Cut energy costs through heat recovery

Waste heat recovery is a significant opportunity for laundries to improve efficiency and reduce energy bills. Many commercial laundries are turning to such heat recovery systems to capture the thermal energy from waste heat and re-use it to preheat freshwater or incoming air efficiently. The most common heat exchanger systems that meet the specific requirements for laundries are water-to-water and air-to-water heat exchangers.

In this blog post, we’ll discuss the efficiency of water-to-water heat exchangers, the most suitable designs for laundries, the benefits of implementing such systems, and how to maintain them for optimal performance.

Highly efficient heat transfer

In a typical water-to-water heat exchanger, freshwater flows in and circulates around the hotter wastewater that flows out. The wastewater transfers its thermal energy to the freshwater through the interior walls, heating the freshwater, and cooling the wastewater as it exits the unit. The average range of efficiencies of such systems varies between 50% to 80%. The efficiency is the result of the flow settings.

There are three primary flow settings:

  • Parallel flow: the two fluids enter at the same end of the heat exchanger and flow in the same direction, parallel to one another. In this design, the temperature differences are large at the inlet, but the fluid temperatures will approach a similar value at the outlets.

 

  • Counterflow: the two fluids enter at opposite ends of the heat exchanger and flow counter to one another. In this design, the temperature differences are less but are more constant over the length of the exchanger. It is possible that the fluid being heated may leave the exchanger at a higher temperature than the exit temperature of the heating fluid. This is the most efficient design because of the higher temperature differential over the length of the exchanger. Both Christeyns’ Heat-X Energo and Heat-X rotor are characterised by this counterflow.

 

  • Crossflow: the two fluids flow perpendicular to one another.

How to select the right water heat exchanger for your laundry?

There are several different types of water-to-water heat exchangers available for waste heat recovery. These include pipe-in-pipe, shell-and-tube, disc and printed circuit heat exchangers. However, the main heat exchanger types that are applied in the laundry industry are shell-and-tube and disc heat exchangers.

Shell-and-tube heat exchangers are the most common design in laundries. They consist of a parallel arrangement of tubes in a pressurised shell. This allows the tubes to conduct heat transfer under higher pressure than some other designs.

Also, in laundries, size and shape are important factors because space limitations may dictate positioning and footprint requirements. This makes shell-and-tube designs more suitable than other heat exchange systems.

 

Christeyns’ Heat-X Energo is a good example of such a
compact design. It is a plug-and-play shell-and-tube heat exchanger
that is positioned vertically.

 

 

 

 

 

Disc heat exchangers are also a good fit for laundries. They contain a rotating hollow disc section placed in a shell. Fresh water flows inside the rotating discs, while wastewater flows around the discs. This design is suitable for laundries where the wastewater is highly soiled. The surface design of the rotor discs ensures that the water flowing around them is always in turbulent motion, which prevents sedimentation of calcium and dirt particles. In that way, they do not need periodic cleaning.

Christeyns’ Heat-X Rotor is an example of such a disc heat exchanger. This design is most suitable for laundries washing workwear.

Benefits of implementing a water-to-water heat exchange system in your laundry

The main benefit of installing a heat recovery system in your laundry is that it will help you reduce your energy consumption and save money on your gas bill.

For example, Christeyns’ shell-and-tube Heat-X Energo allows an energy reduction of more than 50% in the washing process. Plus, as the waste heat is used to preheat the rinse water, textile temperatures are higher, leading to less moisture retention in the linen. The result? Additional savings of up to 20% in the drying and finishing process.

The graph below shows the benefits of warm rinsing. The Y-axis shows the moisture retention in the linen in percentages whereas the X-axis represents the seconds of pressing at full pressure. When the textile temperature is 27°C, residual moisture will be approximately 58%. However, when the same linen has a temperature of 48°C, residual moisture will be approximately 52%.

 

Moreover, implementing a heat exchange system can also help extend the lifespan of your equipment by reducing strain on mechanical parts due to reduced operating temperature.

Finally, such a system can help you comply with environmental regulations regarding emissions reduction. Especially for commercial laundries that use city sewers for their wastewater, water-to-water heat exchangers may be beneficial to cool their wastewater to meet local regulations.

Maintenance Requirements for Optimal Performance

Thorough maintenance of heat exchange systems can deliver quick wins by ensuring the equipment is performing to its potential. Much of this effort is aimed at countering the effects of fouling. In general, fouling occurs when particles accumulate on heat exchanger surfaces and prevent heat transfer and restrict fluid flow. To stop the precipitation of particles chemical additives can be used.
Additionally, simple preventative maintenance activities such as flushing or repairs that require the tube bundle to be removed from the heat exchanger shell for cleaning, can help prevent fouling. 

 

 

For example, Christeyns’ Heat-X Energo has
an automatic backflush to prevent blockages.

 

Keep the heat in motion. Contact us!

There are several different types of water-to-water heat exchangers available for waste heat recovery systems in laundries. Each type has its own advantages and disadvantages that should be considered when selecting which one is best suited for your laundry operations.  Contact your Christeyns expert to help you choose the best solution for your laundry.

 

Bibliography

IPIECA – https://www.ipieca.org/resources/energy-efficiency-solutions/efficient-use-of-heat/heat-exchangers-2022/
Consulted on February 3, 2023.

Jiri Jaromir Klemes, Olga Arsenyeva, Petro Kapustenko, Leonid Tovazhnyanskyy. “Compact Heat-exchangers for energy transfer intensification– CRC Press (2015).

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