1956 factory air BTU rating

[Ron Draper]

Hi,
I was interested in how you calculate the BTU rating of the 1956 factory air condenser and evaporator.

I know that it is based on a lot of variables which include air volume, temperature, fin material (copper, aluminum, steel) and pressure.

I was looking for a basic rule of thumb calculation such as the following:

condenser or evaporator fin area (number of fins per inch) minus the area of the tubing ((length times area of the tubing) times the number of tubes) times some factor like the number of square inches to dissipate 1 BTU (for steel, copper, and aluminum) at some given temperature.  

I have no idea as to what was used as design guides the air volume, pressure, and temperature and copper tubing with aluminum fins.

This condenser is made of steel tubing and steel fins and was originally painted with some type of thin black paint.

I thank you for having takening the time to read this message and hopefully replying with some type of answer or person that I could send to as an email.

[Geoff Newcombe #4719]

Try putting calculate BTUs (without the quotation marks) in your search engine, all kinds of sites come up.  You might also find the link below interesting, it is a pdf file and takes a little time to download but interesting reading ........

http://www.ashrae.org/content/ASHRAE/ASHRAE/ArticleAltFormat/2003627102420_326.pdf TARGET=_blank>http://www.ashrae.org/content/ASHRAE/ASHRAE/ArticleAltFormat/2003627102420_326.pdf

[Ron Draper]

Thank you - An very information filled with nuggets of information  like the water dripping from the roof ducts - I do not know of any other article that touches on this problem.

Ron

[Chris Arneson #22170]

Ron,

You are absolutely right about there being lots a variables involved to calculate [estimate] the capacity of your AC system.  But, you are on the right track with all the attributes mentioned above.  The reality is, there is no rule of thumb, or at least not one simple enough to answer the question even given the information we do have.  Lots of laboratory work would be required to even get to the rule of thumb point of a calculation.  It would be far easier to simply measure the performance, which was likely done by GM at one time but something not generally published.

If you had some time measuring the temperature change across the evaporator along with the volume of air being moved by the blow will give an answer.  This would have to be repeated for different temperature humidity conditions both [condensing and evaporating] in order to give the entire picture.

Im not sure what interest is with the information but the company I work for sell a AC system for Class 8 tractors here is the states, and they have a capacity of 13,000 BTU/hr [3,810 kW].  I would guess this is pretty close to what properly functioning 56 system would do with R12, less with R13A.  Hope that helps.

Chris.

[Ron Draper]

Thanks Chris.

What I was thinking was using two factory condensers in series or parallel to get slow speed cooling with a 134a conversion.  I am wanting good cooling that does not disappear when i come to a stop at a red light.  Or would that be too much overkill on condenser capacity that I would not have any cooling at all?  I have searched the net and found that there are no rule of thumbs as you said.  And none of the formulas that I found allow for all steel construction.  Just copper and aluminum.  I know that more condenser capacity is required with 134a (generally 20percent more) and that too much is overkill but these are commercial formula where cost matters in a production run.

Thanks Again.

Ron

[Geoff Newcombe #4719]

If getting better AC cooling at low vehicle speeds is what youre after, and since you are apparently prepared to do some modifications, why not just put an electric fan in front of the condenser and turn it on manually when traffic is  slow or stopped.  There are a variety of types and sizes available out there made for just what you are wanting to do, if I understand your above post correctly.

[Chris Arneson #22170]

Considering your modivation the electric fans wouldnt hurt.  You might also try a modern condenser out of a large truck taking advantage of new materials and manufacturing techniques.  

I recall reading an indepth article about converting to 134a, but dont remember if it was in the SS or somewhere else.  Maybe someone else can chime in with a reference.

Good luck.

C.

[Bob CLC-22117]

Hi Ron,
If the 56 is anything like my 59, the first thing I would try would be to add seals from the condenser to the radiator.  This way all the air that goes through the radiator first goes through the condenser.  This should make a big difference in the low speed cooling.  I also replace my steel condenser with what I have been told is a late model Corvette condenser.  So far it is doing a great job and it didnt require a lot of modification to fit.
Hope this helps.
Bob CLC-22117