Why Service A Unit That Produces Cool Air?
INTRODUCTION:
Contractors often lament the fact that a customer who is already
getting cool air is a hard sell for maintenance and service
work. What these customers may not realize is that this “If
it ain’t broke, don’t fix it” attitude can
be expensive. The performance of air conditioners is sensitive
to service-related issues. Degradation faults, such as fouled
heat exchangers, commonly make air conditioners run inefficiently
and lead to premature equipment failure. However, if the unit
provides cool air, the customer may not appreciate the need
for service.
Imagine a unit that produces cool air but, based
on the measurements, is not operating well. How can you get
the customer’s confidence that servicing the unit, even
when they are happy with the cool air, is in their best interest?
Our suggestion: Define the goals of servicing
a unit. The reasoning behind each goal can be discussed with
the customer when justifying needed services.
There are three reasons for servicing an air
conditioning unit:
- To maintain or restore reliable comfort;
- To protect the unit from expensive premature
failure; and
- To save energy.
AUTHOR: Marcus V. A. Bianchi,
Ph.D.; Jon D. Douglas; and Todd M. Rossi, Ph.D.
CITATION: The Air Conditioing, Heating, and
Refrigeration News, 6/24/02
Guidelines For Troubleshooting R-410A
Systems
INTRODUCTION:
The big push is on to replace R-22 unitary air conditioners
and heat pumps, and it looks like the industry has really
and truly decided that R-410A systems are “it.”
This article offers an overview of some of the issues related
to R-22 and -410A in the field: operating pressure differences,
oil characteristics, and temperature glide.
AUTHOR: Barb Checket-Hanks
/ Service/Maintenance and Troubleshooting Editor with comments
from Todd M. Rossi, Jon D. Douglas, and Marcus Bianchi
CITATION: The Air Conditioing, Heating, and
Refrigeration News, 5/20/02
Smart maintenance for rooftop units
ABSTRACT:
States that packaged HVAC equipment is the most common source
for HVAC in small and medium commercial buildings, including
retail stores, supermarkets and restaurants in the US. Rooftop
and unitary air conditioning equipment accounts for 62% of
total energy consumption for cooling commercial buildings.
The large numbers of units means that service technicians
cannot spend much time on each unit and in addition they are
'out of sight, out of mind.' Notes the trend to outsourcing
facility management services to specialist companies and the
development of new technologies to aid service and maintenance
practices. Defines smart maintenance as involving the application
of technology to identify when maintenance is required and
to monitor performance and diagnose problems more quickly
and accurately than through traditional means. States deciding
when service should be performed must be complemented by anticipating
service needs without relying exclusively on human expertise.
Explains how this can be accomplished by using automated fault
diagnostic systems. Addresses two issues for rooftop air conditioners
- identification of faults that drive maintenance costs and
performance degradations and common approaches to smart maintenance
that reduce operating costs.
AUTHOR: Breuker M, Rossi, T,
Braun J
CITATION: ASHRAE Journal, November 2000,
vol.42, no.11, 41-47, 4 tabs, refs ISSN-0001-2491
Download
this article in PDF format (306KB).
Common faults and their
impacts for rooftop air conditioners
ABSTRACT:
Uses the analysis of a database of over 6000 separate fault
cases to identify important faults and their performance implications
for rooftop air conditioners. Estimates the frequency of occurrence
and relative costs of service for different faults. Quantifies
the impacts on several performance indices through transient
testing for a range of conditions and fault levels. The transient
test results indicated that fault detection and diagnostics
could be performed using methods that incorporate steady-state
assumptions and models. Also derives a set of generic rules
for the impacts of faults on measurements that could be used
for fault diagnoses. Evaluates the average impacts of the
faults on cooling capacity and coefficient of performance.
Uses the data set to design and evaluate the performance of
a fault detection and diagnostics (FDD) method.
AUTHOR: Breuker M S, Braun
J E
CITATION: International Journal of HVAC&R
Research, ASHRAE, July 1998, vol.4, no.3, 303-317, 1 figs,
16 tabs, refs ISSN-1078-9669
Evaluating the performance
of a fault detection and diagnostic system for vapor compression
equipment
ABSTRACT:
Presents a detailed evaluation of the performance of a statistical
rule-based fault detection and diagnostic (FDD) technique.
Steady state and transient tests were performed on a simple
rooftop air conditioner over a range of conditions and fault
levels. Combines all of the necessary components of the technique
and evaluates the robustness and sensitivity of the technique
for realistic operation of a typical rooftop air conditioner.
In addition, studies the impact of design variables such as
thresholds for detection and diagnosis and the number and
choice of sensors on the sensitivity and robustness of the
technique. States the approach developed could be used as
a design and evaluation tool when applying the FDD method
to other packaged air conditioning systems and might also
be modified to evaluate the performance of other FDD methods.
AUTHOR: Breuker M S, Braun
J E
CITATION: International Journal of HVAC&R
Research, ASHRAE, October 1998, vol.4, no.4, 401-425, 13 figs,
13 tabs, refs ISSN-1078-9669
A statistical, rule-based
fault detection and diagnostic method for vapor compression
air conditioners
ABSTRACT:
Presents a method for automated detection and diagnosis of
faults in vapour compression air conditioners that only requires
temperature measurements and one humidity measurement. The
differences between measured thermodynamic states and predicted
states obtained from models for normal performance (residuals)
are used as performance indices for both fault detection and
diagnosis. For fault detection, uses statistical properties
of the residuals for current and normal operation to classify
the current operation as normal or faulty. Performs a diagnosis
by comparing the directional change of each residual with
a generic set of rules unique to each fault. States this diagnostic
technique does not require equipment-specific learning, is
capable of detecting about a 5% loss of refrigerant and can
distinguish between refrigerant leaks, condenser fouling,
evaporator fouling, liquids line restrictions and compressor
valve leakage.
AUTHOR: Rossi T M., Braun J
E.
CITATION: International Journal of HVAC&R
Research, ASHRAE, January 1997, vol.3, no.1, 19-37, 9 figs,
6 tabs, refs. ISSN 1078-9669
Minimising operating costs
of vapor compression equipment with optimal service scheduling
ABSTRACT:
Describes the use of dynamic programming to obtain optimal
service schedules and costs for cleaning the condensers and
evaporators of air conditioning equipment. Obtains results
for a range of service and energy costs, characteristic fouling
times, and equipment sizes for a single building and location.
Compares minimum operating costs with regular service intervals
and a strategy where service is only performed when a constraint
is violated (eg a comfort violation). Finds that optimal service
scheduling reduced lifetime operating costs by as much as
a factor of two over regular service intervals, and by 50%
when compared to constrained-only service. States that for
practical implementation, a simple, near-optimal algorithm
for estimating optimum service scheduling was developed that
does not require on-line forecasting or numerical optimisation
and is easily implemented with a micro-controller. States
that over the wide range of cases tested, the near-optimal
algorithm gave operating costs that were within 1% of optimal.
Notes that this technique could also be applied to other systems
where performance degradations are important, such as large
chillers and power plants.
AUTHOR: Rossi T M., Braun J
E.
CITATION: International Journal of HVAC&R
Research, ASHRAE, January 1996, vol.2, no.1, 3-26, 11 figs,
1 tab, refs. ISSN 1078-9669
Address inquiries regarding these articles
to Todd M. Rossi, Ph.D.
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