new install of KRACK condensing unit

[icemeister]

What would change that TD their using the same coil so it's not a coil efficiency difference. What about air flow across the coil wouldn't that change the TD ?

The initial TD is determined by the condensing temperature you select when you size the compressor. With a condenser selected, the Total Heat of Rejection (THR) determines the final TD.

[VTP99]

I see so I'm gonna have to run your formula (post #11) a few times to get it sunk in.
I now realize you have to obviously include the heat of compression and mechanical heat total (which is the KW factor) to determine overall required TH of R.

[icemeister]

I see so I'm gonna have to run your formula (post #11) a few times to get it sunk in.
I now realize you have to obviously include the heat of compression and mechanical heat total (which is the KW factor) to determine overall required TH of R.

Just remember this is a situation where the equipment has already been selected, so you're goal here is to determine if the condenser is a good match. As I said earlier, without any specifics we had to go with nominal capacity data at standard design conditions.

[VTP99]

I'm somewhat surprised how much TD changes THR.
So with the newer larger higher efficiency condensing coils THR must go up.

[icemeister]

I'm somewhat surprised how much TD changes THR.

TD is directly proportional to the capacity of a condenser. The same is true with any heat transfer.

So with the newer larger higher efficiency condensing coils THR must go up.

Larger coils give greater greater surface area for heat transfer.

The higher efficiency typically comes from creating more surface area within the same face area ans depth of the coil, a basic example being finned tube vs bare tube coils.

Efficiency can also be increased by increasing the heat transfer coefficients between the coil and the air as well as between the coil and the refrigerant. Examples of air-side enhancement would be using a wavy fins instead of flat stock to create more turbulence. From the refrigerant side, velocity and the type of refrigerant are factors which can influence heat transfer.

[VTP99]

Thanks again icemeister for the help. That did help clear things up.
Now if I could just use it before I lose it.

[icemeister]

Thanks again icemeister for the help. That did help clear things up.
Now if I could just use it before I lose it.

I'm glad it helped you understand more about condenser sizing. If you want a good step-by-step example of a typical selection, I have on my website a short article I wrote a while back:

https://icemeister.net/backroom/icem...zing-selection

It was the basis for a similar one I did for the RSES Journal a couple of months ago.