PSA - How hot is too hot?

[AntonioGG]

@cxagent take a look at my ride from yesterday https://www.strava.com/activities/2475474003 in the hottest part of the day.  It was a bit of an experiment (stupid one) after following this thread.  I wore my Pearl Izumi sun sleeves and a club jersey.  The sleeves were drying even though I was sweating.  The jersey and my skin (other than my arms) stayed moist.  It mostly felt OK except for the 620 climbs (with some tail wind) and some of the 360 climbs where the south headwind was being blocked by the hills.  The worst was the climb from the dam to past Marshal Ford (and the two stupid super long lights in a row there) the Garmin-indicated temp at the dam wad 93°F and at the top it was 100°F.   The sleeves definitely did their job but the "technical" fabric of the jersey did not work as well as the sleeves.  I had to stop 3 times to get water even with 3 bottles when normally I could do the whole thing without stopping.  The best was the Chevron on 2244 that had sprinklers running on the bit of grass with a picnic table.  

The sleeves I think help pull moisture off the skin, and increase the surface area for evaporation.  What I don't know is if it's possible for a material to increase the rate of phase change of the water.  I know they make nano-materials that increase condensation or make it possible when it isn't condensing anywhere else.

My sleeves are a few years old, but when they were new, the amount of cooling was freaky.  I mostly got them to block the sun since I hate putting on sunblock, but now I wish I could get a whole kit made out of this material.

I'm not sure what the dew point was yesterday, but I'm curious what my experience says about evaporation cooling based on the conditions.

[throet]

1 hour ago, AntonioGG said:

I'm not sure what the dew point was yesterday

73+

[AntonioGG]

I just read @cxagent's link on dry bulb, wet bulb, and dew point.  Thanks!  I'm definitely saving that link.  So to summarize my above post, what I'd like to know is if the material choice in the wet bulb would make a difference.  Would wet bulb temp with muslin be higher than wet bulb temp with a tech fabric?

[Anita Handle]

How many muslins does it take to change a wet bulb? 

 

I couldn't think of a punchline. I'll sharia if I think of anything.

[Ridenfool]

56 minutes ago, Anita Handle said:

How many muslins does it take to change a wet bulb? 

 

I couldn't think of a punchline. I'll sharia if I think of anything.

Pretty good. Some might say "that's a wrap" at this point.

Others might crank up the turbans and see where the hot wind carries it.

Edited June 24, 2019 by Ridenfool

[Anita Handle]

Didn't mean to sheikh things up and go off topic.  Hopefully the admin doesn't mecca me delete my comments.

[cxagent]

5 hours ago, Ridenfool said:

If I were to visualize "phase change" as a part of the movement of heat it would look like a layer or a step in the process.

Example: Sweat absorbs heat from body, pores move sweat to skin surface, phase transition changes heat in liquid to heat in vapor, convection moves the vapor into the surrounding air, carrying heat away from the skin.

Phase Transition is like a part of the path, much like the thermally conductive compound between CPU and Heat Sink is a layer the heat must efficiently move through before being carried off by convection from air passing over the fins of the Heat Sink.

The wet bulb effect is interesting. This essentially determines the maximum potential cooling that could be achieved under perfect conditions. So, if 82 is the daily low (wet bulb/dew point), and the OAT is 94, under routine conditions with reduced (lets use 50%) efficiency there may only be 5 or 6 degrees of cooling, at best.

If the OAT is 100 with an overnight low of 85 the cooling effect might only be just approaching that 93 degree F point where no actual cooling of the skin occurs. (change the numbers based upon whatever the realistic percentage of cooling under these conditions might be)

(I typed this once before the power went out and it all disappeared. So this will be the 'lite' version.)

Heat transfer is a "layered" process. Typically one or two of the 'layers' dominate the process. Think about it as each 'layer' being a resistance to heat transfer. some of the 'layers' has a resistance of 1. Some of the layers have a resistance of 3. But one of the layers has a resistance of 100. (numbers for engineer types Rtotal = 1+1+3+3+100 = 108) You could half all of the other 'layers' so they each have 1/2 the resistance as they had before, but it would make almost no difference as long as the 100 resistance layer is not changed (Rtotal = .5+.5+1.5+1.5 = 104). The convection heat transfer coefficient is typically the 100 resistance value. Evaporation makes the ~100 convection coefficient more like 0.1 (Rtotal = 1+1+3+3+.1=8.1). So even though all of the other layers and their resistance is still there, the total resistance went WAY down.

Central Texas low temperatures rarely vary much. Normally in the 65F to 75F range. It might be 80F by the time we get out of bed and ready to ride - but that is not the low temperature for the day. The Central Texas dew point temperature is also in about that same range. If we get a summer cold front or a summer rain shower it might change for a short time. But then it goes right back to that range.

Mentioned before but left out of the recent discussion is the impact of sun exposure on body temperature. I don't think I have to tell you that being in the sun makes you feel hotter than being in the shade. That feeling is real. The sun is transferring a lot of heat by radiative heat transfer. Radiative heat transfer generally takes "larger" temperature differences. Five to 10 degrees F does not move much heat. The sun at a few thousand degrees moves a lot of heat to our puny bodies at under 100F.

