How are Triple Duty Valves (TDV’s) on HVAC HTG and CHW systems still a thing in 2017?
I saw this arrangement on a CHW system recently;
- Outdated technology;
- Over 50% of TDV’s I have tested on site do not give accurate flow rate readings;
- There is an energy penalty over time for the high pressure drop across the TDV if it is regulated to reduce flow rate on an inevitably, oversized pump;
- There is an energy penalty over time for the relatively high pressure drop across the TDV, although it may be fully open;
- It is IMHO, poor engineering practice to regulate pump flow rate using fixed, in-line valves.
Design of HVAC HTG and CHW hydronic systems for optimum efficiency and operation across load ranges, requires the following:
- Right sized equipment with low pressure drops (not withstanding sizing correctly for authority).
- Correct flow rates throughout the system to match flow rate with demand.
- Accurate control of flow rates from the pump through to terminal devices.
My revision to the CHW system configuration above plus notes
- Pump total flow rates should be regulated to 105% of design flow rate by VFD setting, derived following system balancing or belt & pulley change or Impeller modification. In a digital world, VFD’s should be first choice.
- Use an Orifice Plate to measure “system total flow rate”. This is a low cost, low pressure drop, accurate and useful Commissioning tool. This replaces the TDV for each pump.
- Commissioning valve (fixed orifice flow measurement device) to be installed with 10 straight pipe diameters upstream and 5 straight pipe diameters down stream to ensure measurement accuracy.
- Install pressure connection points to measure the pressure drop across the strainers and pumps. These cost very little but provide a life time of commissioning and diagnostic use.
- IMHO, Isolating valves should be high performance butterfly valves. These valve types provide rapid isolations i.e. 90 degree movement to close plus there is an instant visual verification that the valve is open or shut. Important for mission critical applications.
- Install paddle flow switch for proof of flow to controls system. Do not use a differential pressure switch for proof of flow. With isolating valves fully shut, a differential pressure switch will give a false proof of flow signal. A paddle switch senses flow not pressure and is therefore accurate and reliable. Important for mission critical applications.
Am I crazy and Christopher Walken like or just a Commissioning guy who likes VFD’s because they have flashing lights?
Maybe, but (movie voice) “In a world” of increasingly cheaper and sophisticated VFD’s connected to the BMS/BAS, Triple Duty Valves seem obsolete to me.
Related posts & links:
#51 – Asked & Answered – Variable Flow Hydronic Systems Cx ( https://www.linkedin.com/pulse/asked-answered-variable-flow-hydronic-systems-cx-adam-muggleton?trk=mp-reader-card )
#43 – This is not OK ( https://www.linkedin.com/pulse/ok-adam-muggleton?trk=mp-reader-card )
#45 Small Detail? Best Coil Detail Ever! ( https://www.linkedin.com/pulse/small-detail-adam-muggleton?trk=mp-reader-card )