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Ecodan flow temperature drops randomly

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(@tuffpro)
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Just looking at my flow temperatures for my mitsubishi ecodan heat pump. I noticed that every now and then the flow temperature drops for roughly 10 minutes before returning to the set flow temperature. 

House temperature is fine, I do notice that the rads cool down during this 10 minute period.. 

I think this is normal but just wondered why the system is doing this.... 

Doesn't seem energy efficient to let the flow temperature drop to be heated up again..

Screenshot 20240105 192031 MELCloud

 

Thanks in advance 

 


   
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(@derek-m)
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Posted by: @tuffpro

Just looking at my flow temperatures for my mitsubishi ecodan heat pump. I noticed that every now and then the flow temperature drops for roughly 10 minutes before returning to the set flow temperature. 

House temperature is fine, I do notice that the rads cool down during this 10 minute period.. 

I think this is normal but just wondered why the system is doing this.... 

Doesn't seem energy efficient to let the flow temperature drop to be heated up again..

Screenshot 20240105 192031 MELCloud

 

Thanks in advance 

 

The heat pump is defrosting, which is easy to tell since the Leaving Water Temperature falls below the Return Water temperature.

 


   
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(@tuffpro)
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35 kWhs
Joined: 5 months ago
Posts: 4
Topic starter  

@derek-m

Thanks for the prompt reply, are you able to tell me more about this defrosting process? Or direct me to an article or post that explains more about why this is needed.. 

I take it that defrosting is related to the liquid chemistry inside the ecodan which produces the heat... But baffled as to how something that produces heat needs defrosting..

Thanks again 


   
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(@tuffpro)
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35 kWhs
Joined: 5 months ago
Posts: 4
Topic starter  

Got it... University of YouTube is very helpful.. 

The heat pump uses a coolant to produce the heat... 


   
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(@derek-m)
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Posted by: @tuffpro

Got it... University of YouTube is very helpful.. 

The heat pump uses a coolant to produce the heat... 

A heat pump uses the 'phase change' of a refrigerant gas to absorb thermal energy from the outside air, and then uses this thermal energy to heat the central heating water.

The compressor within the ASHP, as the name suggests, compresses the refrigerant gas, and in so doing increases the pressure and the temperature of the gas. The gas coming from the compressor flows into a heat exchanger called the condenser, where some of the thermal energy is transferred from the refrigerant gas into the central heating water, and in the process the temperature of the refrigerant gas is lowered and it condenses from a gas into a liquid.

This liquid is allowed to flow from the condenser into the evaporator via a control valve, the evaporator is the finned coils at the rear and side of the heat pump unit. As the liquid refrigerant flows into the evaporator its pressure falls and it commences turning back from a liquid into a gas, but to be able to do so it must absorb some thermal energy. The heat pump gets this thermal energy from the outside air, but again by doing so cools the air in contact with the evaporator coils and fins, which is why the heat pump needs a fan to keep drawing fresh air through the evaporator coils.

The outside air contains water vapour, which starts to condense on the evaporator coils and fins, and at some point the evaporator surface will become cold enough to cause this water to freeze. As the ice builds up on the evaporator it starts to prevent the airflow from going through the evaporator, which reduces the amount of thermal energy that the heat pump can absorb, so periodically the heat pump needs to get rid of the ice build up. During the defrost cycle the heat pump passes the refrigerant gas in reverse, so hot gas goes into the evaporator and thermal energy is extracted from the central heating water, hence the fall in LWT and RWT.

 


   
Morgan, Tuffpro, Mars and 1 people reacted
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(@tuffpro)
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35 kWhs
Joined: 5 months ago
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Topic starter  

Thanks for surch a detailed explanation... This explains why on very cold days I see a ploom of steam coming from unit now and then.. 

Appreciated.. 


   
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