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GEA's Global HVAC Technology Blog

GEA's Global HVAC Technology Blog covers a range of topics including:

  • Core HVAC Technologies
  • Technology & Patent Evaluation
  • Manufacturing Technologies
  • Product Quality Improvement
  • Materials/Failures/Corrosion
  • Product/Technology Commercialization
  • Business Strategy Development
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We'll draw upon our range of experts to provide comments, insights, technical articles and a little humor from time to time

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Water Chiller Performance Calulations-Basic Cycle

Posted December 10, 2014 1:00 AM by larhere

Water chillers are commonly employed to chill water for air conditioning systems. This chilled water is circulated thru cooling coils. Air is passed over the coils to be cooled and dehumidified for indoor comfort. The basic components of a water chiller are a compressor and motor, an evaporator, a condenser and assorted piping and controls. In this article we will describe the performance calculations for the basic water chiller thermodynamic cycle.

As an example for our discussion, we will use a compressor with R134a, a flooded evaporator (refrigerant on the shell side) and a shell & tube water cooled condenser also with refrigerant on the shell side. For simplicity of illustration we will assume an 85% efficient centrifugal compressor and no pressure drop in suction or discharge piping. Chilled water enters the evaporator at 54 oF and leaves at 44 oF. Cooling water enters the condenser at 85 oF and leaves at 95 oF.

The evaporation is a constant pressure process and the evaporator saturation pressure must be at a temperature colder than the leaving chilled water temperature for the heat transfer to occur. The refrigerant leaves the evaporator shell as a saturated vapor and enters the compressor.

The compressor supplies work to raise the refrigerant to the condenser saturation pressure. The condenser saturation pressure must be higher than the leaving condenser water temperature for heat transfer to occur. The compressor work required is the product of the refrigerant mass flow times the vapor enthalpy at the entrance to the condenser minus the vapor enthalpy leaving the evaporator.

The heat rejected in the condenser is the sum of the heat transferred in the evaporator plus the work input of the compressor. The condensed refrigerant leaves at the condenser saturation pressure, passes thru an expansion device that reduces the pressure to evaporator pressure, and enters the evaporator. In the expansion process, some of the liquid flashes to gas and the refrigerant entering the evaporator is a two phase mixture.

The chilled water is cooled in the evaporator by evaporating the refrigerant. The evaporator heat transfer capacity is equal to the building load. The refrigerant mass flow that must be delivered by the compressor is equal to the building load divided by the difference in enthalpy of the entering and leaving refrigerant conditions.

In the basic cycle, the liquid refrigerant leaves the condenser at its saturation temperature.

The refrigerant properties at various points in the cycle are:

Condenser Saturation Temperature, Tsat=97 oF

Evaporator Saturation Temperature, Tsat=42 oF

Enthalpy leaving Evaporator, hg=172.9 Btu/lbm (saturated vapor @ 42 oF )

Enthalpy leaving Condenser, hf=107.8 Btu/lbm (saturated liquid @ 97 oF )

Entropy entering Compressor, sg=0.412 Btu/lbm-R (saturated vapor @ 42 oF )

Enthalpy leaving Compressor, hg=181.3 Btu/lbm (ideal isentropic compression)

Isentropic enthalpy rise due to compression, ∆hcomp=181.3-172.9=8.4 Btu/lbm

Compressor efficiency, Ƞ=0.85

Enthalpy leaving Compressor hg=172.9+8.4/0.85=182.8 Btu/lbm

From these values several performance parameters of the cycle may be calculated on a per ton basis.

Capacity=12000 Btu/h-ton

Evaporator enthalpy rise=172.9-107.8=65.1 Btu/lbm

Refrigerant mass flow rate=12000/65.1=184.5 lbm/h-ton

Compressor work=184.5*8.4/0.85=1824 Btu/h-ton

= (1824 Btu/h-ton)/(3412 KW-h/BTU)=0.535KW/Ton

In future blogs we will discuss the performance improvements of subcoolers and economizers.

See other blog posts by Jim Larson

Water Side Pressure Drop in Shell and Tube Heat Exchangers

Designing Water Cooled Condenser Tube Bundles

Designing Flooded Evaporator Shell & Tube HXRs

Editor's Note: CR4 would like to thank Jin Larson, GEA Consulting Associate, for contributing this blog entry, which originally appeared here.

3 comments; last comment on 12/13/2014
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Conquering Information Overload

Posted November 19, 2014 1:00 AM by larhere

Who isn't battling Information Overload?

According to Daniel Levitin, McGill University psychology professor " Americans took in five times as much information every day in 2011 as they did in 1986". In 1976 the average grocery store had 9,000 products, today its 40,000 products. All of this is more than the brain is configured to handle.

