New GSHP installation Vaillant VWF 58/4 with integrated DHW cylinder, 140m deep vertical loop

Hi all,

Finally my ground source (140m deep, double loop, dia 32mm) heatpump was installed and commissioned. It’s a Vaillant VWF 58/4 FlexoCompact with integrated 175l DHW cylinder. It’s an upgrade from a Vaillant gas heater VCW346 from 2015.
The house is a “house in the row”, build in 1958, fully converted (also in 2015) to underfloor heating. Street side is still uninsulated full bricks 30cm. Wooden windows with U=1.0 glass. Roof is U=0.2. Walls gardenside also around 0.2 and triple glazing U=0.6.
Our yearly gas consumption was between 8000-10 000 kWh. So in theory (didn’t do any heatloss calculations) I should be fine with the 5kW heatpump. This winter will tell…

Ofcourse, since I bought my first OEM hardware in 2012/2013, stuff needs to measured/monitored… I have an Eastron SDM120 on the 16A breaker (heatpump) and another SDM120 on the 25A breaker (5 kW electric heater).
Then 10 DS18B20 sensors:

  • Cold water in from the drinkable water network
  • Brine circuit flow
  • Brine circuit return before the passive cooling module
  • Brine circuit return to the groundloop
  • Heating circuit flow
  • Heating circuit return
  • Hot water circuit flow
  • Hot water circuit return (I installed a circulation pump to shorten waiting time)
  • Inside the boiler insulation left
  • Inside the boiler insulation top right

And then the magic, for even more data, an ebusd v3 adapter to get a lot of data from the heatpump itself:

  • FlowT before all valves (super handy since otherwise I cannot see the DHW cycle in my graphs)
  • ReturnT before all valves
  • Flow rate, this is coming from the Grundfos UPM2 25-70 180 its PWM out, since I cannot spot any “real” flow rate sensor in the unit as well in the spare parts catalogue.
  • Current consumed (in kW measured by the HP itself), bad 100W resolution
  • Current yield (in kW), same 100W resolution
  • COP heating circuit “current”
  • COP heating circuit this month
  • COP DHW cycles “current”
  • COP DHW cycles this month
  • Thermostat outside temp
  • Thermostat inside temp

So that gives us quite some data. But I have some questions/remarks.

COP calculation according to Vaillant is (Pelec + Pyield) / Pelec which more or less corresponds with the COP reported by the machine.

Then as “check” I wanted to calculate heat with: heat transfer (W) = specific heat (J/kg.K) x flow rate (kg/s) x DT (K) to compare to the reported heat output by the heatpump itself.

the 1.1666 calibration is 4200/3600 since my flow rate is in liters per hour.
As you can see there’s quite some delta, the Vaillant being very optimistic about it’s heat output compared to the calculated heat. Ofcourse I’m not sure if the flow rate reported by the system is any accurate. But as there’s no flow sensor installed, Vaillant is probably using this data themselves.

I made a PWM read sensor using ESPHOME and a PC817 on the PWM out of both the Wilo brine pump as the Grundfos heating circuit pump. If we compare PWM to Flow rate reported, pattern is identical. (FYI PWM 95% = pump standby)

Since we have warmer days here in Belgium, I’m using the passive cooling 24/7. 130W electrical for 1200-1500W of cooling power. That’s a really nice COP :blush:.
How does the Heatpump app handle negative heat? I would expect a 9.5 / 10.5 COP instead of the -12.96? Also are the Wh accumulators getting crazy off negative values?

Anyway a lot of information and some first questions. BTW I used the Brine Flow temperature as OutsideT graph, since that’s influencing my performance and not the air outside the house.

Open to suggestions, comments etc.


Thanks for posting this @fluppie007 it’s interesting how your own heat output calculation shows a much slower output rate than the vaillant itself. I’ve sent a message to John Cassells at Vaillant to see if he might have any insight.

and yes the emoncms MyHeatpump does not deal at all well with cooling, adding cooling support gets quite complicated it needs to distinguish between summer cooling and winter defrosts, winter defrosts should subtract from COP but summer cooling should not. To cater for this it needs both a signal to tell the app what mode it is in and a whole load of extra feeds to separate all the different modes out in a sensible way… I started work on it and realised it was a much bigger job than I originally thought so it’s back on the todo list for a bit.

I turned off passive cooling since 15h15 Today 24/08. So from then on, it’s logging like most heatpumps :slight_smile:.
The DHW cycle at 15h15 is also a bit weird since my wife was showering for a ridiculous amount of time :smiley:

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Hello @fluppie007 John kindly replied, he isnt familar enough with the FlexoCompact to be able to say why you are seeing what you are seeing, but suggests that the results are unlikely to be the same as the Vaillant arotherms as the arotherms do have an inbuilt vortex flow meter for heat calculation. Older models used the pump in the way you describe but newer ones include the dedicated flow meter.

OK cool, so in theory those units should be quite accurate compared to a heat meter.
I also think there’s no real room in this system to fit a flow meter, since I need to do it before the 3-way valve. And also, I don’t think Vaillant will offer warranty if you modify the internals :smiley:.

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