OT Which direction is your ceiling fan SUPPOSED to run?

On Fri, 04 Jul 2014 21:33:06 -0400, snipped-for-privacy@attt.bizz Gave us:

Higher and more often gun maint program. Can't let the sweaty little bastard get rusty.

On Fri, 04 Jul 2014 22:18:11 -0400, snipped-for-privacy@snyder.on.ca Gave us:

But what idiot in their right mind, especially in greater SF would buy or use such a cheap POS in a perm install?

From New York: A roof covered with solar-reflective white paint reflects up to 90% of sunlight as opposed to the 20% reflected by

reducing cooling costs up to 40 percent.

The problem is that the temperature of the roof only tells part of the story. If the ceiling area was super insulated, the indoor temperature would be independent of the roof temperature. Kinda looks like this is based on the assumption that some of the roof heat is conducted into the building interior. That works, but I suspect varies radically with building construction and ceiling insulation.

The advantage of a black roof might be because black radiates heat better than white. The black roof might be hotter during the day, but as soon as the sun goes down, a black roof will cool down quicker than a white roof. That might affect the average.

More:

Unscientific anecdotal drivel: My office building was blessed with a shiny new white roof in Oct 2013. It was previously black asphalt and a thin layer of fine gray rock. It seems much cooler inside this summer, but I have no measurements to prove it.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Depends a bit. If the cooling coil is kept only a little below room temperature and you depend on sheer volume for heat transfer, you may not condense much water compared to having a sub-zero cooling coil and lower air volumes.

As usual, it depends on the circumstances. At rest, the head radiates about 7-10% of the body heat. When exercising, the increased surface blood flow increases this to 50%. Presumably, the OP is not exercising under his ceiling fan:

Correct, although I suspect the cooling is mostly from evaporative cooling, not convection. The part of my rant that you trimmed indicates that this was in reference to the relative merits of the fan blowing air down or up. I indicated that blowing down would be more effective for cooling because the head is closer to the air source and therefore has a higher air flow rate. Further away would be less effective. If the fan it going to cool the head, the optimum location would be closest to the fan (unless the OP is into standing on his head).

However, the OP didn't specify the temperature of the air near the ceiling. If the ceiling air were hotter than body temperature, a downward blowing fan will heat the cranium instead of cooling it. It would be like trying to stay cool using a hair dryer blowing from above. I can believe that blowing HOT air downward might result in heating instead of cooling.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

I do "get" your point, I just don't agree with it.

I don't think that follows. Most of the power in an AC unit is in the compressor which creates the cooling. Reducing the temperature of the air is going to take the same total amount of cooling, so there is no power saving in a smaller unit. They size units to keep the initial costs down and to provide enough cooling for the warmest days.

Your conclusions simply don't follow your premise. Unless there is something less effective about the condensation of water in the large unit it will end up collecting the same amount of moisture from the air. But in reality there is an effect that makes the larger unit work better. If the airflow over the coils does not cool the air below the dew point, no water condenses at all. A sufficiently small unit with an adequate air flow may well not lower the air temperature enough to extract enough water during the process.

Again, no substantiation, just a claim. Running the small dehumidifier removes small amounts of water AND warms the room requiring the AC to run. Running the large AC unit will remove the water more quickly. If it does not remove enough water heat must be added as it runs to remove enough humidity (becoming a dehumidfier). The question is which unit is more efficient as a dehumidifier and talking about "big-assed" ACs does not answer the question. You are coming up with an answer based on an emotional analysis of inadequate data.

The one fact I know is that my AC unit produces enough water to require a pump to remove it and runs repeatedly all day. A dehumidifier I have used will fill the two gallon bucket in a day or so in the worst humid days of summer in the DC area. Still not sufficient data to prove one or the other since I have never measured the output. But the AC only cycles on and off while the dehumidifier runs continuously 24/7 until the bucket is full.

You still fail to understand that is *exactly* what you are doing with the dehumidifier. It had a hot coil and a cold coil. The hot coil produces all the heat entering the cold coil plus the electrical energy coming from the outlet. So you actually warm the room with that unit requiring the AC to turn on even if it is otherwise not needed.

I'm not sure what you mean by the fraction comment. ALL electrical energy consumed by this unit ends up as heat, mostly at the hot coil.

The condensed water has had its heat removed and then put back into the air on the hot side of the unit. The question is where does that heat go? Only part of the heat at the hot coil was from cooling the air, most of it was from condensing the water. With a dehumidifier the entire latent heat of evaporation is returned to the room along with the heat from the electrical power required to make it all work. This will heat up the room. With an AC unit that heat is exhausted outside reducing your cooling costs. Don't think the latent heat of evaporation needs to be returned to the room to maintain a temperature. When water evaporates it cools. When it condenses it releases that heat and will warm the room.

I guess one difference is that we have few days when we need dehumidification but not cooling. If you actually need your space warmed with dehumidification rather than cooled, then the dehumidifier might be more efficient. But if you don't need the extra heat the AC unit will have to run to maintain a temperature.

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Rick

I like to do the same thing when we have cool nights like tonight. More important than cooling the air in the house is cooling the house itself. Air heats and cools quickly, the materials of the house, not so much. So let the house cool as much as possible then shut the house when the temperatures start to rise. I can't remember the house ever reaching the outside temperature by noon, the equal point is usually in the evening when the outside starts to cool again.

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Rick

Ok, I found this discussion and clicked the link for the first reference on the exercise issue...

