BAS PROGRAMMING CONSIDERATION FOR PUMP VFD’s AND HEATING WATER RESET TO MINIMIZE VALVE DAMAGE, IMPROVE COMFORT AND REDUCE ENERGY CONSUMPTION ENERGY AND DAMAGE ISSUE When VFD's are only used for soft start, the initial water balancers set the fixed VFD settings on heating pumps to match the buildings’ heating water requirements at maximum load conditions; therefore, too much flow exists at all other times, causing the actual system differential pressure to sometimes exceed damaging levels. As presented in the accompanying graph, generated at a high school in Etobicoke, the significantly varied hot water requirement during each day is altered by BTU input from body load in the most heat demanding room. Systems that do not control pressure differential may cause the pressure drop through the modulating control valves variation to attain destructive levels. The graph from G.L. Roberts was generated in a 1979 experiment and the Etobicoke graph is from a 1996 case study. Both graphs illustrate the conservation benefit of resetting the heating supply water based on coordination with both the cooling and heating devices of the zone most demanding heat. Outdoor air reset limitation is suggested. The seats and discs tend to wear prematurely and sometimes the disc assemblies loosen, causing aggravating noise issues when the pressure drop through modulating control valves is too high. BENEFITS OF SUGGESTED NEW CONSIDERATION 1) Reduce valve damage caused by excessive pressure drop through control valves. 2) Reduce energy waste by overall average temperature reduction in piping systems. 3) More even heat delivery to rooms because the convector temperature differential from inlet to outlet will be minimized most of the time. 4) Reduce service calls for noisy valves. 5) If the heating requirement is minimal at the coolest spot in the building, the heating water will automatically be at minimum temperature and the pump VFD’s will automatically be at minimum flow. 6) Minimize hidden energy loss caused by system cooling compensation for hot water passing through damage valve seating. SOME EQUIPMENT CONSIDERTIONS 1) Be sure water temperature does not drop below boilers’ acceptable low firing limits or flow rates. 2) Before starting 100% outdoor air units, raise the heating water temperature to an outdoor air reset temperature, then start the 100% outdoor air fans and then allow system logic to seek the appropriate water temperature and flow, matching the actual existing load. Ideally have 100% outdoor air units on a separate water supply than the rest of the building with secondary piping loops or equivalent for both. Both approaches prevent fan shut downs due to low limits tripping on 100% OSA units on startup. 3) Greenhouses should be on separate heating sources. 4) Do not run VFD’s below minimum acceptable levels. 5) Set minimum water temperature for heating loops. 6) If boilers are sensitive to thermal shock, ease cool return secondary water into primary water loop when the system alters from night mode to day mode, causing the primary loop to maintain an acceptable temperature for the boiler. 7) Shut down unnecessary boilers and pumps in warm weather. SUGGESTED APPROACH 1) Determine the greatest requirement for heat from occupied rooms and 100% OSA fans or large minimum fresh air volume fans via BAS sensors or pneumatic signals with P/I transducers. 2) Reset supply water temperature upward after the most demanding zone for heat has opened its control valve fully to heating water flow and the space temperature continues to decrease. 3) Limit the hot water supply temperature by an outdoor air reset schedule. 4) Vary the heating pumps gpm based on the most demanding requirement for heat after the reset water temperature is at minimum temperature. APS analystsofpneumatic@bellnet.ca 5.43E (NOTE: PAGES 5.43E, F & G ARE ONE PAPER)
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