Boiler Modulation and weather compensation

[Disk]

I understand the idea of boilers having their power requirements modulated by sensing either flow water or internal air temperature.

I can also understand the idea that a boiler can modulate dependant upon external weather data ie Weather Compensation.

But I don't understand how, if they do, fit together.

Does WC override the modulation by flow water or internal air temp or do they somehow work together?

I'm only trying to understand how it all fits together as a Consumer so would be grateful if you could please keep any replies in simple laymans terms.

 

[gas4you]

Very simply thw WC will tell the boiler the maximum flow temp to work at according to the outside temp. It will then modulate between the minimum output and this notional maximum.

In the case of the Vaillants I fit, if you fit a WC you are supposed to leave the boiler stat on full so the WC does all the work.

 

[Onetap]

Does WC override the modulation by flow water or internal air temp or do they somehow work together?

I'm only trying to understand how it all fits together as a Consumer so would be grateful if you could please keep any replies in simple laymans terms.

Simple WC would set the flow temperature depending on what the outside air temperature was. A common problem with this was that this was OK for steady-state conditions, when the building was warm, but it was inadequate when you needed a fast heat up from cold.

A more complex control strategy is needed with some sort of over-ride facility. BMS systems (custom programmed) will typically over-ride the WC until the inside temperature approaches the set-point, and only then allow the WC to reduce the boiler flow temperature.

 

[billy bob]

The systems I install use OpenTherm controls, these have an outside temperature sensor and a room sensor, these work together with the boiler control, so the boiler reads the outside temperature, the room temperature, then decides what to do with the boiler flow temperature based on both readings.

 

[Disk]

I think that the problem highlighted by "Onetap" is probably what was nagging me about how the two worked together.

"Gas4you" - do you know how the Vaillant WC deals with the problem of the initial 'fast heat up' phase or does it also require something more sophisticated to override it until the room space temp has reached it normal level?

 

[Disk]

"Billy Bob" is the 'Opentherm' control you mention the make of the controls?

Is it compatible with all boilers?

 

[billy bob]

"Billy Bob" is the 'Opentherm' control you mention the make of the controls?

Is it compatible with all boilers?

OpenTherm is a type of controller, a supplier of these controls is Time Guard, the boiler would also need to be compatible with Opentherm.

 

[D_Hailsham]

"Billy Bob" is the 'Opentherm' control you mention the make of the controls?

Is it compatible with all boilers?

OpenTherm is a type of controller, a supplier of these controls is Time Guard, the boiler would also need to be compatible with Opentherm.

The OpenTherm Association is an organization consisting of boiler manufacturers and control system manufacturers who have got together to create a common protocol for communicating between their products. The members include: Danfoss; Honeywell;Invensys (Drayton); Grasslin; SIT; Siemens; Remeha and Viessman.

The technology is far more sophisticated than the usual on/off thermostats as it allows the sending of realtime data such as temperature between the boiler and the control unit.

It is definitely the way to go but, unfortunately UK boiler makers do not seem to be interested, though I believe Keston boilers are compatible.

 

[gas4you]

I think that the problem highlighted by "Onetap" is probably what was nagging me about how the two worked together.

"Gas4you" - do you know how the Vaillant WC deals with the problem of the initial 'fast heat up' phase or does it also require something more sophisticated to override it until the room space temp has reached it normal level?

Vaillant WC will tell the boiler the outside temp and assess it with the internal temp required. The boiler output will be set to achieve the most efficient warm up time.

Similar to range rating an appliance. If you have 24Kw to heat and don't range rate it then boiler will start off at 24Kw to only heat say 12Kw = inefficient. If you range rate it to 12Kw then boiler will run at 12Kw max = more efficiency.

 

[billy bob]

Viessman and Geminox boilers are OpenTherm, it is the future for heating controls, but as you say the UK as usual are behind the times, that is why I mainly use Geminox boilers.

 

[Doctor Drivel]

"Billy Bob" is the 'Opentherm' control you mention the make of the controls?

Is it compatible with all boilers?

