1.
CFD webinar
Ensure Thermal Comfort and
Energy Efficiency with CFD

2.
1. Brief of thermal comfort and energy efficiency in LEED buildings
2. How is thermal comfort assessed? (PMV/PPD/MRT)
3. How can SimScale CFD help evaluate thermal comfort?
4. Our Case: Analysis of an office space
○ Project overview
○ Simulation setup
○ Results
■ Thermal comfort
■ Energy consumption
○ Importance of insulation
○ Air supply temperature
5. Key learnings / Conclusion
Today’s Application
Thermal comfort and
energy efficiency

3.
● ASHRAE 55 standard:
○ “Thermal comfort is the condition of mind
that expresses satisfaction with the thermal
environment and is assessed by subjective
evaluation.”
● How can this be assessed?
○ Using predicted mean vote (PMV) and
percentage of people dissatisfied (PPD)
Today’s Application
What is thermal comfort?

4.
Thermal Comfort
How can SimScale CFD help evaluate thermal comfort?
CFD Computed Values
● Air temperature (°C)
● Mean radiant temperature (MRT)
● Air speed (m/s)
Thermal Comfort Parameter Inputs
● Clothing coefficient (clo)
● Metabolic rate (met) / activity level
● Relative air humidity (%)

5.
Airspeed (v)
Metabolic Rate (M)
Clothing Coefficient (clo) (image source)
(image source)What environmental
factors contribute to
thermal comfort?
Understanding Thermal Comfort

6.
Relative Humidity (RH):
Mean Radiant Temperature (MRT):
What environmental
factors contribute to
thermal comfort?
Understanding Thermal Comfort

7.
Understanding Thermal Comfort
What is mean radiant
temperature?
● A way to express the influence of
surface temperatures on
occupant comfort
● One scalar value (on SimScale)
● Size-weighted average across all
domain surface temperatures

8.
Office Thermal Comfort in Qatar
Example case

9.
● Identify the ideal setup so that all occupants are in a
state of comfort. Variables to consider:
○ Wall insulation
○ Cool air supply rate and temperature
● Aiming at a value of predicted mean vote (PMV)
between -0.5 to 0.5
● Using the least amount of energy
Project Objectives
Our Case: Office Thermal Comfort In Qatar
Velocity streamlines from an HVAC diffuser in an office space

10.
● 5x5m office space
● 4 occupants
○ Wearing short sleeve clothing (0.65 clo)
○ Typing metabolic rate (1.15 met)
○ Relative air humidity (65)
● 4 workstations emitting 72 W of heat
● Middle Eastern summer conditions: 42°C
outside
Scenario Overview
4 Colleagues 80 W each
4 Workstations 72 W each

11.
Defining thermal
insulation
2 Existing external walls
The lower this value, the
less heat will be
transferred through the
wall

12.
The lower this value, the
less heat will be
transferred through the
window
Defining thermal
insulation
Window
Added solar radiation

13.
Defining thermal
insulation
2 Internal walls:
Considered to be adiabatic
Well insulated ceiling and floor:
0.18 U-Value

14.
● One air supply for simplicity (19.85 °C)
● Air change rate between 6-8 changes per hour
ensure indoor air quality
● Two outlets in the room corners
Project Overview
The scenario

15.
● Different ceiling diffusers:
1. Generate different patterns (swirls, jets, etc.)
2. Drop and throw values to consider
● Diffusers usually use the Coandă effect to
distribute the air around the room
Diffuser selection
The scenario
Our candidate
Low pressure
zone causing
Coanda effect

16.
CAD model import
Simulation setup
Analyze results
1
3
Thermal Comfort
Analysis with SimScale
2

17.
Results

18.
Occupant 2: Warm 2.08
Occupant 1: Warm 1.8
Occupant 3: Warm 1.9
Occupant 4: Warm
1.78
How is the thermal comfort of
occupants (PMV Values)?
Results
The occupants are feeling
too warm! (by ASHRAE 55 -
ISO 7730 standards)

19.
What is the air speed in the room?
Results
Note the Coandă effect
from the diffuser
The overall air speed stays well below
the 0.8m/s value recommended by
ASHRAE for comfort.
Low air speed around
0.2m/s near the occupants

20.
What is the temperature in the room?
Results
Cold air coming from
the diffuser
Radiation from the warmer walls
impacts the thermal comfort of
those closest
Uneven distribution of temperature, not
likely to be comfortable for all.
Average temperature
is 27.1°C!

