Thermal Comfort in Buildings Explained - HVACR Design

Summary

This video explores the concept of thermal comfort in built environments and how HVAC systems maintain it. It discusses factors like temperature, humidity, air velocity, radiant temperature, metabolic rate, and clothing that affect comfort. The video also highlights the use of CFD simulations for design analysis, showcasing how to achieve optimal thermal conditions for various spaces and occupants, with a focus on health and productivity.

Takeaways

• 🌡️ Thermal comfort is crucial in indoor environments, and it's affected by factors like temperature, humidity, air velocity, radiant temperature, metabolic rate, and clothing.
• 🏢 HVAC and HVACR systems are designed to control and maintain thermal comfort within buildings, ranging from small units to large systems for skyscrapers.
• 🤒 The ideal room temperature for comfort is around 20 to 22 degrees Celsius, but it can vary based on individual activity levels and clothing.
• 💧 Humidity plays a significant role in comfort; a relative humidity of 30 to 50% is generally comfortable for people.
• 🌀 Air velocity impacts heat exchange and comfort; high velocities can cause discomfort due to rapid heat loss from the body.
• 🔥 Radiant temperature, the heat from surrounding surfaces, can be managed by blocking the path of thermal radiation.
• 🏋️‍♂️ Metabolic rate, which varies with a person's activity level, affects how much heat the body generates and needs to dissipate.
• 👔 Clothing acts as an insulation layer, influencing how individuals perceive temperature and comfort within a space.
• 💻 CFD (Computational Fluid Dynamics) simulations are valuable tools for predicting and improving thermal comfort in building designs.
• 🌐 SimScale is a cloud-based CFD and FEA platform that allows for easy simulation of thermal designs and other engineering applications.

Q & A

What is thermal comfort in the context of the built environment?

Thermal comfort refers to the condition of an indoor environment where the temperature, humidity, air velocity, and other factors are at levels that allow occupants to feel comfortable while performing their tasks.

What does HVACR stand for and what is its purpose?

HVACR stands for Heating, Ventilation, Air Conditioning, and Refrigeration. Its purpose is to control and maintain thermal comfort for the occupants and equipment within a space.

How can CFD simulations help in assessing thermal comfort?

CFD, or Computation Fluid Dynamics, simulations can help in assessing thermal comfort by allowing engineers to visualize and analyze the temperature distribution, air flow patterns, and humidity levels within a space, which can then be optimized for better comfort.

What are the factors that affect thermal comfort in a room besides temperature?

Besides temperature, factors that affect thermal comfort include humidity, air velocity, radiant temperature, metabolic rate, and clothing worn by the occupants.

What is the ideal room temperature range for most occupants to feel comfortable?

As a rule of thumb, occupants will feel comfortable when the room temperature is around 20 to 22 degrees Celsius, although this can vary depending on the person's activity level and clothing.

How does air velocity impact a person's comfort level?

Air velocity impacts comfort by affecting the heat exchange between the body and the environment. Higher air velocities increase heat loss from the body, which can make a person feel colder and less comfortable.

What is the significance of relative humidity in terms of thermal comfort?

Relative humidity is significant because it affects the body's ability to cool itself through sweating. High humidity can hinder sweat evaporation, leading to overheating and discomfort.

What is the recommended range of relative humidity for human comfort?

The recommended range of relative humidity for human comfort is between 30 to 50%. Above 70%, conditions become conducive to mold growth, and comfort levels decrease.

How does radiant temperature affect thermal comfort?

Radiant temperature, which is the temperature of surrounding surfaces emitting thermal radiation, affects thermal comfort by influencing the heat exchange between the body and its environment. High radiant temperatures can make a person feel warmer or cooler depending on the temperature of the surfaces.

What is metabolic rate and how does it relate to thermal comfort?

Metabolic rate is the amount of energy the body burns, which is associated with a person's level of activity. It relates to thermal comfort because higher metabolic rates generate more heat, which needs to be dissipated to maintain comfort.

What is PMV and how is it used in thermal design?

PMV, or Predicted Mean Vote, is a metric used in thermal design to predict the average vote of comfort for a group of people based on various thermal conditions. It helps in assessing and optimizing the design for better thermal comfort.

