Barely Tolerable

"Don't Try This At Home (except in emergency)"

My 7 year old (then and still perhaps state of the art) central air conditioner failed on early Sunday morning, around 4am.  I had fallen asleep and left the back door open from midnight to 3am.  It was "cool" outside after midnight, about the same temperature as indoor air, but way more humidity.  That pushed my blower motor over the edge as it was probably doing a lot of low speed dehumidification.  Due to an installation mistake, my system may have a smaller blower motor than would be called for.  I hope the repair fixes that.  Now I'm waiting for I hope will be warranty repair at no cost to me, with my full parts and labor contract.  Any kind of "emergency" service by anyone else (especially me) might invalidate my warranty.

Waiting for about one week, in daily temperatures that reached as high as 105 by my measurements, or possibly higher.

Outdoors, note peak (right sidebar) high temp of 104.7F with 21% Humidity

Now I realize one must always have a backup plan.  Last time my (previous) air conditioning went out (not counting the many times I flushed the drain and fixed drain faults) it was only a mild May, with highs around 90, and I just opened the windows in the evenings until morning, and it was tolerable.

That would probably not be a workable solution under current temperatures, though I haven't tried, and the 15 hours without any backup wasn't bad, but as the day wore on I became aware that I was heating up inside thermal mass, and the next day would be must much harder to take, and then the next one harder still, as the interior floor, foundations, and walls heated up to a new level and were no longer helping to keep me cool.  (My sense is that it would take about 3 days to fully reach the new higher equilibrium temperature...which would be near deadly).

Instead, within 14 hours, my best friend lent me her spare portable air conditioner, which they quit using after they went entirely to window units throughout their home and cabin shed on a permanent basis with no central air.

BTW, Consumer Reports says window units are far more effective than "portable air conditioners," and they can't recommend a single portable air conditioner.  You should generally follow their advice unless you are adventurous and at least somewhat knowledgeable about math and engineering stuff like me.

But I'm not trying to cool one room on a regular basis.  I'm trying to cool my entire 1250 square foot living space, with an emphasis on the bedroom (which I don't want to disturb with a window unit) and the kitchen (which has no window except a sliding glass window).  Just enough to make it through the repairing of my central unit.  Just enough to be tolerable and survivable.  Not necessarily comfortable.

Peak kitchen temp on Thursday Night, 90F at 35% Humidity, "Tolerable"

The only two rooms which have conveniently accessible windows are the very rooms I care least about cooling.

The gym in particular, which is the converted half of the originally 2 car (now 1 car barely) garage.  It has one very accessible window, near the doorway to the rest of the house.  It made perfect sense to me to put a portable air conditioner right in the doorway to the gym, blowing out cold and dehumidified air into the hallways to the bedroom and to the living room.  I have fans assisting those two flows on the ground (where they should be, to blow the coldest air) and also thence from the living room into the kitchen.

Since I set up all the flows like this I'm getting tolerable but barely tolerable conditions in both the kitchen and the master bedroom (at the other end of the hallway from which all other doors are now closed).  The two rooms I care about, with more attention rightfully given to the master bedroom.  And the rest of the house is about the same too. Before the last fan re-positioning, the kitchen was intolerable from 3-9PM.

Also I've decided it's necessary to close the electric kitchen vent after 1pm or whenever the temperature reaches 100F (or perhaps as much as possible).  At lower temps, despite higher wet bulb temperature outside, it sometimes feels better to have the vent open.  My temporary portable AC system is doing a much better job of controlling humidity, actually, than temperature.  It's not doing very good at temperature at all, but the low humidity levels it is producing may actually be more important than doing a mediocre job at temperature with no control over humidity.

All this with an "ineffective" 8000 BTU (old) 6000 BTU (DOE new) portable air conditioner, set to 60F (lowest temperature).

It's an LG dual inverter type which is quieter than my fans and never cycles on/off either.  I presume it may not always be running at 100% depending on many variables, the difference between set point and average temperature, the humidity and how much needs to be removed, and so on.

I was worried whether I could move a portable to the doorway and use it like I am, because of the limited length of some of the flexible ducts they come with (and they always advise you never to add more).

But the LG has a very good length duct, it looks like it could expand to 10 feet or more.  I'm worried that other units, in particular dual duct units, couldn't do that.

I'm also worried that dual duct units might suck stuff in, like freak rainfall.  With the exhaust port constantly blowing out, that risk seems minimal.

But if you are contemplating more ordinary usage, window mount makes the most sense followed by dual duct.

However I don't know if any dual duct type units have the highly desirable Dual Inverter that LG has (in only some models, I've found out the hard way, the white ones in particular, and not the black ones they sell at Home Depot).  

