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Mr. Sphinx and I are having a stand-off, so I need you people to weigh in.
Our house is a three-level Colonial built in 1958, with the bedrooms upstairs. It has central air, but the bedrooms upstairs get less cooling than the main level or basement. That's just how it is and always will be.
Once the kids left, Mr. Sphinx and I got a window a/c unit for our bedroom. This allowed us to turn off the AC to the rest of the house at night and still remain blissfully cool. This saved money.
The window unit crapped out, and Mr. Sphinx bought one one of those portable units that sits on the floor and has tubes going through the window:
It was huge and unsightly, so I had him buy another window unit, and we put the portable unit into a closet.
Well, Little Sphinx lives with us, so it no longer works to turn off the AC at night. As luck would have it, LS' room has small dormer windows positioned way up high, so it is not possible to get him a window unit or even have him use the portable unit. His room gets very hot during the day, when he is up there working, and at night.
Here's the disagreement.
I contend that the most efficient way to keep us all cool is to turn on the whole house A/C to a reasonable level and not use either the window unit in our bedroom or the portable unit.
Mr. Sphinx contends that we should (1) run the whole house A/C (at a somewhat higher temperature); (2) run our window unit; and (3) hook up the portable unit in an empty bedroom, keep the door open, and position a fan to blow the cold air from that bedroom down the hall toward LS. The idea is to use the smaller A/C units to supplement the whole house unit. He says that using the portable and window unit reduces the load on the whole house AC, and it doesn't take much electricity to operate the portable unit and window unit.
So. What do you think? Does it save money to run portable units in addition to your whole house A/C?
1. Move LS to the basement. It’s naturally cooler there per your description ==> child taken care of
2. Institute au naturale sleeping policy for your own bedroom ==> natural cooling + marriage saved
3. Turn off all air conditioning at night ==> money saved
|(self-titled) semi-posting lurker|
Ugh, this sounds complicated and hard!
I think the answer here depends on 1) how old your HVAC is, and 2) the energy draw of your portable AC units.
I suspect those small ACs will be more expensive than the whole house AC. Do they have compressors? If yes, then they probably use a lot of energy.
I have a free-standing dehumidifier (it has a compressor) in my piano room because last summer, even though we have a brand new, efficient HVAC, AC wasn't doing enough dehumidifying for the piano. So last summer I ran that dehumidifier probably 8-12 hours a day (a rough estimate, I turned it off overnight, and I turned it off while playing piano).
This year, somehow I got the idea of putting a small fan in the hallway (I could feel moist air stagnating in one spot), set on the lowest setting and oscillating. And then I also got into the habit of keeping the ceiling fan on in the family room (which is next to the piano room and there's just a doorway there, no door).
These two adjustments have made it possible to maintain the humidity in the piano room without the dehumidifier (seriously, it's like a miracle!)
And guess what? Our electric bill is about $100 less each month so far.
So, sorry that was a lot of thread drift.
But I think running those ACs with compressors will be expensive and you may be better off with the whole house AC and adding some fans here and there.
Alternatively, you will have to do a comparison over a period of two months, with small ACs versus without.
Not enough information to answer this question, but I'm rather dubious about how effective trying to blow air down the hall to a closed room will be. I suppose you can try it and see.
If you save your electric utility bills, you probably have the information you need to analyze the cost of the alternatives. At one time, you ran the whole-house A/C and can get a reasonable estimate of what it cost by comparing the bills for months with it on versus "shoulder" months (spring & fall) when it doesn't run much but a furnace fan is not contributing to electrical load. Then do the same thing for the years you just ran a window unit and the years you ran the portable unit. Add the two and compare them to the whole-house years. That will give you an either-or comparison. Then reduce the whole-house portion by some factor (I've heard 7% for each degree above 72, but that's also dependent on climate). That may give an idea of what electricity the combination may require if the whole-house A/C does not have to cool the whole house to the same degree as you may require in the two rooms. Since the window and portable units exhaust heat to the exterior, the main influence they probably have on the whole-house load is the portion of the house that is removed, presumably by isolating the rooms/areas being cooled by the window and portable units.
