blockPredictedOutletTemperature

Information

The waterside economizer (WSE) is enabled or disabled based on the predicted WSE heat exchanger (HX) leaving water temperature, y. This block predicts y based on current plant load and ambient wet bulb temperature with respect to the design conditions, as described in ASHRAE Guideline 36-2021, section 5.20.3.1.

The block calculates the predicted WSE output temperature y as a sum of these three components:

• Current outdoor air wet bulb temperature TOutWet.
• Predicted heat exchanger approach at current part load flow, which equals the product of the design heat exchanger approach heaExcAppDes and the lesser of 1 and predicted heat exchanger part load ratio (PLRHX). PRLHX is a ratio of the current chilled water flow rate for primary-only plants or the current secondary chilled water flow rate for primary-secondary plants, VChiWat_flow, divided by the design HX chilled water flow rate VHeaExcDes_flow.
• Predicted cooling tower approach, which is a sum of the:
  • Product of the tuning parameter uTunPar and the difference between the design TOutWetDes and current wetbulb temperatures TOutWet. The tuning parameter uTunPar is an output from the Buildings.Controls.OBC.ASHRAE.G36.Plants.Chillers.Economizers.Subsequences.Tuning sequence.
  • Design cooling tower approach cooTowAppDes.

Parameters

Connectors

Revisions

• October 13, 2018, by Milica Grahovac:
  First implementation.