On Jan 10, 1:27*pm, (Doug Miller) wrote:
In article , Bert Hyman wrote:

TimR wrote:

Cold panels in the ceiling for air conditioning are new to me, but are
beginning to be used.

I've never heard of them; what's the mechanism for cooling them?

Pumped circulation of cold water. The human body radiates heat to its
surroundings; when those surroundings include a large mass that's
significantly cooler than human skin temperature, you feel cool.



Offhand, I'd think they'd only be safe to use in places with very low
humidity, otherwise the condensation would be annoying.

The panel temperature doesn't have to be at or below the dew point to be
effective at making the room feel cooler -- it just has to be low enough to
absorb a significant amount of the heat radiated from your body. Radiant
cooling is markedly less effective in areas of high humidity for two reasons:
first, the higher dew point means a higher minimum panel temperature, and
second, because they are operated above the dew point, they don't dehumidify
as forced-air air conditioners do.

As we've tried to become more sophisticated at cooling living spaces
like dormitories and military barracks, we've tried to separate the
cooling function, the dehumidification function, and the fresh air
ventilation function.

Fancoil units used to be cooled with chilled water and have a vent for
fresh air. This resulted in an inability to control humidity and mold
growth, and mold growth is a pretty hot topic now.

So we went to fancoil units with no vents, and supplied ducted
dehumidified air to the space. That let us pressurize the building
and control humidity, and let the comfort cooling be adjusted with the
fancoil in each room.

The cold plate is an improvement on that idea. Rather than cool all
the room air, we want to use radiant cooling to cool just the human in
the room. This does require we supply pressurized dehumidified
outside air via a separate duct system. You're right, if we don't
control humidity it will rain in the room.

I've worked on building renovations with the separate fancoil and
dehumidified air systems, but have yet to personally see a cold plate
system. I suspect my employer will do one soon, hope so.