So far the tiles on the ground floor have been great. They feel warm on cold days, and cool on warm days. Six months after moving in, the extremities of the slab have warmed up, and it will now hopefully work as a passive heat sink.
The only thing that seems to have been a waste of time is the active system for pumping heat around the slab. I had over-ambitious hopes for the tiles to absorb direct sunlight and help bring the heat of the sun into the thermal mass of the concrete slab.
I think this was also tied up with earlier ideas using solar thermal collectors and pumping excess heat into lower levels of the slab, from where it would keep everything warm. The pumping system we have for the underfloor heating is not wasted, of course, as it still works with the heating system, which would have strained to pump hot water around the floor area we have, and would have been sending it at far too high a temperature.
When we were choosing tiles I was interested in how much of the sun's heat they would absorb, but asking the supplier about this was like asking the fishmonger how many microgrammes of mercury are in his salmon. Perhaps something they should know, but certainly not something they do know.
The answer from the Passive House lady was more than nothing, but less than you think. This seems to have been accurate.
From a thermal point of view we should probably have got darker tiles with a matt finish. I don't know how this would have affected the aesthetics of the room though.
