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HVAC Equipment Optimization with the SimScale Platform

HVAC equipment

The heating, ventilation, and air conditioning (HVAC) is one of the industries facing many challenges related to digital transformation and emerging technologies in product and process manufacturing, construction building, or factory and plant infrastructure design.

HVAC equipment and systems are essential in a wide range of areas, from home heating and ventilation to industrial ecosystems based on energy savings, thermal comfort, and air quality and noise standards. At the same time, the manufacturers of HVAC equipment need to achieve industry standards and performance criteria in order to keep efficiency and control in a very competitive market. In industrial areas, such as factories and plants, the engineering team should work in close cooperation with architects, constructors, and designers, as they need to fit building plans with infrastructure and utilities.

Due to their complexity and the high-quality standards, the HVAC systems require intensive testing. Coming as an addition to physical prototyping, Computer-Aided Engineering (CAE) ensures maximum design optimization, efficiency, and performance while offering significant cost reductions and control on investment. As the first cloud-based 3D engineering simulation platform, SimScale allows anyone from the product development team to simulate the physical behavior of products or building structures within a standard web browser.

5 Ways to improve an HVAC system

Here are 5 applications of HVAC systems and ways how 3D simulations with SimScale can be used to optimize HVAC designs:

1. Optimize thermal comfort

The most common functionality of HVAC systems is related to maintaining and optimizing thermal comfort. But what means “thermal comfort” and which metrics should we consider in any optimization analysis?

We have ventilation and heating equipment in many places, from home apartments, cars, and any vehicle cabin, school classrooms, office and meeting rooms, entertainment spaces such as restaurants or cinemas, to industrial facilities dedicated to computer servers, manufacturing machines, warehouses or industrial heating equipment. Any thermal comfort analysis for an indoor space or industrial facility should consider equipment optimization and ventilation air control.

Although the air temperature is the most commonly used indicator in thermal comfort analysis, it should always be considered in relation to other environmental and personal factors. The factors affecting thermal comfort are both environmental (air temperature, radiant temperature, air velocity, and humidity) and personal (clothing insulation and metabolic heat) [1].

These factors may be independent of each other but together contribute to general thermal comfort. The environmental factors can be controlled by the HVAC equipment and the optimal thermal comfort is provided only if the heating, ventilation, and air conditioning systems are well designed to meet all specific indoor conditions. While air temperature is easily controlled, the radiant temperature has a greater influence on how heat is lost or gained by the environment. Air velocity and humidity are also important factors in thermal comfort.

Considering all these factors and giving a solution for them to be tested in a virtual environment, 3D engineering simulation (CAE) is the technology helping HVAC engineers design, analyze, and optimize AC, heating, and ventilation systems.

Let’s take a look at some HVAC simulation examples available in the SimScale Public Projects:

Car Cabin Airflow Analysis

car cabin airflow analysis with SimScale

In this project, a steady-state natural convective heat transfer analysis was done to simulate the internal airflow. The geometry includes a standard wagon type four-door car, modified for internal flow analysis. The cabin interior has 4 front inlet air conditioning ducts and one outlet vent on the hood. The initial car temperature was 30 degrees Celsius and the temperature of the airflow was set at 10 degrees Celsius. The final results demonstrate the airflow velocity contour through the cabin and the temperature.

Another similar project available in SimScale Public Projects is this analysis of the ventilation in an aircraft cabin, in which two configurations and their effect on the airflow pattern are shown.

2. Save energy

Energy consumption in data centers and server rooms is a critical issue that the IT industry has been improving over the last decades. The exponential growth of information volume related to data center globalization and cloud computing infrastructure are requesting more powerful equipment and more complex IT services. In the past, the focus of energy saving measures has been to build efficient solutions for power supply and cooling. New measures addressing IT hardware efficiency are considered more recently, based on hardware and power management energy saving strategies[2].

Energy consumption is driven by the number and the hardware capacity of IT rooms from office buildings, including servers, networking equipment, data storage racks, and the cooling and power conditioning that support them. In many cases, a data center infrastructure is using more energy annually than traditional HVAC and lighting loads from normal office buildings. A survey conducted by Uptime Institute shows that 30% of servers in data centers are unused, each one costing over $3,000 per year in energy, space, and maintenance costs.

