common pitfalls in high-rise domestic hot water ...the building commissioning association is a...

Common Pitfalls in High-Rise Domestic Hot Water Recirculating Systems

Miles Ryan, PE, CEMQuestions & Solutions EngineeringChaska, MN

AIA Quality Assurance

The Building Commissioning Association is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES). Credit(s) earned on completion of this program will be reported to AIA/CES for AIA members. Certificates of the Completion for both AIA members and non-AIA members are available upon request.

This program is registered with AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product.

Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

BCxA Conference – Chicagoland, IL – 2019 2

Learning Objectives

BCxA Annual Conference – Chicagoland, IL – September 2019 3

• Understand how pressure reducing valves (PRVs) are to be appropriately accounted for in DHW recirculating systems.

• Identify best practices in the balancing of DHW recirculating systems.

• Analysis high-rise DHW recirculating system design to preemptively identify operational concerns.

• Apply the step-by-step approach presented to efficiently analyze complex DHW recirculating system designs.

Motivation – Why Should We Care?


• Why DHW recirculating systems?• Why is such a system worth commissioning?• What the sign of insufficient operation?• Why don’t we hear about such insufficiencies more often?

Closed Hydronic Systems: HVAC Application


Operating Point

System Curve

Pump Curve

Closed Hydronic Systems: DHW Application


Design Flow

Slightly Oversized

Slightly Undersized

Open Hydronic Systems: HVAC Application


Cooling TowerHeight

Open Hydronic Systems: DHW Application


Common Pitfall #1: Undersized recirculating pumps; No flow

Design Flow Slightly

Oversized

Undersized

Case Study #1: Existing High-Rise Condo


Lower floors’DHW pressuretoo high!



History◦ Installed PRV◦ DHW no longer

available System curve changed

Same pumpcurve



How to fix:◦ Bigger pump◦ Keep it in Penthouse

Common Pitfall #2: Inappropriate pump location; Negative gauge pressures



How to fix:◦ Bigger pump◦ Move it to lower floor



How to fix:◦ Additional pump◦ Located at lower floor

Case Study #2: New High-Rise Office Building




Common Pitfall #3: Same recirculating pump serving different pressure systems

Will lower floors DHW recirculate?



Common Pitfall #4: Unequal pressures at fixturemixing valves

Recap: That Tricky Little PRV!


• Often needed to maintain appropriate fixture pressures• Configure them to maintain roughly equal pressures with DCW• Ensure loop with PRV has dedicated recirculating pump• Ensure PRV is properly accounted for pump scheduling/selection ΔPpump > ΔPPRV at no flow

• Ensure pump placement does not create negative gauge pressures

Balancing The Risers


More water flowsthrough path ofleast resistance!

Riser 3 may starve

Common Pitfall #5: Inadequate balancing of DHWrecirculating system

Balancing The Paths Within A Riser


Direct Return Piping

Common Pitfall #5: Inadequate balancing of DHWrecirculating system

Balancing The Paths Within A Riser


Reverse Return Piping

Designer Estimated System Curve

ActualSystem Curve

Design Flow

Higher-Than-Intended Flow


Slightly Oversized Pump

Case Study #3: Church


Common Pitfall #6: Excessive velocities due to unthrottled flow

Piping Replaced

Leaking after fitting

Scheduling


Manual Enable/Disable Building Automation System Mechanical Time Clocks◦ Are they reset after power outages?◦ Are backup batteries ever replaced?

Case Study #4: Elementary School

Common Pitfall #7: Out of sync time clocks

Scheduling


Demand Controlled Operation◦ Aquastats

Case Study #4: Elementary School

Common Pitfall #8: Unnecessary (and often overridden) aquastat control

Step-by-Step Approach to Analyzing Systems


• Step 1: Identify reference pressure(s)• Step 2: Identify if PRVs are present• Step 3: Are pressures available at each level of fixtures appropriate?• Step 4: Is positive gauge pressure maintained throughout system?• Step 5: Are various pressure systems served by the same pump?• Step 6: Is pump serving PRV circuit appropriately sized?• Step 7: Is the system balanced appropriately?• Step 8: Does TAB specification call out balancing of plumbing systems?• Step 9: Is the intended operation schedule sustainable?

Applying the Step-by-Step Approach


• 14 ft stories • Lower Level Pump

3 GPM 50 ft head

• Upper Level Pump 3 GPM 10 ft head

Learning Objectives


• Understand how pressure reducing valves (PRVs) are to be appropriately accounted for in DHW recirculating systems.

• Identify best practices in the balancing of DHW recirculating systems.

• Analysis high-rise DHW recirculating system design to preemptively identify operational concerns.

• Apply the step-by-step approach presented to efficiently analyze complex DHW recirculating system designs.

Miles Ryan, PE, CEMQuestions & Solutions EngineeringChaska, [email protected]

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Common Pitfalls in High-Rise Domestic Hot Water Recirculating SystemsSlide Number 2Learning ObjectivesMotivation – Why Should We Care?Closed Hydronic Systems: HVAC ApplicationClosed Hydronic Systems: DHW ApplicationOpen Hydronic Systems: HVAC ApplicationOpen Hydronic Systems: DHW ApplicationCase Study #1: Existing High-Rise CondoCase Study #1: Existing High-Rise CondoCase Study #1: Existing High-Rise CondoCase Study #1: Existing High-Rise CondoCase Study #1: Existing High-Rise CondoCase Study #2: New High-Rise Office Building Case Study #2: New High-Rise Office Building Case Study #2: New High-Rise Office Building Recap: That Tricky Little PRV!Balancing The RisersBalancing The Paths Within A Riser Balancing The Paths Within A Riser Higher-Than-Intended Flow Case Study #3: ChurchSchedulingSchedulingStep-by-Step Approach to Analyzing SystemsApplying the Step-by-Step ApproachLearning ObjectivesMiles Ryan, PE, CEM�Questions & Solutions Engineering�Chaska, MN�[email protected]

common pitfalls in high-rise domestic hot water ...the building commissioning association is a...

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