HP & Boiler - Shunt

Owned by Jonas Cleiren (Unlicensed)
Last updated: Apr 04, 2022 by Dennis De Beuckeleer
5 min read

HP & Boiler - Reverse shunt in return - HP on/off control

Working principle

The heat pump has a reverse shunt configuration in the return pipe with the boiler. More information about the different configuration possibilities can be found in https://hysopt.atlassian.net/wiki/spaces/HRM/pages/3089204289.

The boiler is activated when the flow temperature of the system drops under 68°C, and deactivated when the flow temperature rises over 72°C. The activation also includes a check for the minimal flow rate, if the flow rate through the system is insufficient, the boiler won’t be activated. For instance, if the installation is shut down, the temperatures in the pipes will drop but the boiler won’t be activated because there is no flow through the system.

The working principle of the HP control is explained in https://hysopt.atlassian.net/wiki/spaces/HRM/pages/1247772751.

The reverse shunt connection also has a pump flow control, which measures and controls to a constant temperature difference between the ingoing temperature to the boiler and the supply temperature from the heat pump. This is further explained in the template “Pump control - Temperature control over open header - 2 points” found in https://hysopt.atlassian.net/wiki/spaces/HRM/pages/3089370633.

A Ground Source Heat Pump (GSHP) is used in this template, but an Air Source Heat Pump (ASHP) can also be used, this is further explained in .

Notices/Remarks

  • The user should lock the nominal thermal power and temperatures of the HP. If not, the software will calculate with the propagated power and return temperature from the installation.

  • When using a thermal energy storage vessel, the user should lock the temperature regime of the heat pump. If not, the software will calculate with the propagated power and return temperature from the installation. The locked temperature regime is visualised in the figure below.

  • There are default COP and power tables for the heat pump, but these can be changed by the user.

  • The user can change the design temperatures, thermal power, end units, … But keep in mind that the controls have to be changed as well. This can be done by changing the setpoint values.

  • If the user changes the power of the end-units, the thermal capacity of the heat pump doesn’t change automatically. The user should implement a correct condenser capacity corresponded with the thermal power of the condenser. The same goes for the capacity of the boiler.

More information about the HP and boiler can be found in and .

HP & Boiler - Reverse shunt in return - HP modulation

This template is a combination of the previous template “HP & Boiler - Reverse shunt in return - HP on/off control” and the template .

The modulating control of the HP can easily be changed to a stage control by replacing the heat pump part with the template .

HP & Boiler - Reverse shunt in supply - HP on/off control

The boiler is a reverse shunt configuration in the supply pipe with the heat pump. More information about the different configuration possibilities can be found in .

Furthermore, this template is similar to the previous template “HP & Boiler - Reverse shunt in return - HP on/off control”, except for the activation signal of the boiler combined with the activation signal of the boiler pump.

HP & Boiler - Reverse shunt in supply - HP modulation

This template is a combination between the previous template “HP & Boiler - Reverse shunt in supply - HP on/off control” and the template .

The modulating control of the HP can easily be changed to a stage control by replacing the heat pump part with the template .

HP & Boiler - Reverse shunt in supply - HP on/off control - LT and HT header separated

This template is similar to the previous template “HP & Boiler - Reverse shunt in supply - HP on/off control”, except in this case there is a Low Temperature (LT) and High Temperature (HT) header which are separated. The heat required for the HT header is only delivered by the boiler, not the heat pump. The HP will deliver as much heat possible to the LT header, but if the heat delivered by the HP is insufficient, the boiler will deliver the remaining required heat.

This is a good concept if the heat pump has a much lower thermal power than the design thermal power of the LT header. This way, the return temperature going to the HP is lower than the combined return temperature from the LT and HT header.

The supplied temperature of the boiler to the LT header is controlled by a 3-way modulating valve. The PI controller of the 3-way valve will make sure the supply temperature is controlled to 45°C. If the supplied temperature of the HP is already 45°C, the threeway valve is closed meaning there wont be any hot water supplied from the boiler. If the supplied temperature of the HP is lower than 45°C, the boiler will deliver the hot water required (in this case at 70°C) to deliver 45°C to the LT header.

HP & Boiler - Reverse shunt in supply - HP modulation - LT and HT header separated

This template is a combination between the previous template “HP & Boiler - Reverse shunt in supply - HP on/off control - LT and HT header separated” and the template .

The modulating control of the HP can easily be changed to a stage control by replacing the heat pump part with the template .