ASHRAE Journal - October 2019 - 36

SOLVING PROBLEMS

Operation & Maintenance
For Condensing Boilers
BY MARY KATE MCGOWAN, ASSOCIATE EDITOR, NEWS

Condensing boilers have great potential for high-efficiency energy savings and reduction in carbon footprint. However, condensing boilers need more than plug-and-play
operations and maintenance strategies to achieve high-efficiency performances.
Engineers need to be mindful in their designs to help
prevent or mitigate potential O&M issues, said Ted
Duffy, P.E., Member ASHRAE, a LAARS Heating Systems
Company regional sales manager.
"It's critical that we design the systems and the equipment with the intent of having low return water temperatures and then ensuring that we operate them in
that way," he said.
Once the system is installed, the conditions
in which the condensing boiler operates affect
the boiler's performance, said Tom Neill, Life
Member ASHRAE, a member of TC 6.10, Fuels and
Combustion, TC 6.01 Hydronic and Steam Equipment
and Systems, TC 6.06 Service Water Heating Systems
and SPC 155P, Method of Testing for Rating Commercial
Space Heating Boiler Systems. To help condensing boilers
operate as efficiently as possible, engineers need to
make sure the systems:
* Are thermally balanced to provide adequate run
time for the mechanical equipment;
* Have adequate water volume and flow rate in gallons per minute to keep temperature rises in the range
designed for the system; and
* Maintain return water temperatures below 130°F
(54.4°C). to allow the condensing boilers to operate in
condensing mode as much as possible to maintain the
highest system efficiency.
36

ASHRAE JOURNAL

ashrae.org

O C T O B E R 2 0 19

Design Strategies

A building that uses condensing boilers must be
operated and designed in such a way that the boilers
will have low enough return-water temperatures, so
that the vapor in the flue gases in the boilers can condense. Designing and specifying boilers with a low ∆T
(20°F or -6.7°C) and high supply temperatures is outdated in most applications and is problematic when
using a condensing boiler. Condensing boilers that
operate at high supply water temperatures and 20°F
(-6.7°C) ∆TT will not be in condensing operation, said
Duffy.
"The condensate line will remain dry and the owner
will have paid for a high efficiency system that operates
at much lower efficiencies," he said.
Hydronic heating systems, including heating coils,
should be designed with higher ∆TT and lower return
water temperatures, less than 120°F (48.9°C), said
Duffy.
"It's really a design strategy looking at the overall heating system to make sure we can accomplish efficient
system operation combined with our coils in the space,"
he said.
Designers should also insist upon commissioning and
balance the systems at the design temperatures and
during the heating season. Continuous commissioning
should be implemented whenever practical, he said.


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ASHRAE Journal - October 2019

Table of Contents for the Digital Edition of ASHRAE Journal - October 2019

Contents
ASHRAE Journal - October 2019 - Intro
ASHRAE Journal - October 2019 - Cover1
ASHRAE Journal - October 2019 - Cover2
ASHRAE Journal - October 2019 - 1
ASHRAE Journal - October 2019 - Contents
ASHRAE Journal - October 2019 - 3
ASHRAE Journal - October 2019 - 4
ASHRAE Journal - October 2019 - 5
ASHRAE Journal - October 2019 - 6
ASHRAE Journal - October 2019 - 7
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ASHRAE Journal - October 2019 - HR1
ASHRAE Journal - October 2019 - HR2
ASHRAE Journal - October 2019 - HR3
ASHRAE Journal - October 2019 - HR4
ASHRAE Journal - October 2019 - HR5
ASHRAE Journal - October 2019 - HR6
ASHRAE Journal - October 2019 - HR7
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ASHRAE Journal - October 2019 - HR10
ASHRAE Journal - October 2019 - HR11
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ASHRAE Journal - October 2019 - HR21
ASHRAE Journal - October 2019 - HR22
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ASHRAE Journal - October 2019 - HR24
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ASHRAE Journal - October 2019 - HR26
ASHRAE Journal - October 2019 - HR27
ASHRAE Journal - October 2019 - HR28
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ASHRAE Journal - October 2019 - Cover3
ASHRAE Journal - October 2019 - Cover4
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