Willis Carrier, Air Conditioning, and His Contribution to Mechanical Engineering and HVAC Systems

Welcome to this special edition of the SoftInWay blog! While we at SoftInWay are known for helpful articles about designing various machines, retrofitting, and rotor dynamics, we believe it is also important to examine the lives of some of the men and women behind these great machines.

Commonly listed among the greatest mechanical engineering inventions of the 20th Century, the air conditioning system has gone from basic use in refrigeration to a staple of living in many countries. Locales that were previously borderline uninhabitable for people sensitive to heat or poorer air quality, became available, thanks to this device that could be installed in homes and businesses. But who invented the air conditioning system?

A portrait photograph of Willis Carrier in 1915

Willis Haviland Carrier (1876-1950) was born on November 26th, 1876 in Angola, a small town in Upstate New York just outside of Buffalo. Carrier was the inventor of modern air conditioning as we know it. While other forms of air conditioning had been around for millennia, what Carrier invented was utterly life-changing for those who were able to use it, and work/live in air-conditioned environments.  His work has been so influential on modern HVAC engineering and the world in general, that his legacy company has a website in his honor.

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Rotor Dynamics Challenges in High-Speed Turbomachinery for HVAC Applications

In comparison to large steam and gas turbines, the rotating equipment found in heat ventilation and air conditioning (HVAC) applications is often seen as more simplistic in design. However, sometimes a simpler model of a rotating machine does not mean a simpler approach can be used to accurately investigate its rotor dynamics behavior. For example, a large number of effects should be taken into account for single-stage compressors used in HVAC applications. Three important ones include:

  1. High values of rotational speeds above the first critical speed;
  2. Rigid rolling element bearing used in the design and therefore a relatively flexible foundation which should be modeled properly;
  3. Aerodynamic cross-coupling adding additional destabilizing forces to the structure.

All these effects should be modeled properly when performing lateral rotor dynamics analyses of HVAC machines. And, in some cases, this simpler model can prove a much more challenging task than building the complex model of a steam turbine rotor.

Let’s consider a seemingly simple example of a high-speed single-shaft compressor for HVAC application (Figure 1). It consists of the compressor and motor rotors, the flexible coupling connecting them, the ball bearings connecting the rotors to the bearing housing joined with the compressor volute, and the structural support.

Fig. 1 - Single stage compressor model
Fig. 1 – Single-stage compressor model [1]
The compressor rotor is connected with the motor through a flexible coupling. Its lateral vibrations can be considered uncoupled from the motor rotor vibrations, and the lateral rotor dynamics model appears pretty straightforward (Figure 2).

Fig. 2 - Rotor dynamics model of the single stage compressor rotor
Fig. 2 – Rotor dynamics model of the single-stage compressor rotor

However, additional factors are discovered if you include the mechanical properties of the supporting structure when considering the lateral rotor dynamics calculations. These factors are very important to an accurate model. Read More

An Overview of Axial Fans

Axial fans have become indispensable in everyday applications starting from ceiling fans to industrial applications and aerospace fans.  The fan has become a part of every application where ventilation and cooling is required, like in a condenser, radiator, electronics, etc., and they are available in a wide range of sizes from few millimeters to several meters. Fans generate pressure to move air/gases against the resistance caused by ducts, dampers, or other components in a fan system. Axial-flow fans are better suited for low-resistance, high-flow applications and can have widely varied operating characteristics depending on blade width and shape, a number of blades, and tip speed.

Fan Types

The major types of axial flow fans are propeller, tube axial, and vane axial.

  • – Propellers usually run at low speeds and handle large volumes of gas at low pressure. Often used as exhaust fans these have an efficiency of around 50% or less.
  • – Tube-axial fans turn faster than propeller fans, enabling operation under high-pressures 2500 – 4000 Pa with an efficiency of up to 65%.
  • – Vane-axial fans have guide vanes that improve the efficiency and operate at pressures up to 5000 Pa. Efficiency is up to 85%.
Types of Fans
Figure 1 Different Types of Axial Fans
Aerodynamic Design of an Axial Fan

The aerodynamic design of an axial fan depends on its applications. For example, axial fans for industrial cooling applications operate at low speeds and require simple profile shapes. When it comes to aircraft applications however, the fan must operate at very high speeds, and the aerodynamic design requirements become significantly different from more traditional fan designs. Read More

Saving the Planet, One Turbine Simulation at a Time

This is an excerpt from the Siemens Blog. You can read the full version here.

Originally written By Erik Munktell  on January 14, 2021


Listening to the turbine experts: a review of 2020

Can a turbine simulation save the planet? One simulation alone is not enough. But one simulation with that intent can inspire other engineers and researchers to do the same. This butterfly effect is happening today in turbine design.

