Unfortunately the heat you gain from condensing water (from air) is your temporary gain.
1 You will spend energy to freeze it,
2 The fan will work harder another loss
3 You will spend energy to melt it using hot gas or electric heaters
4 All time your defrost cycle is on electrical strip heater in providing heat for your furnace (with hydronic system this part can be different)
I saw heavy ice build up in just 30-40 minutes. Hot gas does melt it quick but it is not free. Residential units usually just revers the valve. Commercial units often use by-pass solenoid for defrost.
Another problem is night temperature is usually much lower then day. This makes your system even less efficient. Loop temperature is very high compare to air and stable this is why GSHP are so efficient.
My next house I will plan ahead using much more green technologies.
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