I recently read a study that using a night setback on a heat pump can have a significant efficiency impact. The study found that a 2 degree night setback can reduce overall efficiency of an air source heat pump by 25%. When the stat calls for the morning warm up, it will force the auxiliary resistance heat to turn on. This will result in a period of resistance heat being used daily, even if it is not needed due to low outdoor ambients. The result was up to a 25% reduction in average COP. It was noted that an outdoor lockout stat reduced the impact.
We should advise customers of this (I have for years told owners to not set turn the temp down at night - but I never realized the impact it could have).
Any of you out there ever seen a programmable stat that either walks up the setpoint 1 degree at a time, until the final setpoint is reached, or have the second stage call up disabled on a setpoint change of more than 1 degree ?
Honeywell, if you are listening, here is idea to improve the VisionPro line.