Outlines

00:00

🌡️ Thermal Comfort and HVAC Systems

The first paragraph introduces the concept of thermal comfort in built environments and the role of Heating, Ventilation, Air Conditioning, and Refrigeration (HVACR) systems in maintaining it. The narrator, Paul from TheEngineeringMindset.com, explains that buildings are designed with specific internal environments in mind, tailored to their purpose. The paragraph highlights the importance of controlling temperature, humidity, air velocity, radiant temperature, metabolic rate, and clothing to ensure comfort. It also introduces the use of Computation Fluid Dynamics (CFD) simulations for analyzing and improving thermal comfort, with a mention of SimScale as a platform for such simulations.

05:00

🛠️ Designing for Optimal Comfort: Temperature and Air Velocity

This paragraph delves into the specifics of designing for thermal comfort, starting with temperature regulation. It emphasizes the ideal room temperature for comfort and the potential health risks of deviating from the body's optimal core temperature. The discussion then moves to air velocity, explaining how it affects heat exchange and comfort levels. The paragraph contrasts a bad design, where an occupant is directly under a cold air discharge, with an improved design that distributes air more evenly. It also touches on the guidelines for acceptable air speeds and the impact of moving air on noise levels.

10:01

💧 Humidity, Radiant Temperature, and Metabolic Rate

The focus of this paragraph is on humidity, explaining its impact on the body's ability to cool down through evaporation of sweat. It defines relative humidity and provides a rule of thumb for comfortable levels. The paragraph also covers radiant temperature, which is the heat felt from surrounding surfaces, and how it can be managed with barriers. Metabolic rate is discussed in relation to a person's activity level and its effect on heat production and comfort. The narrator suggests separating people with different activity levels within a building to provide tailored thermal comfort.

🧥 The Impact of Clothing on Thermal Comfort

In this paragraph, the discussion on thermal comfort continues with the role of clothing as an insulator. It points out the contrast between fashionable and practical clothing in terms of providing insulation and comfort in different temperature conditions. The paragraph also introduces the Predicted Mean Vote (PMV) as a metric used in thermal design to predict the average comfort level of a group of people, with a goal of achieving a neutral vote at zero. The PMV is used to compare the effectiveness of good and bad designs in providing comfort.

Keywords

💡Thermal Comfort

Thermal comfort refers to the condition of an environment where the temperature and humidity are at a level that is agreeable to the human body, allowing individuals to feel at ease without needing to adjust their clothing or the surrounding environment. In the video, thermal comfort is the central theme, with examples given of uncomfortable conditions in classrooms and stations, and how HVAC systems are engineered to maintain it.

💡HVAC

HVAC stands for Heating, Ventilation, Air Conditioning, and is a critical system in buildings designed to provide thermal comfort by controlling temperature and air quality. The script discusses how HVAC systems range from small units for homes to large systems for skyscrapers and their purpose in maintaining a comfortable internal environment.

💡HVACR

HVACR is an extension of HVAC, adding 'Refrigeration' to the acronym. It encompasses all aspects of heating, ventilation, air conditioning, and refrigeration systems. The video mentions HVACR to highlight the comprehensive role these systems play in managing the internal environment of buildings for optimal thermal comfort.

💡Computation Fluid Dynamics (CFD)

CFD is a branch of fluid mechanics that uses numerical analysis and algorithms to simulate and analyze the behavior of fluid flows. In the context of the video, CFD is used to simulate and compare the performance of different building designs to ensure thermal comfort, with SimScale being highlighted as a platform for such simulations.

💡SimScale

SimScale is a cloud-based platform for engineering simulation, which is mentioned in the script as a tool for performing CFD simulations. It is used to analyze and improve the design of HVAC systems and other thermal comfort-related aspects of building environments.

💡Temperature

Temperature is a measure of the average kinetic energy of the particles in a substance and is a primary factor in determining thermal comfort. The video explains how room temperature significantly affects comfort levels, with ideal temperatures for occupants being around 20 to 22 degrees Celsius.

💡Humidity

Humidity refers to the amount of water vapor present in the air and affects thermal comfort by influencing the body's ability to cool itself through evaporation. The script discusses how high humidity can lead to discomfort and the importance of maintaining relative humidity levels between 30 to 50% for comfort.