Without the Dual Inverter, even if you do like most people do (and not Consumer Reports) and simply set the temperature to the very minimum, like 60F, to squeeze the last bit of power out of it...even if you do all that, the unit WILL STILL be cycling on and off as it deters itself from freezing up via that means too.

The Dual Inverter can simply back down to just below the frost point...and keep it there...with no cycling whatsoever.  I've been in hotel rooms with those noisily cycling machines which often mean you can't easily get to sleep (though I usually do, it still feels nightmarish).

And that's the joy and beauty of Dual Inverter.  I simply leave it to 60F running all day long (as well as the fans and various baffles I am using) and squeeze the last bit of cooling power to keep an emergency situation from getting worse, until my main unit gets repaired.  AND cool my entire house with one "ineffective" portable unit.  At least to some level that's barely tolerable.

But that's also why the Dual Inverters may not always seem to be blowing colder (they can blow 100% of the time if needed) because they must optimize the compressor level to deal with the frost point without shutting down.

So I (mistakenly) bought the largest black LG portable at Home Depot but fortunately figured out that it was not a Dual Inverter unit like I had borrowed before starting the very challenging job of unloading the 80 pound box from my car.

Now I've ordered the largest white LG portable from Lowes (who had an even better price than Amazon, and I've traditionally had the best handling from Lowes as well).  It's rated about 60% more capacity, 14000 BTU by the old standard and 10000 BTU by the new standard, than the one I am using now.  But before it arrives I will have to endure a few more days with the smaller unit, and after it arrives, I hope my central AC will work

Other than the weight, it should be possible to use it just as effectively as I'm using the smaller loaned unit, but with hopefully some better comfort (though still unlikely to be perfect) and to survive even hotter temperatures (which could occur in August or September).  Should once again my central AC fail.  I need to be more prepared.

And a personal AC failure is far more likely than an extended grid failure, despite frequent feelings to the reverse.  But having a portable generator which could also power a refrigerator and a large portable AC could be a lifesaver too, I am thinking now.

Meanwhile, with my emergency AC system forcing me to, I'm learning a lot more about where the limits of comfort and survival actually are.  The beginning of this learning starts with understand wet bulb temperature, and also how humidity constantly (and hugely!) varies with temperature on a typical day.

Most people have this sense that "all the bad stuff happens at once (or just to me)" even though in many cases this isn't true.  Most often it's one thing, or the other, and that's also sort of how it works with temperature and humidity.

And so, over the past 24 hours outside there was a high temperature of 104.7F (which I'll round to 105) at which time the humidity was 21%.  Then, in the evening, there was a more comfortable (very comfortable outside in fact, thanks to slight breezes) low of 79 at 82% humidity.  That's what my meter shows (though an untutored person might surmise that the high of 105F went with the 82% humidity instead, from looking at the inside display of my outside thermometer) and applying the usual "all the bad stuff happens at once (or just to me)" filter.

We would expect those two readings of 105F/21% and 79F/82% to represent more or less the same actual moisture in the air, which doesn't change much, but under different heating conditions (heated by the intense sunlight, or not).

That greater consistency is somewhat reflected by the wet bulb temperature, which is the temperature of a bulb covered in damp cloth which is evaporating water.  But what the wet bulb temperature is really useful for is determining how much evaporative cooling can help.

Our bodies are partly if not largely cooled by water evaporation.  (Other sources will imply our bodies are entirely cooled by water evaporation, but clearly there is also a certain degree of regular convection as well.)  So it is precisely the wet bulb temperature which informs us how well we can cool ourselves, or not.

The wet bulb temperature would be identical to the regular "dry bulb" temperature under the condition of 100% humidity.  So with anything less than 100% humidity, the wet bulb temperature will be lower than the dry bulb temperature, and at 0% humidity it will be as low as it can get relative to the dry bulb temperature.

35 C (equivalent to 95F) is the theoretical 'maximum' wet bulb temperature under which our bodies can still cool themselves.   Above that is quickly fatal for even very healthy people who are just relaxing.  But for people with less than optimal health and vigor, lower thresholds have been proposed, including 30C and 31C.

Here are some temperature/humidity combinations which yield the usually fatal 35C:

95F, 100%  (obviously)

100F, 82%

105F, 68%

110F, 55%

115F, 45%

120F, 37%

122F, 35%

These conditions are rarely seen in even the hottest cities, because as the dry bulb temperature shoots up way past 95F, usually the relative humidity drops to the floor at exactly the same time.  For example, the condition I measured here a few days ago, 104F with 21% humidity has a wet bulb temperature of only 73.5F, quite far away from 35C.

