An interesting poor refrigeration performance question

[Richard Kollmann]

If the compressor is cycling say five times an hour and pulling 10-15 amps each time it may accumulate to a significant consumption of watt hours over a 24 hour period. What are the possible causes of this unit’s poor daily energy performance?

[StuM]

Depedns on what you conisder "significant" and "poor".


5 times an hour is 120 times a day.

Conservatively. assume 3 seconds going from locked rotor (LR) draw of say 200W (approx 15A) down to a normal draw of say 50W. Let's be conservative again and say the average over that 200W to 50W ramp down is 150W - or an extra of 100W.

That would be a total 360 seconds (1/10th of an hour) at an extra 100W.
So the extra consumption over 24 hours would be 100/10 = 10Wh or less than 1Ah @12V.

To answer your question about causes, the first thing I'd look at if I considered 1Ah per day a major prroblem would be the thermostat sensitivity.

[Richard Kollmann]

Originally Posted by StuM

Depedns on what you conisder "significant" and "poor".


5 times an hour is 120 times a day.

Conservatively. assume 3 seconds going from locked rotor (LR) draw of say 200W (approx 15A) down to a normal draw of say 50W. Let's be conservative again and say the average over that 200W to 50W ramp down is 150W - or an extra of 100W.

That would be a total 360 seconds (1/10th of an hour) at an extra 100W.
So the extra consumption over 24 hours would be 100/10 = 10Wh or less than 1Ah @12V.

To answer your question about causes, the first thing I'd look at if I considered 1Ah per day a major prroblem would be the thermostat sensitivity.

You are probably correct but why is compressor operating so in efficiently?

[OzeLouie]

Originally Posted by Richard Kollmann

If the compressor is cycling say five times an hour and pulling 10-15 amps each time it may accumulate to a significant consumption of watt hours over a 24 hour period. What are the possible causes of this unit’s poor daily energy performance?

Good question Richard but the answer is dependant upon many possibilities. But lets assume it's a well insulated fridge (+2 to +4C) cabinet operating in a moderate 30C environment. And assuming you are quoting for the old DOL type MDM (motor driver module) as the current 'soft start MDM's should not exceed run current rate while on start up.

As you suggest, five starts per hour is excessive, the result of poor engineering and easily avoided as that is simply a controller (thermostat) function.

The first thing is to ensure that the system uses a digital thermostat so that cut out (SET) temp and Cut in temp (SET plus HYS) are programmable and accurate, and temperature can be monitored.
Next locate the digital thermostat's sensor sealed inside a small container of water (or oil) and in the cabinet away from the evaporator. (Not on the evaporator!) That should reduce the start ups considerably and provide accurate product / cabinet temperature. Suggest SET to be at +1C and HYS at 4C as a starting range. (Alter SET colder or warmer as required.)

There are two main reasons why excessive start ups waste a lot of energy. The first is the energy used to actually get the motor / compressor up to speed each time but more importantly the refrigeration effect (heat pumping) is ineffective until the system has run long enough to lower the suction and increase head pressure to operating levels. This rate of loss is not calculatable with any accuracy therefore a test trial totalling daily consumption would most likely be the best way to compare.

[Richard Kollmann]

Sorry Louie all your theories are wrong. Maybe the answer will come from an experienced working Technician. Precise answer is normally going to be the solution hopefully saving boater time and money.

[OzeLouie]

Originally Posted by Richard Kollmann

Sorry Louie all your theories are wrong. Maybe the answer will come from an experienced working Technician. Precise answer is normally going to be the solution hopefully saving boater time and money.

So why did you start this thread Richard? If you know the answers, why ask the question? Is this your latest attempt to demean others and make yourself relevant?
Instead of your smart axxxxd response, why don't you explain what theories I proposed that are wrong?

Despite suspecting your typical 'game playing' with this thread, I responded correctly as many genuine members want answers to such questions and deserve correct answers.

Richard the CF is a space where we can assist boaters with fridge issues, not a space for failed refrigeration industry wannabes to vent their intense jealousy towards those who are successful.

[RaymondR]

I posted the following in answer to a post in the other thread we were abusing each other in. The question was how would one go about measuring the power wastage which occurs on compressor start up. I think it's a little more complex than just the power surge at power on aspect.

Functionally two things occur when a capillary tube flow regulated refrigeration circuit start up.

On The High Side (That part of the circuit between the compressor output and the flow metering device)

Since the capillary tube allows pressure equalization between the condenser and the evaporator liquid refrigerant may be present in both however because it is colder would more likely to be present in the evaporator.

Two things occur on compressor start up and the physical gas laws, particularly P1V1T1 = P2V2T2 come into play .

