Studies report 60% thermal energy savings in the cooling demand related to ventilation loss by replacing natural ventilation with mechanical ventilation with self-adjustment by special extracts (ATEE 2006). In addition, adding heat recovery devices to mechanical ventilation systems can further increase these savings (ventilation component of heating and cooling energy) to 90% though at a higher capital cost but with recurring energy cost savings on the premium. Further, through the use of sensors-based variable air volume systems usually 30 to 40% of electricity for mechanical ventilation (especially, energy consumption of fans) can be saved compared to traditional constant air volume systems. All of these figures relate to buildings operated in closed mode, e.g. with cold or hot outside temperatures. In mild weather conditions or appropriate warm and arid climates, however, natural ventilation may use less energy than mechanical ventilation.
Ventilation in buildings will ensure optimized exchange of fresh air and thereby contribute to comfort and hygiene of occupants. Controlled mechanical ventilation found increased application in modern centrally air-conditioned buildings for its merits over natural ventilation. For example, mechanical ventilation with heat recovery mechanism ensures thermal energy savings during peak heating and cooling seasons (ATEE 2006). Ventilation is the process of letting in fresh air into a building while removing accumulated stale air within. Mechanical ventilation in buildings is done by three popular strategies. They are supply, exhaust and balanced ventilation. Exhaust and supply ventilation systems work on the principle of pressurizing or de pressurizing the space using a fan to aid the process. A balanced system is a combination of both supply and exhaust systems and offers to include more energy saving features such as heat recovery ventilation compared to exhaust and supply systems.
Different types of mechanical ventilation |
|
Mechanical ventilation of dwellings is common in some developed countries, while in most of the developing nations, natural ventilation is by far the most common method of ventilating residential buildings. Mechanical ventilation in commercial sector has become the norm in most of the modern centrally air conditioned buildings all over the world. The increase in the market is attributed to increasing awareness about energy efficiency and simultaneously driven by energy code compliance requirements.
Mechanical ventilation in residential sector has started and been on the increase in the USA since 1950s, when more than 50 % of the houses built have central air conditioning equipment with nearly 90 % of new homes built in 2000s being centrally air-conditioned (EIA, 2009). Whole house mechanical ventilation is also common in Scandinavian countries (e.g. 90% of the new houses uses supply and exhaust ventilations while 30% of the existing buildings have the same) and France (95% of the new houses use exhaust ventilation while 40% of the existing buildings have the same) (Le Dean, Febvre and Bernard, 2007). Other European countries such as the UK, Italy use local ventilation by fans and airing, trickle fans ventilation etc.
In order to meet the ambitious targets set by Energy Performance Buildings Directive (European Commission, 2010) most of the European countries have been working towards implementing whole-house mechanical ventilation and also aiming to improve the efficiency of the existing ventilation systems. In general, closed building concepts such as for Ultra-Low-Energy Buildings and nearly Zero Energy Buildings require energy-efficient mechanical ventilation (Händel, 2011). As nearly Zero Energy Buildings are to become the standard in new buildings in the European Union by 2021, the trend to using it in new buildings is clear.
Projection studies in Europe show that in new individual dwellings there will be more Decentralized Ventilation (DV) systems (25-35%) in countries making the shift from natural or few DV improvements in mechanical ventilation (e.g., Poland, Lithuania, Slovakia, UK etc.) while more centralized systems (approximately 75%) will be installed in countries where decentralized ventilation systems are already in place (e.g., Finland, France etc.) (Le Dean , Febvre and Bernard, 2007). However, the projections show an almost 50-50 figures for Decentralized Ventilation and Integrated centralized ventilation in collective housing.
Australia has approximately 12% central air conditioners (with means of mechanical ventilation) in 2005 and their share is expected to increase minimally by about 2% by 2020. However, non-ducted split units (reversible) are expected to rise from about 45% in 2006 to about 55% in 2020 (Commonwealth of Australia, 2008). Though it is not clear if stand-alone mechanical ventilation systems will be integrated with non-ducted units.
The following figure demonstrates the AHU market worldwide. An Air Handling Unit (AHU) typically houses the core of mechanical ventilation system.
It is estimated that in the UK ventilation cum air conditioning market has a total value of € 1.21 billion at manufacturers selling prices (MSP) in 2012. Its core sectors include ventilation of 18%, air conditioning of 54% and accessories of 28% (AMA Research, 2013). In the US sales of ventilation equipment (including fans, ducts, AHUs, heat recovery ventilators (HRV) etc. (and not air conditioning and heating equipment) stood at 23.43 million units. It is expected to increase up to € 2.88 billion by 2015 as against € 1.86 billion in 2006 (Industry Experts, 2011).
Market value of non-residential ventilation systems in Norway has been estimated at approximately € 0.35 billion and in residential sector it is estimated at € 0.12 billion.
