Fridge/Freezer Optimizer Smart thermostat replacement

This "Refrigerator optimizer" is more than just a thermostat.

Features

• Liquid Crystal Display with digital readout of the actual refrigerator temperature, target temperature, trend, voltage and status.
• Automatic boosts cooling effort and uses the refrigerator as a "cold bank" when a charge voltage is detected.
• Adaptive Energy Optimization by varying the RPM of the compressor.
• Temporarily pauses cooling when the voltage drops due to a heavy load.
• Switches beverage-only fridges off during the night or when the electricity is in short supply.
• Quick menu to select between program modes.
• Smart Fan Control, depending on evaporator temperature, and with configurable after run.
• Minimizes ice-buildup on the evaporator.
• Automatic de-icing mode.
• Temperature alarm when the temperature has exceeded a configured level.
• Logging of power consumption over the last 24 hours.
• Battery protection (shuts off below a configurable voltage).
• Fully configurable by an on screen menu with touch button interface.
• High precision temperature sensor(s).
• Configurable between degrees Celsius and Fahrenheit, 12 and 24V systems, Fridges and Freezers.
• Monitoring and diagnostics of BD-compressors
• Low energy consumption.
• Easy to install.
• See also my generic project backgrounds page for more information about the design philosophy.

Description

Let's talk a bit more about these features and how they work.

Auto boost

The auto boost feature uses more energy when it becomes available, and then uses less energy during the moments that less energy is available.

When the on board voltage exceeds a certain level, it indicates that a charge current is present. The refrigerator will then lower its target temperature, increase the RPM of the compressor, and uses the refrigerator as a "cold bank". When the charge current disappears, the refrigerator then needs less energy from the batteries for some time to maintain a sufficiently low temperature.

• For a beverage fridge you can set the maximum and minimum temperatures far apart (unless you want to have very cold beer drinks early morning), resulting in the fridge to shut off around sundown and to start up again somewhere in the late morning when the solar panels have increased the voltage high enough.
• For a standard fridge the energy saving is less dramatic but still a lot of energy can be saved, especially if a wide margin between allowable temperatures is set.
• For a freezer there is no lower limit, so they are ideal to store lots of cooling energy when free energy is available, and then to switch off for quite a long time until the temperature has climbed up to the upper allowable limit.

If your compressor has a connection box like this, it is a BD-compressor.

Adaptive Energy Optimization

Some 95% of all marine refrigerators use the so called BD-compressors from Secop (formerly Danfoss). A little known feature of these compressors is that it is possible to control their RPM (rotation speed). Almost no thermostats use this feature and just toggle the compressor on and off to maintain the set temperature. But this Refrigerator Optimizer varies the RPM of the compressor and tries to find the sweet spot where the desired temperature can be maintained with the lowest possible RPM. This has the following benefits:

• It saves some 15% of the energy compared to just on/off cycling.
• Faster cool down times, but with less "overshoot".
• Less icing on the evaporator because of a higher evaporator temperature.

Auto pause

The auto pause temporarily halts the compressor when the on board voltage drops due to a heavy load, such as an anchor winch, water cooker, induction stove, etc. This way more current is available to the heavy consumer and the battery load is kept smaller.

Quick menu

A quick menu allows you to instantly switch between Automatic mode, Boost mode, Eco mode, Defrost mode, or just switch the refrigerator off.

Smart Fan Control

Some evaporators are encased and have a fan to force air through.

Usually the condenser/compressor unit has a cooling fan (or water cooling pump). Sometimes, the evaporator (inside the refrigerator) has a fan too. The fans are normally wired in parallel with the compressor, so they turn on and off at the same moment the compressor turns on and off.

There is however a smarter way to control the fans: When the compressor starts, it takes some time for the condenser and compressor to warm up, until that time there is no need for the fans and any energy used to run them is wasted. The fan inside the fridge should not switch off together with the compressor, but should run a bit longer. This makes sure that the "cold" which is still inside the evaporator is not used to form an ice-layer but is distributed inside the refrigerator to further cool its content. Again the energy is used more wisely and it reduces the ice buildup on the evaporator.