Levitin says there are steps we can take to reduce Information Overload. I've condensed his 10 steps to the 5 most important ones. (Read all ten, and the full article "Ten Steps to Conquering Information Overload" authored by Laura Shin.)

1. Don't Multi-task - Switching between taks will actually make you feel exhausted, disoriented and anxious says Levitin.

2. Take Breaks - "People who take a 15-minute break every couple of hours are much more efficient in the long run".

3. Delegate - Push down authority and empower people under them to exercise their good judgment.

4. Daydream - the daydreaming mode acts as a neural reset button and replenishes some of the glucose you use up in staying on a task.

5. Do Toughest Tasks in the Morning - "Important decisions should be made at the beginning of the day, when gumption and glucose is highest".

Read More

Editor's Note: CR4 would like to thank Larry Butz, President, GEA Consulting Associate, for contributing this blog entry, which originally appeared here.

3 comments; last comment on 11/20/2014
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Corrosion Analysis: Understanding the Equipment

Posted November 05, 2014 1:00 AM by larhere

Back again. Today we'll discuss the third step in the corrosion evaluation/mitigation process

1. Identify the corrosion mechanism.

2. Understand the environment, both external and internal.

3. Understand the equipment - materials of construction, operating cycles, hours.....

4. Identify alternatives - materials, coatings, limiting operating envelope, changing the environment (water treatment, alternative lubricants/refrigerants, filter the air, etc.), redesign the machine (better drainage, eliminate contact of dissimilar metals, .....)

5. Implement change.

6. Monitor results.

3. Understand the equipment - materials of construction, operating cycles, hours…..

In the previous post in this series we discussed how important understanding the operating environment is when working to solve a corrosion problem, not surprisingly, it is just as important to understand the equipment which operates in that environment.

One of the challenges for a failure analyst working with a client to solve a corrosion problem is thoroughly understanding the equipment that is failing - what are the materials of construction, how are the materials processed, why were the materials selected, is there more than one supplier of materials or components, what is the typical duty cycle for the equipment, what are the extremes of the operating map, etc., etc., etc.?

A lot of these questions can be answered by reviewing engineering drawings and documentation, but much of this information is only available via the tribal knowledge of the people who work with, or on the equipment every day. Thus, it is crucial for design, manufacturing, service and purchasing personnel to share their tribal knowledge regarding how and why the equipment is designed and built the way it is with whomever is charged with analyzing the corrosion problem. Again, just like understanding the environment, the better we understand the equipment, the better and more robust and more economical will be the solutions that are found to address the corrosion problem.

Editor's Note: CR4 would like to thank PJ Sikorsky, GEA Consulting Associate, for contributing this blog entry, which originally appeared here.

6 comments; last comment on 11/12/2014
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Reshoring Gains Momentum

Posted October 29, 2014 8:50 AM by larhere

Earlier this month we highlighted a BCG study ("The Shifting Economics of Global Manufacturing") showing the dramatic changes in manufacturing competitiveness in the leading 25 countries.

BCG has followed this study up with a survey eliciting responses from 252 senior level US based manufacturing executives. Results were compared to a similar survey one year ago in August 2013. The summary report ("Made in America, Again") consist of 13 slides which can be viewed at the BCG Website.

(Note: This study is of manufacturing capacity serving the US market)

Most noteworthy findings include:

  • 54% of respondents are considering bringing production back to the US
  • US based executives believe that a larger share of their manufacturing base will be US based five years from now.

  • The US has surpassed both China and Mexico as the most likely destination for new capacity to serve the US market.

  • Access to US skilled labor is a major factor in reshoring.
  • Three times as many executives believe there will be net manufacturing job growth (vs. loss) over the next 5 years.

Read the Summary Report slide presentation here.

Editor's Note: CR4 would like to thank Larry Butz, President, GEA Consulting Associate, for contributing this blog entry, which originally appeared here.

3 comments; last comment on 10/31/2014
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Trane Introduces HFO1233zd in Series E Centrifugal Chillers

Posted October 22, 2014 9:23 AM by larhere

Trane introduced the first chiller using R1233zd at the Chillventa Expo last week in Italy. Air conditioning manufacturers are scrambling to comply with the revised EU F-gas Regulation going into effect 1/1/2015 limiting and banning "F Gases" in the EU.

HFO 1233zd is described as a single component refrigerant, both low toxicity and non-flammable. It was originally developed for use as a blowing agent but has also been found to be a high efficiency alternative to R123. It has been submitted for ASHRAE designation and classification and is expected to be classified as A1. Its GWP is low, listed under the F-gas regulations as 4.5 but variously described as 6, by UNEP, or 1, by Honeywell.

