Aging boilers may need a makeover

boiler, Buderus, refurbishment
The economic and energy case for replacing boilers — Richard Evans.

Richard Evans explains why waiting for your old boiler system to reach the end of its natural life, is not necessarily the best course of action as it continues to waste energy and money.

In the current economic climate, companies are looking even more closely than usual at all areas of expenditure. Building services are coming under increasing scrutiny, and the provision of heating and hot water provision is no exception.

Significant savings can be achieved by replacing even 10-year old boilers with new high specification condensing or high-efficiency systems, and there are tax benefits in the form of the Enhanced Capital Allowances (ECAs) available to businesses looking to upgrade.

Businesses effected by the CRC Energy Efficiency Scheme must further factor in the substantial cost of not achieving carbon reduction into their calculations. Those responsible for company finances have recognised this, and investment in modern heating systems is now seen as a growing priority for many businesses and institutions. However, making the right choice can be a complex decision — with many issues to consider.

In new buildings, high levels of insulation allow for low-temperature solutions such as condensing boilers or even heat pumps to be used effectively. At the design stage storage can be planned for biomass, and roof space can be optimised for solar thermal in buildings where hot-water usage will be high.

The final heating-system specification will take into account numerous factors — including the requirements of the local building regulations, the carbon emissions objectives set by the investor or architect and, of course, the available budget.

We have seen fundamental and radical changes in the commercial heating market in the last five years. Sales of atmospheric boilers have collapsed because of the requirement to meet the 84% seasonal efficiency target set out in part L2B of the Building Regulations. At the same time, investors suffering from rising energy costs, have demanded even higher efficiency from their boilers. The outcome is that 75% of the commercial boilers installed today are condensing types — the vast majority being wall-hung units combined into cascades.

However, in the replacement market, one solution definitely does not fit all, and the requirements of each installation need to be carefully weighed to identify and consider the benefits of the available solutions. Detailed analysis of the options, together with full explanations of the expected returns, will allow investors to make the right decisions and reward them with the energy savings they expect.

Whilst it may seem strange still to be talking about ‘old’ technology, forced-draught high-efficiency cast-iron and steel boilers have benefited from improvements in design which have meant that Buderus cast-iron boilers, for example, can exceed Building Regulation requirements by up to 2%. They give a seasonal efficiency rating of up to 86% and, considering that a 20 year old atmospheric boiler will be operating at around 65% efficiency, achieve a massive saving of energy and carbon. Cast-iron boilers are robust in systems with large water volumes operating at permanently high temperatures. They are also ideal for plant rooms where access is difficult as they can be built on site and are still the best option where oil is being used either as the sole fuel or as a secondary fuel to gas.

Forced-draught, cast-iron and steel boilers with an added condensing economiser are especially suited for situations where access is restricted but where system design permits condensing. They may also be worth considering as a future upgrade option with the boilers installed to allow retrofitting of an economiser when planned system upgrades make lower system temperatures possible. They can deliver seasonal efficiencies of up to 93% and, although not a low-cost option, they are a superb solution for older systems with large water volumes where access is poor and condensing is specified or is likely to be possible in the future.

Forced-draught condensing boilers have a high water capacity, which makes them perfect for large systems with high flow rates. They have no minimum-flow-rate requirement, so primary pumps are not required, providing additional electricity savings. Seasonal efficiencies of up to 96% are achievable.

Premix condensing boilers, such as the Buderus GB162, are among the most popular systems today — delivering seasonal efficiencies of up to 96.5%. NOx emissions conform to BREEAM code 5, they have a high modulation range, especially when used in cascades, and operate with very low noise. They are extremely compact and offer flexible flueing solutions. They mostly operate with low water content and higher flow resistance and should therefore be installed with a hydraulic separator and primary pumps, together with a low loss header or, in an old, open system, with a plate heat exchanger.

To check that premix condensing boilers are the right choice, it is important to know the design parameters of the system. Such boilers are excellent for systems operating at low temperatures or on systems with fully weather-compensated controls, where higher temperatures are only required on a few extremely cold days. One caveat: some makes of boilers of this type have extremely high hydraulic resistance, so they need large pumps which use considerable amounts of electricity — a factor often overlooked when specifying premix condensing boilers.

boiler, Buderus, refurbishment
Such has been the improvement in the performance of cast-iron boilers, such as the Buderus GE615 range, that they can exceed the requirements of Building Regulations. Such boilers are well suited to systems with large water volumes.

When replacing older boilers, it is important to check the existing domestic hot water system. Stored water means having to reach high temperatures, with potentially high energy losses. A new high-efficiency boiler with a correctly sized DHW plate heat exchanger allows hot water to be delivered with the boilers operating under optimum conditions. Ideally, systems should be designed to allow the boilers to operate at their most efficient with, for example, 70/40˚C on the primary side and minimum 10/55˚C on the secondary side, giving hot water on demand and maximum energy efficiency.

Replacement boilers are often sized like-for-like to deliver the same output as the existing boiler, but this is not good practice and can eliminate the potential savings for the investor. It is important to check the actual demand as building usage and design practice may well have changed. Insulation may well have been improved. Often new extensions have been added meaning the boiler plant is undersized. Some areas may now be heated independently. Whatever the building, its usage, both present and future, should be assessed with heat-loss calculations.

Surprisingly, perhaps, one of the biggest benefits for an investor comes from making simple changes to the hydraulic layout and ensuring that pumps are correctly sized. We often encounter situations when we are called in to advise on replacement heating systems where the pumps really are massively oversized, giving rise to imbalanced systems, unnecessarily high operating costs and noise.

Another key area is the controls specification. Simply fitting a new boiler to old controls, whilst offering good savings, will not maximise the efficiency of the whole system. A check on the controls should consider if they are capable of weather compensation and whether they can facilitate timed and optimised control of individual heating zones.

Equally important is the efficient production of domestic hot water. If renewables are to become a part of the heating upgrade, then the controls must be able to efficiently manage the integration of the different technologies.

Whilst arriving at the most effective solution to each and every commercial heating system requires a great deal of knowledge and investigation, the time and effort spent will be richly rewarded in terms of fuel savings, reduced carbon footprint and greater flexibility.

 

A combination of new boilers and well specified controls will make enormous energy cost and carbon savings over the next decade, and these savings should guide the decision to invest in upgrading old equipment sooner rather than later.

Richard Evans is commercial director with Buderus.

 

Related links:
Related articles:



modbs tv logo

New Sustainability Director for Wates Group

Wates Group, a family-owned development, building and property maintenance company, has appointed Cressida Curtis as its new Group Sustainability Director.

Domus Ventilation appoints new contractor sales managers

Ventilation systems manufacturer Domus Ventilation has announced the arrival of three new Contractor Sales Managers.