Residential sector
Supply air ventilation systems are by far the most prevalent type of residential ventilation system. While considering the merits of ventilation systems, its efficiency, capital costs, operation and maintenance costs have to be taken into consideration. Performance of different systems could vary across different climate zones and it is also subject to the type of cooling and heating system being used. The type of ventilation systems and ducting involved determines capital costs and maintenance costs. Fan is a critical component contributing to running electrical costs of a ventilation system and is the prime energy consuming component.
Ventilation systems with centralized mechanical exhaust including all system and installation costs were priced at around € 1,250 in new constructions and € 1,650 in renovations in major European markets. Room-based extract fans cost € 850 in new constructions and € 950 in renovations. Centralized Heat Recovery ventilation systems cost approximately € 4,000 for new construction and € 5,500 for renovation. Controls such as switches and sensors cost about an extra € 300 – 400 (Fachinstitut Gebäude-Klima e.V., 2010). Similar energy recovery ventilation systems in the US cost about € 1,300 while other exhaust or local ventilator systems cost from € 550 - € 1,150 (Russell, Sherman, & Rudd, 2005). In such cases the cooling is done though all air systems, which requires duct work to carry the cool air, which also carries the required fresh air.
Service sector
The following figure gives an estimate of various types of ventilation equipment in Europe with an esti-mate of cost breakdown in typical commercial building. Energy consuming elements (fans, sensors, actuators etc.) in the whole system typically cost approximately 20% of the system capital cost.
The following figure gives a rough estimate of cost of different kind of heating, cooling and ventilation systems (cost estimate including both cooling generation, distribution and ventilation). However, it should be noted that system costs vary significantly between systems types and between building types.
In modern buildings mechanical ventilation is often integrated with cooling/heating systems. Central air conditioning refers to systems in which a central cooling/heating plant and a ventilation unit serves all conditioned areas of a single building or serves multiple buildings. The majority of commercial buildings certified under various green building and energy rating systems all over the world uses some form of mechanical ventilation systems. Central air conditioning and ventilation is divided into two broad categories.
|
Central air conditioning refers to systems, in which a central cooling/heating plant and a central ventilation unit serves all conditioned areas of a single building or serves multiple buildings. Read the document for more information on mechanical ventilation systems. |
|
Air water systems are in general more energy efficient compared to all air systems for comparable applications. Air water systems can effectively divide latent and sensible cooling load compared to All air systems. In air water systems cooling/heating is done through radiant systems/zone terminal units rather than forced air convection (central) and fresh air is circulated separately. This results in the reduction of required airflow, thus reducing the fan size and fan energy consumption leading to the down sizing of the ducts. In addition, cooling/heating energy is also reduced in Air water systems compared to All air systems due to the latter’s requirement of low supply temperature (of chilled water/refrigerant).
The following figure provides a comparision of savings incurred due to the use of Air water system (radiant+DOAS systesm) Vs the use of All air system (conventional VAV system). The saving % figures are obtained from various sources (however, by a common author) comparing similar systems (radiant+DOAS Vs conventional VAV system with Demand Control Ventilation (DCV)) in all the cases. They are intended to represent in sequence the merits of using Air water systems over All air systems.
Inherent outdoor air requirement for an Air water system is around 80% less than for an All air system. This is because for the same uncorrected design outdoor air, corrected outdoor air requirement for Air water systems stays the same while in a All air VAV system (with demand control ventilation) the corrected outdoor air requirement increases by 20% to 70% to meet the requirement of multiple spaces (as per ANSI/ASHRAE StandardStandard 62.1) (Mumma, 2002). Assuming the DOAS uses total energy recovery and VAV uses DCV system (without energy recovery, as DCV is being used), the outdoor air load component on the chiller in the case of a DOAS system is considerably (83%) reduced (Mumma, 2002).
Air water system supplies only fresh air unlike in All air systems where supply air consists of both fresh air and a component return air. This results in the downsizing of fan and duct sizes in Air water systems. Further, in addition to reduction of outdoor air load on the chiller (Mumma, 2002), at times the temperature of chilled water that is circulated in case of radiant+DOAS systems is higher. Both these factors contribute to the reduction in chiller plant size. Extra investment costs in a radiant+DOAS system includes the use of enthalpy wheel and radiant panels. However, the costs are offset by the reduction in chiller, fan and duct sizes, thus lowering the total investment costs of an Air water system (Mumma, 2002). All these factors contribute to reduction of fan and chiller plant operation energy in Air water systems (radiant+DOAS) compared to All air systems (conventional VAV systems) (Jeong, Mumma and Bahnfleth, 2003).
The following tables summarise various technological improvements leading to more efficient ventilation systems.
Sriraj Gokarakonda
Christopher Moore
makes energy efficiency in buildings and appliances transparent. For investors, policy-makers and actors involved in implementation and consultancy. Learn more ...
Buildings Guide 
Policy Guide 
Appliances Guide 
India
South Africa
