Trials Tribulations & Rewards High T Heating Systems

Transcription

1 Trials Tribulations & Rewards High T Heating Systems ASHRAE Cleveland Chapter October Presented by Norman Hall R. L. Deppmann Company

2 THE CALL OF THE DAY ASHRAE 90.1 Green technology High Efficiency Boilers, Pumps, Motors, Leadership in Energy & Environmental Design (LEED) Renewable energy Sustainable energy Just plain mad at oil and gas prices Save the environment

3 Today s Example Just for the shock value I am using a 60 degree delta T system as an example today 180 to 120 degrees

4 Trials, Tribulations, and Rewards High Delta T Hydronic Heating Systems Boilers Pumps Minimum Flow issues Piping Terminal Units Balancing and Commissioning Condensing and Domestic Water Q&A

5 Don t try this at home Please do not send 120 degree return water to your scotch marine or traditional flex tube boiler They don t like rain in the flue! We are talking about condensing boiler technology made to accept the rain

6 Don t try this at home part 2 Watch existing systems. Today we are talking about new systems with terminal units and equipment sized for lower flow and higher delta T

7 Published Boiler Efficiencies non-condensing Up to 102%?? What we know 85% Condensing 88%? Thermal Efficiency up to 96%? 90% Combustion Efficiency

8 Realistic Boiler Efficiencies - Full Load Boiler Efficiency % Condensing (published) Conventional (est.) 80 80F 100F 120F 140F 160F Inlet water temperature Inlet water temperature OLD (est.)

9 Return Water Temp Effect on Boiler Efficiency Thermal Efficiency condensing zone Published Efficiency Rating in accordance w/ ANSI Z21.13, but warranty may be void if operated with RWT <140F! non-condensing zone Inlet Water Temperature As the inlet water temp. falls below ~135 F, condensing occurs and boiler efficiency is dramatically increased. ASHRAE Equipment Handbook, Boiler Chapter

10 Condensing High Efficiency Boilers at design HTG LOAD 160 F The Boiler is most efficient At lower return temperatures How low do we GO! 180 F

11 System Water Temperature Adjusting the reset adds efficiency to a System already condensing at design When Condensing Occurs Outdoor Air Temperature Outdoor Air Temperature

12 Full & Part Load Efficiency Curves 98% Efficiency 97% 96% 95% 94% 93% 92% 91% 90% 89% 88% 87% 86% 5% % 130 5% Input 20% Input 40% Input 60% Input 80% Input 100% Input 85% Return Water Temperature (ºF), with 20º Rise

13 Impact of Partial Heating Load ASHRAE Bin Data Typical Ohio Bin Hours Outside Air Temp (Deg F)

14 Why Modulate the Fuel/Air Input? Turndown of 3:1, 5:1, 8:1, 20:1? Turndown Increases Efficiency Eliminates Cycling Losses No Energy Waste Match Energy Input to Actual Heating Load No Energy Waste Precise Temp Control at All Loads 100% Efficiency 0% Full Modulating Burners Staged & On/Off Burners Load 100%

15 Besides Boiler Efficiency Burner Cycling Impact Efficiency Losses - Less Efficient When Cycling Pre-Purge Purge & Post-Purge Purge Thermal Stress on Heat Exchanger Wear & Tear on Components Spark Plug, Switches & Etc Higher Energy Consumption, Higher Emissions, Shorter Product Life Span!

16 Multiple Boiler Control Strategy Boiler Management System (BMS) controls entire heating plant, optimizing boiler operation to maximize seasonal efficiency BMS controls firing rate of each boiler; reads all boiler parameters and faults Stage multiple boilers at low fire. (4 boilers at 25% are better than 1 at 100%)

17 Trials, Tribulations, and Rewards High Delta T Hydronic Heating Systems Boilers Pumps Minimum Flow issues Piping Terminal Units Balancing and Commissioning Condensing and Domestic Water Q&A

18 GPM at 20 deg ΔT Q = 500xGPMxΔT Assume 6,000,000 BTUH at 20 F T GPM is 600 Let s assume a 70 foot head

19 Pump Selection - 20 F T 15 hp

20 Impact of Increased ΔT Q = 500xGPMxΔT For the same BTUH, a higher ΔT will result in a similarly lower GPM. Changing the ΔT from 20 to 60 deg F will drop the system GPM to one third. GPM is now 200 GPM.

