Defrost
In cold and wet weather, the outdoor unit can start to freeze up causing a sheet of ice to form on the fin coils at the back and side of the unit.
In conditions below -2°C, the coils are less likely to freeze as there is less water in the air. If a coil was to be blocked by the ice then the unit will need to run
in defrost mode. To do this it reverses the operation of the unit by using the heat from the system to heat the coils. The effect of this is that it will start to take
heat from the dhw or heating system and the temperature will start to decrease.
In worst case scenarios, the unit can enter the defrost mode for around 6 minutes every hour.
After the defrost process has complete, all of the ice will have been melted from the back of the heat pump and pour out into the drain off system.
Every time water is put through the unit it will lose up to 5°C, the flow rate will be at 20 L/m. This means that if the system volume is considerably small then
the temperature can drop dramatically. An example of this would be if there was around 20 litres within the system all of the fluid will circulate through the
unit 6 times in 6 minutes and this will cause a 30°C drop in temperature. This is where a volumiser or a buffer tank can come in handy as this will increase the volume of fluid and also the heat will be taken from the store rather than the property.