HI Richard, You can't get very much cooling out of the slab with wood overlayment. You also choose thermal mass which can really help in Menlo Park. Have you considered a Passive House design? The concepts are clear and simple. 1.) Limit east and west window exposures, OK to have windows if very well shaded. 2.) Include thermal mass in the interior design, several options available for that. 3.) Based on the thermal mass increase south facing glass with an overhang that shades in summertime. 4.) Provide nighttime ventilation to cool the mass, the Echo system provides this. 5.) Select appropriate glass for each cardinal direction the windows face. If the house design ie wood floors and ceilings limit the capacity for radiant heating and cooling, we can thermally activate portions of the walls to do the job. The walls are "furred out" 3/4" by the active lathing, nothing actually shows on the surface of the walls. It is easy to survey the walls to avoid sticking the tubing while hanging pictures etc.

In my passive solar, the purpose of "radiant cooling" is more to keep the slab from getting warm in the first place than actually cooling the interior. Ambient temperatures are pretty mild, but up at 49N, even with substantial overhangs, it is hard to keep the Summer sun from sneaking in and getting to the same slab that keeps you warm in the Winter. The cooling circuits help remove heat from the slab so we don't overheat in late afternoon.

Hi ICF Hybrid,
This is a radiant cooling forum not passive design. Radiant cooling can be achieved in a passive house when nighttime ventilation is used to cool the mass. The climate zones where this works well are very limited. In other climate zones where the diurnal temperature variation is moderate, some method of active cooling needs to be used. If the climate zone is dry, evaporative cooling can be effective, but in many cases a chiller will be the best choice.

This is a radiant cooling forum not passive design.

Oh. Sorry.

Radiant cooling can be achieved in a passive house when nighttime ventilation is used to cool the mass.

That's what we do!

The climate zones where this works well are very limited.

Oh.

In other climate zones where the diurnal temperature variation is moderate, some method of active cooling needs to be used.

That's us!

If the climate zone is dry...

(sadly) That's not us....

evaporative cooling can be effective

That's really not us.....

but in many cases a chiller will be the best choice.

Yeah! That's what we do!

I do have a lot of glass (i.e. whole walls -- this is a contemporary design) facing west. The rest of the house is under a lot of shade. We really hope we can take advantage of ventilation at night -- since on most days the outside temp drops at around 6pm. For radiant cooling, I'm hoping to just prevent the loads from the sun that comes in through the glass, potentially heating the slab/floor, and any warmth that might make it through the walls/ceiling (I'm assuming that's minimal if we do the right insulation?).

Anyone want to take a guess at how many BTUs/sqft we could get through the floor and ceiling if they are covered with wood? Not all areas have wood on the ceiling -- so we can likely incorporate radiant (xlath) into the ceiling in many places.

We're in Menlo Park, California. Any idea if we would need dehumidifying during the day to complement any radiant cooling in that area?

Thanks,

Richard.

Richard, As mentioned the most difficult side of radiant cooling is maintaining the RH in the conditioned space. As a design build contractor , I am very interested to learn more myself. I was approached about 20 years ago by EHT a German mfg. which was doing radiant cooling in Europe and radiant in the USA. They are not around anymore and the problems which they were having was controlling condensation.I have seen commercial jobs but a home is somewhat more complicated do to operable windows,showers,etc. I do believe you are going to need dehumidification. Commercial projects use DOAS and chilled beams, and sophisticated controls to keep dewpoint from being reached. Good luck, I am very much intersted in what you end up with.

the most difficult side of radiant cooling is maintaining the RH in the conditioned space

Agreed, and not just in the room but particularly next to the radiant surface. Ie, the room might be 50% but below thick carpeting and wood floor it might be 80% - which will cause mold.

A conditioned space is just that, conditioned. When you open a window it is unconditioned. Unfortunately you have to pick one.

Passive solar is another misnomer. If you think a severe sunburn is caused by "passive solar" you will likely be quite comfortable with lots of glass, passive solar, open window cooling and the like.

Yes it is hot during the day and cooler at night in most climates, but the dew point follows the sun. If you open a window, you let "conditioned" air escape along with your fuel investment and almost always at the risk of your comfort.

There is no need to guess at heating and cooling loads as we have had Manual 'J' for some time now. This is the place to start along with some informed and realistic HVAC design goals.

We are only assuming a low load -- so that we can keep the house cool during the 95% of days, and if we have a few hotter days (which are rare, typically only 1 or 2 days in our area), then we won't keep up with this system. We just want to design for the common case, rather than the peak.

Richard