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How to Design Better Air Conditioning Systems with Simulation

How to Design Better Air Conditioning Systems with Simulation

Air conditioning systems are under an evolutionary trend generated by digital transformation’s vortex. Part of the larger category HVAC, air conditioning equipment, and industrial systems become more than thermal comfort tools.

Can you imagine everyday life in the absence of air conditioning systems? Of course, we can live with simple fan blades, but this is not true everywhere and especially throughout a calendar year. The air conditioning systems (AC) have become more than a simple commodity. In many cases, it is a vital requirement for life and human activities.

From simple air conditioning systems to intelligent buildings and smart cars

fan

The world is changing. Due to climate changes, many countries in Europe frequently face temperatures above 40 degrees Celsius in the middle of summer. In winter time, the snow often forgets to fall in areas that traditionally enjoy winter sports euphoria. In these conditions, we are forced to use facilities and equipment of air conditioning systems almost everywhere: at home, at work, places of relaxation, in factories, but also in vehicles.

By innovations assimilating perspective air conditioning systems are parts of larger entities that must take into account not only the minimal thermal comfort conditions. These must refresh air quality, save energy resources and boost performance. Our modern air conditioning systems are integrated with all other utility services, forming an ecosystem of smart resources that help us to live and work more comfortably and efficiently.

Improving the efficiency of AC systems is now part of keeping ecosystems alive. A big role in this increasing efficiency and optimization process is assumed by the engineering simulation techniques. CFD, FEA, and thermodynamic analyses help air conditioning designers and engineers to improve the equipment functionality, regardless if the systems are used in home environments, office, cars or for industrial purposes.

SimScale could be an ideal tool for AC systems manufacturers in their performance optimization efforts. SimScale 3D simulation platform enables fast product improvement that addresses many aspects such as endurance, reliability, performance, noise reduction, thermal comfort, and energy efficiency for any air conditioning system.

Passive houses, a solution for tomorrow’s smart homes

Reducing energy prices, environmental constraints, and the associated demand to enhance efficiency are key topics in the design of single and multi-family houses. One of the trends for increased efficiency in housing is passive houses, which don’t require classical building heating due to their excellent thermal insulation. These houses, however, need a complex ventilation system which often causes criticism because it doesn’t allow a natural fresh air supply.

passive house simulation

Based in Klagenfurt, Austria, IBEEE is a holistic development and engineering service provider for electronic systems and energy concepts for buildings. Working in a passive house project, IBEEE used the SimScale simulation platform to find the better solutions to guarantee fresh air supply and the heat distribution across all rooms using dual outer walls. By smart planning, the air hull surrounding the building can be used to control temperature and air distribution without the installation of ventilators. Only the stack effect is used. In this way, convective flow effects help in summer cooling and winter heating.

Two SimScale simulations for identical designs were carried out for this purpose: one with the active system and the other with the passive one. The simulation showed that the fan could not only be replaced by the stack effect but that this is actually 40% more powerful than the active solution. Air mixing at the entrance leads to a temperature homogenization and reduces the buoyancy effects. Using high-performance computing power on the SimScale platform, the engineers from IBEEE were able to complete the simulation in less than 2 hours and for only 50 Euros overall costs of simulation. 

Smart offices in smart buildings

air conditioning systems

Modern research is looking to the intelligent integration of Internet of Things sensors in smart buildings systems. AC intelligent systems can be based on mobile phones, smart sensors, and wearable devices placed on the human body.  The feedback signals related to occupants’ information provided by phones and personal bracelets can be used to adjust air conditioners in advance according to humans’ intentions, in so-called intention causing control. Experimental results show that the indoor temperature can be controlled accurately with errors of less than ±0.1 ° [1]

Let’s see few SimScale simulation examples showing how easy and efficient are simulation analyses for optimizing AC systems in office spaces. Here is an airflow analysis inside an office space.

The analysis was set up using the natural convective heat transfer analysis type. A quite simple boundary condition setup was chosen (fixed temperature at the walls and inlet, fixed inlet velocity condition), but one could easily apply other boundary conditions such as a warm or cold window and adiabatic walls. The resulting images show a streamline visualization of the velocity field and a temperature contour plot that indicates where it is warmer and colder within the office space.

