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BMS - optimise the performance of BMS installations
Transcript of BMS - optimise the performance of BMS installations
Analyse BMS reports and data to optimise the performance of BMS installations
Analyse the demonstration of a BMS graphic showing the real time operation of a hydronic system. Produce a report describing the control function and the control logic of the system and the parameters necessary for effective control.
P4.1 Analyse BMS installations to obtain performance reports
P3.4 Carry out BMS software procedures to achieve required control strategies
P4.2 Analyse BMS settings to modify and adjust BMS installations
P4.3 Produce planned preventive maintenance strategies using BMS reports and data
P4.4 Produce energy management optimisation strategies using BMS reports and data
What is the purpose of the system, what is it trying to achieve?
Describe how you would obtain data from a BMS system which is used to produce a performance report.
Make reference to the remote login facility of modern BMS systems, the ease at which data can be extracted and how this can be collated into a report format, i.e. (raw data) is extract into excel format, the data is normalised data, and possible displayed in chart format etc for ease of viewing and to align to benchmarks (energy or other?).
You are a commissioning engineer who has been called to the school because their heating control valves keep failing! Described what is happening with the control system & why you think this is happening.You must make a recommendation to resolve the problem
Refer to P3.4 for guidance on achieving this credit
D3.4 Clearly and coherently discuss the fault and measures to correct the problem.
For the given brief review the BMS data provided and suggest how the maintenance activity can be planned/ initiated through the BMS. Suggest also how other preventative maintenance strategies can be assisted by using data from the BMS
For the given brief suggest how the BMS system can be used to reduce energy & carbon consumed by the building
BMS // POE Report
Post Occupancy Evaluation (POE) data is used to assess how a building’s actual performance matches the user’s needs and design targets set as well as identifying ways to improve building performance and fitness for purpose. You have obtained data from the BMS on a monthly basis for the four newly built schools, in order to assess building performance and fine tune the operation of plant and equipment in the new buildings to reduce energy consumption and improve the overall internal environment.
How is the controls set up achieving its purpose?
What parameters (inputs & logarithms) are required to make the control logic work effectively?
Logarithms (when described in the context of BMS) are calculations performed in the BMS software to relate a control output against the control action i.e. you may want to achieve a 50% balance of fresh air with return air however this may not be simply driving a damper 50% open!
Another example is weather compensation (below)
You have been tasked with minimising maintenance costs. Suggest how this maintenance activity can be planned/ initiated through the BMS.
Detail how preventative maintenance strategies can be assisted by using data from the BMS
DPS, when filter becomes clogged, resistance will increase when this reaches a preset level, replace the filter.
Current draw on motors to predict failure of motor
Run hours on fans to ensure other components have not failed.
log run hours on major plant to sequence maintenance inspections on a usage basis rather than time.
many more examples....
Energy consumption targets have been developed, these represent the level which the design team believe could be achieved.
The heating and hot water energy consumption is considerably higher at the schools ranging from 18% to 45% above the benchmark for previous schools. The teaching spaces are largely kept up to occupied temperatures at off peak times including school holidays. The average internal ‘out of hours’ space temperature (which includes overnight periods as well as school holidays) exceeds 19°C. The systems were commissioned and handed over with a setback condition of 12°C. This has had a significant impact on the overall heating and hot water energy consumption.
A biomass boiler has been installed at each site, alongside conventional gas boilers in order to reduce CO2 emissions from the heating systems. The biomass was designed to act as the lead boiler, providing 75% of the total heating demand. The contribution of the biomass is considerably lower than design aspiration (between 26-52%) therefore there is scope to improve the CO2 emissions.
Suggest how the BMS system can be used to reduce energy consumed by the heating system and how the biomass boiler can be controlled to maximise this low carbon heat source.
Room by room control, time scheduling, override switch,
Why the biomass might not be used to its optimum to discuss in class!
Specification items to facilitate this:
Consistent time steps across all data logs
pre-defined tables for descrete control systems configured during BMS commissioning
Suitable commissioning of BEMS
automatic data drops
Practical methods of setting up a controller
Each controller has to be set up individually to match the characteristics of a particular system. Although there are a number of different techniques by which stable and fast control can be achieved, the Ziegler-Nicholls method has proven to be very effective.
Instability caused by increasing the controller gain, with no 'I' or 'D' action
The procedure for selecting the settings for PID parameters, using the Ziegler-Nicholls method, is as follows:
1.Remove integral action on the controller by increasing the integral time (T i) to its maximum.
2.Remove the controller's derivative action by setting the derivation time (T D) to 0.
3.Wait until the process reaches a stable condition.
4.Reduce the proportional band (increase gain) until the instability point is reached.
5.Measure the time for one period (T n) and register the actual P-band (proportional band) setting on the controller at this point.
6.Using this setting as the start point, calculate the appropriate controller settings according to the values in Figure 5.5.6.
The technical specifications for controllers include many other terms and one that is frequently encountered is 'bumpless transfer'.
Most controllers incorporate a 'Manual' - 'Auto' switch and there can be times when certain control situations require manual control. This makes interruption of the automatic control loop necessary. Without bumpless transfer, the transfer from Auto to Manual and vice versa would mean that the control levels would be lost, unless the manual output were matched to the automatic output.
Bumpless transfer ensures that the outputs - either Manual to Auto or Auto to Manual - match, and it is only necessary to move the switch as appropriate.
Contemporary microprocessors provide the ability for some functions, which previously required a computer, to be packed into the confined space of a controller. Amongst these, was the ability to 'self-tune'. Controllers that no longer require a commissioning engineer to go through the process of setting the P I D terms have been available for many years. The self-tune controller switches to on/off control for a certain period of time. During this period it analyses the results of its responses, and calculates and sets its own P I D terms.
It used to be the case that the self-tune function could only apply itself during system start-up; once set by the controller, the P I D terms remained constant, regardless of any later changes in the process.
The modern controller can now operate what is termed an adaptive function, which not only sets the required initial P I D terms, but monitors and re-sets these terms if necessary, according to changes in the process during normal running conditions.
Such controllers are readily available and relatively inexpensive. Their use is becoming increasingly widespread, even for relatively unsophisticated control tasks.
The Ziegler-Nicholls method
The Ziegler-Nicholls frequency response method (sometimes called the critical oscillation method) is very effective in establishing controller settings for the actual load. The method uses the controller as an amplifier to reach the point of instability. At this point the whole system is operating in such a way that the temperature is fluctuating around the set point with a constant amplitude, (see Figure 5.5.5). A small increase in gain, or a reduced proportional band, will make the system unstable, and the control valve will start hunting with increasing amplitude.
Conversely, an increased proportional band will make the process more stable and the amplitude will successively be reduced. At the point of instability, the system characteristic is obtained for the actual operating conditions, including the heat exchanger, control valve, actuator, piping, and temperature sensor.
The controller settings can be determined via the Ziegler-Nicholls method by reading the time period (T n), of the temperature cycles; and the actual proportional band setting at the point of instability.
The controller settings may be adjusted further to increase stability or response. The impact of changing the setting of the PID parameters on stability, and the response of the control, is shown in Figure 5.5.7.
Optimised Free cooling
Poor Control of environments
The Building performance gap is a hot topic in our industry at present, with buildings often consuming twice as much energy as designers predicted and sometimes as much as four times the predicted consumption.
There is a great deal of research you can reference in your assignment but make sure you keep it related to BMS! How can we use controls, BMS & 'Big Data' to help tackle this issue?
Benchmarking and quantitative savings through BMS / control improvements
a BMS providers view!