I live in Sweden, the same country as Greta Thunberg. Her message is that we must act now to save the planet. For a long time, Sweden’s electricity has come mainly from Hydropower and Nuclear power. But lately a lot of focus has still been on building wind and solar power plants. Here in Sweden we also have more trees being grown than being cut down. As a result we are close to being carbon negative, transportation and industry included.

With this country-wide energy focus friends often ask me why I work with gas turbines. Surely, they are not needed?  I rarely get them to listen to my answer for more than a few minutes, as in my enthusiasm it quickly gets technical! But in short – I do it to save the planet. Or rather, we do it to save the planet. Because I am not alone in this effort. Many people work on making turbines run more efficiently, with fewer – or even no – polluting emissions. We can’t do everything by ourselves, but our work can inspire others and together we can create a clean energy future.

My small part in this plan is to make sure the actual makers of gas turbines have the best tools in the world for designing new and better electricity generating or flight enabling propulsion products. In this blog, I take a look at the many ways we saw in 2020 that turbine companies are using our simulation tools to do just that.

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An Introduction to Accurate HVAC System Modeling

HVAC (Heat, Ventilation and Air Conditioning) is all about comfort, and comfort is a subjective feeling associated with many parameters like air quality, air temperature, surrounding surface temperature, air flow and relative humidity. For example, while it is easy to understand how the temperature of the air in your living impacts how good you feel, the surfaces with which you are in contact also strongly affect your comfort. For example, last night I got out of bed to clean up after my dog who thought it would be a good idea to swallow (and give back) her chew toy. If I was wearing my slippers, it would have been much easier to go back to sleep between the warm bed sheets without the discomfort of waiting my cold feet warm up to normal temperature.

Speaking of sleep discomfort, many stem from HVAC imbalances.  If you wake up in the middle of the night quite thirsty, then you should probably check how dry your bedroom is. The recommended range is 40-60% relative humidity. A higher humidity puts you at risk for mold while lower humidity can lead to respiratory infections, asthma, etc.

Now that we know how HVAC contributes to our comfort, let’s look at the HVAC unit as a system and see its role, functioning and simulation at a high level. The following examples provided are for a house, but similar concepts apply to residential buildings, offices, and so on.

Controlling Temperature

The easiest parameter to control is the air temperature. It can be set by a thermostat and regulated according to a heating or cooling flow distributed from the HVAC unit to the different rooms through ducting. Without the introduction of thermally-different-than-ambient air, the house will heat or cool itself based on a combination of outside conditions and how well the building is insulated. Therefore, to keep a constant temperature a certain amount of energy must be used to provide heating (or cooling) at the same rate the house is losing (or gaining) heat.  This is a match of the house load and heating/cooling capacity. Figure 1 provides a graph of the energy needed.

Illustration of dependency of house load and heating capacity on outside temperature
Figure 1 Illustration of dependency of house load and heating capacity on outside temperature

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A Century of Chiller Technology

A convergence of technologies had to occur to make the modern, high-efficiency centrifugal chiller a reality. To appreciate the technology fully, we must go back in history and understand the origins of the air conditioning and refrigeration industry. Along the way, we will find an important diversion in aerospace and the critically important centrifugal compressor. Ultimately, we will find that the modern chiller is a testament to advanced technology that was developed in multiple fields.

Some of the first advances in and applications of modern industrial refrigeration were in the United States. In May 1922, Willis Carrier revealed the “Centrifugal Refrigeration Machine” – a very early incarnation of what we now call a chiller [1]. The first installation went to a Philadelphia candy manufacturer; it’s interesting to know that the birth of modern refrigeration and air conditioning started on a large scale. Back in those days, economy of scale enabled the technology to be developed. It was not until a decade later that the core technology began to be adopted into compact units that could be used in smaller businesses such as boutique shops. It took several more decades for smaller residential air conditioners to take off commercially.

Shown in the photograph below is Carrier’s first centrifugal chiller in his New Jersey factory [1].

First Centrifugal Chiller
Photo from [1]
The size of this machine is evident, as is the fact that its design, at the time, necessitated components be spread out in space for assembly and maintenance. By modern standards, the same footprint space could be used to accommodate a modern chiller with over 500 refrigeration tons in capacity. By comparison the original design has less than 100 refrigeration tons of capacity.

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Combined Cycles – A Brief History and Evolution of Cycles

Combined power cycles are a common source of energy, since they offer higher energy efficiency while also making use of common technology. The idea of combining two different heat-engine cycles, however, has been around longer than you think. Today’s blog is going to cover the basics of combined cycle power plants, and their history of how they went from experiments to one of the most common sources of energy in the United States, for example. But how did this come to be, and what really is a combined cycle?

