Scope

Client X aims to decrease the carbon emissions and energy usage of one of their buildings by at least 20%. Company Y has been tasked with designing the refurbished energy system for this project. In pursuit of the most cost-effective solution for these refurbishment requirements, Company Y opts to utilize the Hysopt Optimizer software to validate their strategies.

The building

The building in question is a residential care center located near the city of Antwerp, Belgium.

Residential Care Center X was constructed in 1980. Over the years, the building has undergone significant upgrades in insulation. Single-glazed windows have been replaced with triple-glazed windows, resulting in a substantial decrease in the building's energy demand. However, the heating system has remained largely unchanged since its original installation.

Opening your first model

• Open your company’s folder structure by clicking on create/open.

Open

Figure 1

• Go to the project folder to find the trial license exercise.

• To avoid changes in the exercise starting point, make your own personal folder in the Trial License Exercise folder(under Project)

Open

Figure 2

Open "0. Residential Care Centre - START" from the Hysopt Trial Exercise Folder on your company account. Make a copy of this model and place it in your personal folder. You can copy-paste the entire model by pressing on the highlighted button in Figure 3 (Upper left corner of Hysopt interface).

A pop-up will open and from there select your personal folder by pressing on the location button. Do not forget to press select in the lower right corner to select the folder where you want to copy the model to.

Make sure to press save. Once save is selected, the copied model will automatically be opened.

Quick Hysopt operation guide + explanation

The Hysopt software enables engineers to correctly design and study heating and//or cooling systems in a detailed and correct way. Hysopt models use commonly used HVAC components(Base circuits (BC)) to enable quick system modelling.

The different Base Circuits can be selected from an extensive library for heating, cooling and control Base Circuits. For this exercise we will only need the heating and control library. The different libraries can always be found on the left side of the screen.

The user can select Base circuits from these libraries and simply drag and drop them on the canvas. The different Base circuits should always be connected to each other. Heating and cooling Base Circuits should be connected to each other with pipes. A heating pipe is visualized by the number 3 on figure 6. Control base circuits should be connected to each other with control signal lines.

To draw either heating or cooling pipes press “D” on your keyboard while you the appropriate library is selected. To select a library, simply click on the library button logo, you can also cycle through these libraries by pressing N.

Analysis of building prior to refurbishments

Hysopt model

The current heating system of the building comprises two boilers (2 on figure 6). These boilers are low water content boilers and thus require a certain minimum flow. They are connected to the main heating collector through a low loss header, which separates them from the main heating system.

Since every HVAC system has control in place that will determine it’s behavior, Hysopt makes it possible to add control strategies to all Base circuits. Here the boilers are controlled by a Cascade controller (1 on figure 6)

Connected to this header is a central heating collector. The main building's end units include radiator circuits, DHW calorifiers, and some local cassette units (ventilo-convectors). Additionally, from the main heating collector, a sub-collector is connected to supply heat to an annex building (circuit 7).

The sub station collector consists of two DHW circuits, a radiator circuit and a small air handling unit with only a single heating coil.

The gas consumption of the two condensing boilers was measured in 2023 and amounted to:

1,110,299 kWh/year.

The load of the energy system was calibrated to match this gas consumption. This process is possible because of all of the end-units were retained from prior to the structural upgrades. The calibrated model has a yearly gas consumption of 1066 MWh/year. On figure [9], the monthly gas consumption of the boilers is visualized. Since the boilers are cascade controlled, the second cascade boiler will only be activated at system peak loads. This is indicated by the significantly lower gas consumption of the second cascade boiler (purple).

The different radiator circuits are connected to the main heating collector. The entire circuit is modelled as a single characteristic radiator. Modelling the entire radiator circuit would make the model unnecessarily complex for the goal of this exercise.

The radiator circuit is controlled in order to achieve 21°C room temperatures between 8 and 18h. The wanted room temperature is lowered at night to 16°C.

All radiator circuits are variable temperature circuits (VT). They use an active mixing distribution circuit ,where the supply temperature to the radiators is changed by using a heating curve. The heating curve changes the wanted supply temperature in function of the environmental temperature. The environmental temperatures during simulation are based on real climatic data from 2023 in Antwerp. There are a lot of available weather profiles to match your project’s location.