Economic reasons and saving energy policies forced IT and energy engineers to find better ways to control the energy usage of IT solutions, and to save money and reduce pollution with efficient airflow management and HVAC adjustments. Between most recommended hardware and software solutions any CIO should consider to reduce the energy costs in a server room [3] are:

• server infrastructure improvement by using virtualization systems which can reduce the number of required physical machines;
• server management software that can substantially reduce the IT power load;
• equipment with internal temperature-controlled variable-speed fans (VSDs);
• equipment with internal/external power management to optimize energy consumption;
• reporting systems that can send temperature and power/energy consumption data to a Building Energy Management System.

For airflow management strategies, here are some recommendations from ENERGY STAR [4]:

• Hot Aisle/Cold Aisle Layout – special equipment arrangements to lower cooling costs by better managing airflow, thereby accommodating lower fan speeds and increasing the use of air-side or water-side economizers. When used in combination with containment, the US Department of Energy estimates reduction in fan energy use of 20% to 25% [5].

Cold Aisle

Image: Hot aisle/cold aisle server row orientation. (Photo courtesy of 42U.com)

• Containment – refers to the various physical barriers used in addition to a hot aisle/cold aisle arrangement that further eliminate the mixing of cold (“supply”) air and hot exhaust air. Containment structures lead to higher allowable temperatures in data centers. Higher temperatures save energy because fan speeds can be lowered, chilled water temperatures can be raised, and free cooling can be utilized more often.

• Variable Speed Fan Drives – computer room air conditioning (CRAC) unit fans consume a lot of power and tend to account for 5% to 10% of a data center’s total energy use. Most CRAC units are unable to vary their fan speeds with the data center server load, which tends to fluctuate. Because data center environments constantly change, variable-speed fan drives should be used wherever possible. Retrofits of many CRAC units are available.

• Properly Deployed Airflow Management Devices – All airflow management strategies strive to either maximize cooling by supplying cooling (“supply”) air directly to equipment, or by eliminating the mixing and recirculation of hot equipment exhaust air. A study conducted by the Uptime Institute in 19 data centers concluded that only 60% of the cool air produced by cooling equipment was pumped into the data center. It also found that 10% of the data centers had hot spots (server too hot or too dry), according to the American Society of Heating.
But problems can also be solved by making simple HVAC adjustments:

• Server Inlet Temperature and Humidity Adjustments – in 2008, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) expanded the recommended temperature range at the inlet of the server from 68°F to 77°F (20°C to 25°C – the 2004 level) to 65°F to 80°F (18.33°C to 26.66°C). However, many data centers traditionally have set their temperatures as low as 55°F (12.77°C). As a result, many of them can save energy simply by raising the thermostat.

• Air-Side Economizer – could bring outside air into a building and distribute it to the servers. Instead of being re-circulated and cooled, the exhaust air from the servers is simply directed outside. If the outside air is particularly cold, the economizer may mix it with the exhaust air so its temperature and humidity fall within the desired range for the equipment.

• Water-Side Economizer – uses the evaporative cooling capacity of a cooling tower to produce chilled water and can be used instead of the chiller during the winter months. A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required. Water-side economizers offer cooling redundancy because they can provide chilled water in the event that a chiller goes offline. This can reduce the risk of data center downtime.

Server Room analysis with SimScale

Server Room Analysis with SimScale

In SimScale’s Public Projects we can find a server room cooling analysis showing how the cooling of a room can be simulated using a SimScale thermo-fluid analysis. The room’s CAD model uploaded in STEP format is meshed using the highly automated hex-dominant meshing operation for internal fluid flow. Two different simulations have been set up: one assuming a laminar flow field as a rough estimation and the second using a k-epsilon RANS turbulence model.

Different boundary conditions have also been used: in one simulation, the room walls have been assumed to be adiabatic and in the other a fixed temperature was assigned to them.

The simulation results allow evaluating the necessary power of the cooling system under different operation conditions, suffering also a detailed look at the resulting velocity and temperature field inside the server room. This shows how different layouts of the server room including the ventilation and air conditioning system can be evaluated in a very early design phase, postponing physical testing for a later stage of the product development.

3. Enhance Efficiency of the HVAC equipment

Efficiency improvement is more often related to the design of more efficient ventilation systems.  One of the trends for increased heating efficiency is passive houses, which don’t require classical building heating due to their excellent thermal insulation. These houses need, however, a complex ventilation system which often causes criticism because it doesn’t allow a natural fresh air supply. A new approach to guarantee the fresh air supply and the heat distribution across all rooms focuses on the use of dual outer walls.

