CoolSaver, really smart fridge control?

Ben Ellison

Ben Ellison

Panbo editor, publisher & chief bottlewasher from 4/2005 until 8/2018, and now pleased to have Ben Stein as a very able publisher, webmaster, and editing colleague. Please don't regard him as an "expert"; he's getting quite old and thinks that "fadiddling fumble-putz" is a more accurate description.

18 Responses

  1. Peter says:

    Oh let it be true. I would love to get a review with a before and after. I could even donate an in line temp gauge so you could take the water temp (assuming you have a water cooled refrigerator).

  2. Henning says:

    As an alternative:
    Indel Marine/Isotherm offer an “ASU” range of fridge (not freezer) units that charge up a holding plate while excess power is available from a battery charging source. To my knowledge, it even behaves differently between 13,6 volt float charge and 14.something bulk charge.
    I have used one of these for 4 seasons for a large box (I think I would fit in with the lid closed but I haven’t tried). When I installed the unit, replacing an older air cooled unit, I also completely re-insulated the box with vacuum panels. The Isotherm unit I use is sized for a box only 2/3 the size of mine but because of the much better then average insulation, it is actually oversized. This leads to the food freezing when I use the “charge sense” feature and the holding plate gets frozen. So I currently use it with the charge-sense off and the holding plate not freezing. I think I will experiment with partly insulating the holding plate with thin PU-foam to reduce the cold-drain from the holding plate into the box (“rate of ingress of heat into the holding plate” probably being a more scientific term).
    I bought this unit with extended living aboard in tropical conditions in mind (which I have yet to experience). I don’t think I would recommend a holding plate for weekend use because it slows down initial cooling on Friday night und extends cooling beyond Sunday night and in that way is a waste of energy.
    Isotherm’s ASU (“automatic start up”) is available only with a holding plate, however.
    And are you sure that using a charging-voltage-controlled compressor without a holding plate is a good idea? If you use the fridge for food and not just beer, then the temperature should not vary a lot, I think. Though you could use 50 beer cans as a kind of replacement holding plate, I guess…
    An a seawater cooled refrigerator is great until you find the intake filter plugged by jellyfish!

  3. Taniwha says:

    I have a couple of comments/thoughts on this topic:
    1) If you’re after temperature monitoring and reporting, Maretron’s TMP100 N2K module allows you to put it on the N2K buss, and thus be available at any display (or one dedicated to your fridge/freezer). Because you can have multiple probes, and multiple TMP100’s, you can effectively monitor all of your boxes by just putting a temp probe in each one, which really offsets the cost of multiple box monitors (it looks to me like you would need 1 Coolsaver device for every compressor). Another great thing about putting the info on the N2K buss is that you can raise an alarm on any display if the temp goes outside your preset limits – so you can see that from the cockpit or where-ever. Also, with Maretron’s N2K view you can log the data on a graph on your computer to not only see min/max, but see the temp profile, which is very useful to maximise efficiency. No, it doesn’t control the compressors, but it gives excellent monitoring.
    2) This type of compressor control is actually already provided by a number of manufacturers e.g. Isotherm with their ASU unit for holding plates, and Frigoboat with their SSC (Smart Speed Controller) for evaporation plates. In fact the Frigoboat SSC can be used with most Danfoss compressor systems also, whether they’re Frigoboat or not, and costs $149. These systems control both the compressor speed and box the temperature, and are well tested in the field.
    3) The info on the Coolsaver website is very sparse. They don’t explain how it works in any detail, and seem to imply that the system in some way magically uses the food to store extra cold when there is more energy available. Well, in my opinion, either they’re really bad at explaining themselves, or they’re just trying to sell marketing phrases. All fridges use the contents to store cold; it is well known that the fuller a fridge is the more efficient it is. Also, they imply that they increase the fridge temp when it is only on battery power to “save” energy (if I interpreted their words correctly). This could be dangerous – one of the key things that some foods need is a stable temperature (especially meats).
    From my perspective, they aren’t offering anything new, and they don’t offer enough info to interpret it properly. However, the mock-up unit does look nice.

  4. David says:

    $360 for the Charge Sense version vs $180 without. Geez, the only difference being one remote voltage sensor and some software. A couple of extra 6V golf cart batteries would do as well.

