Some questions about cooling my upstairs with existing radiant floors. It won't take much: Manual J says about 9kbtu for 600 sf in two bedrooms and a bath. Any thoughts on min/max entry temperature range for this floor (in order): 3/4 oak planks, transfer plates, subflooring, 1/2 cork soundproofing, pex 12 inches OC. No worries about dew point. The chiller will be in a chimney chase, where its dehu will be distributed by low speed continuous circulation. Mini splits may be the cheapest approach here but does an inverter make any difference if the heat pump is chilling 200 gallons of water, which in turns cools the floors? Easy enough to use set points to make it run flat out for extended periods. Any reason not to use one if it's the least expensive? Finally, any comments on a $100 hack of a mini-split duct head involving sheet metal and a tube-and-cooling-fin heat exchanger? No worries about inefficiency. The continuous circ will recycle "waste" cold.

Well dewpoint CAN become a problem if you cool the floor below that point...

I have a concrete radiant slab and am about to install the proper plumbing to route my sprinkler system through the slab for cooling.

Since my thermostats will not be calling for heat......is there a way to manually open the zone actuators?
I realize I can set my thermostats as high as possible and unplug the circulator pump (my boiler is turned off for the summer) but would rather open all the zones manually for the summer.

Are all of the components in you HR system rated for domestic water pressure which is often 50-70 psi? There is often a 35 psi pressure relief valve installed in the HR system to protect other components from over-pressure failure...

If your zone actuators are installed on manifold (s), they can be unscrewed and removed which will open the zone valves. Do you have balance valves on manifold(s)? These may create significant hydraulic resistance and may need to be opened.

I can’t say that I would endorse this approach for HR cooling.