According to the announcement...

The Trane Series E CenTraVac is a large-capacity chiller (capacities from 2600kW to 14,000kW) for applications like comfort cooling of large commercial buildings including district cooling. It is available in Europe, the Middle East and other 50Hz markets, and received Air-Conditioning, Heating and Refrigeration Institute (AHRI) Certification.

Honeywell markets the new refrigerant under the tradename Solstice zd, a US SNAP-approved alternative to R123 and 245fa. It has a GWP of 1. It will have applications in large centrifugal chillers, organic Rankine cycles and high temperature heat pumps.

Also Read:

U.S. EPA Moves to Phase-out Familiar HFCs

Editor's Note: CR4 would like to thank Larry Butz, President, GEA Consulting Associate, for contributing this blog entry, which originally appeared here.

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Manufacturing Cost Competitiveness is Changing Worldwide

Posted October 10, 2014 2:00 PM by larhere

Boston Consulting Group, BCG, just released a "must read" report "The Shifting Economics of Global Manufacturing" if your company manufactures in multiple international locations. What is so great about this report is that it presents, analyzes and summarizes a 2014 study on the cost competitiveness of the top 25 exporting nations, an update of the previous study done in 2004. It is

  • available online at the BCG Perspectives website (no cost)
  • contains an interactive Cost competitiveness Index tool
  • a readable 12 to 15 pages in length
  • has great illustrative graphics

(Disclaimer: GEA receives no compensation and does not have a business relationship with BCG. We are excited about good work on a critical topic for manufacturers around the world. This includes the global HVAC industry. Our compliments and thanks to BCG for this fine work and the sponsors who paid for the study.)

The study analyzed manufacturing costs for the world's 25 leading exporting economies along four key dimensions: manufacturing wages, labor productivity, energy costs, and exchange rates.

What BCG found was a lot of change...Who would have thought a decade ago that Brazil would now be one of the highest-­cost countries for manufacturing-or that Mexico could be cheaper than China?...or that China's estimated manufacturing-cost advantage over the U.S. has shrunk to less than 5 percent. Brazil is now estimated to be more expensive than much of Western Europe.

Cost structures in Mexico and the U.S. improved more than in all of the other 25 largest exporting economies. Because of

  • low wage growth,
  • sustained productivity gains,
  • stable exchange rates, and
  • a big energy-cost advantage,

these two nations are the current rising stars of global manufacturing. BCG estimates that Mexico now has lower average manufacturing costs than China on a unit-cost basis.

The authors conclude "These dramatic changes in relative costs could drive a large shift in the global economy as companies are prompted to reassess their manufacturing footprints. (See Exhibit 3.)

One implication is that global manufacturing could become increasingly regional. Because relatively low-cost manufacturing centers exist in all regions of the world, more goods consumed in Asia, Europe, and the Americas will be made closer to home."

There are profound implications for manufacturers with operations in all countries. They must (continue to):

Enhance productivity. As once-enormous gaps between wages in developed and developing economies continue to shrink, improving the value added by each worker is becoming an increasingly important factor in manufacturing competitiveness across the globe

Account for the full costs. While direct costs such as labor and energy will continue to have a strong influence on decisions about where to manufacture, logistics, obstacles to efficiently conducting business, and the hidden costs and risks of managing extended global supply chains, for example, can offset much of the savings from labor or favorable exchange rates. It is also crucial to take into account hidden cost advantages of operating shorter supply chains, such as speed to market, greater flexibility, and a better ability to customize products for specific markets.

Consider the implications for the broader supply chain. Reliable local suppliers may not yet be available to provide important inputs. In other cases, deconstructing the value chain could involve added logistics costs or unanticipated tariffs, duties, or other penalties.

Promote better business environments. Maintain a dialogue with relevant regulators and policy makers in countries in which you manufacture.

Reevaluate your business model. To take full advantage of production in an economy, a one-size-fits-all model that uses the same processes and materials is unlikely to be optimal. Many companies should consider adjustments in their products or business models to better meet the needs of that manufacturing environment. It may make sense to use different materials that are locally available.

The shifting economics of global manufacturing requires approaching the world with a fresh mind-set. Rather than seeing the globe in terms of low cost versus high cost, manufacturing investment and sourcing decisions should increasingly be based on a more current and sophisticated understanding of competitiveness within regions.

Read the complete report here

Editor's Note: CR4 would like to thank Larry Butz, President, GEA Consulting Associate, for contributing this blog entry, which originally appeared here.

1 comments; last comment on 11/06/2014
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