Formula for CFM-Tonnage
ftwhd
wrote:
>
If you really want to be KoolDood, please post in plain text not html.
Thanks.
Mike
KoolDood
Would any one here know of any formulae (not metric) for calculating a
compressor's capacity in tons of cooling with the CFM of the compressor
as a givin?
TIA
HVACFREAK
TURTLE
"KoolDood" <can...@zensearch.net> wrote in message
news:3D07FEBB...@zensearch.net...
> Alrighty, is this any better?
>
> Would any one here know of any formulae (not metric) for calculating a
> compressor's capacity in tons of cooling with the CFM of the compressor
> as a givin?
> TIA
>
This is Turtle.
5 tons ----- 2,000 cfm
4 tons ----- 1,600 cfm
3.5 tons --- 1,400 cfm
3 tons ------ 1,200 cfm
2.5 tons --- 1,000 cfm
2 tons ------ 800 cfm
1.5 tons ---- 600 cfm
TURTLE
Abby Normal
p...@see_my_sig_for_address.com
Geez, gotta teach you everything......
"Abby Normal" <a_bee_...@spamyahoo.com> , pondered and said :
>Compressor CFM? Please elaborate.
>
Paul
>~~>~~>~~>~~>~~>~~>~~>~~>~~>~~>~~>~~>~~>~~>~~>~~>~~>~~>~~
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Abby Normal
Seaside
Greetings,
Would any one here know of any formulae (not metric) for calculating a
a givin?
TIA
KD
Isn't this guy asking about CFM compressor displacement rather than CFM
airflow per ton requirements?
p...@see_my_sig_for_address.com
"No Freon Going".
"Abby Normal" <a_bee_...@spamyahoo.com> , pondered and said :
>But what if it is NFG, Not Freon, Genetron?
>
profft
"Seaside" <sea...@refrigerationbasics.com> wrote in message
news:q_2O8.11782$Aa4.6...@news0.telusplanet.net...
KoolDood
all sorts of technical data, but they do not indicate how to identify
the tonnage of the compressor. They do however list the CFM of
refrigerant that is pumped by each model. From that, I was wondering if
it is possible to calculate the size of the compressor in tons.
Thanks,
KD
Allen King
Measure the wet bulb and dry bulb temperature drop across the
evaporator coil.
Use Paul Milligan's PM Therm (a free download from his website)to
calculate the enthalpy difference. Apply the enthalpy difference and
supply flow to this formula. BTUH=CFMxenthalpy
differencex4.5
Allen King
Jim Lavelle
>refrigerant that is pumped by each model. From that, I was wondering if
>it is possible to calculate the size of the compressor in tons.
>
>Thanks,
>KD
>
Yes, you can do it, but it will be different based on the operating conditions.
Most of the confusion here has been focused on the assumption of CFM across the
outside of the coil, etc. It seems he's talking about the compressor
displacement in terms of cubic feet per minute of refrigerant vapor moved by
the compressor INSIDE the system (usually expressed in terms of suction
condition).
So what you need to assume is the condition of the gas entering the compresor.
Typical supermarket conditions assume 65 F superheated gas at the suction inlet
to the compressor, I would expect air conditioning to run a little higher
maybe.
You must find the vapor density of the refrigerant at the suction pressure and
the entering (superheated) temperature on a superheat table. For R-22, for
example, at 20 degrees in the evaporator coil you will get 43 psig, and you
will superheat 45 degrees up to 65 F, so the superheat thermodynamic tables
show the vapor density to be 0.957 lb/cubic foot.
Now that we know the vapor density we can multiply by the CFM of the
compressor. If I push 10 cubic feet/minute X 0.957 lb/cubic foot I will be
moving 9.57 lb/minute of R-22. We also assume at this point that the pounds of
refrigerant flowing through the compressor is equal to the pounds of
refrigerant flowing through the evaporator (and the valve and the condenser
etc.).
Now all I have to do is go back to 20 degrees and multiply by the latent heat -
9.57 lb/minute X 90.5 BTU/lb = 866 BTU/minute or 51,965 BTU/hr - which is the
tonnage for the system at 20 degrees.
If I work the same example at 45 degrees I get a different number. Vapor
density is now 1.587 lb/cubic foot at the compressor inlet, and I'm now moving
15.87 lb/minute at 10 CFM. My tonnage is now the latent at 45 degrees times
the flowrate - 85.7 BTU/lb X 15.87 lb/minute = 1360 BTU/min, or 81,619 BTU/hr.
Easy to do if you have the data. Usually the compressor manufacturer has done
the math for you and they give you a Rating Table for their compressors for
various applications, suction temperatures, etc.
Jim Lavelle
National Refrigerants
www.refrigerants.com
Angelo
this rule of thumb: 400CFM per ton of air conditioning.
"KoolDood" <can...@zensearch.net> wrote in message
news:3D07F88C...@zensearch.net...
Greetings,
Would any one here know of any formulae (not metric) for calculating a
compressor's capacity in tons of cooling, with the CFM of the compressor as
a givin?
TIA
KD
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Bill
wrote:
> Your whole question doesn't really make sense, but for the CFM per ton, use
> this rule of thumb: 400CFM per ton of air conditioning.
He means refrigerant circulated. Not air flow.
--
Rick Thompson
(Actual Compressor Displacement (CFM) divided by the Specific Volume of
Suction Vapor (Cubic feet per pound) multiplied by the Net Refrigeration
Effect (Btu/Lb)= Capacity of Compressor (Btu/Min).
Then you can divide the Btu/Min by 200 to get system tonnage.
The system must be plotted on a PE Chart to obtain the specific Vol. & NRE.
Angelo <apr...@taconic.net> wrote in message
news:3d0fe...@corp.newsgroups.com...