INTRODUCTION

Replacements for chloroflurorcarbon (CFC) were developed using HCFCs (hydro-chloro-fluoro-carbons) and HFCs (hydro-fluoro-carbons). In addition to use of pure fluids such as the HFC 1,1,1,2-tetrafluoroethane (R134a), numerous blends and azeotropes based on HFCs and HCFCs were developed. Today these refrigerants, among them R-410A, R-507, R-407C, R-404A, R-408A, R-402A, R-409A are familiar to most everyone in the HVAC&R industry.

Cesare Soffientini, Honeywell Fluorine Products Italia, Lainate MI, Italy

Gary J. Zyhowski, Honeywell Specialty Chemicals Buffalo, NY, USA

Mark W. Spatz, Honeywell Specialty Chemicals Buffalo, NY, USA

INTRODUCTION

Replacements for chloroflurorcarbon (CFC) were developed using HCFCs (hydro-chloro-fluoro-carbons) and HFCs (hydro-fluoro-carbons). In addition to use of pure fluids such as the HFC 1,1,1,2-tetrafluoroethane (R134a), numerous blends and azeotropes based on HFCs and HCFCs were developed. Today these refrigerants, among them R-410A, R-507, R-407C, R-404A, R-408A, R-402A, R-409A are familiar to most everyone in the HVAC&R industry.

Identification of replacements for some ozone-depleting refrigerants like CFC-113, is a low-pressure refrigerant typically used in centrifugal chillers, has proven more difficult. CFC-11 is also used in centrifugal chillers and has been successfully replaced with HCFC-123 and HFC-134a.

As the HCFCs still contain chlorine and have an associated ozone-depletion potential, they will be phased out in the EU Community as a virgin product from the 1^st of January 2010. So, the availability of HCFCs for equipment servicing following the phase-out may not allow for predictable economical use.

As well, the quick phase out of HCFC-141b as a blowing agent in thermal insulation and solvent originated a significant amount of work for the appliance industry and field applications, like systems flushing, in finding acceptable solutions.

With the commercialization of the HFC 1,1,1,3,3-pentafluoropropane (HFC-245fa; R-245fa as refrigerant grade) there is the availability of a product the thermophysical properties and environmental characteristics of which make it suitable for a number applications such as centrifugal chillers for comfort cooling, Organic Rankine Cycle for energy recovery and power generation, sensible heat transfer in low-temperature refrigeration, secondary loop fluids for commercial refrigeration, Heat Pump and passive cooling devices. As well, it has a broad range of uses like foam blowing agent, solvent and aerosol. This paper analyzes some of the properties and explore some applications of HFC-245fa as working fluid.

PHYSICAL AND THERMODYNAMIC PROPERTIES OF R-245fa

Table 1 shows most of the pertinent properties of HFC-245fa.

HFC-245fa shows a high Critical Temperature (154 °C), which means a higher efficiency of the refrigerating cycle respect, i.e., the one of R-134a (T.C. = 101°C).

Laboratory tests indicate HFC-245fa to have a high degree of thermal and hydrolytic stability.

As far as material compatibility is concerned, tests have been carried out in static and dynamic conditions. While the compatibility of plastics is good, the elastomer one should be evaluated at the condition of use.

ENVIRONMENTAL CHARACTERISTICS AND REGULATORY INFORMATION

Table 2 contains pertinent regulatory and environmental information for HFC-245fa

Table 2 - Regulatory and Environmental Information

CAS Number…………………………………………………………………………………….. 460-73-1 Ozone Depletion Potential ….………………………………..………………………………….…….. 0 Global Warming Potential (100-yr time horizon) ...............……………………………............ 950 US VOC status ………………...………………………………………………………………… Exempt Exposure guidelines ACGIH TLV……………………………………………………………………….………………….. None OSHA PEL …………….………………………………………………………….….……………… None WEEL (AIHA) TWA - 8 hrs (1). ….………………………………………………………….… 300ppm US DOT Hazard Class .…….....………………………………………….……………… Not regulated US RCRA ………………..………………………………………. Unused Material Not RCRA Waste US TSCA Inventory Status ….……………………………………...…..……………………… Listed US SNAP Approval ………...........…………….….. Approved for use in new Centrifugal Chillers

