I cut my fridge power by 75%. Really. No joke, no trick, no compromise.

[jhulmer]

Originally Posted by patprice

Hello jen1722terry
I have a question please and apologies to all as slightly off topic.
It is my intention to drill and pump in closed cell foam to fill the void between the two walls.
But! I am concerned the pressure of the expanding foam may implode my FG box liner?
Should I position some temporary wooden structs in the box to prevent implosion?
How many holes did you make for the foam intrusion?
Did you do the job sort of slowly or quickly. Too slow I guess would prevent further ingress of foam?
I am in Tasmania but in a week or two will finally get to Greece to sail again on our Bavaria 42 after 21/2 years.
Which raises another issue. I wonder if the fridge has enjoyed being unused for all that time?
Any comments please.

This is how I re-insulated my fridge/freezer -

https://www.cruisersforum.com/forums...ay-204423.html

[Bbolino]

A thermostatic expansion valve doesn't control the freezer (or whatever it feeds) temperature. And it doesn't have a temperature setting. It has a superheat setting which is intended to protect the compressor from liquid refrigerant (which it wont pump). The difference between a capillary tube expansion device and an expansion valve is that the expansion valve is able to control refrigerant flow over a much wider variation of operating conditions than a capillary tube metering device. The capillary tube device relies on a relatively stable set of operating conditions and a critical refrigerant charge (the charge quantity is crucial for proper operation).

In any refrigeration system, the thermostatic expansion valve is generally the last thing you ever want to adjust

A freezer/refrigerator that runs 24 hours a day has something else wrong with it

And it is a good idea to keep something in a refrigerator - it provides “thermal inertia” that stabilizes operation. The amount of time it runs is load dependent which is totally driven by thermal loss through the casing and door seals, the frequency and duration of door openings, and the addition of warm food.

Proper frozen food storage would be at 0 deg F. Not all small refrigerator/freezers are designed for 0 deg operation. Check the specs on yours

[moonmist]

sailingharry A call to Cleave at Sea Frost (he's been putting these together for 30 years) should help you sort out the various components in your system. Call him and let us know what he recommends.

[Matt Johnson]

Originally Posted by patprice

Hello jen1722terry
I have a question please and apologies to all as slightly off topic.
It is my intention to drill and pump in closed cell foam to fill the void between the two walls.
But! I am concerned the pressure of the expanding foam may implode my FG box liner?
Should I position some temporary wooden structs in the box to prevent implosion?
How many holes did you make for the foam intrusion?
Did you do the job sort of slowly or quickly. Too slow I guess would prevent further ingress of foam?
I am in Tasmania but in a week or two will finally get to Greece to sail again on our Bavaria 42 after 21/2 years.
Which raises another issue. I wonder if the fridge has enjoyed being unused for all that time?
Any comments please.

We did this with Slow Rise closed cell spray foam with good results. The slow rise has lower pressure than the normal stuff.

Edit - Here is an old blog post on the subject (which seems to have issue from a website update) https://www.mjsailing.com/projects/r...on-spray-foam/

[sailingharry]

Originally Posted by Bbolino

A thermostatic expansion valve doesn't control the freezer (or whatever it feeds) temperature. And it doesn't have a temperature setting. It has a superheat setting which is intended to protect the compressor from liquid refrigerant (which it wont pump). The difference between a capillary tube expansion device and an expansion valve is that the expansion valve is able to control refrigerant flow over a much wider variation of operating conditions than a capillary tube metering device. The capillary tube device relies on a relatively stable set of operating conditions and a critical refrigerant charge (the charge quantity is crucial for proper operation).

In any refrigeration system, the thermostatic expansion valve is generally the last thing you ever want to adjust

A freezer/refrigerator that runs 24 hours a day has something else wrong with it

And it is a good idea to keep something in a refrigerator - it provides “thermal inertia” that stabilizes operation. The amount of time it runs is load dependent which is totally driven by thermal loss through the casing and door seals, the frequency and duration of door openings, and the addition of warm food.

