Author: Andy Smale, lecturer for the Energy Efficiency in Buildings Course run by European Energy Centre. The course is available distance learning, and also as a two day classroom based course held at major Universities.
The European Energy Centre (EEC) promotes best practice in renewable energy and energy efficiency with major universities and in partnership with the United Nations Environment Programme (UNEP).
Monitoring is a cornerstone of any energy management strategy – a paucity of data related to energy use makes any effort to reduce consumption much more challenging. Without this kind of information it is impossible to compare performance against industry benchmarks for a particular type of building or industry sector, and to determine whether BREEAM targets are being met.
Trends cannot be assessed over periods of time, and consumption cannot be compared over the same periods across a number of years to determine any whether improvement or deterioration in energy performance has occurred.
Although there is a growing awareness of the power of smart metering to provide detailed information on gas and electricity consumption at a site or building level, in isolation this rarely provides much insight into where the source of any problem might lie, especially in larger buildings. Sub-metering can be installed for areas under suspicion, however this is often a costly gamble, with no guarantee of results. There are plenty of more cost-effective routes to tracking down energy wastage using resources that are often currently unexploited, or using tools which can be purchased at low cost.
This article explores some of the untapped potential for improving energy management by broadening the scope of energy monitoring to include parameters beyond utility meter readings.
Lighting is an essential building service - according to the Carbon Trust lighting accounts for up to 40% of a building’s electricity use, however potential savings are often not fully realised. An effective strategy to reduce lighting-related energy consumption will encompass much more than just the installation of energy-efficient lamps – very often little regard is given to appropriate levels of illuminance in the workplace. For example, paper-based desk work will require around five times the illuminance required for safe passage along a corridor, and yet many offices maintain a consistently high level of illumination throughout, wasting energy where it is not required.
Basic light meters are low-cost tools which can be used in any working environment to determine appropriate levels of lighting. When considered alongside factors such as daylighting and occupancy, the identification of areas of over-illumination can present opportunities for reducing energy consumption through the implementation of improved control or changes in lighting specification.
The process of monitoring of lighting levels can also help to identify problems with lighting maintenance, for example lamp failures and ageing or dirty luminaires. Areas of under-illumination can also be a concern from a health and safety or security perspective – a comprehensive lighting survey can ensure that standards are being met, reducing the risk of crime or claims from accidents.
In a typical building, the largest proportion of energy use goes towards space heating and/or air-conditioning. According to the Energy Saving Trust, each degree of heating can add up to 10% to heating bills, and excessive cooling can result in an even bigger financial hit due to the high cost of electricity. Furthermore, energy conservation legislation precludes the heating of workplaces above 19degC, on the basis that incidental heat gains will usually bring the ambient temperature up to a comfortable 20-21degC.
Typically, room temperatures are controlled via wall thermostats, however it should not be assumed that they can simply be set and forgotten about as thermostats can fail or be tampered with. It should also be remembered that heating systems are often installed alongside ventilation and cooling services – systems are frequently poorly commissioned and it is not unheard of for complex heating and ventilation/cooling systems to inadvertently work against each other. Unfortunately such problems are often only discovered when temperature-time profiles are monitored - it is a mistake to assume that just because controls are set correctly, everything must be working as intended.
Figure 1 illustrates the temperature profile of a kitchen in a sixth form college over a week, revealing rapid changes in temperature at around 7:30am on weekday mornings. The profile suggests that hydronic radiator-based heating system is fighting the AHU-based heating. Different setpoints and a lack of dynamic control of heating start times result in warm air actually being flushed out by cooler air from the AHU and lost on Thursday morning.
Figure 1 - illustration of college kitchen air temperatures suggesting contention between heating and ventilation systems
Keeping tabs on ambient temperatures is therefore key to ensuring a heating system is working efficiently, and that building services as a whole have been correctly configured. In buildings with Building Management Systems, monitoring can often be carried out centrally via remote sensors, with logging configured over a representative period of time. In smaller buildings or discrete locations, small USB data loggers can be left in appropriate locations for a period and then taken away for later analysis.
