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Just for the Helluvit, I took Pearl out for a nice ride around town with the outside temp around 90F and dew point around 70F, just to see what it would be like.

Honestly, I don't know how you guys in the Southwest can stand it.  

It was awful out there!

And we're getting to be like @WOLFGANG and @Panhandle Bob; Quick downpour somewhere around 4pm but the humidity persists.  

Time to stay in and watch a movie.

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Regarding the SW - I can roll all day long in the car if it's 95° with a 60° dew-point and I've got a hat and a Polar-Pop from Circle-K. Any time the dewpoint gets above 70°, it's going to feel like you are suffocating in a wet sleeping bag.

... and that's exactly how it's been for a couple of weeks. We get raging t-storms, but the weather doesn't break.

It's August. Be thankful. Winter is coming soon enough.

@Lane Anderson we were only there in August once, when we bought the place.  That would be in the middle of Hurricane Francis but we both remember it being really hot and humid.  When we sold the place and moved out was in the middle of Hurricane Sandy so I guess 2012.  It has only gotten hotter and humidier, since.  Always arrived just after Labor Day and headed North for Carlisle in mid-May.  That was our season, and I miss it.

These days if I'm taking a drive in the summer I'm getting up early.  630-930 is just about right.  Then I have all day to sit on the beach or go to a brewey or whatever.  I've decided I'm not getting heat or AC in my Conv D.  When I had my IM I spent over $1000 twice to fix the AC.  Compressor died twice.  Don't ask my why.  And where I live in Va Beach VA I really don't need heat.  I'll just get heated seats and bundle up on drives.

I will be asking Carey to give me fresh air vents that I can open and close.  Hopefully this is possible.

Last edited by 550 Phil

Read the other day about a soon to be shortage of beer coming soon!  Now that caught my eye.  Seems there's a shortage of CO2 need to add the fizz?  WTF?  This is affecting craft brewing at this time.  I thought the whole Climate Change was due to CO2.  Hey, I'm willing to help out now that it's striking close to home .

The shortage of carbon dioxide, which is used to make beer is due to a contamination issue that happened in a Mississippi factory. And carbon dioxide supplies were already tight because pandemic shutdowns forced many key suppliers offline, a disruption they still have not recovered from. The summer is also a pressure point in the supply of carbon dioxide as key facilities go offline for scheduled maintenance.

@Theron posted:

No perceptible humidity and 80 degrees today.  Can someone explain what a dew-point is?  Of course we have no water to drink, but the weather is great!
-=theron

As I understand it, the dew point is the temperature at which water must condense out of the air.  Air can hold less and less water as the temperature falls.  The temperature cannot fall below the dew point, which often defines the overnight low.  That’s why it can get quite cold at night in a desert, even after a triple digit daytime high.  This time of year our overnight lows are usually in the low 80s here in Charleston, meaning dew points in the 80s.  I know that was a poor explanation, but hopefully it helps.

@IndianBob posted:

Going to by about 70°F and dewpoint and humidity around 50% for Monterey Car Week. Can’t wait to get out of this 100°F Sacramento weather for a few days.🥵

I'll bet.

If the sensible temperature in Monterey is 70°, and the RH is 50%, the dew-point is 52°. Dew point is expressed as a temperature.

FWIW, 70-75° with 40-50% RH is what most people find to be "perfect" - at those conditions, very few people complain. It's what we try to hit with comfort cooling.

Last edited by Stan Galat
@Theron posted:

No perceptible humidity and 80 degrees today.  Can someone explain what a dew-point is?  Of course we have no water to drink, but the weather is great!
-=theron

As I understand it, the dew point is the temperature at which water must condense out of the air.  Air can hold less and less water as the temperature falls.  The temperature cannot fall below the dew point, which often defines the overnight low.  That’s why it can get quite cold at night in a desert, even after a triple digit daytime high.  This time of year our overnight lows are usually in the low 80s here in Charleston, meaning dew points in the 80s.  I know that was a poor explanation, but hopefully it helps.