21 Pump Selection - 60 F T 7.5 hp

22 Effect on the pumping Horsepower reduced in half Operating Energy Savings Pump size is smaller Lower first cost Lower electrical and VFD costs. Less space required Lower carbon footprint

23 With some boilers No need for Primary Secondary HTG LOAD Conventional 6000MBH: 20F ΔT T System GPM = (BTU/hr)/(500*ΔT) T) GPM = 600 gpm High Efficiency 6000MBH: 60F ΔT T System GPM = (BTU/hr)/(500*ΔT) T) 66 GPM Each GPM = 200 gpm

24 What about Minimum Flows in Boilers and Pumps?

25 Using On-Off Control valves Now the minimum system flow is 25 GPM Return Supply 25 GPM Minimum per boiler for example

26 Boiler Valve Controller Allows the Minimum System Flow to be a Single Boiler s Minimum Flow! Controller should stage boilers, control temperature, and open and close valves at minimum flows. 26

27 Insufficient Flow Failure Analysis Radial Loads Recirculation Radial Loads Pump Failure Heat

28 Hydronic Minimum Pump Flow End suction pumps need less flow than double suction pumps. High energy pumps need more flow than low energy pumps. Variable speed pumps require less minimum flow By reducing the flow, we reduce the pump size and horsepower and reduce the minimum flow.

29 Pump Selection - 60 F T

30 Trials, Tribulations, and Rewards High Delta T Hydronic Heating Systems Boilers Pumps Minimum Flow issues Piping Terminal Units Balancing and Commissioning Condensing and Domestic Water Q&A

31 Piping Impact of Increased ΔT 6,000,000 BTUH = GPM X 500 X (T R -T S ) 180 F Supply 20 F T 600 GPM 40 F T 400 GPM 60 F T 200 GPM Pipe Size 6 5 4

32 Effect on the pipe sizing At 60 F T instead of 20 F T Pipe size is smaller Expansion tank/ air separator are smaller Valves are smaller Initial cost is lower Less space used Lower carbon footprint

33 Trials, Tribulations, and Rewards High Delta T Hydronic Heating Systems Boilers Pumps Minimum Flow issues Piping Terminal Units Balancing and Commissioning Condensing and Domestic Water Q&A

34 Coil Performance Water Out Airflow Q=UA(LMTD) Water In

35 Thermodynamics 101 Q = BTUH A = Heat Transfer surface area U = the U value or 1/R ( LMTD = Log mean temperature difference

36 Thermodynamics 101 T T water out water in T T air inlet air outlet T L T LMTD is about the Average of TL and TG G

37 LMTD BUT FOR THIS PRESENTATION WE ARE USING THE AVERAGE

38 Thermodynamics water out water in air inlet air outlet 95 L 110 G LMTD is about the Average or 102.5

39 Thermodynamics water out water in air inlet air outlet 55 L 110 G LMTD is about the Average or 82.5

40 Thermodynamics 101

41 Thermodynamics 101 Area Goes Up LMTD X.8

42 Thermodynamics 101

43 Thermodynamics water out water in air inlet air outlet 75 L 130 G LMTD is about the Average or 102.5

44 Fin Tube

45 Fin Tube Radiation Convectors CUH 35% more fins $20 per room VAV/Reheat 25% more surface AHU Units 38% more surface Ceiling Rad Use 40 T Max Example added $ Stay with low T

46 Summary of terminal units In general we need to size understanding the goal is not the lower price unit Keep velocities up at the lower flow.

47 Trials, Tribulations, and Rewards High Delta T Hydronic Heating Systems Boilers Pumps Minimum Flow issues Piping Terminal Units Control Valves, Balancing Condensing and Domestic Water Q&A

48 Coil Output Control % Flow at Constant PD % R. Stroke L. Deppmann Co. Equal Percentage Valve Characteristic 20 Deg F

49 Typical Curve

50 Flow Tolerance & % Coil Output Coil Output Control 20 Deg F 40 Deg F 60 Deg F R. % L. Flow Deppmann Co.

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52 Trials, Tribulations, and Rewards High Delta T Hydronic Heating Systems Boilers Pumps Minimum Flow issues Piping Terminal Units Control Valves, Balancing Condensing and Domestic Water Q&A

53 Domestic Water Applications With high turndown ratios like 20:1 you can efficiently operate a large boiler such as 2,000,000 BTUH at 100,000 BTUH You may consider saving the water heater real estate by using an instantaneous domestic hot water heat exchanger system.

54 Your boiler for domestic hot water Specify Double Wall Electronic Control Plate type exchanger allows for temperature cross sizing for low approaches, even in reset mode.

55 Trials, Tribulations, and Rewards High Delta T Hydronic Heating Systems Boilers Pumps Minimum Flow issues Piping Terminal Units Control Valves, Balancing Condensing and Domestic Water Q&A

56 False pretenses If you use 30 degree TRY 40 or 50 degree Select terminal equipment for the largest Delta T you can then figure out the summation of the system

57 Thank You! For Your Time and Attention Today! On your next design --- challenge old school and look at larger ΔT Questions?