Taking the best course of action
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 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 several grants and loans available to businesses looking to upgrade.
Those responsible for company finances have recognised this, and as such 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 and emissions objectives set by the investor or architect and, of course, the available budget.
Increasingly, the specification will involve multiple technologies with renewables supported by condensing boilers to cover peak demand and to provide back-up. Here the challenge of applying the latest technology to maximise the reduction in energy costs and carbon emissions is a great test of a design engineer’s skill.
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. As such almost 75% of the commercial boilers being installed today are condensing types, with the vast majority being wall hung units combined into cascades.
However in the replacement market, one solution definitely does not fit all and the individual requirements of each installation need to be carefully weighed to identify and consider the benefits of each 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.
Make a choice
Let’s have a look at the basic types of higher efficiency boilers available and for which situations they are best suited.
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 the Buderus cast iron boilers can exceed the 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, this is a massive saving of energy and carbon. Cast iron boilers are robust in large water volume systems which operate 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 the system design permits condensing. They may also be worth considering as a future upgrade option with the boilers installed to allow retro fitting of an economiser when planned system upgrades make lower system temperatures possible. They can deliver seasonal efficiency of up to 93% and although not a low cost option they are a superb solution for older, large water volume systems 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 efficiency levels up to 96% are achievable.
Premix condensing boilers such as the Buderus GB162 are among the most popular systems today delivering seasonal efficiency levels up to 96.5%. NOx emissions conform to BREEAM code 5, they have a high modulation range especially when used in cascades, operate with very low noise, are extremely compact and offer flexible fluing 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 they are the right choice it is important to know the design parameters of the system. Premix condensing 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 boilers of this type have extremely high hydraulic resistance which means they require the fitting of large pumps which use considerable amounts of electricity – a factor often overlooked when specifying premix condensing boilers.
When replacing older boilers, it is important to check the domestic hot water system. Stored water means having to reach high temperatures and therefore potentially produces high energy losses. Using a new high efficiency boiler with a correctly sized plate heat exchanger allows hot water to be delivered with the boilers operating under optimum conditions. Ideally, systems should be designed to achieve 70/40 on the primary side and 10/55 on the secondary side, giving hot water on demand and efficiently.
Replacement boilers are often sized like for like to deliver the same output as the existing boiler. However 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.
Perhaps surprisingly, 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 system where the pumps really are massively oversized, giving rise to imbalanced systems, unnecessarily high operating costs and noise. Having a new high efficiency boiler system is the opportunity to make sure that any previous errors in system design are corrected for maximum efficiency and therefore cost savings.
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
control of domestic hot water production. 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.
A major factor in getting the best from the system is for the controls to make sure that the output of the boilers precisely matches the demand from the building which means controlling modulation of the boilers and of the system temperatures.