💡Air Velocity

Air velocity is the speed of air movement and impacts thermal comfort by affecting the rate of heat exchange between the body and the environment. The video describes how excessive air velocity can cause discomfort and gives guidelines for acceptable air speeds in different settings.

💡Radiant Temperature

Radiant temperature is the temperature of the surfaces surrounding a person, which can affect thermal comfort through thermal radiation. The video explains how radiant temperature can be managed by using barriers to block the path of thermal radiation from heat sources.

💡Metabolic Rate

Metabolic rate is the rate at which the body consumes energy while at rest, digesting food, or engaging in physical activity. In the video, it is mentioned that metabolic rate is associated with a person's level of activity and affects how much heat the body needs to reject to maintain thermal comfort.

💡Clothing

Clothing acts as an insulating layer between the person and their environment, affecting thermal comfort by influencing the body's heat exchange with the surroundings. The script discusses how the type of clothing worn can significantly impact an individual's comfort in different temperature conditions.

💡PMV (Predicted Mean Vote)

PMV is a metric used in thermal comfort research to predict the average vote of comfort for a group of people on a scale, considering various environmental conditions. The video mentions PMV as a tool to evaluate and compare the thermal comfort levels of different building designs.

Highlights

Thermal comfort is crucial for concentration and well-being in various environments, such as classrooms and offices.

Buildings are engineered to control the internal environment for different purposes through HVAC or HVACR systems.

HVAC systems range from small units for homes to large systems for skyscrapers, aiming to maintain thermal comfort.

Various factors like temperature, humidity, air velocity, radiant temperature, metabolic rate, and clothing affect thermal comfort.

Computation Fluid Dynamics (CFD) simulations can analyze and compare the performance of different thermal designs.

SimScale is a cloud-based CFD and FEA engineering platform that simplifies thermal design simulations.

Room temperature significantly impacts comfort, with optimal levels around 20 to 22 degrees Celsius.

Humidity levels should be maintained between 30 to 50% for comfort, with higher levels leading to overheating and mold growth.

Air velocity impacts heat exchange and comfort; design should avoid direct high-velocity air on occupants.

Radiant temperature from surrounding surfaces affects thermal comfort and can be managed with barriers.

Metabolic rate varies with activity levels and influences the amount of heat a person needs to reject.

Clothing acts as insulation and affects comfort levels within a thermal environment.

PMV, or Predicted Mean Vote, predicts the average comfort vote in a building, aiming for a neutral zero score.

ASHRAE 55 and CIBSE Guide A are key industry guides for thermal design and comfort.

SimScale offers free webinars, courses, and tutorials for users to learn simulation technology.

The cloud-based nature of SimScale allows for accessible and powerful simulation capabilities through a web browser.

Transcripts

We've all experienced it.

We've sat in a classroom or an office

which was just so hot and stuffy

you found it hard to concentrate

and even started falling asleep.

Or maybe you've sat in a station or a terminal

which was breezy and cold.

These are both examples of bad thermal comfort.

We construct buildings all over the planet

to shelter us from the elements

and allow us to do specific tasks.

We engineer these buildings to control

the internal environment.

Each building has a different purpose,

and so the design of the internal environment

will be slightly different.

We can control the internal environment

through HVAC, or HVACR, which stands for Heating,

Ventilation, Air Conditioning, and Refrigeration.

These systems can range from a small air conditioning unit

for a home or apartment up to enormous multi-chiller

and boiler systems for skyscrapers.

All of these systems have one purpose:

to control and maintain thermal comfort

for the occupants and equipment within a space.

Hey there guys, Paul here from TheEngineeringMindset.com

and in this video, we're going to be looking

at what makes a built environment comfortable

and how we can improve bad ones.

When we consider what makes a room comfortable,

we tend to think of temperature first.

That's true, but there are other things we need

to consider also.

Like, the humidity, the air velocity,

the radiant temperature, the metabolic rate,

and also our clothing.

We'll go through each of these a little later in the video

and discuss how they impact our built environment.

But, if we think about times when we've been in a room

which was thermally uncomfortable,

then the air was probably too hot or cold,

the humidity way too high, and the air circulation

was either not enough or far too much.

