Nigel Goodwin

I suggest you check the relative consumptions, fridges are reasonably high, far more so than a TV or computer - modern, energy efficient ones, obviously take less than older ones though.

But you're also completely missing the point, TV's and computers are doing something with the energy, with only a fairly small amount lost as heat. A fridge is a heat pump, it's pumping heat out of the food and in to the room - and an efficient heat pump will provide considerably more heat than the energy it consumes.

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crashsite

You do make some very good points, Oznog.

Roff

Some good points, Gonzo. I looked up a 25 cu. ft. Kenmore fridge just for the hell of it, and they rate it at 721 kilowatt Hrs per year. That averages out to about 82 watts, 24 hours a day. Not a very significant heat load, as you pointed out.

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Ron

mneary

You can consider a refrigerator located inside an air-conditioned area to be part of a two-stage heat pump. The refrigerator could be optimized to operate at a constant temperature differential.

Oznog

Right. So a fridge may consume 80W average and remove another 100W average from the fridge (really I have no idea, it's a Wild Ass Guess).


Now a desktop PC and monitor can consume 250W and put out 250W of heat to warm the room. A big screen TV can produce heat near that too. So one could wonder why not vent that heat to the outside too.


There's a subtle difference here too. A fridge cooling the condensor with 70F air require less power to produce the same cooling effect than one working off 90F outside air. A PC or TV however won't require more power if cooled by 90F outside air. However, they DO have a shorter Mean Time Between Failure at higher temp.

So you'd need specific numbers on how much energy is used by the A/C system to remove that 180W of heat generated by the fridge.
You can also evaluate the case for taking inside room air, using it to cool the condensor, and venting the warmed air outside rather than try to reuse it. All the cubic feet of air vented out this way have to be drawn in from the outside and cooled by the A/C to replenish the air inside the house. This is counterproductive for sure if the rejected air is still cooler than the outside air temp.

Actually there's another case. Where the coolant exits the compressor, it's very hot. We could run outside air past one condensor, maybe getting the coolant down to 100F with 90F outside air. Then use a SECOND condensor cooled with 70F inside air to get the coolant temp down to 80F, which has significantly more cooling power than coolant at 100F for the same electrical input to the compressor. So we maintain the compressor's efficiency while rejecting the lion's share of the heat outside. A downside is that longer coolant lines and more condensor passages present additional restrictions to the coolant flow and the compressor will have to do more pumping work to make it flow quickly.

Well you can figure nobody's gonna rip a hole in the side of the house and route huge hoses out to shave a fraction of a % of the A/C bill. But for battery-driven RV systems and space stations hell yeah it's something to look at. And for building large-scale cooling systems this sort of issue can become quite significant to consider.

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I thought what I'd do was I'd pretend I was one of those deaf-mutes.

Roff

Yeah, but that 100W that was removed from the fridge came from the room in the first place (unless you just put some hot food in it that wasn't prepared in the house, or there's some serious exothermic process going on inside ), so I don't think that adds to the heat load on the AC.

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Ron

Nigel Goodwin

That's where you're making your big mistake!.

A PC, or a monitor, or a TV, isnt a heater - it doesn't put out all it's energy as heat - the heat is only the waste after it fulfills it's purpose, providing air movement, light, and sound energy.

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Hero999

But all that air movement and sound energy eventually ends up as heat which warms the room.

Also a typical TV will take 150W and only produce less than a watt of light and a couple of watts of sound.

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Nigel Goodwin

A TV produces a LOT more than 1W of light! - probably about 25W at full beam current (for a CRT).

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Roff

But won't all the light, except that which leaves through windows, be absorbed and reradiated as heat?

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Ron

crashsite

There's a BIG difference between the beam power in a CRT and the actual amount of light radiated from the phosphors of the tube (or the energy required to light up an EL panel and the luminence energy radiated from the pixels).

And, an average of 1 Watt of audio power is a LOUD sound. I would be surprized to find that the true average of the "useful" output of a TV set (picture and sound) is a Watt.

Roff

Sound, too, for that matter.
You guys are ignoring me.

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Ron

Nigel Goodwin

Put a plain 100% white raster on a TV, you can read by it in a fair sized room - bearing in mind it's not a point source like a light bulb.

And yes Roff, we're ignoring you!

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Hero999

Given that a 100W light bulb only produces only 2.6W and a TV tube lit at full brightness isn't as bright as a 30W, there's no way it's giving more 1W of light output.

The point is that all of the energy coming out of an appliance is eventually converted to heat which warms the room, apart from the small amount radiated as acoustic waves through the walls and electromagnetic waves through the windows.

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Get Opera it's simply a superb browser.

Roff

My sentiments exactly.

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Ron