The DHW system is controlled to maintain 60°C in your DHW storage tank. Due to local requirements, the DHW system is heated to 70°C once per day. The boiler system takes this daily requirement into account and temporarily increases the wanted supply temperature to the building accordingly. During other instances, the boiler supply temperature is also controlled with a heating curve.

System check - Hydraulic validation

Before we can do any analysis on the model, the Hysopt- user should always verify if the system is modelled correctly and if there were any hydraulic errors made in the design. This can be done very easily by the integrated system check functionality. The system check button can be found on the top of the Hysopt canvas and is visualized on figure 13. Press the system check button.

After you press the System check button, a pop up window opens that shows you an indication of the system was modelled correctly. As can be seen from figure 14, there are still hydraulic errors present in the model and these should be removed before analyzing the system further. On the pop-up window, press the close button.

All the errors and warnings are then visualized on the canvas in red and yellow. The red colored base circuits indicate hydraulic errors and the yellow colored base circuits indicate warnings about sub-optimal hydraulic design. If the user hovers over these base circuits with the cursor, the error/warning message is displayed on the canvas, indicating the root cause of the error.

The causes of the corresponding errors are listed below:

1. There is no pump providing head for the collector bypass.

2. The low loss header separating the main building from the annex building is connected at the wrong side of the distribution circuit.

   1. This results in the main annex feed pump being connected in line with the collector pumps of the annex building.

3. The pumps of the active mixing distribution BC’s are connected in line with pumps upstream of these base circuits.

   1. By adding an extra bypass between the two pumps, the two pumps will not interfere with each other.

4. For the ventilo-convectors' circuit and the DHW circuit there are pumps in line.

Solving hydraulic issues

1. Remove the collector bypass.

   1. Click on the collector bypass BC.

   2. Press Delete on keyboard.

   3. Do the same for the pipe that was previously used to connect the header bypass to the heating collector

2. Change the position of the low loss header.

   1. Click on the low loss header base circuit

   2. Press Delete on keyboard.

   3. Since the previous step also deletes the connecting pipes. The pipes should be redrawn.

      • Press “D” on keyboard. heating pipes can now be drawn.

      • Click on unconnected node of the appropriate connection of the pump. Afterwards, click on the unconnected node of the sensor BC.

      • Click on the pipe that was just drawn. On the left side of the screen, the parameter entry window appears. Since the default value of pipe length is zero, this parameter should be changed when drawing in pipes. Fill in 1 m as pipe length, then press the adjacent lock symbol, so that it turns red. Make sure to repeat this step when you draw any pipes during this exercise.

         

         

   4. Replace a sensor by a low loss header on the downstream side of the active mixing base circuit.

      1. press on the sensor that you wish to replace with the low loss header. (Sensor to be replaced indicated on the figure below).

      2. press Cntrl+H

      3. A pop up window opens, that shows you the heating library.

      4. Under Header configuration, click on the low loss header and then on Apply. The sensor BC is now changed to a low loss header

3. Replace the Active mixing base circuit with the active mixing with primary bypass base circuit.

   1. Select all Active mixing circuits connected to the main building collector.

   2. Press and hold Cntrl button. While the button is being pressed, manually click on all active mixing circuits connected to the main building collector. Once every BC is selected, release the Cntrl button (see figure below, green color indicates the selected BC’s).

   3. Press Cntrl+H.

   4. Under distribution circuits, click on Mixing circuit with primary bypass.

4. Delete the most upstream(= closest pump to production) pump on the DHW (circuit 8 on main building collector) and ventilo-convector circuit (circuit 6 on main building collector).

   1. Delete the pumps.

   2. Reconnect with new heating pipes.

   3. Fill in 1 m pipe length for all newly drawn pipes.

5. Press system check again to ensure all hydraulic errors have been resolved.

Compute design flows

The next step of the design process in Hysopt is to compute all design volume flows and heat flows.

The way the software deals with this is by propagating the necessary heat flows from the end units to the production units. To make sure this happens correctly, the Hysopt user needs to fill in the design heat flow and the design temperature regime for every end-unit. For this example, this was already prepared but this can be easily verified.

1. Click on one of the end units from one of the radiator circuits connected to the main building collector. For circuit 4, the design heat flow is 150 kW with a design temperature regime of 80/60°C. The user can verify that 150 kW with a temperature delta of 20°C leads to a volume flow of 6.63 m³/h.