What you cannot do is simply combine the humidity you may have heard reported last night (such as the 79% I measured last night) and apply it to the dry bulb temperature you measure today.  Computing the wet bulb temperature requires that both temperature and humidity be measured at exactly the same time.

This relationship is not just cause-and-effect, it is definitional because the "relative humidity" itself is a measure of home much moisture is in the air compared to how much moisture the air can possibly hold--at that temperature.  As the temperature rises, the air can possibly hold more moisture, so given the same amount of moisture at a higher temperature the relative humidity will go down.  You will observe exactly the same effect of declining relative humidity even in a greenhouse or locked car in the sunlight, except under conditions where the moisture is being added to (such as from the breath and perspiration of the person or dog in that locked car, and by the way, never leave a person or dog in a locked car).

Now while the wet bulb temperature is a good measurement to make to determine how safe the temperature/humidity is for humans or similar animals, it is not necessarily equivalent to a comfort index.  It appears to me anyway that we can also sense the dry bulb temperature to some degree independently of humidity.  If we have trained ourselves to recognize hotness based entirely on the dry bulb temperature sensation, the effect of high humidity can creep up on us like a sledgehammer.  (This happened to me, born and raised in the relatively dry environments of Southern California, on a summer trip to Indianapolis, where the temperature was only mid 80's--something I was very used to, but the relatively high relative humidity was a knockout which almost made me sick.)

Speaking of which, air conditioning was mostly something I only lusted for in my 36 years of living in Southern California.  It mostly wasn't needed at all during my 14 years in San Diego.  But growing up in the San Fernando Valley, with temperatures reaching above 110F, it would have been nice.

Instead, it seems, we took long summer vacations...  And our cars were (mostly) air conditioned (at least after 1963 or so).

We had been sold a swamp cooler, and it seemed it never worked.  (Now I realize it may have simply not been properly maintained.  Coming from Minnesota, and being traditionally female, my mother did not know anything about keeping mechanical things working.  Nor did I at the age of 11 when my father passed away, despite my sense that I knew everything.  Somewhere along the line we did call for 'service' but probably to the wrong kind of agency.  They simply told us that "swamp coolers are not effective in the San Fernando valley."  That could have been mostly wrong.  It might have simply needed better--or at least some--maintenance.)

So I sat in my tiny 9x10 bedroom looking out the window at our fancy pool and covered patio, with both the indoor and outdoor temperatures above 100F.  Real air conditioning cost thousands of dollars.  Our entire home had only cost $20,000 in 1960 (and before all of my mother's ambitious improvements, which included everything except air conditioning).  So air conditioning seemed like a significant portion of what an entire house cost.  Most people on my street and most people I knew did not have air conditioning, until after 1970 or so.  After winning some wrongful injury lawsuit related to a car accident, a best friend's family splurged on air conditioning.  That was the kind of money you needed, and which my strapped family didn't have, especially given my mother's later ambition to build a second summer home in Mexico on the beach.  Well, that was her air conditioning.

Well even though central air was plenty expensive in the 1960's (and, we were told, would require all new duct work in our house because the 'heat' ducts were too small for air conditioning) it seemed that room air conditioners were already pretty affordable.  So for a few years just before I left the valley to go to college, I wondered what I could do with a room unit.  And, in my imagination, I wouldn't just be cooling my tiny bedroom (where I rarely spent much time anyway, it seemed).  But the entire house.  I figured it would be better than nothing.

But somewhere along the line, somebody disabused me of this notion.  They said that a tiny air conditioner would have basically zero effect on a large house.  They even implied it would make it worse.  I recall someone (possibly my chemistry teacher) told me that a small air conditioner would be "running all the time" and as a result it would reduce humidity*, but it would not lower the temperature by much.  At the time (and not realizing yet how important humidity was), this did not sound like a win.

(*The dehumidification is determined mostly by how much and for how long air is in contact with the evaporator coils.  So 'running all the time' gets you to maximum dehumidification, but not necessarily the coldest dry bulb temperature.)

But here I am today, with vastly more knowledge generally and also 32 years of experience actually using (and maintaining) an air conditioning system of which some kind is virtually required to live where I do now, San Antonio Texas, and I'm doing the experiment I wanted to try as a kid.  I'm cooling (or actually, mostly just dehumidifying) my entire house using a small air conditioner with no more capacity (and possibly less) than an old window unit.

And just as I expected, it's better than nothing.  It may even be a life saver.  And a kind of backup I'm going to always need.  Also a small air conditioner is about the only thing I could imagine powering with a generator or backup electrical system of some kind, except for a very big backup electrical system that can power 220V.

It's not "comfort" but it works.

