HVAC cooling

The Alfa Laval AlfaQ range of heat exchangers are certified according to the AHRI* Liquid to Liquid Heat Exchangers (LLHE) Certification Program (AHRI 400) which ensures thermal performance according to a manufacturer's published specifications. Typical HVAC applications include district cooling substations, ice-storage systems, data centre cooling and free cooling systems. To read more about the Alfa Laval AlfaQ range.

• Eliminate uncertainty about thermal performance
• Reduced system-wide energy use and operating costs
• Uncompromised environmental performance
• Independent assurance
• Three-year warranty

Under-dimensioned heat exchangers can lead to higher system-wide energy use, higher operating costs and compromised environmental performance. With AHRI certification, you are assured that the plate heat exchanger will function as required. No risk of underperformance. No uncertainty. It does what it says on the box, guaranteed.

What is a chiller bypass?

Traditionally the chiller in an air conditioning system runs continuously during the entire cooling season, even when full capacity is not required. Previously, the only alternative to constant chiller operation has been a chiller bypass system using a strainer. This strainer removes impurities, but at the same time it requires costly maintenance, chlorination and other chemical treatment. By installing a plate heat exchanger – and sometimes a filter to protect it – in the chiller bypass system, corrosion, scaling and constant maintenance can be virtually eliminated. Another advantage is that this system can use any type of cooling, such as a cooling tower or free cooling with river or well water, even seawater or brackish water, without ruining sensitive equipment like air conditioners.

How to avoid dirty and clogged condensers shutting down condenser?

A dirty, blocked or fouled condenser means less heat transfer can take place from the refrigerant to the surrounding ambient and increases the risk of a chiller shutting down. The condenser is vulnerable to attacks from corrosion-causing chlorides, fouling impurities and biological activities in the water.

What performs better – cooling tower vs chiller

Both options should be considered not just for its upfront investment, but also for running cost and serviceability. A cooling tower / heat exchanger system is the easiest to clean with the least downtime.

What is an acceptable fouling factor?

Velocity is important to prevent fouling.

In a shell and tube heat exchanger, there is the option to make the tube longer to include a fouling margin. By contrast, in a plate heat exchanger, you can add in more plates, which creates more channels but also reduces velocity.

We don’t advocate high fouling margins, otherwise it can become self-fulfilling. The rate of deposition is higher and eventually, this leads to loss of performance.

Heat load or performance of the heat exchanger drops over time and levels out over time. Fouling from salts, chlorides etc settles on the plates and decreases the size of the channel. How quickly fouling occurs depends on various factors such as water quality, temperature, etc.

How do you manage thermal fatigue?

Thermal fatigue and / or mechanical stress is created by large temperature and / or pressure fluctuations. The number of cycles and degree of cycling may have an effect on the plate heat exchanger, depending on its design. Gasketed PHEs are very good at handling the stress.

Alfa Laval has also been working with brazed plate heat exchangers to increase resistance to thermal stress. The R&D has resulted in the development of unique product features such as the Alfa Laval RefTight™ sealing system that guarantees a long lifetime sealing between the welded channels; and Alfa Laval IceSafe, that allows controlled, non-destructive freezing.

What type of plates is suitable for seawater cooling?

Free chloride ions (free radicals), left behind when chlorine breaks down, are looking for a site to deposit and attach themselves to metal parts. Seawater sits around 30,000 parts per million (ppm) of chloride ions or 3%. Stainless steel has limited resistance to free chlorides. It makes it unsuitable for seawater as the lifecycles of the plates would be very short.

The other factor to consider is the temperature inside the heat exchanger. The higher the temperature, the higher the corrosive factor.

By contrast, plates made of titanium grade 1 are very well suited for seawater cooling, withstanding temperatures inside the heat exchanger of up to 100 degrees Celsius before reaching the critical pH point (pH7).

Does the heat exchanger require insulation?

The amount of energy radiating from the edge of the plates relative to the throughput is minuscule. An insulation case, which slows down heat loss / heat gain, can be applied but is not required in most HVAC applications as the financial gain would be negligible.

For refrigeration applications, however, where the surface of the heat exchanger is well below ambient, condensation can occur. To prevent condensation from occurring, it might be appropriate to insulate the heat exchanger.

What is the correct procedure for backwashing?

There are two procedures for backwashing: Reverse one side, or reverse both sides at the same time. If you reverse both sides simultaneously, you won’t have a drop in performance.

It is important to note that backflushing will only remove loose debris. Backflushing will not remove scaling and fouling.

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What is scaling?

Fouling and scaling lead to contaminants that coat the surface of heat exchanger plates. Scaling is different from fouling. Suspended solids lead to soft fouling. They can be washed off the surface. By contrast, sodium carbonate and calcium carbonate form what it known as hard scale. Scaling has to be dissolved with an acid.

What is the correct filtration procedure for heat exchangers?

The correct filtration procedure depends on the application that it is running under and the type of filter used. For applications with a high percentage of suspended solids or large particles, it is recommended that a screen filter is in place. The heat exchanger needs to be selected with the correct channel gap, and the filter should be selected for the heat exchanger model.

Are heat exchangers suitable to be used in a Reverse Osmosis stream?

Reverse osmosis water can be used for heat exchangers, as often found in pharmaceutical applications.

How do you size a heat exchanger for low differentials?

Calculating the heat exchanger for low and high differentials is part of the design process. Alfa Laval can design a differential down to 0.5 degrees Celsius and still provide a performance warranty.

What are the most common heat exchanger certifications?

Certifications are increasingly important as builders look for certainty around energy savings and energy efficiencies in commercial and residential construction. The AHRI certification provides independent, third party certified labelling for products that meet performance standards. There are other energy efficiency standards such as Leed and Green Star which - while not stipulating heat exchangers specifically - consider a system’s overall energy efficiency.