SAMPLING RATES | Using them in Commissioning

January 1, 2023 |

A sampling rate is a pre-determined requirement that should be specified by the Owner and Commissioning Authority at the outset of a project, usually during the OPR, detailing the percentage [%] requirement of reviews and inspections needed to be completed by the Commissioning Authority/CxA relating to documentation and site activities to ensure compliance to the project requirements.

The sampling rate is aimed at the works completed by the CxA, and the contractor should ensure that all works are reviewed and inspected [100%].

Why should sampling rates be used?

Used mainly for budget control, sampling rates, if used effectively, can cut considerable costs from the Owner’s commissioning services by a significant amount.

Cx Resource vs ProgrammeSampling Rates
Sampling Rates Resource [example]

During the Commissioning Process, depending on the facility’s complexity and as the project progresses, the requirement for the Owners Commissioning Resource increases substantially, peaking at some point during the Construction Phase.

To control the resource and costs to owners, clients, and commissioning agents can utilize a Quality-Based Sampling Process.

Where can more information be found?

The process is well defined within the ASHRAE Standard 202 [Link], where it details and provides examples for:

  • Commissioning Design Review [commissionability study]
  • Submittal/Document Reviews
  • Site Visits &
  • On-Site Testing

How, where, and when do we stipulate the requirement?

If your project has decided to utilize the Quality-Based Sampling Approach, the requirements must be considered and specified from the outset [during the Pre-Design Stage of the Commissioning Process].

As the Owner and Commissioning Authority are writing and detailing the Owners Project Document [OPR], the requirements should be included to provide the project team or tenders with correct information.

This is so that it is clearly detailed in the contract documents and the Owner/Client has fully agreed.

After the OPR is written, the same information should be clearly identified in all subsequent Commissioning Specifications and Plans.

NOTE: That this Sampling only relates to the Commissioning Authority working directly for the Owner/Client. The General/Main Contractor is expected to complete 100% sampling and inspections with their teams.

What would be covered under the Sampling Approach?

Generally, anything that would be normally reviewed or inspected would be covered. The only difference would be the quantities:

  • Owners Project Requirement Reviews
  • Commissioning Design Reviews
  • Factory Testing Document Submittals
  • Factory Testing Witnessing
  • Material/Technical Submittals relating to Commissioning
  • Check Sheets
  • Site Visits [using Check Sheets]
  •  Field/Site Acceptance Testing Submittals
  • On-Site Acceptance Testing
  • Observations
  • Final Testing and Commissioning Documentation

How to determine the Sampling Rates?

If we simply use ASHRAE as an example we can determine the Sampling Rates required pretty easily:

Submittals/Documents/Reviews

FactorGuideSample Rate
ComplexityAs the facility’s systems and components operate and need more and more integration and interconnectivity, the complexity usually increases with documentation requirements to explain how things will be tested and recorded.
Items such as Control Systems would be deemed complex.
Higher Sampling Rates required
To provide an example, we have various control systems, from a thermostat in a general corridor to full plant chiller control logics and integration with other systems and sensors.
Temperature Sensor 20%Chiller Controls 100%
Criticality/RiskEvaluate the Criticality and Risk of the systems and components. Criticality and Risk would be reviewed against impacts to the Facility, Health, and Environment if items failed or were deemed not to operate properly.Higher Sampling Rate Required
To provide an example, we have various types of criticalities and risks, from a thermostat in a general corridor to pressure control of hazardous areas.
Temperature Sensor 20%Hazardous Areas 400% [4 different reviewers, using different equipment as the risk is so high]
Submittal/Document Sampling Rate Table

ASHRAE also notes the length of the document. Shorter, less information high sampling rate against one longer and more information.

This is because, in our experience, a longer document can be a lot worse in the quality of content than a shorter one.