OpenTherm is a type of controller, a supplier of these controls is Time Guard, the boiler would also need to be compatible with Opentherm.

OpenTherm is an open standard, not a controller type. This is a standard that any maker conforming to, can communicate with all other makers equipment. An open system, not a one makers proprietary system. All makers equipment can talk to each other. In short a Honeywell temp controller can be hooked up to an Atmos boiler and it will modulate the burner to what the room temperature dictates.

They exchange data both ways between a room temperature sensor and the boiler. The temp controller may be just a simple room sensor with a knob that looks like a stat - it is not stat. Or it may be full blown on-off timer optimiser.

For e.g., a temperature controller can get the flow temperature from a boiler, a boiler the room temp. A typical application is the temp controller has a time clock and the boiler modulates the burner to maintain the setpoint room temp. Other functions as on-off optimisation with the temperature controller may be added.

The OpenTherm standard does not stretch to Weather Compensation yet. Some makers may use the data from the OpenTherm standard to use as room temperature influence on outside weather compensation. It may raise or lower the flow temp dictated by the outside sensor to maintain the room temperature. Beware an OpenTherm room temp controller not not necessarily integrate the outside weather and room temps so they act together. They be quite independent control loops.

 

[Doctor Drivel]

"Billy Bob" is the 'Opentherm' control you mention the make of the controls?

Is it compatible with all boilers?

OpenTherm is a type of controller, a supplier of these controls is Time Guard, the boiler would also need to be compatible with Opentherm.

The OpenTherm Association is an organization consisting of boiler manufacturers and control system manufacturers who have got together to create a common protocol for communicating between their products. The members include: Danfoss; Honeywell;Invensys (Drayton); Grasslin; SIT; Siemens; Remeha and Viessman.

The technology is far more sophisticated than the usual on/off thermostats as it allows the sending of realtime data such as temperature between the boiler and the control unit.

It is definitely the way to go but, unfortunately UK boiler makers do not seem to be interested, though I believe Keston boilers are compatible.

The OpenTherm standard only take in room temperature sensing at the mo'.

I believe the Mikrofill Ethos is OpenTherm too. But that is designed in the UK and made in Holland.

Many others are OpenTherm but do not advertise the fact.

 

[Doctor Drivel]

I think that the problem highlighted by "Onetap" is probably what was nagging me about how the two worked together.

"Gas4you" - do you know how the Vaillant WC deals with the problem of the initial 'fast heat up' phase or does it also require something more sophisticated to override it until the room space temp has reached it normal level?

Vaillant WC will tell the boiler the outside temp and assess it with the internal temp required. The boiler output will be set to achieve the most efficient warm up time.

Similar to range rating an appliance. If you have 24Kw to heat and don't range rate it then boiler will start off at 24Kw to only heat say 12Kw = inefficient. If you range rate it to 12Kw then boiler will run at 12Kw max = more efficiency.

Weather compensation is unusual as it is feed-forward control, not the usual feedback. It anticipates the coming heat losses or gains of a building. The commercial compensators have outside temp sensors that also sense the temperature of the brickwork of the building as well. This tells it the rate of building heat up and cooling.

 

[wavetrain]

Apologies in advance for the hijack on this thread.

I have a RAMSES 850 OT connected to a Keston C55. The building is only heated once or twice a week and has a slow response. It can take over 6 hours to bring up to temperature so it would be nice to use the Optimum Start feature of the RAMSES 850 OT. Sadly this controller will only start the heating a maximum of 1 hour early (undocumented feature) so it is of no use to us.

I have searched on the net for info Open Therm controller features without much luck.

Does anyone know of an OT controller that is more flexible in its Optimum Start abilities?

The controller also has to have a connection for remote internal sensor fixed away from an internal wall as the internal walls get very cold in the winter.

 

[Agile]

On last posting, I think he means away from an EXTERNAL wall!

Some of the simpler external compensators dont actually measure the internal temperature so they only assume what heat input is required from the fixed setting factor. This will produce an error if the outside is getting hotter or cooler.

On my Agile Compensator I measure both inside and outside temps and feed them to a simple boilers single input.

Tony