‘We are using 3D printing to test our heat exchangers’

In 2016, CEEE, in partnership with 3D Systems and the US Department of Energy’s Building Technologies Office, used direct metal printing (DMP) to manufacture a miniaturised heat exchanger as a single, continuous piece. Could you further elaborate on the project and comment on its implications for the HVACR industry? In our centre, we have been working on all sorts of heat pump technology in systems and components. In my particular research, I look at next- generation air-to-refrigerant heat exchangers. We have been doing that for over 10 years now, when we got this funding from the US Department of Energy to develop that technology further and come up with a heat exchanger that is 20% lighter, smaller and more efficient than current state-of- the-art [technology]. This project started in 2013, and as part of that research we developed some algorithms and a heat exchanger innovation framework that allows us to invent new heat exchangers. The big simulation core can invent a new heat exchanger for new applications. [Now] we can dream up heat exchangers, but you cannot manufacture it using conventional manufacturing technologies – that is where 3D printing comes in. With 3D printing, you can circumvent most of the challenges [associated with] traditional manufacturing techniques. For this heat exchanger, we decided to combine traditional [methods] with 3D printing and [then] tested the performance. When I say ‘test’ I mean really measuring the performance of the heat exchangers in our laboratory. That gives us a lot more confidence in the analysis and design of the heat exchangers. We need to [see the] performance to make sure our design is correct, so we use 3D printing to prototype the heat exchanger and see that it, indeed, had a good design [and] the benefits we claimed it had. The idea is to present the result to the conventional HVAC industry. The hope is that it will motivate them to invest in manufacturing technologies so they can make more efficient heat exchangers. For a conventional manufacturer to set up a new assembly line is a significant investment. We are talking about multi-million dollars over multiple years and they need to make sure the design actually works. We use this 3D-printing technology to fabricate the heat exchanger and show them it works. The centre used titanium for this prototype, correct? An expensive material that is unlikely to be replicated in conventional manufacturing assembly lines... That is where it gets interesting. We are using 3D-printing technology for prototyping purposes to test our design. At the time, titanium was the only option available for 3D printing, [so] we went with that. It is by no means cost-combative with heat exchangers [in the market]. We cannot use titanium, it’s for prototyping only, to make sure the design, indeed, beats current designs. [It’s] meant to serve as an impetus to manufacturers to start investing in conventional technology that can make the same design using the traditional materials, such as aluminium and copper. Since it concluded in 2016, we were awarded a follow-up project as well, which is being negotiated. [There is] some interest from manufacturers to continue to do this work, to address technical barriers. Has the centre explored other materials for 3D printing? There was also something done in plastic, if I’m not mistaken? The underlying technology [we have used] for this heat exchanger has many different applications; [it’s] not limited to air conditioning. That framework and underlying approach [is] used by two other professors for other applications. One of them is [for] plastic heat exchangers. The heat exchangers we are designing have very small flow channels or tubes. When you go into these small dimensions, the thermal conductivity of the material doesn’t matter anymore. Traditionally, we use aluminium and copper [owing to their] strength and thermal conductivity, but when you [use] this new design, thermal conductivity doesn’t matter. [This] points to a whole new of avenue of materials to [consider].

Is the centre looking to 3D print other components of HVAC equipment? Our focus for now is heat exchangers, because when you look at an air conditioning system, there are four main components, and two of them are heat exchangers. Heat exchangers already comprise more than 50% of the material and cost, and [have] a significant impact on the efficiency of the [overall system]. That’s the reason we are focusing on heat exchangers. My colleagues are looking at [other] components, such as compressors, but not necessarily with 3D printing. Do you believe that the HVACR industry would one day integrate 3D printing for large-scale manufacturing purposes? I think that [it] will come. We are doing some research work in that direction, but it will take some time, because a conventional manufacturing industry, like the HVAC industry, is huge. [There are] so many suppliers and OEMs involved. For that change to happen, it takes time. What I see happening is kind of an intermediate or bridging step, where these OEMs will leverage 3D printing and we see a hybrid heat exchanger – a part is manufactured with conventional low-cost [materials and techniques], and a certain part [is] manufactured using 3D printing to get a more exotic design, [for a] performance and cost trade-off. Would such products be able to withstand the high-ambient conditions in the Middle East region? I think it can be applied to high-ambient conditions. It’s not so much [about] the heat exchanger, [or] the high level of design; [what] matters more is the [overall] system design. Do you think this approach would help with the overarching environmental goals being presented by many countries? I think it would help. With 3D printing as an enabling technology you can make this efficient, not only to reduce overall energy consumption, but these new designs are [also] more compact than current designs. What that means is your air conditioning system will use less refrigerant, which contributes to emissions. The majority of the refrigerant in air conditioning [equipment] is in the heat exchanger. When we make the heat exchanger smaller and more efficient [while having the] same cooling performance, we help to not only reduce cost and consumption, we also help the environment [by using] less refrigerants. Depending on how compact the new design is, you can expect a reduction of 10-30%. It also depends on system design. If you have an outdoor unit on the roof, there is still the pipe [needed] to connect it; we cannot get rid of the pipe. But the heat exchanger itself, the volume can be reduced by 10-30%. That may not translate to 30% reduction of refrigerant because of piping, [but there is] a lot of potential there. What do you consider to be the main bottleneck preventing manufacturers from implementing more efficient designs and adopting an approach that utilises 3D printing? The research that we do is all published and public, so today these designs and information are already available to manufacturers. The biggest challenge is the cost, because when you want to manufacture this new design you need to set up and invest in a new assembly line. If you do 100% 3D printing you need to invest money in getting a good 3D-printing machine, and more than one. And you have to cultivate the skill set [of the people] to operate and maintain [the equipment]. I think, at the end of the day, it comes down to [the] first cost [involved in] fabricating these heat exchangers. In the Center, our research is supported by more than 30 HVAC companies, worldwide, and they are aware of the design. These are big [companies]. But there are about 400 or so, worldwide that make heat exchangers, and not everyone has the access to a level of capital to make that move. That’s why I think there might be a hybrid approach, where they don’t have to scrap investment they have made over the years but leverage it – [they can have] part of heat exchangers [manufactured in a] conventional [manner] and have more specialised components 3D-printed. My comments about the adoption of 3D printing are in the context of the conventional and stationary HVAC market. Other markets, such as automotive and aerospace, where space/weight is at a premium, I think would adopt this technology sooner.