CIBSE TM22 sets out a methodology for assessing the energy and systems performance of a building (CIBSE, 2006a). The procedure is based on work carried out by Field et al. (1997) and was implemented throughout the PROBE studies (discussed in Section 2.2.2), allowing energy consumption to be broken down into a number of end-use categories. These include two categories of particular interest to this EngD: (i) office equipment; and (ii) local kitchens and vending. From a sub-metering perspective; it is often not possible to disaggregate both these end-uses as they are commonly included in the same electricity sub-circuit. Hence, the commonly used term ‘small power’ is used as an end-use category throughout this thesis, accounting for office equipment and local catering equipment, as well as miscellaneous plug loads.
The methods implemented in this research project are based on CIBSE TM22 and its underlying bottom up tree-diagram approach illustrated in Figure 3-3. The level of sub- metering in a building will dictate the amount of ‘high-level’ information that can be used to initially assess the energy performance of the building. The information shown in Figure 3-3, labelled A and B can typically be obtained from a combination of readings from individual electricity meters and sub-meters. The methodology then provides a framework for estimating the expected energy consumption of individual end-uses through a bottom-up approach based on the information in boxes C through H. These are generally obtained from design documentation and an in-depth understanding of how the building is used and managed including operating hours and management characteristics. Regular reviews of bottom-up calculations must be carried out to ensure reconciliation with metered data.
Figure 3-3: CIBSE TM22 approach for analysing energy consumption in buildings
When dealing with individual items of equipment, the TM22 methodology relies on a combination of nameplate ratings and electrical load factors to estimate the actual load of the equipment. Nameplate ratings refer to the maximum load of a device and an electrical load factor is often used to convert the rated load into a more usable ‘typical’ power demand value. Although this is an appropriate method for major pieces of equipment such as chillers and fans, nameplate ratings are notoriously unrepresentative of the actual power demand of small power equipment (as discussed in Section 2.3). Moreover, electrical load factors can be difficult to accurately estimate without a detailed understanding of the installed equipment specification. As such, an alternative method was employed when assessing the power demand and electricity consumption of small power equipment (see Section 3.2.2.4).
It is worth noting, CIBSE TM22 provides a flexible framework that can be tailored to suit the specific objectives of the assessment. As such, a number of additional and harmonising methods were used throughout the research project to complement the underlying principles of CIBSE TM22. These are detailed below.
Research Methodology
3.2.2.1 Walkthrough Audit
A walk-through survey is typically the first step in any energy audit, consisting of an exploratory site visit to visually inspect each of the energy using systems (Thumann et al., 2009). Focusing on small power equipment, walkthrough surveys were used throughout this EngD to provide an assessment of the installed equipment throughout the building, allowing for detailed inventories to be produced regarding the types and quantities of installed appliances in individual building zones.
3.2.2.2 Meter Readings
Meter readings provide valuable information regarding the consumption of electricity over a given period of time. Depending on the sub-metering of a building, meter readings can provide further insight to the energy consumption of specific end-uses and/or individual zones. Sub-metering by zone is a common feature in most multi-tenanted office buildings allowing for individual tenants to be billed for their electricity consumption. This is usually based on monthly meter readings obtained by facilities managers. Buildings with Automatic Meter Reading (AMR) systems allow for electricity demand to be monitored in shorter intervals (typically half-hourly or 15-minutely). This can be particularly useful in order to analyse the variation in electricity consumption over a given day.
3.2.2.3 Power Demand Monitoring at Sub-circuit Level
When appropriate sub-metering is not available, electricity consumption can be measured at a sub-circuit level using a portable electrical energy profile logger such as ‘El Component SP Max’ (used in this research project). This piece of equipment monitors power using current and voltage transducers, and has a published accuracy of 0.25% on primary parameters. It can be used to monitor most sub-circuits by connecting current transformers to a low voltage panel or distribution board. However, there are practical limitations to the use of this monitoring technique as it is not possible to disaggregate separate end-uses that have electricity supplied through the same sub-circuit, and electricity is often supplied for lighting and small power through a single sub-circuit in office buildings (Lanzisera et al., 2013).
3.2.2.4 Power Demand Monitoring at Equipment Level
Electricity consumption and power demand can be measured and monitored at individual equipment level through the use of plug monitors with logging capabilities. According to Lanzisera et al. (2013), this novel type of monitoring is considered the best method for collecting energy data of small power equipment, providing high quality data at the device level, which can be extrapolated through the use of inventories of installed equipment to achieve higher level data. Class-1 accuracy ‘Telegesis ZigBee Plogg-ZGB’ plug monitors were used throughout this research project and have a published measurement uncertainty of <0.5%. These monitoring devices can measure and record power demand in time intervals of 1-minute, yet they have limited internal memory capabilities. In order to increase the capacity for data storage, monitored data can be wirelessly transmitted and downloaded to a computer, yet this must be located within approximately 10 metres of the ‘Ploggs’ in order to ensure
successful data transfer. Data acquired through equipment level monitoring can also be used to estimate electricity consumption for small power as an end-use by extrapolating the results using detailed inventories of the installed appliances.