Within this section, base circuits are stored that represent peripheral equipment within the system. They do not have a direct influence on the real-life energy flows, but can affect the pressure drops. Additionally, a few base circuits that affect the design conditions within the system are also stored here.
Peripheral equipment base circuits
Here, all base circuits are discussed that represent peripheral equipment. Currently, the optimiser has seven peripheral BCs:
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Fixed hydraulic resistance
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This BC is an exception in the sence that it does not represent something in particular. It’s only function is to represent a pressure drop in the system. As such, this BC can be used whenever there is no other BC that can represent the real life component or real measured pressure drop.
The BC has two parameters:
KV-value supply: A parameter for the pressure drop at the supply pipe . The KV value expresses the amount of flow for a pressure drop of 1 bar. By default, this value is set at 1 billion, effectively indicating that there is no pressure drop.
KV-value return: A parameter for the pressure drop at the return pipe. By default, this value is set at 1 billion.
Example
A possible application for the ‘Fixed hydraulic resistance’ BC is an energy meter. Energy meters have no specific BC within the Optimiser, as all information is read out on sensors. They nevertheless can create a pressure drop that might be required to take into account in the model, especially for technical studies. The ‘Fixed hydraulic resistance’ BC is then the most suitable building block to use.
Assume that we have an energy meter put in the return pipe of a real life system that generates a pressure drop of 3 kPa. In our model, we use the ‘Fixed hydraulic resistance’ BC and we implement the pressure drop by changing the the 'KV-value return' parameter.
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Sensor
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Sensors are useful BCs as they visualise system parameters captured during simulations. It is therefore good practice to place sensors in every branch of your model. It has only one parameter:
Temperature sensor integration time: This parameter determines how much weight is given to measurements previously done by the sensor. If the integration time is set at 30s or lower, the sensor will only look at the instantaneous measured temperature value. If the integration time is set higher, the sensor output value will be a weighted average between the instantaneous measurement and measurements from the past. The higher the integration time is set, the more weight the previous measurements get.
By default, this parameter has a value of 600 seconds. It’s adviced to let this parameter untouched in the system as to make sure all your sensors are working with the same time integration.
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Important: There are two exceptions to the previous advice.
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The sensor BC captures five system parameters:
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Sensor abbreviation
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Sensor output parameter
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Unit
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Tx
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Supply temperature
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°C
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V
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Volume flow rate
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m³/h
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Ty
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Return temperature
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°C
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dp
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Pressure delta
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Pa
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Q
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Heat flow
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W
All five parameters are also outputs of the BC and can therefore be used as input in your control stratey or visualisation graphs.
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Tip: If you want to work with different units in your control strategy (e.g. l/s instead of m³/h for volume flow rate), you can easily convert the output signal by multiplying it with a conversion constant (e.g. multiply by 0.2778 to convert from m³/h to l/s). |
Expansion vessel
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In closed hydronic systems, expansion vessels must be placed in order to be able to cope with varying pressure and volume levels. As liquids are quasi-incompressible fluids, pressure levels in the system are stronly affected by volume changes.
It is important to adequately design expansion vessels in order to avoid strong pressure build-up or air infiltration in the system.
The BC itself has seven parameters:
Mixture: This parameter is linked to the next one. It defines the concentration of the fluid that is mixed within the brine. By default, this parameter is set to 50%.
Brine: This parameter is linked to the previous one. It defines the fluid type that is used within the system.
The fluid type can be changed by pressing the Brine scroll-down button. The mixture composition can be changed by the mixture percentage setting. (e.g.: 30% mixture correlates to a mixture of 30% ethanol and 70% water). It is important to apply the correct fluid type as different brine mixtures have different heat transfer properties and will behave differently compared to pure water.
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By default, this parameter is set to ‘None’, implying the fluid type is pure water.
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Note that within the Optimiser, the ‘Expansion vessel’ BC can be used when the type of fluid used in the system changes. |
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In the depicted example, a heat exchanger hydronically seperates a primary circtuit with a glycol-based heating fluid from the water-based secondary heating circuit. Using the ‘Expansion vessel’ BC and by selecting the right brine & mixture, the Optimiser will take its heat transfer properties rightly into account.
System volume: The total fluid volume within the system. It can either be manually filled in by the user (but don’t forget to lock the parameter afterwards!) , or calculated by the Optimiser. When the latter is chosen, the Optimiser will calculate the total system volume by taking the propagated heat flow at the ‘Expansion vessel’ BC and by multiplying this value with the value obtained from the ‘Estimated volume per propagated kW’ parameter.
Propagated power: This is a informational parameter that cannot be changed by the user. It shows the heat flow that is propagated at the ‘Expansion vessel’ BC.
Estimated volume per propagated kW: This parameter is used to estimate the total system volume. By default, a value of 0.01 m³ is used, following the DFTK17 method which estimates that there is 10 litres per kW installed power within a system. Note that, when the ‘System volume’ parameter is locked, this parameter is not taken into account.
Maaximal static height: By default, this value is set to 0 m.
Safety valve height difference: By default, this value is set to 0 m.
System volume
The system volume is equal to the sum of the pipe volumes in the hydronic system. Make sure to add the correct pipe lengths and diameters.
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Based on the system volume, the expansion vessel design volume is calculated.
Dirt separator
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This BC is merely a placeholder for the representation of a dirt separator. It does not mimic the chemical separation proces, nor changes something to the enegy flows. Its only use within the Optimiser is to take the pressure drop into account that the dirt separator creates within the real life system. Therefore, this BC is only of importance when analysing the pump sizing and/or consumption.
The BC has only one parameter:
KV value: A parameter for the pressure drop at the dirt separator . The KV value expresses the amount of flow for a pressure drop of 1 bar. By default, this value is set to 100.
Deaerator
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For this BC, the same principles apply as for the ‘Dirt separator’ BC. It also has the same parameter.
Dirt separator/Deaerator
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For this BC, the same principles apply as for the ‘Dirt separator’ BC. It also has the same parameter.
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Here, all base circuits are discussed that are related to the design of the system. Currently, the Optimiser has three such BCs:
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Design values extractor
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This BC is rather particular as it does not have any parameters, nor does it directly affect the system in any way. The ‘Design value exctractor’ BC instead can be used to extract the design conditions that are propagated in the system. These values can then be used elsewhere in the system as input for control strategy or visualisation.
Just as for the sensors, this BC exctract the following five parameters:
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Sensor abbreviation
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Sensor output parameter
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Unit
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Tx
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Supply temperature
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°C
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V
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Volume flow rate
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m³/h
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Ty
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Return temperature
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°C
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dp
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Pressure delta
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Pa
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Q
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Heat flow
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W
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The design conditions override BC is a BC specifically designed for uncommon circumstances. It allows the user to override the design power & temperature regime that will be propagated further upstream during the ‘Compute design flows’ step. These uncommon circumstances can be for instance:
Incorrect reference or initial design condition in which the thermal power and/or temperatures were incorrectly propagated from the end-units to the production side.
Desired “diversity” or “redundancy” override. For instance when 2 end-units are used but only one of them can be activated at any point in time, never 2.
The BC has two parameters:
Power: The override design power. This value must be manually filled in & locked by the user.
Temperature regime: The override temperature regime. This value must be manually filled in & locked by the user.
A small example of the application is visualised in the figure below.
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Note that the BC should only be used when specifically needed! The incautious use of it can result in incorrect component selections and simulation results! |
Design supply temperature override for heating
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