...
The design flow rates are separately calculated for “Cold withdraw” and “Cold deposit”. All the temperatures and thermal powers are needed. To clarify the design conditions, the user can toggle the hot key hotkey “Ctrl+O”, which shows the two full load design conditions. “Cold withdraw” is visualised in the figure on the left and “Cold deposit” in the figure on the right.
...
In the figure below the required input data is visualised to calculated calculate the volume flow rate for “Cold withdraw”.
...
The borehole temperature regime can’t be altered by the user, because the temperatures are already set for the heat exchanger. It can, however, be visualised by clicking on the pensil pencil icon, which shows a popup window shown in the figure below. Depending on the power spread between cold withdraw and the production side, the temperatures are recalculated. The outgoing cold temperature from the borehole and the ingoing hot temperature in the borehole are visualised with the blue and red dot.
...
In the figure below the required input data is visualised to calculated calculate the volume flow rate for “Cold deposit”.
...
The temperature regime of the borehole can be altered by the user by clicking on the pensil pencil icon. In the popup window shown in the figure below. The ingoing cold temperature in the borehole and the outgoing hot temperature from the borehole are visualised with the blue and red dot.
...
There are two heat exchanger in the BTES BC, a plate heat exchanger and the borehole heat exchanger. The UA-value of both heat exchangers are is calculated when the user does the calculation “Compute design flows” in Hysopt.
In the figure below the parameters of the plate heat exchanger are shown. The KV-values are needed for the pressure drop calculation on the primary and secondary side of the heat exchanger. The UA-value is only calculated for the design condition “Cold withdraw”. The user can change and lock the UA-value if the value of the heat exchanger is known. Furthermore, the heat exchanger flow type can be selected, for instance, counter flow or parallel flow.
...
If for instance the UA value for “Cold withdraw” is larger than “Cold deposit”, the temperatures for “Cold deposit” aren’t correct anymore. With that in mind, the design temperature of the soil is recalculated. This example is given in the figure below.
...
There are also two pipes inside the BC itself, visualised in the figure below. These pipes represent the length between the energy center centre with all the pumps, valves and header, and the heat exchanger (borehole tubes).
...
The information needed to select the pipes is the length and pipe type. With the information, the pipe diameter can be calculated, and if needed overwritten and locked by the user.
...
There should also be a pump on the secondary side of the BC for the operating condition “Cold withdraw”. This pump needs to overcome all the pressure drops of every active component in the operating condition “Cold withdraw” on the secondary side of the BC. The pump does not doesn’t have to overcome the pressure drop of any component on the primary side of the BC or inside the BC or , except for pressure drop on the primary secondary side of the BC because an open header is usedheat exchanger.
Pump warnings
If a pump is missing on the secondary side, an error is shown when doing a “system check”, because if there is no pump, there won’t be any cold delivered to the cooling end units.
...
A warning is also shown during a “system check” if a pump is placed on the primary side , because two pumps are in series, which is suboptimal in most cases. More info on pumps can be found in Pumps.
...
Simulation
In a simulation, controls are needed to make sure the BTES BC does what the user wants it to do. To control the BC correctly, different enable signals (green) and measuring signals (red) are implemented in the BC.
...
Pump modulation signal
If a signal between 0 and 1 is send sent to this node, the pump will modulate between 100% rpm and its minimum modulation (in default 10%). This is only the case if the pump is activated.Pump activation signal
If a signal 1 is send sent to this node, the pump is activated. If a signal 0 is send the pump is deactivated and wont won't generate any flow.Borehole temperature production side
Soil temperature
Borehole temperature end-unit side
Simulation parameters
Furthermore, there are still a few setting the user can change for simulation. To change these settings, the user should activate the simulation layer on the right side of the library.
...
After the activation, the user can see a couple more parameters, visualised in the figure below. The minimal pump head percentage and change speed are not discussed in this page because these are specific parameters for the pump itself, which is the same as in other BC’s. More info on pumps can be found in Pumps.
...
