The Need for Advanced Heating Controls

As the future unfolds, no matter what heating source is used, it is the way in which the energy is controlled that will make the difference; and it will be necessary to adopt improved controls concepts if we are to make the required energy savings.

Around 27 million dwellings plus thousands of small commercial premises (shops, offices, etc.) are equipped with domestic-type heating systems. Many of these are using traditional heating controls that are no longer achieving the energy-efficiency levels needed. More flexible control technologies based on electronics are required to enable, previously neglected areas of energy wastage to be eliminated.

Such advanced technologies, of course, are already being used in larger commercial and industrial complexes where small percentage savings represent substantial cash sums. Now is the time to upgrade the smaller installations.

UK dwellings alone generate over 25% of total national greenhouse gas emissions. Add to this the emissions from small commercial premises and a very worthwhile reduction target emerges. This could create huge opportunities for electrical contractors who choose to refurbish these smaller heating systems across the UK.

Installation of advanced controls seems ideally suited to the skills of electrical contractors and this work certainly does not need to be abdicated to plumber/heating engineers.

Background

Today’s high prices for heating fuels, coupled with the pressures being applied for environmental conservation, have stepped up awareness of the need to consume fuel only when and as necessary.  Past revisions to the Building Regulations Part L (Conservation of Fuel and Power) have imposed improved levels of heating control in new-build properties and in those undergoing major refurbishment. The latest change directs that only high-efficiency condensing boilers may be installed, and this has had far reaching effects.

Whenever one of these more expensive replacement boilers is installed, the heating system’s controls also need to be updated, as appropriate, to latest Building Regulation standards.

However, although many of these existing controls meet the basic letter of the law, in operation, not all of them are able to respond sufficiently quickly to temperature changes to maintain the boilers in their condensing modes. Thus, the high efficiency rating of the new boiler is often not achieved, making it little more energy-efficient than a non-condensing type.

Tests

Condensing boilers can be massively more efficient than conventional types, but only if they are supported by the other heating system components. A year or two after their introduction, there arose a generally held assumption that, by doing nothing more than installing high-efficiency condensing boilers, reductions of 10% - 14% in central heating energy consumption and carbon emissions would be achieved automatically.  

For this to be true, it meant that, when replacing boilers, existing room temperature controls had no influence whatsoever on boiler efficiency.

Controls manufacturers felt that the choice of room temperature controls does have an important bearing on system efficiency. Members of The Association of Control Manufactures (TACMA) decided to carry out investigative tests.

In a purpose-built, environmentally-controlled test house, carefully measured trials were conducted on three types of room thermostats in a gas-fired central heating system using a Class A condensing boiler.

■ A standard mechanical room thermostat

■ An electronic on/off room thermostat incorporating a microprocessor operating a PI control algorithm.

■ A similar electronic thermostat operating in chrono-proportional mode. This method of control divides each hour into sections (usually 3 or 6) and calculates the percentage of these periods for which the boiler should operate to maintain desired comfort.

High-efficiency condensing boilers

To achieve their high efficiencies, condensing boilers need to extract and use heat from the combustion gases that are discharged through their flues. Removing this heat (typically dropping the flue gas temperature from140°C to 50°C) causes moisture to be precipitated in the form of a slightly acidic condensate.

Unless these boilers operate in this condensing mode they will not achieve extra savings or attain optimum efficiency ratings.

Most current published advice on controls merely states that the basic set of controls needed with a condensing boiler comprises an electronic time control allowing independent switching of heating and hot water, a room thermostat, thermostatic radiator valves (TRVs) and separate temperature control of hot water

Some advice also mentions programmable room thermostats, weather compensators, boiler energy managers and zone controls.

Test profile

The in-house tests simulated a ‘Winter Weekend’ profile where the external temperature was maintained at 10°C, the test room was allowed to cool to 15°C before commencing the run and the room temperature control was set at 20°C.  The run was a single 12-hour operation, turning the system on once and controlling at a fixed temperature. The total system load was 13kW at start-up.

This set-up allowed the effect of temperature control alone to be accurately monitored with all other factors remaining constant.

Impact on boiler efficiency

Test results confirmed that the relatively slow temperature-triggered on/off cycling of conventional mechanical room thermostats did little to assist the boiler attain condensing mode.

By measuring the temperature of the water returned to the boiler it was found that, controlled by the mechanical thermostat, the boiler hardly ever operated in full condensing mode during its ‘On’ cycle. This was due to the control’s relatively slow response and indicated that too much heat was lost from the water in the system during the ‘off’ period to maintain the condensing temperature.

Using the on/off electronic room thermostat produced slightly better control and room comfort. Control again relied on a temperature-triggered on/off cycle. Gas consumed was just over 3% lower but there was a small increase in electricity consumption due to the more frequent pump operation and the fact that pumps have peak electrical demand when they are switched on.

