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| Saving energy, improving air quality  Energy efficiency and indoor air quality are increasingly considered equally vital factors in building design. At the same time, there is proof that performance and productivity are influenced by the working environment. With the importance of noise, lighting, temperature and humidity already understood, the role of air quality is receiving greater recognition. A variety of Sick Building Syndrome symptoms are known to be aggravated by even slight air quality deterioration. Once, ventilation needs were weighed against the cost of implementing solutions. Considered the necessary evil of building services, ventilation was often seen as an area offering cost savings and compromise, with aesthetics being viewed as more important. Those days have gone. Now, with energy conservation at the top of every agenda, the need to consider the whole life-cycle cost of delivering indoor air is increasingly recognised. Designing ventilation and air conditioning systems into buildings is subject to numerous regulations. These include updates to the Building Regulations, where Part L1 and L2 (Conservation of Fuel and Power in Buildings) should be viewed alongside Part F (Ventilation). A key Part F change increases the mandatory minimum fresh air quantity per person in buildings from eight to ten litres per second per person. This brings an implicit reduction of CO2 carbon dioxide build-up within occupied spaces, but this can be accomplished by changing how fresh air is introduced to the occupied space. Displacement ventilation, offering a solution which addresses both energy conservation and indoor air quality, has been used in the UK for some years. It delivers clean fresh air at low level directly into the occupied space, at the correct temperature. The spent warm air, carrying any contaminants, rises and is extracted through the exhaust air system. As long as the supply air flow is adequate, the system is self-regulating. It offers a ventilation efficiency, whether or not the space is occupied, around four times more effective than that of traditional mixing systems. Displacement ventilation systems can deliver fresh air at a suitable temperature and, operating at both low velocity and very low pressure, with minimal draught and low noise levels. The temperature gradient promoted by such a system means that the temperature is higher at ceiling-level than in the occupied zone. This permits a higher supply temperature than is possible with traditional mixing systems, reducing flow rates. A higher return temperature also makes it ideal for use with an air handling unit which has an energy recovery device, which can offer a major reduction in the amount of heating energy needed to meet room conditions. If the recovery method is a thermal wheel, it is even possible that heating energy may not be needed at all. A higher supply temperature also allows free cooling for much of the year. With a thermal wheel in the AHU and an evaporative humidifier in the extract, the cooling load required by any chiller or condensing unit can be cut by 50%. Using a thermal wheel and indirect evaporative cooling not only reduces peak cooling loads, but also significantly increases the amount of time that cooling recovery can occur. The energy recovery capabilities are key to minimising the energy usage of such a system. In this area, the state-of-the-art can be seen in Econet, the packaged liquid-coupled energy recovery system from Fläkt Woods. Its unique optimising control system incorporates highly efficient energy usage, with space and installation flexibility. It comprises supply and extract coils, invertor driven pump set, and all necessary valves and sensors. With coils installed within the AHU, the pump pack is supplied as a pre-piped, pre-configured, pre-programmed and pre-commissioned unit suitable for direct connection to the supply coil. Large coils maximise the energy recovered from the extract air, using water as the most efficient recovery medium. Up to 12 rows of coils and 76 waterways enable energy recovery efficiencies of up to 70-75% at equal supply and extract airflow. Complete heating and cooling is supplied with the same coils when the system is supplemented by injecting energy from hot water or chilled water through plate heat exchangers. Due to the efficiency of the large coils, this supplementary energy can be low grade, waste or renewable energy: condenser water from chillers at 35 °C can supply all the heating and bore hole water temperatures of around 11 °C can cool the supply air down to 14 °C. The optimising controls sense supply and extract input water temperatures, calculating the optimum way — recovery, waste heat etc. — to deliver the required temperature. Combining the optimiser and invertor-driven pump delivers full-range efficiency: if 73% efficiency is achieved, 73% is maintained through all airflow and system variables. The result is that Econet delivers high-quality indoor air in an extremely energy-efficient way, offering significant long-term savings. As an AHU's running cost over 20 years can approach 10 times the initial capital investment, at current plant and energy prices, so cutting energy demands brings important whole life-cycle cost savings. Use such a system with Econet and free cooling, winter energy recovery and indirect evaporative cooling are all available for the benefit of occupiers, building owners and specifiers alike for the whole life of the system. By Neil Yule, UK Business Unit Director, Fläkt Woods write your comments about the article :: © 2008 Construction News :: home page |