Heating and Ventilating

Using appropriate controls for heating systems is just common sense and a way to improve the payback on the boiler investment by maximising energy savings. But don’t forget to ensure the occupants of the building want plenty of hot water and comfortable levels of heat, says Bob Walsh, technical director at Hamworthy Heating
CONTROLS technology is changing fast, constantly bringing new benefits to heating systems, and Hamworthy Heating has always advocated that getting the best out of new commercial boilers requires complete integration into the system. There is no point in buying the latest in boiler technology if it isn’t partnered with controls which return optimum performance.

In the past, the controls signalled the boiler to switch on, and once the required temperature was achieved, they signalled it to switch off; it was that simple. Today, controls tell the boiler to modulate once it is nearly up to temperature, by monitoring the flow and return temperatures, to maintain operation and to avoid the repeated on/off scenario. Control packages need to be able to sequence multiple boilers and handle modulation properly, and the algorithms required to do this are considerably complex.

Changes in regulations

In 2005, the Building Regulations Part L brought in the need for domestic boilers to be SEDBUK rated (Seasonal Efficiency for Domestic Boilers UK) and now only those rated A or B, essentially high efficiency condensing boilers, are installed in a house. But domestic requirements are vastly different and far less complicated than commercial applications. In a commercial building, where several boilers are needed to supply the system, replacing one of a bank of old boilers with a new high efficiency boiler is not practical, as it would not be able to perform to its optimum.

In the new Building Regulations 2006 Part L, which came into force in April this year, new Approved Documents (AD), have been introduced. AD L1 is for dwellings (domestic) and AD L2 for buildings other than dwellings.

A change in 2006 is that they are further divided to separate the regulations for new and existing buildings. AD L2A applies to new buildings other than dwellings and AD L2B­ for work in existing buildings that are not dwellings.

A second tier guide has been introduced: The non-domestic heating and cooling compliance guide, which covers the requirements for space heating systems. A significant change in the requirements is that controls are now a mandatory element of changes to heating systems and there are minimum controls requirements specified as part of the overall compliance with the building regulations.

There are different minimum controls requirements applicable to new buildings and to existing buildings, as summarised in the tables on this page.



Controls functionality

In refurbishment of older systems, the biggest improvement in efficiencies will come from system controls. Many of these controls are currently used by the majority of boiler manufacturers in installations, and include direct weather compensation, where an outside sensor sends temperature information to the controls, which then compares the inside and outside temperatures and if necessary re-calculates the flow temperature set point, modulating the burner to meet the new demand.

Timed and zoned control also help to manage the system more efficiently and are predictive tools that know when to turn heat on and off to achieve the desired condition. Timed control acknowledges the occupancy profile of a building with optimised start and stop. Sensors inside and outside decide when the system needs to switch on to achieve the required temperature by the time it is needed. An optimised stop recognises that the building has some inertia, and calculates a switch off time that will maintain temperature during occupancy, for example until 5pm when staff leave an office, but being able to switch off the heating in advance of that without detrimental effect. The system looks at the temperature conditions throughout the day and when the next off period is due, it determines when it needs to switch off.

Zone controls maybe used where different parts of a building have differing uses, and can be driven by time, or temperature. This method of control divides the heating system into several smaller elements known as zones, for example, a school with classrooms, a sports hall, staff rooms, library and domestic hot water requirements.

A sensor in each zone sends information to the controls to ensure each zone is maintained at the correct level. Zoning can also be applied to counter the effect of solar gain, where for example a south facing office has sunshine but the north facing office will be colder.

Each will require differing levels of heat input.



Heating system seasonal efficiency

Hamworthy provides a range of condensing, high efficiency and fully modulating boilers to suit heating loads from 25kW up to 750kW from a single appliance. Its core business is modular boilers and it has always offered controls packages to manage boiler performance, either stand alone or in association with a Building Management System (BMS). The Purewell VariHeat cast iron high efficiency condensing boiler achieves excellent performance levels with seasonal efficiencies of more than 95% gross, which exceeds the minimum Part L requirement of 84% gross. It is suitable for refurbishment or new build projects and comes equipped with a comprehensive range of on-board controls as standard, including cascade sequencing for up to eight boilers, 0-10V input from BMS for remote signaling and temperature compensation to reduce flow temperatures and maximise energy savings. Hamworthy works with its customers to ensure a practical solution, providing the end-user with a fully integrated heating system, with the boiler and controls working intuitively together to maintain the building at constant temperatures, while taking into account the buildings usage, occupancy and outside temperatures.

Good controls in practice

An example of good practice is the Avon building at the University of Warwick. Three Wessex ModuMax 120 series high efficiency boilers, which are fully modulating pre-mix modular gas fired condensing boilers, each module with an output of 120kW, were installed to provide a more efficient system. They were chosen for their high efficiency, energy saving condensing performance and low environmental impact, allowing the university to improve its boiler performance and controls strategy within this building, by incorporating thermostatic radiator valves (TRV) throughout, and fully integrating the Wessex ModuMax boilers within the university building management system. The design achieved a reduction in energy consumption of 39% for the first six months of the heating season 2005/2006, with a subsequent saving of 27 tonnes of CO2 projected for the first year of operation. The boilers not only do the job, they do it properly and as part of a system.

In essence, the new regulations are setting minimum efficiency requirements for boiler systems and introduce the requirement for control strategies. The onus is squarely on the boiler manufacturer to provide a compatible interface between the boilers and BMS, or a comprehensive standalone controls solution. In my mind, this is just common sense, but obviously a prerequisite to this is the need to involve building services controls engineers, to establish a practical controls philosophy, which recognises the functionality of boilers.

Hamworthy commercial boilers and controls T: 0845 450 2865