When a similar electronic thermostat was used in chrono-proportional mode, results showed reductions of over 10% compared to the mechanical thermostat in both energy consumption and carbon emissions. This can be explained by the faster chrono-proportional control reaction with its time-calculated modulating action that kept the boiler almost permanently in condensing mode

The tests indicated that, if a property has only a simple mechanical thermostat installed, then the energy-saving benefits of a replacement high-efficiency condensing boiler will not be realised as the boiler will rarely be running in condensing mode. Switching to an on/off electronic room thermostat produces reductions of over 2% in both energy cost and carbon emissions.

Use of an electronic thermostat with chrono-proportional capability provides closer temperature control plus possible reductions of 10% in both fuel cost and carbon emissions.

The reductions identified in the tests are tabulated below.

Tests carried out with other manufacturers’ on/off controls produced similar figures.

Test conclusions

Changing just the boiler from a non-condensing to condensing type in a domestic-type central heating system does not necessarily optimise potential energy and carbon emission savings. An electronic room temperature control, preferably with chrono-proportional capability, is often needed to justify the cost of replacing the boiler.

Upgrading not difficult

Chrono-proportional room thermostats are readily available and are just as easy to install as traditional electro-mechanical units. To make the job extra easy and quick, RF (wireless signalling) thermostats overcome any question of having to run fixed wiring and eliminate the need for any making good.

Probably the best upgrade currently would be to replace the existing room thermostat and programmer system with one chrono-proportional programmable room thermostat. This enables a number (say up to six) of room temperature levels to be automatically programmed each day, allowing space heating to be ‘tailored’ to occupants’ needs. In this way, only necessary heating fuel is consumed.

These advances provide just a taste of what will be happening until the government’s low-carbon economy becomes a reality. Who knows what further exciting energy-saving products, fuels and heating technologies will be forthcoming. It is, however, very clear that heating controls are essentials for now and the future and could be an important part of every electrical contractor’s work.

It seems likely that, rather than having stand-alone control systems for all the energy-consuming functions under one roof, a more integrated set-up will become the norm in order to optimise total energy usage.

The arrival of one-way proprietary wireless controls some years ago has thrown up enormous possibilities for the future; not just in saving energy and reducing harmful emissions, but for overall convenience and comfort. Rather than being stand-alone propriety products, heating controls are instead probably going to have to be able to communicate with many other systems controlling other functions such as lighting, security, electrical appliances, home entertainment equipment, access control, garden sprinklers, etc.

Most people currently have only standard heating controls in their home network but, as the wireless home controls market expands, electrical switching solutions, security systems and even utility metering operating are likely to be included. As a consequence, many heating controls manufacturers are beginning to produce two-way wireless controls.

A well known widely used 2-way wireless technology is the Z-wave, already incorporated and available in room thermostats, programmers and cylinder thermostat. Further compatible heating controls are constantly being developed.

Z-Wave is a wireless communication protocol that allows products using it to understand what each is saying, even if they have no actual interaction. Over 125 companies have formed the Z-Wave Alliance, all of these active in developing products like domestic electrical wall sockets, light switches and luminaries, garage door openers, security products and heating controls.

As an open protocol, Z-Wave offers huge benefits for home automation and integration. Z-wave based control systems can be expanded as and when needed without the need for a large up-front investment in a total home control system and without the need to stay with one supplier of various controls. Users can buy Z-Wave security, garage door opening, heating and lighting systems from different suppliers and they will all work happily together. 

Existing one-way proprietary wireless communication technology normally employs 433MHz transmission frequency. These systems are relatively difficult to expand at a later stage and some installation rules have to be strictly followed in order for the system to work satisfactory.

A two-way Z-Wave based communication overcomes many of the installation restrictions experienced with a one-way based communication by enabling signals to pass from one product (regardless of its function in the system) to another in a network automatically creating the optimum route for the wireless signals. This technology offers truly exciting possibilities – improved home comforts, convenience, easy installation and operation plus energy and fuel cost savings – for householders.

Are you prepared?

Changes in the way we all handle our consumption of energy are already happening. The government is committed to a massive 80% reduction in greenhouse gas emissions by the year 2050. There can be little doubt of its determination to achieve this target.

Every possible tax, law, restriction, incentive and measure is likely to be utilised to bring about the required huge change in public attitude to reducing energy consumption and fuel wastage. All relevant new technologies are sure to be incorporated into our changing society.

Advanced heating controls will be required as a part of ensuring that essential energy consumption is properly used. All installers working in this sector will need to become increasingly knowledgeable about controls technology.

Are you prepared? If not, are you prepared to do something about it? If you are, a very remunerative area of work could be open to you simply by supplementing your present skills with improved controls knowledge.

Heating controls information is freely available by visiting the TACMA website www.heatingcontrols,org.uk or by making contact direct with TACMA member companies.