WORKING FLUID APPLICATIONS: CENTRIFUGAL CHILLERS

Currently, most centrifugal chillers intended for comfort cooling applications are designed to operate with either R-123 or R-134a. Despite the fact that R-123 has a very low ozone depletion potential (0.016 relative to R-11), it has been already phased out in new equipment in Europe. The issue with the exclusive use of R-134a as replacement is that there is a thermodynamic efficiency penalty associated with this refrigerant relative to R-123 and other lower pressure refrigerants. There are also changes necessary for manufacturers of lower pressure refrigerant chillers to adapt their product lines and manufacturing operations for R-134a.

Another option is to use R-245fa. This refrigerant would be considered a lower pressure refrigerant but not as low as R-123. Its normal boiling point is 15,3 °C, so evaporation would take place below atmospheric pressure like R-123 but condensing pressure would likely exceed 1 bar so a coded pressure vessel would be required.

Table 3 shows the results of the thermodynamic analysis of both single-stage and multi-stagechiller applications. Although there is slightly lower thermodynamic efficiency than R-123 for single-stage machines, this difference decreases with multiple stages. Superior transport properties can also reduce any thermodynamic differences. In addition, this refrigerant can be used to increase the capacity of an existing R-123 product line.

From the heat transfer stand point, there are some recent evaluations according to which the condensing heat transfer is at least comparable to that of R-123 and of R-134a and there is some indication that it may be superior to that of R-123 for some enhanced surfaces.

To understand the economic impacts of the choice between R-134a and R-245fa, an evaluation of the present value of the operating cost differences was conducted. The results are shown in Table 4. The analysis was based on comparing the thermodynamic efficiency at conditions that would be seen when running tests to establish the Integrated Part Load Value for efficiency. This analysis does not include the impact of any work recovered by an expander turbine. The analysis is done for a 750-ton chiller.

The economic analysis was based on the performance of a single-stage R-134a machine and compared against single and two-stage R-245fa machines (multi-staging is only used for low-pressure chillers). It assumes a 15% annual rate-of-return with a 15-year life and a cost of electricity of 6,3 Eurocents per kW-hr (average cost in Europe in year 2002). The present value of the operating cost savings for a single-stage R-245fa is in excess of 12.700 Euro. The savings associated with a two-stage R-245fa machine would have a present value in excess of 29.000 Euro.

Chiller Economic Analysis
Comparison of R-134a and R-245fa
	R-134a	R-245fa	R-245fa
	Single-Stage	Single-Stage	Two-Stage
IPLV COP	9.494	9.734	10.060
Chiller Capacity (kW)	2638	2638	2638
Power Consumption of Chiller (kW)	278	271	262
Cooling Hours (per ARI Std 550-590-98)	5010	5010	5010
Annual Power Consumption (kW-hr)	1392015	1357584	1313575
Cost of Electricity (Euros/kW-hr))	0.063	0.063	0.063
Operating Cost (Euros)	87,697	85,528	82,755
Savings Relative to R-134a Single-Stage	-	2,169	4,942
Present Value Analysis:
Annual Rate of Return(%)	15%
Number of Years	15
Present Value of Savings (Euros):		12,684	28,896
Assumptions:
1. Evaporating temperature of 4.4oC based on a 2.2oC ΔT between entering water and saturation temperature
2. Condensing temperature dependent on load and based on a 2.8oC ΔT between leaving water and saturation temperature
3. Compressor isentropic efficiency of 80%
4. Superheat and subcooling of 1.1oC
5. Entering water temperature for evaporator and condenser per ARI Std 550-590-98
6. Condenser leaving water temperature based on water flow rate per above standard.
Table 4

In order to determine the environmental impact of the choice of refrigerants for this application, an analysis of both the direct and indirect contributions to global warming (respectively from refrigerant emissions and the indirect contributions are due to the burning of fossil fuels to supply the power consumed by the equipment) were conducted. To compensate for the emissions and energy associated with the production of the refrigerants, the GWP values (IPCC, 2001) have been increased by values shown as per the Arthur D. Little report of March, 2002 (⁷) and are shown in Table 5.

