It would probably work, but I would contact one of the many makers of this equipment and get their advice. They have worked with a lot of different situations and know their systems best. If you are at the design stage, it is time to get help from the folks that know best.
Matt
Radiant floor heat works by "radiating" the heat into the living space. The more surface area, the better. When the tubing is placed within the concrete, the entire slab becomes the radiator. Otherwise, you'll most likely need the aluminum plates to take the heat from the PEX and radiate it into the room. I doubt you would get enough heat from the bare tubes to be efficient.
If you insist on hydronic floor heat, there are companies that make panels with the aluminum plates and tubing channels ready to go. One source is:
If you really want radiant, you might want to consider electric radiant. Very low profile, and easy to add as a retrofit. The warmzone site above also offers some of those too.
Of course, the simplest option would be to add in-wall electric heaters like those made by Cadet or King Electric. We heat our entire house using King Electrics "Pic-A-Watt" heaters. They're quiet, efficient, and we can zone each room for only the heat we need.
Anthony
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.