Refrigerant quantity vs efficiency etc?

is the 410a vs 22 efficiency the refrigerant or the system design, was higher efficiency required around the time r22 was phased out? in 2001 when i bought my split system if i recall there was not much in the way of efficiency requirements, you could buy systems with different efficiencies but i don't think it was mandated yet.

you can find the densities of different refrigerants on wikipedia.

the evaporator has to remain full of liquid but the amount of liquid and gas in the condenser could vary with different refrigerants.

if there is less refrigerant you have to pump less stuff but i don't know if that is the efficiency reason. maybe a higher ratio of tube surface to tube volume means the compressor has to move less stuff but that is pure speculation.

@ChrisJ asked "Why do some refrigerants require less of a charge I.E. R134A vs R12 in a retrofitted system, or R152A in a R134A system. Why does the system suddenly need less liquid in areas? Does the liquid weigh less, so it's technically the same volume but less weight? Or is there something else going on?"

Yes the refrigerant is less dense, for example: In many R-12 automotive retrofits, the recommended R-134a charge was often roughly 80–90% of the original R-12 charge by weight.

A major reason is that R-134a liquid is less dense than R-12 liquid at typical A/C conditions. So if the condenser, liquid line, and evaporator contain roughly the same liquid volume, the R-134a charge will weigh less.

R-152a is even more dramatic. It has a much lower molecular weight and lower liquid density than R-134a. R-134a has a molar mass of about 102 g/mol, while R-152a is about 66 g/mol. CoolProp’s R-134a data page lists R-134a’s molar mass as 0.102032 kg/mol.

That does not mean you use exactly 66/102 of the charge, because charge is not based only on molecular weight. But it helps explain why the required weight can drop a lot.

With R-152a, you may need enough refrigerant volume to wet the evaporator, maintain a liquid seal to the metering device, and establish proper subcooling, but that same volume weighs much less.

But that is not the only factor…. there is much more going on, however the difference in density is a big reason.

The condenser i have is the most efficient system Lennox had in 2001 without going to 2 stage and it is the size of a small porch. All the parts are scaled up so it doesn't look big but it is huge for a 2.5 ton condenser.

I don't claim to be smart enough to comment but I will anyhow.

One reason for limiting the amount of charge in a system (in the old days at least) was to minimize the amount of liquid refrigerant in the system. They talked about this in many of the older books including Copelands

By limiting the charge it reduced or prevented liquid getting back to the compressor, slugging and liquid migration are reduced preventing compressor damage.

I too wonder about the pressures required with different refrigerants.

Some like R-12 run at lower pressures than like 410A whose suction pressure (for AC systems) is probably higher than R-12s discharge pressures.

Common sense you would think R-12 with lower pressures would require lower HP compressors than a 410A unit but

That just shows I don't know what I am talking about.

Line set sizes between refrigerants doesn't seem to change all that much in spite of the higher pressures.

I always refer to my old Copeland books for stuff like this. The density of the refrigerant as @EdTheHeaterMan mention is part of the discussion and section 1 & 2 in this book go into detail

I don't remember, i'd have to look, I think it is somewhere in the ballpark of 10/12.

remember the compressor is working against the differential, not the gauge pressure although power is a function of volume and pressure so refrigerants with a higher pressure differential are moving less volume at that higher pressure.

The latent heat of vapourization does affect things — it determines how much refrigerant you need to compress to transfer a certain amount of heat. Higher values would mean less mass of refrigerant (NOT VOLUME) for a given amount of heat.

There's another complication, though — the energy put into the fluid by compression also counts, though it's relatively small — except at the extremes of performance. It is one of the factors involved in the lower efficiency of heat pumps at low source temperatures, though.

Incidentally, water os one of the best refrigerants. Just plain water. Inconveniently, though it freezes at much too high a temperature to be useful in most mechanical applications. It's very high heat of vapourization, though, is what makes steam heat such a wonderful thing…