Ejectors in NH3 DX Evaporators

In the past few decades, the world around us has undergone a lot of changes. The world of Direct Expansion (DX) ammonia refrigeration, however, hasn’t changed a whole lot. Enhanced tubes or fins have brought some improvements to the tried-and-true evaporators we are all familiar with. Controls technology has advanced to allow us to utilize electronic expansion valves or pulse width valves to have better control over our evaporator’s superheat. Therefore, it’s exciting when something new shows up on the market. With Evapco now utilizing ejectors in DX evaporators, we may be witnessing a fairly substantial upgrade to the technology we all know so well. Hopefully the utilization of ejectors will have little impact on operational performance or maintenance but will increase evaporator performance, to as high as 95% or recirculated capacities, according to Evapco’s data.

The concept of using an ejector in a DX evaporator is relatively simple and rather clever. I’ll do my best to summarize it without getting too far into the weeds as far as the details or the science of it all. Evapco’s new line of EJET evaporators are designed to run at a relatively low superheat, controlled by a required electronic expansion valve. This low superheat leads to some liquid overfeed that exits the evaporator coil and is collected in an oversized suction header, allowing for better coil performance at the cost of some slop over. Secondly, liquid and flash gas are separated on entry into the unit using a small chamber. The gas is cycled around to feed an ejector and the liquid feeds the coil like normal. Then that gas that was separated on entry to the coil is injected into the distributor on the coil, and it passes through an ejector that takes any excess liquid that exited the coil due to low superheat temperatures and draws that liquid with the flash gas into the coil once again. This allows the recirculating of already expanded liquid for added performance, and the only cost is feeding vapor that is traditionally fed through the coil anyhow. One challenge that may arise is that an oil separator/float is required on DX units that are not defrosted with hot gas. Though the oil separator seems simple and cleverly designed, it does add another level of cost and complication to the process.

In summary, Carlson & Stewart Refrigeration hasn’t yet seen the Evapco ejector technology in action. The benefit of this technology is smaller coils or getting more performance out of DX coils than we could in the past. In production spaces where DX coils can occasionally be “maxed out” on traditional product offerings, engineers at CSR are glad to see a single unit offer a higher Tons of Refrigeration (TR) capacity out of a single unit. Also, the ejector has no moving parts and shouldn’t affect operations or maintenance of the unit in any impactful way. As far as downsides are concerned, the coils do require electronic expansion valves, which hasn’t always been the norm at every facility. Also, this arrangement is relatively new to this application, so as with anything new there is a small amount of risk. However, it certainly seems like the worst-case scenario is seeing performance similar to the traditional DX coil, making the risk fairly minimal. If you’d like to inquire about Evapco’s new EJET evaporators, feel free to reach out to them or to Carlson & Stewart Refrigeration. Our team of engineers will be happy to start a discussion on EJET, and if you really like them, our team of installers will be happy to help you install them at your facility.

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