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The Green Building |
What is needed for the future UK energy scene is a magic wand.
With dreamy music,a wave and a twinkle of falling stars, every piece of equipment needed for alternative energy systems including complete understanding of the design and installation requirements and its maintenance would descend gently towards us. Oh, and unlimited budgets for building services.
Guess what, it’s only a dream. What is not a dream is the urgent need to replace as much fossil fuel use as possible with alternative energy. As CO2 warnings become more urgent and fuel prices rise every month,ignoring the need for sustainable energy could become a nightmare.
Now I guess most of us see the need to move to sustainable but we lack the equipment and the know-how to design and install it. Now I acknowledge there are designers, installers and manufacturers who are doing a superb job. My point is that the majority of the industry, and the clients too, do not feel comfortable with switching over to sustainable without knowing much more about the systems and their effects.
In lieu of a magic wand may I suggest another approach? What might be called the softly,softly approach. Some sustainable systems, especially solar water heating and heat pumps are becoming more common and a knowledge base is building up around them. Solar water heating systems are now installed in their thousands each year and the number is rising in both domestic and commercial installations. So the combination of solar with high efficiency condensing boilers to support them (and provide the heating load) is the most obvious first step.
Why is this? Obviously the design and installation of solar though different, is only one step away from the expertise base of the industry, so what are the key factors to bear in mind when combining solar water heating with a conventional boiler system?
• Solar water heating may not suit every building. In offices,for example,with a small number of hot water outlets,used irregularly, solar water does not make sense.Buildings where it does are those with large, day round demands; schools, leisure centres, health premises, hotels. With a large well insulated store a solar input of 50 percent or more might be expected.
• Solar panels supply hot water on a ‘little and often’ pattern.
This means that the DHW store capacity of the building needs to be larger than normal, to capture as much of the solar energy as possible.
• Similarly the control system between the boiler and solar panels needs to be responsive to minute by minute changes in solar input as well as integrating the water store already built up.
Step by step
A possible sequence of steps to consider the use of solar heating in a commercial building might run as follows;
1. Assess the total hot water load and the pattern of consumption. A small office with perhaps two or three outlets would not be a candidate. A large building with multiple outlets and random use through the day could well be suitable. Buildings with large water use such as schools, leisure centres, hotels and health premises offer the most likely opportunities.
2. Look at the available roof space.A large south facing roof which is not shaded by buildings or trees is an ideal candidate. Flat roofs can also be suitable if they can carry the weight. Solar panels can be mounted at an angle on struts to give the orientation to the sun
3. Is there space in the plant room for a storage cylinder and the controls between the boiler and the solar circuits?
4. Costs. Will the return on the investment be acceptable? It may be worth making some assumptions about future fossil fuel energy costs rather than taking present costs.
5. Grants. Depending on the type of building, grants may be available. Clear Skies is a good example for a non-profit organisation like a school or local authority building.
Commercial buildings may qualify for Enhanced Capital Allowances and your local authority may have its own sustainable energy grant support.
Even the best designed solar system in the UK’s climate is likely only to provide around 50 percent of hot water demand. Therefore the control of the supplementary form of energy, usually a boiler needs careful thought. The ideal is for the control circuit to measure the water temperature available from the panels,the water temperature in the store and then decide where the optimum supply should come from.
The aim is not to let the boiler and the panels both try to provide water at the same time. My company’s control for this, the Vitosol Divicon and Vitosolic controller provides control in a package and has the further advantage that the use of solar energy can be tracked and recorded for later study.
Heat Pumps too
Heat pumps can also be used in conjunction with conventional energy inputs, though for different reasons.Heat pumps, and in the UK that usually means ground source heat pumps, work on the principle of ‘a little, but all the time’. This in turn means that a buffer store cylinder should be included in the system design. In turn this means that the heating system is drawing from a larger available store of heat than may be generated by the pump at that particular moment. An overdraft facility if you like- but without interest charges.
The economics of heat pumps is that the heat pump and especially the ground source borehole or loop system have a direct relationship to the heat requirement. Since in the UK the maximum design demand may only occur for about 30 days out of a 220 day heating season there is a good argument for letting another fuel ‘peak lop’ at a greatly reduced capital cost. Electric flow boilers are a useful way of providing the additional input and although this will be at higher running costs than the heat pump for a few days a year,this is balanced by the considerable saving on capital costs.
Whatever the source of alternative energy it will require the skill of the building service designer and contractor to make use of it within the building. Moving from the present heat technology to alternative ones requires a different set of skills but these skills are not completely different and they are certainly ones that can be approached step by step.
Case study
St Jerome’s Catholic Primary School,in Formby,near Liverpool was faced with replacing an earlier school that was fire damaged.
The Liverpool archdiocese, their architects and designers set about ensuring that the replacement would be as sustainable as possible, both in the materials it is built with and especially the energy and water the school uses.
Wherever possible the materials used in the school’s construction were either recycled or capable of reuse at the end of the school’s life. The construction was also designed to minimise energy use through high insulation levels.
The heating is supplied from Viessmann Vitodens 200 condensing boilers. These serve the underfloor heating circuits throughout the school and also act as the back-up to the domestic water heating. The solar water heating is supplied from six square metres of Vitosol solar panels with a Vitosolic controller and Divicon controlling the source of thermal input to the two 500 litre Vitocell storage cylinders. This control ensures that heat input is only taken from the boiler when solar energy is not available.
The services contractor was M J Quinn of Liverpool and the services consultant Davies M&E Partnership of Farndon in Cheshire.
The Green Building
Adding to the excitement of the Manchester skyline is the Green Building; part of Taylor Woodrow’s Macintosh Village development. However the Green Building is more than a striking architectural design.It features alternative energy and sustainable technology making it one of the most environmentally friendly new developments in the country, with a SAP rating of at least 100. A wind turbine generates power for the communal areas;natural ventilation saves power as does the energy efficient lighting.
Viessmann solar water heating panels and five Vitodens 200 condensing boilers provide the heating and hot water services for the 32, one and two bedroom apartments.
The Vitodens boilers give an operating efficiency of 96 percent and their controls are interlinked with the Vitosol panels to ensure that the hot water service makes optimum use of the free energy available from the sun. Over the year it is estimated that some 35 to 40 percent of the hot water will be provided this way.
