OT Which direction is your ceiling fan SUPPOSED to run?

[clare]

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.

[dadiOH]

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 :)

[clare]

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.

[dadiOH]

:)

I used to get to SF 2-4 times a year, usually between October to May. I tried to avoid July, BITTER cold!

My first experience with SF "summer" was in July, 1952. I was in the navy, waiting to be shipped to Hawaii. There used to be a jazz club on Geary just off Powell called - IIRC - Club Hangover. To this day, I remember turning the corner off Powell and being met with a blast of arctic air. DAMP arctic air.

[clare]

Give it a rest already. Rour totally unballanced psyc is showing!!

[Stormin Mormon]

Those keyboard commandos sure can waste a lot of your time.

[Stormin Mormon]

Part of the def'n of Totalitarian is trying to suppress opposing views.

[Ed Pawlowski]

So are you saying a heat pump can change the laws of physics, but just a little bit? Thanks, I must have missed that class.

[RobertMacy]

I didn't paint the roof, it's tile and its color is its color.

I painted the walls which receive oblique sunlight and sometimes no sunlight with the eaves shading. I only experienced 'cooler' HOT temperatures in the garage and the fact our inside home stayed a 'tighter', and lower, average when we weren't running A/C etc.

I would expect that during the day a white roof would be cooler. Having a superheated black structure above your head just can't be as cool. No aspersions on life style meant.

[Jeff Liebermann]

Right. My problem is that my house is environmentally incorrect and far from typical. There's no attic. The roof and ceiling are non-insulated 2x T&G pine[1]. There's considerable (double pane) glass in the walls. Add two single pane sliding glass doors and two single pane French doors. Air leaks around some doors and windows. With so many leaks, my rule of thumb is that the house temperature never goes above or below about 20F from the outside temperature, even when running the woodburner. Such a house would not be practical in any extreme environment, but reasonably functional in a dense redwood forest, where the trees moderate the temerature swings. As you note, the door/window temp regulation method is functional for most houses. However, my efficiency, as indicated by the equal temperature time, is far from optimum.

10 year old photo:

[1] The roofing is 20 years old and probably has another 5-10 years of useful life reamining. I plan to insulate the roof when it is replaced.

[HerHusband]

Thanks for the real world example. That's what I would have expected from mixing up the warm and cool air. Once the air is mixed up, there's no further change in the temperature from the ceiling fan.

Of course, if you have a loft or something up near the ceiling, dropping from 33C to 24C would be very welcome. :)

Anthony Watson

[trader_4]

I agree. A dehumidifier is not "exactly like" running a central AC and the heat at the same time. As you say, a dehumidifier is a heat pump and it's transfering heat from the cold side to the hot side. Since both the cold and hot side are in the same room, that part of the energy is constant. Since the heat pump does take energy to run, the electricity used does result in some heat being added to the room. But because the COP of a dehumidifier is much greater than one, you're moving 2x or 4X the energy that dehumidifier takes to run. Running the AC is essentially a heat pump too. Except there you're pumping the heat from inside outside, where it's lost. And then you're running the heat, ie gas heat, electric resistance heat, whatever, to make up for all the lost heat. That's a huge difference in efficiency and a very inefficient and costly way to dehumidify compared to running a dehumidifier.

[Jeff Liebermann]

A few web pages recommend painting your tile roof white: Of course they're selling the paint, which does tend to bias the point of view. I'm not sure it will make a difference or an improvement.

There are charts available showing the SRI (solar reflectance index) but I don't want to dig through them to determine if coating your tile roof will offer any benefits.

A roof with a clean, smooth "cool color" surface, such as a cool red tile, can reflect about 35% of incident sunlight (R = 0.35) and emit thermal radiation with 90% efficiency (E = 0.90). This surface has an SRI of 38 and a delta T of 56°F [31 K]. The cool red tile is much warmer than the bright white roof, but still cooler than a standard red tile (R = 0.10, E = 0.90, SRI = 6, delta T = 78°F [44 K]).

[John Larkin]

That's nice, in the woods.

When we refurbed our business building, and redid the flat roof, we added a roughly 4" thick thermal insulator, and painted that aluminum. The ceiling in my office stays just about the seme temp as the floor.

[Ralph Barone]

Not at all. You're welcome.

[Stormin Mormon]

333 lines of text --- got to be a record. Do you know how to trim, or do we have to teach you?

[rickman]

There is your fallacy. The heat produced at the hot coil is largely balanced by the cold at the cold coil (with the exception of the power drawn from the outlet which is not trivial) but the cold coil does not cool the air as much as the hot coil heats the are. Most of the heat entering the cold coil is used to condense the water which does *not* cool the air. The opposite of evaporative cooling is condensative heating. Heat has to be extracted from the moisture to condense it which does not cool the air while that same heat at the hot coil *does* warm the air.

Ok, but not a useful point.

I'm having trouble following your statements because I can't tell what "drawing" and "heat input" refer to. Are you saying the unit draws 280 Watts from the power line? I don't really see where you are going with this and I certainly don't see how you can compare the two types of units in this vague way.

Ok, but until you understand the real heat flow, you can't say you understand what is happening with your dehumidifier. If it is 20°C outside and you run your dehumidifier you will be heating the air which may not be insignificant. So if you want your home to be 22°C with 50% humidity then a dehumidifier may be the right choice.

[rickman]

I think Ralph's point is moot because AC units don't cool "only a little below room temperature", but the concept is valid. Moisture condenses only when cooled below the dew point. It doesn't even depend on the temperature of the coil, but rather of the air passing over the coil. If the air never reaches the dew point (either because the coil is not that cold or because the air moves over the coil so fast) no moisture will condense.

Those *are* the laws of physics.

[rickman]

What about suppressing idiotic views? Is that totalitarian or just hard to resist?

[John Larkin]

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You ARE Sloman!