Prevention/cure of ice buildup on the evaporator

The Adaptive Energy Optimization and Smart Fan Control both help to prevent ice buildup. In addition (Fridge mode only) there is a defrost mode that can be either manually or automatically activated. What it does is to wait for a moment when the temperature difference between the evaporator and fridge contents is low to begin with (such as after having switched from boost to normal mode) and it then keeps the fans running while the compressor remains off, until the evaporator temperature increases to just above the freezing point. Then it switches back to normal mode again.

Temperature alarm

When the temperature inside the refrigerator exceeds a configured temperature for more than 10 minutes, it will show an alarm, even if the temperature drops down to safe levels again afterwards. Especially in the case of freezers, it can alert you when, for some reason, the temperature has at some moment been too high for the food to remain safe.

Logging of energy consumption

The Refrigerator Optimizer is aware of the power profile of the BD-compressors and can, based on their RPM and evaporator temperature, closely approximate their power consumption. This power consumption is logged over a rolling 24 hour window, for the total and eco mode, and allows you to study the effect of different settings, environment temperatures, ice buildup, etc.

Battery protection

You can configure a minimum allowable voltage, to protect your batteries and/or to keep other equipment (GPS) running longer.

Monitoring and diagnostics of BD-compressors

The BD-compressor has a diagnostics output to help troubleshooting. The Refrigerator Optimizer monitors this output and signals any problem in clear text on the LCD. No more cumbersome and confusing LED diagnostics!

Configuration

All relevant information is not just only visible on the LCD, but also fully configurable by an on screen menu and touch button interface.

Easy to install

The Refrigerator Optimizer is easy to install in any panel, thanks to the flanges on its front panel. You have the choice between using double sided adhesive tape or glue on the rear of the flanges, or drill holes through the marked spots and either screw it with two (center holes) or four screws (corner holes) onto the panel.

All electrical connections are with marked screw terminals on the rear side.

Project background

For more information about the general design philosophy of my projects, please visit my Project Backgrounds page.

Ordering

The Refrigerator Optimizer can be bought as a completely assembled version, or as a kit.

The completely assembled version costs 147 USD, the kit version 122 USD. One temperature probe is included with the kit.

Ordering information will be available soon. If you are in a hurry, contact me.

Specifications

Voltage:	8-30V
Current:	<1mA with the compressor stopped and LCD in glow mode, <10mA with running compressor and LCD backlight fully on.
Temperature accuracy:	+/-0.5°C
Voltage accuracy w/o calibration:	+/-0.1V
Front panel dimensions:	110 x 68mm
Required panel cut out:	90 x 55mm
Compatibility:	Any fridge, but Adaptive Energy Optimization, logging, and compressor diagnostics are only available with the BD35, BD50 and BD80 compressors.

ZwerfCat Example

On ZwerfCat, one of our fridges is dedicated to beverages. In the morning we usually don't drink any beer cooled beverages so it is useless to use energy during the night to cool them. Actually, we only start to use cooled beverages in the afternoon. So, before we had the fridge optimizer, we turned off the "beverage fridge" at sundown, and turned it on again somewhere late morning when the solar panels were already generating a lot of power. This was giving the fridge enough time to cool our drinks to be ready early afternoon. Another observation was that our demand for cool beverages (not surprisingly) correlates with the amount of sunshine. The more sunshine, the more power the solar panels generate, and the earlier our drinks reach the target temperature. This whole process is now automated.

De-icing

We often had ice accumulation on the evaporator inside the fridge, even though we had the temperature of the fridge set above freezing temperature. What's going on?

• The interval (hysteresis) of the fridge is too low. The thermostat starts the fridge again before all the ice has melted.
• If you have fans inside the fridge, they stop together with the compressor, while they could be running for much more time to make sure that all the cold energy stored inside the evaporator is used to cool down the fridge and its ice layer has been melted off before the compressor fires up again.

After installation of these Refrigerator Optimizers, we use far less power from the batteries, yet have a higher comfort and less icing up of the evaporator.