Air source heat pump condensate????

[Vortex2]

Hi team,
The drain pipe for our air source heat pump condensate got blocked the other day.
I had to divert the water into a large glass demi-john.
I thought that I would see a few cc every now and then due to the defrost cycle.
However we see several litres of drain water a day!
So where all this water coming from?
And why is there zero at some times and tons at other times?

[adam2]

An air source heat pump cools the outside air in order to warm the interior of of a building.
If this outside air is cooled below the "dew point" then condensation will form on the heat exchanger.

The volume of this condensation will depend upon two main factors, firstly on the heating demand, and secondly upon the dew point of the outside air, damp, humid, or misty conditions will produce more condensation than dry.
In cold weather ice may form rather than liquid water, but this will be melted by the defrost cycle and emerge as water.

The condensed water will contain various pollutants from the air and I would not re-use it except for toilet flushing.

[Vortex2]

Ah, that explains it.

So the heat pump dehumidifies the incoming air too - at least some of the time.

[adam2]

Most types of heat pump do not dehumidify the INTERNAL air of the space being heated, the condensate that you have observed is extracted from the OUTSIDE air as it passes over the cold external heat exchanger.

During the UK heating season, internal air of heated spaces often tends to become dryer than desired, and drying it further would be undesirable most of the time.

A REVERSIBLE heat pump can chill the internal air when this would otherwise be uncomfortably warm, under these conditions water WILL be extracted from the interior air in cooling mode during humid weather.
Reversible heat pumps are not common in the UK and no subsidy is available for units that can cool as well as heat.

[BritDownUnder]

I notice that with my heat pump / aircon in Australia. When cooling the water will come from one pipe and when heating water will come from another pipe. All is collected for garden use.

[Catweazle]

My favourite youtube channel has done some interesting experiments with aircon.
https://www.youtube.com/watch?v=R_g4nT4a28U