Will replacing a boiler save a household money on their fuel bills?

Published:  22 May, 2014

Anthony Brunton asks whether a straight boiler replacement will really give households the boiler savings they want.

Since society has become obsessed with energy and how to conserve it, all manner of solutions to people’s energy problems have appeared. Unfortunately, when the solution involves replacing the existing appliance very little proof is offered that the replacement will in fact save money, or what the extent of those savings may be.

A recent article containing information on the Energy Related Products Directive (ErP) has been issued by the European Union. Due to come into force in 2015, this directive sets out the minimum efficiency requirements for individual energy-using appliances and would appear, in setting these minimum standards, to require all non-condensing appliances be replaced with condensing appliances.

The article goes on to explain that manufacturers have developed products which not only exceed the required efficiency standards set out in the ErP, they also offer a smaller footprint, higher outputs, quick and easy maintenance, module sequencing to increase longevity and far more advanced control systems. On top of all these advantages, the appliances also offer reduced fuel bills and other financial advantages such as access to the Capital Allowance scheme.

The big difference between this information and the previously mentioned solutions is that this article also set out the possible drawbacks, including the unsuitability of condensing boilers for some systems. It did, however, say that even if the boiler was not in full condensing mode, it will still be more efficient than a standard efficiency model. Probably the most important statement was that ‘the first vital step when designing a replacement system (not appliance) is to conduct an in-depth survey of the building because, depending on its age, a number of modifications are likely to have been made'.

So, replacing an appliance has now escalated to possibly replacing a system, including the controls, in addition to which any part of the original system that is to be retained would need to be chemically cleansed before it could be incorporated into the new system. It is therefore highly likely that the predicted savings would not take into account the capital cost of the appliance, or the eventual overall cost of whatever peripherals are required to produce the 'new' system.

There have been several instances where condensing boilers have replaced standard efficiency boilers and, when the end user complained of no saving in fuel usage to the manufacturer, they were told after the installation had been inspected that operation in the more economical condensing mode was not possible because of the methods of connection and control. It has also been found that where primary fluid temperature of 80 degrees C is required to satisfy the requirements of a particular aspect of the system, the 70 degrees C maximum capability of the condensing appliance has proved to be inadequate.

Based on much of the available evidence on condensing boiler installation, while the running costs may be reduced by 15% if the appliance is installed correctly, the costs can escalate significantly, reducing savings to an estimated 5% or less, if the appliance operates but is not able to take advantage of the heat reclaimed through condensation. This 5% may be further reduced if the condensing appliance is required to run longer than necessary to satisfy a particular system requirement. What is even more disappointing is that increases in the cost of fuel, which appear to be inevitable, may well cause the running costs to increase to a point where they are higher than they were before the replacement took place.

So in summary, when this exercise is carried out properly by replacing the appliance, carrying out the detailed survey, replacing the control system if required and cleansing those parts of the existing system to be incorporated into the new system, the return on investment, particularly if the 15% savings were reduced to 5% or less, could prove unacceptable with any escalation in fuel costs only serving to exacerbate the situation further.

So the question becomes: 'is there a solution to the problem of reducing fuel usage which does not require the same significant expenditure or massive upheaval that replacing an appliance can apparently create, and what form would such a solution take?”

In consideration of this matter a detailed inspection of the existing system is essential to establish the potential for fuel savings. Where single appliances are in use, close control of the appliance is required and how that is done will be discussed later in the paper, but this control in itself is not enough.

Energy losses must be reduced to a minimum through adequate insulation. It is not unusual to find installations where the insulation is far from satisfactory, particularly around those elements of the installation, such as valves, which needed the insulation removed for servicing work to be carried out and where the insulation was seen to be missing altogether. Modern high tech wraps which close using Velcro or some other reusable proprietary closing mechanism are an easy and often economical remedy in terms of expenditure per energy savings.

Where modular systems have been installed, significant energy loss occurs where no control has been installed to prevent the primary fluid circulating through those appliances which are not in use. The inner shell of the combustion chamber acts as a radiator and the heat accumulated in the combustion chamber is allowed to escape up the flue. It has been estimated that the loss per appliance during the period the system is in operation is in the order of 3.62kw/hr so it is something to be avoided if possible.

The solution is to fit an electronically operated valve into the return line of each appliance, which is activated just before the appliance is activated to ensure that the heat generated by the burner is dissipated safely.

Finally, we come to the question of how to control the appliance in such a way that fuel usage is reduced to the minimum while maintaining the required comfort conditions and supply of services. The design process guidance requires the appliance to be able to cope with an outside temperature of -1 or -4 degrees C, dependent on the exposure level of the building being served, resulting in an appliance being theoretically oversized for approximately 90% of the year. 

To take advantage of this - and of the variations in the load requirements of the building due to changes in the level of occupation and energy input from the appliances used in the building - various techniques are used.

Some end users favour a Building Management System while others prefer to install modulating appliances but Building Management Systems rely on space temperatures to switch the appliances on and off and appliance modulation is often limited. One other method of control is load optimisation, where the appliance firing cycle is controlled by an external device which, in its simplest form, merely delays the firing of the appliance. In its most complex form, it uses the flow and return temperatures to compute the load demand and then controls the firing cycle to limit the energy injected into the primary fluid to match the computed load.

In its infancy, this technology gained something of a bad reputation because of poor design or improper use, but there have been significant improvements in the design of this technology and the new generation of units have proved to be very reliable and returned, in some cases, significant savings.

In addition to this, it is also possible to build into the control the ability to record discrete activities such as flow and return temperatures, when the boiler control thermostat calls for heat, when the control allows the appliance to fire, and when the firing cycle ends. This data is then stored for recovery on a cyclic basis. Initially this data would be available as binary data but it can, when recovered, be processed for display in either tabular or graphical form with the tabular form used to describe the system operation and reduction of fuel usage. The graphical display can be used by experienced heating engineers to identify system mal-operation, manual interference by a third party, failure of system maintenance provider to carry out servicing procedures at the correct intervals and proof of compliance with requirements concerning carbon footprint issues and maintenance or operational parameters.

One aspect of ensuring maximum efficiency that is very rarely considered, even though it can involve significant costs, is the maintenance of the installation. All appliance manufacturers are required to provide a comprehensive servicing schedule with each appliance they supply and it has been shown that neglecting this aspect can result in significant costs. Another costly requirement these days is the employment of manpower so if functions can be monitored without the need for additional staff this automatically reduces operational costs. Having the ability to monitor the system operation also enables the end user to identify that maintenance is being carried out at the intervals required by the manufacturer.

While reduction in fuel usage will, in many cases, be the prime motivation for the installation of this type of control, once the additional benefits of having the operational information have been demonstrated, many end users will appreciate the value of being able to see how certain peripheral activities are being carried out and the effect this has on the cost of the provision of space heating and hot water.

By matching the energy provision with the load requirement, fuel usage is reduced to a minimum. By recording operational data the end user has the benefit of being able to monitor the operation of the system constantly, without the use of additional manpower. The maximum cost of this type of control is usually less than the cost of the new appliance alone and has been shown to produce very credible results.

It is not the intention of this paper to endorse any particular product, but to give the reader an insight into the many and varied requirements that go to making energy savings. Very few companies can afford to adopt the tear everything out and start again strategy, which is in effect what detailed surveys of buildings will no doubt conclude is required. Adopting the approach set out above will allow building owners to carry out those measures that they can afford on an as and when basis or schedule the works over a preset period and budget for those works in advance of their commencement.

-- A G Brunton IEng. MSOE. MIPlantE. LCGI. MCIPHE. RP. Master Plumber