We can simulate and even compare the performance

of different designs, quickly and easy, using CFD,

or Computation Fluid Dynamics.

These simulations on screen were produced

using a revolutionary cloud-based CFD

and FEA engineering platform by SimScale,

who have kindly sponsored this video.

You can access this software using the links

in the video description, below.

And they offer a number of different account types,

depending on your simulation needs.

SimScale isn't just limited to thermal design.

It's also used for data centers, AEC applications,

electronics design, as well as structural analysis.

Just a quick look through their site

and you can find thousands of simulations

for everything from building's HVAC systems,

heat exchangers, pumps and valves,

to race cars and airplanes,

which can all be copied and used as templates

for your own design analysis.

They also offer free webinars, courses, and tutorials,

to help you set up and run your own simulations.

If, like me, you have some experience

creating CFD simulations, then you know that this type

of software is usually very expensive

and you would need a very powerful computer to run it.

However, with SimScale it can all be done

with a web browser.

As the platform is cloud-based,

their servers do all the work

and we can access our design simulations from anywhere,

which makes our lives, as engineers, a lot easier.

So, if you're an engineer, a designer, an architect,

or just someone interested in trying out

simulation technology, then I highly recommend

you check out this software and get your free account

by following the links in the video description, below.

Temperature.

The temperature of a room is one

of the most noticeable factors in comfort.

Our bodies will try to maintain a temperature

of around 37 degrees Celsius.

This is to keep our internal organs functioning optimally.

If our core body temperature deviates

from this by just a few degrees,

our bodies will begin to fail.

You can lose consciousness, go into cardiac arrest,

which can lead to brain damage and even death.

If we compare the two office designs again

for temperature distribution,

the first room design has three inlets at the top right

with two outlets at the bottom left.

The occupants are sitting at desk in the center of the room,

represented by these cylinders.

As we look at the temperature of the air,

we can see that the cold air is pouring out of the inlets

and the central grill is discharging

directly onto an occupant.

So, this is clearly a bad design.

The person on the left might be quite comfortable,

but the person under the discharge is going

to feel very cold and will probably become unwell.

Now, in the improved design, the outlets have been moved

under the inlets and only the central duct is being used

to deliver the same quantity of air.

However, now we see that the distribution

is spread across the upper regions of the room,

giving a more stable and equal environment.

Both occupants now experience the same conditions.

When we are too hot, our bodies will sweat.

This liquid will form a thin layer over our skin,

which will evaporate.

As it evaporates, it will carry the heat away

and cool us down.

When we get too cold, our bodies will shiver.

This causes rapid movement of the muscles,

which will generate heat to warm us up.

So, we need to be in a room which is not too hot

and not too cold.

As a rule of thumb, occupants will feel comfortable

when the room temperature is around 20

to 22 degrees Celsius, but this will vary

depending on things such as the activity of the person

and also what they're wearing.

To give you an example of a real world design,

this is an extract from a CIBSE TM31 building logbook

for a new office building in London.

You can see the building was designed

for outside conditions in the summer of 29 degrees Celsius

and in the winter, it's negative four degrees Celsius.

The office area within the building is designed

to be 22 degrees Celsius with a two degree buffer.

That means it can be anywhere from 20 to 24 degrees Celsius.

You can also see that this one has no humidity control,

but we'll look at that a bit later.

If you want to get deep into the details of design,

then ASHRAE 55 and CIBSE Guide A

are some of the most widely used industry guides

for thermal design and comfort.

I'll leave some links in the video description

if you wanna check those out.

Air velocity.

Air velocity is another aspect

which will make a big impact on a person's comfort levels.

The faster the air moves,

the greater the heat exchange will be.

So, as we see in the bad design,

the person on the right won't be comfortable

because the air is moving fast over them

and so the heat is going to be leaving

their body very rapidly.

In the improved design, we have a high velocity

over the top of the occupants,

but this time it isn't falling directly onto them.

The occupant on the left might just feel this

on the top of their head

and probably so if they were to stand up.

There's also a high velocity region under the ankles,

so some improvements could still be made

for the location and quantity of the grills.

