How to achieve 20 degrees C drop between flow and return?

[croydoncorgi]

If you want to spend money on better control for this boiler (Ecotec Pro28), you'd probably be better off with the VRC 400 controller, which will automatically adjust the boiler Flow temperature according to the external temperature (ie. it's a weather compensator). You won't be able to do much more about the Return temperature except minimise the flows through individual rads by winding down the lockshields, as already suggested. Unfortunately, the Pro28 only has a single-speed pump, so cannot modulate the flow rate itself.

At least with a weather comp,the Flow temp will be adjusted to the minimum required to warm the house, so for 25% of the heating season at least (given warmer winters!), the Flow will be at 65 or less, giving a good chance that the Return will be 55 or lower, so the boiler will condense.

 

[Onetap]

If you want to spend money on better control for this boiler (Ecotec Pro28), you'd probably be better off with the VRC 400 controller, which will automatically adjust the boiler Flow temperature according to the external temperature (ie. it's a weather compensator). .

Yes, but. A simple weather compensation system resets the flow temperature according to the outside air temperature. The reduced flow temperature is suitable for steady-state operation but is too low to quickly heat the building up from cold. Commercial weather compensation systems usually have some boost facility, which refers to the indoor temperature.

I enquired about the VRC 400 once and Vaillant's technical department told me that it had no boost facility, which put me off the idea. It would be OK for 24/7 operation as used in some UFH. I would be wary of using it with rads.

I also asked a Vaillant supplier for a price for one and his comment was "We've never sold one of those before."

Which is sad.

 

[werewolf]

Has your boiler been range rated to the correct value since you only have a tiny flat?
It`s easy to do and will be found in MI page 35 sec.5.11

Paul

 

[croydoncorgi]

If you shoot from the hip, you miss - and then get nailed!

You appear to be referring to very old weather comps GENERALLY and very low function ones in particular.

With the VRC400, there are several different factors affecting room temperature and also the calculated flow temperature that the boiler will produce. In fact, you can even have the actual room temperature factored-in to the current Flow setpoint calculation! There's a night setback IN ADDITION to the compensated temperature (which might have been what confused you. ) There's also a Party Mode setting (VERY Germanic!) which overrides the night setback for when you want to stay up late. And of course the Flow temperature setpoint when the boiler is called for hot water is handled separately.

In other words, you can make the thing play pretty-much whatever tune you want. Trouble is, the majority of installers, maintainers and suppliers don't actually know how it works and so far haven't bothered to find out.

Which is sad.

But even sadder is the extent to which energy efficiency in an 'average' house in an 'average' heating season actually DEPENDS on using a weather compensator (OR on the owner constantly adjusting the boiler and settings). There are already very large numbers of 'high efficiency' boilers installed which hardly ever condense and therefore operate perhaps 7 or 8% less efficiently than they could. PLUS the wasted energy when the building is over-heated during warm weather. Governmment policy which mandated condensing boilers in Building regs without any reference to improved control was (IMHO) a con trick. Whether the manufacturers conned government or they both conned Joe Public, I'm not sure. Either way, a trick was missed!

My principal bitch about the 'Vaillant approach' to controls is the use of a 'private' communications bus on the boiler, so you have to buy an expensive Vaillant controller instead of a 'commodity' product. But then again, there are very few commodity products that come close to what the VRC400 does.

'Yeah,well. It's cos there's no demand, Guv!'

'nuff said!

PS VRC400 costs £90 - 100 + VAT

 

[Agile]

The problem with a proportional controller in this situation i.e. one that varies the boiler output temperature, is that in a very small property the boiler's minimum output power will still be way too high for the heat loss from the rads.

It will therefore just be operating as an on/off control and its main advantage will not be realised.

The boiler must be range rated to its minimum output and will then be operating in an on/off mode which will be less efficient but I cannot see any way to significantly improve the situation with that arrangement.

Tony

 

[croydoncorgi]

(Yawn)....
The Ecotec Pro28 AUTOMATICALLY modulates down to 7Kw CH output and can be range-rated down to that if necessary.

Anyway, I can't imagine why you'd expect a weather-comp to operate as an on-off control in this situation (even without stopping-down the CH rating), Tony.

 

[ChrisR]

I can, in that it can't modulate below 7kW, so all it can do is switch on-off.

 

[croydoncorgi]

Yes - but (once flat is warmed up) it will be switching on and off with a WEATHER- COMPENSATED Flow temperature!!
I can't see why either Chris or Tony think that weather-comp-modulated flow temperature and on/off of the system according to actual room temperature are related to each other! They operate independently.

 

[giblets]

Ahh, bring back the old AQ6000.

 

[gas4you]

As you would all expect I fit the VRC 400 on all my ecotec Pluses as long as there is a convenient north wall.

I don't know where you are buying them from at that extortionate price croydoncorgi

They do as you say control everything very well and compare outside temp to requested indoor temp. You can also set the heating curve depending on what part of the UK you are in.

If you fit with a Unistor they will control the hot water temp as well. They also have an anti -legionnaire program built in for every wednesday if you want it, very handy if you are installing in an old peoples home etc. When used for the unistor they will boodst the flow temp to around 70C to let the water heat correctly.

They really are the state of the art in controls at present.

 

[croydoncorgi]

Well at least it's not just me who knows how to spell 'VRC400'!!!
The price I quoted was 'Plumbase standard'. How much do you pay?

They really are the state of the art in controls at present.

Ok - for Vaillant only.
Atag, Keston (even!), Atmos, ACV, and other GOOD boiler manufacturers also offer similar controls. Atag and Keston build them into the boiler as standard!
It's only the Neanderthals at Baxi and other UK makers who think that UK installers are too thick to cope with a bit of quality!

 

[gas4you]

Well at least it's not just me who knows how to spell 'VRC400'!!!
The price I quoted was 'Plumbase standard'. How much do you pay?

Just under £70 + VAT

 

[nickso]

......Keston.........GOOD boiler manufacturers

 

[croydoncorgi]

I did say 'even'!!
And when did you last hear (for example) of an electronics problem on a current Keston model?
Some design aspects are a bit 'unusual' but they usually stay in one piece for longer than many other makes.

 

[nickso]

I did say 'even'!!
And when did you last hear (for example) of an electronics problem on a current Keston model?
Some design aspects are a bit 'unusual' but they usually stay in one piece for longer than many other makes.

sorry i disagree ...but ive only worked on the celsia

the electrics arent too bad i suppose, i have had hassle with the pcbs though. the wiring isnt very heat resistant in places. the choccy block at the bottom is always damaged by the case. thats the old ones i guess.....not seen any newish models thank god.

the celsia case and flue arrangements are simply a joke.