Ashre Tables and Cap tubes, how do they test compressors?

[born2dive9702]

I can not remember (it has been 25 years since I apprenticed in my teens, and I have since changed careers, so forgive me)

With the Ashre tables on a compressors specifications for a compressor, how do they test the system to determine the BTU rating.

What I mean is the following,

If I use the -25c on the (ASHARE LBP) that is the lowest temp on the chart, and then use a capillary tube for the -25'C temp, will this give me all the BTUs/ temp range on the table.

Or to say it another way will it if capped for -25'C Will the system reject everything from 15'c @5459 BTU's on the table down through the -25'C @559 BTU's

OR

Does each temp/BTU rating on the table have its own cap tube diameter/ length?

1. Which scenario is correct the first or the second?

Thanks for your help every one
Brad

[pecmsg]

A lot has changed in that time frame.
Today we use the Compressor Performance Curve from the manufacturer

[Poodle Head Mikey]

Scenario 2.

The BTU capacity of the compressor is primarily determined by the suction pressure.

The suction pressure is primarily determined by the balance point of liquid refrigerant entering the evaporator, the heat load being applied to the evaporator, and the pumping capacity of the connected compressor

If you use a cap tube rated to flow a certain BTU capacity at a certain suction temperature - that is the capacity which will result. Assuming a total system of matching components.

Increasing the capacity of a certain compressor will require elevating the suction pressure. Elevating the suction pressure will decrease the pressure drop across the cap tube which will decrease the refrigerant flow rate through the cap tube.

What is your present career and why did you switch to it from refrigeration?

PHM
-------------

I can not remember (it has been 25 years since I apprenticed in my teens, and I have since changed careers, so forgive me)

With the Ashre tables on a compressors specifications for a compressor, how do they test the system to determine the BTU rating.

What I mean is the following,

If I use the -25c on the (ASHARE LBP) that is the lowest temp on the chart, and then use a capillary tube for the -25'C temp, will this give me all the BTUs/ temp range on the table.

Or to say it another way will it if capped for -25'C Will the system reject everything from 15'c @5459 BTU's on the table down through the -25'C @559 BTU's

OR

Does each temp/BTU rating on the table have its own cap tube diameter/ length?

1. Which scenario is correct the first or the second?

Thanks for your help every one
Brad

[born2dive9702]

Hello Poodle Head

Thank you for that information, Scenario 2 was my initial recollection but as I said it has been years and as PCMSG said a lot has changed.

I still dabble in refrigeration (mostly consumer freezers refrigerator repair for friends and relatives) But my career is in aeronautic design, (designing and building fixed winged drones for Scientific and conservation organizations like NOAAH and National parks to prevent poaching). Currently I am in Egypt and there is a blown freezer unit here at archeology camp, and I am the only one here that has any experience in refrigeration.

Thank you again
Brad

Scenario 2.

The BTU capacity of the compressor is primarily determined by the suction pressure.

The suction pressure is primarily determined by the balance point of liquid refrigerant entering the evaporator, the heat load being applied to the evaporator, and the pumping capacity of the connected compressor

If you use a cap tube rated to flow a certain BTU capacity at a certain suction temperature - that is the capacity which will result. Assuming a total system of matching components.

Increasing the capacity of a certain compressor will require elevating the suction pressure. Elevating the suction pressure will decrease the pressure drop across the cap tube which will decrease the refrigerant flow rate through the cap tube.

What is your present career and why did you switch to it from refrigeration?

PHM
-------------

[hvacker]

Egypt has refrigeration?? Just kidding...
Some of us have had the feeling of being all alone with a problem but you raised the bar.

[Poodle Head Mikey]

What is "blown" about the unit?

PHM
--------

Hello Poodle Head

Thank you for that information, Scenario 2 was my initial recollection but as I said it has been years and as PCMSG said a lot has changed.

I still dabble in refrigeration (mostly consumer freezers refrigerator repair for friends and relatives) But my career is in aeronautic design, (designing and building fixed winged drones for Scientific and conservation organizations like NOAAH and National parks to prevent poaching).

Currently I am in Egypt and there is a blown freezer unit here at archeology camp,

and I am the only one here that has any experience in refrigeration.

Thank you again
Brad

[born2dive9702]

The compressor (Russian built) I have replaced with a SC15G 220v 50/60hz compressor, the cap tube was damaged and the filter was junked.

I am also trying to figure out what Evap temp I should be running, the Perfect system says I should be at 90'F ambient and 115'F condensing

but Danfoss ASHARE tables say in order to meet the BTU rating posted on the table I should be at 90'F ambient, and 130'F condensing

Now in a hot environment with an ambient temp of up to 115'F I believe that I should be setting the unit up for the 90/130 according to the ASHRE tables correct?



Thank you for your help Poodle Head Mike
Sincerely
Brad

What is "blown" about the unit?

PHM
--------

[icemeister]

I can not remember (it has been 25 years since I apprenticed in my teens, and I have since changed careers, so forgive me)

With the Ashre tables on a compressors specifications for a compressor, how do they test the system to determine the BTU rating.