Not Found

The requested URL /12401.php was not found on this server. Apache/2.2.3 (Red Hat) Server at researchfrontiers.uark.edu Port 80

The second section refers to a reference that is a Wilderness Medicine Newsletter. I have not heard of them and they do not give references to the work of the people they say they interviewed. So I'm not sure what to believe of the conclusions. They say...

... discovered that we do indeed lose heat through any exposed part of the body and the amount of heat we lose depends on the amount of exposed surface area. The rate of heat loss is relatively the same for any exposed part of the body not simply the head. You do not lose heat significantly faster through the scalp than any other portion of the body with the same surface area.

Later...

As you begin exercise, cerebral blood flow increases due to increased cardiac output and the percentage of heat lost through the head accounts for about 50 percent of total body heat loss. As exercise continues, more oxygen is directed toward muscle and blood flow to this tissue increases. Core temperature has to be maintained and as body heat increases, the skin arterioles expand, or vasodilate, redirecting blood flow to the skin which cools the blood. Hence, total blood flow to the brain is decreased and the percentage of total body heat lost through the head is reduced to about 10 percent. The percent lost through the scalp returns to 7 percent after sweating begins.

So depending on the phase of exercise they claim 50%, 10% and 7% but in contradiction to the initial statements that there is little if any difference in the different parts of the body regarding heat loss.

Earlier in this discussion a post is made the references an old US Army training book, US ARMY SURVIVAL MANUAL, BASIC PRINCIPLES OF COLD WEATHER SURVIVAL. The info in this book has been widely misinterpreted where they talk about wearing a survival suit but with no head protection; then the head does loose 50% of the heat from the body.

Regardless, your claim is about a person nominally at rest I would assume. If you are referring to a person exercising the 50% number only applies during the initial portion of the exercise before they warm up.

This link discusses (again with no verifiable references) that there are parts of the body with higher heat loss per square inch than other areas when not vasoconstricted. But nowhere is there info to support the statement, "The only temperature of importance is your head, which radiates most of the waste heat from your body."

So in the words of Mythbusters... BUSTED!

I objected to this statement...

The point is any reference of cooling the head vs. the rest of the body in invalid. The more important part of the issue is that a ceiling fan blowing up will only cause an indirect, dispersed air flow to the person with nearly no effect.

To talk about the hot air next to the ceiling assumes that that hot air is not dispersed in the first minute of use which is not valid.

The relative cooling has to do with the airflows, not with the thermal emission of the head.

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Rick

That's not being nice.

Unless there is

You are turning into Sloman, if you aren't Sloman already. Constant droning insults.

Running the small dehumidifier

See what I mean?

Can't recall. $40 at Home Depot. Works great.

It moves air nicely, looks good, and it's well balanced and quiet. Nothing sub-par in sight.

There cannot be that great a savings between them, even if

I bought it and installed it. We use it maybe 5 nights a year, when it's hot in San Francisco, which is rarely is.

We passed a big billboard this morning, downtown, right beside highway

101. It must cost a fortune. It's by Nest, the thermostat people. It says, as I recall,

"San Francisco, get a NEST thermostat and save on your summer heating bill."

I love our ceiling fan. My wife loves our ceiling fan. You don't like our ceiling fan. Fortunately, you don't matter.

Hey, it's famous already:

Sun Tzu, and the Art of Ceiling Fans? Does not have the right ring to it.

Since we're a free nation in the USA, I'm only slightly surprised we don't have an Executive Order, and a department of about a million heavily armed DHS or DCF (Department of Ceiling Fans) guys in Humvees, inspecting for compliance. It's the Obama Chicago Thug way.

--
. 
Christopher A. Young 
Learn about Jesus 
     www.lds.org 
.

Probably a Faux news viewer?

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. 
Christopher A. Young 
Learn about Jesus 
     www.lds.org 
.

You "dunno" about anything, Bloggs. It's surprising you have enough gray matter to breathe.

You're projecting again. It's all you do here.

Better; move.

Stainless.

But show me a HEAT PUMP that works that way??? A water chiller, perhaps (running spring water through a cooling coil) but even 50 degree coil will cause condensation in a humid climate.

I still have three Hunters from circa 1975. They were $200+ then (each); that would be almost $1000 each in today's funny money. None of them have a reverse switch. I guess they figured that people bought fans to blow air on them, not the ceiling :)

--

dadiOH 
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Taxes out of hand? Maybe just ready for a change? 
Check it out... http://www.floridaloghouse.net

But the heat produced on the hot coil is mostly ballanced by the cold on the cold coil. The heat on the hot coil is NOT "produced" like it is with resistance heating. It is a "heat pump" and produces a lot more BTUs of heat transfer than the wattage of the power consumption.

What I meant to say is that of the total heat output, only a fraction is produced by the dissipation of electrical energy. The rest is from the Latent heat of condensation.

Obviously I understand that - I gave the calcs for the heat gain from condensing a gallon in 12 hours - which my little dehumidifier does quite handilly on a Muggly day. My 40 pint dehumidifier dreaws 280 watts maximum. at steady run. So total heat input per hour would be

280+200=480 watts or about 1300 BTU. If it collects the full 5 gallons in 24 hours, it is still less than 800 watts. If you run your AC to remove that humidity I reccon you will need more than a 600 watt heater to make up for it or the AC will be cycling and using a lot more power, and the efficiency in gallons per KW will be a lot lower.

And here we have many days where we require dehumidification, without NEEDING cooling. When it's only 20 C out but 80% humidity, you do not need AC but dehumidification makes a huge difference.

As for your arguments - ask a REAL HVAC professional.

I'm done.