blockController

Information

The chiller plant control sequence is implemented according to ASHRAE Guideline 36-2021. It is composed by the subsequences in this package. The applicability of some sequences is listed in the table below. The yes means that the sequence is applicable to the system type.

1. Plant reset

In Guideline 36-2021, the sequences for following types of plant have been specified. However, they have not yet been implemented in this library.

• Primary-only system serving a single large load, e.g. large AHU,
• Primary-secondary systems where there are any coil pumps,
• Plants with series chillers.

2. Head pressure control

If there is the head pressure control signal from chiller, the sequence is not needed. In Guideline 36-2021, it assumes:

• The plants with fixed speed condenser water pumps do not have waterside economizer.
• If the plants have variable speed condenser water pumps and have waterside economizer, the condenser water pumps are headered.

The sequence is not applicable to the plants with air-cooled chillers.

3. Minimum chilled water flow

In Guideline 36-2021, the sequences for the following types of plants have not been specified.

• Plants with primary-secondary systems

4. Primary chilled water (CHW) pump control

In Guideline 36-2021, the sequences for the following types of plants have been specified. However, they have not yet been implemented in this library.

• Plants with series chiller, section 5.20.6.4 and 5.20.6.5.
• Primary-secondary plants and primary-only plants where the primary pump speed is not controlled to maintain differential pressure, section 5.20.6.13 and 5.20.6.14.
• Primary-only plants and primary-secondary plants with variable speed primary pumps that are intended to operate at a fixed speed, section 5.20.6.15.
• Variable primary-variable secondary plants with primary and secondary loop flow meters, section 5.20.6.16.
• Variable primary-variable secondary plants with a flow meter in the decoupler, section 5.20.6.17.
• Variable primary-variable secondary plants without flow meters from which to deduce decoupler flow, section 5.20.6.18.

5. Secondary chilled water pumps control

In Guideline 36-2021, the secondary chilled water pumps controls have been specified. However, they have not yet been implemented in this library, section 5.20.7.

6. Condenser water (CW) pumps control

For the headered condenser water pumps, the sequence assumes that all the pumps have same size. In Guideline 36-2021, the sequences for the following types of plants have not been specified.

• Plants with the series chiller

The sequence is not applicable to the plants with air-cooled chillers.

7. Chiller staging control

In Guideline 36-2021, the sequences for the following types of plants have been specified. However, they have not yet been implemented in this library.

• Water-cooled primary-only parallel chiller plants with headered CHW pumps and dedicated CW pumps, section 5.20.4.18 and 5.20.4.19.
• Water-cooled primary-only parallel chiller plants with dedicated CHW pumps and headered CW pumps or air-cooled primary-only parallel chilled plants with dedicated chilled water pumps, section 5.20.4.20 and 5.20.4.21.
• Water-cooled primary-only parallel chiller plants with dedicated CHW pumps and dedicated CW pumps, section 5.20.4.22 and 5.20.4.23.
• Water-cooled primary-secondary parallel chiller plants with headered primary CHW pumps and headered CW pumps or air-cooled primary-secondary parallel plants with headered CHW pumps, section 5.20.4.24 and 5.20.4.25.
• Water-cooled primary-secondary parallel chiller plants with headered primary CHW pumps and dedicated CW pumps, section 5.20.4.26 and 5.20.4.27.
• Water-cooled primary-secondary parallel chiller plants with dedicated primary CHW pumps and headered CW pumps or air-cooled primary-secondary parallel chiller plants with dedicated primary CHW pumps, section 5.20.4.28 and 5.20.4.29.
• Water-cooled primary-secondary parallel chiller plants with dedicated primary CHW pumps and dedicated CW pumps, section 5.20.4.30 and 5.20.4.31.
• Water-cooled primary-only series chiller plants with headered CW pumps or air-cooled primary-only series chiller plants, section 5.20.4.32 and 5.20.4.33.
• Water-cooled primary-only series chiller plants with dedicated CW pumps, section 5.20.4.34 and 5.20.4.35.

8. Cooling tower control

In the current implementation, the tower sequence assumes that the cells are enabled in the order as it is labelled, meaning that it enables the cells as cell 1, 2, 3, etc. Note from the Guideline 36-2021,

• The tower control sequence is applicable to the plants with dynamic load profiles, i.e. those for which PLR may change by more than approximately 25% in any hour, for controlling condenser water return temperature.
• It is not applicable for the plants where 2-position tower bypass control valves are needed to prevent tower freezing.

In Guideline 36-2021, the sequences for the following types of plants have been specified. However, they have not yet been implemented in this library.

• Plants with cooling tower fan speed control, for controlling the condenser water supply temperature, section 5.20.12.2.b.

The sequence is not applicable to the plants with air-cooled chillers.

9. Device lead-lag

The devices lead-lag control is not implemented.

Parameters

Connectors

Components

Revisions

• August 30, 2021, by Jianjun Hu:
  Cleaned implementation and added documentation.
• May 30, 2020, by Milica Grahovac:
  First implementation.