  5. Ben Ellison Ben Ellison says:

    CoolSaver answer to my question “can the user set the low and high temp range that Charge Sense uses?”
    The answer is yes. A detailed explanation follows
    The controller uses a setting called hysteresis for temperature control which is the same value whether it senses charging or not. Hysteresis is how many degrees the temperature is allowed to rise above the set point before it turns on the compressor. The cooling then brings the temperature down to the set point and the compressor is turned off. Small hysteresis means tight temperature control but more cycling of the compressor.
    Unlike another product, CoolSaver does not simply increase the hysteresis when there is no charging. CoolSaver has a setting called in the refrigeration industry a “set back”. This setting shifts the set point by the set back amount. The hysteresis remains the same ensuring that your temperature range around the set point is constant.
    So for example, you can set CoolSaver for a set point of 20 deg F with a 5 degree hysteresis. The temperature will then range between 20 and 25 degrees. If the set back is 6 degrees, then when CoolSaver senses that there is no charging it will then control between 26 (20+6) degrees and 31 degrees (25+6) degrees. So energy savings are achieved by allowing the temperature to rise and also by slowing the compressor when it is actually running and there is no battery charging.
    Another advantage to the set back approach is the ability to set both high and low temperature alarms relative to the set point. A high alarm of 8 degrees above the set point will be at 28 degrees when charging and at 34 degrees when not charging in the example above. You also have the choice of having the alarms be absolute values.
    We are also working on a version with 2 separate personalities (sets of configuration settings) that can be switched based on the charge sense. This will provide even more flexibility as the set point, hysteresis, alarms and everything else can be different for each mode.

  6. Ben Ellison Ben Ellison says:

    From CoolSaver, for Taniwha:
    Answering your points.
    1.Maretron’s TMP100 is nice but costs $220+ and you need a NMEA 2000
    network and display device.
    You need a CoolSaver for each compressor. CoolSaver supports 2 probes
    so you could monitor a second temperature whether it is in the same
    cooler or another space or even your condenser temperature. If you
    monitor condenser temperature, you can use it to shut down the
    compressor if it gets too high.
    For simple temperature monitoring that uses low light for energy,
    checkout the Solar
    powered temperature monitor at
    CoolSaver has a serial port that supports the MODBUS RTU protocol.
    MODBUS is an industry standard protocol that is supported by hundreds
    of graphing and display software packages. Using one of these packages
    you are able to  configure, monitor for alarms, log and trend all the
    CoolSaver variables. If you want the MODBUS register mapping for
    CoolSaver, request it by email.
    Sorry no NMEA 2000 yet but it will come.
    2. ASU and SSC
    Based on published information the ASU controller only works with
    holding plate and Isotherm units.
    Also according to the published information, SSC is compressor speed
    control only and does not change the set point. It does one of the 2
    energy savings measures that CoolSaver does and does not have the
    digital full featured thermostat. Hence the difference in cost.
    So I must politely disagree with your general statement “These systems
    control both the compressor speed and box the temperature, and
    are well tested in the field.”
    3. You are correct that the website is sparse. We are working on
    providing more information.
    We do explain how it works which I will repeat here:
    When there is excess energy the compressor is run at full speed and a
    user selected low set point is applied to bring down the temperature.
    The user must ensure that the set point temperature selected will not
    damage produce.
    So a full fridge or adding freezer packs or water jugs helps.
    When running from batteries the set point is raised by an amount
    configured by the user. If the compressor needs to be run to maintain
    this set point, it is run at the lowest speed where it is most
    efficient. The user is responsible for setting these set points to
    ensure that food is kept at safe temperatures.
    There is no magic. The concepts are not new but I could not find
    anything that would do what CoolSaver does for my evaporator type Nova
    Kool unit, so I created CoolSaver.
    Jack Chadowitz

  7. Bob S says:

    The old tech way to accomplish much of these benefits but most importantly to keep refrigerators from wiping out your batteries was to simply run the refer power leads through a voltage sensitive relay that would allow the refer to only run when a charging voltage was present at your battery bank. The $20 don’t-have-to think-about-it solution . . .

  8. Dave says:

    SCAD Technologies ( also has their SensiStat controller that provides similar functionality and is available from Sailor’s Solutions ( I ran across this in a Practical Sailor writeup sometime back and have been considering replacing my current controllers with this one as my 12v system always seems to kick on right after I’ve shut down the engine or generator (it has a 6th sense for this). This is based on a Carel refrigeration controller.

  9. Ian says:

    Oh come on! The photo is identical to the standard Dixell controller which I am already using in my boat.
    With a relay (£2.20 and a resistor I can short out the sensor and ‘set’ the temperature reading 5 degrees lower when the engine is running.
    The shelf price for a Dixel round here is about $50.

  10. Ian says:

    Further to my earlier comment …..
    The Dixel XT121C does exactly this – out of the box. Cost is £70 and it runs off 12 or 24v.

