Waste not, want not through demand controlled ventilation
Improving ventilation control enhances building performance and staff productivity, while reducing fuel bills and carbon emissions. David Cook, explains how demand control ventilation saves energy and reduces carbon while providing the comfort staff require
CARBON IS KEY. With climate change one of the biggest threats to the modern world the UK Government has been driving a reduction in its carbon emissions. Since the built environment accounts for 40 per cent of the UK's carbon emissions it is a key sector to target for reductions. For the commercial building sector the fast approaching 2019 zero carbon target for new non-domestic buildings has brought energy efficiency into focus for big businesses.
However, in the current climate of austerity there are also other issues driving energy savings. With fuel prices soaring and tight business budgets many companies have recognised they could benefit from such efficiency measures.
Energy bills have risen dramatically in recent months as energy companies hike prices due to higher wholesale costs. Therefore many UK firms are now considering energy efficiency as a way to alleviate the costs of rising fuel prices while lowering their carbon emissions.
So what simple, cost effective measures can be taken to cut both a building's fuel costs and carbon emissions in one fell swoop? With the vast majority of commercial buildings fitted with inefficient, energy hungry A/C fans that either
have no controls or only simplistic controls, ventilation represents a key area for improving building performance. Not only do these inefficient fans cost more to run but their unsophisticated controls provide low comfort levels which can lead to unproductive staff.
Comfort is a key issue. Energy efficiency is essential to lower the UK's carbon footprint but it cannot be at the expense of occupier comfort. Indoor air quality, noise and thermal comfort are all integrally linked to staff performance. The 2005 report 'Impact of Office Design on Business Performance', produced by CABE and the British Council for Offices (BCO) cited differences in productivity of 25 per cent between comfortable and uncomfortable staff, due to basics, such as air quality, temperature, overall comfort, noise and lighting. In the current financial climate, where companies are tightening their belts gaining potentially up to 25 per cent in staff productivity is a huge incentive to improve indoor air quality.
With traditional fixed volume ventilation the system is either on or off irrespective of the number of people in the room. Here, you run the risk of creating a mediocre and unproductive office environment though over or under ventilation with a resulting waste of energy and poor levels of comfort for staff.
Instead, demand ventilation works by responding to the exact demands of a room, supplying or extracting air only when and to the level it is required. As a result there is greater comfort for building occupiers and the improved energy efficiency of the fans means a reduction in fuel costs and carbon emissions.
Demand ventilation operates according to sophisticated control and sensing options that are designed to provide ventilation appropriate to the comfort needs of the occupiers. A range of sensors, such as CO2, PIR occupancy detection, humidity or temperature, are employed to determine the room's air quality condition, adjusting the ventilation requirements automatically and managing the system's ventilation rates accordingly. The sensors communicate with the main unit which, in turn, drives the fan to the required speed to deliver the airflow responding exactly to room conditions. These sensors can be combined to generate a hierarchy of control for the ventilation system and its operation can be easily linked to a Building Management System for full control and monitoring, if required. Therefore only the energy that is needed to ventilate is actually used.
The latest demand ventilation systems, such as, the recently launched Sentinel Totus 2 Demand Energy Recovery Ventilation system (D-ERV), integrate 90 per cent energy recovery into the ventilation system.
This type of system extracts the energy from the room's warm, stale air before it is exhausted outside, while fresh, incoming air is preheated via the high efficiency plate heat exchanger and supplied into the room. The energy recovery process is proven to utilise up to 94 per cent of the heat energy which would otherwise be wasted.
In addition, not only do these types of systems provide high efficiency good indoor air quality they also add to thermal comfort. Demand ventilation control also limits summer gains and winter losses as only the required ventilation is delivered based on occupancy and indoor air quality need, reducing summer overheat and heating losses in winter.
As buildings become increasingly air tight the problem with buildings overheating is increasing. Therefore D-ERV systems have now been developed with 100 per cent summer bypass. When temperatures rise the automatic summer bypass now closes off the airflow from the heat exchanger while simultaneously opening a bypass which the air flows through, thus avoiding overheating. This also allows the building to take advantage of any free cooling available when ambient temperature is below the room design conditions, typical in spring and autumn.
Plus, a user-enabled night-time purge facility can reduce the startup loads for a building's air conditioning plant helping reduce overheating in summer from non-air conditioned spaces.
In the winter the high efficiency heat recovery of these systems tempers the air to such a level that the building should not suffer from draughts eliminating the need for re-heaters, for example typically at -5°C ambient, 22°C room conditions the supply air temperature is maintained above 19°C. However, with comfort at the forefront of manufacturers' minds the latest systems now include frost heaters so that in extreme winter conditions on perhaps a couple of days a year the system can provide a heating boost to achieve thermal comfort for occupiers.
Meanwhile noise-related stress can also affect staff's comfort and so performance. This is why DERV systems feature improved acoustic installation and well designed heat exchangers that also lower noise by reducing turbulence in the ductwork. Good system design and installation are also essential to avoid ductwork turbulence and so ensures the system works efficiently, effectively and quietly.
In addition, demand-controlled ventilation rarely operates at full power for any considerable length of time to achieve the desired indoor air quality and comfort level. Since the fans are not running at full speed it makes a very quiet ventilation system even quieter providing an environment free from noise-related stress. As the Government continues to raise the bar on efficiency targets in a bid to meet carbon targets it is important to consider the functionality of building services technology and the comfort it brings occupiers. It is essential that manufactures develop low carbon systems that ensure a building is efficient as possible. D-ERV systems achieve this through only using the energy that is necessary to suit room occupation. At the same time the systems ensure that occupiers experience the comfort they expect.
// The author is the product marketing manager - Industrial at Vent Axia //
27 February 2014