Good Fridge Design
A good fridge, should just work.
Buying a portable fridge can be difficult. There is so much information readily available and every manufacturer seems to make the "most efficient" fridge there is. So to help you sort the wheat from the chaff, we've created this simple guide to good fridge design. We hope this goes some way to helping you make a more informed decision.
To start with, here's a simplified drawing of a cooling system:
The refrigerant (which is a gas) passes from the compressor, out into the condenser (where it releases any heat into the atmosphere), then into the sides of the fridge cabinet (where it absorbs heat). The refrigerant continues this cycle around and around. Picking up heat from the fridge cabinet and releasing it outside the fridge cabinet. A fan assists by blowing air across the condenser to help release the heat.
All fridges have an insulated cabinet. This is the main body of the fridge. The main difference between cabinets is in their construction. Some are plastic and some are steel.
If the cabinet is the body of the fridge, then the compressor is the heart. This is the most important and also the most expensive component in your fridge. The compressor is a small DC (12 volt and 24 volt) engine that pumps the refrigerant around inside your cooling system. If this fails, it will be very costly to fix.
Be sure to buy a fridge with a well-known compressor brand. Look for a company that has been making compressors for many decades and be careful of manufacturers that have only popped up in the last 5 or 10 years. Think about how long you want your fridge to last?
All portable fridges that use a compressor in Australia have the same refrigerant. This is called R134a.
The evaporator is the metal plate inside the fridge cabinet that gets cold. As the refrigerant passes through the tubes inside the evaporator, it absorbs the heat from inside the fridge cabinet. Look for a fridge where the evaporator plate goes all the way around the inside of the fridge cabinet. This helps the fridge cool faster and more evenly.
Here's a birds eye view of an evaporator that goes all the way around the inside of the fridge cabinet, and from the top to the bottom:
Once the refrigerant reaches the condenser, it is hot from the heat that it absorbed from the fridge cabinet. As the refrigerant passes through the condenser, it releases the heat outside the fridge cabinet. There are 2 main types of fridge condensers.
1. Finned condenser
These are like a small car radiator. They usually have a fan screwed to them, which blows air through the fins. These work fine when the fan is running, but when the fan stops, the heat is often trapped inside the compressor area. Another problem with finned condensers is their propensity to get blocked up with dust and lint. Once this happens their ability to function efficiently is greatly reduced. If you have a fridge with a finned condenser, be sure to blow it out with compressed air from time to time to keep it clean.
Here are a couple of photos of finned condensers. The first is new, the second is used:
2. Wire on Tube condenser
This condenser takes up more space than their finned counterparts, as the tubes are much longer and are spaced further apart. This has 2 distinct benefits. 1- It greatly reduces dust build-up. 2- It allows for much better heat release when the fan is not running. Originally these types of condensers were designed to be effective even without the use of a fan. It's for these 2 reasons we prefer wire on tube condensers whenever possible.
Here's a photo of a cooling system showing the wire on tube condenser in black. You can also clearly see the evaporator plate in white, the large fan and the compressor:
Most fridges use a fan to assist in providing air flow across the condenser. Note that while fans help provide additional air-flow, they only run when the compressor is running.
The thermostat is a small wire that detects the temperature inside the fridge cabinet. There are 2 types of thermostats, manual and digital. A manual thermostat provides a very rough range of cooling and they are usually set on a scale from 1 to 5 or 1 to 10. A digital thermostat on the other hand will detect the exact temperature inside the fridge to the closest 1ºc.
You will use your control panel to set your desired fridge temperature. The control panel will monitor the actual temperature inside the fridge and will tell the compressor when to start and when to stop. We always recommend looking for a simple and easy to use control panel with a digital display.
We consider ventilation the holy grail of good fridge design. No matter how powerful the compressor, how thick the insulation or how big the evaporator is, without enough ventilation, the heat from your fridge cabinet has nowhere to go. This leads to longer compressor running times, more power use, slower cooling and overall poor performance from your fridge.
There are generally 2 types of ventilated portable fridges on the market. Side vent only, and Sides + Top + Bottom venting.
1. Side Vent Only
With side only venting, the fan forces hot air out of the compressor compartment horizontally. This is fine when the fan is running, but when it cycles off, the heat rises and is trapped inside the compressor compartment with nowhere to go. This leads to increased running times, slower cooling, poorer cooling ability in hot weather and overall places more stress on your compressor as it doesn't get time to recover between cycles.
Here's an image of 2 different side venting portable fridges:
Fridge No.1 has a small amount of vents in the front side. This manufacturer has even gone to the trouble of making false vents on the end of the fridge, to make it look like it has more ventilation than it does.
Fridge No.2 has a much better ventilation design. Not only does it have side and end vents, the vents cover a much taller area, continuing well above the height of the compressor and condenser. This helps the hot air escape from the top vents and allows cooler air to be drawn in the lower vents.
2. Top, Bottom and Side Vent
Compressor compartments with top, bottom and side vents are the ultimate. They work with the natural thermal dynamics to efficiently release heat between compressor cycles, even when the fan is not running. The hot air naturally rises drawing cooler air in through the bottom of the compressor compartment at all times. This greatly reduces running times as it allows the condenser and compressor (which also gets very hot) to release heat into the atmosphere 100% of the time. We strongly recommend looking at fridges with the maximum ventilation.
Here's a photo of a fridge showing ventilation on the side, top, and end. The second photo is of the bottom of the compressor compartment, where you can clearly see the vents right underneath the compressor.
Generally when it comes to portable fridges, you will get what you pay for. That being said, their are some exceptions to this rule. So read up, work out whats most important for you, and you will be well on the way to buying a fridge that suits your needs.
We hope this guide has been of benefit to you, as we are all very passionate about good, simple fridge design.
As always, if we can help you in any way, just let us know.