Low-GWP Blowing Agents
Thanks to recent developments in high-performance, low-global warming potential liquid blowing agents, the reign of low-GWP insulation may begin sooner than you think.
Editor’s Note: In the original printed edition of this article (April 2012 issue), appliance DESIGN wrongly referred to Solstice Liquid Blowing Agent as “HFC-1234yf.” The molecule has been correctly identified as “HFO-1233zd” in this article. The original version has been retracted, and the corrected version appears below.
Blowing agent technology plays a critical role in the refrigerator industry by allowing foam insulation to expand and mold to the inside of refrigerator doors and walls, creating an energy-efficient and structurally sound appliance. Many refrigerator and freezer manufacturers have relied upon HFC-245fa, the blowing agent most commonly used in the U.S. today, because of its superior insulating properties, low total refrigerator cost, non-flammability, and VOC-exempt status. However a new liquid blowing agent, thanks to a lower greenhouse gas footprint, may already represent the end of the hydrofluorocarbon dynasty.
Marketed under the brand name Solstice Liquid Blowing Agent, HFO-1233zd, unlike hydrocarbon alternatives, is not expected to be categorized as a volatile organic compound as a result of its low MIR ratio (relative to MIR of ethane). The average ratio of mass-based incremental reactivities relative to ethane was 0.19±0.03 and the MIR ratio was 0.16±0.02.
Its carbon footprint however is the thing to be most excited about. Independent scientific assessment has found the GWP to be less than 7. Its makers predict that adoption of this new blowing agent globally has the potential to save about 60 million metric tons per year of CO2 equivalent.
OEM Refrigerator Trial
The blowing agent was recently tested in large-scale refrigerators by some of the world’s largest appliance manufacturers. With global focus on increasing energy efficiency standards and attention to using more climate friendly materials, Honeywell and Whirlpool, using a Bayer MaterialScience optimized PUR system, attempted to validate the energy efficiency of the blowing agent in typical household refrigerators. The energy efficient refrigerator/freezer model met the requirements of proposed DOE 2014 energy standards without using additional costly energy solutions, such as vacuum insulation panels or compressor modification.
The results of those trials, reported recently at the Polyurethanes 2011 Technical Conference in September 2011, noted that refrigerators manufactured with foam insulation that included the new blowing agent showed a 4-percent system-level energy efficiency improvement compared to HFC-245fa, and exceeded the current DOE Energy Star label by 9.5 percent. The commercial household refrigerator/freezer platform also exceeded the proposed DOE 2014 energy standard (see Figure 1).
The full-scale trial incorporated the new blowing agent, with an optimized polyurethane (PUR) system supplied by a major PUR systems house, in a commercially available 623 liter (22 ft³) household refrigerator/freezer (bottom freezer, counter-depth platform). Thirty refrigerator cabinets, with associated door sets, were foamed to investigate:
- Lambda (k-factor) performance
- Liner compatibility
- Dimensional stability
- Freeze stability
- Compressive strength
- Foam closed cell content
- DOE Energy Performance
- Energy consumption with 134a refrigerant working fluid
- Reverse Heat Leakage (RHL)
The baseline comparison for these refrigerators was the same commercial household refrigerator/freezer product using 245fa blowing agent and 134a refrigerant (unmodified compressor system). The new blowing agent was substituted for 245fa at an equal molar level in the PUR foam formulation.
The formulation was developed with commercially available materials and the foaming process conditions were identical to those for 245fa. HFO-1233zd processed very similarly to 245fa, and no modifications were made to the PUR foaming equipment or process, making it a near drop-in solution. The new blowing agent met or exceeded all requirements, including liner compatibility, compressive strength, dimensional stability, and freeze stability.
Reverse Heat Leakage (RHL) Assessment
Assessment of reverse heat leakage for food preservation, such as household refrigerator/freezers, is a methodology to isolate and assess the insulation performance. While RHL is not utilized in the U.S. for energy efficiency standards testing, the method is used in other regions of the world. For those regions with unreliable electricity supply and distribution, RHL measures provide some indication of the ‘time to food spoilage’ in the event of extended electrical outage.
Prototype refrigerators from this trial were assessed for RHL, along with baseline 245fa refrigerators. The refrigerators using the new LGWP blowing agent exhibited a reduction (in total) RHL exceeding 5 percent, illustrated in Figure 2. While refrigerator size and wall thickness directly impact heat leakage, these refrigerators were a direct comparison from baseline 245fa refrigerators.
Further, the reverse heat leakage improvement correlates to the separate DOE energy consumption improvement, a validation of the efficacy of the new blowing agent in an optimized PUR system.
Plastic Liner (HIPS) Compatibility
Differing plastic liner materials react differently with polyurethane insulation foams, and the associated blowing agent utilized. High impact polystyrene (HIPS) liner material, which is currently utilized with 245fa polyurethane foams, was assessed with the new LGWP blowing agent.
Four refrigerator/freezers with doors were placed in an environmental chamber and exposed to 54ºC (130 °F) for 10 hours, followed by an exposure to -34 °C (-30 ºF) for 10 hours. This cycle was repeated for five consecutive days, after which the liners were observed for blistering or cracking.
At the conclusion of the test, the HIPS liners did not show any signs of blisters, cracks, or any visual degradation. The HIPS liner material in refrigerators that underwent a similar trial in 2009 continue to be free of blisters and cracks after two years.
Manufacturing and Availability
As of this print date, the manufacturer is still pursuing commercialization. The development of the blowing agent is nearing completion, with major successful customer trials completed or underway. Regulatory approvals are in process in major markets, and the product is planned to be commercially available by the second half of 2013. Filings for SNAP and PMN have been completed and are currently under EPA review.
Solstice is a trademark of Honeywell International Inc.
1. 2007 Technical Summary. Climate Change 2007. The Physical Science Basis. Contribution of working Group 1 to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. (Except where noted)
2. Generally accepted value according to authors
3. Internal Honeywell PEL