HVAC (AC) question

[tcsenter]

We have a master bedroom furthest from the AC (evaporator/coil) i.e. the longest duct, AND happens to receive more direct sunlight during the hottest period of the day, heats up more than the rest of the house, thus lags behind the rest of the house when cooling i.e. the rest of the house gets acceptable temp but we have to keep running the AC just to bring down that one room. Big disparity there. We've had a pro check there are no gaps or leaks in the ductwork when servicing/inspecting the AC. He said lots of houses have this problem of "that" one expletive room.

So I am looking into a AC unit just for that room; portable or window unit. For portable units, dual hose (intake and exhaust) seem to be recommended because the single can create negative pressure and pull warm air into the room. But air from where, other parts of the house or from some presumed gaps/leaks in the window apparatus that the hose is mounted to?

I think it would be better for air to move from COOLER parts of the house (nearby) to that room. That isn't a downside, but an upside. I guess this recommendation is based on an assumption that one is trying to cool only THAT room and the rest of the house is like uncooled or warmer? That's the only assumption/configuration that makes sense.

 

[Red Squirrel]

2 hose is way better as it creates a closed cycle so the hot side uses outside air only and cold side is indoor air only. Before I got central AC I modded mine to have 2 hoses. Essentially I was able to locate the intake on the condenser side of the unit and then built a box that sits next to it and had another hose going outside. Otherwise it will just try to force air into the house form any crack it can while expelling cold air. You're essentially paying money to cool air, and then some of that air gets sucked right outside, while hot air gets sucked inside the house somewhere else.

If you have access to do so, I would look at running another duct, maybe even a 6" to an additional supply vent. If you typically close the door maybe even run a return or just add a grille on top of the door.

But if that's not feasible you could look into a mini split. The downside with portable units is that they are LOUD so that may not be feasible for a bedroom. It's not soothing white noise either, it's more like 10 hair dryers on max setting and every time the compressor cycles on or off it's a jarring noise as well so if you do manage to fall asleep that will probably wake you.

 

[Paperdoc]

Yes, the two-hose design is much better. Why? What goes in must come out. And the other way around. Both systems run the room air through the A/C cooling coils (evaporator) in the unit. PLUS they run some room air (hopefully NOT what was already cooled, but depends on unit design) over the OTHER heat exchanger (condenser coil) to cool it off and send the heat out the window via the exhaust hose. So in a ONE-hose system the unit is always pushing air from the ROOM outside. That means that somewhere (all air leak locations) in the house some OUTSIDE (hot) air is being sucked in to make up for that, adding heat load to your central air system. But in a TWO-hose system the unit sucks outside (hot?) air IN from the outside via that Intake Hose and uses that to cool the Condenser coil before exhausting it out of the other hose. So NO outside hot air gets sucked into the house at leaks.

We had a one-hose unit for years and used in on our main floor with success. It tended to run for long periods. In our area the hottest days of summer can get into the 30 to 35 C range (86 to 95 F), rarely over that. After a few years I noted it seemed less efficient even though I cleaned its intake air filters regularly. The manual said nothing else about cleaning. So I figured out how to remove all the covers and found inside that there was significant dust built up on BOTH of the heat exchanger coils, blocking air flow. I vacuumed them off carefully, plus other dusty spots, and replaced covers. It performed MUCH better then! That also would have applied to a two-hose unit, too, if I had one. And that laid to rest my fear that reduced efficiency was due to loss of refrigerant gas.

Three years ago we replaced our high-efficiency gas forced-air furnace (about 40 years old, a surprise to many) and had the contractors supply and install a A/C system in that new furnace. So now the entire house gets cooled throughout the summer, and interestingly our electrical bills have NOT gone higher since then. So we're getting better cooling for the same cost from a good central unit than from a smaller "portable" unit, no surprise. We gave the portable unit to our grand-daughter for her apartment.

BEFORE you go ahead, check for this other possibility. I am sure there are small dampers in several locations in the ductwork in your house, each able to reduce flow of air to a particular area. If you can locate them all and reach them, you could try partially shutting off air flow to most of the area near the central air system, and ensuring the duct to that distant bedroom gets max air flow. OR, even if you can't do that you could go the the air registers in each room and partially close the ones near the central system so more air flows to the bedroom. In the fall, reverse that to re-balance air flows for the cold weather. Repeat the spring and fall adjustments each year.