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Heating and cooling FAQ

Below you will find a number of common questions on heating and cooling applications, along with answers from Alfa Laval’s experts. Don’t see your question here? Contact us today to get a personal response from our experienced team.

For a quick and simple selection of standard products, you can also explore our Product guide

Why is asymmetry so important in brazed heat exchangers used as condensers for heat pumps?

The narrow channels on the refrigerant side allow for higher internal velocity, enhancing heat exchange even at partial load. At the same time, the larger channels on the water side reduce pressure drop throughout the unit. Together, this has a positive effect on the heat pump’s coefficient of performance, improving performance for the whole system.

Why is a water-side filter so important in brazed and fusion-bonded heat exchangers?

In the water circuit, there are many small parts and debris in circulation. Most of these are welding residuals, which can be trapped in the small channels of the unit. This can cause a number of problems, ranging from higher pressure drop to irregular fluid distribution across the plates and even corrosion that leads to leakage between the circuits.

Why can refrigerant pressure drop be particularly high in brazed heat exchangers used as evaporators?

Brazed heat exchangers, even longer or taller models, operate with an internal distribution system that distributes refrigerant in all channels. These distributors must have a dedicated geometry, often with small passages and chambers. This, in turn, can lead to pressure drop in many cases. However, this is not a problem in itself as long as the expansion valve is designed accordingly (in most cases, slightly bigger).

Why are AlfaNova fusion-bonded heat exchangers more resistant to corrosion than brazed heat exchangers?

AlfaNova heat exchangers are copper free—built with 100% grade 316 stainless steel. In brazed designs, copper is the material that holds the stainless steel channel plates together. Unfortunately, copper is less resistant to certain types of corrosion, such as in applications where ammonia is used as the refrigerant or where there is aggressive water due to, for example, higher chloride content. In these applications, the 100% copper-free AlfaNova model is therefore recommended.

Why is the refrigerant inlet connection so important for 2-phase evaporators?

The S3 refrigerant inlet connection is more than a connector for brazing the copper pipes. It is a pre-distributor, and its geometry influences the distribution of refrigerant along the unit. The internal diameter of the S3 connection impacts the velocity and turbulence of the fluid, so the refrigerant is equally distributed in every single channel. With each additional plate in a unit, S3 geometry becomes more and more important. Alfa Laval’s evaporators are optimized with dedicated connections to achieve the best performance depending on refrigerant, number of plates and application.

Can the same brazed or fusion-bonded heat exchanger be used both as a condenser and as an evaporator?

Yes. This is possible and has been done in many different applications. The distribution system of evaporators does not jeopardize performance when used as condensers, and the additional pressure drop is generally negligible. However, the condensation needs to be full of subcooled liquid at the condenser exit, a partial condensation can lead to problems. In reversible systems, it is recommended that the condenser have a distribution system in order to provide decent performance as an evaporator as well. 

How do I ensure oil return in evaporators?

The design of both the distribution system and the channel plates in Alfa Laval evaporators ensures the return of the oil to the compressor. This is particularly relevant to inverter-driven compressors, because the amount of refrigerant and velocity can vary greatly in the course of operation. Software that verifies the performance of the evaporator at minimum load is mandatory in order to ensure safe operation. 

Can the same brazed or fusion-bonded heat exchanger be used with different refrigerants in 2-phase applications?

Yes. Alfa Laval heat exchangers can be used with many different refrigerants. During the initial design phase, one heat exchanger can be optimized for one or two main refrigerants. Alfa Laval’s latest technology is highly flexible for both inverter-driven compressors (with high capacity variations during operation) as well as the growing number of new refrigerants entering the market due to environmental reasons. Thanks to innovative distribution systems and the new channel plates design, this flexibility allows the units to be used with many different refrigerants at high performance.

What is important to consider when it comes to freezing in heat pumps?

Freezing is one of the main issues to consider in heat pump operation. Alfa Laval heat exchangers are specifically designed to avoid freezing during defrost in air-to-water heat pumps. Nevertheless, preventing freezing depends on the operative conditions you set for the system, especially with regard to compressor capacity, brine flow and temperatures. Alfa Laval regularly performs simulations, both in a laboratory and via software, which can help you identify the limits for safe operation.

What are the maximum and minimum allowed capacities for a certain brazed or fusion-bonded heat exchanger?

Maximum and minimum capacities are both determined according to levels of acceptable performance. As capacity increases, the unit can experience lower evaporating temperature, higher condensing temperature in 2-phase applications, higher temperature difference in 1-phase applications, as well as water or brine pressure drop. All of these lower the overall performance of the system. Conversely, the lowest possible capacity is limited by oil return to the compressor and the related possible drop due to the reduced velocity into the channels.