MAXIMIZING HYDRONIC SYSTEM DESIGN PART III

Transcription

1 MAXIMIZING HYDRONIC SYSTEM DESIGN PART III Presented by Cleaver Brooks Steve Connor & DCEs David Grassl June 21, 2017

2 TODAY S TOPICS Dispelling common myths about condensing boilers Supply water temperature System Delta T Hot water reset System pumping choices and implementation strategies System piping choices and myths The REAL factors affecting efficiency Key points to know when designing new and retrofit condensing hot water systems Summary of the Three Part Series Q&A 2

3 David Grassl President, Dynamic Consulting Engineers 3

4 MYTH #1 NEED TO MAINTAIN 180 F HWS TEMPERATURE Logic with 180 F Hot Water Supply Flue Gas Temperatures Examples: AHU heating coils VAV box reheat coils Miscellaneous terminal equipment New Design Paradigm: As low of HWS as possible (reduces HWR) Wide delta T Evaluate existing conditions 4

5 MYTH #1 NEED TO MAINTAIN 180 F HWS TEMPERATURE Logic with 180 F Hot Water Supply Flue Gas Temperatures Examples: AHU heating coils VAV box reheat coils Miscellaneous terminal equipment New Design Paradigm: As low of HWS as possible (reduces HWR) Wide delta T Evaluate existing conditions 5

6 MYTH #2 NEED TO MAINTAIN A 20 F ΔT Logic with 20 F ΔT Heat Transfer Ability More flow Higher hot water return temperature New Design Paradigm: Increase ΔT as allowed by boiler Reduces flow rates, pump sizes, and piping Increased time in condensing mode 6

7 MYTH #2 NEED TO MAINTAIN A 20 F ΔT Logic with 20 F ΔT Heat Transfer Ability More flow Higher hot water return temperature New Design Paradigm: Increase ΔT as allowed by boiler Reduces flow rates, pump sizes, and piping Increased time in condensing mode 7

8 MYTH #3 HOT WATER RESET DOESN T WORK Logic with Constant HWS New Design Paradigm: Aggressive HWS reset Less energy to heat to lower HWS More time in condensing mode 8

9 MYTH #3 HOT WATER RESET DOESN T WORK Logic with Constant HWS New Design Paradigm: Aggressive HWS reset Less energy to heat to lower HWS More time in condensing mode 9

10 MYTH #4 VARIABLE FLOW PRIMARY IS TOO COMPLICATED Logic with Primary-Secondary System Consists of Control Valves Desire for Flow Measurement New Design Paradigm: Fewer pumps Energy management Less pumping energy Reduce/eliminate mixing 10

11 MYTH #4 VARIABLE FLOW PRIMARY IS TOO COMPLICATED System Requirements: Boiler isolation control valve Two-way coil control valves Minimum flow protection Minimum flow bypass control valve Three-way control valves 11

12 MYTH #4 VARIABLE FLOW PRIMARY IS TOO COMPLICATED System Requirements: Boiler isolation control valve Two-way coil control valves Minimum flow protection Minimum flow bypass control valve Three-way control valves 12

13 MYTH #5 HOT WATER SUPPLY & CONDENSING EFFICIENCIES Logic with hot water supply temperature and & efficiencies Boiler Flue Gas Temperatures Counterflow Arrangement New Design Paradigm: Reduce hot water return temperature Multiple boilers at part-load Increased system efficiency 13

14 MYTH #5 HOT WATER SUPPLY & CONDENSING EFFICIENCIES Boiler Efficiencies are Dictated By: Hot water return temperatures Boiler Firing Rates 14

15 MYTH #5 HOT WATER SUPPLY & CONDENSING EFFICIENCIES Boiler Efficiencies are Dictated By: Hot water return temperatures Boiler Firing Rates 15

16 MYTH #6 CONDENSING BOILERS REQUIRE ADDITIONAL WORK Logic with Condensing Boilers Robust Heat Exchanger & Venting Condensate Production & Treatment New Design Paradigm: SS heat exchanger minimal maintenance SS category IV venting Condensate occurs naturally 16

17 MYTH #6 CONDENSING BOILERS REQUIRE ADDITIONAL WORK Logic with Condensing Boilers Robust Heat Exchanger & Venting Condensate Production & Treatment New Design Paradigm: SS heat exchanger minimal maintenance SS category IV venting Condensate occurs naturally 17

18 CONDENSING BOILERS & RETROFITS COMMON ITEMS IN ALL RETROFITS Type of Boilers System mass Piping & pumping configuration Building Loads Temperatures required Minimum & maximum design loads Dual temperature applications Hot Water Supply & Return Temperatures Temperature Control Valves Two-way vs. Three-way valves 18

19 CONDENSING BOILERS & RETROFITS COMMON ITEMS IN ALL RETROFITS Pumps Reuse or replace VFD or constant speed Condensate Treatment Venting & Combustion Air Gas Pressures System Controls Pump control Hot water reset Boiler management 19

20 CONDENSING BOILERS & RETROFITS RETROFIT #1 Small, simple building Single non-condensing boiler 20

21 CONDENSING BOILERS & RETROFITS RETROFIT #1 Replace boiler with condensing boiler Evaluate HWS temperature required 21

22 CONDENSING BOILERS & RETROFITS RETROFIT #2 Medium sized building Multiple parallel boilers 22

23 CONDENSING BOILERS & RETROFITS RETROFIT #2 Replace boilers with condensing boilers Variable primary flow conversion 23

24 CONDENSING BOILERS & RETROFITS RETROFIT #3 Large building Multiple parallel boilers 24

25 CONDENSING BOILERS & RETROFITS RETROFIT #3A Keep an existing boiler add condensing boilers Maintain P-S pumping 25

26 CONDENSING BOILERS & RETROFITS RETROFIT #3B Keep an existing boiler add condensing boilers Variable flow primary conversion for condensing boilers 26