Proper frozen food storage would be at 0 deg F. Not all small refrigerator/freezers are designed for 0 deg operation. Check the specs on yours

Some facts. I'll not try and draw conclusions from them -- I'll leave that to you.
* A TXV has a temperature bulb that is placed on the inlet to the cold plate -- it senses and responds to temperature (hence, the "Thermostatic" in the name)
* My freezer did run 24/7.
* The low side pressure (regulated by the TXV) was around 15PSIG. The boiling point of R134A is 15F as shown here:https://www.igasusa.com/pt-charts/R134A-PT-Chart.pdf
* As I adjusted the TXV, the pressure changed.
* I stopped with a pressure of around 5 (actually, I can't read that accurately -- it's just over 0). The boiling point at 5PSIG is around -5F.
* With the new TXV setting, and the T-Stat shorted (constant run), my freezer box is about -2F and the cold plates are frosted for about 90% (the last 10% not frosted).
* With the T-Stat re-enabled (same setting, 10F on the cold plate), it was running about 25% duty cycle and maintaining temps around 12-13.
* With the T-Stat set up to about 13, I'm holding at around 17F and a 25% duty cycle. We'll tweak the final setting come summer.
* We can get 0F now. But we prefer temps closer to 15 -- softer ice cream and lower running costs (heat loss is directly proportional to the temp delta across the insulation -- not counting gasket losses). But, yes, the food experts will want to see sub-zero temps.



I'm open to suggestions on what is wrong with my system as it currently is operating -- or what was wrong before I adjusted the TXV.



Oh -- one other detail. The clue to look at the TXV was from Nate Horton. He's Clive's son.

[RaymondR]

"A TXV has a temperature bulb that is placed on the inlet to the cold plate -- it senses and responds to temperature (hence, the "Thermostatic" in the name)"

Whilst the TXV valve uses thermostatic principles to operate the valve it is fairly strictly a flow control device. It controls the flow into the evaporator so that the maximum volume of liquid refrigerant can be maintained in the evaporator to maximize heat sinking whilst ensuring that liquid refrigerant will not be allowed to overflow the evaporator and find it's way back to the compressor.

[Bowdrie]

The sensing bulb of the TXV goes on the outlet tube of the evaporator.

[sailorboy1]

Originally Posted by sailingharry

* With the T-Stat re-enabled (same setting, 10F on the cold plate), it was running about 25% duty cycle and maintaining temps around 12-13.
* With the T-Stat set up to about 13, I'm holding at around 17F and a 25% duty cycle. We'll tweak the final setting come summer.

The temperature setting makes a HUGE difference is power use I have found. And the change to make big power savings isn't that much. At a setting of 13F my freezer uses a lot less that if I set it to 10F. It hasn't even seemed the problem has anything to do with insulation. Inside temp of the boat of course greatly effects the cycle time because the system cycles back on sooner. But the thing I noticed is that since I have digital thermostats I can watch the temp change and as it gets colder you can really see the drop slow down.

Currently I have my freezer set to 15F. This is a lot more than what they said for food safety. But the thermostats on boat system till to be next to a wall in an upper corner of the box. That is the warmest spot and yes things on the top aren't as solid as the lower and you can plan around this.

[Quebramar]

SB, thanks for your insights. I’m planning on putting an electronic thermometer also, will follow the same approach as you did.

[flyingnut40]

Follow

[Bbolino]

A Thermostatic expansion valve is a flow regulating valve that responds to three pressures
1. The thermostatic bulb attached to the line leaving the evaporator
2. The pressure in the evaporator (which corresponds to a temperature)
3. A spring in the valve (which is what the adjustment moves)
The spring and evaporator pressure work to close the valve, the thermostatic bulb works to open it.
It is responsive to temperature because the sensing bulb is refrigerant charged to create a response to temperature change.
The purpose of the valve is to regulate the refrigerant flow into the evaporator to the amount that can evaporated under the operating conditions, preventing liquid refrigerant from entering the compressor
There are no circumstances or types of systems where the operating conditions would be set using the thermostatic expansion valve.
There many reasons why the system could be behaving as described and I cannot more than speculate on what they may be.
I would also ask if your sure its a thermostatic expansion valve? They are a little unusual on very small systems and when used are usually not adjustable

[NYSail]

Originally Posted by sailingharry

So I think I've commented in other threads about my fridge/freezer baseline consumption. I had been running about 160Ah/day, which is a lot of power. Since the freezer keeps the fridge cold, the fridge compressor almost never turns on. The compressor burns about 6A, and so 160Ah/day is about 24 hours of run time a day. It basically NEVER turns off. Worse, I only get the freezer down to about 20F. I think this is really not cold enough for hamburger, but the admiral thinks it is awesome for ice cream. Hmmmm.....


So I did some digging. The results are too good not to share!


WARNING -- ENGINEERING MUSINGS. PROCEED AT YOUR OWN RISK!



First, some engineering. In refrigeration, Pressure = Temperature. Lower temperatures result from lower pressures, higher pressures lead to higher temperatures. So refrigeration gauges actually have numbers for Bars, KPA, PSI -- and Temp. Really, same gauges. Keep this in mind.