The compressor pumps refrigerant vapour from it's suction to it's discharge side. Consequently the pressure in the evaporator decreases and the liquid refrigerant starts to absorb heat and boil off.

Concurrently the pressure at the compressor discharge, and consequently in the condenser, increases until it reaches a pressure and temperature where the condenser can "waste" it's heat content and allow it to liquify. The liquid is then metered into the evaporator via the capillary tube.

Unfortunately capillary tubes are not an un-loader type valve which does not allow fluid through until a fixed pressure is achieved and as soon as there is a pressure differential between condenser and evaporator flow will occur and the compressor will have to "chase" this bleed off whilst trying to pressure up the condenser. Similarly in the evaporator boil off of refrigerant may occur before sufficient temperature difference has occurred to create a heat sink.

The system stability operating parameters are achieved when both heat rejection from the condenser heat exchanger and heat acceptance by the evaporator are stable however heat acceptance and refrigeration effect at the evaporator will probably begin to occur prior to stability being achieved.

From a power consumption viewpoint the matter is further complicated by power draw variations caused by the load on the compressor which is generally governed by the compressor speed and, since a hermetic compressor occupies a pressure vessel subjected to the compressors suction pressure, the differential pressure between suction and discharge.

Since, in the instance under discussion, we are interested in the electrical consumption we can start recording consumption data at the point in time when power is switched to the compressor motor. However, since in the subject instance we are only interested in the power consumption between switch on and the commencement of refrigerating effect at the evaporator a sensitive differential temperature control will be required to detect the stop point for power consumption recording.

[Uncle Bob]

Louie I am surprised that you responded, in my opinion this thread was started with the sole purpose of enabling the self gratification of one to sustain some sort of personal relevance. The demeaning comment I believe was designed to elicit a response where you refered to your experience and then another could jump in claiming advertising contrary to the forum rules. I really don't know why you bother.
A genuine thread such as this is of immence value to the members, and before I am catergrised as an appoligist for a certain refrigeration company, I will support and defend anyone that is obviously demeaned and targeted by those that are more interested in their own self gratification/relevance that anything else.

[Richard Kollmann]

Uncle Bob, OzeLouie has an excellent refrigeration design as confirmed by the recent satisfied customer after 20 years in operation.
Uncle Bob I took a statement from a member that believe was and could be correct and I used it as a question that could be discussed.You want honest discussion comments to be identified as ranker. Yes I and Louie have both served in industry so we qualify you want to promote personal confrontations.

This questionable system poor performances question was in tended to be taken seriously. There was a clue in the problem that prevented a good answer without asking one or two questions, asked and answered should come first. It is true I dislike it when any question asked on the forum you get a shotgun answer back of it could be. If you do not have an answer investigate then offer a practical solution.

[Turtle Blues]

aside; RK was the guru when I was still in short pants and r12 was state of the art so if he wants to be a curmudgeon that's ok by me.
Back to class; disregarding the energy usage part of the question the service start point is why is the compressor in an existing system suddenly short cycling.

So, if I get 2 questions; what are the system temps/pressures and what is the control?

[newhaul]

Originally Posted by Richard Kollmann

If the compressor is cycling say five times an hour and pulling 10-15 amps each time it may accumulate to a significant consumption of watt hours over a 24 hour period. What are the possible causes of this unit’s poor daily energy performance?

Honestly I would be looking at the insulation for degradation and or water saturation . Also would be considering what the condition of the lid/ door gasket is .

There is also the question of local conditions to be considered as well.

[Bill O]

Originally Posted by Richard Kollmann

If the compressor is cycling say five times an hour and pulling 10-15 amps each time it may accumulate to a significant consumption of watt hours over a 24 hour period. What are the possible causes of this unit’s poor daily energy performance?

Refrigerant overcharged and possible frozen lines outside of box back to compressor. Also possible oil clog in capillary heat exchanger.

[guyrj33]

Originally Posted by Richard Kollmann

If the compressor is cycling say five times an hour and pulling 10-15 amps each time it may accumulate to a significant consumption of watt hours over a 24 hour period. What are the possible causes of this unit’s poor daily energy performance?

Moderators - this post sounds like a classic troll.
Next the poster will be telling all how smart he is.

Please remove this thread.

[Sailshabby]

Originally Posted by Richard Kollmann

Sorry Louie all your theories are wrong.

So if I’m understanding this, you don’t know what the answer is but you know his are wrong. The gentleman took time to give you a well reasoned response (and further educating others, in the process), but you weren’t interested. Sign me up to the first to answer your next question…

[Bill O]

Originally Posted by guyrj33

Moderators - this post sounds like a classic troll.
Next the poster will be telling all how smart he is.

Please remove this thread.

What???
Richard is one the CF experts on refrigeration and poses questions like this from time to time to help people trouble shoot systems.