Simple HVAC solution for an ADU

Question

I am looking for a HVAC solution for an ADU that wont break the bank. Talking about providing HVAC for two rooms roughly 250 sq ft and 300 sq ft in size. I live in a region where both the summers and winters are quiet mild. HVAC contractors have quoted upwards of $10K for ductless multizone mini splits. I am thinking of portable ACs(both heat/cool) as a solution like the ones below. Do these things work? Are there other solutions?

https://www.amazon.com/Portable-Conditioner-Dehumidifier-Black-SIlver/dp/B094X3G2SV/ref=sr_1_22_sspa?hvadid=557282111240&hvdev=c&hvlocphy=9051977&hvnetw=g&hvqmt=e&hvrand=5876836791749693719&hvtargid=kwd-325946514688&hydadcr=28751_14526974&keywords=outdoor+air+conditioner+portable&qid=1696975486&sr=8-22-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9idGY&psc=1

Answer 1

Some Mini split systems and all PTAC units can be self installed.

The PTAC units usually only need a 30 amp circuit. Mini splits for small rooms can be 110V and 20 amp, but to be fair usually require 220 and 40 amp.

If you can follow directions well and can do things like find a stud in a wall and drill a hole you can install Mini splits and PTAC units.

For the Minis you will need an AC gauge set and a vacuum pump. Both can be had without breaking the bank.

I know product recommendation is prohibited, but here is an example.

And PTAC here. Again these are just examples and I do not support either.

Answer 2

Portable A/Cs are not even stupid

I won't even speak of the 1-hose models. Even the 2-hose models are not efficient, and your building will certainly not receive its occupancy permit if portable A/C is the only heat source.

If you MUST be "temporary units as permanent HVAC"... then good grief man, build your house friendly to "window A/C units" - I guess some builders save $100/window going with anti-A/C windows like casement types, and their poor tenant must spend $300 extra on a portable unit that's half as efficient. Don't be that jackass. Build the right windows for window A/Cs (which absolutely do exist as heat pumps), because they are both cheaper and more efficient than portables. And also take less floor space and don't have ungainly hoses.

They also make "through-the-wall" A/C and heat pump units, however since you're cheap, you should know the units are much more expensive than window units (and window units don't work where a wall unit belongs).

And of course the ultimate "through the wall" unit is the wide rectangular PTAC, seen in cheaper hotels all over the nation. But they're not cheap. And many of them use resistive heat for heating, on the logic that the hotelier is getting $100/night so who cares.

But we're still in "A/C in a single box" world.

Split systems are better.

The traditional HVAC industry (Lennox, Carrier, Trane, Bryant, etc.) is exactly where Detroit was in the late 70s - the key fossil fuel is no longer cheap, nor sourced from friendly countries. Consumers wanted change, and the handwriting was on the wall. But the American industry denied, manipulated the market and government rather than retool for modern products. Oil shocks then gave them problems (the Persian Gulf then; Russia now). HVAC contractors today are like American car dealers then.

You will find prices are reasonable on a forced-air gas furnace and "That 70's Air Conditioner". The problem is, you very reasonably want a split heat pump system, since that is modern technology. To resist change, the domestic manufacturers price that "over the moon", hoping to trick you into believing such systems are inherently costly. Utter faff - just look at any of the bombed out Soviet era apartment buildings from the early Ukraine war. That ain't luxury housing so those occupants are probably under the per-capita GDP of $4000. Yet every other apartment had a mini-split they say is $11,000. Nonsense.

The $11,000 is the "I don't wanna sell it" price.

So you should be looking at the Asian style systems - they're more efficient anyway. I'd love for Panasonic or LG to start building a US dealer network that directly competes with the entrenched American dealers. But some systems are actually designed-for-DIY. I'm not the biggest MrCool fan as I think their "self-sealing" line-sets won't age well... But several makes have you install normal refrigerant lines, and simply supply the outdoor unit pre-loaded with enough refrigerant for the whole system (assuming line set lengths are reasonable). You build the line-set, dry-pressurize it with nitrogen to check for leak stability, then evacuate it and open the proper refrigerant valves. And that's it.

Rather than a dual-head system, I would propose two redundant single-head systems - that way you have an "insurance policy" if one of them goes down.