Dear Hosein,

for the first iteration You could start with DuPont software.

http://www2.dupont.com/Refrigerants/en_US/products/DUPREX/DUPREX.html

Regards,

Tomaz

Dear Hosein,

As it was mentioned by Tomaž it is convenient to start with some software. Except the Duprex software you can also use Solkane software (http://www.solvaychemicals.com/EN/products/Fluor/Software.aspx) or Coolpack software (http://en.ipu.dk/Indhold/refrigeration-and-energy-technology/coolpack.aspx). Both of them can solve the refrigeration cycle and help you design the pipes.

You will need some more infromation to calculate the refrigeration cycle. The most important one is the condensing temperature (i.e. the parameters of cooling medium for the condenser). If you know the condensing temperature you can start the design using the softwares and compare different refrigerants. Once you select the suitable refrigerant you can start looking for the compressor. There are some selection tools (softwares) from the compressor producers which can be used to do this job. The last step is to select the condenser and expansion valve.

Good luck

Jiri

Dear Hosein,

as Tomaz and Jiri said there is a procedure to follow and software could help. In case you prefer to it by yourself please refers to reference books like ASHRAE fundamentals and refrigeration.

Here is a summary of the procedure (just a summary more details is needed depending on the level of accuracy of your calculation).

One should: 

1) calculare cooling capacity from an energy balance on water side (calculate specific heat of water+antifreeze from tables available on line). It should be around 65 kW;

2) fix the evaporating temperature: a minimum difference of temperature is required from exit water temp (8 °C) and evaporating temp. Usually, 5 °C is fine. So 3 °C could be a good value to start. Lower the evaporating temperature, higher the energy consumption;

3) fix the condensing temperature: it depends on the way you can condense the refrigerant. Air-cooled condenser ? in this case a minimum difference of temperature with the ambient temperature equal to 8-10 °C would be fine to have a good compromise for performance. The higher the condensing temp the higher the energy consumption. Also, account that, differently from the evaporating temperature related to the process and almost constant during the year, the condensing temperature will follow the ambient temperature.

During the design of the thermodynamic cycle (what we are doing now) is important to use the maximum value to avoid undersizing of the compressor, but further important technical considerations have to be done in the next steps to avoid too low condensing temperature and, consequently, evaporating temperature;

4) choose the refrigerant: start from safety considerations. Where is your plant? you have people near the plant or a part of it? is it a vent place? If you have closed places take care about use of toxic fluids like ammonia. Ammonia is a very good refrigerant, but also highly toxic and flammable. Also consider the use of natural refrigerants like CO2 or hydrocarbons. CO2 needs transcritical cycles for ambient temperature over 20 °C and is not easy to be handled due to high pressure, but is  friendly for the environment. Propane is also a very good refrigerant even if flammable. These three refrigerants need components twith particular selection procedures and higher costs than HFC refrigerants (a general rule with exceptions).

Other refrigerants to be considered are: R134a, R404A or R410A. Sizing of components in terms of pressures, displacement of the compressor and of surface of the heat exchangers are higly affected by refrigerant choice. Probably in your case R134a could be a good compromise

5) calculate the mass flow rate (kg/s)  of refrigerant in the evaporator from an energy balance, fixing a saturated liquid condition at the condenser exit and a superheat of about 10 °C at the evaporator exit. 

6) calculate the volumetric flow rate (m3/h) of refrigerant at compressor suction through the density of the refrigerant. The volumetric flow rate is  the swept volume of your compressor available on catalogues;

7) choose compressor type: if the compressor ratio (condeser pressure vs evaporator pressure) for R134a does not exceed 7 and you have stable conditions at the exit of the evaporator, and do not need a large capacity control, you can choose a reciprocating compressor, choosing it from a catalogue of manufacturer (dorin, frascold, bitzer, gea, maneurope, copeland). Reciprocating compressor generates noise and needs a good manegement of oil through appropriate design of the piping. Otherwise a  scroll compressor will give less noise and needs less oil, but the efficiency will not be as high as for a reciprocating compressor. (screw compressors or centrigural compressor  could be a solution, but requires higher technical care not always motivated in terms of costs). In your case the best would be a reciprocating compressor and you can choose it through the swept volume from point 6);

