#920 Haystack 4 Equipment tags on a point

Leroy Simms Wed 19 May

I just noticed I have been ignoring a lint error which should probably be addressed. We have a lot of situations were we have points monitoring the power usage of a piece of equipment. These are not full blown meters but individual points which are either under a piece of equipment such as a RTU, chiller, or in an electrical panel. I would typically tag these points with the equipment they are monitoring for example:

{'chiller','elec', 'power', 'sensor', 'point'}

However, chiller will cause a warning because it is only supposed to be on an equip. This seems to be the case for most equipment tags, with the exception of pump and fan which can be on a point or an equip.

If the point is under the piece of equipment it is monitoring you may be able to use the use the equipment relationship to identify the point, but that approach cannot be used in identify what a circuit feeds in a panel unless the equip is modeled as well, which it often is not.

Is there any disadvantage of allowing these tags on a point as well as equip just like the fan and pump?

Jay Herron Thu 20 May

My advice is to remove the chiller tag from the point and either create a separate elec meter equip, or add the elec meter tags to the chiller equip. Is that a workable solution for you?

Leroy Simms Thu 20 May

Perhaps a better example might be a packaged air-cooled chiller which has power usage for the condenser fans, compressors, and total chiller as points on the chiller controller.

Options would be

  • Create sub-equip for the condenser fans and compressors placing their power points under each of them and the total chiller power point directly under the chiller.
  • Pull out each of these power points as a separate meter; however that would still require the sub-equips to reference the meter back to as loads.

Or - In my opinion the simplest solution would be to tag each point with what it is monitoring, then it doesn't matter if they are sub-equip or all under the chiller a search would identify them either way.

So the question is why should a fan or pump be different than a chiller or rtu when it comes to being able to use them on a point or equip?

Brian Frank Thu 20 May

So the question is why should a fan or pump be different than a chiller or rtu when it comes to being able to use them on a point or equip?

The difference is that the community decided several years ago that fans and pumps could be optionally modeled as either a point or an equip. So those terms must be qualified in the ontology as fan-point or fan-motor to uniquely identify the type.

But otherwise virtually all equip types have always been assumed to model an equip. For example meter, ahu, chiller, boiler all have always meant an equip type. As such the Haystack ontology treats them as unique terms in its vocabulary. For example coolingCapacity is registered as a tagOn chiller, not chiller-equip. In fact the ontology doesn't define a term called chiller-equip because chiller is defined be a subtype of equip. So the terminology is very important. Forcing everything to be qualified with a xxx-equip conjunct would be awkward and would make the vocabulary less precise IMO.

But Haystack has always recommended a specific design pattern in your use case. Whenever an equip provides elec power monitoring, then it should just act like an elec-meter and contain the associated power, energy, current, etc points as children on itself.

In your specific use case with chiller sub-components, the ontology doesn't fully describe that nesting and how to flatten it. But in the case of an AHU its very well defined so lets look at that use case. Lets say we want to model the power measurement of the discharge and return fan, then we have several options:

// flat
discharge fan elec power sensor point
return fan elec power sensor point

// fans as first class equip
discharge fan motor equip
  discharge fan elec power sensor point
return fan motor equip
  return fan elec power sensor point

// ducts + fans as first class equip
discharge duct equip
  discharge fan motor equip
    discharge fan elec power sensor point
return duct equip
   return fan motor equip
      return fan elec power sensor point

Leroy Simms Mon 24 May

Brian, I think your fan example perfectly illustrates the power and flexibility of using the equipment tag (‘fan’) at the point level. Which is exactly why I think it should be available for all equipment types rather than an exception that only applies to some equipment.

With that flexibility the same options would be available on all equipment:

//flat under a plant
chilled water plant equip
  chilled water plant elec power sensor point
  chiller elec power sensor point
  tower elec power sensor point
  condenser pump elec power sensor point

 //nested under sub-equip
chilled water plant equip
  chilled water plant elec power sensor point
  chiller equip
    chiller elec power sensor point
    compressor elec power sensor point
  coolingTower equip
    coolingTower elec power sensor point
  condenser pump equip
    condenser pump elec power sensor point

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