WARM Enough to Swim- Jump Right In
ICING
BELOW 42°F (5°C) is a Heat Pump Issue
For most humans, if it is warm enough to swim, the average daily air temperature will be above 60°F (15°C).
That usually means at night it will go down to 55°F (13°C) and mid-day it will hit 65°F (18°C) or higher.
Still pretty chilly but YOUR HEAT SIPHON WILL RUN 24/7 if needed to keep the water as warm as you want.
It is when the air is BELOW 42°F that heat pumps have an icing issue. That means an average daily air temperature around 50°F or lower - POLAR BEAR SWIM CLUB TIME.
In order to take heat out of the air, the refrigerant inside HEAT SIPHON's evaporator tubes must be about 10°F COLDER THAN THE AIR so at about 42°F (5°C) air temperature the tube is approaching 32°F (FREEZING-0°C) and any moisture in the air will begin to FREEZE on the coil and ice it up.
Icing clogs the small fins, insulates the tubes and stops air flow all of which severely reduce the efficiency. If a lot of ice is allowed to build up it will take a long time to thaw out and melt.
Heat Siphon is designed to shut off when the air can cause icing and automatically restart when it is safe again as the air temperature goes over 50°F. In swimmable weather this off period is not more than a few hours in the spring or fall and should have no significant effect on your water temperature.
HEAT SIPHON FAST FACTS - There is a reversing valve built into the heating/cooling Heat Siphon models which could be used to melt the ice forming in sub-42° air, but it would take the HEAT FROM YOUR POOL TO DEFROST THE COIL - A NET ZERO SUM GAIN. Running the fan only while shutting off the compressor is also a defrost option but it takes a lot of 42°F air to melt an ice cube. The most economical design is to shut-down BEFORE ICING OCCURS and wait to run when the air temperature is swimmable - above 50°F.