One of the hottest topics of discussion to emerge from the

recent years of uncertainty in commercial refrigeration

is the concept of retrofits. Retrofits are often viewed as a

method to preserve a company’s capital investments by extracting

the maximum lifespan from its existing refrigeration systems. The

primary goals of most retrofit projects include: improving system

reliability; reducing energy consumption; achieving true load

matching; and enabling more precise temperature control.

To meet these goals, system engineers and service contractors

typically rely on some form of variable capacity modulation in the

retrofit, which refers to a design strategy that enables the ability

to precisely match system capacity to varying refrigeration load

requirements. But, what many have learned through countless

retrofit projects is that not all methods of variable capacity

modulation are created equal.

Capacity modulation: Mechanical vs. digital methods

Mechanical strategies to modulate compressor capacity come in

various forms and offer varying degrees of effectiveness:

• Uneven rack systems: utilize a bank of compressors with varying

capacities (20K, 40K, 60K BTUs) to offer somewhat improved

load matching capabilities; prone to high cycling rates (on/off)

and incapable of providing precise temperature control

• Variable-speed drives: integrate variable-speed drives into the

compression cycle to provide capacity modulation; often cost

prohibitive and offer limited modulation range

Digital capacity modulation is a relatively lesser-known

compression technology that allows for infinite capacity

Digital Compressor Upgrade Addresses Multiple Retrofit Challenges

By Ani Jayanth

Director, Product Marketing

Emerson Commercial & Residential Solutions

adjustments from 10 to 100 percent. Otherwise referred to as a

digital upgrade, this retrofit involves replacing one fixed-capacity

compressor in a refrigeration rack with a new digital compressor as

the lead compressor — with the goals of achieving load matching

and subsequent energy benefits while minimizing the required

modulation range.

This process is relatively straightforward and benefits from

the latest technology and electronic controls to upgrade an

existing refrigeration system.

Instead of having to cycle on and off to meet varying capacity

requirements, the digital compressor-led system is capable of

adjusting the entire rack’s output to match dynamic refrigeration

loads. Digital capacity modulation may deliver many benefits to

an end user:

• Decreases power and energy consumption

• Reduces compressor cycling (on/off)

• Increases contactor life/system reliability

• Enables true system load matching capability

• Provides tight temperature control (suction setpoint range)

How going digital addresses trends in supermarket refrigeration

In many ways, digital upgrades are tailor-made for supermarket

applications, where many operators are seeking retrofit opportu-

nities to address modern operational challenges. Let’s take a look

at some of the leading trends in supermarket refrigeration and

how digital capacity modulation can help operators achieve their

operational goals.

1) Improve energy efficiencies. Independent tests have verified

the energy-efficiency benefits of replacing a fixed-capacity

compressor with a digital model on a parallel rack. This test

evaluated energy efficiency in two steps: 1) replacing the

compressor; 2) enabling capacity modulation. According to

these results, simply installing a digital compressor in place of

the weakened one yielded a 4 percent energy consumption

reduction. Then, when the digital capacity modulation capability

was activated, the retrofit yielded 12 percent additional energy

improvements, resulting in annual savings of $17,215.

2) Adding doors to open display cases. Open display cases are the

largest consumer of refrigeration system energy in supermarkets,

The primary goals of most retrofit projects include: improving system reliability; reducing energy

consumption; achieving true load matching; and enabling more precise temperature control.

In addition to achieving accurate load matching

capabilities, digital modulation can deliver numerous

reliability, performance and energy efficiency benefits.

• More precise case temperature control —

temperature fluctuations in cases may be reduced

up to 90 percent to produce much more consistent

operating temperatures.

• Tighter suction pressure setpoint ranges —

suction pressure setpoint ranges may be reduced

up to 89 percent.

• Increased system reliability — compressor start/stop

cycling in parallel rack applications may be

reduced by 50 percent,

reducing unnecessary wear

and maintenance costs.

• Reduced energy

consumption — reduced

compressor cycling com-

bined with accurate load

matching can provide 10

to 30 percent reduction in

energy consumption.

Capacity modulation: Benefits at a glance

prompting many retailers to install doors. While adding doors can

greatly reduce cold air loss, potentially resulting in a 50–80 percent

load reduction and significant system energy savings, it can

also result in a refrigeration system that’s grossly oversized for

capacity. This scenario is a perfect candidate for digital capacity

modulation, which would allow the system to adapt its capacity

to the reduced load and deliver additional efficiencies.

3) Achieve true capacity control. System engineers have long

attempted to design a system capable of matching the

fluctuations in dynamic supermarket refrigeration loads. Among

all these methods, digital compressors with capacity modulation

have proven most effective — and less expensive and easier to

5/2018

Operators can maximize the retrofit benefits of a digital compressor upgrade by also deploying a full-system approach to efficiencies. Here are a few of the additional system components that can further enhance digital capacity modulation capabilities.

• Case controls — provide precise temperature, defrost, variable compressor and evaporator controls; capable of tying into larger facility/building management and supervisory systems

• Electronic expansion valves (EXVs) — enable accurate control of refrigerant flow and system superheat

• Low condensing operation — equips systems to float head pressures in accordance with changes in ambient temperatures down to a minimum setpoint; helps reduce energy consumption by up to 30 percent in refrigeration systems

A full-system approach to efficiency

install than variable-speed drives. Unfortunately, many system

designers and contractors aren’t even aware of the potential to

retrofit an existing system to enable the modulation of capacity

from 10 to 100 percent.

Applicability in foodservice

Many of these same challenges are shared by the foodservice

sector, where restaurant operators are also keen to retrofit or

replace refrigeration systems to reduce one of their biggest

sources of energy consumption. Digital compression technology

and capacity modulation have also proven effective in these

applications.

System design typically utilizes a multiplex architecture,

where one digital compressor provides the cooling for multiple

fixtures in each temperature group. Multiplex systems also feature

a backup fixed-speed compressor for complete redundancy

and require significantly less piping and refrigerant charge than

conventional systems.

As with the grocery example, this digital setup allows for

precise capacity modulation in response to a facility’s varying

refrigeration loads. But the proof, as they say, is in the pudding.

Restaurants have successfully utilized this architecture to reduce

annual energy costs up to 33 percent. Meanwhile, operators also

appreciate the enhanced electronic controls that enable remote

monitoring, alarms and refrigeration management.

With digital compression technology, operators are finally

able to solve the age-old problem of accurately sizing refrigeration

systems to the needs of a particular facility. So, whether you’re

running a grocery store or a restaurant, digital capacity modulation

provides a reliable method to reduce your energy footprint.

While we’ve primarily focused on retrofit opportunities in

this article, making the transition to digital compression technology

is as effective for new or replacement systems. Regardless of your

specific operational priorities, at the end of the day, all operators

share a similar goal when it comes to refrigeration: make sure

it provides the required cooling for the job. Among its many

other operational advantages, digital capacity modulation is a

particularly effective method of achieving this goal.