As a rule of thumb, air speeds of up

to 0.8 meters per second are allowed without local control

and 1.2 meters per second with local control.

Moving air creates noise too,

so that's also something to consider.

There are design limitations for ductwork velocity

and we covered this in our previous video,

where we designed a simple duct system.

Do check that out for more details.

Humidity.

When we talk about humidity, we're talking about

the amount of moisture in the air.

The higher the humidity level, the more water vapour

there is within the air and that will make it harder

for our bodies to reject its unwanted heat.

That's because our bodies sweat

to evaporate the heat away,

but if there's too much moisture in the air,

then the sweat can't easily evaporate and we will overheat.

When we talk about humidity, we mean relative humidity

which is the ratio between how much moisture is in the air

versus the maximum amount that the air could hold

at a given temperature and pressure.

For example, a cubic metre of air at 20 degrees Celsius

or 68 Fahrenheit at 50% relative humidity

will contain around eight grams of water,

but at 100% humidity,

this air will hold 17 grams of water.

We can read this information from a psychrometric chart,

but I won't go into the details of that in this video.

As a rule of thumb, people are comfortable

in 30 to 50% relative humidity.

60% is quite uncomfortable

and as we reach 70% relative humidity or above,

that's when we start to see mould developing rapidly.

You'll probably notice this in bathrooms

where there's high moisture levels

and very low ventilation.

We can also reduce static shock

by keeping our environment at around 55%.

As an example, if I Google the current weather

for my location, we can see that it's showing

21 degrees Celsius outside and 43% humidity,

and that's very comfortable.

I'm quite happy sitting here in a T-shirt.

Things like kettles or water boiling, showers,

or even drying clothes, will all add moisture

to our environment, so we want to try and isolate these

and keep them separated and well ventilated.

In homes we can control the humidity

using small portable devices,

but in large office buildings we tend to use

the central ventilation systems.

Again, we've covered that in another very detailed tutorial.

Radiant temperature.

This is the temperature of the surfaces

which surround the person, his thermal radiation.

Everything, including you, give off some thermal radiation

due to differences in temperature.

We can feel this when the sun shines on us

or even just reflects onto us.

We can also feel it when we walk past a hot oven

or some heated material.

And we can even feel it when we place our hand

in proximity to a hot cup.

We can visually see the source of the heat

using thermal imaging cameras.

Now, these shots are filmed using a pocket-sized camera

which attaches to my smartphone

and I use it for inspection and trouble shooting.

I'll leave a link down below if you want to check that out.

We can improve or reduce the radiant temperature

by basically putting a barrier up

between us and the heat source.

Whether it's a shade, a wall, or insulation,

we just need to block the path of the thermal radiation.

Metabolic rate.

This is how much energy our bodies will burn

and it's mostly associated

with a person's level of activity.

For example, someone who sits down at a desk all day

will consume far less energy and will feel cooler

than someone who is constantly moving around all day.

The more energy we consume, the more heat we need to reject.

We need to try to keep people of different activity levels

separated within a building, so that we can provide

thermal comfort levels tailored to their needs.

Clothing.

Clothing can provide an insulation layer

between the person and their environment.

When it's hot outside, people like to reduce

their clothing and relax.

When it's cold, we like to wrap up warm.

Same within buildings.

The clothing people wear will affect their comfort.

In our buildings and place of work,

we provide protective clothing

for people working in cold or hot conditions.

The problem we face within buildings

is that fashionable clothing usually isn't practical.

So, people who wear this will feel the cold more.

PMV.

Something you're probably going to come across

in thermal design is PMV, or Predicted Mean Vote.

This takes into account the conditions discussed

in this video and then predicts

what the average vote of comfort will be

within the building for a large group of people

on a scale of plus three to negative three,

with the best scenario being at zero.

Again, we can simulate this

and if we compare the good and bad designs,

then we can see that the bad design

has multiple regions within the negative one region,

whereas the good design is fairly constant

and close to zero.

So, as you might imagine, the occupants

within the good design will be much more comfortable.

Okay guys, that's it for this video,

but if you want to continue your learning,

then check out one of the videos on screen now

and I'll catch you there for the next lesson.

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as well as TheEngineeringMindset.com.