Another detail. Cheaper systems (like a little dorm fridge, or even your car) use a capillary tube as the control from the compressor high side to the fridge. This drops the pressure, and as indicated above, the temperature. Crude, but it works. Well, on my Sea Frost, it has a Thermal Expansion Valve, or TXV. It senses the temperature going into the cold box, and adjusts the flow (ie, pressure) to get the desired temperature. Keep this in mind.


Well, my box, as I got it at purchase, had the TXV set for about 15F. I was unaware of this. I set my thermostat at 10F. So, the TXV is controlling the freon going into the icebox at 15F, and it won't shut off the compressor until the box gets to 10F -- never gonna happen! The result is I run my compressor 24/7, sending 15F freon into the box, and the box holds nicely at 20F -- while burning 160Ah/day! Crap.


So I took the cap off the TXV. On my boat, it's a red vinyl tube, about 1" in diameter and 1" long. There is a nut under it. I turn it clockwise to drop the pressure/temperature. I tweaked it down until my gauges read -5F on the low side. and hot wired the thermostat to let it run non-stop. The next day, the box was -2F. YAAAY! Too cold, of course (remember the ice cream?), but if you CAN get to -2, you can CONTROL at 19 (actually, we have agreed on 15). So I fiddled with the thermostat (for some weird reason, boat fridges control cold plate temp, not fridge temp), and am currently holding around 18F.


The acid test. I sat on shore power to keep the batteries at 100%, and let the fridge run for a few days to stabilize. Then I turned off everything but the freezer (fridge off too), and turned off shore power and solar. After about 4 days, I had burned 155Ah. I used to burn that in a SINGLE DAY! The freezer is holding around 18F, the fridge at around 33F (actually too cold, but I'm not sure how to fix that since the compressor never runs). This is a daily burn of 40Ah for our freezer/fridge.


I do realize it's still early spring. Highs are in the 60s and 70s, lows in the 40's. I'm sure consumption will rise in warmer climates (but not for us -- we are going north! LOL). But the current results are just staggering!


If anyone finds this MORE than just interesting (ie, you think it applies to you), I can provide more details


Harry
Circe -- 1998 Saga 43 #19
Mill Creek, Annapolis

Haven’t got to reading everything in the thread and I will…… but right off the bat my freezer stays at 28f and freezes everything.

Btw I am no engineer….. just a happy sailor.

Greg

[FlyingScot]

Sea Frost doesn't use a real TXV. It's my main gripe with the system.
It's nothing more than a spring loaded relief valve. I spent A LOT of time messing with our system.

I found to increase system performance, mount a couple of 120mm fans on the outside of the box pulling air across the condensing cools. Make sure you don't exceed 1A total draw on the fans. Many are 0.2A or so.

Messing with that relief valve will affect flow and pressure.

Sea Frost calls it an "automatic expansion valve" and the factory setting is 0-2 evaporator pressure. Search for PDF named: Sea Frost BD Air Freezer

IIRC when adding a lot of air flow across the condensers my optimum setting was slightly different than the factory setting. Maybe 4-5.


I believe the bulb the mentioned is being confused with the thermstat bulb not a bulb for a TXV.

[sailingharry]

Originally Posted by FlyingScot

Sea Frost doesn't use a real TXV. It's my main gripe with the system.
It's nothing more than a spring loaded relief valve. I spent A LOT of time messing with our system.

Mine seems to be at least a little more than a spring loaded relief valve. It has incoming coolant, outgoing coolant -- and a third thin line that exits the box (I haven't followed it, but I'll be it is alongside the return line to the compressor).


I would assume that that thin line is measuring temperature -- and the valve is more than a relief valve.

[FlyingScot]

Originally Posted by sailingharry

Mine seems to be at least a little more than a spring loaded relief valve. It has incoming coolant, outgoing coolant -- and a third thin line that exits the box (I haven't followed it, but I'll be it is alongside the return line to the compressor).


I would assume that that thin line is measuring temperature -- and the valve is more than a relief valve.

The thin tubing (1/8") is the high pressure liquid line (before expansion valve). The fatter tube (5/16") is the low pressure liquid line (after expansion valve before evap plate).

Each evap plate has a line in and a line out. So if you see 3 lines, you need a 4th for the TXV sensing bulb. Real TXVs will have an additional line with a bulb attached to the outlet of evaporator plate, not leaving the box. This measures superheat (temp/pressure).

Sea Frost has other names for the valve, but they never use Thermal or TXV in the wording that I can find. They have a lot of documents on their website. Constant Pressure Valve is one of them you will see under the replacement parts section.
Please let us know what you find.