Dx coil design

[abbasi]

The formulae to design the DX coil is

rows= Total Capacity......
........440xFace areax(Tc-Tr)

Tc is critical temperature
Tr is the refrigeration/evap. temperature


now this is for R22 what would u all suggest for R407C/R134a

also can somebody share his knowledge for aircooled condenser

[frank]

also can somebody share his knowledge for aircooled condenser

Hi Abbasi

What specifically do you want to know? How to size? number of rows, fin spacing?

[abbasi]

Hi Abbasi

What specifically do you want to know? How to size? number of rows, fin spacing?

As a matter of fact all of the above i.e face area rows and fin spacing

How do we design it? also is there any formulae like that with DX coil

[Lc_shi]

Hi Abbasi,
where you find the formula?
i'm puzzled by the design for DX coil or water coil for air handling. I checked ASHRAE handbook and read some the calculation formula for both DX and water coil. it's complex and limited with some conditions.
The best way is to ask coil manufacture to design and calc for you. It's a speciality.
I'm not sure to what level your formula can work effectively.

[shogun7]

The formulae to design the DX coil is

rows= Total Capacity......
........440xFace areax(Tc-Tr)

Tc is critical temperature
Tr is the refrigeration/evap. temperature


now this is for R22 what would u all suggest for R407C/R134a

also can somebody share his knowledge for aircooled condenser

Condensers are rated in terms of total heat rejection (THR). The correct condenser size for a given compressor depends on the design conditions at which the system will operate and on the extremes of coolant temperature and compressor motor loading that may occasionally happen but should not cause overloading problems.
Design conditions for an air cooled system specify a certain compressor capacity (net refrigeration effect, NRE) at given evaporating and condensing temperatures. Some compressor ratings also include condenser heat rejection; but in most instances it is necessary to calculate this quantity as follows:
THR = NRE × HRF (Btu/hr)
HRF (1.34) in this case is a heat rejection factor from a table which accounts for the heat energy added to the refrigerant stream by the compressor. As seen from the table, this factor is higher for hermetic compressors in which the refrigerant passes over the compressor motor and picks up additional heat while cooling its windings.For example if we take a 2 hp hermetic compressor with NRE rating of 20,000 Btu/hr at 40°F evaporating and 120°F condensing temperature will have a THR of 20,000 × 1.34, or 26,800 Btu/hr, which must be rejected by the condenser.The condenser capacity CHR within its normal range of application is directly proportional to the temperature difference (TD) between refrigerant and coolant (air or water), as follows:
CHR = KC × TD (Btu/hr) where KC is the condenser heat rejection per one degree TD from manufacturers' rating tables. For correct condenser selection, CHR must be equal to or greater than the compressor THR. If our 20,000 Btu/hr system is designed for 120° condensing temperature at 90° air, the TD will be 120°F -90° F = 30°F and we will require a condenser whose KC is at least 26,800/30, or 893 Btu/hr per degree TD .Then looking at the manufacturers' table, the nearest KC from a condenser catalog is 960 so that this condenser's heat rejection will be
CHR = 960 (KC) × 30 (TD) = 28,800 Btu/hr which is slightly more than the required 26,800 and adds a small safety factor to our selection.

Evaporator design
The design of a unit evaporator evolves around the fundamental formula for heat transfer which is capacity = (Surface) x "U" x (Mean Temp. Diff.)
Surface is defined as the outside area of the tubes and both sides of the fins, that is exposed to the air flow.
"U" is called the over-all heat transfer coefficient and is defined as the amount of heat which will be transferred by one square foot of coil surface for each degree Fahrenheit mean temperature difference between air and refrigerant.
MTD is the mean, or average, temperature difference between the air and the refrigerant. Difference in temperature is the force which drives heat from one medium to another. Since both the air and refrigerant change in temperature as they pass through the coil, it is necessary to determine the mean difference to obtain the true driving force.
Considering each of the factors in the formula, it is clear that increasing the surface would increase the heat transferred. This, however means increasing the size and cost of the unit, and should only be done after all other possibilities are exhausted. Also, it is easy to see that increasing the temperature difference between air and refrigerant will increase the heat transferred. However, the temperature difference is limited by other considerations, such as humidity control, which shall be discussed later. The only remaining item is, therefore, the heat transfer factor, "U".
Calculation of "U" is probably the most important step in coil design, and careful consideration of all the factors which influence "U" will result in the most efficient unit.

[Lc_shi]

thx for your guideline for condenser and evaporator coil design. it's good principles. Is there any specific design materials for engineers?
it's rather a complex issue which involve kinds of fins and tubes and circuits type,all this leads to different heat transfer effect.
I hope more guys in this forum can offer your own ideas and make it clear.

[RogGoetsch]

thx for your guideline for condenser and evaporator coil design. it's good principles. Is there any specific design materials for engineers?
it's rather a complex issue which involve kinds of fins and tubes and circuits type,all this leads to different heat transfer effect.
I hope more guys in this forum can offer your own ideas and make it clear.

As you say, coil design is very complicated. Coil companies have the software and experience to do this efficiently. Unless this is part of your doctoral dissertation, I would advise letting them do the job.

When I have had to do this, I always work with a coil company. I provide the specifications: any required dimensions, cooling capacity or heat of rejection, face area, air velocity, etc. The coil company engineers come back with choices available to achieve the design: coil depth, fin spacing, number of passes, etc.

Remember that published coil capacity ratings are not calculated values but measured values. Even the best calculations will leave you with a large margin of error. If you need one coil, you overbuild, but if you are planning to sell competitively, you will have to build competitively and that means accurate software, building and testing.

Rog

[shogun7]

Lol, Shogun, I don't think you meant to post that here, it looks rather out of place. Was there perhaps another thread you were hoping to paste that copy into, or, you're trying to be a nuisance posting something almost entirely off-topic.

Marc Jelousy wiil get you nowhere except constapated, however if you can help the lad instead of finding fault with me ,then by all means do so
It looks out of place to you because you too dense to see the relivency. The recipient seems to like it

[abbasi]

Hi Abbasi,
where you find the formula?
i'm puzzled by the design for DX coil or water coil for air handling. I checked ASHRAE handbook and read some the calculation formula for both DX and water coil. it's complex and limited with some conditions.
The best way is to ask coil manufacture to design and calc for you. It's a speciality.
I'm not sure to what level your formula can work effectively.

I have read it from a design book this formulae is used for evaporator having refrigerant in the lines aso "Tc" is the critical temp that is obtained by (1)intersection of entering dry n wet bulb(2)intersection of leaving dry n wet bulb

then joining above 2 points to saturation line to obtain critical temp
Tr is refrigerant temp normally 45F

Believe u me we design dx coils for 1-100 tons with same formulae with 3/8" tube with gr8 successs

[abbasi]

Condensers are rated in terms of total heat rejection (THR). The correct condenser size for a given compressor depends on the design conditions at which the system will operate and on the extremes of coolant temperature and compressor motor loading that may occasionally happen but should not cause overloading problems.

CHR = KC × TD (Btu/hr) where KC is the condenser heat

.

where can we find Kc can u help me in mailin it to me


secondly i know about Heat rejection but after we know how much Btus are required to design can u elaborate on

1. no of rows
2)fins per inch
3)face areea

as a design engineer i want to know the next step

u can mail me also at

engineerali@gmail.com
ali_abbasi28@yahoo.com

[abbasi]

Hi Abbasi

? How to size? number of rows, fin spacing?

still waitin for ur reply

[Lc_shi]

Which design handbook? Do you have e-text for it?
I appreciate your experience.