Sensing the future
Are you up to speed on the capabilities and aesthetics of modern sensors? Trevor Palmer is here to help.
Building-management systems (BMSs) have been a major success story in UK commercial buildings over the last 25 years. They combine energy-saving control techniques, such as optimum start and dead bands, with communication and information systems that allow active management of the building services and the capability to achieve and maintain a high level of energy efficiency and lower carbon emissions.
For all the sophistication, advanced feature-sets and benefits that these control systems bring to their occupants, they depend for their success on the humble sensor.
Room temperature and humidity sensing and transmitting products began with the development and proliferation of centralised building-management systems in the 1980s. Traditionally, the manufacture of these 2-wire products was limited to the major system manufacturers of the day — companies like Honeywell, Johnson Controls and Barber Coleman (today owned by Schneider Electric).
Right from their original introduction as the eyes and ears of the BMS, misconceptions have persisted in terms of how accurate these devices really need to be, how fast they should react and what precisely constitutes a high quality room and/or duct sensor. These factors are important and demand closer consideration from consultants, contractors and systems integrators charged with delivering energy-efficient control systems for today’s buildings.
As an example, many consulting engineers continue to specify 0 to 10 V transmitters equipped with PT100 type temperature elements as standard. The commonly held view is that these products are more accurate than box-standard thermistors. In fact, quite the opposite is true. Thermistors are today available in different grades and types, which quite often exceed the accuracy of transmitters of old.
Measurement accuracy versus stability is another talking point. Generally speaking, the industry has relied, and continues to rely, on temperature sensors that are low cost and tolerate ±0.3 K over the entire range (-10 to +70°C). As a result, this specification has become standard within the UK market. However, what is really important from a sensing perspective is longer-term stability rather than absolute accuracy. It is much more important for devices to remain accurate within the manufacturer’s specification (±0.3 K) for the life of the device than their absolute accuracy. After all, these devices are being applied within commercial buildings to enhance occupant comfort and improve energy savings over the long term. If our balance of priorities shifts in favour of performance stability over absolute accuracy then these benefits can be successfully realised.
Sensor cost also remains an issue. Accounting for just 2% of the budget for a whole project, room sensors themselves are not always the main focus of attention when it comes to selecting and specifying the building control system. However, different price-points often reflect a differential in quality. Choosing the lowest cost sensors increases the risk of compromising on long-term measurement reliability and performance stability. Device failure can lead to the time and cost of unnecessary call out and product replacement issues, alongside the unwanted cost of reputational damage to the specifying contractor and consultant.
Increasingly popular wireless sensor technology is also having a fundamental impact in transforming how we think about the cost of sensor installation. By eliminating the need for cabling during sensor installation, wireless devices can greatly reduce engineering time and installed project cost. This enables faster and easier installation on new buildings and also opens up the opportunity for control specialists to retrofit energy efficient HVAC controls into existing commercial and public buildings. In projects using our SonNet family of wireless sensors, we are typically finding total installed cost savings of 30% and more over comparable wired sensor installations. At a time, when reducing costs is a priority on many projects, proven wireless technology can bring significant benefit.
Changing aesthetics and increased functionality are also important drivers in helping us re-evaluate how we look at sensors.
Sensors located in the space have traditionally been selected with little or no regard to design aesthetics. In contrast, the latest devices on the market enable specifiers not simply to satisfy the functional demands of their client but also the impact of the sensor on the interior space and the look and feel of these devices. Our new range of TT-1000 space temperature sensors, for example, features a specially designed low profile and curved fascia to ensure that they can blend stylishly and seamlessly into a room’s design scheme whilst still helping to deliver greater energy efficiency, cost savings and carbon reductions in new build and retrofit building applications. The bland and, frankly, cheap-looking design of the ordinary room sensor need no longer be a barrier nor an unwanted intrusion into the design scheme of the upmarket commercial office building.
At the same time, the longer-term trend is away from single-use sensors, such as one for temperature and one for humidity, to multi-functional environmental sensors. These modern devices can measure several important variables within the overall space conditions which may include air quality and CO2 for occupancy, alongside traditional temperature and humidity measurements. This combined approach offers numerous advantages to the systems integrator and the client. The building owner enjoys the ability to monitor and report on total environmental conditions and yet service only a single device in the future. He can also minimise the wall acne that will often occur if multiple devices are required. The systems integrator can also provide much more sophisticated control strategies at a lower total installed cost with fewer devices to install and service in the building.
Today’s sensing devices are providing much better aesthetics and greater functionality for a relatively low and, in the case of wireless, significantly lower total installed cost. These devices can provide a better picture of the true building conditions over the long term in smaller packages that are more pleasing to the eye. The result is the creation of a broader market opportunity for control-systems specifiers and installers and, ultimately, the potential for buildings that use less energy and have lower carbon emissions.
Trevor Palmer is managing director of Sontay.
