ASHP + Buffer Tank Questions

[joth]

1 hour ago, Dan F said:

 

 

How do you get just 1kW? What flow rate is this based on?

1kW is from looking at the primary energy monitor of the heat pump, so it's delivering 3-4 kW into the slab assuming a reasonable CoP.

The UFH circuit doesn't have a flow rate meter, but yes I could try increasing the secondary circulation pump speed. 

[joe90]

1 hour ago, Marvin said:

This is what I am working towards...

Great minds think alike ?

[Dan F]

3 minutes ago, joth said:

1kW is from looking at the primary energy monitor of the heat pump, so it's delivering 3-4 kW into the slab assuming a reasonable CoP.

The UFH circuit doesn't have a flow rate meter, but yes I could try increasing the secondary circulation pump speed. 

 

And/or increase the temperature. Rather than a buffer being required to take advantage of cheap electriciity, I think it's probably more a case of how much control flexibility you have to increase UFH temperature or flow-rate during the period of cheap/free electicitiy vs. the ability to simply increase a buffer tank set point.

 

In my case, there is no buffer tank setpoint that I know of and, until I get my hands dirty with ebus, no way to adjust flow temperature from outside the heating system either.  So I'll be limited to whatever the power of UFH is. I think it'll be a fair bit more than 1kW though, even at 30C. 

 

 

 

[J1mbo]

What system do you have @Dan F?

[Dan F]

1 minute ago, J1mbo said:

What system do you have @Dan F?

Same you you, just 7kW.  Vaillant does support a buffer temprature probe, but it's 100% optional and I've no idea how it is used.

Edited December 2, 2021 by Dan F

[J1mbo]

Presumably you have the heat pump controller and VRC700?

[Dan F]

1 minute ago, J1mbo said:

Presumably you have the heat pump controller and VRC700?

 

Hydraulic Station + VR 71 (wiring center) + VRC720f (SensoComfort) + VR921 (SensoNet)

[J1mbo]

38 minutes ago, Dan F said:

In my case, there is no buffer tank setpoint that I know of and, until I get my hands dirty with ebus, no way to adjust flow temperature from outside the heating system either.

Setting the room temperature higher in the period of cheap electricity will shift the flow temp curve up (2 degree increase in room temperature is a 5 degree increase in flow temperature in the example in the manual).

 

The system can apparently also be configured for buffer maintenance (would need VF1 sensor) but Vaillant told me it’s not generally recommended.

Edited December 2, 2021 by J1mbo

[Dan F]

1 hour ago, J1mbo said:

The system can apparently also be configured for buffer maintenance (would need VF1 sensor) but Vaillant told me it’s not generally recommended.

Mind sending me any information you have on this via DM? Thanks.   

[joth]

9 hours ago, Dan F said:

And/or increase the temperature. Rather than a buffer being required to take advantage of cheap electriciity, I think it's probably more a case of how much control flexibility you have to increase UFH temperature or flow-rate during the period of cheap/free electicitiy vs. the ability to simply increase a buffer tank set point.

Increasing flow temp further will start to put the bamboo flooring at risk. Doable, but definitely more faff as from Loxone I currently only have on/off control, no way to modulate the flow temp. And their cloud API does not support setting the compensation curve at all. 

 

The Ecodan has a couple of dry contact inputs specifically for "smart grid" readiness to indicate cheap or surge prices. The built in function for cheap rate is to boost the cylinder up to max temp and likewise heat the buffer tank up.  Without a buffer and temp probe, it doesn't have much purpose for heating. Only found that out after we installed. But using these would be much simpler and safer than messing with cloud API (that could muck up normal running mode functionality)

 

 

[J1mbo]

7 hours ago, Dan F said:

Mind sending me any information you have on this via DM? Thanks.   

 

Have a look at the installer manual for 720 specifics but in VR700 terms (I presume 720 substantially the same) I think the config would be to have the VF1 in the buffer, heat curve set, adaptive heat curve off and room temp mod none.

 

Maybe setting the multi-function input to 'PV' and then configuring 'buffer cylinder offset' to e.g. 10K might do what I think you want, i.e. heat the buffer more overnight (obviously a time-clock input would need to be provided to the multi-function input to trigger it). And likewise the legionnaires function can be used to heat DHW to 65°C or so in the same time window.

Edited December 3, 2021 by J1mbo