Taking total control

Published:  11 January, 2011

Lochinvar, boiler, space heating, control
Enabling boilers to deliver their potential — David Pepper.

With the efficiency of boilers approaching its theoretical maximum, heating engineers will have to focus on a full system approach from now on, says David Pepper.

There is a revolution taking place in heating system design. The high efficiencies we will be expected to deliver in coming years cannot be achieved by simply tweaking the performance of individual products. We have to approach this challenge in an holistic way by configuring complete systems to maximise the energy efficiency of each component part.

The Government is considering its response to the consultation on the future of non-domestic buildings, which has the ultimate aim of making all new buildings zero carbon from 2019, with the public sector challenged to achieve this target a year earlier. There is huge pressure, therefore, on specifiers to start driving through low- and zero-carbon solutions now.

The Department for Communities & Local Government (CLG) wants to build the non-domestic legislation on the same principles as those adopted for zero-carbon homes, but adapted to reflect the increased complexity of commercial buildings and their greater intensity of energy use.

 

A number of financial incentives will run alongside the legislation, particularly feed-in tariffs (FiTs) and the renewable-heat incentive (RHI), which was backed by all three major parties during the General Election in 2010. There is also considerable support for the district or ‘community’ approach of linking buildings together to extend the holistic principle to creating heat networks that further reduce overall carbon footprint.

Impressive

 

The recasting of the European Union’s Energy Related Products Directive has also put considerable impetus behind the ‘whole-building’ approach. No longer will it be possible to comply with energy-efficiency legislation simply by making your individual product as impressive as possible; it will be the performance of the whole system that will be judged.

Condensing technology has taken boilers and water heaters onto a new level with gross efficiencies beyond 90%, but these are, largely, based on test-house conditions and may or may not reflect actual project operating efficiency. This is what the UK and European legislation is now setting out to address and, in the process, is creating exciting opportunities for our sector. But with those opportunities come considerable technical challenges.

To meet the new standards, all systems should be properly controlled, with products able to work in close harmony with building-management systems (BMSs). Innovations like cascade-boiler control are also becoming increasingly popular as engineers look to manage heating plant in a way that both responds quickly to changing demand in a building while also minimising energy waste — and also extends the operating life of the equipment.

The on-board controllers we use at Lochinvar, for example, are designed to ensure a fully integrated solution — including automatic modulating combustion that closely matches the operation of the appliance to the prevailing demand conditions. Our EcoKnight boilers can modulate down to just 20% of capacity without losing efficiency when heating demand is low, for example.

Almost every new heating system being installed in a commercial building consists of a number of separate zones, each with individual thermostatic controls. Heating and air-conditioning heat-pump systems must now have the inbuilt flexibility to respond to zonal commands in large buildings to ensure comfort conditions are maintained, but without equipment running unnecessarily. Zoned systems 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.

Lochinvar, boiler, space heating, control
Modern on-board boiler controls such as those installed in Lochinvar’s EcoKnight boilers are designed to ensure a fully integrated solution that matches boiler output and flow temperature to demand.

Weather compensation is also being specified more widely as building-services engineers look to maximise total system efficiencies. 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 plants’.

 

This means a total system approach should be adopted by combining weather optimisation with high levels of insulation and improved building airtightness. All modern condensing 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. A high-efficiency appliance is no guarantee of good overall performance; it is how that appliance operates within the system that counts.

Condensing operation

When the return temperature from the heating system is sufficiently low (about 56°C) moisture in the flue gases can be condensed to recover its latent heat, giving a step change in efficiency. The efficiency increases even more as the return-water temperature falls further below the dewpoint of the flue gases.

Weather compensation takes full advantage of this increase in efficiency 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 gases.

The aim of weather compensation is to minimise flow and return temperatures to maximise efficiency and allow the boiler to operate in non-condensing mode during the coldest days of the year, if at all. This means the end user will get the full benefit of their condensing solution.

A good control strategy should also take the energy used by the circulating pump into account. Variable-speed pumps can be linked directly to the heating controller and so can accurately match their speed to the system demand. Many existing heating systems have a constant flow rate and so use the same amount of power for pumping all year round; this is not efficient. Not only do variable- speed controls reduce energy consumption by varying the flow to meet demand, they also improve comfort conditions by controlling heat distribution more effectively.

Variable-speed drives should also be considered as they help contractors with commissioning and achieve a better balance across the system.

 

However, as solutions become increasingly sophisticated we must take care not to bamboozle the end user. The facility manager will be central to the successful operation of the building, and user behaviour is, ultimately, the most important aspect of a low-carbon building long after the engineers have left the site. The FM must be able to clearly understand and adjust controls where necessary. Too often in the past, over-complex controls have been simply ignored or bypassed, with consequent energy penalties.

David Pepper is managing director of Lochinvar.



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