SUPERHEAT: 8° F is wrong ?

[Acrisoft]

Hi

The carrier bus AC manual states "it uses a nonadjustable block valve with an 8° F superheat setting".

But 8° F is something as -13° C, which seems nosense for me.

I would like to know if there a mistake in the manual or how understand its equivalment in Celcius.


Moises

[monkey spanners]

There are two types of temperature, actual temperature and temperature difference.

With super heat we talk about temperature difference so 8F is about 4.5C meaning that the valve maintains a suction superheat approximately 8F (4.5C) warmer than the evaporating temperature.

Really temperature difference should be R for Rankine in the Fahrenheit scale, and K for Kelvin in the Celcius scale but i expect few in our industry would understand the relevance of an R or K in regards to temperature.

[The Viking]

Don't get me started on units of measurement again…

Well said (typed) Mr Spanners, sadly I can not add to your reputation.

[Magoo]

Well stated monkey spanners, totally agree.
A small amount of knowledge in the wrong hands can be a dangerous amount.

[moideen]

To convert to centigrade, divide the temperature difference in Fahrenheit by 1.8. ex:8F/1.8=4.5c

[question mark]

m like a same problem which i had too. i used hvac buddy app and just out of blue ,plugged the figures as below.
suction presure 60 psi = 1 deg celcius and suction line temp 10 . as per me i would have said 10-1 = 9 deg superheat.

but the app says actual superheat = -8.8 don't know how the figure became negative to start with and the 8.8 . how ? please help
target superheat = -8.8 due to my figures return wet temp 18 cel and outdoor dry temp 26 cel
please help i want to get it right.

[B G Scott]

As Moideen correctly states you cannot just convert a given quantity in TD (temperature difference) as you are not comparing a given mathematical quantity but an element of the equation.
To understand where Moideen got his 1.8 from you must appreciate the relationship between the two scales, F & C.

One degree F is 9/5 the value of C therefore the conversion will be 9/5 = 1.8 and the reverse if you are converting the other way C is 5/9 the value of F so 5/9 = 0.56.

So your 8F superheat will be 8 divided by 1.8 = 4.5 and 4.5C superheat will be 4.5 multiplied by 1.8= 8 or so if you round up the second decimal places.

Or to avoid any further confusion the same result will be found by dividing your 4.5 by 0.56 you are only dealing with simple ratios of one value to another

[aircon50]

The problem is with the way that the figures are notated. 8 degrees of superheat, or subcooling using Celsius,
should be written as 8Cº, not 8ºC! It is a temperature difference, not an indicated temperature.

[frank]

It is a temperature difference, not an indicated temperature.

Which is why for S.I. we normally use the Kelvin temperature scale when we refer to temperature difference, i.e. 4.5K of superheat

Not sure what is used instead of degrees F for Imperial measurements though

[passandscore]

Which is why for S.I. we normally use the Kelvin temperature scale when we refer to temperature difference, i.e. 4.5K of superheat

Not sure what is used instead of degrees F for Imperial measurements though

When dealing with the Imperial method we are expected to use degrees F for both actual temperature and temperature difference. Well, that's what the trade schools taught me anyways.