A recent blog post on Electrek by Fred Lambert discussed several reported heating concerns with Musk's famous electric vehicles in the winter. The author wondered if the issue could be linked to the change to ‘heat pump’ cycle heating systems that Elon’s team has apparently begun applying. Couple this with posts from Elon himself about potentially entering the home HVAC market and it makes me wonder if we may soon see Elon at a HARDI conference.
Why Heat Pump? While internal combustion engine vehicles use recovered heat from the engine for cabin heating, electric vehicles have thus far used electric resistance heat for cabin heating. Think about that – you spend all that money on an expensive lithium ion battery, electrical energy to charge it, then burn up that energy in a dead short (electric resistance heater) to product heat for occupants. It doesn’t take much of an internet search to discover people complaining about the reduced range of their electric vehicles in the winter, as a load of electrical energy is being devoted to running that electric resistance heater.
Enter the heat pump – Since the 1960’s the HVAC industry has realized that you can use a vapor-compression cycle to do the heating job for 70 – 80 percent less energy than a resistance heater, by reversing the function of the heat exchangers to draw heat from cold outside air and ‘pump’ it (via electrically driven refrigerant compressor) indoors to heat the air. The Heat Pump. And Elon and his crew were smart enough to apply this to the electric vehicle industry to reduce ‘range anxiety’ of EV owners in cool and cold climates. Brilliant.
But Heat Pumps are Different. Just as manufacturers and consumers of residential and commercial heat pumps have learned over the past 50 years, heat pumps are different. The heating capacity varies with outdoor air temperature. Because of that, temperature recovery times can be slower. Over the years, the HVAC industry has solved many of these early objections with advanced controls, variable speed airflow, advanced heat exchanger design, inverter driven compressors, and more. It looks like Elon’s team has utilized a lot of advanced technology in their change to heat pumps too.
Enter the OctoValve. While residential and commercial heat pumps utilize a reversing valve to redirect high pressure refrigerant flow for heating and cooling cycles, Elon’s vehicle application is different.
Rather than use a conventional refrigerant condenser coil up front, and a traditional cooling coil for cabin air, Elon’s team has developed the OctoValve, an eight-port stepper motor driven assembly that controls the flow of a glycol solution to convey heat throughout the system.
In an electric vehicle there are multiple potential sources of waste heat available, power control devices, batteries, motors, etc. as well as outdoor or cabin air. So, it appears the Octovalve serves as the conductor of an orchestra of multifunction heat transfer aimed at climate control, as well as handling a few other mission-critical equipment cooling operations along the way. While the additional intermediate step of heat transfer to glycol costs some efficiency points, the added flexibility in ‘switching’ the flow of low-pressure glycol rather than high pressure refrigerant does add some simplicity and sustainability. Brilliant.
Why worry? So, what could be the source of potential operational concerns? Elon’s team has employed a variety of amazing design and production technologies to this application.
Friction stir welding on the accumulator, semisolid forged aluminum refrigerant manifold (a thing of beauty) attached to a nylon coolant manifold, compact high efficiency plate heat exchangers, and more.
Most of the fluid piping and switching are in two flat planes, one aluminum, and one nylon, that look more like two mated circuit boards than a collection of piping. It may well be the most impressive HVAC system design I have seen. But Heat Pumps are different. And in the end, there is a consumer whose expectations can vary as much as the heat content of the winter air.
It took the residential HVAC industry a while to make heat pumps equally appealing to consumers, builders, and contractors. Along the way our industry addressed comfortable supply air temperatures, optimal defrost strategies, refrigerant charge compensation, advanced operation to achieve target space temperatures, and more. These are all unique challenges to heat pumps and aren’t too easy to see in a laboratory. And Elon’s heat pumps are moving through varying weather and moisture conditions. But Elon’s deployment of ‘over the air’ addressable control systems could once again provide part of the solution, if one is needed.
What can we learn? Elon’s team of innovators is world class. The unique system approach may lead an HVAC manufacturer to simplify residential heat pumps to a single outdoor package with a glycol loop to indoor unit or units. Would that greatly simplify the changeover to A2L refrigerant? No refrigerants in the building? Could the use of compact plate heat exchangers and enhanced manufacturing techniques offset the intermediate efficiency loss to glycol? And could Elon’s thinking of fluid switching in flat planes that resemble printed circuits more than plumbing become a more manufacturable standard?
What about Elon’s residential HVAC comments? He’s said he is coming. A residential system that has HEPA filters. Okay, we’ve got that. And we can offer the position that there are at least 7 different sizes of residential product, several different fuels, many different configurations, millions of installation variations, existing ductwork and architectural limitations, a dizzying combination of code differences, labor skill levels, price points, and consumer expectations. But hey, he’s Elon.