An alternative would be to try each alternative over the next two billing periods and compare the results. If your bill is like mine, it shows average temperatures over the billing period so you can make some adjustment if one month is significantly hotter or cooler than the next.
Can you move LS to a room where it would be possible to use a window unit?
If not, have you considered a through-the-wall unit for his room? Probably not the easiest thing to install, but a permanent solution to the HVAC woes in his room. Something like this: https://www.walmart.com/browse...133032_133026_587565
Have you looked into zoning your HVAC so you can send more air to the upstairs? I have heard there are ways to retrofit that into an existing system using baffles and duct fans. Then you could set the downstairs to a higher temp and still have it decently cool upstairs.
Otherwise, I have no idea what is more efficient and cost effective. I imagine, like SK said, it would depend on the age and efficiency of your main system and the size and energy consumption of the portable/window units.
Oh ETA - is there really no way to run the tubes up to the high window? Can you extend the tubes or sit the portable unit on a tall stand or something? Or is it a question of the window not opening at all? Since you already own the portable unit, I would probably try every method possible to make that work in his room.
So those upstairs rooms - There are booster fans available (though I've just used a little window fan over the vent on one rental house) that will increase the amount of cooling/airflow to those underserved rooms. Combine that with closing off vents near the thermostat to keep the system from turning off before the rest of the house cools.
Yeah, I'm cheating by not following your rules!
|Has Achieved Nirvana|
Try the options to find out.
There are too many variables.
Put the portable in a table or stand.
|Has Achieved Nirvana|
We have a two story house built in 1960, bedrooms are all upstairs. Second floor is frame and insulated to 1960s standards, so not so good.
In the summer the second floor feels warm and in the winter it's cold.
Along the lines of what Ron said....we can adjust the air flow to various registers in the house. The thermostat is on the first floor in the living room. The living room is also directly above the HVAC, so it gets all the hot air from the furnace in the winter and from the A/C in the summer.
We found that if we close off the first floor registers in the LR during the summer, it forces more cold air upstairs and it's much more comfortable up there.
We also have some registers in the basement. They are closed during the summer (no sense in cooling a cool basement) but we open them up a little in the winter.
I have to admit I was really surprised at what a difference five minutes of seasonal register adjustments made in the comfort of our home.
Your setup may be different and you might not get the benefits we did, but might be worth a bit of experimentation.
How high up are the dormer windows? Can you just use a cheap table or stool of some sort to hoist the portable unit up to reach?
|Pinta & the Santa Maria|
Has Achieved Nirvana
IIRC (assuming my son had a similar arrangement at his place in Vancouver) the tubes are for condensation run-off so they need to be at or below the unit itself. Closing vents to unused rooms might also be a good idea. We did this in Arizona and it made a difference (perhaps more to our bill than to the temperature in the rest of the rooms, though).
Once my kids became adults (had lived on their own not in a dorm room) I cut the cord to "their room." They are always welcome here, and can always return to live if their life situation warrants it (or ours does, I suppose!), but if it makes sense for them to move to a different room, they understand they need to just do it.
So yeah, any chance you could move LS to a room where he could use the portable unit?
Other than that, I don't have much. I don't like AC so I get by as long as possible with just a room fan. But I also know that summers in DC are crazy hot and humid, so this may be a laughable option.
LS to the basement. A cool lair for work and play.
Having the A/C going plus portable units plus fans just sounds loud and unsightly. Blergh.
|Has Achieved Nirvana|
Cut another window banger in to a wall. Very cheap.
|Has Achieved Nirvana|
Cindy, Portable units in my experience leaked water because of the condensation. The two I had included a drip pan and water had to be collected every day. Nina's right that the placement of everything has to be planned carefully. Mine were impossible to clean and only lasted about two years. I know your question was about cost but personally I'd vote to skip the portable unit.
It seems that moving the kid to a different room is the simplest solution. Any reason that won't work?
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