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Robust CHW System Design

Robust CHW System Design

Quality, Consequences and the Construction Industrial Complex (part 220).

Last year I was asked to advise on how to design and implement a “robust, low maintenance” Chilled Water System.

This client wanted a CHW system design to support a mission critical building plus a “super luxury” hotel. The clients past experience with systems maintenance and operation was horrific.

The design solution had to solve for two objectives:

  1. Persistence of performance.
  2. Low maintenance in terms of call backs and building user complaints.

My answer was long and expensive but the short form answer was to include the following:

  1. Reverse return pipework to provide a level of “self balancing”.
  2. Primary secondary low loss header for hydraulic separation of chilled water production and secondary distribution system.
  3. Configure chillers in parallel and size for redundancy.
  4. Depending on climate zone, consider a separate chiller sized for winter loads to optimize chiller operational efficiency.
  5. A large, inline air separator in the plantroom and AAV’s at the top of each pipework riser.
  6. Verified, flushing and water treatment to BSRIA standards.
  7. Cyclonic in line filter located in the plantroom to ensure continual, high quality water in circulation.
  8. VFD’s on all CHW pumps.
  9. Symmetrical distribution pipework configuration wherever possible.
  10. Assuming FCU’s in the hotel, eliminate individual strainers for each FCU.
  11. Strainers with micro mesh and isolating valves plus “binder points” at each floor take off from the riser.
  12. Commissioning valve at each floor take off from the riser to verify floor flow rates.
  13. Assuming some degree of symmetrical FCU pipework configuration, consider eliminating balancing valves at each FCU.
  14. For each FCU only install necessary isolating valves, a PICV for control plus “binder points” across each coil for diagnostic use. That’s it, no more.
  15. Explicitly specify certified Testing, Adjusting & Balancing plus systems Commissioning with 100% verification.
  16. Manage system BMS alarms and maintenance based on empirical KPI’s from the CHW system commissioning process.

This assignment came about because the client had been “burned’ several times before and came to accept that the mission trumped capital costs going forwards. Yes, this is a rare beast indeed!

On a ‘normal project’, the advice above would not survive value engineering or contractors mischief during the submittal process.

IMHO, developers and owners are their own worst enemy when it comes to designing for systems that actually work. It normally takes a bad and expensive experience to move to a new level of understanding. Sad, but true!

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Twitter: @BLDWhisperer

Related posts & links:

#131 – Reflections on Horrific MEP Spec’s

#66 – Chillers – Read the Small Print!

#51 – Variable Flow Hydronic Systems Cx

Edifice Complex Podcast

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