27 CONDENSING BOILERS & RETROFITS RETROFIT #3C 110ºF VSD System pump 150ºF Solutions Larger-capacity condensing boilers Condensing control strategy Outdoor air reset 150ºF 110ºF 27

28 SUMMARIZING THE THREE PART SERIES 28

29 EFFICIENT CONDENSING BOILER INCLUDES Boiler Efficiency Improves Dramatically with Condensing Counter-flow Heat Exchanger Effective Heating Surface to promote condensing Cold water return inlet temperature introduced near the optimum flue gas temperatures with counter flue gas flow as water rises in opposite direction 29

30 BURNER WITH CONSISTENT FUEL/AIR RATIO CONTROL 30

31 DEW POINT CHANGES WITH EXCESS AIR AND RETURN WATER TEMPERATURE Boiler Efficiency Improves Dramatically with Condensing Condensing Efficiency Drivers: Low return temperatures Effective heat exchanger Burner with effective fuel/air ratio control Flue Gas Dew point moves left (lower) based on rise in Excess Air 31

32 BOILER MASS MAKES A DIFFERENCE High Mass Low Mass 32

33 PRIMARY/SECONDARY SYSTEM PRIMARY SECONDARY 33

34 VARIABLE FLOW PRIMARY SYSTEM 34

35 REDUCE FLOW RATES, REDUCE PIPING AND PUMP SIZE Movement toward larger ΔT s Reduce pumping flow Reduce piping sizes, pumps, & accessories both in size and number required Decrease hot water return to the boiler Greatly increases efficiency! 35

36 SYSTEM CONTROL STRATEGIES Hot Water Supply Temperature Reset Return temperature Outdoor reset Pump Control with VFD Delta P Delta T 36

37 BUFFER TANK RATIONALE: Stores excess energy Prevents boiler cycling (Low mass) Allows for better temperature control Assists in system efficiency Not required in High system mass applications 37

38 BUFFER TANKS Tank Sizing Calculations 1. Minimum Boiler Cycle Time 2. Minimum Boiler Output 3. Minimum System Load 4. Temperature Differential in Tank 38

39 CONDENSING BOILERS VENTING Flue Stack Temperatures & Materials: Condensing boilers: Flue gases are generally less than 200 F Stainless steel, polypropylene, or CPVC Highly recommend stainless steel (could always operate in noncondensing mode) Non-condensing boilers: Flue gases are approximately 250 F to 350 F Aluminum, galvanized, carbon or stainless steel Consult the boiler manufacturer prior to choosing the stack material 39

40 NON-TRADITIONAL SYSTEMS WITH CONDENSING BOILER Low grade heating is a perfect application for condensing boilers: Water source heat pumps Geothermal Radiant systems Ceiling panels In-floor heating Snow melt Pool heating Series loop 40

41 CONDENSING BOILER WITH DUAL RETURN Accepts hot water return from two sources Eliminates mixing high hot water return with low hot water return Promotes condensing that would otherwise be lost 41

42 THE HYBRID SYSTEM 42

43 DISPELLING THE SIX MAJOR MYTHS 43

44 MYTH #1 MUST HAVE 180 DEGREE F SUPPLY WATER True of legacy systems, not condensing boilers Some VAV box and finned radiation can still be lower temps. Some may require more or larger coils Check for air side Delta P and coil output for the space. Reduce supply water temperature as much as possible! 44

45 MYTH #2 MUST HAVE A 20 DEGREE DELTA T Needed to protect non-condensing boilers Higher Delta T, LOWER FLOW Low mass boilers normally degree Delta T High mass are tolerant of LOW FLOW, HIGHER Delta T Lower returns increase efficiency Impacts pump sizing, pipe sizing, accessories size, LOWERING COSTS 45

46 MYTH #3 HOT WATER RESET Required to meet ASHRAE 90.1 Reducing Supply also reduces Return temperature With condensing boilers aggressive setback possible Especially high mass boilers! 46

47 MYTH #4 VFP IS MORE COMPLICATED THAN P/S PIPING LOGIC: P/S assures proper flow through the boiler VFP has one set of pumps = Simpler VFP has less pump horsepower, less piping and accessories; lower operating and install cost Most valves and meters required for P/S are same for VFP Exception are boiler isolation valves. 47

48 MYTH #5 MUST REDUCE SUPPLY TEMP. FOR HIGH EFFICIENCY On the right track, but not always helpful when condensing Reduce from 180 to 160 with 20 degree DT Yipes! Not condensing!! What s key is return temp at or below flue gas dew point temp and excess air levels Condensing boilers most efficient at lower firing rates 48

49 MYTH #6 HIGHER MAINTENANCE WITH CONDENSING BOILERS LOGIC: Condensation causes inordinate corrosion problems Actually the heat exchanger is designed for this So are the venting materials If properly sized for load, less cycling, less problems Exception: Condensate neutralization; monitored and replaced 49

50 RETROFITTING CONDENSING BOILERS Boiler and system mass decision Buffer tank required? Low mass boilers will require P/S, high mass VFP Flow is critical with low mass! Building load, max and min affects boiler sizing and turndown Dual return opportunity? 50

51 RETROFITTING CONDENSING BOILERS Fan coil sizing and building efficiency enhancements? If converting to VFP, two way control valves in system allow for variable flow VFD capability on pumps Venting for condensing boilers must be Category IV. Masonry chimney needs liner Gas pressure requirements Boiler and system control strategy. A combination of the boiler mfr. and the building control people. 51

52 THAT S IT FOR THE SUMMARY! 52

53 QUESTIONS? Catie Van Wormer Dave Grassl