[TRNSYS-users] TYPE 938 - defrosting cycle

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Dear All,

I'm trying to simulate the behavior of air source heat pump during a year.

Does anyone know how to take into account defrosting cycle (reverse mode of
heat pump) during winter time ?

kind regards

Michal Klimas

Poznan University of Technology

Michal Klimas's picture
Joined: 2016-04-05
Reputation: 0

Type938 does not take a defrosting cycle into account because the
sequence of controls used to run a defrost cycle change from one
manufacturer to another. You can create your own defrost cycle, however
by using a thermostat model to watch the outdoor unit outlet temperature
and turn the heat pump on in cooling mode for a period if the outlet air
temperature falls too far. Depenging on how the defrost cycle works in
your case you can also use some other components if an electric heater
runs to keep the supply air warm during that cycle.

As a side note, please remember that Type938 (and all the components
that read performance data from an external data file) can interpolate
performance data within the range given in the file but cannot
extrapolate beyond the range. If you expect to run your heat pump in a
climate where defrost will be needed please also make sure that both the
heating and cooling data files contain capacity and input power
information for temperatures that low.
kind regards,

David BRADLEY2's picture
Joined: 2011-10-02
Reputation: 0

Thank you David !

Then idea to connect outside air to electric air heater and control it
by an equation sounds reasonable.

All the best,

Michal Klimas's picture
Joined: 2016-04-05
Reputation: 0