Weather Compensation

[John D v2.0]

Now I was under the impression that most kick space heaters would stop blowing when the temperature flow drops below a certain point, but I could be wrong of course.

True I nearly wrote that but it's pretty low and unlikely to be an issue, mine - Smith's ss5 model is about 38c. Basically so it won't come on randomly in summer.

 

[Dan Robinson]

It varies. We did a system that had such low design temps that we got the manufacturer to send us different thermostats to put on the heaters to get the fans on. Was a few years ago now; it might have been Smiths.

 

[mrshr]

Yep you’ll also need the vr66(I think it’s called) wiring centre.

me too although I’m not a Vaillant man.
@sweet may be able to help you
Alternatively contact Vaillant with your details and ask for details of installers in your area. Not sure if they specify controls specialists.

So I'm thinking of going down the vsmart route.
Do I need the VR66 module too? I have a system boiler with a single heating zone and a single HW zone, currently controlled via a honeywell digital clock.

 

[hard-work]

On low temperatures Kickspaces do not perform well blowing coolish air which can be uncomfortable defeating the object of having one. Rads being just warm is fine and are ideally suited for WC. To get a Kickspace to work effectively with WC the set slope has to be so shallow it is not worth having it. Even if you limited the lowest flow temperature to a Kickspace heater it will not give out the kW so will be ineffective. They are not big output heaters. The Myson wall mounted fan heaters can be a lot larger but not the Kickspace or the Smiths.

Beware! Do not assume a Kickspace can work effectively with WC.

 

[hard-work]

Now I was under the impression that most kick space heaters would stop blowing when the temperature flow drops below a certain point, but I could be wrong of course.

You are right. But at the lowest temperature just before the stat cuts out the fan the air flow can be very cool making it a more uncomfortable draft than heating. These heaters need a hot flow and decent volume of water to them. High temperature heat emitters (kickspace) and variable temperature emitters (rads) do not mix well on the same circuit.

 

[John D v2.0]

Even if you limited the lowest flow temperature to a Kickspace heater it will not give out the kW so will be ineffective

That's the whole point of weather compensation, to make the heater less "effective" when the heat loss is lower.

blowing coolish air which can be uncomfortable

Fair point, although personally I wouldn't recommend installing a plinth heater in any location where the draughts would be uncomfortable, regardless of the temperature of the draught.
Same applies to somewhere noise sensitive such as a bedroom.

 

[hard-work]

That's the whole point of weather compensation, to make the heater less "effective" when the heat loss is lower.

Depends. If the kickspace is on the north cooler side of a building it will need more heat to it than the southerly facing rooms.

Fair point, although personally I wouldn't recommend installing a plinth heater in any location where the draughts would be uncomfortable, regardless of the temperature of the draught.
Same applies to somewhere noise sensitive such as a bedroom.

Kickspaces having a flow temp of 40C to them can be quite `drafty` indeed, although they will be raising the temperature of the room. As I emphasised they need high flow temps to them to avoid drafts and give the output. My point is, beware when mixing high temp emitters with variable (low) temp emitters. You have know what you are doing to get them to coexist properly and that particularly includes WC.

To get a kickspace and full WC control of rads you need a zone for each. To get efficiency it is best yo have a boiler giving a constant 60C which the Kickpsace will be happy with most of the time. But oversize the rads to ensure a low return temperature to promote condensing efficiency having rad valves on them.

 

[John D v2.0]

If the kickspace is on the north cooler side of a building it will need more heat to it than the southerly facing rooms.

I don't see how that's any different from normal radiators. Just size them correctly.

they need high flow temps to them to avoid drafts

The draught I'd object to too, but it is the same regardless of the flow temperature. But i agreed above that some may object more to cooler draughts than to warmer ones.

To get a kickspace and full WC control of rads you need a zone for each. To get efficiency it is best yo have a boiler giving a constant 60C which the Kickpsace will be happy with most of the time. But oversize the rads to ensure a low return temperature to promote condensing efficiency having rad valves on them.

So basically to get WC you need to not have WC? You just contradicted yourself!

 

[hard-work]

I never contradicted myself, I mentioned two zones. Low flow temps give e cool air flow from a kickspace which is generally regarded as a draft, defeating one of the objects of having a Kickspace `heater`. Once again, if you have a Kickspace and rads on the same circuit controlled by a WC you had better know what you are doing. A general rule I would say avoid. `To get efficiency it is best to have a boiler giving a constant 60C which the Kickspace will be happy with most of the time. You will not get maximum output unless to has a 80C flow temp into it. But oversize the rads to ensure a low return temperature to promote condensing efficiency having rad valves on them.

 

[John D v2.0]

I never contradicted myself

Well that's kind of true due to the fact that it's hard to gather any concrete assertions from your postings, but you did suggest that for full WC you need a constant flow temperature:

To get ... full WC control ... is best yo have a boiler giving a constant 60C

You will not get maximum output unless to has a 80C flow temp

The whole point of WC is to not give maximum output, so that's not a useful comment.

I feel like we're going round in circles here, so either make your point clearly (ignoring anything We're already agreed on) or I'll leave you to it!

 

[hard-work]

My point is using a kickspace on the same circuit as rads using WC. It is not an ideal setup at all. Best forget WC, have a constant 60C output boiler and oversized rads using rad valves to improve condensing efficiency.

 

[John D v2.0]

My point is using a kickspace on the same circuit as rads using WC. It is not an ideal setup at all. Best forget WC, have a constant 60C output boiler and oversized rads using rad valves to reduce condensing efficiency.

Fixed that for you, agreed with everything else!

 

[hard-work]

The whole point of WC is to not give maximum output,

The point of WC is to inject the the ideal level of heat (view as temperature) relating to the outside temperature compensating for the heat loss/heat gain of the building. WC is a `feed forward` controller, unlike a thermostat which is a `feedback` device. It anticipates the coming heat loss or heat gain of the building fabric, having the heating system to input heat before the heat gain or loss takes effect. This maintains comfort conditions. The ideal temperature of the injected heat may be 80C for days on end. If the ideal input temperature is say 40C, it may be too low for proper operation of a kickspace, which may be blowing coolish air.

 

[hard-work]

Fixed that for you, agreed with everything else!

I wrote:
"My point is using a kickspace on the same circuit as rads using WC. It is not an ideal setup at all. Best forget WC, have a constant 60C output boiler and oversized rads using rad valves to improve condensing efficiency." Which is correct! The oversized rads and 60C boiler temp ensure excellent condensing efficiency - and decent operation of a kickspace. That is easy to understand.