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Thread: Charge amount at altitude?
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20-10-2008, 10:45 PM #1
Charge amount at altitude?
I have a strange one here.....
If we charge a capillary tube system with 180g of R404a at sea level the charge amount is perfect. If we charge the exact same unit at altitude with 180g it appears to be under-gassed?
Help!
Andy
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20-10-2008, 10:55 PM #2
Re: Charge amount at altitude?
Welcome to the forum.
There was another thread relating to charging at altitude which may be of interest....
http://www.refrigeration-engineer.co...light=altitude
By what critirea are you saying that it appears undercharged, can you give us some readings?
Did you actually re-evacuate and reweigh in the charge at altitude or are things being done in a test chamber?Brian - Newton Abbot, Devon, UK
Retired March 2015
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20-10-2008, 11:05 PM #3
Re: Charge amount at altitude?
Basically we have a plant in Mexico (@6500ft ASL) and a plant in Dallas and the UK. We have a unit we have been producing in the UK for years that is a cap tube system. We weigh in 180g and the unit has frost on the suction return about 1" away from the compressor. This is what I would call a critical charge (I am no refrigeration expert by the way).
If we charge the unit in Mexico (on different scales) the unit looks undercharged and has no frost anywhere near the compressor. To gain the same result as a UK unit we need to use about 250g of refrigerant. If we then ship this unit to the UK it is overcharged and we have frost on the compressor.
Sorry if the explanation/terminology isn't perfect
Andy
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20-10-2008, 11:40 PM #4
Re: Charge amount at altitude?
Explanation not bad, thanks
What are the ambient temperatures in the different locations ?
If the dew point temperature changes then the pipes may or may not start freezing/frosting.Brian - Newton Abbot, Devon, UK
Retired March 2015
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20-10-2008, 11:45 PM #5
Re: Charge amount at altitude?
We have a test lab in the uk and the ambient temp is both 24 deg C in both locations, humidity is virtually identical too. In Dallas we shipped a unit and again similar conditions and the unit worked perfectly with 180g, The only obvious difference is altitude.
We shipped some units back to the uk from Mexico and these we reclaimed the gas and got 230g to 240g. The guys here in Mexico had been critically charging the units and this is the amount it took.
I am puzzled!!
Andy
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20-10-2008, 11:46 PM #6
Re: Charge amount at altitude?
I should also say that this is a coiled well unit and 3/4 of the well has frost the last third does not unless I add more R404a.
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21-10-2008, 10:13 AM #7
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Re: Charge amount at altitude?
This is what I think about your problem.
You need to pressurize charging plant at sea level pressure of 1013 millibars to achieve simmilar density of air there and in, say, UK.
Because of thinner air in your altitude evaporator gets lower amount/density of air and therefore it have lower superheat (and heat absorption capacity) and subcooling (and heat rejection capacity) than at sea level. That is why you need more refrigerant at higher level to compensate for lower density of air.
If your products are for market at that high sea level then they should be calculated and charged for that air density.Last edited by nike123; 21-10-2008 at 10:21 AM.
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21-10-2008, 05:52 PM #8
Re: Charge amount at altitude?
That does make sense but would you expect the 6500ft altitude to give as much as 30% differential in the charge amount? I would have thought 10% but we are charging a unit that normally has 180g with 230g or more!
Andy
Thanks for the answer by the way
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21-10-2008, 06:07 PM #9
Re: Charge amount at altitude?
I'm thinking a comparison of data might reveal the differences.
Low side:
Evap air in temp
Evap air out temp
Saturated suction temp (SST) converted from pressure
Suction line temp at evap outlet
High side:
Cond air in temp
Cond air out temp
Saturated condensing temp (SCT) converted from pressure
Liquid line temp at receiver outlet
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21-10-2008, 06:14 PM #10
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Re: Charge amount at altitude?
I don't know. I am not designer of refrigeration equipment.
That was only my logical thinking when I consider different air density on different altitudes.
Inside the circuit, different altitudes cannot have any influence, because system is sealed from environment pressures.
P.S.
Do you have any difference in frequency and voltage on that locations?Last edited by nike123; 21-10-2008 at 06:16 PM.
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21-10-2008, 07:13 PM #11
Re: Charge amount at altitude?
There is one difference.....
The units are designed for 230VAC 50Hz and we run them here at 230VAC 60Hz.
This is a small 10cc single phase compressor.
Andy
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21-10-2008, 07:20 PM #12
Re: Charge amount at altitude?
Last edited by Gary; 21-10-2008 at 07:25 PM.
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21-10-2008, 07:35 PM #13
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Re: Charge amount at altitude?
OK, as Garry already said, that is what is your problem!
You cannot use same compressor, evaporator, condenser and same amount of refrigerant at different frequencies because mass flow of refrigerant is not same with different frequency. Imagine that as you have inverter compressor.
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21-10-2008, 07:35 PM #14
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21-10-2008, 08:06 PM #15
Re: Charge amount at altitude?
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21-10-2008, 08:41 PM #16
Re: Charge amount at altitude?
Yes, I thought we were running a genorator but I only found out today we run a transformer and don't alter the frequency! As we say in the UK - assumption is the mother of all f**k-ups!!
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21-10-2008, 08:52 PM #17
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22-10-2008, 10:13 PM #18
Re: Charge amount at altitude?
One thing though....
We ran a unit in Dallas at 208Vac @ 60Hz and this ran ok and the charge amount was correct. If we run the same machine here in Mexico at 230Vac @ 60Hz it works totally different! I wouldn't have thought dropping 10% on the voltage would make up for the 20% increase in frequency would it?
Andy
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27-10-2008, 07:47 PM #19
Re: Charge amount at altitude?
if a system is designed to run on certain specifics be aware if you change something on what makes it to go to work ,power or pressure,the whole outcome will change.remember we are working whit thermo dynamic fluid and gases.
Ice
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27-10-2008, 07:54 PM #20
Re: Charge amount at altitude?
have seen it on two units,one next to the other,working on the same power line. stand alone they worked perfectly,together yore worst nightmare. giff them each a power line of their one and problem solved.
we learn surprisingly each day,if we let it happen.
Ice
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27-10-2008, 08:22 PM #21
Re: Charge amount at altitude?
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