Rooftop Unit HVAC Efficiency: Repair, Retrofit, Replace

Introduction 

This primer provides an overview of the challenges, scope and solutions to improve the efficiency of existing unitary heating and cooling equipment, commonly known as rooftop units (RTUs). We begin with a discussion of market size and examine evidence of how RTUs fail resulting in lower efficiency. To assess how utilities are currently pursuing efficiency in RTUs, we include findings from a survey of over 120 existing major utility efficiency programs targeted at RTUs and what aspects of the RTU efficiency they address. 

The measures that influence RTU performance are often described by their product names or monikers that have developed over time. To simplify the landscape of what options are available we organize the most common measures into a framework that addresses the level of invasiveness: repairing, retrofitting, or replacing the RTU and its components, as well as what components are affected—either the equipment outside the facility (usually on the roof) or the equipment inside the facility including ducts, controls/thermostats and associated sensors. 

With this Indoor/Outdoor, and Repair/Retrofit/Replace framework established we describe the measures that fall into these categories with a broad presentation of what occurs, the relative costs and savings, a highlight of the anticipated cost-effectiveness, and any programmatic best practices and notes. 

Calculating energy savings and establishing justification for a program to a regulator presents a challenge. One must find enough data, especially data specific to the climate zone of the area, to establish a basis for incentives. For RTUs this is complicated by the weather dependency of RTU performance. Savings results for a test in Oregon are not relevant to a test in Chicago. This results in redundant testing by various entities. New Buildings Institute (NBI), working with the Bonneville Power Administration (BPA), has identified a method for normalizing performance data to improve translatability between climate zones. The use of a single methodology by many testing entities results in a leveraged data set that bolsters the case for RTU efficiency programs and improves the accuracy of incentives. 

Lastly we discuss industry organizations and efforts that are underway to better unify the approach to RTU efficiency. There is tremendous opportunity for savings and advancement nationwide.

For over 10 years state energy organizations, public and investor-owned utilities and regional organizations, building owners, managers, operators, engineers and contractors have examined methods for improving the in-field operating efficiency of the class of lighter commercial unitary heating, ventilation and air conditioning (HVAC) equipment commonly known as RTUs. 

RTUs provide heating and cooling combined with ventilation air and are a commonly used technology in commercial buildings. Upfront costs, installation, controls, and maintenance are well understood. In a world increasingly driven by speed and reducing overhead in construction and operation, the RTU is an ideal solution for many owners and managers of commercial buildings. 

While this market paradigm is not ideal for energy efficiency, it does present an opportunity to access energy savings through modifications to existing RTUs. This primer examines some of these methods, their relative costs and impacts, as well as best practices in analyzing energy savings. NBI has invested considerable time and resources in identifying leading best practices in the industry.

Table of Content :-
1.Introduction

2.RTU Background

• HVAC and RTU Research
• RTUs in Commercial Buildings
• RTU Performance Degradation
• Utility Incentives and Rebates
• Potential Savings Still Available.
• Accessing These Savings
• Non-Energy Benefits
• Ducts, Zoning and Lockouts, and the Building Envelope 

3.The RTU Efficiency Framework

4.SUMMARY OF STRATEGIES .

5.REPAIR

*Outside Equipment 

• RTU Maintenance 
• Fault Detection and Diagnostics

*Inside Equipment 

• Fixing Thermostats, Sensors, and Controls

6.RETROFIT 

*Control Upgrades to Outside Equipment.

• Advanced Variable Speed Controllers 
• Enhanced Economizer + Controllers 

*Control Upgrades to Inside Equipment 

• Wireless Web-based Thermostats and Sensors

*RTU Upgrades: Adding Equipment

• Air-Side Economizers
• Electronically Computated Motors (ECM)
• Evaporative ‘Side Car’
• Evaporative Condenser Pre-Cooling 

7.REPLACE

• High Efficiency RTUs
• HVAC System Redesign 

8.Utility Programs and Measuring RTU Savings – Two Standard Methods 

• RTU Savings Protocol and Calculator
• EZ-Sim Whole Building Savings Protocol and Calculator 

9.RTU Coalitions and Programmatic Efforts.

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