Supply chain model
In building automation and control, media, such as warm water, cold water, warm air, and cold air are generated using energy, such as oil, gas, and electricity, and distributed to consumers.
Each medium can be assigned a supply chain. The supply chain starts at the generation or handling of the medium. The distribution system then transports the medium to one or several consumers. A supply chain for building services systems comprises the following links:
The consumer supplies the energy contained in the hot water medium to the room as per the requested demand (e.g., via a radiator).
The distribution system transports the medium from the producer to the consumer and adjusts it to the individual requirements (minimum losses).
The production consists of a boiler where hot water is treated by means of energy (e.g., heating oil, gas) and provided to the process.
Supply chains of various media
The following illustration shows a schematic view of the supply chains for the media air, hot water, and cold water with their respective production (treatment), distribution (e.g., heating circuit, pre-control), and the consumers.
The supply chain for the medium electricity, which normally begins at supply or at production, if electricity is produced on-site (e.g., cogeneration plant, photovoltaic) is also shown.
A tree structure opens to the right for the individual supply chains. In other words, one or more generators supply multiple primary controllers and each primary controller for its part supplies one or more consumers or other primary controllers.
From the air supply chain point-of-view, air treatment is a part of production (handling). From the hot water and cold water point-of-view, air treatment (or air heater/cooler) belongs to consumption.
The air supply chain comprises the central air treatment plant, optionally supplemented by pressurization control and air posttreatment.
In each supply chain, the medium flows from the producer, through the distribution system to the consumer. This flow within the supply chain is referred to as the supply flow.
Supply chain structure
A supply chain consists of at least one producer and one consumer. It can also have multiple chain links, that is, producers, distributors, and consumers, and be structured as follows:
- One producer with one distributor and one consumer.
- One producer with two distributors in series and one consumer.
- One producer with two distributors in parallel and two consumers in parallel.
- Multiple producers, distributors, and consumers in parallel.
In practice, however, there are often multiple producer units, e.g., boilers with the same or similar power, or a mixture of different units, e.g., boiler combined with a solar plant and cogeneration plant (usually with additional storage units).
From the distributor and consumer point-of-view, there is only one single producer within the supply chain, the logical producer, with exactly one supply point as the interface to the distribution network. This logical producer knows nothing about the structure of the distribution network and the connected consumers. Also, neither the distributor nor the consumer knows whether the producer consists of one or multiple units.
The distributor or distribution transports the medium within the supply chain. In this process, energy losses and energy consumption of pumps and fans is to be kept to a minimum.
Conversion (transformation) of the medium, e.g., in a heat exchanger, is assigned to a supply chain of distribution. A change of temperature (e.g., pre-control in the heating circuit) is also seen as conversion. Pre-controllers can be arranged in series (cascading).
The following consumers, e.g., belong to the various supply chains:
Air treatment and air posttreatment (heating register)
Radiators (radiator, convector)
Floor heating, domestic hot water heating
Air treatment and air posttreatment (cooling register)
Cooling surface (chilled ceiling)
Air posttreatment (dampers)
HVAC consumers, other consumers
Coordinator and dispatcher
In addition to the three chain links producer, distributor, and consumer, there are the logical links named coordinator and dispatcher.
Supply chains for a room
You can define different consumer needs for a room, such as heat, refrigeration and fresh air.
The hot water supply chain exists for heat demand. The medium hot water is prepared in hot water generation and distributed via a heating circuit. The heat is emitted to the room as needed via a heating surface. If air is the carrier of heat, this is done via pre-control and air posttreatment.
The cold water supply chain exists for refrigeration demand. The medium cold water is prepared in cold water generation and distributed via a cooling circuit. The refrigeration is emitted to the room as needed via a cooling surface. If air is the carrier of refrigeration, this is done via pre-control and air posttreatment.
Fresh air demand
The need for fresh air is met by the air supply chain, where the medium is produced by the air treatment plant, distributed via the ducting, possibly adjusted to differing requirements of the room by an air posttreatment plant, and transferred to the room via air outlets.
HVAC application architecture
The HVAC application architecture contains an overall view of typical heating, ventilation and air conditioning plants with distributed applications and is based very strongly on the supply chains (energy and substance flows) in building services systems.
- The mutually standardized exchange and re-use of HVAC-relevant demand and coordination signals is possible in distributed applications.
- The HVAC application architecture structures the HVAC functions into meaningful units, interfaces and functional mechanisms.
- The HVAC application architecture is scalable and independent of product and communication standards.
HVAC system view
The consideration and definition of the HVAC application architecture and its functionality gives rise to the HVAC system view, which comprises:
- Plant (primarily HVAC plants)
- Operator interventions
- Functional units
A plant consists of partial plants, aggregates, and components, which, as a rule, form a supply chain with the chain links producer (here: boiler), distributor (pre-control, heating circuit), and consumer (radiator).
Commands are executed at each link of the chain through operating interventions via HMI commands. The impact on the plant (or the process) takes place via the corresponding function unit and automation station.
Functional units represent the software map of chain links and plant elements. The functional units contain all control, monitoring, and limiting functions that are necessary for operation.
Energy demand information can be passed on implicitly via the medium within the supply chain, e.g., if the hot water supply temperature falls because of a rise in heat consumption, more heat energy must be produced.
Information can also be represented by an explicit signal and transferred via a signal path (e.g., via a bus). The following explicit signals have been defined in the Desigo system:
Consumer to producer
A plant functional unit communicates its demand (that is, operating mode, set points) to another partial plant functional unit in the direction of the producer. The demand signal eventually arrives at the producer.
Producer to consumer
A plant informs the downstream plants about its currently effective operating state. This signal is only used as an exception and is therefore switched depending on the situation.
Producer to consumer
The producer demands a certain operating mode from a consumer. Forced signals are more the exception than the rule and are therefore not implemented in sample plants. Forced signals are used for solar plants and wood furnaces among others, where the minimum heat production cannot be controlled.
In addition to the functional units, there are two further elements that belong to the supply chain on the software side:
- Coordinator: The coordinator combines the demand signals of downstream (to supply flow direction) plants and delivers a resultant demand signal to the upstream plants. The coordinator also signalizes the operating state of the upstream plants to the downstream plants.
- Dispatcher: The dispatcher determines the demand signals for the producers on the basis of the resultant consumer demand signals. It decides which and how many producers must be activated.