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A good indoor climate is fundamental for people to perform, rest and thrive inside built premises. However, energy efficiency is in nearly all cases on top of the agenda when designing an indoor climate solution – sometimes leading to a perceived conflict between indoor climate and energy consumption. It is crucial to recognise that good indoor environmental quality (IEQ) and comfort can go hand in hand with energy efficiency, it is all about optimising the design and use of selected units and systems. In this blog post, our expert, Niklas Jacobsson, Product Manager at Swegon, will explain more.
The most common way to ensure IEQ in an indoor space, is to design a solution which offers a minimum air flow in each room. The determination of the minimum air flow is based on factors such as room usage, occupancy levels and activity within the space. Ventilation duct work is often designed like branches on a tree, where the room farthest from the source will be the last for the air flow capacity to reach. In order to ensure the minimum air flow in this “last” room, the air pressure in the duct system has to be increased. What follows, is that the other rooms along this duct branch must take care of the increased pressure by closing their dampers. This may sound easy, but is in fact delicate and can lead to unnecessary energy consumption and/or unwanted noise.
Constant air volume contra demand controlled ventilation
A traditional solution is most often of a type called constant air volume ventilation (CAV), in which excess of energy use or noise is tried to be minimized through the design and commissioning process. However, a CAV solution does not consider variations in occupancy or use of the room. As many rooms, at many times, are either vacant or used at less than maximum capacity there is a substantial risk of wasting energy and causing disturbing noise.
Demand controlled ventilation (DCV) on the other hand, is a solution which can adjust the air flow according to the actual need. Beyond damper adjustments and numerous other functionalities, a DCV system can also alter the fan speed in the air handling unit (AHU) to minimise the energy consumption. A feature commonly called pressure optimisation. Further, if the duct system is instead designed in zones, with zone dampers for each zone and room dampers for each room, pressure optimisation of the AHU will ensure a further efficient air flow distribution throughout the system and hence energy savings.
2-step optimisation for further energy savings
Now, to unleash the full potential of a DCV system, 2-step optimisation is recommended. This means, that the zone dampers optimise their positions depending on the room dampers “below” them, and the AHU pressure is set depending on the zone dampers “below” the air handler. What happens is that, when a room damper requires and increases air flow, the zone damper can open to increase the flow. If the air pressure is still too low to be able to fulfil the needs in the room, the AHU pressure set point will be increased. In reverse, if the requirement of air in a room is reduced, the zone damper can close to reduce the air flow and the AHU can decrease the air pressure, hence lower its energy use.
When strategic adjustments of damper positions and the control of pressure levels are included in the same optimisation algorithm, several benefits can be gained. I will elaborate on four:
- Noise reduction, has been mentioned above, but is now explained - large air flows tend to be turbulent which can cause noise in itself or cause mechanical components to vibrate and make noise. Optimised damper positions and pressure levels allow for a quieter operation.
- Energy efficiency, also in focus in the above discussion, is definitely a result of optimised damper positions and pressure levels, as air is only directed to the rooms and spaces of a building where it is needed. The risk of over-ventilating an empty or sparsely occupied space is reduced which also considerably reduces the workload and energy consumption of the ventilation solution.
- The equipment's lifespan is most likely prolonged thanks to an optimized operation. The strain on components and the need for maintenance is clearly lessened with an optimal use of the solution.
- Indoor comfort, strategic damper positions allow for temperature control, which answers to the actual needs taking into account varying occupancy levels and preferences. This increase not only the indoor environmental quality and comfort, but it also caters for increased well-being - for people to feel good inside.
In summary, a 2-step optimisation algorithm enhances both energy efficiency and IEQ, ensuring a comfortable indoor climate conducive to productivity and well-being. At Swegon our system for demand controlled ventilation (DCV) is called WISE, it is a highly advanced, yet user-friendly, system solution for an indoor climate that meets set requirements, features significant energy savings, and creates a good indoor climate where people can be at their best, today and tomorrow.
