Which set point are they talking about?

[JohnMo]

Boiler runs on weather compensation, so can deliver anything from 25 to 35 degrees.  Boiler just monitors the return temp and gives more heat to system as required.  Buffer is just more system capacity, plumbed as a 2 port buffer, with an oversize tee at the buffer ports to act as a hydraulic separator.  Buffer sits at about the same temp as the heating flow temp, hotter at the top than the bottom.

[Radian]

37 minutes ago, JohnMo said:

Boiler just monitors the return temp and gives more heat to system as required. 

I wish I knew the exact algorithm used by my boiler. Still not cracked the proprietary ebus protocol to monitor flow & return temps and adjust it for separate HW and radiators. Last ditch will be to A/D convert the thermistor connections so I can at least log the most significant behaviour.

[SimonD]

On 03/01/2023 at 22:49, MJNewton said:

With the T6 being CH-only I was intending on continuing with a 'dumb' timer to control the DHW. Do the Ideal's still allow different flow temperatures to be set for CH and DHW (noting it knows which is calling given the separate SL1 and SL2 demand inputs, as well as the Opentherm connection)? A quick skim of the Vogue system boiler IMs suggest it might not be able to. If not I could always swap for a T6R which would presumably allow the controller to dictate these?

 

The Vogue MIs don't cover the ins and outs of using SL1 & SL2. All you need for SL2 is a switched live from your wiring centre & programmer to the boiler SL2 IN when the cylinder calls for heat so it can be as dumb as it needs to be. The bit that does the modulation is the room stat which is what gets connected to the opentherm on the boiler. SL1 is then just bridged between L & IN at the boiler so there's no switched live to SL IN on the boiler from the programmer/room stat as this is managed through opentherm.

 

If you were to upgrade to the T6R you wouldn't get any particular benefit from this perspective because as soon as you wire it up to opentherm the heating switched live connections are automatically disabled on the receiver (this permits the installation of the receiver for dumb on/off ch control using switched live, or load compensation through opentherm - the disabling of the switched live when opentherm is connected ensures you can't double connect to the boiler and confuse things).

[MJNewton]

Thanks for all the info @SimonD. I've been reading/watching a lot about the Vogue now and I think I'll definitely be going for one when the time comes. I don't think I've found a bad word about them and there seems to be plenty of positive experiences of using them in a dual-temperature PDHW setup, and with the T6 family of controllers too so all in all seems a pretty safe bet. 

Edited January 6, 2023 by MJNewton

[tuftythesquirrel]

On 30/12/2022 at 13:55, SimonD said:

I've personally gravitated towards Ideal boilers because they have a separate switched live for DHW that gives a flow temp of up to 80C and a normal switched live that can be set to 55C or lower for CH.

Hiya, would it be possible to tell me which of the Ideal boilers this is? I looked at the LOGIC SYSTEM manual but couldn't see this arrangement. Thanks.

[Radian]

On 04/01/2023 at 10:07, Radian said:

I wish I knew the exact algorithm used by my boiler. Still not cracked the proprietary ebus protocol to monitor flow & return temps and adjust it for separate HW and radiators. Last ditch will be to A/D convert the thermistor connections so I can at least log the most significant behaviour.

 

No need for the last ditch measure of using an A/D. ebusd  and a RaspberryPi to the rescue...

 

So now I've got a better handle on the boiler algorithm and I'm close to dynamically setting the flow temperature. But the first thing I see today is how there's still a short cycle while heating my UFH buffer (HW cylinder):

 

The UFH has constantly been cycling the HW store all night (-5^oC outside) so when the roomstat for the radiators in the house calls for heat at 2AM, the boiler fires-up and the radiators begin restoring the temperature to the overnight setback value. When the roomstat goes off, and the zone valve for the radiators closes, there's a big spike in the return temperature as all the circulation is now only flowing around the UFH/buffer combo. Modulation rapidly drops at this point but it's too late in responding and as the differential between flow and return drops to nothing, the only thing the boiler can do is shut off entirely.

