Delta in heat pump heating

[krzbor]

I have a question regarding the delta in heating. I have a Series K pump. The temperature is set to 22°C, and the delta is 2°C. The heating turns off at 24°C and turns on at 19°C. How is this calculated? Because I get +2°C and -3°C.

[MiG-41]

How your pomp is set ? Is it temperature of water outlet , or yuo are using internal thermostat ?

[krzbor]

panasonic_heat_pump/main/Main_Outlet_Temp

[MiG-41]

So what is your temperature in rooms then , if your outlet temp is max 24 deg ( 3min and off ,so more of the time 23 or less).

As i recall this function correctly..... So when your target temp is 22 , HP starts modulating to keep it. When modulation is not enough , and temperature reach more then 2deg of target ( basicly 2.25deg is enough) then after 3min HP will switch off ( or temp will drop to 2 deg difference or less). But during stop HP remembers the Inlet temperature. And this Inlet temperature is now reference , and have to drop again 2 deg before this reference to turn compressor on.

So it could be like this , that your outlet is like 24,25deg , but your inlet has only 21deg , and HP wait to have it 19deg to turn on again...

[krzbor]

Perhaps I was too quick to point out an error. I need to carefully analyze my pump settings related to the possibility of activating the internal heater. According to the manual, there are as many as four control parameters.

[geduxas]

I heard some rumors from daikin community, that pump decides in which condition it would be more economically to start compressor or just quickly use heaters.. it's possible could be new features in K/L models.. they're pretty new.. maybe it's first season for them :)

[krzbor]

[MiG-41]

No , not this menu...
Serwice menu to enter while HP turned off by holding 10s LEFT-DOWN-MENU

[geduxas]

@MiG-41 it should be done with caution.. it's not recommended to disable heaters.

[geduxas]

Delta is only to maintain inlet/outlet proportion.. it will drive circulation pump to maintain that different. And off indicator is inlet temperature.. if it reaches outlet temperature then it indicate pump to switch off.

Whole logic is very well described in service manual.

[krzbor]

You wrote what the condition for turning off the pump is. My question is—what is the condition for turning it back on?

[geduxas]

Here is snipet from service manual:

• Compressor is OFF when Water Outlet Temperature – Internal Water Setting Temperature > 2°C for
  continuously 3 minutes.
• Compressor is ON after waiting for 3 minutes, if the Water Outlet Temperature – Water Inlet Temperature
  (temperature at thermostat OFF is triggered) <-3°C

[geduxas]

And this from H series service manual, it might be that in K it changed.. or left the same logic..

[krzbor]

Thank you for the explanations! As you can see, this is exactly how my pump behaves, and I mistakenly connected it to the delta.

[krzbor]

I decided to analyze the condition for restarting the pump:

Water Outlet Temperature – Water Inlet Temperature
(temperature at thermostat OFF is triggered) < -3°C

Substituting, we get:
Water Outlet Temperature – (Internal Water Setting Temperature + 2°C - delta) < -3°C

After rearranging the formula, we get:
Water Outlet Temperature – Internal Water Setting Temperature < -1°C - delta

So it seems I wasn’t mistaken after all—delta also has an impact on turning the pump back on.

[geduxas]

Delta, is difference between supply an inlet which pump trying to maintain. Outlet is target setpoint, and to keep inlet in delta range, pump control it's flow.. and temperature difference with heat capacity is heating energy which your house consumes.. by that compressor is modulated to not generate more than your house consumes...
But it's not ideal, and compressor maybe produces mire energy.. so inlet starts increase. And pimp shutting down.

[krzbor]

Did you analyze my formula thoroughly? It is precisely about this:

Water Inlet Temperature (temperature at thermostat OFF is triggered) = Internal Water Setting Temperature + 2°C - delta

[geduxas]

No, it's not like that. Off condition is not related to delta at all.

[geduxas]

Sorry, i little bit confused my self, and you, yes and no.. in theory you are right, maybe in most conditions.. it depends in some situations :)

[krzbor]

I will describe my calculations in detail.

The condition for switching off is:
Water Outlet Temperature – Internal Water Setting Temperature > 2°C

Additionally:
delta = Water Outlet Temperature - Water Inlet Temperature

Therefore:
Water Inlet Temperature + delta - Internal Water Setting Temperature > 2°C

For the calculations, it’s better to assume equality (switching point):
Water Inlet Temperature + delta - Internal Water Setting Temperature = 2°C

Next, we have:
Water Inlet Temperature = 2°C + Internal Water Setting Temperature - delta
This is the compressor shut-off point, hence:

Water Inlet Temperature = 2°C + Internal Water Setting Temperature - delta = Water Inlet Temperature (temperature at thermostat OFF is triggered)

Now, we use the second formula:
Water Outlet Temperature – Water Inlet Temperature (temperature at thermostat OFF is triggered) < -3°C

Substituting, we get:
Water Outlet Temperature – (2°C + Internal Water Setting Temperature - delta) < -3°C

Which simplifies to:
Water Outlet Temperature - 2°C - Internal Water Setting Temperature + delta < -3°C

Finally, the condition for switching on again:
Water Outlet Temperature - Internal Water Setting Temperature < -1°C - delta

This is not an exact switching point, as the pump usually has a smaller delta when stopping, but in general, this is how it should work, or at least that’s what the Panasonic formulas suggest.