8) choose size of the plate evaporator by the DTml method. Dtml should be almost 18°C; using a first value of U=600 W/m2K, the area of the evaporator can be easily calculated.Further adjustments accounting for an accurate sizing depends on the geometry of the plate exchangers (pressure drops at refrigerant side, effect of oil) are needed: usually the manufacturer of the brazed plate give these details (Alfa-laval,swept, cipriani..there are a lot in Europe and all around the world);

9) choose the size of the condenser: it depends of the type you choose..  Use catalogues for air-coolers (LU-VE and Guntner are two imporant companies .. but a lot of companies are available in the world)

10) choose the expansion valve: thermal expansion valve or electronic expansion valve (carel, danfoss, parker, saginomia...). Easy procedure from catalogues;

11) size piping to limit refrigerant charge in the liquid line, avoid flashing in the liquid line, assure lubricant return through risers sizing properly diameter of the piping;

12) choose the accessories: liquid receiver at condenser exit, liquid separator at compressor inlet (if necessary), shut-off and cut-off valves, pressure transducers for safety, safety valves for high pressure, electric panel and controls;

13) study load variations and consider inverter control and/or energy storage trough a tank;

14) refine calculations through softwares.

This is the procedure I follow for my prototypes and I suggest to my students..

Anyway you need more data to have a clear idea of what you need. Also please take into account that this procedure give you something that should work properly.

If you want to deal with costs of plant, costs for energy consumption several scenarios you need to apply for. Of course if some basic information about the application should be available (food industry? particular process? air conditioning?),  context (people or not? noise is possible?) , ambient temperature (stable during the day/night? variation during the year? maximum temperature?), load variations (strong? seasonal? weekly?) , the scenarios could be easily limited to few alternative and it will be possible to evaluate costs and pay-back times through energy savings

hoping this couls help

regards

Alfonso William Mauro

Dear hossein,

As above mentioned the procedure for design of refrigeration cycle by Mr. William and also some major point by Mr. Juri, the cooling medium of condenser  and the total refrigeration load (capacity) that to be cooled the water should be the objective. but taking care of exit temperature of coolant it should be less than 5 deg C as environmental issues. by taking some constraints as outlet temperature of coolant, refrigerant which is selected should not be harmful and follow the government standard rule which is available in ASHRE.  and u analyse on software as above mentioned with some refrigerant and calculate the objective as well as fullfill the constraints. then u choose the best suitable refrigerant for the cycle.

Pl refer to the book written by by Doosat.  

Dear Tomaž, Jiri, Alfonso, Rajesh and Dr. Ravindran,

Very very thanks for your helps. I could solve my problem base of your suggestion. thanks again...

so, from compressor catalogue we have volume displacement and we can find density from refrigerant property table. Now, we can calculate mass flow at compressor from this data.

i have question that is this mass flow is same at condenser, capillary tube and at evaporator ?  

For the unit design, it's better to use some website/App sizing tools to size your condenser or evaporator air coils. You can try our e-Tools available at www.Refriglab.com for your refrigeration condenser and evaporator air coil sizing (coil tube OD ranging from common 16mm, 12mm, 9.5mm, 8mm to the new 7mm, 5mm, 4mm). At the same website, you can use it for your coil circuiting/pass number sizing, your CAP (capillary) tube sizing and suction line accumulator sizing. You can also use the e-Tools to quantify the optimal refrigerant charge amount if you have all components (compressor, air coils, CAP/TEX/EEV, Acc, SLHX) data ready. You have the 39 refrigerants option including R134a/R404a/R290/R600a/HFOs/R410a/R407c and etc..