Measurement is the key

Sensor on wall

Building operators need to balance the need for good ventilation and comfort for users, whilst minimising carbon output and energy costs, and measurement is the key to that balance. Andrew Hamshere of Sensing Precision explains how and why. 

The new post pandemic world with new and different ways of working has set new requirements on building services. Not only to ensure the continuing safety of building users, but also to provide comfortable flexible workspaces to encourage workers to return to the workplace and to aid productivity when they are there. These are in addition to the ever growing need to address climate change through energy efficiency and reduced CO2 outputs. This has been further exacerbated by spiralling energy costs brought on by the Russian invasion of Ukraine.

All these new requirements are perhaps contradictory in some respects and the solution is a balance between these conflicting parameters: the need for good ventilation and comfort for building users, whilst minimising carbon output and energy costs. It is a significant challenge to get the balance right, but without accurate data it is near impossible. Airflow needs to be measured accurately and consistently.

Where do we need higher specifications

General office and retail applications have never needed to have these higher specifications; they are usually reserved for clean rooms, healthcare / life science applications and data centres. The push for energy efficiency has improved performance and specification to a significant degree in recent years, but it has been the reviewing of airborne risk following the pandemic which has led to greater changes.

Designers, facilities managers and end users are looking more closely at existing and planned building services installations to see what can be done to provide the required ventilation rates to mitigate future infection risks whilst balancing the energy consumption of the ventilation system. The growth of hybrid working practices has accelerated demand for Variable Air Volume / Demand Controlled Ventilation systems which, while offering energy saving potential, leave the door open for Indoor Air Quality (IAQ) issues if not measured and monitored accurately.

A key issue is being able to demonstrate air flow and ventilation to reassure occupants, staff and visitors that they are safe. Measurement is key, but most building systems have levels of uncertainty of measurement as much as ±20% of volume flow, which is too wide a margin for this purpose.

Higher specification measurement is required, such as Wilson Flowgrids (WFG) which provide levels of uncertainty to ±2% across multiple points. A standard 150mm radial WFG will take positive and negative readings from 36 specially located points within its unique design.

Alternative methods only rely on 12 points or less: the vagueness delivered by such means of measurement leads to poor system control and can have a massive impact on a building’s running costs as well as indoor air quality. More and more clients are conscious of climate change and have been looking to significantly reduce energy consumption and carbon waste by installing WFGs in both new buildings and refurbishment projects, and at the same time enjoying the added life cycle and IAQ benefits.

Pressure signals

WFGs generate “enhanced” differential pressure signals which directly relate to volume flow within the duct, and when used with a pressure transmitter produce an instrument with ‘real time’ flow measurement accuracy usually associated with clean rooms and data centres. In general HVAC applications, apart from demonstrating required levels of ventilation, a WFG will greatly improve the effectiveness of building management systems and enhancing energy efficiency and IAQ.

It will also help with the adjustments and enhancements required to the HVAC system to combat poor IAQ: The ability to provide real time data and linking with ‘smart’ building technology allows for rapid adjustment of ventilation rates and outside air quantities to cater for situations such as spikes in CO2.

Andrew Hamshere
Andrew Hamshere of Sensing Precision

Demand controlled systems

The additional growth in Demand Control Ventilation systems provides opportunities to reduce operating costs in several ways, but ultimately without accurate measuring devices such gains are limited. A demand controlled indoor climate system is energy efficient as the system delivers exactly what is required. It ventilates and conditions neither too much (which costs energy) nor too little (which adversely affects comfort) but only as much as is needed. With the help of WFGs, the indoor climate is measured and controlled according to the exact needs, which potentially decrease energy bills and carbon footprints.

Having such levels of accuracy provides the real time assurance that the right airflow and ventilation is being achieved in all parts of the building. It also helps avoid low airflows and under ventilation which potentially reduces IAQ and impacts health and performance of building occupants, and the longevity of materials. Indeed, one factor that is frequently overlooked when discussing investments and savings is the productivity of the people who are in the building. Building occupants are more aware than ever of their working environment thanks to the availability of extensive data about temperature, air quality, lighting levels and more on smart phones and other portable devices, and this Indoor climate and air quality is strongly linked to human wellbeing and performance.

Employers appreciate consequences

With a demand controlled indoor climate and WFGs, the indoor climate can be adjusted on an individual level, which has a positive effect on performance. Historically, few employers would have given much thought to the quality of an indoor environment, but with the wide availability of data, they are starting to better appreciate the quality and productivity implications. A badly-ventilated office can severely impact an employee’s cognitive ability, as studies have found that high levels of carbon dioxide have a significant negative impact on both cognitive ability and strategic thinking.

This makes a powerful business case for including measures for good air quality as early on in the project as possible, and requires the manufacturer to help with early-stage design, as a properly joined up approach is the only way to achieve the best results.

The drive for SMART buildings and net carbon neutral targets is widening both the scope and necessity of accurately commissioning and monitoring airflows, as reflected in programs such as LEED, BREEAM and others. For example, with LEEDv4 (BD+C new construction), it is possible to obtain 1 Point under EQc1 Outdoor air delivery monitoring Indoor Environmental Quality. This requires provision of a direct outdoor airflow measurement device capable of measuring the minimum outdoor air intake flow.

This device must measure the minimum outdoor air intake flow with an accuracy of +/–10% of the design minimum outdoor airflow rate. These conditions can be achieved using WFGs even when combined with the error of the DP transmitter used.

Although high accuracy devices like WFGs can be more expensive to purchase than other volume flow or velocity measurement devices, they offer a rapid payback due to minimal maintenance requirements, reduced operating costs, a comfortable indoor climate, and increased employee performance. Other systems using less efficient measurement are costing their owners, and the world, dearly; proving that measurement really is key.

Andrew Hamshere is MD at Sensing Precision 

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