#874 Haystack 4.0 Chiller tag gaps

David Waterworth Mon 23 Nov 2020

The following are what I've identified as a number of gaps - based on an analysis of a large number of Australian chillers. It's likely some exist with different terminology

The most important is compressor. Each chiller has 1 or more and there are a number of compressor related points which appear in the top 20 most frequent points in our dataset. In particular the compressor amps is important for the chiller staging control straegy.

The next is fault. Almost every chiller I investigated has an enable, status, and fault point. The first two exist but I wasn't sure what to use for the latter.

Then maximum and minimum, i.e. Maximum Chilled Water Valve Position - I believe this is a setting rather than a sensor. Google uses high_limit / low_limit to distinguish between a limit/design value and an aggregation across time of a value.

Then suction as in the opposite of discharge (Compressor Discharge Pressure) {Compressor Suction Pressure}.

A number of points use design ie Design Flowrate

Then I found it difficult to express the concept of chiller staging - I'm not sure if this control strategy is unique to Australia? It's covered on Pg 29 of https://www.environment.nsw.gov.au/resources/business/150317HVACGuide.pdf

Basically you have a number of points which indicate the building load, which are termed cooling call. This might be calculated from the AHU's (i.e. each AHU has a cooling call % value and the CHWS averages them. If the load exceeds the capacity of the running stages then the system stages up (starts another compressor or chiller for example).

The CHWS then has points that represent when chillers stage up / down (the points correspond pretty closely with the guideline in the linked document). For example

Stage Up Return Water Temperature Setpoint

Stage Down Return Water Temperature Setpoint

Stage Up Delay

Stage Down Delay

Cooling Call Enabled Setpoint

Cooling Call Disabled Setpoint

Stage Up Leaving Water Temperature Setpoint

Manual Cooling Call

Master Cooling Call

Number of Compressors Running

Cooling Call On Delay

Cooling Call Off Delay

Cooling Call Disabled Setpoint

Number AHUs Calling for Cooling

Building Load

Staging Settling Time Delay Setpoint

Stage

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