About the refreshing
The refreshing via the ground is terrible because, on the one hand, cold air stay at ground level (it is heavier than hot air) thus cold at the feet and hot at the head. On the hother and, hot and humid air ( in summer, hot air is humid due to the evaporation of all the water surfaces, it is not the same than hot air from the radiators) produces condensation when cooling off, hence humidity at the foot of the wall and with the years delamination of the tapestry among other things. It is better worth addin convectors high, for instance upstairs. This complicates the heating installation which becomes an air-conditionning installation.
We can also convert the VMC into an air-conditionner.
We add on the circuit some insuflatted air, at the end of the interchange, a supplementary caisson which contiains a radiator water-air, sort of car radiator. We plug this radiator on the (supplementary) circuit of the heating dispenser of the room (like if there were a room more).
So in summer, when the installation is in refreshing mode, this refresh the insufflated air, in winter, this brings to the air the few degrees that it lacked (see before).
The water flow must be well adjusted so that not to change the VMC into "blizzard".
When heating, a softening of 5°C must be brought, when it is below 5°C outside
it must then be brought : 0.3×100×5 = 150 kilocalories per hour.
Let's admit that the water is at 30°C, and that we take 5°C from it
there thus must be a flow of 150/10 = 15 dm3/Hour, with a yield of 70%, this makes about 40 dm3/Hour, which represents about 10% of the debit of the installation.
In refreshing mode, the water will be around 15°C, if we want to bring the air from 35°C to 25°C, we have a gap of 10°C.
We must thus take 300kcal, if the temperature of the water increases by 5°C, this gives a flow of 300/5=60 dm3 per hour, that is to say, with a yield of 70%, about 85 dm3 per hour.
To refreshing, we may make a direct interchange between inside water, and water of the outside circuit, sort of "canadian well"