Thanks to advice from this group I have successfully fitted a room
thermostat to my central heating system.
I noticed however on reading the spec sheet that came with the unit
(Drayton Digistat 1) that there is a spec for "Differential <0.6 degrees
c at 4 degrees c per hour" just curious to know what this means if
I can only guess! The differential is the amount of in-built hysteresis -
i.e. the difference in temperature between opening and closing. This is less
than 0.6 deg C.
For example, if the stat opens at 20 degC, the room would have to cool to
something approaching 19.4 degC before it would close again.
The 4 degC per hour bit seems to be referring to the rate at which the room
temperature is changing. It seems to suggest that the differential is <0.6
at a rate of 4 deg/Hr - but may be different at a different room temperature
change rate (for reasons which are not immediately apparent to me!).
Maybe someone who knows about these things rather than guessing can explain
They're telling you the conditions of the test: The chamber in which the
thermostat was tested was heated at a rate of 4 degrees per hour until the
thermostat switched (off) and the temperature was recorded, the room was
(perhaps heated further) then cooled at a rate of 4 degrees per hour until
the thermostat switched again (on) and the temperature was recorded. The
difference between the two temperatures was less than 0.6 degrees.
At a higher or lower rate of change temperature the thermostat may behave
differently, eg. at a high rate of change the differential may be lower, or at a
lower rate of change, the differential may be higher - or vice versa.
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