Buffer Control Mode and Configurations

Depending on the value of the parameter CFG-01, the buffer control mode will be:


Charging control means that the buffer will be charged by the controlled heat generators as soon as it cannot provide the temperature requested by the heat consumers. In this configuration the buffer can be loaded to a certain level, depending on the number of connected sensors. The buffer lower sensor “BufLowerTemp” is mandatory for this configuration. For a staged loading you can configure up to three middle sensors and connect up to four bypass valves – see section Buffer Charging Control.


Discharging control means, that the buffer will not be charged by the controlled heat generators. It will be charged only by uncontrolled heat sources like solar panels, heat pumps, solid fuel boilers, combined heat and power plants (CHPs)… In this case the buffer will be always loaded up to the maximum upper temperature limit. The buffer lower sensor “BufLowerTemp” is optional in this case.


The buffer configuration depends on the number of sensors connected and the buffer control mode, as shown in the next figures.

  1. For discharging control the simplest configuration with an upper sensor is sufficient. All the other sensor inputs can stay on their default value “999”.
  2. If the buffer has two charging inputs or heat exchangers, you can get a better stratification of the buffer temperatures levels. This is recommended if the buffer is relatively big compared to the solar panel surface (> 100 litres per m2). It also allows higher upper temperatures (typically +10 K) even in transition periods with less solar radiation.

For this configuration we need a minimum of three sensors and one bypass valve.

  1. Configurations with more charging levels are recommended to increase energy efficiency in multivalent systems with buffer charging control, where the buffer is charged by the controlled heat generators consuming conventional fuel. This can be systems with solar panels, boilers, CHP or heat pumps. This is the case when using weather forecast or any other external energy source where we can predict the availability. Depending on the predicted availability of the renewable energy source we will charge the buffer with conventional fuel only up to a higher level depending of the amount of predicted renewable energy for the next period.

For this configuration the user has to add own code to override the input “BufLoadLevel” depending on the available renewable energy.


Simple configuration

3 sensors and
two bypass valves

Maximum configuration 5 sensors and 4 bypass valves

Configuration for simple solar or heat pump buffer, where the buffer is always charged down to the lowest sensor.

Buffer with two stages charging. Depending on the input “BufLoadLevel” the buffer can be charged only in the upper part or completely. For this configuration you need two bypass valves

Can be used in complex buffer strategies, where the charging level depends on weather or other external energy forecasts. The higher the expected external energy for the next day will be, the less conventional energy has to be spent for buffer charging.

Fig. 1.   Buffer configurations for charging control


Discharging control configuration

For discharging control you always need a changeover valve. The external heat sources are not controlled by the buffer.

Fig. 2.   Buffer configuration for discharging control


Table 1.   Parameter List

Description

Value Range

Default Value

Unit

CFG-01: charging/ discharging control

1 = charging control

2 = discharging control

1/ 2

2

-