  11. Peter says:

    I cruise on my sailboat for weeks and months at a time and it seems like my refrigerator has become self aware. It too waits until I drop the anchor in a quiet harbor after motoring for most of the day when my refrigerator kicks on. I have a low tech answer to this. I have a 60 minute timer switch that overrides the normal thermostat. I turn it on as I am approaching the harbor and get my refrigerator very cold. Also, I sometimes turn it on later in the day when the solar panels have charged the batteries and I have extra power.
    While this is a nice extra solution I would like to have a more automated solution. After reading more about the available smart thermostats I don’t know if they really answer my desires. They actually change the normal setting on the thermostat. What I really want is for my freezer to stay in a very small range close to the low setting. Say 1-2 degrees. My range is 12-18F. It typically takes .5 – .75 of an hour to get from the high to the low and 4-5 hours to get from low to high. When I have extra solar power or my alternator is running I would like to have the thermostat overridden to keep the system close or at the low temperature.
    The problem with lowering the low is it tends to freeze the stuff in my refrigerator. It tends to ruin produce, explode soda cans, etc.
    I guess what I really need is a second thermostat that senses the charging voltage and takes in a external relay(s) (one for normally open and one for normally closed) to override the thermostat already installed on the refrigerator. This would let me set a small range for when I have extra power.
    Just my 2 cents.

  12. Ian says:

    Turns out the standard Dixell controllers all do this. At the command of an external digital switch ( VSR ) the unit will switch from regulating to the normal setpoint to regulating to an offset setpoint. The offset, sense and timing of the switchover can all be programmed.

  13. Ben Ellison Ben Ellison says:

    Let’s be clear, Ian. The Dixell devices are designed to control/monitor systems based on temperature, humidity, or pressure. They don’t seem specifically meant for refrigeration, let alone marine refrigeration. It might be possible to get one to do most of what the CoolSaver claims to do, but would it be worth the effort? The instructions are not consumer friendly, let alone boater friendly.

  14. Jack says:

    The CoolSaver can do what you need. I would set the hysteresis (also known as deadband) to as tight or loose as you want. Probably 2 or 3 deg F. Then set the setback to the number of degrees by which you want to reduce the set point when you have excess energy. You can now control the minimum temperature which is better and safer than a timer overide. By adding cold bags or keeping the fridge full you increase your “coasting ability”.
    As you can set the alarms relative to the set point, they will “float” with the set point and be relevant in either mode.
    We will be coming out with a new model which allows switching between two separate sets of parameters depending on whether energy savings mode is active or not. This will be your equivalent of two controllers. A second hysteresis as well as other parameters will then be available.
    A new feature that has now been added is the ability to control using one thermistor, say in the freezer attached to the gas return, and display the space or refrigeration temperature.
    This avoids the common confusion where users think their space temperature is actually the much colder evaporator temperature.
    The user can choose which thermistor is displayed continuously and can also view the other temperature using the buttons.

  15. Jack says:

    The latest compressor control from Danfoss can be programmed with a resistor to shut down the compressor when the voltage gets below a set value. You can choose the voltage by choosing the resistor value. Its free!

  16. Jack says:

    CoolSaver is similar to the Sensistat. The folks at Scad designed the Sensistat for cold plate systems. It is based on the Carel which is user unfriendly. I believe they use hysteresis setting change instead of set point change for energy saving.

  17. Jack says:

    I looked up the xt121c. If you read and understand the instructions you will see that it is very different to CoolSaver. Its popular use is for heating and cooling operations.

  18. Jack says:

    Thanks for your comment. I have been working with Dixell and their controllers since 2004 in commercial systems. We OEM their hardware which in our opinion is better than Carel.
    Dixell do an excellent job but aim their products at specific European markets and have created amazing controllers which unfortunately often miss the needs of the US market. Their instructions as you say are not consumer or boater friendly.
    We take their excellent hardware and program it for the needs of our target customers creating products which are not available as Dixell products. We also add user friendly instructions suitable for the user.
    An example of this flexibility is the feature we recently added which is the ability to control with one thermistor and display the temperature with another. Very useful for evaporator controlled refrigerators.
    This came about when Gary, a refrigeration installer in Australia was kind enough to spend an hour on the phone with me telling me what he believes is needed for his customers. We appreciate guys like Gary who share their experience and help us improve our products.
    Another point I would like to share is that we add conformal coating to our electronics to add to their reliability when used in the marine environment.
    As always, feedback and ideas from you and folks who follow your blog are welcome.

Join the conversation

Your email address will not be published. Required fields are marked *