The annual power consumption was taken from Table 4. Assumptions needed to complete this analysis were taken from the ADL report. This included a value of 0.65 kg of CO₂ per kW-hr of electrical production, a 1% annual leakage rate and a 30-year life. The impacts were determined by:

Direct Effect = Refrigerant Charge (kg) x (Annual loss rate x Lifetime + End-of-life loss) x GWP

Indirect Effect = Annual Power Consumption from Table 3 (kW-hr) x Lifetime x 0.65

Using this information a LCCP analysis was performed and is shown in Figure 2. It is very clear from these results that the indirect contributors dominate any contributions from refrigerant emissions. In addition, all three refrigerants are have similar climate impact. R-245fa nearly matches the very favorable characteristics, especially when using multiple stages.

Figure 1

WORKING FLUID APPLICATIONS: ORGANIC RANKINE CYCLE

The Organic Rankine Cycle (ORC) converts thermal energy to mechanical shaft power.

The benefit of ORC systems is that they recover useful energy, often as electrical output, from low-energy sources such as the low-pressure steam associated with steam-driven turbines for electricity generation (Figure 2). The efficiency of an ORC is typically between 10 and 20%, depending on temperature levels and availability of a suitably matched fluid. ORC is an attractive option for heat recovery in the range of 150ºC to 200ºC, particularly if no other use for the waste heat is available on site. The greater the difference between source and sink temperatures, the higher the cycle efficiency. When source temperatures drop low enough that steam cycle is no longer thermodynamically efficient, certain organic fluids can be used.

Figure 2. Simple Organic Rankine Cycle System Diagram

Previous use of this technology has been limited. With R-245fa, the match between the working fluid and the energy source being recovered, for example, in the case of low-pressure steam is favorable. Within a homologous series, as chain length and molecular weight increase, the molar heat capacity and entropy increase. More specifically, with comparable latent heats, as the slope of the entropy lines decrease, the cycle efficiency will increase. Given the proportionality between the natural log of pressure and the inverse of temperature, the slope of the entropy line will be approximately the change in enthalpy with change in temperature (for small changes in temperature), that is, the heat capacity. Even though R-11, R-123 and R-245fa are not in the same homologous series, the longer molecular chain length of R-245fa means that the vibrational component of heat capacity will increase as well the entropy due to the increased degree of freedom (⁸). The way in which entropy and enthalpy, affected by the increased heat capacity, translates into improved efficiency is illustrated in Figure 3.

Until recently, most halogenated working fluids have been based on one- or two-carbon molecules. In general, the demand for Organic Rankine cycle fluids was small; manufacture of fluids solely for this purpose was not practiced. The favorable performance of R-245fa in the Rankine cycle provides an opportunity to realize greater electrical energy output from power generation facilities that rely on steam-driven turbines. Likewise, large industrial enterprises can now consider recovery of waste heat with the option to convert the energy to useful electricity.

With the employment of R-245fa for conversion of waste heat to useful energy in fossil fuel-fired power generation facilities, the amount of available electrical energy per unit weight of fossil fuel burned would increase thus helping to satisfy demand without increasing facility emissions.

The favorable performance of R-245fa in energy recovery, if adopted by industrial facilities, would ease demand for electricity, concomitantly decrease the burning of fossil fuels, and increase the consumer’s overall energy efficiency. Solar-driven energy conversion systems could also be developed around R-245fa. In the same way, this would lead to lower pollution levels by curbing fossil fuel burning.