Close.

The temperature can drop below the dew point (clearly, or winter would be pretty wonderful here). But if it does, the moisture in the air will condense and drop out either as dew or fog or both.

Warm air has the capacity of holding more water, if the water is available to hold. The dew-point is the temperature that the air needs to drop before you reach "saturation" - when the temperature drops to the point where the water suspended in the air starts precipitating (dropping out of suspension). The more water suspended in the air, the higher that point will be. If the dew-point in Charleston is 80° (and I've seen it for myself), that air is really heavy with water - "air you can wear". If the dew-point in Phoenix is 50°, there's not a lot of water in suspension.

Water in the air is a huge heatsink and moderates the temperature. There are other factors at play, but on the surface of the moon (a 0% humidity environment), the temperature gets to 260° on the side facing the sun, and -297° on the dark side. The lack of moisture hanging in the air is why deserts are blazing hot in the day, and pretty magical at night.

With all the water in the air in places like Charleston and Peoria (to a lesser extent), once the air temperature reaches dew-point, the heat transfer goes from sensible (what you can measure on a dry-bulb thermometer) to latent (which is measured with a wet-bulb psychrometer). Latent heat is the heat energy is being used to condense the moisture before the dry-bulb thermometer drops any further. As Lane got (almost) right, if there's a lot of moisture in the air, the sensible temperature will often not drop past the dew-point. With less water in the air, it can punch through... once the condensable water has already dropped out of suspension (again, the desert night).

There is an enormous amount of heat energy absorbed with the evaporation and condensation process - an enormous amount of heat energy is used to turn 211° water into 213° steam (much more than to raise the temperature of water 2°, and much, much more than the heat energy to raise the temperature of steam the same amount). It works in reverse too - there's an enormous amount of heat energy used to take humidity suspended in the air and drop it out in the form of dew.

Swamp coolers work in low humidity environments because the heat energy absorbed by evaporating the water in the cooler actually cools the space. Your body does the same thing by sweating. This is why swamp coolers only work in the desert, and why sweat rolls off your nose in the deep-south. When you sweat in Barstow, your perspiration evaporates almost immediately and cools you to some degree (which is good, because the sensible temperature is over 100°. When you sweat in Charleston, the air is already near its carrying capacity for water - so rather than evaporating (and cooling you), your sweat just pools and rolls off. It's kinda' gross feeling.

Dew-point is used to calculate RH (relative humidity), which is a calculation based on the sensible temperature and the dew-point and expressing it as a percentage. Think of RH as a "gas gauge" for water in the air - it measures the percentage of water in the air as compared to the capacity of the air to hold water at a certain sensible temperature. The humidity is never "100%" unless it's pea-soup fog or raining, and the RH is always higher in the early morning, because the air temperature (and therefore, it's capacity to hold water) has dropped, but the water that was in the air is still there (until the temperature reaches dew-point and drops out of suspension). It feels worse in the afternoon, but the RH is actually lower (because the sensible temperature is higher)

It's kinda' cool (in a geeky sort of way) when you stop and think about why things work the way they do.

Last edited by Stan Galat
@550 Phil posted:

These days if I'm taking a drive in the summer I'm getting up early.  630-930 is just about right.  Then I have all day to sit on the beach or go to a brewey or whatever.  I've decided I'm not getting heat or AC in my Conv D.  When I had my IM I spent over $1000 twice to fix the AC.  Compressor died twice.  Don't ask my why.  And where I live in Va Beach VA I really don't need heat.  I'll just get heated seats and bundle up on drives.

I will be asking Carey to give me fresh air vents that I can open and close.  Hopefully this is possible.

With the IM on my aircooled model the AC needed top up a lot.  

I have had to replace my compressor on my new IM, I discovered that the underdash hose was leaking and slowly killing the compressor so I went with EZ clip to install a new line and try to have the AC looked at for pressure more often as the lines are pretty long on this car.

