We tested whether absorption chillers are suitable for use in the marine sector

Traditional conditioners are popular, but consume a lot of energy. Thankfully though, there are other options, and a solution could be found with the use of either absorption and adsorption chillers.

Despite the promise of these technologies, there has been minimal research on how these machines operate in a water-based environment. A building, for example, stays relatively static, while boats are constantly changing angles due to their movement in the water.

We decided to find out.

To begin this experiment, we focused on absorption chillers. From here, we had a simple question: could this technology be as efficient on water as it is on land?

Let’s see.

How did the experiment work?

First, we selected a Yazaki absorption chiller that would fit on a boat. Then, we needed to find a way to discover whether the machine would work effectively at the sort of positions it may find itself while on water.

To achieve this, we measured the coefficient of performance (COP) and the chilling power of the Yazaki machine while at different degrees of tilt. This was done by putting the chiller on a gimbal, a device that enables the rotation of an object.

In order to keep the experiment as unbiased as possible, we also had to control the heat source the absorption chiller was using. With that in mind, we fed the Yazaki with hot water stored in a 220L tank, which was heated by four 9kW electric heaters.

Now we have that out the way, let’s talk about the chiller itself.

What actually is an absorption chiller?

It’s worth spending a little bit of time on how this technology works.

First off, an absorption chiller doesn’t use a compressor, which is standard in many other heating and cooling hardware. Typically, a compressor is used to drive specially-designed refrigerants (normally in a vapor) through the system needing temperature control.

Now, an absorption chiller is different. Rather than using a compressor and electricity to regulate an environment, this machine uses heat to cool a location.

Confusing? A little — but we’ll explain it as clearly as possible.

Instead of the aforementioned specially-designed refrigerants, an absorption chiller uses water to assist with cooling. This is generally mixed with lithium bromide, a type of salt.

This mixture is exposed to a source of heat (normally water or steam). When this occurs, the water and lithium bromide separate. This is the same principle as those experiments you did at school where you’d heat up a water and salt mix, and see the latter left behind.

In the absorption chiller, the water in the lithium bromide mixture evaporates and is now a vapor. Now, do you recall using a spray bottle when watering plants? And how when the mist is produced, the air feels cool? This is because the multitude of droplets have a large surface area, so can absorb a lot of heat. The principle is the same in this chiller.

The water vapor in the machine is then fed into a cooling coil. This makes it a liquid again, before it’s fed into an evaporator which reduces the pressure. In turn, this causes a huge drop in temperature. This cold liquid is then used to collect all the unwanted heat of a building or structure.

That, then, is how heat is used to power the cooling of an environment.

Of course, this is a very high-level view of how an absorption chiller works. If you’d like more detail, we’d advise you to watch this very informative video.

Now we know how an absorption chiller system works, we can look at the results of our experiment regarding its operation at different angles.

Understanding the results

The outcome was unequivocal: the more the Yazaki chiller was titled, the less power it produced.

This table shows the results in full:

Let’s delve into what these results actually mean.

The clearest indication of how the chiller gets less effective at a tilt can be found in the ‘Chilling power’ section of the table. Notice how rapidly this figure drops from an upright position (14.0kW) to a 9-degree tilt (5.49kW).

This clearly shows how this chiller wouldn’t be a green or efficient solution for a boat, as the various angles it would have to operate at while on water severely diminishes its power.

There’s more interesting data in the table though. Take a look at the COP (that’s the coefficient of performance) figures. As the machine tilts, these are actually rising.

On paper, this should be a good thing, as it suggests the chiller is operating more efficiently — but this doesn’t tell the full story. Most likely, the COP’s improvement is down to the smaller variation in input temperatures that occurred when the chiller was at an angle.

So why did tilting impact the performance?

Well, one possible explanation is due to how the water in the chiller interacts with the coils in the heat exchange. Effectively, the liquid is meant to run down the paths in the coil, but tilting it can lead it to running down the sides of the machine and avoiding this altogether.

Of course there are other explanations considering the complexity of the machinery, but this is a big reason why absorption chillers may not be suitable for use on boats or ships.

What does all of this mean? And what’s next?

When we consider how important it is for any waterfaring vessel to be as efficient as possible, it becomes quickly apparent that this sort of heat pump isn’t suitable.

Fundamentally, absorption chillers are not efficient enough under the conditions that boats operate in. This means that if we’re trying to build the greenest, most climate friendly vessel around, we’ll have to keep on searching for a way to regulate its temperature.

Thankfully, we have another avenue to explore: adsorption chillers. Stay tuned for an update on that experiment and whether the technology can outperform its absorption counterpart.