 

What I don't understand is why the boiler starts up again within a couple of minutes presumably at the expiry of the Anti cycling period (although I can't see this parameter in the big list I have, and 2 minutes seems very short) but when it does, modulation is a lot lower <40% and the UFH buffer is brought nicely up to temperature - at which point demand goes off ant the UFH freewheels around the HW cylinder for over an hour as intended.

 

I didn't expect to see this brief boiler shut-off glitch as I was only plotting demand before. I need to figure out a way of getting a softer landing when the roomstat goes off and circulation is restricted to the UFH. Of course all this was predicated on having a single, relatively high, set-point for boiler flow but now I may be able to reduce that for the radiators - given that I can have independent flow temperatures for radiators and hot water.

[Radian]

15 hours ago, Radian said:

(although I can't see this parameter in the big list I have, and 2 minutes seems very short)

 

Vaillant say

"If you are an engineer, the maximum anti-cycling time can be adjusted under the setting D.002 using the following table to produce the desired lockout time."

 

reading the parameter D.002 that I already thought was the right one I see:

bai BlockTimeHcMax minutes0=20 min [max. burner anti cycling period at 20°C Flow temperature setpoint] d.02

 

Which is why I expected 20 minutes but that's for a 20^oC flow setpoint. This table sort of explains why I'm only getting something like 2 minutes as the setpoint at the time was 66^oC

[Dan F]

15 hours ago, Radian said:

No need for the last ditch measure of using an A/D. ebusd  and a RaspberryPi to the rescue...

Apoligies if off-topic, but interested to know how you achieved the ebusd connection and how you "found" the registers relevant to heat pump etc.

[Radian]

5 hours ago, Dan F said:

Apoligies if off-topic, but interested to know how you achieved the ebusd connection and how you "found" the registers relevant to heat pump etc.

Take a look at my zombie boiler topic 😃

[SimonD]

@Radian, I'm looking at this with interest. You're not the only one to find a glitch with Vaillant modulation and anti-cycling - a discussion you may have already come across http://vaillantcyclingproblem.blogspot.com/2012/01/anti-cycling-mode-and-d2-parameter.html.

 

There is clearly a link between the flow & return delta, but I'm interested to understand the size of your buffer and volume of ufh system. It would also be interesting to know actual room temp, plus the time points of motorised valve on/off switching for ch. How have you set up the valves? E.g. when calling for heat does your system provide heat to both ufh/hw and ch, or do you swtich between the two?

Edited January 27, 2023 by SimonD

[SimonD]

On 25/01/2023 at 14:38, tuftythesquirrel said:

Hiya, would it be possible to tell me which of the Ideal boilers this is? I looked at the LOGIC SYSTEM manual but couldn't see this arrangement. Thanks.

 

Details are all in this thread, but as per my earlier comments about the Vogue Max, you won't find this arrangement detailed within the Logic manual either, but the Logic has an SL2.

[Radian]

On 27/01/2023 at 18:06, SimonD said:

@Radian, I'm looking at this with interest. You're not the only one to find a glitch with Vaillant modulation and anti-cycling - a discussion you may have already come across http://vaillantcyclingproblem.blogspot.com/2012/01/anti-cycling-mode-and-d2-parameter.html.

 

There is clearly a link between the flow & return delta, but I'm interested to understand the size of your buffer and volume of ufh system. It would also be interesting to know actual room temp, plus the time points of motorised valve on/off switching for ch. How have you set up the valves? E.g. when calling for heat does your system provide heat to both ufh/hw and ch, or do you swtich between the two?

 

I somehow missed the latest activity in this topic. I think the behaviour I've logged is to be expected - there's nothing for it but to shut down the boiler when the modulation bottoms out (10kW in my case) but the return keeps climbing. There's evidently a couple of degrees of grace allowing the flow temperature to exceed the setpoint - but then enough is enough and cycling begins. What threw me was the expectation I had before I looked at the table. Quoting the delay for a flow temperature of 20^oC is always going to be unrealistic.

 

As for my setup, it's constantly evolving 😃 The plot above was just for the UFH zone which runs of the 160L 'buffer' of my HW cylinder per:

Somewhat unconventional but it works for me!