2016 ASHRAE Annual Conference

Industrial heating consumes a significant fraction of the energy consumed globally. Heating at temperatures higher than about 100°C is predominantly provided through combustion of fossil fuels with uncertain prices and well recognized environmental impacts. A significant fraction of industrial input energy is lost as low temperature waste heat (e.g. warm exhaust gases or cooling water) that could be lifted by high temperature heat pumps to process relevant temperatures. This paper assesses the potential for providing heating at temperatures between 100^oC and 150^oC through electrically-driven mechanical compression heat pumps. It reports the measured performance of a lab-scale reciprocating heat pump with HFO-1336mzz-Z (CF₃CH=CHCF₃; previously referred to as DR-2) as the working fluid over a range of conditions representative of intended applications (e.g. drying or steam generation). HFO-1336mzz-Z has attractive safety, environmental and thermodynamic properties and high chemical stability at high temperatures. Various compressor technologies, compressor lubricants, heat exchanger designs, expansion valve types and cycles with and without an internal heat exchanger were considered. Suitable equipment components were selected to meet the requirements for testing at evaporating temperatures between 30°C and 115°C and condensing temperatures in the range of 75°C to 150°C. Test results are compared with predictions based on ideal cycle thermodynamic modeling and the advantages of HFO-1336mzz-Z over other refrigerants are discussed. HFO-1336mzz-Z could enable more environmentally sustainable industrial heat pumps for the utilization of abundantly available low temperature heat to meet heating duties at higher temperatures, with higher energy efficiencies and lower environmental impacts than with incumbent working fluids.

The HVAC&R industry continues to evaluate low global warming potential (GWP) alternatives to R410A.  This paper reports performance of a 4 RT commercial rooftop heat pump with R410A as a baseline along with potential alternatives DR-55, DR-5A (R454B), and R32.  An adjustable frequency drive (AFD) was installed to allow the same capacity to be achieved with each refrigerant, matching compressor capacity to heat exchanger capacity.  Adjustable thermal expansion valves (TXVs) were installed to achieve the same compressor suction superheats in each case. 

Measurements of performance at the AHRI Standard 210/240 rating points were made with each refrigerant.  In addition, tests were run under outdoor temperatures ranging from 65F to 125F (18C to 52C).  A simple thermodynamic cycle model that matches average saturation temperatures in the evaporator and condenser along with a common compressor isentropic efficiency indicates that the capacity with DR-55 should be 2.5% lower than with R410A and should have an efficiency 1% higher.  Actual performance with DR-55 matched the capacity of R410A at the same compressor speed (60 Hz) with an efficiency 4% higher.  Similarly positive results were obtained with DR-5A.  With R32, the compressor speed needed to be reduced to 53 Hz to match the baseline capacity.  Efficiency was 3% higher than baseline.  As expected, R32 produced compressor discharge temperatures (CDTs) that were elevated by 20F and increased to 40F at the higher ambient conditions over R410A while DR-55 and DR-5A CDTs were only 10F above the baseline.  

The results here demonstrate that DR-55 and DR-5A are "design compatible" alternatives to R410A.  That is, they can be used in existing equipment designs with very little modification.

This paper explains the drop-in test results of R410A and R32/1234ze blend to a R32 dedicated mini-split air conditioner as well as simulation results. Usually, R32 and blends are dropped in to R410A units, but here the tests were carried out in opposite direction. As the test unit employs variable speed compressor, the paper clarifies the relative performance between these refrigerants under wide range of capacity. Since 32/1234ze blend is zeotropic, the impact of the change in flow velocity of refrigerant in heat exchange is clearly observed. Tests and simulations of the sample unit are also performed at high ambient conditions with these refrigerants. Such operation is now focused on due to the Montreal protocol discussion.

In response to environmental concerns raised by the use of refrigerants with high Global Warming Potential (GWP), the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) has launched an industry-wide cooperative research program, referred to as the Low-GWP Alternative Refrigerants Evaluation Program (AREP), to identify and evaluate promising alternative refrigerants for major product categories. After successfully completing the first phase of the program in December 2013, AHRI launched a second phase of the Low-GWP AREP in 2014 to continue research in areas that were not previously addressed, including refrigerants in high ambient conditions, refrigerants in applications not tested in the first phase, and new refrigerants identified since testing for the program began. Although the Ozone Depletion Potential of HFC-410A is zero, this refrigerant is under scrutiny due to its high GWP. Several candidate alternative refrigerants have already demonstrated low global warming potential. Performance of these low-GWP alternative refrigerants is being evaluated for various applications to ensure acceptable system capacity and efficiency. This paper reports the results of a series of compressor calorimeter tests conducted for the second phase of the AREP to evaluate the performance of R-410A alternative refrigerants in a reciprocating compressor designed for air conditioning applications. It compares performance of alternative refrigerants ARM-71A, L41-1, DR-5A, D2Y-60, and R-32 to that of R-410A over a wide range of operating conditions. The tests showed that, in general, cooling capacities were slightly lower (except for the R-32), but energy efficiency ratios (EER) of the alternative refrigerants were comparable to that of R-410A.

Faced with more stringent regulatory pressures, the demand for environmentally friendly substances is high. The number of low global warming (GWP) refrigerants entering the market is rapidly increasing to meet market needs.  Many of the new low GWP refrigerants are “mildly flammable” or “2L” as classified by ISO 817 and ANSI/ASHRAE Std 34. The new refrigerant flammability class provides the heating/air-conditioning/refrigeration industry potential options to meet environmental regulations with equipment designed to meet reduced flammability concerns.  Mildly flammable refrigerants are defined as refrigerants which have burning velocity less than 10 cm/sec and heat of combustion (HOC) less than 19,000 kJ/kg.  Although not part of classification requirements, mildly flammable refrigerants have higher lower flammability level (LFL) and exhibit higher minimum ignition energy (MIE).  Current MIE testing of 2L refrigerants has employed ASTM E582, which use an electrical spark ignition source.  Results from that testing has shown that typically, class 2L refrigerants have MIE values which are two to four orders of magnitude greater than highly flammable or ISO 817/ANSI 34 class 3 refrigerants. The high MIE values determined for mildly flammable refrigerants denotes that they are typically very difficult to ignite. A relatively unexplored potential ignition source is a hot surface which can be found in air conditioning auxiliary heaters and other refrigeration systems.  Maximum hot surface temperatures are also specified in several equipment standards.   Recently, work was conducted to review potential ignition/non-ignition for several 2L refrigerants which were released onto a hot surface. A new test was designed to simulate a 2L refrigerant leak onto a hot surface within a piece of equipment.    In particular, individual refrigerants were released onto a heated metal surface and potential ignition was observed for a set time period after the refrigerant was released.  Interestingly, ignition values noted were several hundred degrees higher than literature auto-ignition temperature (AIT) values. This work summarizes the test apparatus used, the hot surface ignition testing conducted with various 2L refrigerants, and ignition testing results.