Construction Verification

FactorGuideSample Rate
Construction Check ListWe would look to be at and witness the first few construction checklists; this is to ensure the correct process and that the documents are being completed in the right way.
Do some spot checks to make sure the contractor is not doing a desktop inspection whilst having a cup of tea.
ASHRAE notes no sampling, but we would suggest including a % requirement to cover ourselves in case do not have much confidence in the contractors, etc
Speed of Construction/number of Scheduled ActivitiesPoints in the programme can be agreed to complete onsite inspections; these could include closing up certain ceilings/floors or covering incoming services such as power and water. Schedule out these activities to clearly define the requirements before certain works can proceed.
As we all know, it is tough to be at the call of the contractor, as usually we are told to come to the site at 11:30 am on a Sunday to inspect, schedule out predetermined times during the month when you will complete certain inspections on ‘x’ systems.
As systems get more complex, the sampling and inspection rates should increase. Much like the Submittal table above
Quantity of ComponentsThis one is pretty simple.
Only 1No. VAV box then 100% review1,000No. VAV boxes then will be a lot less.
Dependant on the quantity.1No. Component = 100%reduce the [%] as the quantity increases
Construction Verification Sampling Rate Table

Note that as with the submittal requirements: depending upon the criticality and risk that the system or component can pose, sampling could be over 100%, meaning multiple reviewers/inspectors and equipment could be needed and used.

Function/Site Testing

This requirement will be much like the Submittal requirements.

FactorGuideSample Rate
ComplexityAs the facility’s systems and components operate and need more and more integration and interconnectivity, the complexity usually increases with documentation requirements to explain how things will be tested and recorded.
Items such as Control Systems would be deemed complex.
Higher Sampling Rates required
To provide an example, we have various control systems, from a thermostat in a general corridor to full plant chiller control logics and integration with other systems and sensors.
Temperature Sensor 20%Chiller Controls 100%
CriticalityEvaluate the Criticality and Risk of the systems and components. Criticality and Risk would be reviewed against impacts to the Facility, Health, and Environment if items failed or were deemed not to operate properly.Higher Sampling Rate Required
To provide an example, we have various types of criticalities and risks, from a thermostat in a general corridor to pressure control of hazardous areas.
Temperature Sensor 20%Hazardous Areas 400% [4 different reviewers, using different equipment as the risk is so high]
Function/Site Testing Sampling Rate Table

Example tables of Sampling Rates

As we all know, each project’s requirement will be different and should be individually discussed and agreed upon with the Owner/Client Team. 

But saying that we need a basis to go from, so below provides information that can be used to start those conversations which we have previously written about in our Commissioning Plan article.

How to use Sampling Rates to CxA advantage…

If used correctly, sampling rates can be a great help to the Commissioning Manager – especially when in a competitive environment, trying to win a project, or when clients are insisting that additional resource is brought in to meet the ever-accelerating project timeline.

There is limited use of them in our experience, and people do not see the benefit they could bring if dictated and agreed on early in the project.

So how can they be used to our advantage?

Tender/Costings/Negociations:

In a tender situation, there is always the ‘Squeeze’ on costs. Clients never have the correct money or budget that we would like, and most do not have a huge understanding of the levels of resources needed or the time it takes to complete the tasks.

They want a saving so that they can tick their KPI [Key Performance Indicator]. Do they care how they get the saving?…

Probably not…

To help, Sampling Rates can be used to reduce our resource requirements whilst also providing some savings to the client and keeping our margins a bit healthier.

Instead of just offering a blanket 20% discount, which basically is a 30% reduction in quality and focus. Provide a 20% discount with an updated Resource and Sampling Rate schedule.

There are many areas we as Commissioning Managers can save money if we really want to.

Do we need to look at 100% of the fan coil units that have been evaluated and deemed no risk or zero complexity to the facility if fail?.

Accelerated Programme:

It’s always an argument; the project programme eats up all the Testing and Commissioning time allowed and sequenced.

The General Contractor then expects to meet the revised accelerated Commissioning Programme for the Commissioning Manager to bring in additional resources and work the weekends and nights.

The Client is unwilling to pay for the additional resources and accelerated costs to the Commissioning Manager, eating into our fees and contract values.

When this happens, an evaluation can be conducted that reviews the work still to complete. Create a resource table focusing upon the systems and equipment’s critical and risky areas, place the resource there first, and then move to the less critical/Risky.

Once that is understood, respond to the project with the Sampling Rate reduction needed to match the originally quoted resource levels.

Conclusion

In conclusion, sampling rates should be seriously considered on every project to provide the best experience for our clients and protect our fees and profit margins.


Related Articles

⬛ Latest Articles


⬛ Author

If you would like to know more about the author, here is my Personal Linkedin Account