Got new central air conditioning system installed last summer. Previous unit was ~20 years old. Didn’t get to see the new evaporator that was installed, but the condenser/compressor unit outside is enormous. As it’s the same tonnage as the old unit but consumes less electricity, I assume the compressor (and its motor) are smaller and lower-powered (it’s definitely a lot quieter) - but the condenser coil itself is physically huge, much bigger than the old unit.
So what accounts for the improved efficiency of this new unit? Different refrigerant with more favorable thermodynamic properties? larger heat exchangers? Something else?
Everything is larger because it’s a r410 unit. Your old unit was (probably) r22 which is a much more efficient refrigerant, it just tends to destroy the environment so it’s illegal.
The real winner is to retrofit more efficient pieces on the grandfathered r22 unit, but that may not have been an option and it’s too late now.
The larger condenser coil allows for quicker and more complete rejection of heat into the atmosphere, thus lowering the condensing (head) pressure of the refrigerant. The lower the pressure required, the less electricity the compressor uses. Lower condensing pressure and temperature also improves the volumetric efficiency of the unit, though I don’t know if that has much impact on non-commercial systems with only one compressor.
This is a big reason why window a/c units haven’t improved appreciably in efficiency for a while. There’s only so much bigger the coils can be made and still fit in a window. They have made improvements by using smaller pipes and tighter fins, but that just makes the coils more delicate and susceptible to clogging. Those improvements were mostly eaten up by the switch from R22 to R410a as mentioned above.
Of course propane (R290) has very similar thermal properties to R22, on top of being much easier to obtain and having few or none of the environmental impacts. The only downside is its flammability, but the rest of the world seems to be totally onboard with it for domestic systems. It’s just the US that seems to be under the thumb of the chemical companies protecting their market for proprietary refrigerants.
What is called “single phase” alternating current [electricity] is not very efficient to power an electric motor. More efficient is “three phase” electricity.
Homes do not have three phase electricity, just single phase typically. Note homes have 3 wires going to the breaker box, but many businesses have 4 wires going to the breaker box - that is 3 phase.
Anyway understanding that different electricity can make motors run more efficiently. And knowing that A/C units have several motors in them (a couple of fan motors and a compressor motor)… Manufacturers have designed A/C systems which “create” their own electricity. The MOST efficient electricity there is to power these motors.
Furthermore in the past A/C motors just had 2 speeds. Off and on. With this newly designed custom electricity (called inverter technology), they can make motors go many different speeds.
So if you need just a little cooling, the motors will all be running slowly.
Two separate repair guys have diagnosed low refrigerant levels (almost certainly due to a leak somewhere) in our roughly 23-year-old unit as the cause for its sudden decision to stop cooling our home.
Then on Friday the cool returned (we were running it just to keep the fan going) and it is a comfortable 73 degrees inside.
Is this just a last fling before it goes entirely, or could there be some other explanation for our low refrigerant level besides a fatal leak?
Interesting that, even in the US, there doesn’t seem to be much opposition to use propane for heating and cooking. Nearly every suburban household (and many urbanites) has a propane grill and rural America has been using LPG (mostly propane) for heating and cooking for a long time.
^ Indeed, and I’m much more concerned about the potential issues with a 20 gallon grill gas tank filled by some yokel at Home Depot, or the giant 120+ gallon tanks sitting above ground in the yard, compared to a hermetically sealed air conditioner or refrigerator.
But the Propane doesn’t get circulated through your house at high pressure…
Still, the risk is probably over-estimated.
On the gripping hand, though, Ammonia is also a very efficient refrigerant, and was used for quite awhile, until enough people were killed to make replacing it desirable.
Propane and natural gas DO get circulated around many houses at high (or at least moderate) pressure, feeding the furnace, water heater, stove, and sometimes fireplaces. Yes it’s not being mechanically pumped and recirculated, but so what? Propane is also the main propellant in most aerosol spray cans, from hairspray to cooking oil. Just because something is flammable doesn’t automatically make it super crazy dangerous. It’s worth weighing the pros and cons of toxic but non-flammable refrigerants versus non-toxic but flammable. Ammonia is very toxic, while HFC and HCFC refrigerants like R22 and R410a are classified as low-toxicity, so they’re not entirely benign. Carbon dioxide is another option except for its propensity to go solid when you don’t want it to, thus requiring systems that run at very high pressure.
There are some serious technical errors in that article.
(Bolding mine)
While an auto AC may contain about 800g of R134a, that is equivalent to about 10 ounces (less than 300g) of R290 (propane), so he is over-estimating the amount of propane in the system by a factor of 3 or so.
I’d also like to know what kind of car he drives. Chrysler’s largest minivan, Town & Country, has an interior volume of just shy of 200 cubic feet. That’s about 5.7 cubic meters, so this guy’s car has about twice the interior space as the T&C. That’s big. For comparison, a Prius has an interior volume of about 3.3 cubic meters, another factor of three.
Now, these errors offset, but my point is that if he doesn’t even have these basic facts correct, how much of the rest of his analysis is flawed?
I’m not saying that propane as a refrigerant is absolutely safe, nothing is. But, if our goal is to fight ignorance, realize that there is a lot of it to be found in that article.
I can certainly see the objection to using a flammable refrigerant in an automotive situation because it’s more difficult to protect. Gasoline tanks and fuel lines are pretty well shielded in the middle of the vehicle and unlikely to be catastrophically ruptured in a collision (Pintos excepted :)). The a/c condenser however has to be right in the front grille, and in fact in front of the radiator. Even minor front-end collisions routinely result in leaking antifreeze, so I assume the a/c system likely gets ruptured in such an event as well, though you don’t see it.
All that said, the amount of trouble the Mythbusters have had getting propane, methane, and other flammable gases to ignite suggests that maybe the incidents of ignition would be small relative to the number of leaks. Plus, unlike gasoline which pools on the ground constantly releasing vapor that could ignite, any gaseous hydrocarbon would pretty quickly dissipate into the air. Plus at the volumes we’re talking about, even if it did ignite, would it likely be no more than a PWOOF before it’s burned itself out?
Most utilities distribute NG at 10-12 inches of water column. There are 28 inches of water column in 1 psi. So if you think about it, NG is being fed at 1/2 of 1 PSI. That"s really low pressure.
Compare that to R410a while may routinely operate at 350-400 PSI.