How CFD Simulation Impacts Design

CFD technology enables designers to predict operating characteristics, validate performance, and visualize flow and/or thermal phenomena which is difficult to capture in the real world. This is critical for AEC applications as prototyping buildings is not practical and retrofitting existing designs is expensive.

The impact of CFD on AEC applications is directly related to the interpretation of simulation results; the ability to assess performance, identify opportunities for improvement, and quantify the impact of modification.  Results visualization provides the opportunity to optimize design performance characteristics such as energy consumption, amount of contaminant entrained, thermal comfort, solar influence, hot air recirculation, and various other metrics of AEC application design performance. 

CFD Impact on the Des­­ign Process

In the past, CFD was really only used by dedicated PhD analysts, with a “throw it over the wall” mentality from the design team.  Since that time, advancements in both hardware and software interfaces have made the technology more practical.

Leveraging CFD simulation earlier in the design process allows potential performance issues to be corrected, eliminating costly rework or retrofitting later on.  This is particularly the case in the AEC industry where many applications, such as buildings, are relatively large and impractical to prototype and test.    

Classic Design Cycle

Many CFD consultants are contacted at Step 7 in a traditional design process when performance is not meeting specifications.  Using CFD, they can determine the root cause of the issue, but implementing the fix can be expensive and require the space to be offline for the end client.

An AEC design cycle that does not implement CFD can lead to problems during the construction and initial start-up phase.  These issues result in a cycle of expensive rework efforts, delays and downtime for the end client.

1 Start

Traditional design process without CFD.

2 Concept
3 Preliminary CAD
4 Engineering
5 Final CAD
6 Construction/Testing
7 Fail - Rework Required

 

CFD Upfront Design Cycle

By contrast, when leveraging CFD early in the design cycle, potential problems can be addressed before construction.  

1 Start
CFD upfront Design Process

CFD upfront Design Process

2 Concept
3 Preliminary CAD
4 Engineering with CFD
5 Final CAD
6 Construction/Testing
7 Pass

 

CFD Impact on AEC Applications

Air Management

Controlling air flow is an important aspect of AEC design and has a direct impact on performance and energy conservation.  A strong plume of cold inlet air directly over a cubicle can make the occupant uncomfortable.  The hot exhaust from machinery or data servers can degrade cooling performance when it is allowed to recirculate back into the intakes.  CFD results visualization is used to spot potential problems upfront and refine the location, size, and layout of system components.

The recirculation of hot air exhaust entering a data server intake can be visualized with the use of particle traces.

The recirculation of hot air exhaust entering a data server intake can be visualized with the use of particle traces. 


CFD is used to reduce energy costs here by visualizing thermal stratification and optimizing a duct extension that will return cooler air to the conditioning system.

Energy Consumption

In building design, significant energy is consumed by equipment which moves and conditions air.  The amount of air and conditioning required can be optimized by assessing thermal stratification and air flow paths in CFD.  Active, passive, and hybrid heating and cooling strategies can all be evaluated to determine the amount of energy consumed by a given design.  A video discussing energy savings can be found here.

Contaminant Entrainment        

Contaminants, such as building or equipment exhaust, should be evacuated without re-entering the ventilation system, or in other words, without being entrained by the ventilation systems intake.


Results visualization of a hospital's external air ventilation is used to reduce contaminant entrainment from exhaust to intake.  

 


CFD is used to optimize an operating room’s exhaust system to reduce contaminant spreading.  Initial design (left), optimized (right).

The design of systems for removing contaminated air from rooms or buildings should ensure that air intake systems are not configured to cause contaminant entrainment.  CFD enables designers to visualize exhaust air and quantify the amount of exhaust entrained by intake systems.  Interpretation of these results can impact design variables such as the location of supplies and returns, filter sizes and air exchange rates.

Human Comfort

Human comfort is an influential consideration when developing a ventilation system.  Design performance relating to air temperature, velocity, humidity, clothing, and metabolic rate can all be assessed in CFD to impact human comfort. 

The ASHRAE definition of human thermal comfort can be found here in the help.


Simulation CFD results visualization provides insight on human comfort.  Uncomfortable (left) vs. comfortable (right).

Solar Influence

The sun provides Earth with energy that can influence the thermal performance of building design.  Walls and rooftops absorb energy while windows absorb and transmit it into buildings.  CFD helps designers understand the implications of solar radiation to either harness or block it.  For more information, a solar heating tutorial is available here.


Warm temperatures predicted in this space (left) are reduced by a solar shade (right).