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Controls fall into two categories, proprietary and Opentherm, the former only work with boilers of the same brand, such as the Viessmann Vitotronic 200 with Viessmann Vitodens 200, 333, and 343 boilers. Vaillant controls work on all Vaillant boilers, and atag controllers work only with Atag boilers
Opnetherm controls work on all boilers so the celsia 20 controler will work with all opentherm compatible boilers such as Broag, Atmos, and the Viessmann vitodens 100 boilers.
OpenTherm – the new kid on the block
The spotlight is on boiler controls to deliver energy savings and the industry is being asked to consider the best approach to optimising the performance of condensing boilers. Timeguard’s Steve Payne argues that the answer is already on the table and that there is no credible alternative to the OpenTherm standard
Once the Building Regulations for England & Wales had been amended to require all new and replacement boilers to be condensing, except in defined special circumstances, the focus shifted to the controls of heating systems. A key player in maintaining this focus is the Market Transformation Programme (MTP), which provides support for the product policy aspects of the UK Government Framework for Sustainable Consumption and Production and receives its core funding from DEFRA (the Department for Environment, Food and Rural Affairs). The government means business and the industry will have to find the right answers. MTP is currently engaged in an evaluation of heating controls with an overall aim of encouraging the development and adoption of more advanced controls.
The principal points agreed at a stakeholder consultation meeting in December 2005 were:
• The present generation of control systems fails to exploit fully the energy saving potential of boilers with modulating burners.
• Integrated control gives rise to a requirement for a standard means of communication between the components of the heating system, for example, between a boiler and remote temperature sensors will help the boiler and controls industries to continue to make products that interact reliably with those of other manufacturers, at lowest cost.
MTP recognises that such a standard means of communication has already been established: OpenTherm. The boiler and controls industries were invited to consider whether OpenTherm meets their needs, or an alternative method should be adopted. In my view OpenTherm is a proven clear leader.
The OpenTherm bus protocol is, as its name suggests, an open standard. It allows more information to be passed a simple on-off signal, and that gives the potential for more intelligent system control arising from better knowledge of current conditions and the difference between them and desired conditions. This overall approach to system control can adjust boiler and pump operation for greater efficiency whenever conditions allow, especially if informed by previous knowledge of response characteristics.
The OpenTherm protocol
The OpenTherm protocol is for communication and control between compatible boilers and programmable room thermostats. It is a standard that is increasingly being adopted by boiler and control manufacturers across Europe, including the UK, who established The Open Therm Association (www.opentherm.co.uk); The Association for example administers and licenses equipment to use the OpenTherm name and logo. The OpenTherm standard enables a constant two way data stream between boiler and controller. Yes, it is digital bus technology, but in practice it calls only for basic two-wire low voltage link between the programmable thermostat and the boiler. A key advantage in the field is that a boiler installer can install the low voltage wire, without the need for a qualified electrician, part P does not apply!
An Open Therm controller will improve the efficiency of a compatible Condensating boiler. Tests have show that savings of more than 15% can be made vs. traditional controls. No additional investment is required from the boiler manufacturer to make equipment OpenTherm compatible, other than to ensure that the right control circuit is installed on the boiler control board – and these have already designed into many boilers.
OpenTherm –viable and proven but still improving
The OpenTherm Association has been around for a decade – the products are tried, tested and installed with many major controls and boiler manufacturers in Europe including the UK. The system is well proven and, in my view, undoubtedly the de facto standard.
The OpenTherm Association is an independent group of manufacturers of products using the OpenTherm protocol. Its 27 members include controls manufacturers such as Honeywell and Danfoss as well as Timeguard’s parent company, Theben. Many boiler manufacturers including as Broag-Remeha, Keston, Johnson and Starley and Mikrofill have Open Therm compatible boilers in their range. I am sure others will be added to this list in the next few months.
The mission of the OpenTherm Association is to manage and promote the introduction and the adoption of the manufacturer-independent OpenTherm protocol and interface specification as the technical standard for point-to-point communication in HVAC control systems.
The Association is continuously improving the OpenTherm standard by adding new functionalities. At a recent Association meeting, the first to be held in the UK, the members discussed the development of an OpenTherm standard for wireless applications. Other developments include integration with telecommunications so that, yes, you can phone home and switch on the heating, and diagnostic facilities so that boiler fault information can be relayed to engineers.
So what does a modulating controller do?
The controller will measure room temperature, or outside temperature in the case of Weather Compensation, and calculate the desired flow temperature depending on the current and desired temperature and time settings. The boiler flame can be modulated accordingly, keeping the living space always at its optimum temperature. At the boiler an intelligent interface will sense and control, among other things, the burner, heating circulation pump, domestic hot water pump and valve and the mixing valve. Optimum Start is also available if required
With the growing pressure to improve energy efficiency customers will expect to be offered the most effective solutions, that give them long term savings It is inexcusable to sell a customer a modern energy-efficient boiler and then deny them the full benefits of a modulating controller, especially when OpenTherm boilers and controls are now readily available in this country.