2. Press the compute design flow button in the top banner(next to the system check button we have used before).

3. The system alerts the user of an error still present in the model. This error relates to the propagation of temperatures and heat flows through the model and is therefore only visualised here.

4. Look at the start of the main building’s heating collector. The total design heat demand for the building is 1380 kW. Note the 62°C return temperature regime. This value was deduced by the use of energy and mass balances at every node in the system, and is therefore the only correct value for the design temperature regime.

Pipe selection

Hysopt uses pipe selection criteria based on industry standards such as:

• ISSO (International)

• WTCB (Belgium & Netherlands)

• CIBSE (England)

• Custom

The standard that is used can be changed by the Hysopt user in the model settings. Verify that the local standard (WTCB is used for pipe selection).

1. Click on Model settings

2. In the top banner of the pop-up window, click on pipes.

3. Verify that under pressure profile, WTCB 14 based is selected.

To let the software select all appropriate pipe sizes in your model, press the pipe selection button.

A pop-up window opens. Press Apply

Go to one of the pipes that you drew during a previous part of the exercise. Verify that the pipe size was changed accordingly.

If it is not wanted that the software calculates the required pipe size, the user can always lock a custom pipe size on every pipe by pressing the lock button. A red lock icon indicates a locked parameter.

Optimize system components

This function calculates all pressure related equipment such as required pump head and required pressure drop over all balance valves.

Press on optimize system components.

There is still an error in the model. Press close on the pop up window.

Press E to automatically jump to the next error.

The selected pump is too small. Unlock the pump curve to make recalculation by the software possible. If the pump curve is not visible, activate the “Simulation layer” to visualize more advanced parameters. The simulation layer can be activated by pressing the simulation layer button. If the simulation layer is active, the button turns blue. The simulation layer is indicated as active on figure 38.

Press on optimize system components again.

Simulation

The model is now ready for simulation. In order to compare the gas usage of the boilers in this model with the measured gas usage of the boilers in real life. We will need to simulate this model for a full year.

1. Press on the simulate button.

2. Verify the simulation duration is 1 year. Otherwise change this parameter. Verify the start date as well.

3. Verify the simulation location is Antwerpen-Deurne. This is the closest location to our building from which the real weather data is available in the software.

4. Press Start

5. Wait until completion of the simulation

Boiler efficiency analysis

Go to the boilers in your model. Hover over the Gas-metering box close to the boilers. The combined gas usage of the two boilers is visualized here. The gas-usage of the boilers is predetermined by both the building heat load as the efficiency of the boilers. The efficiency of the boilers is in turn determined by the return temperatures they are subjected to.

Once this is verified, hover over the upper boiler first. This is the lead boiler in the boiler cascade. The weighted average of the boiler efficiency is shown once you hover the boiler base circuit. The efficiency of the boiler is 87.5%. This is low for condensing boilers. This is because the return temperature going to the boilers is on average very high.

Secondly, verify your building load on the sensor BC on the downstream side of the boiler low loss header. Hover with the cursor over the sensor and check the thermal energy. This is the building’s thermal energy load that can be delivered by the energy centre. Note it down because you will need this at a later instance. Since we made changes to our calibrated model, the user should check after every optimization step check if the building’s thermal load is still able to be delivered. If it is not reached, the optimization is not achieving similar comfort level’s as the reference case.

The power-weighted return temperature (Here 58.3°C for return temperature upstream of boiler low loss header) is visualized on every sensor when the cursor hovers over a sensor. Condensing boilers typically need return temperatures below 50°C in order for the condensing of the water content in the air. More information about this temperature criteria can be found in the Hysopt E-Academy.

The reasons for this return temperature is so high are:

• The mixing circuit with primary bypass base circuit also leads to additional mixing of hot supply temperature water back into the return.

• The low loss header at the boilers, to ensure the boilers of minimal flow. The presence of this low loss header results in mixing hot supply water back in to the boiler return if there is a mismatch between primary and secondary volume flow rate.

• The low loss header separating the primary building from the annex building.

• The Passive dividing circuits for the ventilo-convectors and AHU cause too high return temperatures.