In Table 6, boiler pressure, condenser pressure and thermodynamic efficiency are compared for R-11, R-123 and R-245fa. It can be seen that as molecular chain length increases, so does the thermodynamic efficiency.

Table 6- Organic Rankine Cycle Comparison (10)   Boiler temperature 149 ºC - Condenser temperature 38 C HFC-245fa HCFC-123 CFC-11 boiler pressure, kPa 3213 1958 1972   condenser pressure, (kPa) 132.4 42.1 61.4 Thermodynamic Efficiency (%) 59.9 56.6 51.8 Molecular Chain Length 3-carbon 2-carbon 1-carbon

WORKING FLUID APPLICATIONS: SENSIBLE HEAT TRANSFER

Sensible heat transfer describes the heat exchange process in which the heat transfer fluid does not change phase. Typically, the heat transfer fluid is in the liquid state for such a heat exchange process. Sensible heat transfer applications include a number of industrial and commercial applications including use as a secondary loop fluid for commercial refrigeration applications, for example, in supermarkets.

In the past, fluids such as CFC-11, CFC-113 and HCFC-141b would have been among the various fluorocarbon fluids used in such applications. The use of HFC-245fa would provide a non flammable, non corrosive fluid with favorable heat transfer and transport properties (high heat exchanger efficiency and low pump power requirements).

The ratio of heat transfer coefficient to friction factor signifies the heat transfer performance efficiency (one wants to maximize heat transfer and minimize fluid friction or pumping power). Figure 4 below illustrates that HFC-245fa has a higher heat transfer coefficient to friction factor ratio than many other commercially available heat transfer fluids.

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Tyfoxit (Environmental Process Systems Ltd)

NOMENCLATURE

-Endnotes-

1. Honeywell Material Safety Data Sheet, Genetron^® 245fa, Section 8, Exposure Guidelines.

2. Output based on National Institute of Standards and Technology, Refprop v.6.01.

3. Lemmon, Eric W., McLinden, Mark O. and Huber, Marcia L., NIST Reference Fluid Thermodynamic and Transport Properties – Refprop 7.0, NIST Std. Database, 2002

4. Carr, Mathew A., Experimental and Theoretical Study of Surface Tension Effects on Extended Surface Condensation, Catholic University of America, Doctoral Dissertation, Washington DC, 2002.

5. Atwood, T., Murphy, K.P, An Investigation of Refrigerants for Single-Stage Centrifugal Water Chillers, ASHRAE Transactions, 1972 No2131.

6. IPPC, Climate Change 2001- The Scientific Basis, Intergovernmental Panel on Climate Change, Cambridge University Press, 2001.

7. Arthur D. Little (ADL), Global Comparative Analysis of HFC and Alternative Technology for Refrigeration, Air Conditioning, Foam, Solvent, Aerosol Propellant, and Fire Protection Applications, 2002.

8. Donald A. Mc Quarrie, Statistical Mechanics, Harper and Row, New York, 1976, p. 137.

9. http://www.epa.gov/ozone/title6/snap/lists/11cent.html.

10. www.eere.energy.gov/der/microturbines/pdfs/haughtats.pdf, DOE Advanced Microturbine Program Update, Debbie Haught, First ATS Annual Program Review Meeting, December 4-6, 2000, Alexandria, Virginia, p.13

11. Air Conditioning and Refrigeration Institute, “Water Chilling Packages Using the Vapor Compression Cycle”, Standard 550-590. Arlington VA. 1998.

Disclaimer

Although all statements and information contained herein are believed to be accurate and reliable, they are presented without guarantee or warranty of any kind, expressed or implied. Information provided herein does not relieve the user from the responsibility of carrying out its own tests and experiments, and the user assumes all risks and liability for use of the information and results obtained. Statements or suggestions concerning the use of materials and processes are made without representation or warranty that any such use is free of patent infringement and are not recommendations to infringe on any patents. The user should not assume that all toxicity data and safety measures are indicated herein or that other measures may not be required.