I have not conducted (and am not even capable of conducting) a proper experiment, but it seems like I may have improved the wet bulb temperature as much as 7F, moving twice as far away from any point which would have been unsafe.

90F, 35% -> 70F web bulb (21C)

Guesstimated w/o emergency portable air conditioning

96F, 40% -> 77 wet bulb (25C)

So, "8000 BTU" works for the whole house, well enough to keep me safe, but I won't call it comfort.

*****

Today (Friday) in the morning I was planning to leave the kitchen vent open, having convinced myself that was ok and even good to do at night (because fostering a kind of heat transfer through the metal itself as well as the very slight air movement I finally felt there).  But instead, I did the opposite experiment.  I pressed the "Bedtime" button on my home control system (which I'd been planning on avoiding) and that closed the vent, as it's long been programmed to do.

At least partly as a result, that morning I saw the lowest morning kitchen temperature I've seen since the first 24 hours of the AC failure.  It was a mere 84F at 43% humidity, pretty nice.

Then, the high temperature during the reluctantly peaked at 91F after holding 90F most of the afternoon.  BTW, the peaking generally occurs right at sundown when the solar heating has stopped, around 9PM.  The continued climb of the temperature even after the outside has started cooling down is no doubt due to the thermal mass of the house, AND it's being warmed by direct solar radiation, for which more is more..

Yesterday, I was wrong in saying it peaked at 91F.  Actually, it peaked at 93F with 33% humidity.  But I'd adjust the other side of the comparison with a guesstimated no AC condition to around 98F, still yielding a guestimated improvement of about 4C in the wet bulb temperature, which is somewhat less than half the way to the 30C temperature advised as the near fatal temperature for the youngest and elderly (instead of 35C).  In short, the weak AC is near doubling the margin from the wet bulb temperatures to be most avoided for the young and elderly, that's my guess.  As a result of AC, that margin is over 10F.

So the lower morning low and evening high are evidence on the side of keeping the kitchen vent closed at all hours to keep the dry and wet bulb temperatures lower (I suppose unless it's needed for some reason, I still think it might be good when running the dryer at night, when the back vent represents an easily preferred airflow source, in contrast to the likely next: the attic.

With all the fans now running, the current 91F (I was going to write 90F, but it may have just now been boosted by the 5 minutes or so I needed to get the newly arrived 10,000 DOE BTU air conditioner inside the house) and 33% is beginning to seem quite fine and normal.  I'm sure I've endured many hotter inside hours in my 36 years of non air conditioned living in Southern California, for example.

And the lower-than-otherwise 33% humidity is a very big part of that, though I'm still don't believe "wet bulb temperature" is the entire story.  Even if the humidity is super low, hot like 122F (50C) is just plain too hot for most life.  That's probably why my wet bulb calculator refuses to go above 122F.

The human body absorbs radiated energy from all sources (which might partly be blocked by clothing, which tends to convert it into infrared energy) and also itself radiates energy slightly, enough to be detected by IR cameras for example.

The shell of a home absorbs much (without white metal roof it is most) of the energy which falls upon it, and after some delay it radiates some of that energy inside to the occupants.  People used to obsess about that but now they tend to obsess more about air leaks, which are generally a bigger issue, but then houses need some ventilation too anyway.

To a limited degree, houses tend to trap moisture inside when it's hot, and they tend to trap dryness inside when it's cold.  The moisture comes from water appliances, people, even the furnishings that expel water as they're heated up.

So I suspect the 'moisture content of air' is generally higher inside during summer unless you have some kind of air conditioner or dehumidifier.  My current vastly undersized air conditioner is serving as much as a dehumidifier as anything else, since it's not dropping the temperature near enough to be fully 'comfortable.'  But in these ranges, the humidity is super important too, and I'm in no great discomfort at all.

The actual moisture content of air is as hard to calculate as anything from the temperature and humidity.

Without low enough humidity, fans are useless.  That's where the 30/35C criteria kick in.  Even with fans, perspiration won't do any good if the wet bulb is above 30C (elderly) or 35C (youthful healthy adults).  With fans, you can push it right to those limits.  So doubling the margin to these temperatures is important.  So, undersized AC is useful for emergency use if not wonderful, and the concurrent approach of keeping home sealed and AC running seems to work best.

Along with obvious tweaks, like shutting down (and not running) big audio and video equipment (just keeping the computer equipment going, at least if dry bulb doesn't exceed 100F) and basically as much as possible, except fans to both distribute the colder air and keep  air blowing past people.

Also not cooking but getting by with prepared meals that can be merely microwaved.  Running stove and oven are going to be impossible for tiny AC to keep up with.

Running dishwasher very late, long after bedtime.