Dampness, lack of cleanliness, certain chemicals given off furniture, household plastics and paint, plus a myriad of other environmental variables can – and do – damage building occupants’ health. This is why we ventilate. Voltimum runs briefly though the different types of ventilation system before turning his attention to the latest developments:
Virtually all buildings can contain a complex mixture of gaseous and particulate contaminants that can affect the health of people living and working in them. The contaminants typically include water vapour, emissions from cleaning products, construction activities, carpets and other furnishings, dusts, unpleasant smells, perfumes, cigarette smoke, electronic machines, water-damaged building materials, microbial growth (fungal, mould and bacterial) and insects.
Indoor temperatures, relative humidity and ventilation levels can also have an effect, and there may also be external contaminants, such as traffic fumes, dusts and in some areas, ingression of Radon gas, which is radioactive.
Indoor air quality (IAQ), combined with energy saving and emissions reducing activities, has become an increasingly important health and safety issue – especially as buildings are being made increasingly airtight for thermal efficiency reasons. So we must now ventilate effectively to ensure a good IAQ.
Effective ventilation, therefore, can and often does improve people’s health and sense of wellbeing. It is also proven to boost people’s productivity at work. And involved electrical contractors and installers can help improve their businesses by showing potential customers how they can save money through having modern ventilation systems.
In fact, good ventilation is now effectively required by regulations. The result has been the rapid development of far more energy efficient ventilating products and systems, using the latest technologies, sometimes together with clever control strategies.
Types of ventilation
There are a number of basic ventilation types, but the essential two are natural ventilation and mechanical (‘forced’). In brief:
Natural ventilation uses the external air to ventilate a room or building without a fan or other mechanical system. It can be achieved using opening windows and/or trickle vents (smaller systems), and in larger, more complex buildings, the ‘stack effect’ can be used, where cool outside air is drawn into the building naturally through low level openings. It then rises, ventilates, and passes out of upper vents to the outside again.
Forced (mechanical) ventilation ensures that internal air is passed through an air handling unit (AHU), which conditions and circulates air as part of an HVAC system (which we are not covering here), or directly into the space by a fan. In addition, an exhaust fan can improve air infiltration or natural ventilation.
In terms of specification and installation, it is important to specify or design the mechanical ventilation system taking into account flow rates (function of fan speed and exhaust vent size), and noise levels. Any exhaust ducting crossing unheated spaces should be insulated to prevent condensation on or in the ducting.
Note that ceiling fans do not ventilate, merely circulating air within a room, but they make people feel more comfortable because they help evaporate perspiration. Ceiling fans can also keep rooms warmer in the winter by stratifying warm air from ceiling to floor.
A feature of the best modern extractor fans is the use of low energy electric motors to drive them; these greatly reduce energy usage.
Whole house ventilation and cooling draws in air from open windows and exhausts it through the attic and roof. This technique can substitute for an air conditioning system for much of the year.
Whole house fans should provide houses with typically 30 to 60 air changes/hour, and this - combined with ceiling fans and other circulating fans - can provide good domestic summer comfort. Note that a home’s central heating and cooling system ducting can be modified to provide whole house cooling.
However, to obtain the highest energy efficiency, modern homes should be fitted with a central ventilation system having heat recovery – such as mechanical ventilation with heat recovery (MVHR). With this, fresh air is continuously drawn into the home by a low energy ventilation unit, typically mounted within the roof space or utility room. Once passed through the integral heat exchanger, warm, clean, fresh, filtered air is distributed around the home through ducting running to bedrooms and living rooms etc.
With the move towards zero carbon homes targets gathering pace. Such systems can recover up to 90 - 95% of the heat normally lost through open windows, trickle vents and extractor fans typically found in buildings.
The latest developments
It might be thought that MVHRs represent the ultimate in mechanical ventilation, and this is true – but there are many other developments under way that will likely change the ways in which we control ventilation and indeed the ways we think about it.
An important element of this is smart homes and automated buildings, which are now rapidly expanding and important sectors. In such buildings, their services (heating, lighting, security, safety, appliances, entertainment – and ventilation too) are becoming under either integrated centralised control or, increasingly, some form of decentralised control, using the fast expanding ‘Internet of Things’ (IoT).
The IoT is the network of physical objects or ‘things’ embedded with electronics, software, sensors and connectivity to enable it to achieve greater value and service by exchanging data with the manufacturer, operator and/or other connected devices. Each ‘thing’ – which might be a room thermostat, security device or fan, for example - is uniquely identifiable through its embedded computing system but is able to interoperate within the existing Internet infrastructure.
The IoT is already providing advanced connectivity of devices, systems, and services and covers a variety of protocols, domains, and applications. The interconnection of these embedded devices, is leading to automation in nearly all fields, including of course, heating and ventilation. Indeed, IoT connected devices can enable a building’s cooling, air-conditioning or heating to be turned on or off according to a calendar schedule – and much more besides.
Other ventilation (and HVAC) related developments – either in being or in the pipeline – include single-time step control, pre-cooling and night time ventilation control, active and passive thermal storage, and the use of multi objective optimisations for dynamic building ventilation strategies that can improve IAQ and reduce energy use. Then there are evolutionary strategies and genetic algorithms being developed to devise adaptive fuzzy logic controllers (AFLCs) for cooling coil comparisons with standard proportional integral derivative (PID) controllers, which continuously calculate an error value as the difference between a desired set point and a measured process variable.
Integration, control and smart devices
In short, the mechanical ventilation future is all about perfectly matching a ventilation system to each building (fan, motor, all ducting, heat exchanger if fitted, air flow rates, required humidity etc) and using the latest low energy technologies, together with clever and careful control. The latter is increasingly being automated but still under the ultimate control of home or building occupants, often using their mobile devices, smart phones and tablets as part of the IoT
