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Seven Design Changes That Reduce Refrigerant Charge

At CMS Mechanical, we offer refrigeration maintenance and service to a number of national restaurants and convenience store chains. Read the article below for some information regarding how systems are designed to increase efficiency and reduce costs.

Optimizing refrigerant charge has always been a key part of designing cooling systems and balancing their efficiency, reliability, performance, and cost. But recently, that balance has shifted, and refrigeration engineers are once again looking at refrigerant as a key piece of the puzzle.

There are two main reasons for this.

First, refrigerant prices are rapidly increasing in certain parts of the world. This is largely driven by dwindling supplies as traditional options are phased down under European F-Gas regulations, and other measures to limit the production of greenhouse gases under the Kyoto, Montreal, and Kigali protocols.

As a result, some refrigerants — such as R-404A — have risen in price by more than 500 percent in Europe since 2017.

Where once refrigerant may have been a relatively minor cost compared to a system’s components, now the charge has a far larger impact on its overall production and installation price – making every saving valuable.

Second, the move to reduce GWP has resulted in the growing use of flammable alternatives. In such cases, having less refrigerant charge materially increases the number of applications where a system can legally and safely be used.

So, in the current climate, reducing refrigerant charge is a key part of gaining competitive advantage — for manufacturers and installers alike — satisfying end users, and maintaining profitability.

The advantages of reducing refrigerant abound

Refrigerant costs seem unlikely to fall in the near future. Supplies of traditional refrigerants are being reduced, and new alternatives being developed will likely carry the price premium that comes with having limited suppliers and competition.

But it is not only the increase in prices that is an issue. Fluctuating costs and supply mean that designing for lower refrigerant charge also reduces a manufacturer’s exposure to risk should things change at short notice.

Reducing charge can also significantly improve installation flexibility. A reduced charge means A2L, A2, and A3 refrigerants can be used in a greater range of settings too — as it becomes easier to satisfy standards like EN 378:2016 and ISO 5149:2014.

And with easier installation comes easier servicing. By making units simpler and lower in charge, servicing and maintenance can be carried out more quickly and safely — further reducing total cost of ownership and offering a competitive advantage.

Ways to reduce refrigerant charge

Potentially, reducing refrigerant charge can make systems safer, more flexible, and more competitive. It can be achieved in a number of different ways — many of which also bring an additional benefit to the system’s full- and part-load efficiency, or overall size.

We’ve identified seven approaches engineers can take to reduce refrigerant charge without the need to compromise on safety, efficiency, or cost.

Reduce internal volume by reducing piping

Internal volume, of course, is an important factor for refrigerant charge, since there is a direct correlation between the two.

Because internal volume is dictated by the size and number of components, minimizing the length of piping or removing it altogether is vitally important. And the smaller diameter you can practically use, the better.

This is especially true in the liquid line. Each refrigerant has its own ratio of liquid to vapor density, but in call cases, the liquid refrigerant density is significantly higher than vapor. So even though most of the volume in a system might be gas, the vast majority of its mass is in the liquid phase, which means each reduction in liquid volume has a disproportionately high impact on the overall charge amount.

A potential solution is to move some components closer to the condenser, or design reversible heat pump systems with bi-flow expansion valves, instead of bypassing it by adding parallel piping with check valves.

As long as refrigerant remains as a liquid before it reaches the expansion valve, and as long as the valve has sufficient capacity, reducing the diameter of the liquid line and the associated increase in pressure loss won’t affect system performance.

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