Adopting the total control approach
Heating system design has undergone major change in recent years with achieving the highest efficiencies possible being the order of the day. It isn’t going to be possible to achieve these efficiencies by simply tweaking the performance of individual products, so a more holistic approach, including the configuration of the complete system, will in turn maximise the efficiency of each component part.
With the government’s ultimate aim of making all new buildings zero carbon from 2019 and with a cash-strapped public sector challenged to reach this target a year earlier, there is pressure on specifiers to start driving through low and zero carbon solutions now. Now is the time for heating engineers to start focusing on a full system approach.
In recent years we’ve seen something of a revolution taking place in heating system design. It won’t be possible to realise the high efficiencies we need by simply fine tuning the performance of individual products and the approach to this challenge needs to be in a much more holistic way, configuring complete systems to maximise performance of each component.
If we are to meet our ultimate aim of making all new builds zero carbon from 2019, undoubtedly specifiers will need to select and deliver low and zero carbon solutions straight away.
The department for Communities & Local Government (CLG) is looking to create non-domestic legislation on the same principles as those being used to deliver zero carbon homes, but adapted to reflect the increased complexity of a commercial building and their greater intensity of energy use.
A series of financial incentives have been initiated to work in conjunction with legislation, particularly feed-in tariffs (FiTs) and the renewable heat incentive (RHI). In addition to this, there is also considerable support for the district or community approach of linking buildings together to extend the holistic principle of creating heat networks that will keep the overall carbon footprint to a minimum.
Since the changes to the European Union’s Energy Related Products directive, there is much more impetus behind the whole building approach. To this end, making an individual product as impressive as possible to meet energy efficiency legislation will no longer be possible, instead it will be measured on the performance of the whole system and this will be the determining factor.
Undoubtedly since the arrival of condensing technology, boilers and water heaters have moved onto a new level with gross efficiencies beyond 90% possible. However, these are generally based on test house conditions and probably won’t reflect the actual operating efficiency of an overall project. It is this that the UK and European legislation has been designed to address and as a result, is creating exciting opportunities for our sector to explore. Inevitably though, such opportunities bring increased technical challenges.
So that systems will meet the new standards, they need to be properly controlled with products that will enable them to work in close harmony with building management systems (BMS). Facilities such as cascade boiler control are also becoming increasingly popular with engineers as they seek to manage heating in a way that not only responds quickly to changing demand in a building, but also minimises energy waste – while at the same time extending the operating life of the equipment.
For example, Lochinvar’s on board controllers have been designed to ensure a fully integrated solution which includes automatic modulating combustion that closely matches the operation of the boiler to the prevailing demand conditions. In addition, the company’s EcoKnight boiler range has the ability to modulate down to just 20% of capacity when heating demand is low.
Virtually every new heating system being installed in a commercial application is comprised of a number of separate zones, each with individual thermostatic controls. Heating and air conditioning heat pump systems are now required to have the inbuilt flexibility to respond to zonal commands in large buildings to ensure comfort conditions are maintained, but equipment is not running unnecessarily. Zoned systems very often provide a lower cost alternative to a full BMS as they are designed to manage just one key aspect of the building services and may be perfectly adequate for the needs of the building in question.
Another innovation that is being widely used by building services engineers to maximise total system efficiencies is weather compensation. According to the relevant British Standard (BS/EN 12098-1 Controls for Heating Systems), outside temperature compensated control equipment for hot water heating “is necessary to reduce the energy consumption of heating.”
This means a total system approach should be adopted by combining weather optimisation with high levels of insulation and improved building airtightness. All of the latest high efficiency boilers have a seasonal efficiency rating based on full and part load. This calculation is designed to average out the official test efficiencies of a boiler in line with a more realistic average at different demand levels experienced over the seasons. Simply selecting a high efficiency appliance will not guarantee good overall performance; it is how it actually operates within the system that counts.
Flue gas temperature is reduced by efficient heat exchanger design in high efficiency condensing boilers, which means the system can also operate satisfactorily at lower operating temperatures. The laws of physics determine that the closer the temperature of the flue gasses is to the dew point of 57°C, the more efficient the boiler will be. Weather compensation takes full advantage of this theory by adjusting the temperature of the flow to the radiators depending on the outside temperature and taking full advantage of the latent heat in the flue gasses.
The purpose of weather compensation is to operate the boiler closer to dew point temperature during the average temperature days and only work the boiler at higher temperatures during the coldest days of the year. This way the end user will receive the full benefit of their high efficiency condensing solution.
Taking the energy used by the circulating pump into account is also a good control strategy. To this end, variable speed pumps can be linked directly to the heating controller and so can accurately match their speed to the requirements of the system. Many existing heating systems will have a constant flow rate and so use the same amount of energy for pumping all year round and this is not the most efficient way to operate. Variable speed controls will not only reduce energy consumption by changing the flow to meet demand conditions, they also improve environmental comfort by controlling heat distribution more effectively.
Contractors can also use variable speed drives during commissioning to achieve an overall better balance across the system.
However, as solu
tions become increasingly sophisticated it is important to ensure we don’t confuse the end user. The facility or energy manager will be pivotal to the successful running of the building and equipment operation and ultimately, user behaviour is the most important factor in a low carbon building long after the engineers have left the site.
Managers need to clearly understand and make necessary adjustments to controls. In the past, over-complex controls have been ignored or bypassed too often and as a consequence, had a detrimental effect on energy performance.
With so much emphasis on energy saving and efficiency, working with equipment manufacturers at the outset to ensure the best possible solution will deliver dividends for those responsible for specification and selection and ultimately, the end user.