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Getting Comfortable with Designer Air

Modulation Technologies: Designing Great Commercial Atmospheres

Getting Comfortable with Designer Air, a new webinar series on how modulation technologies are enabling enhanced comfort and improved efficiency in homes and businesses around the U.S.  This webinar series is designed specifically for air conditioning contractors and facility managers to become more informed on the latest information about compressor modulation and the role it plays in enabling ‘Designer Air’.

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In the next installment of Getting Comfortable with Designer Air webinar series, Bart Powelson, Director of Commercial Air Conditioning Marketing, and Jacob Groshek, Director Global Commercial Scroll Engineering discuss “Modulation Technologies: Designing Great Commercial Atmospheres.”

The lighting and décor need to be perfect.  Why not the air? This webinar is designed to give a deeper dive into how modulation technologies, ranging from multiple fixed capacity compressors to variable speed scrolls, can help every commercial space meet their desired objectives in achieving the perfect atmosphere.  Take this opportunity to expand your knowledge with our experts to discuss the benefits of capacity modulation technologies.

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CO2 as a Refrigerant — Properties of R744

This is post number 3 of a series.

Carbon dioxide is a naturally occurring substance; the atmosphere is comprised of approximately 0.04 percent CO2 (370 ppm). It is produced during respiration by most living organisms and is absorbed by plants. It is also produced during many industrial processes, in particular when fossil fuels such as coal, gas or oil are burned to generate power or drive vehicles.

The triple point of carbon dioxide is high and the critical point is low compared to other refrigerants. The chart in Figure 1 shows the triple point and the critical point on a phase diagram.

Figure 1: R744 / CO2 phase diagram

Figure 1: R744/CO2 phase diagram

The triple point occurs at 4.2 bar (60.9 psi) and -56.6 °C (-69.8 °F). Below this point there is no liquid phase. At atmospheric pressure (0 bar/0 psi), solid R744 sublimes directly to a gas. (Dry ice produces 845 times its volume in gas at 59 °F and 1 atm. Example: 1 oz. of dry ice will produce 845 oz. of CO2 vapor as it sublimes.) Solid R744 (also known as dry ice) has a surface temperature of -78.5 °C (-109.3 °F). If R744 is at a pressure higher than the triple point and the pressure is reduced to below the triple point (e.g., to atmospheric pressure), it will deposit directly to solid. For example, this can occur when charging an evacuated refrigeration system with liquid R744.

The critical point occurs at 31 °C (88 °F), which is below typical system condensing temperatures for part or all of the year, depending on the climate. Above the critical point the refrigerant is a transcritical fluid. There is no phase change when heat is removed from a transcritical fluid while it is above the critical pressure and temperature. In a refrigeration system transcritical R744 will not condense until the pressure has dropped below the critical pressure.

CalloutNo other commonly used refrigerant has such a low critical temperature. As a result, other refrigerants always condense as heat is removed on the high side of the system.

The boundaries of the transcritical fluid region are:

  • The critical temperature (31 °C / 87.8 °F) to the sub-cooled liquid region
  • The critical pressure (72.8 barg / 1,055.9 psig) to the superheated gas region

Table 1 compares the basic properties of R744 with other refrigerants commonly used in the retail sector.

Table 1: Basic properties of R744 compared with other refrigerants

Table 1: Basic properties of R744 compared with other refrigerants. Footnotes: 1. The GWP values are from the Intergovernmental Panel on Climate Change, 4th assessment report: Climate Change 2007; 2. GWP for R407A from EN388; 3. GWP for R407F from supplier’s data.

The pressure enthalpy chart in Figure 2 shows the critical point and the extent of the transcritical fluid region.

Figure 2: Pressure enthalpy chart for R744

Figure 2: Pressure enthalpy chart for R744

A significant challenge with the application of CO2 as a refrigerant is the higher operating pressures compared to other commercial refrigerants. The chart in Figure 3 compares the pressure of R744 with R404A and R134a.

Figure 3: Pressure-temperature relationship comparison

Figure 3: Pressure-temperature relationship comparison

The saturation curve for R744 does not extend beyond 31 °C (88 °F) because this is the critical point. Above this condition there is no distinction between liquid and gas. Operation above this pressure is current practice in transcritical systems, which we will discuss in the next post.

Andre Patenaude
Director – CO2 Business Development, Emerson Climate Technologies

Visit our website for additional information on CO2 Solutions from Emerson.
Excerpt from original document; Commercial CO2 Refrigeration Systems, Guide for Subcritical and Transcritical CO2 Applications.

 

EEVs Make Low Condensing Refrigeration a Reality

217-P-EX6_M21_ART6It’s a problem all operators face: if I lower the head pressures in my refrigeration systems, I can lower operating costs. On top of that, I can meet the Department of Energy’s 2017 energy reduction targets. But, how do I do that with existing technologies?

Some in the industry have tried using thermal expansion valves (TXV) to lower head pressures, but TXVs can’t maintain capacity and digest flash gas that forms when pressures float lower. So operators are still forced to keep head pressures near 105 °F.

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CO2 as a Refrigerant — Criteria for Choosing Refrigerants

This is post number 2 of a series.

How R744 meets different conditions and criteria

Table 1: How R744 meets different conditions and criteria

Multiple factors need to be carefully considered when selecting any refrigerant, including its cooling capacity, safety, environmental impact, ease of use, cost, and availability of components and expertise. Table 1 summarizes these and other key criteria, and shows how well R744 meets them.

In general, the table shows that R744 offers a more superior cooling capacity than conventional refrigerants while meeting the demand for a natural refrigerant with low global warming impact, but presents challenges in both its application and handling.

In the next post, we’ll look at the properties of R744 as a naturally occurring substance.

Andre Patenaude
Director – CO2 Business Development, Emerson Climate Technologies

Visit our website for additional information on CO2 Solutions from Emerson.
Excerpt from original document; Commercial CO2 Refrigeration Systems, Guide for Subcritical and Transcritical CO2 Applications.

Commercial Refrigeration Industry Prepares for Next Generation of Refrigerants

217-P-E360_Compass_ART5

The commercial refrigeration industry is at a crossroads. In one direction, the Environmental Protection Agency (EPA) is proposing to ban many commonly used refrigerants in favor of low-GWP alternatives. In the other direction, the Department of Energy (DOE) is mandating significant reductions in energy consumption for reach-ins, walk-ins and ice makers by 2017. If that wasn’t challenging enough, the two regulations at times conflict — with the DOE’s new standards based on the EPA’s delisted refrigerants.

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