Modern Building Services

MODERN BUILDING SERVICES JUNE 2021 23 FEATURE COOLING & VENTILATION If the supply air temperature exceeds the tolerance band, the SMV may enter the automatic bypass mode were the supply air bypasses the heat exchanger. The bypass opens in small increments mixing down the supply air temperature. If the room temperature is too high, the bypass will open fully, bypassing the heat exchanger, introducing the cooler outdoor air to the classroom. During summertime, there is a high risk of well-insulated buildings overheating, so whilst the automatic bypass modemay reduce the supply air temperature, the buildingmay continue to overheat. The SMV will activate the night-time cooling mode, whereby air is brought in overnight to cool the thermal mass of the room to act as a heatsink the following day. This process will continue until the SMV has measured a successful reduction in day-time room temperature. Most SMVs are fitted with CO2 sensors, enabling demand control year-round. To allow for monitoring of the SMVs, they can be fitted with online ethernet modules, which enable remote monitoring of the equipment via an Internet of Things (IoT) platform, or the digital BMS system by way of an application programming interface (API). The benefits of Smart Mechanical Ventilation In making use of the temperature and indoor air quality control functions built into SMVs, the practical operation of the systems becomes very simple. They are easy to install, have a low impact on the building construction, requiring only a pair of penetrations, mounting brackets, and electrical connection, and are plug and play. The result is a simple method of providing fresh, draught free air into well-insulated rooms, whilst recovering great amounts of energy already in the room. SMVs normally have a very low fan power for MVHR, ranging from0.50 to 1.24W/l/s. This is made possible by the nature of a decentralized ventilation unit: the air reaching the unit must travel a very short distance to the fans, meaning that pressure drop is minimal. Furthermore, the Coanda effect requires a low pressure to operate, so specific fan powers can be kept to aminimum. When we combine a low specific fan power and a high heat recovery efficiency, the holistic energy consumption of a classroom’s building services could be cut by as much as 40%. We estimate that the average hybrid ventilation system in a classroom has an average annual electrical and heating demand of approximately 600 kWh. We estimate that for an SMV, the combined demand is approximately 256 kWh annually. This is made possible by the dramatic reduction in heating demand. When considering the energy consumption of classroom ventilation systems, it is therefore vital that one considers both the electrical and heating demand, as looking at the electrical demand only can bemisleading. More information on this can be found in our document entitled, “Decarbonizing UK School Ventilation” and is available on our website. The future of ventilation There is no doubt that mechanically assisted ventilation will become the desired ventilation solution in resolving our indoor air quality needs. However, we should be aware the mechanical ventilation category is not comprised of one monolithic technology, but a combination of differing technologies and strategies. For classrooms, one of the most beneficial ventilation strategies is SMVs. By combining efficient heat recovery ventilation and low specific fan powers, classrooms fitted with SMVs can expect good air quality with a low carbon footprint, all without teacher-intervention. More information can be found at www.sav-systems.com