(no subject)

[nibot]

This is sort of a physics question: Could you pump cold water through radiators to cool your house? The obvious flaw is something like "cold doesn't radiate," but, then, don't we have the general principle that a good antenna for transmission is usually a good receiving antenna too, and hence the cold "radiator" should absorb thermal radiation from other objects? (In addition to cooling by convection.)

Comments

they won't radiate cold

[nibot.livejournal.com]

but will they effectively "absorb radiant heat"?

Re: they won't radiate cold

[sfllaw.livejournal.com]

It will absorb radiant heat that radiates to it. However, radiation is straight-line propogation so you're not going to absorb much of the ambient heat in the room. The reason why heaters work is that they can radiate heat in all directions into the room.

And radiation is probably not your biggest heat worry in the summer. Conduction will be, and to remove that you'll certainly need to be moving air across your cooling element.

Re: they won't radiate cold

[(Anonymous)]

You've nailed it on the radiation absorption issue - its all about line of sight surface area. Fins don't help, neither do rows of tubes.

Heaters work by running at a higher delta T from the room than is possible with cooling.

Radiation is, surprisingly, your biggest heat worry in the summer (unless you have a very leaky old house). It's all about sunlight - coming through the windows is a huge load, and the roof surface commonly will be 30-50F hotter than ambient. That high temp pumps heat through the roof (OK, you got me, that is conductive heat transfer, but it is due to radiation on the roof!).

Human comfort is impacted greatly by the radiant temperature around you, but modern systems (modern meaning as envisioned by Mr. Carrier around the 1910's - ugh) address this by over conditioning the air temperature so the air conductively warms or cools exposed surfaces. Some squishy numbers are people transfer around 45% of their waste heat radiatively to the surroundings, 20% evaporatively, and 35% convectively.