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Frikkie
28-02-2012, 10:08 PM
Hello to everyone, it's been long since I have been here and I see things look a little different. Maybe this is because I have a new computer screen which is wider, I'm not sure. It's good to catch up with the new threads and see some of the guys I recognise are still around and I would ask please for some advice.

I would like to get some information about the electrical consumption of commercial refrigerating units (glass door Coke type fridges), mainly what the difference in power consumption would be between a condensing unit that is clean and one where the condensor that is blocked.

I'm not a technical refrigeration person but I know the unit would run high head and be inefficient, I would like to know exactly how inefficient and how much more it would cost to run on the power bill.

Would a blocked unit have a lower power factor as well so would a person being billed in KVAR be more punished than someone paying by the Kilowatt?

Would the blocked condensor cost more in power if the supply was single phse or if it was 3-phase.

Are there any peer reviewed studies on this subject I could read? I'm interested in units between 1/3HP and 2HP.

I know there will be lots of unknown variables that will affect the results but I'm just looking for general information. The ***** type would be R12, 134A, or 22. The fridge temperature would be maybe set at 3 Celsius and the ambient climate would be between 15 and 45 Celsius and 85% humidity. When I am saying the condensor is blocked pleaseassume it's running in the zone just before any HP protection or Klixon would shut it down or just before the compressor damages the valves. I'm not sure what other pointers you would need to help with reply, I hope this enough.

Thank you in advance,

Frikkie.

Tesla
29-02-2012, 03:03 AM
Hi Frikkie
The best way to deal with this problem is measurement in the field as there would be many variables to consider (ambiant, refrigerant & condenser rejection rate etc.) then apply basic conditions and then compare with percentages.

Frikkie
29-02-2012, 07:21 AM
Hi Tesla,

Thank you for your reply. I agree that actually making the tests would be best but unfortunately I'm not able to do this. I was just hoping there may be some study or manufacturer information already available.

taz24
29-02-2012, 09:58 AM
.

Hello Frikkie.

Use the free software refrigeration utilities (cool pack)

http://www.ipu.dk/English/IPU-Manufacturing/Refrigeration-and-energy-technology/Downloads/CoolPack.aspx

I just did a quick calc based on 1 Kw with constant evap, superheat and subcooling temperatures.

Based on 1Kw with a condensing temp at 40 degC, power used would be 233w
Based on 1Kw with a condensing temp at 50 degC, power used would be 310w

So if you know some basics you could put the variables into the software and
it will give you some very realistic values in return.

All the best

taz

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Frikkie
29-02-2012, 04:21 PM
Thank you Taz24.

I like the idea of using the software, I have downloaded it and I will give it a try tonight. I am always amazed that software like this can be for no cost. I wonder sometimes what is the catch.

The 33% extra power consumption for just 10 degC higher condensing temperature is very high compared to what I expected. Can this be right? If the relationship is anywhere near linear that would mean 20degC difference would see nearly double the electrical energy consumed to run the same unit.

Thanks again for your suggestions, I'll make some calculations with the software although I think it might take some time for me to learn how it works.

The Viking
01-03-2012, 12:05 AM
Frikkie,
Unfortunately for users of refrigerating plant, and luckily for most of us I guess, it is a very steep and mostly linear graph...

BUT

The energy consumption for your system will only go up so far, pretty soon the energy consumption graph will flatten out. What have happened at that point is that the system is running flat out but is not able to cope with the load, the produce within the fridge will start to warm up.

:cool:

.