the thermostat is not the only thing that we can change to feel cool.
At certain heat indexes wind can offer cooling. This is due to the wind chill and the way that skin interacts with sweat. Many studies have been done that show that the presence of a draft is felt and preferred when the human body is at a elevated heat state.
This can be shown in any temperature when the wind is colder than the human body- (why its called wind-CHILL) when the wind reaches 98.2F or 37C (internal body temperature) the air then warms the body instead of cooling it.
Here the heat indexes and the wind speed affect the feel like temperature by several degrees.
In many parts of the world, where winter climates far exceed warm days, this temperature where the wind begins to warm the body instead of cooling it is only reached on certain days out of the year.
This shows that there is not a significant need for air conditioners in the everyday climate of boston/new england. Therefore aiding the natural ventilation in homes in these areas can reduce the use of ACs where they are primarily not needed. This saves emissions but also allows areas that need to rely on air conditioners to do so by reducing emissions in areas that don’t need them.
Only in record temperatures do we reach the 95F or 35C switch in air cooling to heating our skin, meaning most of the time, the air will cool us. Also in the summer it is less windy than the rest of the year, meaning our perception of heat increases, thus why we are using air conditioners in the first place.
To do this we need to begin to focus on how wind is felt on the human body, and where the sensations of cool are most wanted. This can then inform design to ensure that comfort can be met when it is needed.
In women, hands and feet are what cool first and determine the rest of the body’s temperature, while in men (and women) it is more efficient to cool the body by focusing on the face. This can inform design by catering to the human body and its needs to cool.
Wind chill are also felt at certain speeds. It was found in most studies that wind at velocities of 1.2m/s the percentage of discomfort can be reduced by 20%. Therefore the creation of a breeze is optimal for cooling in hot months.
CFD can be used to check wind speeds according to certain geometries. This can be read in colors or lines. Blue is slow air, gradually increasing to purple dangerous gusts. Comfortable air is at the 1.2-3m/s breeze green areas.
CFD was run and looked at for certain vernacular models. I looked at models of natural cooling all over the world to see how certain climates offered cooling. Most cultures used a mix of operable- and this is important- awnings, shutters, louvers, or window designs. Others used pressure differences such as courtyards or towers. Venturi effect, when the air is squeezed into smaller areas or screen type openings were also used in desert or extreme climates. Thus creating a breeze. Many of these examples are still around today and cool people without air conditioning.
As you can see here, faster wind moves over the top of rooves, creating a pressure difference that pulls air out of other sides. This suction allows for air changes within the buildings keeping a constant supply of airflow.
A variety of models were examined including windcatchers of Iran, skywell buildings of Southern China and Vietnam, large porch design and awning found in southern USA and in African countries. These offer shade to windows as well as a pressure difference for airflow.
Normal cross ventilation was looked at in terms of ceiling height as well. European buildings were found to have larger ceiling heights than the 8ft standard in USA buildings. This allows hot air to rise away from the face and keep the bottom area cooler. USA buildings do no have this thermal effect because the ceiling is much shorter, only a couple feet over the head.
Ventilation also stops with closing of windows in most homes. If one window were to close the wind flow would look more like the louver connections.
When we look more closely at the velocity changes according to specific geometries inlets and outlets are increasingly important. This is because they create pressure differences. Wind loves pressure and moves around based upon it. Large velocities of wind, as seen in the red are looked at here in a laminar flow- meaning very streamlined. However this is not how wind in the world works.
Almost all wind is turbulent wind. Meaning it moves in a chaotic fashion. This is due to the different pressures in the air, the height of the atmosphere, and the billions of objects such as buildings, trees, animals and us that are on the surface of the earth. Therefore to read this in a more natural way- we have to look at this in terms of where we would get gusts of wind. Pressure differences are what creates large velocities of wind which then are felt on our bodies as gusts of wind. Therefore the red here would be in spurts. Same with the green. Changes in direction also cause this.
Here we can see both of the interactions. The increase in speeds of the wind and the decrease in temperature. This showcases the need to circulate the air in a cooler environment. For in the areas of the slowest wind (blue) the temperature is the least. As it starts to speed up temperature is increased.
Now- I just said earlier that we need to increase the velocity to drop the temperature….
This is the dry-bulb temperature- not the feel like temperature. Therefore in the areas of the higher temperature but higher velocity, this would feel cooler to the human body. However, by looking how temperature, not just geometry influences the directions and speed of wind, temperature can be felt much lower in specific areas over others. This can inform design of geometries in the future.
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Looking at geometries and how they influence the wind flow now that we can see that windflow and temperature play a connected role in cooling and moving air. Starting to analyze the geometries starting with more basic forms then gradually adding more and more to begin to design and understand pressure zones, boundary layers and flow correction.
First looking at Velocity and the Direction, then at Pressure and how these are related. Starting with basic geometries to understand basic flow patterns.
Then looking at how Pressure and Velocity are Related. Velocity comes at the higher pressure areas and where there is the largest pressure differences.
Then taking a look at how the formation of Eddies correspond with pressure differences. Eddies are prevalent in turbulent flows. Turbulent flows are areas of chaotic airflow.
Although studies are done in Laminar (Straight) Flow, the world is almost all turbulent flow due to the pressure differences created by temperature and both stationary and dynamic objects.
Afterwards taking a look at geometries in the physical realm within a Laminar Flow Water Tank helps to play with real space and faster iterations of geometries and channels. It is important to look at real spaces, as Lisa Moffit says, “ Environmental models generate spatial and material moments, captured through photography, that immerse the viewer into atmospheric worlds, revealing architectural space charged by environmental effects”. This was experimented with basic shapes that allowed the visualization of the invisible.
