Fiddling with the controls

Well it all works pretty much, but we have had a fine time fiddling with the settings and may have to make more adjustments before we are done. For unexplained reasons (?concern over local disturbances) the controls favour indirect 'feedforward' control via an external temperature measurement and a fudge factor ('slope') to estimate the heat needed (rather than direct feedback control using the house thermostat). The machine comes with a generic fudge factor of 4.0 programmed, but radiator systems expect a larger factor and we have raised this to 6.0, which may be a tad too high as there may be a slight (less than 0.2 degrees) tendency for the house to warm as the temperature falls, though with a time constant of several days (with up to metre thick stone walls) experiments are not so easy!* We need our WEL data logger. The Alertme power logger works OK (with a few glitches on the software).

And the long time constant gave us an initial problem - the house was very slow to warm up and the HP was not putting in enough extra effort. Raising the fudge factor on the internal house thermostat from 4.0 to 9.0 (in the special menus) to make the system more responsive to house temperature (after all that is what we really want!) helped, as did moving the 'radiator return' temperature sensor (which seems important) onto the radiator return arm and away from the accumulator tank where it was originally sited, but we are warmed up now anyway. The system now thinks the house temperature is 19.5, though 2 local thermometers think only 18.6, but anyway it is quite comfortable.

Other details are that the two oldish Myson fan convectors we had do not much like the water temperature being low - they have a switch to shut them off if the circulating water temperature falls too far (ie in summer as normally arranged). But they have a panel switch that I supposed by-passes this in case you want summer air flow. This is fine but the switch is very counter-intuitively marked, so you need to select the red 'hot' setting (?summer) rather than the blue 'cool' one. We have external room (ie some metres away) thermostats on both units anyway.

I am not sure that the radiator circulating water pump runs 24/7 (as we would wish), though it is mostly on.

Since the HP cycles I am not sure to what extent the efficiency (by physics a function of the temperature increment from the ground and thus of the circulating water temperature) is affected by the mark/space ratio on the cycle, which is what actually varies.

* FYI if you have a similar IVT system we have ended up with a 'slope' fudge factor of 6.0 (default 4), a target room temperature of 20.5 (actually ~19.5) and a sensitivity to room temperature of 9.0(default 5). This seems to work fine.