VR65/VR66 for HW flow temp control

[fezster]

I see - so you've disconnected the grey/orange on your HW 2 port valve from any power, and rely on the VR65 using ebus to activate the boiler when the HW zone valve is open?

Another question - As the VR65 is not used to control the zone valves, I assume there is no HW priority? I.e. if the HW zone valve is open, the CH zone valves may also be open at the same time?

 

[notorious]

>> I see - so you've disconnected the grey/orange on your HW 2 port valve from any power,
>> and rely on the VR65 using ebus to activate the boiler when the HW zone valve is open?

Exactly.
Power of HW 2 port valve is controlled by Nest according to Nest's HW schedule.
Nest's on/off switch activates the HW 2 port valve via 240v.
When HW 2 port valve is fully opened the misroswitch closes.
And that gives command to VR65 to bring the boiler to hot water mode using ebus, when and only when the HW zone valve is open of course.

>> As the VR65 is not used to control the zone valves, I assume there is no HW priority?
>> I.e. if the HW zone valve is open, the CH zone valves may also be open at the same time?

This is how boiler software works: If during an existing demand for heating (via switched live controls) the boiler receives eBus command from VR65 to activate hot water mode the boiler will switch to hot water mode to deliver 80C hot water to charge the cylinder, ignoring the fact that there's also a demand for heating (via switched live controls) until demand for hot water via eBus is satisfied. The boiler will then switch to normal heating mode if call fir heat via switched live is still there.

As you correctly say, the CH zone valve will be opened depending on heating demand. This is because you own valves control, not the Vaillant.

In my specific example I accept the fact that water hotter than normal will be delivered to radiators during cylinder charging times. Respective Nest room thermostats will of course terminate heating demand a bit earlier in such "hotter" scenario and that’s all.

An alternative method of 240v wiring (via a relay) can easily keep all CH zone valves closed when HW zone valve is activated via 240v. That will put heating to "wait mode" until HW demand is fully satisfied. The downside of this architecture is lack of heating in the house while cylinder is being charged.

P.S. Boiler will always return to heating mode if heating mode was interrupted by HW demand via eBus. If during hot water mode a switched live demand is received the boiler will ignore that request and will continue with hot water mode. So boiler software works in hot water priority mode. And you control valves any way you want.

 

[fezster]

Very useful notorious. I think I may give it a go. Although I'm not certain how much saving the lower flow temps are likely to give in reality - and will this translate into lower bills.

Be interesting to hear from you how your bills differ once you have used the new setup for a while.

 

[notorious]

Cheers bro. I will watch my bills.
Lower temps will give very, very comfortable conditions in the house.
I've been testing this for months and I won't go back since I love it.

The original idea of the thread is yours.
I highly appreciate that you aired your thoughts in December 2017.
Without reading your thread I would't risk this project.

Relevant controls can be found used on eBay for pennies, so ROI is huge.

 

[fezster]

Thanks for sharing the info here

 

[rbranco]

I have the VR66 which controls both valves, the boiler controls the pump, (exact setup depends on if you are 4xx/6xx/8xx ecotec, on 4xx you need the VR66 to control both valves idealy).
I have the VRC720f as its the newest model and got it cheaper than the older one, but I did use the setup before without a VRC on a standard timer/thermostat but you need to do some non-standard wiring to make it work ie using standard timers/nest etc.
As said before if the CYL is closed and the boiler RS (3/4) pins are closed it will be in DWH mode, if CYL stat opens then it will be in CHW mode until RS opens. So you can essentially switch the CYL & RS using timer/thermostat+cylstat to get it to work without VRC.

When running a full ebus system you always leave 3/4 bridged, ebus is a stop signal system, its always running if the bus fails (ie the VRC).

I now have full eBUS system but still have my old timer connected in the circuit so if all else fails the boiler keeps running I can then just go to my timer and turn it back to old timer mode

 

[ScottishGasMan]

I got mine reasonably cheap with the intention of trying to monitor the ebus commands it sends to the boiler to activate the DHW mode.
That project didn’t work out although I still have a raspberry pi hooked up to the bus and that can send a variety of other commands to the boiler.
I’d still really like to know the sequence of commands to start and stop DHW heating.

What software do you use for the pi to read ebus? Can you monitor and data log using it?

 

[jackthom]

What software do you use for the pi to read ebus? Can you monitor and data log using it?

I used one of these to link to the boiler ebus using raspberry pi USB port.

https://www.esera.de/shop/en/products/ebus/135/ebus-coupler-usb

Then run ebusd software on the pi, which handles the sending and receiving of data on the bus in the correct format.

https://github.com/john30/ebusd/wiki


Had to write a python program to send the required commands and receive the data requested from the boiler via ebusd.

 

[notorious]

Boiler wiring at fezster's request

This is before the setup was extended with VRC 470,
which added edge connector to wire the external temperature sensor.

 

[fezster]

For the benefit of anyone else wanting to do this. I, too, am using 2 x nest 3rd gens to control heating and hot water.

My setup was slightly more complicated in that I have a low loss header and a secondary circulation pump wired to the SL for all 3 zone valves (u/s, d/s, DHW). With the knowledge of another member @bruce_miranda I wired my DHW zone valve live (ie. HW on) to the right hand CYL terminal of the VR65. The left hand terminal is 230V and is documented as needing bridging to the right terminal via the cylinder stat. In actual fact, it works just like terminal 4 on the vaillant boilers - any 230V live on the right hand terminal activates HW mode.

I also used a VRC 470f, so my outside temp sensor is wireless.

Thanks again @notorious for posting about this and for the info you gave re your setup.

When fine tuning the heat curve, what is an acceptable amount of time for the heating to increase the room temp? For example, on curve 1.5, I found the boiler on a very low burn, but the room stat was taking an age to increase 1 degree. At 1.75, it is better at the expense of a higher flow temp (albeit still very low - sub 50s). There must be a methodical way to identify the sweet spot for a particular house.