Through skillful planning, the air hull surrounding the building can be used to control temperature and air distribution without the installation of ventilators, only based on the stack effect. Convective flow effects can help to achieve both cooling in summer and heating in winter.

Another very common topic in HVAC engineering is improving the air quality. SimScale Public Projects include a simulation of air conditioning in an office space.

Air Conditioning Simulation in an Office Space

Air Conditioning Simulation in an Office Space

In this project, the CAD model of the air domain of the office space was uploaded as a STEP file to the SimScale platform and meshed using the automatic hex-dominant mesh operation. 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 image above shows a temperature contour plot that indicates where it is warmer and colder within the office space.

4. Reduce the noise level of HVAC systems

Effective noise reduction is an important factor in creating a more pleasant living and working environment. Most common noise sources in any building are related to fans, variable air volume systems, grilles and diffusers, roof top units, fan coil units, chillers, compressors and condensers, pumps, stand-by generators, boilers, and cooling towers.

The alternatives available for noise reduction include: using more silent ventilation equipment, protecting HVAC components with silencers and insulation materials, or implementing noise optimization analysis.

The acoustics simulation capabilities based on the Finite Element-based solver integrated by SimScale include multiple natural and induced frequency analysis of complex geometries for different room or car cabin configurations.

5. Boost performance of industrial heat exchangers

Heat exchangers are devices whose primary role is the transfer (exchange) of heat, typically from one fluid to another. They are not only used in heating applications, such as space heaters, but also in cooling applications, such as refrigerators and air conditioners. [6]

Many types of heat exchangers can be distinguished based on the direction of the liquid flow.

In such applications, the heat exchangers can be parallel-flow, cross-flow, or counter current. In parallel-flow heat exchangers, both fluids involved move in the same direction, entering and exiting the exchanger side by side. In cross-flow heat exchangers, the fluid paths run perpendicular to one another. In counter-current heat exchangers, the fluid paths flow in opposite directions, with each exiting where the other enters. Counter current heat exchangers tend to be more effective than other types of exchangers.

According to MIT [7], there are three heat transfer operations that need to be described:
• Convective heat transfer from fluid to the inner wall of the tube
• Conductive heat transfer through the tube wall
• Convective heat transfer from the outer tube wall to the outside fluid

The project dedicated to a conjugate heat transfer analysis of a heat exchanger shows an example of how certain phenomena involved in heat exchangers can be simulated with SimScale.

heat exchanger 3D analysis

This project contains an analysis of the shell and tube heat exchanger. We have a solid pipe volume and two fluid volumes, one fluid flowing inside the tubes and other inside the shell.

After uploading the CAD file, the Hex-dominant Parametric mesh was used to generate the mesh for the 3 volumes (1 solid and 2 fluids). This is used to create refinements and maintain the volumes as different regions to later define interfaces.

A laminar steady-state simulation was then carried out using the ‘Conjugate Heat Transfer’ solver. The outer fluid is considered to be at a higher temperature. The picture above shows a post-processing image representing streamlines of temperature.

All projects described in this article can be imported into your own workspace for free, to help you start your own simulation with minimum effort. Also, you can watch the recorded webinars to learn from SimScale experts how to start with simulation for HVAC projects.

This case study shows how the Austrian company IBEEE optimized the airflow of a ventilation system by 40%.


References:

[1] “The Six Basic Factors”, Health and Safety Executive/ Guidance/ Thermal comfort
[2] „Energy efficient IT and infrastructure for data centres and server rooms”, PrimeEnergy IT Project Consortium, July 2011
[3] “Guide to ICT – Server Room Energy Efficiency”, Public Sector ICT Special Working Group, Sustainable Energy Authority of Ireland
[4] Energy Star – „12 Ways to Save Energy in Data Centers and Server Rooms”
[5] “Best Practices Guide for Energy-Efficient Data Center Design”, Energy.gov, Office of Energy Efficiency & Renewable Energy, revised 2011
[6] „Use of random noise for on‐line transducer modelling in an adaptive active attenuation system”, Erikson l.J., Allie M.C, Acoustical Society of America, 1989
[7] “Thermodynamics and Propulsion”, Thermodynamics Course Notes, Massachusetts Institute for Technology.
[8] Featured image photo source: FreeImages.com/Sue Byford

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