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Old 02-25-14, 05:50 PM   #36
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Originally Posted by AC_Hacker View Post
I think that your comparison breaks down because the water analogy assumes pressure at one end of a pipe, and no pressure at the other end.

In the refrigeration circuit, all events take place within a hermetically sealed 'world', thus the pressure is balanced. Refrigerant flow is caused by the "unbalancing of pressure" due to the work of the compressor.

Ok, lets get detaily.

In a typical R22 unit, we have 70 psig low side and 225 psig high side pressures. In a R410a unit, these pressures are 120 psig and 350 psig respectively. So we have twice as much pressure, nearly. R410a therefore has nearly twice as much gas per unit of volume compared to R22. This helps the heat capacity a lot. So much that it throws everything off balance by 40%. You need either 40% less compressor or 40% more heat exchanger to balance the load.

With home- or mini-split-sized heat pumps, the trend has been to add 40% more heat exchanger. A previously 1 ton sized compressor has now been spec'd to 1.5 tons for R410a use, and that part was easy. The heat exchangers have been altered to have more capacity per square inch of face area by doing what? Instead of a hx that has 3 circuits of 3/8 inch pipe in them, they now have 6 circuits of 3/16 inch pipe in them. The pipes are also stacked closer together.

The result is just like a new 1.5L vtech motor that has more horsepower than an old 2.8L slant six motor used to. The new breed of heat exchangers have much lower internal volumes, less weight, and higher flow rates than the old ones did. Guess what? Noone cares that they have 15% more pressure drop. The R410a works anyways. Less refrigerant charge, less copper, less weight, more capacity. TADA!

Last edited by jeff5may; 02-25-14 at 06:03 PM..
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