In the summer with the top down and vents to the floor it is surprising how nice it can be with 100 degrees in the sun.  I would not go without it but some do.

Your idea of a vent for outside air a la Davis at IM is what I wish I had for fall weather it would help with the windshield too.

@IaM-Ray posted:

Your idea of a vent for outside air a la Davis at IM is what I wish I had for fall weather it would help with the windshield too.

Agreed, AC can make the difference between an enjoyable cruise and a sweltering one, even with the top down.

Re: a vent for outside air, I've wired up a switch under the dash to turn off the compressor so we can get ventilation through the AC vents. The AC blower still moves the air around. Our AC doesn't recirculate air from the cabin, it's always fresh air from the battery box area.

Agreed, AC can make the difference between an enjoyable cruise and a sweltering one, even with the top down.

Re: a vent for outside air, I've wired up a switch under the dash to turn off the compressor so we can get ventilation through the AC vents. The AC blower still moves the air around. Our AC doesn't recirculate air from the cabin, it's always fresh air from the battery box area.

That is how the VIntage air unit does the heat portion of the heating AC in newer IMs.

The Davis mod is pretty cool as it uses outside air and has pull knobs to control it and it has the ability to close when it gets cold. Also to deal with water infiltration. Then they added it to a 911 fan under the front hood, a scroll fan.  AFAIK the same thing could happen with a hose and ram air vent to get outside air in at speed in my car, but the sophistication would have to be added to deal with rain etc.

With your set up and your island temp all you need is a sealed battery and constant on.  I am sure it works well.  Good for you.

.

So that was a psychrometer I was messing around with in fourth grade science class.

We called it a ‘wet and dry bulb hygrometer’, which was impressive-sounding enough for me at the time, but Mr. Google says the two are pretty much the same thing, only ‘psychrometer’ has fewer syllables.

We made the thing out of two dime-store thermometers (we had ‘dime-stores’ back then) taped to a milk carton that we filled with water. There was a shoelace from inside the carton that we wrapped around the bulb of one of the thermometers. The ‘wet-bulb’ thermometer was supposed to read less than the dry-bulb thermometer (due to all that stuff that Stan explained) and there was a chart from a book that let you look up the relative humidity based on what the two thermometers read.

That was probably the first time I ever thought about relative humidity (in the fourth grade you don’t think a lot about things you can’t see). But that probably planted the seed in my head that told me I would eventually have to move to California.

For the record, the current humidity in Santa Barbara (OK, relative humidity) is 50 per cent. And here's what the next week is looking like:



SantaBarbaraWX



I'm guessing that no one in Santa Barbara has any idea what a dew point is.

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  • SantaBarbaraWX
@Sacto Mitch posted:

.I'm guessing that no one in Santa Barbara has any idea what a dew point is.

Probably not.

They definitely don't have any idea about what snow is really like (pro tip: it's not like "It's a Wonderful Life" - if George Bailey were facing an actual winter in Bedford Falls, he'd probably have jumped off the bridge).

They've definitely never had the moisture collected in their nose hairs freeze and close off their nostrils.

The fun they miss out on. It makes me feel so sorry for those poor souls.

Last edited by Stan Galat

My wife and I were in Loudon, NH at NHMS for a Formula Vee race this past weekend.

I thought the Northeast would be cooler than New York's Hudson Valley. I was wrong. It was even more humid, sticky, and hot than it was at home.

Good aircooled acid test though. All cars survived, even mine. More on that in another thread, later. I'm waiting on some pictures to get emailed.

As a once-practicing, but now retired, theoretical thermodynamicist, I was going to pontificate on dew point and relative humidity, as I understand it pretty well.  But Stan, whom I will call a practicing thermodynamicist, insofar as he actually makes stuff that deals with this sort of physics vs. just sits there with his computer and contemplates the pertinent partial differential equations, has nailed it down pretty tight.  So I defer.  We live in a water world, and nothing quite affects just about everything so much as the evaporation and condensation of water in our atmosphere.   Your beer is going to get warmer quicker on a 90F, 80% RH day (dew point 83F) than on a 90 degree 40% RH day (dew point 62.4F).  The dew point is the temperature of the water molecules as they condense on the outside of that cold beer can.

