Sustainable technology for the 21st century
The opening of the Monodraught Gallery at the University of Nottingham demonstrates a range of practical applications of renewable energyThe application of sustainable solutions to control the internal environment and the generation and use of renewable energy does not need to be complex or carried out on a large scale. Indeed Professor Saffa Riffat, head of sustainable energy at the University of Nottingham, advocates simple applications and avoiding complicated approaches. While grants are available to stimulate the take up of alternative energy, He is not keen on them, expaining that it can take 18 months to get a grant and asking if that length of delay is worthwhile. The concept of simplicity is well illustrated by the opening of the Monodraught Gallery in the School of Sustainable Energy. Not only does this new gallery, financed by Monodraught, provide a venue for meetings, events and seminars, but it also acts as a showcase for Monodraught’s approach to sustainable services and renewable energy. Some developments exploit input from the university and were developed in time for the opening. All are characterised by simplicity of concept and being self-contained. Natural ventilation
A case in point is Monodraught’s Windcatcher, which has been used for 15 years to provide natural ventilation whenever there is more than a slight breeze. The amount of ventilation, and associated cooling, is determined by wind speed. On a hot, still day, very little ventilation will be provided. Fan assistance is one obvious way of overcoming this problem, but in requiring mains electricity would depart from being totally natural. Monodraught’s response is to observe that hot, still days are ideal for generating electricity using photo-voltaic cells. Mounting a PV panel on top of a Windcatcher generates electricity to drive a fan to provide extra ventilation. The more sunlight that falls on the panel, the more electricity is generated and the greater the amount of air that can be moved by a built-in fan. For example, a 600 mm-square Windcatcher can deliver up to 285 l/s of ventilation with a wind speed of 3 m/s. A built-in fan could provide an additional 195 l/s powered by a solar panel with a peak power output of 30 W. Motorised dampers control the amount of ventilation. A 1200 mm-square system with three fans could deliver up to 1050 l/s with a wind speed of 3 m/s and a further 780 l/s with fan assistance. Three solar panels could deliver up to 40 W each of electricity. The performance of the fans in response to the amount of solar electricity available is optimised by a control system. If less than 5 V is available, fans do not run. If more than 14 V is available, the control system boosts it to 25 V, enabling the fan-assisted air volume to be increased by a factor of 2.6. Evaporative cooling
The cooling capacity of the fan-assisted Windcatcher can be further increased by incorporating evaporative cooling. Passing air entering the building through a desiccant cooling core charged with water can provide up to 10 K of cooling. To provide 4 kW of cooling, the water usage is about 45 litres a day, so the running cost is less than 5 p a day. Sola-Cool, as it is called can provide up to 500 m3/h of cooled air. Electrical power for the system is provided by integral 60 W PV panels. Sola-Cool has three modes of operation. • As a normal Windcatcher to provide natural ventilation driven by external wind. • As a fan-assisted Windcatcher (Sola-Boost), with electricity provided by the built-in PV panels. • In evaporative-cooling mode (Sola-Cool), when external temperatures are high, to provide energy-free cooling and natural ventilation. Monodraught has also addressed the use of alternative energy to generate electricity. This novel system, called Sola-wind, uses a wind turbine and PV panels to general 12 V d.c. This electricity can be converted to 240 V a.c. using an inverter. The concept is that the electricity is fed to a ‘green’ electrical circuit in, say, a house. Excess electricity is stored in lead-acid batteries, which can provide electricity when alternative energy is not available or insufficient to meet demand. The philosophy is that it is illogical to sell such electricity to the Grid, only to buy it back later at, perhaps, four times the price. If no ‘green’ electricity is available, the load can be switched to the Grid within 10 ms, so that equipment such as computers does not crash. A single enclosure houses all the equipment except wind turbine, PV panels and ‘green’ electrical circuit. Sola-wind is intended for steady, small loads — not, for example, electric kettles and fan heaters. Monodraught’s figures suggest that the mixture of wind and solar power would amount to about 3 kWh a day, or a steady supply of 125 W. Larger configurations are available. For comparison, 125 W could power fluorescent lighting with an efficacy of 100 lm/W to provide an illuminance of 500 lx for an area of 25 m2. In a home, refrigerators, freezers, televisions and computers could all be powered. The development of these, and other, new ideas, provide, believes Terry Payne, Monodraught’s managing director and a Special Professor in Building-Services Engineering in the School of the Built Environment, a response to rising fuel costs and the need to move towards renewable energy. Professor Safa Riffat describes the Monodraught Gallery as ‘showing sustainable technology for the 21st century’.