Energy use has never been such a hot topic for commercial refrigeration as it is now. Kitchen refrigerators and freezer units drive a significant proportion of energy bills across the food service industry. Authorities and customers alike are focusing on efficiency standards and ratings to understand not just what a unit costs to buy, but what it costs to operate. For the refrigeration design engineer, that's a challenge. Because many efficiency improvements have already been made, they need to look again at the fundamentals, and consider new approaches.
At Danfoss, we believe it's time for commercial kitchen refrigeration manufacturers to adopt hot gas defrost techniques that are already saving so much energy in cold rooms and ice machines. The technology is proven, it's familiar, and many of today's professional refrigeration units already use the multifunction refrigeration controllers needed to make it work.
That means hot gas defrost is actually simpler and more cost effective than many of the alternatives currently being tested at some manufacturers. And with around 8 – 10% energy savings, the benefits are significant. In this article, we'll recap how hot gas defrost works and why it's so efficient – and suggest some approaches to implement it in a straightforward, low-maintenance way.
If you're also involved in designing larger refrigeration applications, cold rooms or ice machines, you'll likely already be familiar with hot gas defrost techniques. You may not have considered it as a realistic option for commercial kitchen refrigeration units – but it's actually an elegant (and, importantly, energy efficient) solution.
Briefly, it works by using a demand controlled solenoid valve to divert the hot gas output from the compressor back into the evaporator coil – heating it from within. Take a glance at the diagram, and you'll see how simple the idea can be.
Calculations and ongoing lab tests suggest this approach will reduce overall energy consumption by around 8 – 10% on a typical professional kitchen refrigerator. That's potentially an improvement of one or more EcoDesign ratings, from a single internal change.
There are two main reasons why hot gas defrost is so efficient. First, it uses heat that was already being generated by the compressor. Unlike conventional electric defrost approaches, no additional heating element is needed – saving a significant energy draw.
Second, hot gas heats the evaporator coil from within, thawing the insulating frost from the inside out. This means much less energy is expended heating the coil's surroundings than when you apply that heat from an external electrical element.
A self-contained controller simplifies your design, and saves time and costs in pre-production, prototyping, assembly and maintenance because each one is already fully tested and approved. Rather than making your system more complicated, adopting this approach could arguably make it more straightforward.
If you have already adopted an advanced, efficient electronic controller, the only technical addition you will need is the solenoid valve. Again, it's important to choose a part that helps you maximize energy efficiency, and keeps design, assembly and maintenance as simple as possible. We recommend Danfoss EVUL solenoid valves for the job, because they're compact and lightweight – fitting comfortably into most commercial kitchen refrigeration units. They have laser-welded bimetal connections, which allow fast soldering without a heat sink or cloth.
Like the ERC controller, the EVUL solenoid valve's design keeps energy consumption to an absolute minimum. It's sturdy, and highly resistant to vibration – with excellent leak integrity and encapsulated coils for a long, problem-free service life – so you can be confident you're building reliability into your system.
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