What I mean is the following,

If I use the -25c on the (ASHARE LBP) that is the lowest temp on the chart, and then use a capillary tube for the -25'C temp, will this give me all the BTUs/ temp range on the table.

Or to say it another way will it if capped for -25'C Will the system reject everything from 15'c @5459 BTU's on the table down through the -25'C @559 BTU's

OR

Does each temp/BTU rating on the table have its own cap tube diameter/ length?

1. Which scenario is correct the first or the second?

Thanks for your help every one
Brad

What you're looking for I believe is not how compressors are tested, but how they are rated. For any decent set of published compressor capacity data there should be a footnote somewhere which details the standard conditions used for those ratings. Nominal capacities will be rated at a standard evaporator temperature of -10 Deg F low temperature, +20 Deg F for commercial temp and +45 Def for high temp. The condensing temperatures, amount of subcooling, return gas temperature, etc, are usually designated by local conventional standards like ARI, ASHRAE or some Euro standard set of conditions.

The important point here for your purposes, is when comparing the capacity of two compressors, just be sure each is rated at the same set of conditions or you could be way off the mark.

[born2dive9702]

Hello Poodle Head Mike and IceMeister

Danfoss stated that for this compressor(sc15g 220v 50/60hz) to reach the BTU ratings, I MUST run a condensing temp of 130'F

Now from what I understand for the different environments the condensing temps are as follows

Tc = condensing temperature
Ta = ambient temperature
te= evaporating temperature
tei = air inlet to the evaporator

TDc = Tc - Ta
TDe = tei - te

For air cooled condensers :
Hot climates ------- TDc = 6 to 8°C
Normal climates ------ TDc = 8 to 10 °C
cold climates ---------- TDc = 12 to 15 °C

From what I understand, is that the last person had used a 115' condenser temp, but due to the hot environment, it was unable to remove the excess heat and this is what caused the unit to blow.

So what I am trying to figure out is what data should I be looking for.

If the Ambient temp is 115'f +15'f for condensing temp so this should be at the 130'F if I am not mistaken.
but this is for cold climate as I remember.

So if I am not mistaken, if I am looking at a 130'F for a hot environment, I should be running at 122'F 130-8=122 and this should be a high side pressure of 171psig, Would this be correct or should I be seeking a P/T of 198.7 PSIG

Also what should be the measured temp be at the condenser should it be at 122+85= 207'F or should it be at 130+85'F =215'F?

Please let me know

Sincerely
Brad

What you're looking for I believe is not how compressors are tested, but how they are rated. For any decent set of published compressor capacity data there should be a footnote somewhere which details the standard conditions used for those ratings. Nominal capacities will be rated at a standard evaporator temperature of -10 Deg F low temperature, +20 Deg F for commercial temp and +45 Def for high temp. The condensing temperatures, amount of subcooling, return gas temperature, etc, are usually designated by local conventional standards like ARI, ASHRAE or some Euro standard set of conditions.

The important point here for your purposes, is when comparing the capacity of two compressors, just be sure each is rated at the same set of conditions or you could be way off the mark.

[pecmsg]

Hello Poodle Head Mike and IceMeister

Danfoss stated that for this compressor(sc15g 220v 50/60hz) to reach the BTU ratings, I MUST run a condensing temp of 130'F

Now from what I understand for the different environments the condensing temps are as follows

Tc = condensing temperature
Ta = ambient temperature
te= evaporating temperature
tei = air inlet to the evaporator

TDc = Tc - Ta
TDe = tei - te

For air cooled condensers :
Hot climates ------- TDc = 6 to 8°C
Normal climates ------ TDc = 8 to 10 °C
cold climates ---------- TDc = 12 to 15 °C

From what I understand, is that the last person had used a 115' condenser temp, but due to the hot environment, it was unable to remove the excess heat and this is what caused the unit to blow.

So what I am trying to figure out is what data should I be looking for.

If the Ambient temp is 115'f +15'f for condensing temp so this should be at the 130'F if I am not mistaken.
but this is for cold climate as I remember.

So if I am not mistaken, if I am looking at a 130'F for a hot environment, I should be running at 122'F 130-8=122 and this should be a high side pressure of 171psig, Would this be correct or should I be seeking a P/T of 198.7 PSIG

Also what should be the measured temp be at the condenser should it be at 122+85= 207'F or should it be at 130+85'F =215'F?

Please let me know

Sincerely
Brad

Too High of a SH at the compressor and the discharge temperature goes up baking the oil.
Too low of a SH at the compressor and you chance slugging liquid.
That's why Ice stated 20 - 40°f SH at the pump @ design operating temp. With a cap tube you can add or remove refrigerant to adjust.

We try and keep the discharge temp below 225°F I like it below 200° my self.

There's a lot of things that can and do effect the life of a compressor.