  • (Check this by hovering over the sensors placed in these circuits)

To resolve these low boiler efficiencies partially, following steps are proposed.

1. Remove the highlighted primary pumps.

2. Change the Mixing circuits with primary bypass by active mixing circuits.

3. Add flow rate control to the primary pumps for both the low loss headers.

   1. Insert an example model on to your canvas. (upper left banner)

   2. Select Low loss header control Model

      1. Press insert

      2. large grey box appears on your canvas.

      3. Move it to an empty space on your canvas.

      4. On the top left corner of the banner press paste.

      5. We will replace the boilers system from the our previous model with the boiler system of the inserted model with the low loss header control. At the boiler low loss header of your initial simulated model, delete everything upstream of the main building heating collector. (Indicated on figure 46)

      6. Select everything on the upstream part of the main building collector of the inserted model and press Cntrl + C.

      7. Press Cntrl+ V to paste this part on another place on your canvas.

      8. On the top left corner of the banner press paste.

      9. Connect this part to the main building collector of your initial model.

      10. Do the same for the low loss header control of the low loss header between the main building and the annex building collector.

      11. Connect the control wires to the appropriate sensor outputs.

      12. Delete the inserted model again.

4. Change for the ventilo-convectors and DHW (main building collector) and the air handling unit (sub-collector annex building) the passive dividing circuit to throttling circuit.

   1. Select the three passive dividing circuits (highlighted on figure 47 in green) (Keep Cntrl pressed while clicking on the three base circuits)

   2. Press Cntrl+H

   3. Under distribution circuits, select throttle circuit and then apply.

5. Redo pipe selection and optimize system component steps.

   1. If you get an error at the collector pump for the ventilo-convector circuit. Unlock the pump curve and restart the optimize system component step.

6. Simulate the model again for the same period and duration.

The boiler performance should have increased to approximately 90% with these simple measures. However, the boiler performance can be increased even further by lowering the heating curve of the system and in turn of the boiler as much as possible.

Downsizing - Utilizing legacy oversizing of end-units

Since the ultimate goal of this exercise is to save carbon emissions, we want to verify if our building is able to deal with lowered supply temperatures. We want to check if the heating system is still able to cover the heating demand if lower supply temperatures are used in the system. Since we are working in a calibrated model, meeting the building energy demand is a sufficient criteria.

This is also necessary to use heat pumps efficiently. Since heat pump performance is partly determined by system temperatures, going to lower system temperature levels will be beneficial for the overall performance of the installation.

Radiator circuits main building

Due to the building refurbishments, the original heat load of the radiator circuits was strongly reduced.

To indicate this, click on the base circuit for a zone. The design load of the building zone was changed to be 20 % of the installed power capacity for that zone. This indicates that providing the radiator circuits with lower supply temperatures while still delivering the desired heat load will be possible for these circuits. However this should be checked.

Since every heating circuit has a separate heating curve, we will combine them into one., which will make future changes easier.

• Select all heating curves of the active mixing circuits for the heating curves. (Do not delete heating curve of circuit 7)

• Press Delete

• Connect the heating curve of the annex building active mixing circuit (circuit 7), to every PI controller’s setpoint control connection(this was were the recently deleted heating curves were connected). To draw control lines, click on the control library button and then press “D” on your keyboard”. To draw lines click once on the canvas on the start point of the control line and click a second time on the end point of the control line. Make sure that all drawn control lines are connected to each other. A control line start or end point is indicated by a black node.

Example:

We will link the heating curve of the production to the system heating curve to avoid mistakes. Example given in figure below:

• replace old boiler heating curve by function expression control block

• change value parameter x to “x+2”. This way the boiler heating curve will always be 2 degrees higher than the system heating curve. Make sure the simulation layer is still activated for the execution of this step.

• Connect the system heating curve to the input of the function expression block. This Base circuit is found in control library under Operators.

Now we will lower the initial system heating curve to check if the system is able to deliver the required building load at lower temperatures. Since the annex building was already designed for a temperature regime of 60/40/20°C we will try to lower the radiator circuits of the main building to the same temperature level.

• Click on the heating curve of the main building radiators

• On the left side of the screen click on the icon that is highlighted on figure 53.

• Change the wanted water temperature at -5°C environment temperature from 70°C to 60°C.

