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MAXIMIZING HYDRONIC SYSTEM DESIGN

– PART III

Presented by Cleaver Brooks’ Steve Connor

& DCEs’ David Grassl

June 21, 2017

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

David Grassl

President, Dynamic Consulting Engineers

3

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


• As low of HWS as possible (reduces HWR)

• Wide delta T

• Evaluate existing conditions

MYTH #2 –

NEED TO MAINTAIN A 20°F ΔT

• Logic with 20°F ΔT

• Heat Transfer Ability

• More flow

• Higher hot water return temperature


• Increase ΔT as allowed by boiler

• Reduces flow rates, pump sizes, and piping

• Increased time in condensing mode

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


• Increase ΔT as allowed by boiler

• Reduces flow rates, pump sizes, and piping

• Increased time in condensing mode

7

MYTH #3 –

HOT WATER RESET DOESN’T WORK

• Logic with Constant HWS


• Aggressive HWS reset

• Less energy to heat to lower HWS

• More time in condensing mode

8

MYTH #3 –

HOT WATER RESET DOESN’T WORK

• Logic with Constant HWS


• Aggressive HWS reset

• Less energy to heat to lower HWS

• More time in condensing mode

9

MYTH #4 –

VARIABLE FLOW PRIMARY IS TOO

COMPLICATED

• Logic with Primary-Secondary

• System Consists of Control Valves

• Desire for Flow Measurement


• Fewer pumps

• Energy management

• Less pumping energy

• Reduce/eliminate mixing

10

• System Requirements:

• Boiler isolation control valve

• Two-way coil control valves

• Minimum flow protection

• Minimum flow bypass control valve

• Three-way control valves

MYTH #4 –


COMPLICATED

11

• System Requirements:

• Boiler isolation control valve

• Two-way coil control valves

• Minimum flow protection

• Minimum flow bypass control valve

• Three-way control valves

MYTH #4 –


COMPLICATED

12

MYTH #5 –

HOT WATER SUPPLY & CONDENSING

EFFICIENCIES

• Logic with hot water supply temperature and & efficiencies

• Boiler Flue Gas Temperatures

• Counterflow Arrangement


• Reduce hot water return temperature

• Multiple boilers at part-load

• Increased system efficiency

13

• Boiler Efficiencies are Dictated By:

• Hot water return temperatures

• Boiler Firing Rates

MYTH #5 –


EFFICIENCIES

14

• Boiler Efficiencies are Dictated By:

• Hot water return temperatures

• Boiler Firing Rates

MYTH #5 –


EFFICIENCIES

15

MYTH #6 –

CONDENSING BOILERS REQUIRE

ADDITIONAL WORK

• Logic with Condensing Boilers

• Robust Heat Exchanger & Venting

• Condensate Production & Treatment


• SS heat exchanger – minimal maintenance

• SS category IV venting

• Condensate occurs naturally

16

MYTH #6 –

CONDENSING BOILERS REQUIRE

ADDITIONAL WORK

• Logic with Condensing Boilers

• Robust Heat Exchanger & Venting

• Condensate Production & Treatment


• SS heat exchanger – minimal maintenance

• SS category IV venting

• Condensate occurs naturally

17

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

• Pumps

• Reuse or replace

• VFD or constant speed

• Condensate Treatment

• Venting & Combustion Air

• Gas Pressures

• System Controls

• Pump control

• Hot water reset

• Boiler management

CONDENSING BOILERS

& RETROFITS –

COMMON ITEMS IN ALL RETROFITS

19

CONDENSING BOILERS

& RETROFITS –

RETROFIT #1

20

• Small, simple building

• Single non-condensing boiler

CONDENSING BOILERS

& RETROFITS –

RETROFIT #1

21

• Replace boiler with condensing boiler

• Evaluate HWS temperature required

CONDENSING BOILERS

& RETROFITS –

RETROFIT #2

22

• Medium sized building

• Multiple parallel boilers

CONDENSING BOILERS

& RETROFITS –

RETROFIT #2

23

• Replace boilers with condensing boilers

• Variable primary flow conversion

CONDENSING BOILERS

& RETROFITS –

RETROFIT #3

24

• Large building

• Multiple parallel boilers

CONDENSING BOILERS

& RETROFITS –

RETROFIT #3A

25

• Keep an existing boiler –add condensing boilers

• Maintain P-S pumping

CONDENSING BOILERS

& RETROFITS –

RETROFIT #3B

26

• Keep an existing boiler –add condensing boilers

• Variable flow primary conversion for condensing boilers

CONDENSING BOILERS

& RETROFITS –

RETROFIT #3C

27

Solutions

• Larger-capacity condensing

boilers

• Condensing control strategy

• Outdoor air resetSystem pump

110ºF

110ºF

150ºF

150ºF

VSD

SUMMARIZING THE

THREE PART SERIES…

28

Boiler Efficiency Improves Dramatically

with Condensing

Counter-flow

Heat Exchanger

Cold water return inlet

temperature introduced

near the optimum flue gas temperatures with counter flue

gas flow as water rises in opposite direction

Effective Heating Surface to

promote condensing

EFFICIENT CONDENSING

BOILER INCLUDES…

29

BURNER WITH CONSISTENT

FUEL/AIR RATIO CONTROL

30

Boiler Efficiency Improves Dramatically

with Condensing

Condensing Efficiency Drivers:

• Low return temperatures

• Effective heat exchanger

• Burner with effective fuel/air ratio

control

DEW POINT CHANGES WITH

EXCESS AIR AND RETURN WATER

TEMPERATURE

Flue Gas Dew point moves left (lower) based on

rise in Excess Air

31

BOILER MASS MAKES

A DIFFERENCE…

High Mass

Low Mass

32

PRIMARY/SECONDARY SYSTEM

PRIMARY SECONDARY

33

VARIABLE FLOW PRIMARY SYSTEM

34

• 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!

REDUCE FLOW RATES,

REDUCE PIPING AND PUMP SIZE

35

• Hot Water Supply Temperature Reset

• Return temperature

• Outdoor reset

• Pump Control with VFD

• Delta P

• Delta T

SYSTEM CONTROL STRATEGIES

36

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

BUFFER TANKS

Tank Sizing Calculations

1. Minimum Boiler Cycle Time

2. Minimum Boiler Output

3. Minimum System Load

4. Temperature Differential in Tank

38

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 non-

condensing 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

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

CONDENSING BOILER

WITH DUAL RETURN

41

• 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

THE HYBRID SYSTEM

42

DISPELLING THE SIX

MAJOR MYTHS

43

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 used @ 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

MYTH #2

MUST HAVE A 20 DEGREE

DELTA T

• Needed to protect non-condensing boilers

• Higher Delta T, LOWER FLOW

• Low mass boilers normally 20 – 30 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

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

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

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

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

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

• 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.

RETROFITTING

CONDENSING BOILERS

51

THAT’S IT FOR THE SUMMARY!

52

Catie Van Wormer

[email protected]

Dave Grassl

[email protected]

QUESTIONS?

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