SS027 SimScale Office AC Systems

SimScale: Temperature contour plot showing where it is warmer and colder within the office space

Green buildings based on intelligent industrial cooling

The concept of green industrial buildings is based on specific materials and healthy ventilation systems able to satisfy energy savings, environmental regulations, building standards, and industry regulations. We are in front of a paradigm shift in ventilation design thinking. In the past, thermal properties of air within a zone determined the heating, ventilation, and air conditioning specifications. In the next future, occupant-specific and highly responsive systems will become the norm. Natural ventilation, displacement ventilation, and micro-zoning with subfloor plenums, along with the use of point-of-source heat control and point-of-use sensors, will evolve to create a `smart,’ responsive ventilation-building dynamic system [2].

One of most frequent industrial application with high impact in green projects is server room cooling systems. In this SimScale project, the air temperature and velocity inside a server room is analysed using a thermo-fluid analysis type.

SS027 SimScale Server Room AC Systems

SimScale: Velocity image in a server room

The simulation was set up using the natural convective heat transfer analysis. Two different simulations were set up: one assuming a laminar flow field as a rough estimation and the second one using a k-epsilon RANS turbulence model. Also, different boundary conditions were used: in one simulation, the room walls have been assumed to be adiabatic and in the other, a fixed temperature was assigned.

The simulation results show the resulting velocity and temperature field inside the server room, allowing the evaluation of the necessary power of the cooling system under different operation conditions. Moreover, different layouts of the server room including the ventilation and air conditioning system can be evaluated in a very early design phase with less physical testing.

This simulation example demonstrates how SimScale can be used to answer “What if” scenarios very fast and efficiently: only 20 minutes for the simulation process, running on a 16 core machine.

Smart vehicles with less consumption

SS027 AC 3 AC Systems

Industry practices and automotive researchers demonstrate air conditioning systems could be considered a high supplementary consumer source for a vehicle. AC loads account for more than 5% of the fuel used annually for light-duty vehicles in the United States [3]. In the same time, AC loads can significantly impact electric vehicle (EV), plug-in hybrid electric vehicle (PHEV), and hybrid electric vehicle (HEV) performance, shows a Mitsubishi research revealing 50% consume improvement [4].

At the same time, increased cooling demands from the battery thermal management system may impact the vehicle AC system. Cabin climate conditioning is one of the main problems for long distance trucks during driver rest periods. Only in the US, trucks that travel more than 500 miles per day use 838 million gallons of fuel annually for rest period idling [5].

SS027 SimScale Car Cabine AC Systems

SimScale: Internal airflow simulation in a car cabin

In the SimScale project for car cabin internal air flow analysis, we can see a simulation analysis based on a steady state convective heat transfer with the K-Omega SST model for turbulence modelling.

The cabin interior has 4 inlet air conditioning ducts (2 in the center and 2 at the sides) and one outlet.

The simulation analyses the flow field and temperature distribution inside the cabin. The simulation results show how flow and temperatures vary at different sections inside the cabin. The whole process was run on 8 compute cores and took around 12.5 hours.

 

All projects described in this article and many other can be imported into your own workspace for free, to help you start your own simulation. Just visit the SimScale Public Projects open library and use any simulation project you need. More than 70 000 engineering professional have already joined the community.


Want to learn more? Download this free white paper: How to Optimize HVAC Systems Designs with CFD


References:

[1] – Cheng, C.C., Lee, D. – “Smart Sensors Enable Smart Air Conditioning Control”, Sensors, 2014

[2] Spengler, J.D., Chen,Q. – “Indoor air quality factors in designing a healthy building, Annual Review of Energy and the Environment, 25 (2000), pp. 567–600

[3] – Rugh, J. P., Hoveland, V., and Andersen, S. O. – “Significant Fuel Savings and Emission Reductions by Improving Vehicle Air Conditioning”, Earth Technologies Forum/Mobile Air Conditioning Summit, 2004.

[4] Umezu, K., Noyama, H. – “Air-Conditioning System for Electric Vehicles (i-MiEV)”, SAE Automotive Alternate Refrigerant Systems Symposium, 2010.

[5] Stodolsky, F., Gaines, L., and Vyas, A. – “Analysis of Technology Options to Reduce the Fuel Consumption of Idling Trucks”, Argonne National Laboratory, ANL/ESD-43, June 2000.

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