I do some of my best thinking in the shower and with wood-heated DHW these days, I get more time to think. So this morning, while pondering yet another future heating system upgrade, it occurred to me that I ought to be able not only to heat our greenhouse on cold days efficiently with infloor radiant, but also cool the floor on hot day. That's the biggest problem with greenhouses in the summer--they get too hot and fry the plants. There are all kinds of ways to cool things off--from automatic roof vents (got that) to fans (don't got that) to moveable shades (had that). But I'm thinking cool water pumped through the pex embedded in the slab might work pretty well. And, if done right, the heat removed could actually be stored and possibly used either for reheating the floor at night, or to preheat domestic water going into the hot water heater. I could even pump it (either directly or through a heat exchanger) back into the bottom of my hot water storage tank if the delta T is high enough. So that's a rough sketch. I'm thinking some kind of a tall, narrow tank for mucho stratification would be the best storage reservoir, and a reverse flow arrangement, depending on what I'm trying to accomplish. Any thoughts on this idea? Am I suffering from early-morning pie-in-the-sky wishful thinking?