converting a calculation to Si

[marc5180]

I have just read a post from a few years back and have noticed this
"Most condensors operate at a close to estimated temperature of 30 degrees F over ambient.
So if we know what the ambient is and add 30 degrees F to it we can safely estimate,

Lets take a look at the suction pressure
similiar as above excecpt normal operating sytems have an average coil temp of 15 degrees f
below temp controlled area".

But if i were to convert these temps to DegC then 30F would be -1.1DegC
and 15f would be -9.44, surely this cant be right for si units?

[nike123]

You have two things when converting Fahrenheit to Si units.
First is actual temperature which is converted in Celsius degree and second is temperature interval converted in Kelvin

You need to distinguish in text what is what and corectly convert that.

Fahrenheit temperature is converted in Celsius degree by subtracting 32 from Fahrenheit temperature and than multiplied by 5/9.
Fahrenheit temperature interval is converted in Kelvin by multiplying Fahrenheit interval with only 5/9.

In your example:
30°F=30x5/9=16,6666666K
15°F=15x5/9=8,33333333K

For ambient temperature:

40°F=(40-32)x5/9=8x5/9=4,44444444°C

[marc5180]

ok so in si units, head pressure should be roughly ambient + what in DegC

and also suction pressure should be space temp - what in DegC?

Just as a rule of thumb.

Ah ok just noticed your edit so the head pressure should be 16Deg C and the sp 8DegC?

[nike123]

ok so in si units, head pressure should be roughly ambient + what in DegC

and also suction pressure should be space temp - what in DegC?

Just as a rule of thumb.

Ah ok just noticed your edit so the head pressure should be 16Deg C and the sp 8DegC?

Read again more carefully. It is once more edited.

[nike123]

If you have condenser air in temperature of 30°C than 30°F over ambient would be 46,66666°C
If you have air in temperature at evaporator of -18°C than 15°F below ambient would be -26,3°C.

[marc5180]

Now you've got me, where have you got 46.6 and 26.3 from? Im confues because you are using both °C and °F.

[nike123]

Now you've got me, where have you got 46.6 and 26.3 from? Im confues because you are using both °C and °F.

You have two things when converting Fahrenheit to Si units.
First is actual temperature which is converted in Celsius degree and second is temperature interval converted in Kelvin

You need to distinguish in text what is what and corectly convert that.

Fahrenheit temperature is converted in Celsius degree by subtracting 32 from Fahrenheit temperature and than multiplied by 5/9.
Fahrenheit temperature interval is converted in Kelvin by multiplying Fahrenheit interval with only 5/9.

In your example:
30°F=30x5/9=16,6666666K
15°F=15x5/9=8,33333333K

For ambient temperature:

40°F=(40-32)x5/9=8x5/9=4,44444444°C

..........................

[marc5180]

Ok so for example if i had a condensor air in of 30°C then (40°F for example only) over ambient would be 52.22°C.

[marc5180]

I hoped there would be a simple way to check like the way the quote sounded

Discharge pressure should = say 15°C plus the ambient
Suction pressure should = say 10°C plus ambient (RA).

[nike123]

I hoped there would be a simple way to check like the way the quote sounded

Discharge pressure should = say 15°C plus the ambient
Suction pressure should = say 10°C plus ambient (RA).

http://www.refrigeration-engineer.co...75&postcount=5

All values here should be in Kelvins, but amount is same.

[nike123]

Ok so for example if i had a condensor air in of 30°C then (40°F for example only) over ambient would be 52.22°C.

Yes, you got it.