On Tue, 22 Oct 2019 19:32:25 +0100, danny burstein wrote:

In op.z92p4mxowdg98l@glass "Commander Kinsey" writes:

Just had a reply elsewhere that said the USA 13 minimum SEER only applie=
s to split units, and that most single units are much lower. Any reason=
why split units would be more efficient?

A bunch of reasons:

1: "mini split" units tend to be inverter controlled,
with variable output cooling/heating. There's more
efficiency with a five degree temperature drop [a]
than a 20 degree one.

The single unit I was looking at was a single, but using an invertor.

2: the mini splits aren't wasting energy pumping all
that air around through ducts. Also, less leakage
in places where, well, the conditioned air is leaking..

I assumed the single one I was looking at wasn't allowing for ducts. It shows it as heating/cooling a single area.

[a] standard units have the compressor (cooling part)
fully on or off. The thermostat will kick it on
and, well, off as needed.

Hence if you only (for simplified example) need 5,000
BTUs/hr to keep your place cooled down (let's say it's
only a tad warm outisde) and your system is rated with
a 24,000 BTU (two ton) output, it'll cycle on for one
minute, then off for four, on for 1, off for 4. Rinse,
cycle, repeat.

A variable output unit will drop its output to 6,000 BTU,
so stay "on" for 4.5 minutes out of five.

The air temperature drop (the "delta") will only be
a few degrees instead of the 25 F typical of a full
power operation.

Ah! I never thought about the air temperature drop. So that's why they use less power.

So does that mean if you need 5000 BTU/hr and buy a 5000 BTU/hr unit, you use way more power than if you buy a 20000 BTU/hr one which never taxes itself? If so, how much difference does this make? Eg. if you run one at 50% power, how more efficient does it tend to become?

NOTE: there are now a _few_ window units that are
finally available in a variable output model.

So far _only_ for cooling, none yet with heating.

I picked one up earlier this year. It is, indeed,
much quieter, no "ker-thunk" when coming on, and
a gentler air flow. More efficient, too.

They're available from LG (formerly Lucky Goldstar).

I knew them as "Life's Good", but the latest thing I got from them says "Best Choice" which er.... is the wrong set of letters.

In the US the _only_ general purpose retailet that
handles them is Home Depot. Others might, soon.

There's a _minor_ feature/annoyance/get used to it... change.

With a standard, say, 10,000 BTU unit, if you left it
off then came back to a 90 degree F room, then turned
it on, you'd get a nice blast of cool air in your face
30 seconds later.

With the LG's, since they're inverter units which measure
how much cooling is needed, they start off with just
a bit of chilling... so you don't get that refreshing
and icy flow.

Strange, you would think they'd adjust their power by how much too hot the room is. If it's marginally over, they should run on low power, but if the room's way too hot, they should give it a good boost. Are you sure it's working right? What on earth would make it think a lot of cooling is needed then? Does it wait to see if it can cool the room in an hour, then only later ramp up the power? Pretty daft really, it's nothing like what you'd actually want.