Lighting is essential in any refrigerated warehouse, but the heat it generates can be costly. But there are ways to achieve substantial savings.
By Aaron Kless, PE
It’s no secret that the biggest energy load for a cold storage facility is refrigeration. Keeping individual rooms at the target temperature is a business imperative, enabling cold-storage providers to meet their contractual obligations to customers.
But it is an expensive endeavor, so facility managers are extremely focused on the finite list of energy efficiency measures they can take, including refrigeration system optimization, better insulation of the building envelope and doors, and/or decreasing load.
While the lion’s share of refrigeration load is from transmission, infiltration and product, lighting is a significant contributor, and often an excellent opportunity for energy efficiency improvement.
“From a refrigeration perspective, lighting is in the ‘necessary evil’ category,” said Greg Robison, Vice President, M&M Refrigeration, Inc. of Federalsburg, Maryland.
“Traditional high-wattage incandescent lights only convert 10 percent of the energy used into illumination, leaving the rest of the wattage as wasted energy that is dissipated as heat. That’s a huge mechanical and energy burden, and a colossal waste of financial resources.”
Lighting and Thermal Load
Energy introduced into a temperature-controlled space as either light (or heat) must ultimately be removed by the refrigeration system. The power used by the lighting is the key to analyzing its impact on refrigeration load. All lights introduce heat into the environment, so by measuring the wattage of the light source, refrigeration load can be calculated.
Here’s an example:
One hundred 400-Watt high-pressure sodium (HPS)
fixtures, which draw 465 Watts each (with ballast factor),
require 46.5 kilowatts and consume 407,340 kWh per year
(46.5 kW x 8,760 hours for a 3-shift facility).
The majority of that energy is added to the refrigerated environment’s load, either as wasted heat given off by the fixtures or as radiated light, which is absorbed into the environment and re-radiated. Because these lights are typically left on all of the time, the heat energy being reradiated by the room reaches steady state with the light energy being absorbed.
Here are the calculations, including the thermal impact:
Light Fixture Power (HPS) 465 W
Number of Lights 100
Total Lighting Power 46.5 kW
Total Lighting Power (BTU/hr) 158,658 BTU/hr
Max Refrigeration Load 13.2 Tons Refrigeration
Assuming a load factor of 90 percent, with the vast majority of this heat load being removed by the refrigeration system, the chiller will have to remove 1.25 billion British Thermals Units (BTUs) of energy each year from the lights alone – enough energy to melt over 4,300 tons of ice!
Challenges of Legacy Lighting
The logical solutions to the thermal load issues presented by traditional lighting are to choose a lower-wattage option and/or to turn the lights off or down when not needed.
The challenge is that traditional industrial lighting typically used in chilled facilities – high-intensity discharge (HID), high-pressure sodium (HPS), and the somewhat-more energy-efficient high-intensity fluorescents (HIF) – are ill-suited to measures such as occupancy sensors or dimming controls that can mitigate energy use.
These lights have warm-up issues that prevent them from instantly reaching safe illumination levels, and frequent on/off cycling shortens their useable life, so facility managers are not comfortable turning the lights off, lest they create a safety issue. In addition, cycling many HIF fixtures on/off in increments of fewer than 15 minutes voids the ballast warranty while abbreviating lifetime and accelerating re-lamping schedules. Many facility managers attempt to manage this process in fluorescent fixtures by leaving half of the lamps in a fixture on, and adding after-market occupancy sensors. This is an expensive half-measure that adds cost to the installation and perpetuates the performance and energy issues; warm-up times are still insufficient, and they are paying to keep half of the lamps on all of the time.
The bottom line is that if you cannot cycle the lights on and off in small increments, and if you have to leave a larger percentage of lights on all the time, you cannot successfully meet lighting energy-savings goals or reduce thermal load.
Savings With LED Alternatives
LED lighting represents a compelling alternative for industrial facilities, and is seeing rapid adoption throughout the cold storage industry, both in lighting upgrades and in new construction. A chip-based illumination source, these small light-emitting diodes are proving to offer major energyefficiency advantages for industrial facilities, particularly refrigerated ones, both in direct lighting energy reductions and thermal load savings.
Well-built LED industrial lighting is highly energy efficient, runs at lower wattages than other industrial lights, is highly controllable (when coupled with systems that manage on/off, dimming, scheduling), has rapid strike times for instant-on capabilities, performs extremely well in chilled environments, and offers long lifetimes – over 60,000 hours of on time before light output decreases below 70 percent of initial output (See sidebar below).
These inherent characteristics make them particularly well-suited to industrial applications, including cold-storage environments. LED alternatives are available in three main categories, each with particular energy-efficiency characteristics:
- Plain LED fixtures – Plain LEDs provide excellent light output with much lower wattage – offering lighting energy reductions of up to 50 percent and significant thermal load reductions. There are numerous products that offer light output equivalent to a 400-Watt HID at only 160 Watts. But the simple LEDs do not have controls and are typically left on, just as traditional other lights are.
- LEDs with after-market sensors – Coupling LED fixtures with after-market occupancy sensors can offer incremental additional energy savings, but can be difficult to manage and adjust. Sensors wired to groups of fixtures preclude focused energy savings by keeping groups of lights on based on existing circuit wiring, and adding individual light sensors adds up-front installation cost and installation time. Either way, adjustments to settings must be done using a lift and handling every fixture, never truly able to keep with a facility’s dynamic needs both over shifts and over years.
- Intelligent LED lighting systems – The most significant energy-efficiency opportunities come from intelligent LED lighting systems, which offer direct lighting energy savings of up to 90 percent. These systems maximize lighting energy savings and minimize thermal impact by combining lower-wattage fixtures that automatically respond to occupancy to provide light only when and where operators need it. Built for maximum energy efficiency, they integrate LEDs, sensors, wireless networking, and centralized control into a single, integrated system for higher levels of savings. For most cold storage facilities, that means that a 160-Watt fixture is only on 20 percent of the time, and uses only 32 Watts or 280 kWh per year (vs. a plain 160-Watt LED, which uses 1,401 kWh per year or a 400-Watt metal halide which uses 4,073 kWh per year).
Comparing Lighting Alternatives
How do thermal loads of lighting alternatives compare? Here is a head-to-head comparison using a standard load factor of 90 percent. While there are variations in the efficiency of refrigeration systems, facility insulation and other factors, this provides a standard formula for discussion. If you use a different factor in your facility, feel free to re-calculate the equations with that data point.
The takeaway? Lower wattage intelligent LED alternatives save significant amounts of thermal load – enough heat, in fact, to freeze over 4,000 tons of water. This is because the lights are intelligently managed to deliver the highest levels of savings.
Adding Up Savings
Rather than view lighting and refrigeration as perennial foes, new intelligent LED lighting technologies present the opportunity to re-think the relationship between the two systems and synthesize their operations to improve the facility’s overall energy efficiency.
With utility rates projected to increase over the coming years, the only way to insulate your operations from unchecked escalation of a large operating expense is to address all of the variables driving the energy bill. Since lighting is one of the largest contributors, understanding the array of energy-efficient options and their potential impact on your overall operations will empower you to make the best possible choices for your organization. If you are updating aging high-wattage lighting, that upgrade could result in a net-negative impact on your overall energy bill – especially if you’re able to reduce lighting energy up to 90 percent and lock in the thermal savings, as well.