Maintaining commercial HVAC economizers – Part 1

Introduction

Economizers bring in outside air for ventilation and for free cooling.  However outside air may be too warm or too humid to offer free cooling or very cold.  Additional outside air that must be conditioned increases the cooling and/or heating load on the building.  Economizers that are properly designed, maintained and set can save significant amounts of energy. However economizers that are not functional, leaking, have sensors out of calibration or miss-set can have large energy penalties.  Maintaining economizers is critical to their function and to their impact on energy use.

This document sets out some basic information about commercial HVAC air-side economizers as well as an expanded maintenance checklist.  See: Maintaining commercial HVAC economizers – Part 2 for specific step-by-step economizer performance testing designed to be compatible with price sensitive commercial maintenance contracts. Please Press "Read More"

Maintaining commercial HVAC economizers – Part 2

Introduction

Economizers bring in outside air for ventilation and for free cooling.  However outside air may be too warm or too humid to offer free cooling or very cold.  Additional outside air that must be conditioned increases the cooling and/or heating load on the building.  Economizers that are properly designed, maintained and set can save significant amounts of energy. However economizers that are not functional, leaking, have sensors out of calibration or miss-set can have large energy penalties.  Maintaining economizers is critical to their function and to their impact on energy use.

This document sets out some specific step-by-step economizer performance testing designed to be compatible with price sensitive commercial maintenance contracts.  See: Maintaining commercial HVAC economizers – Part 1 for basic information about commercial HVAC air-side economizers as well as an expanded maintenance checklist.

Minimal visual inspection tasks (common to all economizers)

1.      Visually inspect the integrity and conditions of economizer components and wiring.

a.       Inspect wiring and wiring connections including the main economizer connection is plugged in, all wires connected to sensors, actuators and controllers

b.      Inspect components for excess corrosion, wear, and mechanical problems such as linkages and economizer hardware.

c.       Check eyebrow / economizer hood and filter assembly for proper sealing, and inspect integrity of moisture screen (bird Screen)

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Implementation of Fault Detection and Diagnostic Technology - In-field Diagnostics

Fault detection and diagnostics technology has the potential to make a positive impact on the cost of operating buildings. That is, to lower utility bills, service and maintenance costs and extend equipment life.  Buildings use a significant amount of the energy used in the United States and around the world, and heating, cooling and lighting buildings consume most of the power used in buildings.  The roles fault detection and diagnostics play includes finding, analyzing, documenting, and communicating the existence of a fault, degradation or operational anomaly. 

Implementation of Fault Detection and Diagnostic Technology

In-field Diagnostics

Common initial approach

When applying diagnostic tools in the field, there are two approaches customers commonly choose in non-incentivized environments.  One is to authorize a pilot program; often five to ten locations chosen based on some criteria related to energy cost or perceived chronic reliability problems.  A second common approach is to add the diagnostic capability to a regularly scheduled visit, usually a maintenance inspection.  These attempts at implementing diagnostics have the objective of gathering data, assessing opportunities, effectively addressing issues and reporting achieved benefits. Please Press "Read More"

Purdue CHPB / NIST / NBI / CEC study validates that Field Diagnostics’ Service Assistant HVAC Diagnostic Protocol is an effective and practical method for evaluating refrigeration cycle faults

A recently released report (HL 2014-8, Herrick Laboratories, Purdue University) that describes work funded by the National Institute of Standards and Technology (NIST), the New Buildings Institute (NBI) and the California Energy Commission (CEC) found that the performance of the diagnostic protocol embedded in Field Diagnostics’ Service Assistant tool with SA Mobile software, which has been available commercially since 1999, was markedly superior to some other publically available protocols that were evaluated.

The investigation into the effectiveness of various HVAC refrigeration cycle Fault Detection and Diagnostic methods was conducted by Dr. David Yuill and Dr. James E. Braun at the Center for High Performance Buildings (CHPB) located within the Ray W. Herrick Laboratories, Purdue University (www.engineering.purdue.edu/CHPB). This study looked at not only the accuracy of the fault detections, but at the “value” of following the tool’s advice. The study compared factors such as cost of detection, sensitivity of detection, number of false alarms, and the costs and benefits of addressing the faults that are reported.

The Purdue team’s innovative evaluator of diagnostic algorithms was used to estimate the value of eight products as well as two hypothetical detectors—one “Correct” detector which reports all the faults present, without consideration of the value of addressing them, and another “Ideal” detector that only reports faults that would be cost effective to address.

One of the conclusions of their study was that none of the protocols tested could provide all the value that the “ideal” detector provided: the SA protocol in fact provided only about a half of this value. However, the study found that “the SA protocol provided significant benefit in all cases” and “the value of the SA protocol was computed to be greater than the value of the fictitious correct protocol”, which indiscriminately reports all faults. “The other protocols did not perform well, generally providing negative value for all cases (i.e. imposing a net cost as compared with the baseline

·         the “RCA method,” sometimes referred to as “the manufacturers’ method”, which is used extensively throughout the industry, particularly as the specified method to test charge levels in California’s current Title 24 – 2013 building energy code (CEC 2012), as well as in many utility incentive programs and by Home Energy Rating System (HERS) raters,

·         the “ADM protocol,” which was developed as part of an ASHRAE research project,

·         the “MPS protocol,” which combines elements of the ADM protocol and CA Title 24 requirements, and

·         the “TM protocol (abbreviation for Thermodynamic Metrics), which is a set of rules for typically measured metrics of performance in air-conditioners.

On the other hand, the Field Diagnostic’s protocol has been extensively tested over many years and the Purdue CHPB study validates that it is a very effective and practical method for evaluating refrigeration cycle faults.

For more information, contact: Todd M. Rossi, Ph.D., Field Diagnostic Services, Inc., rossi@fielddiagnostics.com, 215/558-5415

Yuill, D. and Braun, J.E., Development of Methodologies for Evaluating Performance of Fault Detection and Diagnostics Protocols applied to Unitary Air Conditioning Equipment, HL 2014-8, Ray W. Herrick Laboratories, Purdue University, December, 2014.