21.
Let’s quickly validate how much
energy is gained by the air
Results
Temperature difference (Outlet-Inlet)
26.97- 19.85 degrees = 7.12 degrees
7.12 x 0.1453 x 1004 = 1039 Watts
Mass flow rate
0.1453 kg/s
Specific heat (how much energy is
required to increase the temperature
of m3 of air by 1 degree)

22.
What can we actually change?
Results
1038 Watts = 320 + 288 + 431
Occupants
(fixed)
Desktops
(fixed)
Energy coming through the
walls+window
(this is all we can change)

23.
Let’s make the building “green(er)” by
insulating its walls!
Design decision
Let’s run the case with
these new values

24.
We are still far from our target
comfort range (-0.5:0.5)
Occupant 2:
Warm 1.94 (was 2.08)
Occupant 1:
Warm 1.68 (was 1.8)
Occupant 3:
Warm 1.88 (was 1.9)
Occupant 4:
Warm 1.64 (was 1.78)
How can we improve
the situation?
Let’s lower supply
temperature.
Results
Very minimal effect of changing the
insulation – new strategy needed
Average temperature
is 26.56°C!

25.
Putting this minor energy saving
into real world terms:
Results - Better Insulated walls
Purely through insulation, the
room absorbs 64W less
For 3800 of sunshine hours per year @4.3 USD/kWh,
this translates to 1052 USD/Year!

26.
Better, but still out of our target
range (-0.5:0.5)
Occupant 2:
Slightly Warm 1.44 (was 1.94)
Occupant 1:
Slightly warm 1.19 (was 1.88)
Occupant 3:
Slightly warm 1.35 (was 1.88)
Occupant 4:
Slightly warm 1.15 (was 1.64)
Results
How does the 18C supply perform?
Average temperature
is 25.43°C

27.
We still haven’t achieved thermal comfort for our
occupants
Results
2 options remain:
1. Increase the air supply speed (preferred option)
a. We need to be sure we stay below 0.8 m/s but have
plenty of scope
1. Lower the supply temperature (more expensive option)
○ At present the difference between the room and inlet
temperature is 9°C
○ We would need at least a 14C or lower inlet temperature
■ It would be costly to cool the ambient air this far

28.
Let’s optimize the design to find the ideal supply flow rate
Results
Multiple simulation runs
in parallel

29.
Results
With an 18C supply, let’s compare the airspeed in the room
x2.5 flow rate - 0.304 m³/s x3 flow rate - 0.364 m³/s
Very acceptable air speed
around our occupants

30.
x2.5 flow rate - 0.304 m³/s x3 flow rate - 0.364 m³/s
Results
With an 18C supply, let’s compare PMV
Occupant 2:
Neutral
0.22
Occupant 1:
Neutral -0.01
Occupant 3:
Neutral 0.13
Occupant 4:
Neutral -0.047
Occupant 4:
Neutral 0.035
Occupant 3:
Neutral 0.27
Occupant 1:
Neutral 0.1
Occupant 2:
Neutral 0.37

31.
Flow Rate: 0.304 m³/s
Occupant 4:
Neutral 0.035
Occupant 3:
Neutral 0.27
Occupant 1:
Neutral 0.1
Occupant 2:
Neutral 0.37

32.
Results
Conclusion and key learnings
In this project
● We assessed and quantified how much energy could be
saved with improved wall insulation
● We found that we need a different cooling strategy than
purely insulation
We have learned that:
● CFD is a highly valuable tool to:
○ Assess thermal comfort
○ Determine energy consumption
○ Optimize the design to solve the problem
● Many simulations can be run for different scenarios, and
compared to observe the impact of:
○ Different types of insulation
○ Increasing or lowering the supply flow rate
○ Modifying the supply temperature
Airflow streamlines
colored by temperature