• Press save

Ventilo-convectors main building

Open the heating curve close to the ventilo-convector equivalent end unit. This curve is not a real heating curve but is just an outside temperature dependent curve.

The installed ventilo-convector capacity is significantly oversized compared to the building load of 2023 (considering all the building refurbishments). This can be understood by looking at the maximum “Water Temperature”, which is equal to 0.5 at -10°C ambient temperature.

The output of this heating curve block is then multiplied by the design capacity of the installed ventilo convectors (150) to achieve a wanted heating output of the ventilo-convector base circuit.

• Click on the ventilo convector BC.

• Press Cntrl + Shift + R, a Change regime and power pop-up opens.

• For target supply and return temperature fill in 60 and 48. (The 48°C return temperature was chosen in order to maintain flow rate levels in supply pipes, as to not need pipe size and pump size changes).

• As you can see the design heat flow was recalculated for the ventilo-convectors with the new supply and return temperatures. The Design heat flow output was changed from 150 kW to 91.216 kW.

• Do the same for all the end units of all the radiator circuits of the main building. The design heat output should have been changed to the following parameters.

• Delete for the annex building heating circuit (circuit 7) the overide supply temperature of 80°C in the active mixing base circuit.

  • Click on the active mixing BC and delete the 80°C from the overide supply temperature parameter entry window.

DHW Main building + DHW Annex building

DHW is required to be operated with temporarily raised temperatures (75°C). However, these high temperatures are not wanted for the implementation of air-sourced heat pumps (ASHP).

A possible solution is to implement a booster HP for all DHW circuits. A booster HP is used to locally increase temperatures of the DHW while maintaining the possibility for lower system temperatures at other points in the HVAC system. Since we have three DHW calorifiers present in the system, a good idea would be to combine them for the booster HP.

Implementation of a Booster HP for DHW

insert “DHW on Booster HP” model in the exercise folder into the current canvas.

Delete all old DHW circuits (both the DHW of the main building collector (=circuit 8) as the two DHW circuits on the annex building’s sub collector) and connect the inserted model to the main building collector. Make sure to reconnect all the necessary pipes as shown in figure below. To draw collector pipes, press on the button indicated in yellow.

Implementation of ASHP

Open the inspiration library

• On the top left corner of the screen click on the icon on the left of the Hysopt logo (1. on figure)

• A drop down window opens, click on the inspiration library (2. on figure)

We are now in the inspiration library, A lot of readily proven concepts are available for quick implementation in the Hysopt model. Since we want to go to a hybrid boiler-heat pump system we will implement a modulating heat pump with a thermal store into our existing model. In the left column, select heat pump.

• With this filtering parameter enabled, only a the possible templates remain.

• For this exercise we will use a single heat pump with heating curve therefore select the following template. For more info, the user can check the available documentation about the template when pressing on “More info”.

• To insert this template into the model, click on the insert button.

• The Paste-box appears, the user should click on the top left corner of this box.

   

• The Template is pasted in to the model. On the figure below, the different parts that should be reviewed are highlighted.

1. Read the instructions and descriptions. The user should not yet perform any action points.

2. Delete the end units from the template. As we will connect them to the existing system.

3. Delete The heating curve , since we will use the same heating curve as we used for the boilers.

4. Select all remaining parts of the template and drag them to a empty place on the canvas below the boilers.

Making a hybrid model

To implement the ASHP in the existing boiler plant room, the following steps should be taken.

1. In the heating library, under hybrid production, click on the “ reverse drag flow power node on supply”

2. Click somewhere between the ASHP and boilers on the canvas. The Base circuit should now be placed at that location.

3. Click on the Base circuit. press R once to rotate the BC so that the big arrow points upwards.

4. Remove the low loss header close to the boilers. The shunt connection in the supply pipe of the heat pump will take over the role of the low loss header in the previous simulations.

5. Draw new pipes to connect the heat pump to the existing system. The result should look something like this:

6. Click on the “reverse drag flow power node on supply” BC. Fill in 90% as a drag flow power percentage. This means that the heat pump will have 10% of the design building heat load. Fill in 60°C drag flow temperature as the boilers will now make 60°C at design conditions.