[born2dive9702]

Hello Pecmsg

I refer you to the photo of the "perfect system" I posted, it states that the design temp is for 200'f with a 85'F super heat but this is set up for a 90'F ambient with a 115'F condensing temp

What I am looking for is the numbers for a 115'F ambient with a 130'F condensing temp to meet the ASHRE numbers

I am a visual learner (I like pictures and diagrams, LOL) Any help you could offer would be great.

Sincerely
Brad

Too High of a SH at the compressor and the discharge temperature goes up baking the oil.
Too low of a SH at the compressor and you chance slugging liquid.
That's why Ice stated 20 - 40°f SH at the pump @ design operating temp. With a cap tube you can add or remove refrigerant to adjust.

We try and keep the discharge temp below 225°F I like it below 200° my self.

There's a lot of things that can and do effect the life of a compressor.

[born2dive9702]

design operating temp.

What is the design operating temp for a Dan Foss SC15g 220v 50/60 hz compressor? I can only find the maximum condensing temp of 140'F (130'F Ideal as per the ASHRE table and test results) and a maximum coil winding of 257'F

So what would the data look like for a hot environment?

Please let me know and thank you

Sincerely
Brad

[pecmsg]

Fig 2 shows 30°f SH at the pump!

[born2dive9702]

Hello Pecmsg

Just to check that we are on the same page can you show me where you found the 30'F SH I am on the ASHRE data I am either blind or have forgotten something from years back

Thanks
Brad

[pecmsg]

The compressor (Russian built) I have replaced with a SC15G 220v 50/60hz compressor, the cap tube was damaged and the filter was junked.

I am also trying to figure out what Evap temp I should be running, the Perfect system says I should be at 90'F ambient and 115'F condensing

but Danfoss ASHARE tables say in order to meet the BTU rating posted on the table I should be at 90'F ambient, and 130'F condensing

Now in a hot environment with an ambient temp of up to 115'F I believe that I should be setting the unit up for the 90/130 according to the ASHRE tables correct?



Thank you for your help Poodle Head Mike
Sincerely
Brad

Copeland, Tecumseh both Recommend 20 - 40° SH on the suction line 6" before the compressor. I believe the other manufactures are in the same range. I know of no compressor that wants 80°.

[born2dive9702]

If using the liquid temp of 90 and the condensing temp of 130 would the SH not be 40?

Fig 2 shows 30°f SH at the pump!

[Poodle Head Mikey]

You are looking at the wrong things / not understanding what you are looking at.

Danfoss did not say this: "Danfoss stated that for this compressor(sc15g 220v 50/60hz) to reach the BTU ratings, I MUST run a condensing temp of 130'F

Or if they did, it would certainly be the first time I have ever heard it. <g>

BTW: This project is just a domestic refrigerator type thing? Something that someone would have in their residential kitchen? Right?

What Danfoss did say was that the rated BTU capacity cannot be achieved unless the condensing temperature is 130º or less. 130º is the maximum condensing temperature at which the compressor will pump the rated capacity. The condensing temperature can certainly be Less - and it would be better if it was. <g>

Stop trying to get complicated here. Depending on the kind / style of condenser the condensing temperature will be about 20º higher than the ambient. So buy a compressor which will operate properly at that point: maximum ambient temperature plus about 20º and it will be fine.

Also: the suction pressure / temperature will want to be at about the desired box temperature. For a kitchen refrigerator this is about -10º F. - assuming a freezer portion in this unit.

Wait; I forget already - do you know the BTU capacity of the original compressor?

PHM
--------------

Hello Poodle Head Mike and IceMeister

Danfoss stated that for this compressor(sc15g 220v 50/60hz) to reach the BTU ratings, I MUST run a condensing temp of 130'F

Now from what I understand for the different environments the condensing temps are as follows

Tc = condensing temperature
Ta = ambient temperature
te= evaporating temperature
tei = air inlet to the evaporator

TDc = Tc - Ta
TDe = tei - te

For air cooled condensers :
Hot climates ------- TDc = 6 to 8°C
Normal climates ------ TDc = 8 to 10 °C
cold climates ---------- TDc = 12 to 15 °C

From what I understand, is that the last person had used a 115' condenser temp, but due to the hot environment, it was unable to remove the excess heat and this is what caused the unit to blow.

So what I am trying to figure out is what data should I be looking for.

If the Ambient temp is 115'f +15'f for condensing temp so this should be at the 130'F if I am not mistaken.
but this is for cold climate as I remember.

So if I am not mistaken, if I am looking at a 130'F for a hot environment, I should be running at 122'F 130-8=122 and this should be a high side pressure of 171psig, Would this be correct or should I be seeking a P/T of 198.7 PSIG

Also what should be the measured temp be at the condenser should it be at 122+85= 207'F or should it be at 130+85'F =215'F?

Please let me know

Sincerely
Brad

[Poodle Head Mikey]

From those two numbers there is no way to say what the superheat is.

The sub cooling would be 40º however.

But anyway; this all has pretty much nothing to do with what I perceive your goal to be - making this broken refrigerator work again.

PHM
---------------

If using the liquid temp of 90 and the condensing temp of 130 would the SH not be 40?