Aircooled condenser selection

[surathad]

Dear sir,
I select Bitzer semi. model 6G-30.2y R404
evap.temp -30 c and cond.temp. 50 cap. 22.6 kw.
if I select cond. heatreject 65 kw( 15K) ,that work
or not.
RemarK. Roomtemp -25 c and ambeint temp 43 c
Thank you for your reply if you kind
Surathad

[nike123]

Dear sir,
I select Bitzer semi. model 6G-30.2y R404
evap.temp -30 c and cond.temp. 50 cap. 22.6 kw.
if I select cond. heatreject 65 kw( 15K) ,that work
or not.
RemarK. Roomtemp -25 c and ambeint temp 43 c
Thank you for your reply if you kind
Surathad

What will be suction gas superheat or suction gas temperature? What will be subcooling?
What is altitude and lowest humidity in place.

For conditions 5K subcooling and 10K total superheat you need 36,2kW condensing capacity.
For 43 ambient and 50 condensation and 5K subcooling at 0m altitude and low humidity of 40% that is Guntner S-MCH 092C/1-N(S) (integrated subcooler)
That condenser is 5,52 Kw per 1K temp.diff which mean that you need condenser with 82,8 kW standard (15K) capacity.

[D.D.KORANNE]

First , select a cut off SST ; say (-15) deg C, and then obtain the compressor capacity at the design condensing. Add the compressor power to the compressor capacity .This will give you an optimum selection of condenser size . However, ensure that the SST is maintained at (-15) deg C at start up / pull down condition . The max SST at start up can be chosen by keeping sufficient margin for pulldown condition .

D.D.KORANNE

[D.D.KORANNE]

Let me know if you need further clarification.

Contact me on ddk0123@gmail.com

Regards,

D.D.KORANNE

[hendry]

some comp supplier will recommend in their data selection sheet the condenser's capacity.
however, you must understand that electric motor will trasnfer heat to the compressor... its heat loads must be accoutned for.

failing which you will always have not enough cooling eefects.

how much to add? some condenser suplier have different opinions. look into each supplier's guide book.

for safety ... add the motor kw into your total heat rejection ...

[dougheret0]

I don't think you have provided all the information needed to determine the evaporator coil capacity when operating with this condensing unit. As you note, the capacity of the condensing unit is a function of SST and condenser entering air temperature. The capacity of any evaporator coil at a given outdoor air temperature is a function of refrigerant temperature at the expansion valve (should be close to SST), evaporator air flow, evaporator entering dry bulb, and entering wet bulb. You can match any air handler using manufacturer's data with any condensing unit by cross-plotting capacity of the condensing unit against SST with capacities (total and sensible) of the air handler at a fixed outdoor air temperature, air flow, wet bulb temperature, and dry bulb temperature on the same plot. To simplify, just use SST. For more accuracy correct the refrigerant temperature back to the SST of the condenser - should be a constant correction.

The match point, where the evaporator total capacity equals the condensing unit capacity, will be the SST at which the condensing unit will actually operate under those conditions. When you get a match, you will have a total and sensible heat capacity of the evaporator coil at its inlet conditions when matched to the condensing unit.

You should plot your room process line and the evaporator coil process line on a psychrometric chart. I show how this is done in chapter 7 of my book HVAC Design Manual – A Mechanical Designer’s Guide to Design of Small Commercial and Institutional HVAC Systems. The book is available for free download on my web site www.nettally.com/doughert . Although the units are IP, I believe you can use the formulas to work your problem in SI.

[nike123]

Condensing capacity for Bitzer's is easily calculated for every possible condition in their selection software.

[dougheret0]

Condensing capacity for Bitzer's is easily calculated for every possible condition in their selection software.

It seemed to me that the original thread was asking for more than condensing capacity - a room condition is mentioned, implying that what is wanted is the system capacity of the condensing unit matched to an air handler and evaporator, to provide comfort conditions for a space. Does the Bitzer software include generic evaporator conditions? Just a question.

[nike123]

[quote=dougheret0;143658]

Does the Bitzer software include generic evaporator conditions? Just a question.

Yes it is. As well as Danfoss (Maneurop), Copeland, Tecumseh, Dorin selection software's (just to enumerate what is installed at my comp.)