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What input is needed?

Central heating and cooling system

The central heating and cooling system (also called "primary system" or "plant") uses purchased or produced energy and provides heat at a desired temperature level, supplying it in form of domestic hot water or in a heating/cooling circuit to ventilation units or heating and cooling units in the rooms (zones).

In IDA ICE, the needs of all consumers (domestic hot water use, heating/cooling coils in air handling units and local heating/cooling units in zones) is added up at every point in time during the simulation. However, it is not the heating/cooling power that is controlled locally and summed up centrally, but rather the fluid mass flow in the circuits. And the inputs for this are not made in the central system, but rather at the peripheral devices.

The data that an IDA ICE plant always needs to provide is:

• Circuit liquid type and supply temperatures (which can lead to a heat/cooling shortage in the building) 
• Circuit pressures (which can effect that local units cannot "ask" for massflow and thus can be used for central control)
• Delivered energy carrier and heat/cooling supply efficiency (which specifies how much of which type of energy must be delivered in order to supply a certain amount of thermal energy to the distribution system)
• Total auxiliary power for pumps and other equipment
• Information on which energy meters integrate the power consumed by the plant over the entire simulation period.

In the default plant, this data is provided by the following parameters:

• Circuit liquid type and supply temperatures (constant for cooling and depending on ambient air temperature for heating)
• Heating limit (outdoor air temperature below which the heating circuit switches off)
• Constant domestic hot water, boiler and chiller (COP) efficiency
• Maximum heating and cooling power (high enough to always reach the requested circuit supply temperatures)
• Domestic hot water temperature and flow schedule
• Circuit pump pressure heads and efficiencies
• Energy carrier and meter for heating and for cooling, as well as for pumps

The figure below shows how the central heating and cooling system (plant) exchanges variables with the local devices, using the example of heating circuits: A central control causes a pressure difference between the supply and return. The same pressure difference is given to all local devices. Under the influence of this pressure difference and a local control system, each local device determines “its” mass flow. The pyhsical model of the local units also calculates their return temperatures depending on local conditions (zone air or wall temperatures and heat transfer coefficients). All local massflows are "sent" back and added up for the central system. The same applies for the return temperatures, which are weighted and averaged based on the mass flows. From total massflow and temperature difference, the plant calculates the used energy and - with help of either a constant efficiency (in case of the default plant) or a detailed plant system model - the energy to be delivered.

Input and output variables for the central heating and cooling system (primary system)

Hot water tank

Cold water tank

Standard boiler

Standard chiller

Thermal solar collector field

Generic heater

Air to water heatpump

Brine to water heatpump

Combined heating and power heater

Exhaust air heatpump

Generic chiller

Brine to water chiller

Simple heat exchanger (with given temperature source)

Ground borehole

Air to brine heat exchanger

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