Renewable retrofit

Published:  05 July, 2012

Buderus, renewable energy, solar thermal, DHW
Practical and cost effective — Stefan Gautsch.

One of the attractions of solar-thermal energy is not requiring alterations to the building fabric, making it ideal for retrofit and refurbishment projects. Stefan Gautsch of Buderus explains how to maximise its benefits.

One of the best ways for a business to reduce expenditure over the long term is to replace a heating system which is over 10 years old with a new and efficient system. By sheer virtue of the efficiency levels, which have improved substantially over the last decade, a well-designed heating system installed today will undoubtedly reduce running costs and emissions, which is another important consideration given the introduction of the CRC Energy Efficiency Scheme.

One of the key things to remember when overhauling a heating system, however, is that like-for-like replacements are not always the best option. With the increase in renewable technologies on offer for commercial and industrial stakeholders, many are beginning to utilise renewable technology alongside a condensing boiler system to maximise efficiency for their business.

Whilst it can never be said that there is a ‘one solution fits all’ philosophy to heating installations, investing in solar thermal is often the most practical and cost effective solution. All renewables, by their very nature, require a certain amount of space and exposure to the elements. However the vast majority of commercial buildings have an accessible and largely unused roof area where solar-thermal panels could be placed. This means that the end-user can reap the benefits associated with renewable heating technology without causing disruption or alteration to the fabric of the building — further limiting the cost incurred by the installation.

A solar thermal system is primarily designed to meet hot-water requirements, but in the right type of low-temperature system can go some way to providing backup for space heating. Up to 60% of a building’s annual domestic-hot water requirement can be met by a solar-thermal installation. A high efficiency or condensing boiler may then only be necessary to meet the remainder of the peak heating load during the winter months when demand is at its highest.

Whilst saving money and reducing dependence on fossil fuels are undoubtedly key issues associated with installing renewable technologies, we are increasingly seeing the reduction of carbon emissions as one of the key reasons for specifying solar systems. Businesses in the public sector in particular are being tasked by the Government to lead the way in lowering the carbon footprint of its buildings, whilst wider businesses are steadily looking to follow suit.

Solar-thermal energy working alongside a condensing boiler is an effective way of meeting a building requirements for domestic hot water.

Using historical weather patterns, it is possible to provide reasonably accurate predictions of estimated fuel usage and savings from a well-sized solar system — either as a standalone system or as part of an integrated heating and hot water arrangement.

As with any heating and hot water system, to maximise efficiency, sizing is a key consideration to minimise wastage. Making sure the thermal-storage and circulation system associated with the solar thermal panels is properly insulated and effectively controlled is also extremely important, as is the fabric of the building, which is often where the biggest heat losses occur.

We often see a tendency for solar installations to be oversized ‘to be on the safe side’ or to future-proof any possible extensions to the building. This is a misconception, as any water which is heated above and beyond the actual requirement is a waste of energy. It is therefore preferable to slightly reduce the output from the solar system to allow an associated boiler to top-up the hot water supply as required. This in itself will have a favourable impact on the overall efficiency of the heating system.

The overall efficiency of a system is very much down to the details of its design. The use of sophisticated controls, for instance, will closely adjust the system in line with demand, whilst additional features such as flow regulators and low-flow taps within the DHW system will contribute towards savings.

We have also seen developments in the solar technology itself, for example with solar evacuated-tube panels that use CPC (compound parabolic concentrator) technology to provide 360° absorption of solar energy, even on cloudy days. This inevitably increases the rate at which water from within the system is heated, further improving the overall efficiency.

Maximising energy efficiency in order to significantly reduce carbon footprint and fuel expenditure requires thorough and accurate assessment of the requirements of each installation. With the correct considerations made from the outset, a well sized solar-thermal system alongside a high efficiency or condensing boiler can prove to be the recipe for success for most retrofit and refurbishment projects.

Stefan Gautsch is a design engineer with Buderus.

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