does balancing increase efficiency?

[D_Hailsham]

d.2 is the minimum time that the boiler will wait after cycling off before cycling back on again. There is also a required minimum temperature drop. Once both the d.2 time and the temperature drop have been reached then the burners come back on if still required.

From observations and what's written in the manual, it's the MAX time (not minimum!) that the boiler will wait before cycling

The manual says:

d. 1 Water pump over run time for heating mode 2 - 60 min (factory setting: 5 min)
d. 2 Max. burner anti cycling period at 20 °C Flow temperature 2 - 60 min (factory setting: 20 min

Could ianniann be confusing "min" meaning minimum with "min" meaning minutes?

 

[UpgradeME]

What I think happens is that boiler calculates its own length of time for the burners to be off, based on various criteria, and the d.2 setting is simply the maximum that this will go up to.

Thanks to keithsb who provided a table for d.2's "Effective burner blocking times" below

Untitled

• UpgradeME
• 20 Mar 2011
• 1

When you say in step 6 "anti-cycle mode (d.2)", you actually get a display of 5.8, right?

Yes.

Can you not control how low a flow the VRT392 will request? Only on the more expensive model? Frankly a flow of 21C is just pointless on a conventional radiator system, worse than useless, and will be wasting you money. Less than 40C is probably pointless although no doubt it could be satisfying to some people to have mildly warm radiators on 18 hours a day.

If the water temperature is > 21C already, the boiler doesn't fire so won't be using any additional gas, however, the pump will be running. The only time I've seen the pump not running is during d.2's (5.8 ) anti-cycle time. During this period, the pump is switched off.

I wonder if the short-cycling might be influenced by radiator flow? If the radiator flow is much less than the boiler flow, the by-pass will open and the boiler will heat up very quickly.

In the interest of being bloody nosey , what happens if you open all the TRVs?

There are three radiators without TRVs (total output of 1.1kW @ 40C (3.36kW@75C)), I've been checking the ABV and as far as I can tell, there is no flow through it during the short-cycling time. I had wondered if it was something to do with flow, so I've changed the pump speed to III which I *think* (not totally convinced yet) helps a little when the flow temp demand is around 45-50C.

 

[ianniann]

Could ianniann be confusing "min" meaning minimum with "min" meaning minutes?

No, I just didn't read the manual

So, from that table, the time the burners are off for anti-cycling *is* driven by the d.2 setting but not directly? That setting is actually the anti-cycle time for a flow temperature of 21C, and then the boiler picks shorter intervals when the flower temperature is higher?

So you have some control at least. I wonder if the table operates using the flow temperature set dynamically by your controller or just goes with the one set with the knob on the front? Out of the available choices, I prefer the ones at the higher end although the delays at low flow temperatures still seem excessively long, and the ones at the high end excessively short. For example, at 75C I don't think I'd be delighted to have my boiler switching on and off every minute or so, but I guess with your controller you won't be in that situation very often.

 

[ianniann]

I've changed the pump speed to III which I *think* (not totally convinced yet) helps a little when the flow temp demand is around 45-50C.

A faster pump speed means the temperature drop/rise across the heat exchanger is smaller and the average water temperature in the circuit is higher. This will reduce cycling by the same amount as if you were running at a higher flow temperature, perhaps like 5C higher for a change from 2 to 3. However, it will also reduce condensing efficiency as if you were running at a higher flow temperature, because the return temperature is higher, so it isn't really achieving much. You could get basically the same result by turning the pump down and turning the flow temperature up.

 

[UpgradeME]

So, from that table, the time the burners are off for anti-cycling *is* driven by the d.2 setting but not directly? That setting is actually the anti-cycle time for a flow temperature of 21C, and then the boiler picks shorter intervals when the flower temperature is higher?

So you have some control at least. I wonder if the table operates using the flow temperature set dynamically by your controller or just goes with the one set with the knob on the front? Out of the available choices, I prefer the ones at the higher end although the delays at low flow temperatures still seem excessively long, and the ones at the high end excessively short. For example, at 75C I don't think I'd be delighted to have my boiler switching on and off every minute or so, but I guess with your controller you won't be in that situation very often.

See this thread for how I believe d.2 operates. I have put it in a seperate thread to hopefully build up a better explanation of all the codes in one place, perhaps also providing a reference for others in the future!

 

[Agile]

In the UK we have become accustomed to using UFH with a temperature reducing blending valve and a shunt pump.

