Best Practices For HVAC Retrofits That Deliver

By Jason Carter
As of the April 2021 issue

AAs HVAC systems age, there are predictable challenges that facility managers and building owners can expect. Depending on their condition, older systems may no longer perform as they once did, resulting in lower efficiency, poor indoor air quality (IAQ) or discomfort to residents. Even if they don’t feel it right away, facility managers and building owners are likely to see the evidence in high utility bills and in maintenance and repair costs. So how can facility managers overcome these challenges while controlling costs? Quick fixes can provide a short-term solution, but best practices require a deeper, more holistic evaluation of systems.

The first step to find this solution is a full building analysis. By performing an analysis on a commercial rooftop unit, it is determined whether a retrofit is more worthwhile than replacing the whole unit. If retrofit is possible, there are two ways to consider: a standard or a deep retrofit.

In a standard retrofit, economizers or controls are added to a unit to reduce both energy and maintenance costs. Two examples include replacing the inlet guide vanes with a variable frequency drive (VFD) on the supply fan to vary the air flow between rooms, or replacing a multi-zone rooftop, which constantly heats and cools with damper control, with variable air volume (VAV) system.

Also known as continuous commissioning or retro-commissioning, a deep energy retrofit (DER) is complemented by an in-depth analysis of building systems to maximize energy savings. Savings on utility services then effectively pay for the equipment, just like a performance contract. Integrating BACNet or another building automation system to monitor and optimize energy consumption is an example of a DER. Whether standard, DER or a combination of both, it is important that HVAC retrofits include compliant solutions specific to a building’s challenges to help facility managers achieve specific cost savings and air quality goals.

Reduce repairs and maintenance

HVAC maintenance, repair and overhaul (MRO) is a significant expense for facility managers. A DER solution such as smart controls provide continuous monitoring and reliable diagnostic feedback that helps prevent problems before they occur, reducing maintenance and repair costs.

Smart plug and play controls are thermostat ready and can be integrated with BACNet control systems. With no configuration and no programming in the field, smart equipment controls provide a diagnostic self-test boot report and have VAV and single-zone functionality.

Some smart controls include fault detection and diagnostics (FDD) that help facility teams get the most out of their rooftop units. FDD technology uses multiple sensors to continuously monitor refrigerant circuit temperature and pressure, economizer operation, and outdoor humidity and temperatures. FDD algorithms then process the collected data and issue detailed alerts if problems arise, helping facility management ensure equipment is always performing as specified (see Figure 1).

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Figure 1: Systems with fault detection and diagnostics (FDD) algorithms process HVAC system data, allowing facility management to ensure equipment is performing as specified. (Map: provided by author)

By monitoring critical variables, facilities managers can respond to problems before they first arise, taking a proactive rather than reactive approach to HVAC management.

Increase energy savings

When completing a retrofit, it is essential to ensure that the specified equipment complies with existing energy standards. Future standards, such as the new Department of Energy’s minimum efficiency standards coming into effect in 2023, and updated ASHRAE 90.1 standards, should also be considered. In addition to efficiency standards, discounts and LEED requirements can also drive equipment specification. To help buildings meet these standards and earn incentives, RTU manufacturers have implemented a number of efficiency-enhancing innovations, including airflow control.

If it is within budget and possible to work in the existing space, VAV is usually the best choice for airflow control as it saves fan energy costs and also provides more comfort for the occupants. VAV controllers offer significant energy savings by using a variable speed drive and pressure transducer to maintain static pressure in the supply duct.

But budget and design do not always allow for a VAV system, and the capabilities are not necessary for all applications. Discrete fan control is an option for constant air volume (CAV) systems where fan compressors are staged to improve energy efficiency as well as comfort and performance. This type of single zone airflow control is ideal for areas such as warehouses. Unlike typical single zone system operation, CRSZ (continuous single zone reset) control is an option that operates with the minimum fan speed required to maximize energy savings and comfort. This can also support passive dehumidification.

Depending on the geolocation, free cooling and other economizer controls can provide efficient cooling. In locations that drop below a certain temperature at night (usually 55 ° F), an economizer brings in outside air to cool a space without the use of compressors or the full cooling capacity of the unit. Different types of controls, including dry bulb, enthalpy and double enthalpy, provide this free cooling.

ASHRAE 90.1 indicates which economizers and controls should be used in which climate zones. Ideal for locations where humidity is not an issue, dry bulb controllers will bring air in without turning on the compressor when the outside temperature is at or below the set temperature. Enthalpy does the same, but can work in a wider temperature range by looking at the humidity as well. Both options can run the compressor just enough to cool the outside air to the set temperature when needed. If the outside temperatures and humidity permit, both can be more energy efficient than circulating return air. With an outdoor and return enthalpy sensor, double enthalpy compares return conditions to outdoor conditions to decide which option will use less energy to cool the room.

Some manufacturers offer free energy-saving calculators and other tools to help engineers and facility managers determine the ROI and energy savings of these systems based on their location. By entering specific application parameters, users can see projected scenarios to help them make informed decisions (see Figure 2).

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Figure 2: Energy-saving calculators help engineers and facility managers determine the expected ROI from HVAC retrofits. (Map: provided by author)

Improving the health and comfort of the occupants

To ensure occupant health and comfort in retrofits, equipment must comply with ASHRAE 62.1. This standard specifies minimum ventilation rates for acceptable indoor air quality. But there are also other considerations when improving a building’s indoor air quality.

Filtration is essential for growing healthy buildings. Some light commercial units are designed to switch from 2 to 4 inch filters, which provide more accurate filtration. And, in addition to efficiency, demand-driven ventilation can help bring fresh air into buildings by raising the level of the outside air intake.

Ultraviolet lamps are also very popular for retrofits. These systems can kill or inactivate fungi, mildew, dander, bacteria and viruses by using UV-C light to damage the nucleic acids and proteins of pathogens. These devices can be mounted in ductwork or packaged units, keeping them clean and operating more efficiently. They can also help fight the fungus and bacteria commonly found in areas with a lot of condensation from system components such as the indoor battery.

Complete a successful retrofit

When evaluating a retrofit, facility executives will benefit from proven experience and expertise. It is beneficial to partner with an expert who has service, controls and equipment knowledge and a manufacturer who provides the equipment to meet different needs. A representative with a local service department can also handle all support needs. Equipment that minimizes repairs, saves energy and improves health, backed by this level of expertise, will ensure that retrofits provide years of efficient performance and comfort.

Jason CarterCarter is a light commercial application engineering manager at Johnson Controls based in Norman, OK. He graduated from the Georgia Institute of Technology in 2002 with a Bachelor of Science in Industrial Engineering. After graduating, he worked for seven years as a Commercial Sales Engineer at Trane before joining Johnson Controls in 2008. He is a LEED Accredited Professional and has been involved in ASHRAE, CEE and LEED committees.

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