Author: Andrey Ushchapovsky
Heating point automation. A heat point (TP) is an installation that is designed to prepare a coolant that will be used by the consumer. The consumer in the general case is the heating system (CO) and hot water supply (DHW).
How does the preparation of the coolant take place? To explain this, let's draw an analogy between a transformer and a transformer. In fact, a transformer is 2 windings with a different number of turns, which are connected by a core, and energy from the primary winding is transferred to the secondary. Likewise, the heat point is the primary circuit in which the main coolant circulates, which is provided by the supplier of thermal energy. The primary circuit is connected to the secondary circuit, in which the consumer coolant circulates. And in the connection of the circuits, energy is transferred from the primary coolant to the secondary one.
There are 2 ways to connect control loops:
- independent;
- dependent.
With an independent connection method, the circuits are interconnected using a heat exchanger.
With the dependent method, the circuits are directly connected to each other.
The amount of energy that needs to be transferred to the secondary circuit changes due to changes in the flow rate of the primary coolant. And this process is controlled by an automatic control system (ACS). The main task of the ACS is to maintain the set temperature of the secondary coolant. As mentioned above, this is achieved by changing the flow rate of the primary coolant. The controller receives a signal from the secondary coolant temperature sensor and generates a control signal to the valve drive through which the primary coolant passes. To generate a control signal, the controller uses the PID law. By changing the position of the valve, the controller changes the flow rate of the primary heat carrier so as to maintain the temperature of the secondary heat carrier at the set value. How is the temperature setpoint formed?
There are 3 main ways to form the set temperature:
- constant - the temperature of the secondary does not change;
- weather-dependent control - the temperature outside affects the set temperature;
- calendar management - the set temperature changes according to the schedule.
Let us briefly describe each of the ways of forming the set temperature.
Constant temperature - in this case, the automatic control system does not pay attention to anything and maintains the coolant temperature at the set value all the time. This method is used for DHW systems where it is necessary to always have a constant water temperature. But this method is very uneconomical, so it is practically not used for CO.
More energy efficient is the weather-dependent formation of the set temperature. In this case, a predetermined relationship between the outdoor temperature and the specified coolant temperature in CO is used. Indeed, why do we need hot water in the pipes, if it's not so cold outside? Moreover, the dependence between temperatures is almost linear.
Calendar control, like weather control, is a way to save energy. In this case, the user of the system sets what temperature and when to maintain. That is, it creates an ACS work schedule. This method, unlike the previous one, is used for heating non-residential premises. It is mainly used to maintain a low temperature at night, when the room is not in use, and during the day, when the room is filled with people, the temperature necessary for the comfort of people. Also in the schedule, you can specify weekends or holidays, during which there is no need to use CO at full capacity.
Throughout the article, it was said that the ACS maintains the set temperature of the secondary coolant. This is always the case for hot water systems, because here you definitely need to have water at a given temperature. But for CO, you need to take into account the moment that they are used to heat indoor air. If in the building in which the TP is installed, you need to heat a lot of rooms, then yes - you need to have a coolant of a given temperature in the CO. But if there is only one heated room, then the temperature should be maintained in it. To do this, it is necessary to slightly modify the ACS operation algorithm.
Maintaining the temperature of the coolant is not the only task of the ACS TP. Another task is to maintain circulation, that is, movement, of the coolant in the circuit. In the primary circuit, this is done by the coolant supplier. But in the secondary, the self-propelled guns should deal with this.
To solve this problem, circulation pumps are used. The controller operation algorithm is designed in such a way as to generate pump operation control signals. Control signals can be both discrete and analog. A discrete control signal means that the controller turns on the pump at full power and the circulation is constantly the same. But more efficient, albeit more complex, analog pump control. In this case, the pumps operate with such a power that is sufficient to form a given pressure drop in the circuit. And for this you need to use an additional device called a frequency converter.
This article briefly described the general provisions for automating the operation of a heat point. For more detailed information about the operation of the units of the heating point, follow the release of new articles on the site.