Edited June 24, 2019 by cxagent
Typos

[cxagent]

3 hours ago, AntonioGG said:

@cxagent take a look at my ride from yesterday https://www.strava.com/activities/2475474003 in the hottest part of the day.  It was a bit of an experiment (stupid one) after following this thread.  I wore my Pearl Izumi sun sleeves and a club jersey.  The sleeves were drying even though I was sweating.  The jersey and my skin (other than my arms) stayed moist.  It mostly felt OK except for the 620 climbs (with some tail wind) and some of the 360 climbs where the south headwind was being blocked by the hills.  The worst was the climb from the dam to past Marshal Ford (and the two stupid super long lights in a row there) the Garmin-indicated temp at the dam wad 93°F and at the top it was 100°F.   The sleeves definitely did their job but the "technical" fabric of the jersey did not work as well as the sleeves.  I had to stop 3 times to get water even with 3 bottles when normally I could do the whole thing without stopping.  The best was the Chevron on 2244 that had sprinklers running on the bit of grass with a picnic table.  

The sleeves I think help pull moisture off the skin, and increase the surface area for evaporation.  What I don't know is if it's possible for a material to increase the rate of phase change of the water.  I know they make nano-materials that increase condensation or make it possible when it isn't condensing anywhere else.

My sleeves are a few years old, but when they were new, the amount of cooling was freaky.  I mostly got them to block the sun since I hate putting on sunblock, but now I wish I could get a whole kit made out of this material.

I'm not sure what the dew point was yesterday, but I'm curious what my experience says about evaporation cooling based on the conditions.

I looked at it. I'm not sure what I was looking for.

Technical (wicking) fabrics do great for encouraging evaporation. The move the moisture from your skin to the surface of the fabric where it can evaporate more easily. Other fabrics (e.g.cotton) soak up the water (sweat) and hold it. They don't encourage evaporation by getting the water to the surface where it can evaporate. And as they hold the water they block more and more of the air flow that would help to cool the skin.

Some (many?) of the technical fabric are treated with a coating that gives them the wicking function. As they are worn and washed the coating gets stripped away. Eventually they don't wick any more.

 

[Ridenfool]

I think we are on the same page.  If I understand it, the convection layer is necessary in order to get cool, and, it is the least efficient of the layers involved. Therefore, regardless of how efficient the other layers are, the ability of the air to carry heat, through thermal transfer and movement of heated water vapor, this layer will be the most significant limiting factor.

The higher the heat, or more specifically, the lesser the difference between body temp and OAT, the more challenging it will be to regulate body temperature while riding.

Edited June 24, 2019 by Ridenfool

[throet]

Thread over - nothing more to talk about 

 

[Ridenfool]

10 minutes ago, throet said:

Thread over - nothing more to talk about 

 

'bout time you unpacked that suitcase ...

[AustinBike]

Putting plans together to get out of dodge for as couple weeks in August. Wife keeps telling me that if the Texas weather is like it has been for June she might decide to cancel and just ride it out here. So I am actually cheering for a couple 100+ days in July to help convince her that a trip is in order.

[Chief]

I work outside on hot pavement in the summer working on even hotter cars. What I can say when it's hot is be sure to have plenty of cold liquids on hand and some type of rag or cooling towel and cold water available. When I start to feel the heat more than I'd like I soak the towel in cold ice water from my cooler ring it out a bit and wrap it around my neck, super effective at getting core temp down a few degrees. The cold towel helps to cool your blood passing through your carotid artery helping to drop your core temp a bit. Works wonders. I know, I know we can't do that on a bike but might be handy info for some when working in the yard.

[cxagent]

1 hour ago, Chief said:

I work outside on hot pavement in the summer working on even hotter cars. What I can say when it's hot is be sure to have plenty of cold liquids on hand and some type of rag or cooling towel and cold water available. When I start to feel the heat more than I'd like I soak the towel in cold ice water from my cooler ring it out a bit and wrap it around my neck, super effective at getting core temp down a few degrees. The cold towel helps to cool your blood passing through your carotid artery helping to drop your core temp a bit. Works wonders. I know, I know we can't do that on a bike but might be handy info for some when working in the yard.

Actually - we can. When it gets really hot or I am feeling the heat more than normal, I pull a mouth full of ice water out of my Camelbak and spit it onto a rag. Then wrap that rag around my neck for a short ride. Rinse and repeat as needed.

Why do I pull the water into my mouth first? I get a little drink and warm the water up just a bit. And I don't waste any water dripping it onto the rag from the hose. YMMV

[AustinBike]

Costco also sells some kind of neck bandana thing that is supposed to keep you cool. Wife bought one and never really used it, I am going to ask her where it is and give it a try.

[Ridenfool]

18 minutes ago, AustinBike said:

Costco also sells some kind of neck bandana thing that is supposed to keep you cool. Wife bought one and never really used it, I am going to ask her where it is and give it a try.

If it is one of those filled with the little water-absorbing rocks inside, they work surprisingly well and last a good while. I've got one somewhere, maybe in my motorcycle gear, and will have to dig it up now that you've reminded me.