In Italy, and probably other parts of Europe its apparently quite normal to let the boiler drive the UFH directly which is why many boilers seem to have controls which work down to 20 C or less.

Tony

 

[UpgradeME]

Just a quick update..

I seem to have now resolved the 'short-cycling' issue I had by changing d.17 to 1 - This changes from flow 'regulation' to return regulation according to the instructions...

When connecting underfloor heating or wall heating to the appliance which does not have its own temperature regulation, the temperature regulation mode can be changed from flow temperature regulation (factory setting) to return temperature regulation

After observing the boiler, I'm pretty sure my ecoTEC 418 burner starts at 70%* of d.0 for the first 10 seconds or so, then modulates itself up/down as necessary. I think what was happening before was during those first 10 seconds, it was quickly reaching the 'demand' temperature requested from the VRT392 (often only 42C) then cutting off.

With d.17 changed, the return temperature is monitored so instead of the boiler increasing quickly to the 42C flow temperature and then stopping after 5 seconds when it was reached, it now monitors the return temperature which doesn't shoot up as quick, so gives enough time to modulate down!

I've changed d.1 and d.2 back to their defaults (5 mins pump overrun and 20 mins for anti-cycle) and will optimise those when it gets colder again.

The other settings I've changed are d.77 (it's the same as d.0 but for HW) to 10kW - Not sure how to determine the 'correct' setting for this one as I don't know how much kW my 117 litre DHW cylinder/coil is? (Is there a way to tell??) And I've dropped d.78 (max temperature for heating DHW) to 70C to try and get a lower return temperature for condensing effeciency whilst heating the DHW.

Pump speed back down to II and I'm getting approx 17C difference between flow/return at the boiler.


* The 70% figure is an 'educated' guess based on the fact that d.15 usually starts at 70% and from the sound it makes.

 

[ianniann]

I seem to have now resolved the 'short-cycling' issue I had by changing d.17 to 1

Interesting idea. The effect is of increasing the flow temperature by 10C-20C compared to before. How will this work with your temperature modulating controller? You may be able to get very similar results simply by increasing the flow temperature by 15C on the original setting.

It will also have the effect of cooling down the overall flow as TRVs close (and the temperature drop reduces) which might be what you want but might not work well when the controller is also reducing the flow temperature. Similarly as the average flow/return temperature decreases and the temperature drop decreases (radiators output less heat) then the output flow temperature will decrease faster than the return temperature.

 

[UpgradeME]

I seem to have now resolved the 'short-cycling' issue I had by changing d.17 to 1

Interesting idea. The effect is of increasing the flow temperature by 10C-20C compared to before. How will this work with your temperature modulating controller? You may be able to get very similar results simply by increasing the flow temperature by 15C on the original setting.

AFAIK, there is no way of increasing the flow temperature as this is controlled dynamically via the VRT392. The VRC430 does have a "minimum flow temperature" setting (which may have resolved the issue) but this isn't available on the VRT392

It will also have the effect of cooling down the overall flow as TRVs close (and the temperature drop reduces) which might be what you want but might not work well when the controller is also reducing the flow temperature.

With d.17 set for return regulation the flow temperature does get hotter as you say, this isn't too bad from a users POV as you can feel the heat from the radiators instead of them being luke warm. The VRT392 appears to compensate for the increase in radiator temperature and so far appears to still maintain the set room temp without overshooting.

Similarly as the average flow/return temperature decreases and the temperature drop decreases (radiators output less heat) then the output flow temperature will decrease faster than the return temperature.

Its hard to tell the full effects with the warmer weather we've had recently (i.e. heating on less) but I've been taking daily Gas/Electric readings, logging max/min outside temperature (from weather.co.uk for my area) and notes of any settings I change so I can see if it decreases/increases overall effeciency ASAP (Although gas hob usage (i.e. cooking) is a variable I've not taken into account as it's difficult to monitor..)

So far I've managed to reduce my Gas usage by around 6% through the new controls and significantly more through optimising the boiler/system (I'm waiting for similar outside temperatures to verify exactly how much, estimated somewhere between 10-15% additional saving).

I've also reduced my Electricty usage by 15% by switching off my Desktop PC (which was on 24/7) and using a Notebook as my 'server' instead (along with some other minor changes such as switching off some electrical devices at night and changing most light bulbs to the fast acting Energy saving type (they are great and were on offer at only 40p each in Asda!!)

Overall well worth the effort!