The soil capacity is the storage capacity of the wells and is expressed in J/K. If for instance the soil has a capacity of 10 GJ/K, and during a certain amount of time the soil is injected with 10 GJ of thermal energy, the soil temperature will increase by 1°C. To use an accurate capacity, the user can simulate and see how the temperatures behave and change the capacity if the temperatures change to too quickly or to too slowly. If the temperatures change to quickly the capacity should be increased , if the temperatures change to slowly the capacity should be decreased. The temperatures in simulation can be matched with measured data if the capacity and other parameters are changed correctly.
The user also has the option to overwrite the soil start temperature during the simulation. As a default, the start temperature is chosen depending on a certain sine wave and the start time of the simulation. The sine wave can be altered in the simulation mode “Sine wave”. If the user, for instance, starts it’s its simulation in the middle of the winter, the soil is filled with cold energy, therefore, will start with a low temperature..
The user should also set the thermal loss coefficient of the soil, which is needed to simulate the thermal losses accurately. The thermal loss coefficient is expressed in W/K, which means that if the stored energy has a temperature of for instance 10°C, the natural soil temperature is 11°C and the thermal loss coefficient is 1000 W/K, the overall thermal power lost to the environment is 1 kW. The thermal loss is higher if the temperature difference is larger or the thermal loss coefficient is higher. Load matching the thermal loss coefficient and the capacity is explained in the next chapter.
The simulation mode “Sine wave” means the temperatures in the soil doesn’t change depending on the injected or extracted energy. The temperatures are exactly the same as the set sine waves by the user. If this simulation mode is selected, the thermal imbalance of the soil won’t be visual by the temperatures of the soil. The pop-up window of the simulation mode “Sine wave” is shown in the figure below.
...
The thermal loss coefficient is the same as in the “Capacity mode”. The thermal loss, however, doesn’t have any impact on the temperature variation of the soil.
To set the sine wave for the soil, the user should instert insert the maximum and minimum temperature. The sine wave is set up in such a way that the minimum value is reached after the piek peak winter days and the maximum value is reached after the piek peak summer days (of an average year). The clarification is visualised in the figure below.
...
Load matching BTES
The BTES system can be load matched with measured data when it is available. When the building owner is interested in installing a BTES system, sometimes a TRT (Thermal Response Test) is used to check the application of a BTES system. This TRT can also be used to load match the BTES BC for an accurate simulation.
A TRT is used to determine the thermal properties of the ground. There is no direct way to measure ground thermal conductivity and borehole thermal resistance. The TRT is vital for designing ground source heat pumps and seasonal thermal energy storage systems. More information about it can be found in:
https://en.wikipedia.org/wiki/Thermal_response_test
An example of the TRT test is visualised in the images below.
...
This principle can be implemented and simulated in the Hysopt software. The template for it is clarified in BTES load matching and can be found in our Hysopt Inspiration Library (Hysopt Inspiration Library). The template is visualised in the image below.
...
Typical results of the TRT test are the following:
undisturbed (natural) soil temperature [°C]
average heat conductivity coefficient [W/m.K]
average heat capacity [MJ/m³.K]
borehole resistance [m.K/W]
The undisturbed (natural) soil temperature can directly be inserted in the base circuit in Hysopt. The other values aren’t directly insertable into the base circuit. They have a direct impact on the thermal loss coefficient and the capacity of the BTES system. For this reason, these 2 remaining parameters have to be load matched. The load matching can be done by using the trend function (also a typical result from a TRT).
The trend function is a logarithmic function and created for the average soil temperature trend. In the graph below, the measured data is visualised in blue and the trend function is visualised in red. The trend function is typically created without the measured data from the first 12 to 24h because only stationary behaviour should be accounted for.
...
This trend function can be imported in the software using a .csv file. When doing so, the template can be used to change the thermal loss coefficient and capacity to load match the BTES system. The image below shows the simulation data (green) and the trend date imported in the software (purple).
...
However, the load matching is only done for 1 probe. So when the user has multiple probes, the parameters should be scaled in a correct way. The correct way to scale them is explained in BTES load matching.