[AntonioGG]

Your posting of special neck cloths got me searching for phase change cooling for sports and I ran into this http://www.mscooling.com/athletes which reminded me of another experiment.  

I have a https://www.coolshirt.com from my racing days.  I had a custom one made where they put the tubing on a technical tee instead of the usual cotton or Nomex.   After a failure of trying to cool my garage with a roll-around AC unit, I thought about deploying my cool-shirt system when using the trainer in the summer.  I didn't last 5 minutes.  Where the coolshirt was perfect under 3 layers of Nomex in a hot race car, it did not have enough cooling power (pure conductive in this case) for doing intervals on the trainer.  Nothing beats air volume so I switched to two massive fans to replace my window box fans.

[jcarneytx]

8 hours ago, AustinBike said:

Costco also sells some kind of neck bandana thing that is supposed to keep you cool. Wife bought one and never really used it, I am going to ask her where it is and give it a try.

I have something similar, basically a stretchy tube you slide over the head after thoroughly damping it up. Cools from the evaporation of that water. Gets body warm, though, so you need to rotate it   every now and again.  DOES work, mostly, but I found that used while riding tends to evaporate it too fast. Seems to work better at a slower pace (not moving at bike speed) If it's really hot and I'm riding, I really want that air flow around the neck.

Edited June 26, 2019 by jcarneytx

[mack_turtle]

On working outside- I lasted less than six months as a commercial electrician a few years ago before taking a big pay cut to work in a bicycle shop again. I worked in several buildings that summer, buildings with no electric other than temporary lights and a few fans, but walls to trap heat in. Long days in 100+ in boots, jeans, hard hat and carrying heavy tools around tool it's toll on my soul.

Iwould lay in bed in a puddle of my own sweat every night trying to get to sleep knowing I had to get up at 4:45 and do it again 6-7 days a week. Lots of overtime pay but I got seriously depressed. I could not drink enough water to stay hydrated, Gatorade didn't help either. Mad respect for people who can do a job like that. That kind of heat makes me not want to ride my bike in modern technical fabrics let alone denim.

[Chief]

20 hours ago, AustinBike said:

Costco also sells some kind of neck bandana thing that is supposed to keep you cool. Wife bought one and never really used it, I am going to ask her where it is and give it a try.

I have those and they work very well.

[AustinBike]

9 hours ago, mack_turtle said:

On working outside- I lasted less than six months as a commercial electrician a few years ago before taking a big pay cut to work in a bicycle shop again. I worked in several buildings that summer, buildings with no electric other than temporary lights and a few fans, but walls to trap heat in. Long days in 100+ in boots, jeans, hard hat and carrying heavy tools around tool it's toll on my soul.

Iwould lay in bed in a puddle of my own sweat every night trying to get to sleep knowing I had to get up at 4:45 and do it again 6-7 days a week. Lots of overtime pay but I got seriously depressed. I could not drink enough water to stay hydrated, Gatorade didn't help either. Mad respect for people who can do a job like that. That kind of heat makes me not want to ride my bike in modern technical fabrics let alone denim.

The guys doing AC work in Texas get my respect. 120F+ in most of those attics in the heat of the summer working on AC units that have died. 

Edited June 26, 2019 by AustinBike

[Anita Handle]

12 hours ago, mack_turtle said:

On working outside- I lasted less than six months as a commercial electrician a few years ago before taking a big pay cut to work in a bicycle shop again. I worked in several buildings that summer, buildings with no electric other than temporary lights and a few fans, but walls to trap heat in. Long days in 100+ in boots, jeans, hard hat and carrying heavy tools around tool it's toll on my soul.

Iwould lay in bed in a puddle of my own sweat every night trying to get to sleep knowing I had to get up at 4:45 and do it again 6-7 days a week. Lots of overtime pay but I got seriously depressed. I could not drink enough water to stay hydrated, Gatorade didn't help either. Mad respect for people who can do a job like that. That kind of heat makes me not want to ride my bike in modern technical fabrics let alone denim.

NUT. POWDER.

[AntonioGG]

When I was in high school I worked at Revco (I think Eckerd ended up buying them..wait, is Eckerd even around?).  I remember road construction workers coming in for salt pills.  I thought it was strange until one explained to me that this was the most efficient and cheap way for them to keep getting in trouble.  They had plenty of water but no electrolytes.  

All the people that work outside or indoors without cooling (like auto mechanics in most shops) have my respect, but like AB said, those working in the attics take the prize.  If I have any attic work to do, I do it in the winter.  One time I had an extra 6" of insulation put in, and they came when it was hot (I figured they'd come in very early).  They'd stay up there at a max of 20 minutes and switch out, and they'd disconnect AC ducts where possible to get some direct cool air on them (part of what they did was sealing all the ducts and registers).

[mack_turtle]

3 hours ago, Anita Handle said:

NUT. POWDER.

Believe me, I tried it. The best but powder. But powder the likes of which you wouldn't even believe. It mixes with sweat under pressure and turns your undies into concrete.

[AustinBike]

56 minutes ago, mack_turtle said:

turns your undies into concrete.

That's what she said