Therma-HEXX ThermaCEILING

I want to compare the effectiveness of panel cooling with an air handler in an environment that needs dehumidification.

Imagine you prefer your space to be 75F and 55% RH in summer. Imagine further that you have a conventional air conditioner where the coil temperature is 40F. When that interior air hits the coil, 61% of the cooling will go to reducing the temperature of the air (sensible cooling) and 39% will go to removing humidity (latent cooling).

Suppose that on a humid day your sensible and latent loads are both 10,000 BTU/hr (I'm in Washington, DC, we get days like that in the summer!). If your AC runs until the thermostat is satisfied, removing 10,000 BTU/hr of sensible heat, it will only perform about two thirds of the needed dehumidification -- 39%/61%, or 64%.

So you add a dehumidifier. When the dehumidifier runs, it dumps the latent heat it extracts from the water vapor, plus the heat of the electricity it consumes, into the house. That heat causes the AC to run more -- which extracts more humidity.

How much more? Let's say the dehumidifier has a COP of 3, so when it extracts 1 BTU of latent heat it uses 0.33 BTU of electricity and increases the sensible load by 1.33 BTU. I can show the math, but what you get is the AC runs at 20,620 BTU/hr and the dehumidifier runs 1860 BTU/hr. The dehumidifier converts the latent load into sensible load, so the entire combined load -- 10,000+10,000 BTU/hr -- now gets handled by the AC. The dehumidifier also does 1860 BTU/hr of dehumidification, which takes 620 BTU/hr of electricity, and the heat from that gets handled by the AC as well. Over 80% of the dehumidification is handled by the AC; if you were to compare the condensate flows the AC would be five times greater. (It's actually kind of neat — or "cool" — how the two devices complement each other).

What happens if you use panels for cooling? The sensible load stays the same at 10,000 BTU/hr. But the panels can't do any dehumidification, so it all — the full 10,000 BTU/hr — has to be done by the dehumidifier. It dumps the heat from that into the house, and with the same COP of 3.0, another 3,333 BTU/hr from the electricity it uses, or 13,333 BTU/hr total. The total sensible load on the cooling is the 10,000 BTU/hr of sensible load, plus the 13,333 BTU/hr dumped by the dehumidifier, for a total load of 23,333 BTU/hr.

So in the first scenario the AC is providing 20,620 BTU/hr and the dehumidifier is providing 1,860, for a total 22,480 BTU/hr of cooling action. (I'm assuming the two devices have COP's that are similar enough that you can just add them.

In the second scenario the AC is providing 23,333 BTU/hr and the dehumidifier is providing 10,000, for a total of 33,333 BTU/hr. This is 48% more cooling required than the first scenario.

Also, the first scenario requires a much smaller dehumidifier. Dehumidifier capacity is measured in pints per day, removing a pint of water vapor requires roughly 1,000 BTU. So 1860 BTU/hr of dehumidification is 44,640 BTU/day, or about 45 pints per day. That's a very small residential dehumidifier, something that you can just tuck in a corner of a utility room.

On the other hand, 10,000 BTU/hr is 240,000 BTU/day, or 240 pints per day. I've never seen even a ducted model with that capacity. If you could find something you'd still need to run ductwork through the house to support it.

Using the panels consumes a lot more electricity and it's not clear what it gains you.

@hot_rod : "In theory radiant energy travels in a line to anything it can "see" So the ceiling panels should heat the objects much the same a floor radiant."

Radiators are kind of misnamed, the heat they provide is a combination of radiant heat from line of sight but also convection from warming the air they are in contact with which causes the air to convect away.

In a floor convection is much more effective than in a ceiling. Siegenthaler* says when designing a ceiling you should use a constant of 0.71 BTU/hr/sf/F, as opposed to the 2.0 which is standard for floors. So at the same temperature you get about 2.8 times as much heat from a floor as you do from a ceiling of the same area.

So with everything else equal, you need 2.8 times as much area on the ceiling as in the floor. On the other hand, you can run the ceiling hotter than the floor without creating objectionable conditions**. Although if you're using a heat pump, you probably don't want to.

*(I've never seen him say where he gets that number)

**(Unless you have sprinklers in the ceiling!)

"Easier cooling" says a lot about the quality of AI answers.

There is so much gibberish in that clanker text I'm not sure which part you're talking about.

Radiant ceiings offer faster response,

Agree

easier cooling,

Disagree, violently

and avoid furniture obstructions,

Agree

making them great for quick adjustments

Disagree

and efficient cooling,

Disagree violently

while radiant floors provide a slower, more consistent heat with high thermal mass,

"Disagree" doesn't do it justice, it's a nonsense statement

ideal for steady warmth

Huh?

but less responsive and affected by floor coverings.

Agree

Ceilings work with lower water temps and higher output per square foot,

Disagree completely

while floors need hotter water for heating

Disagree

but can run colder for cooling

Utter nonsense

(if not used for heating simultaneously)

Wha?

and are more impacted by carpet/furniture.

Agree