I was out in Albuquerque New Mexico in May once upon a time, and it was a really beautiful day, Blue-bird sky, gentle breeze upper 70s, may be 80,, hard to tell. Had the radio going,  The guy came on and mentioned the current weather by noting the temperature and humidity, which he said was 5%.  FIVE!!??? Is that even possible?  I think he made a mistake, or I heard wrong.  Even at 90F air temp and 5% RH the dew point is 10F.  We were not freezing.

... and I'll pick a tiny nit with Stan, my main HVAC man.  He uses the term suspension to describe the amount of water vapor in the air.  that's a misnomer.  A suspension is like what makes dirt (solids) in water (liquid) muddy, and does not involve a change of state, the solid dirt is suspended in the liquid water, not disolved in it.  Dust is "suspended" in air, kind of a physical thing.  water vapor is held in the air as a gas and so is the same state (gaseous)  as the air itself.  So humid air is just a bunch of Water molecules and air molecules (nitrogen, oxygen plus some other stuff too) all bumping around and into each other with energies depending on ( or measured by) the temperature.  The thermodynamics is such that the water vapor (gas) molecules will decide to coalesce into a liquid (and will release  their heat of fusion when they do so) at temperatures significantly higher than the air molecules (mostly nitrogen) will do the same.  Liquid nitrogen at atmospheric pressures will form at -320F; oxygen at 1 atm will liquify at -297F.

I now have an enhanced appreciation for past "Tech Writers" who could take highly technical or abstract concepts and write them up in ways that "Common" people could understand.  Most Engineers in my past never had that talent, as most of them thought in abstract terms that were not part of my normal "jargon".

Kelly does a pretty good job of bridging that knowledge gap, and that's a rarity in the technological world, for sure.  Dinner conversations with him are usually pretty interesting, too.

Txs Gordo ... I have believed that most stuff (with the possible exceptions of string theory and the time before the Big Bang), if truly understood, can be explained to an interested and intelligent, but otherwise ignorant, listener.  I had a lot of practice in my many years as a rocket scientist.  Early efforts were pretty dismal, I must confess.  It took a fair amount of practice, and some coaching.

PS: as to the question of how fast does my beer warm up on a hot, humid day vs. a hot not so humid day, I have thought I could actually write a paper about that, with all the proper equations, charts, graphs, and eight-by-ten colour glossy photographs with circles and arrows and a paragraph on the back of each one explaining what each
one was to be used as evidence against us.  -- with apologies to Mr. Guthrie, Jr.

to Stan: if you just use the word "mixture" vs suspension, you got it.

Jargon can be tricky. Air, humid or not, is a mixture of gaseous molecules.  Put sugar in water and it dissolves (up to a point), and is called a solution.  The way molecules dissolve and interact in liquids is fundamentally different than how they interact as gasses.  Likewise, solids are sometimes regarded as solutions because they form when in the melted, liquid state, and then organize in complicated ways as the liquid cools and solidifies.  And here the interactions, esp'y wrt to temperature can be very complex.  The different ways in which those atoms/molecules interact are called phases.  metal alloys are a staggeringly complex universe of solid solutions (phases) that if I told you I understood, I'd be lying. Carbon and iron together make steel, add chrome and vanadium, get stainless steel, and ... ad nauseum.

Isn't glass actually a liquid?

I had heard that it was (and once believed it), but it is really an amorphous solid - an in-between state between true solid and true liquid.

The idea that glass is a true liquid comes from old window panes that were thicker at the bottom than at the top, making people think that the glass had 'melted'.  But, the reality is that old window makers simply put the thicker part of a pane toward the bottom of the panel.  Old glass was never perfectly made, and one side/end could be thicker than another.

The things you learn when you get into restoring a 160 year old stone house...

Last edited by Bob: IM S6

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