I recently attended a Chicago ASPE Chapter meeting that had a presentation on heat pump water heaters. The presentation was excellent. The information and the way it was presented was extremely beneficial to the plumbing and mechanical engineering community.
Basically, the program pointed out that heat pump water heaters will be a part of your future. There is no denying this fact. Furthermore, heat pump water heaters and heat pump hydronic systems will become more of a standard product for engineers to consider in the very near future. While products are currently available, as the program pointed out, the major switch will be to low-GWP refrigerants.
Low-GWP simply translates to low global warming potential. Gone will be the R-410A refrigerant, replaced with low-GWP refrigerants, such as R-32 and R-454B. Both refrigerants mentioned, as well as the majority of low-GWP refrigerants, fall into the category of Group A2L refrigerants. This is a classification of lower flammability refrigerants in accordance with ASHRAE 34. Hence, the refrigerants do burn but they burn very poorly.
The AIM Act, signed into law at the end of 2020, mandates a change to low GWP refrigerants and a phaseout of higher GWP refrigerants. Soon, hydrofluorocarbon (HFC) refrigerants will be completely phased out.
The U.S. EPA has issued new SNAP rules listing acceptable low GWP refrigerants. The SNAP rules are directed toward manufacturers of refrigeration equipment; however, they apply universally throughout the United States. Hence, the plumbing and mechanical codes cannot violate SNAP rules.
As a result, there are numerous changes taking place to the mechanical codes, ASHRAE 15 and product standards. This month, UL will issue the draft of the fourth edition of UL 60335-2-40 for public review. This is the product standard that regulates refrigeration equipment, including heat pumps.
This standard contains important requirements that will impact the design of systems utilizing heat pumps and other refrigeration equipment. Since the newer equipment will utilize flammable refrigerants, greater care will be required when analyzing refrigerant charge size. If a charge size is greater than 1.8 kg or 4 pounds, there may be certain measures required to mitigate any potential leak of refrigerant. The standard requirements are based on catastrophic leaks of refrigerant. Mitigation measures include detection systems, systems designed for enhanced tightness, circulation fans, increasing the size of the room or designing the system with connected spaces, to name a few.
If you are asking why heat pump water heaters and heat pump hydronic systems, think of the terms climate change, electrification and saving the world. There is a transition occurring worldwide away from fossil fuels. Efficient refrigeration systems are an economical alternative to fossil fuels.
If you have ever been involved in a geothermal system, you have most likely dealt with heat pumps. Going back many years, water-source heat pumps used R-22 refrigerant. The problem with R-22 refrigerant is that it destroys the ozone layer. Hence, there is a worldwide ban of R-22 refrigerant. However, R-22 remains a widely used refrigerant in existing systems. Once a repair is required on an R-22 unit, it must be replaced and cannot be repaired.
When R-22 was phased out, R-410A became the common refrigerant for heat pumps. As previously stated, R-410A is a high global warming refrigerant. It is interesting to note that refrigeration equipment manufacturers always considered R-410A to be a transitional refrigerant. It was an easy replacement refrigerant, but it still had problems. Furthermore, it is not the most efficient refrigerant to use in a system.
The transition to R-32 and R-454B will improve refrigerant efficiency. We have actually been using R-32 for many years since R-410A is composed of 50% R-32 and 50% R-125. Similarly, R-454B also has approximately 70% R-32, the remainder being R-1234yf, which is also a low GWP refrigerant.
The increased efficiency of R-32 and R-454B varies depending on which manufacturer you ask. The numbers given range from 10% to 25% better efficiency with these refrigerants. Realize that equipment efficiency does not change when the refrigerant is more efficient. All it means is that you need less refrigerant to accomplish the same heating or cooling.
Another interesting aspect of R-32 is that it operates at a higher temperature. That means it will perform better in a heat pump water heater or water source heat pump. The refrigerant is giving off heat during the phase change, thus heating the water.
You may also encounter the term, “de-superheater.” Simply stated, a de-superheater is a heat pump that generates hot water whether in heating or cooling mode. The term has been used in geothermal applications when there is a combination water heater with a heating and cooling system. In other parts of the world, there are de-superheaters for normal building heating and cooling systems whereby the waste heat is used to either heat or preheat potable hot water to the building. De-superheaters will be catching on in the United States for systems other than geothermal.
The last part of the presentation at my ASPE meeting was on economics. I was thrilled about the accurate presentation of the economics — it was not a sales presentation with exaggerated figures; the presentation was by an engineer with realistic numbers.
The numbers did not hide the fact that gas-fired water heaters are still the lowest cost for providing hot water. Then the presentation expanded into the long-range cost of continuing to burn natural gas for hot water. When you measure the impact on the climate and health of the Earth, heat pump water heaters start to look more economical. The question for the plumbing and mechanical engineer is: “Can you sell a healthy world?”
Many years ago, engineers were afraid to talk about designing for climate change and a healthy environment. But times change. That should be an easier sell today.
If you have not already investigated heat pump water heaters, it is time to take a look. Continue to follow the development of new products using low-GWP refrigerants as they enter the market over the next three years.
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The views expressed here are strictly those of the author and do not necessarily represent PM Engineer or BNP Media.