An animated exterior of a combined cycle power plant, image courtesy of General Electric
An animated exterior of a combined cycle power plant, image courtesy of General Electric


At its most basic form, a combined cycle is the synthesis of two independent cycles into one, which allows them to transfer thermal energy into mechanical energy, or work. On land, this is typically seen in power-generation, so the heat of these two cycles makes electricity. At sea, many ships operate using combined power cycles, but instead of just electricity, the mechanical energy is put to work by propelling the ship as well as providing onboard power.

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Hydrogen in Combined Cycles

Hydrogen is a clean and carbon-free fuel and is considered a key element for energy transition. Renewable power generation by solar and wind is increasing, which requires flexible operation to balance the load on the energy grid with the ability to rapidly adjust the output. Gas turbines with a combustion system for hydrogen operation offers a low carbon solution to support the stability of the energy grid. This provides a solution to the need for energy storage, in the form of hydrogen, and flexible power generation.

Discharging green-house gases and particulates into the atmosphere has an impact on the global climate. With this current trend of increasing awareness towards the environment, alternative fuels are again being examined to reduce the impact of emissions. Hydrogen is perceived as the only long-term solution to global warming concerns. It is also the only fuel that can create large reductions in carbon emissions. There are zero CO2 emissions produced in hydrogen combustion. Hence, NOx emissions are the only remaining concern. Micro-mix combustion is used to implement miniaturized diffusive combustion to combust hydrogen with low emissions. With miniaturized diffusive combustion, local flame hot spots, which are caused by arising stoichiometric conditions of hydrogen, are reduced substantially with an increase in the local mixing intensity. Improvements in the mixing quality provide reduced emissions of NOx with a more balanced flame profile. Micro-mix combustion was also studied with different mixtures of fuels including hydrogen, kerosene and methane establishing an adaptive combustors [1,2].

Power generation systems based on hydrogen could be an important alternative to conventional power systems based on the combustion of fossil fuels. The main effort in the field is oriented towards the use of hydrogen in fuel cells and combustion with gas turbines. Consider the main options for combined cycles based on a hydrogen-fueled gas turbine unit shown in Figure 1.

Basic Simple and Combined Co-generation Cycles

Figure 1. Brayton - Rankine combined cycle
Figure 1. Brayton – Rankine combined cycle

One of the most widely used combined cogeneration cycles is the Brayton – Rankine cycle. This cycle is a symbiosis of the Brayton (simple cycle gas turbine) cycle and the Rankine (steam turbine) cycle.

Figure 2. Typical efficiencies of various types of plants
Figure 2. Typical efficiencies of various types of plants [3]
Figure 2, above, shows the efficiency of the power plant depending on the type of cycle. The power plants referenced are: the simple cycle gas turbine (SCGT) plants with firing temperatures of 2400°F (1315°C); recuperative gas turbine (RGT) plants, where the exhaust gases from the turbine are used to heat the incoming air to the combustion chamber; the steam turbine plants; the CCPPs; and the advanced combined cycle power plants (ACCPs), such as CCPPs using advanced gas turbine cycles. Read More

Single-Shaft Combined Cycle Power Plant: a Great Invention or an Elaborate Joke?


A combined cycle power plant (CCPP) uses both steam and gas turbines which increases the efficiency up to 50 percent compared to a simple-cycle plant. Conventional CCPP applications use separate gas and steam turbines and route the waste heat from the gas turbine to the nearby steam turbine to generate extra power. In recent years, an alternative design for a CCPP has been developed with single-shaft rotors.

So, what are the drawbacks and advantages of single-shaft CCPP design? Is it both possible and (more importantly) a good idea to have a single-shaft CCPP? To answer that we need to look at how one would work.

The typical steam and gas turbine rotors for a conventional CCPP application (high power ~200MW) are presented in Figure 1. The first power train (gas turbine) consists of a generator, compressor, and gas turbine parts. The second power train (steam turbine) contains high-intermediate and low-pressure turbine rotors and another generator.

Separate Gas Turbine and Steam Turbine Rotors
Fig. 1 – Separate gas turbine and steam turbine rotors (AxSTREAM RotorDynamics models)

In a single-shaft application, only one generator would be driven by the gas-steam-turbine power train. An optimal variant would be to have the generator between the gas turbine and a steam turbine as shown in Figure 2. Read More

Gas Turbine CFD – Driving Innovation with Data and Insight

This is an excerpt from the Siemens Blog. You can read the full version here.

Originally Written By Chad Custer – February 2, 2021

Once upon a time in a world without gas turbine CFD simulation.

Manager: The design team came up with a new blade concept, but they need to know the maximum possible temperature in the machine.

Test engineer: Anywhere in the whole machine?

Manager: Yes. And for any operating condition the machine might get used for. How long until you can have those results to the team?

Test engineer: Uhh

Terms like “virtual prototype”, “simulation testbed” and “digital twin” have become so common that you may dismiss them as buzzwords. However, to me, these terms not only still have meaning. These words do drive how I look at simulation. Read More