7. Execute Compute Design flows, pipe selection and optimize system components.

• Connect the setpoint for the boilers to the control node were you previously deleted the heat pump’s heating curve

8. Click on Pipe selection and afterwards on optimise system components

9. Delete the time dependent boiler heating curve for the old DHW sanitation function. As this will now be done by the HP booster. (1 on figure)

   1. Delete the Low loss header flow control as this will no longer be needed. (2 on figure). Make sure you also delete all the control connections that were previously connected to the deleted BC’s.

Selection of the optimal HP-capacity and thermal store capacity.

Hysopt enables the quick-comparison of different design options by use of the sensitivity functionality. The sensitivity functionality makes it possible to perform simulations of the system for different heat pump sizes.

The user can then easily select the appropriate design variant based on certain Key Performance Indicators.

For this exercise, we will gradually increase the heat pump capacity (and thermal storage size accordingly). This measure is done because HP with higher capacities will obviously require higher capital costs to the end client. Going to larger HP capcaities is only feasible when the contribution of the HP is proportional to the capacity increase.

To select the parameters that you want to change in the sensitivity analysis:

1. On the top bar click on the sensitivity analysis button to activate the sensitivity layer.

2. We will select the HP capacity on the Hybrid production BC. (1 on figure 69)

3. Next to the parameter: Drag flow power percentage we will press on the sensitivity button that has appeared by enabling the sensitivity layer.

4. On the thermal storage tank next to the ASHP (2 on figure 69), make sure that the sensitivity button next to the design volume parameter is colored red. (if not click on the button)

We will now go to the sensitivity input window, where we will manually choose our different design variants that should be evaluated.

• Click on the sensitivity input button

As the sensitivity input window opens, we will first visualize the two sensitivity parameters that were selected previously, namely:

1. Design Volume of the thermal storage tank

2. Drag flow power percentage , which means the relative distribution of building design load between the boilers and the heat pump. Filling in 0% will lead to the heat pump being sized for the full design load of the building.

Example: When the building design power is 100 kW. Filling in 90% will result in the selection of a heat pump of 10 kW.

To visualize these parameters input fields, click on the drop-down button on the figure. (1 on figure 71)

We will now add 5 variants were will gradually increase the ASHP capacity. Note that when increasing the ASHP capacity, the thermal store needs to increase as well to prevent cycling behavior of the heat pump.

• Click on the Add variant button (2 on figure 71)

• To keep the different variants clear, type the name visualized on figure 72 in the name input field

• Press apply

• Repeat this procedure until you can not create any more variants, make sure to name them as shown in figure 73 and the table below.

• In the different input fields that appeared when creating the different variants, take over the following combinations (2 on figure):

• Verify that the simulation duration is set for 1 year on the correct location and start time (3 on figure 73)

• Start the sensitivity analysis (4 on figure 73)

For all the variants, all the design steps are automatically completed. Wait until all loading bars turn green, indicating a finished sensitivity analysis. (All of the variants are simulated for a full year so this can take a while).

Once all the loading bars have turned green, click on the Open pareto button (1 on figure 75)

Energy analysis settings

The user can manually change different production efficiencies and prices for electricity, gas and water based on the local requirements. For the case of this exercise, the default values will be used.

In the top right corner, the Hysopt user can also change the used currency for the analysis.

Click on Next

The cost of the different optimization variants can than be filled in if known. For the case of this exercise, the user is not required to fill in any parameters. Press on Start.

The Pareto analysis window opens, where the different variants are compared to each other. We will only analyze the different variants based on energy performance and consumption. Therefore, only the energy analysis report should be opened.

• Click on Open under Energy (visualized on figure 77)

The Energy report is shown. Note that the boiler thermal power stays the same for all variants, as we chose to retaine the old boilers that were already present in the building.

The capacity for the ASHP does increase for all variants. The reference model uses a ASHP of 90 kW, the last variant uses a HP of 720 kW.

The capacity for the booster HP stays constant for all variants.

Scroll down for an in depth energy analysis and comparison of the different variants. Check which of the variants fulfill the building owner’s requirement for the energy system refurbishment.

Reminder: The owner requires a 20% carbon reduction while also achieving an energy consumption reduction of 20 %.

Solution:

Variant 2, with a 270 kW heat pump is the cheapest solution that full fills the client's needs while retaining the old existing boilers that were already present in the building.

You have now successfully finished your first Hysopt project from start to finish.