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HVAC & R Skills Worskhop
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Table 1: Common methods for estimating gas use at a site without existing meters.
Typical energy stream
Air
Steam
Water
Temperature indicators
Surface measurement, infrared thermometers, SCADA / BMS data Surface
measurement, infrared thermometers, SCADA / BMS data
Surface measurement, infrared thermometers, SCADA / BMS data
However, there are situations( for safety reasons for instance) where it is beneficial to keep the energy monitoring separate from process control systems.
Guidance on how to design a SCADA system or BMS is beyond the scope of this guide. However, some suggestions are provided below regarding:
• communication technologies in metering devices
• long-term data storage
• energy management software.
Communication technologies in metering devices
Metering devices measure a parameter and generate an output. This output needs to be interpreted into a value that can be recorded by the BMS or SCADA system.
Typically a meter is connected to a data logger or programmable logic controller( PLC), which interprets the meter output and sends the value to the data acquisition server. Increasingly, metering
Equipment / flow indicators
• Differential pressure method using pitot tubes in ducts
• Equipment cycle times and operating manuals
• Fan curves and duct pressures Utility bill analysis
• Temporary ultrasonic flowmeter
• Control valve positions and valve flow characteristics
• Heat exchanger characteristics
• Equipment cycle times and operating manuals
• Empirical theoretical calculations of heat required by processes
• Utility bill analysis
• Temporary ultrasonic flowmeter
• Control valve positions and valve flow characteristics
• Heat exchanger characteristics
• Pump curves and system pressures
• Pump motor current and system pressures
• Pipe sizes
• Equipment cycle times and operating manuals
• Empirical theoretical calculations of heat required by processes
• Utility bill analysis
Example of engineering method to calculate an energy stream
Energy carried by air can be measured when the mass flow is known at two different temperatures.
The mass flow can be estimated using engineering calculations based on fan curves, along with motor power, and system characteristics such as pressure differentials and / or damper positions.
Temperatures loggers can be installed along pipework.
One approach is to look at all end-user equipment manuals to estimate the energy flow of the steam. Another is to align end-use equipment times with the firing rate of the boiler. Another is to look at steam control valve positions, using the pipe diameter, valve characteristics, and system pressures to estimate a steam balance across the system.
Energy carried by water can be measured when knowing the water mass flow and two different temperatures. The flow can be measured with a temporary ultrasonic clamp- on flowmeter, or estimated using pump curves and pump power measurements. Temperatures loggers can be installed along pipework.
devices include interpretation and communication capabilities to send data in a format directly readable by the SCADA system.
Different communication technologies are used between metering devices and SCADA / BMS systems with the most common being:
• dedicated wire connection
• microwave / VHF / UHF radio
• ethernet, Modbus, Wi-Fi
• cellular network 3G / 4G.
When selecting a communication technology for a new meter, the cheapest option is usually to select one that is consistent with the existing data acquisition system. However, wireless technologies can significantly reduce installation costs related to wiring.
Long-term data storage
Over time metering devices generate a significant amount of data that needs to be collected and stored into a database. For energy management,
data covering several years are a valuable source of information. As such, the database is a critical part of a SCADA and overall energy management system. This database( software) is stored in a computer or data centre( hardware).
There are several commercial and technical possibilities for long-term data storage. The three main technical options are:
• storage on site – data and hardware are located within the facility( the data centre may be managed by the data owner or a third party)
• storage off site in a dedicated facility( co-location for instance) – a space is leased in a facility specially designed to accommodate hardware for data storage( the data centre can be managed by the data owner or a third party)
• cloud computing – everything is outsourced to a third party data centre provider( the actual data centre can be virtually anywhere).
Appendix I provides a checklist to help with the process of selecting a data management solution.
Energy management software
Data needs to be analysed and preferably used via energy management software( software). The main benefit of software is reporting capability, and it also offers the possibility of tracking comparative performance over time of plant, buildings, process and facilities. Amongst other features, software can have alerting capabilities( via SMS or email), which can help in the early detection of energy waste.
Choosing software can be difficult due to the wide range of products and commercial offerings available. These include software-only, hardwareonly, and hybrid software and hardware products. Software can be local or cloud-based. Pricing and business models differ and include outright purchase, payments based on shared savings, or blended models.
Therefore, a clear definition of the need for energy management software is essential before you commit.
The main steps in selecting software are: 1. Define and prioritise the needs of the different services required from software. 2. Assess the existing tools and software used within the site. 3. Define needs related to real-time data and time-criticality. 4. Evaluate available technical and commercial software offerings. n
MORE INFORMATION
This month’ s Skills Workshop was adapted from the NSW Office of Environment and Heritage’ s Gas Measurement and Monitoring Guide.
For more information, visit www. environment. nsw. gov. au
PROUDLY SPONSORED BY
Next month: Gas measurement and monitoring guide part II
August 2016 | www. hvacrnation. com. au | HVAC & R Nation | 17