Air quality is rarely considered past the commissioning stage of a building, however it can be an important indicator in relation to energy conservation, as well as having a major impact on staff wellbeing.
Modern buildings are often installed with ducted ventilation systems which are fed by one or more air-handling units (AHUs). An AHU is a large electrically-powered fan – just one can draw several kilowatts, and as a result the power used for ventilating an office building can dwarf all other electrical loads.
In an efficiently-run building, ventilation should only be supplied “on demand”. Replacing stale air with fresh (especially if it needs to be heated or cooled) can use a huge amount of energy, and so unnecessary ventilation should be avoided. Carbon dioxide acts as a proxy for air quality in general, and monitoring CO2 concentrations over time can help site managers to assess whether AHUs are running excessively, and determine whether improved control measures are required.
As with other environmental factors, a balance must be struck – too little ventilation can lead to a build-up of pollutants, with a resultant impact on building users. For example, once carbon dioxide levels exceed 1,000 parts per million, occupants start to become lethargic and concentration suffers, potentially leading to a reduction in productivity. Incorporating automatic air quality monitoring into the building controls can help to ensure that the balance between energy consumption and air quality is optimised.
Hydronic Heating and Domestic Hot Water Circuits
Hydronic heating and hot water systems are widespread in both domestic and commercial buildings. Although configurations vary widely, in most systems there is plenty of scope for improving control and operation. Monitoring of temperatures at points around the circuit can help to indicate where such improvements can be made.
Flow temperatures in heating systems can provide clues to the efficiency of operation. For example, excessive temperatures during the shoulders of the heating season can indicate poor control leading to excessive boiler cycling and setpoints being overshot. Overly high return temperatures are bad news for boiler efficiency, as well as increasing heat loss throughout the circuit. Particular patterns of flow temperature over time may indicate problems with boiler regulation or sequencing.
Figure 2 illustrates a typical “sawtooth” flow temperature from a cycling boiler – in this case it was replicated across three boilers running in parallel, leading to excessive wear and heat loss which could have been reduced by sequencing the boilers to match load.
Figure 2 - typical sawtooth flow temperature profile from a cycling boiler
Monitoring flow timings in DHW and heating circuits will help site managers to check system running against programmed timings, potentially highlighting commissioning problems. Similarly, sensors linked to thermal stores can be useful in determining how well the storage capacity is being utilised, especially if operating in conjunction with CHP or biomass boiler systems.
One important aspect of monitoring that is often neglected is the user interface. It is common for a modern building to be set up with the capability to monitor dozens of parameters, however because little thought has been given to the user-friendliness of the building management system, site managers often struggle to understand how to set up logging or extract this data for analysis. As a result, the monitoring capabilities of BMS’s are rarely exploited to anything like their full potential, and opportunities for saving energy are lost.
With the rapid growth in low-cost internet-based devices, BMS manufacturers have a major opportunity to improve the usability of their systems by integrating them with the technology we use every day. Controls and monitoring tools with Wi-Fi technology have the advantages of flexibility and rapid deployment, and with the development of common communication standards they will have the capability to interface with a wide range of portable devices.
In commercial settings, building management systems can already be interrogated over wireless networks using tablets and smartphones – a capability that, with well-designed applications, encourages more use of the system. On the domestic side, there are an increasing number of systems offering internet monitoring and control of heating and hot water – a real boon for householders who are frequently away from home.
Plug-in power monitors have been available for many years, facilitating an understanding of how individual appliances consume electricity. Some can now be connected to wireless networks, and in conjunction with the use of smart metering, potentially allow a detailed picture of patterns of energy use to be built up over a site.
A comprehensive energy monitoring strategy should extend beyond reading the main electricity and gas meters, and exploit the technologies already available for analysing other metrics related to the build environment. With the appropriate software and a basic understanding of the configuration of the building services on site, the scope for energy and cost savings increases dramatically.
Andy Smale is Technical Director with independent energy consultants Expert Energy, working with public and private-sector organisations to reduce costs and carbon emissions through improved energy management.