Busting Four Myths About Engine Driven Chillers

Since the early 20^th century, mechanical engines have been used to drive refrigeration cycles, but it was not until the 1970’s when many modern-day benefits were realized once the push for energy efficiency became of interest. Then, the principles of combined heat and power (CHP) were applied to the engine-driven chillers which would maximize the energy use by providing chilled and captured hot water simultaneously. Now with thousands of chillers operating successfully in all varieties of applications, it’s time to uncover the myths about these chillers.

Myth 1: Engine-Driven Chillers are Less Efficient

COP of an engine-driven chiller is defined as a “source” COP, so it doesn’t directly compare to a “site” COP which is commonly used by electric chillers. Using the COP of only the equipment ignores the inefficiency associated with the production and distribution of electricity which is how electric chillers can inflate the overall system efficiency.

Typical electric chillers have a “site” COP of 3 to 6.5 while engine driven chillers have a “source” COP of 2 to 2.6. If we calculate each COP to include the source, we will need to account for the inefficiencies of the powerplant and losses during transmission and distribution. The resulting source COP of electric chillers would then be 1.1 to 2.4 which has a best-case scenario of being equal to that of an engine-driven chiller.

What electric chillers cannot escape is that high cost-electricity is 3-6 times more expensive per energy unit than natural gas. This better tool of comparison results in the different applications when engine-driven and electric chillers can be beneficial to a facility. For engine-driven chillers, the cost savings are calculated mostly by the price of electricity in the area. The price of gas becomes irrelevant when utilizing the waste heat because the heat recovery offsets the boiler gas already used on site. In other words, if the gas is expensive then the resulting heat recovery is more valuable and if the gas is cheap then the heat recovery is less valuable. For engine-driven chillers, you can expect to find an energy cost reduction when the electric rate is above $0.07/kWh and as rates continue to rise, this is becoming more and more prevalent across the US.

Myth 2: Engine Driven Chillers are Expensive

If one is to only compare an electric-driven chiller to an engine-driven chiller by looking at the cost of the products themselves, then sure engine-driven chillers will be most expensive. They do after all have a more complex prime mover, heat recovery systems, and emissions gear that their electric chiller counterparts don’t have. Much of that cost is pushed off to the power plant operators that produce the high-cost energy they need to operate.

When one takes a step back and looks at the system holistically the expenses of an electric chiller begin to add up. Larger switchgear, more copper wires, and larger back-up generators to provide the resiliency that engine-driven chillers inherently provide. When you think about it, it’s a bit unfair to compare two items directly in cost when they do not provide equal benefits.

Myth 3: Engine-Driven Chillers Require a lot more Maintenance

This is actually not a myth, but it should be given a little bit of context. The average electric chiller requires less than 8 hours per year worth of preventative maintenance, in comparison, an engine-driven chiller only requires on average 16 hours per year in preventative maintenance, hardly a cause for concern. Engine-driven chillers are routinely used in critical process cooling applications providing in excess of 99.6% uptime, very similar to their electric chiller counterparts.

Myth 4: The Power Source is not as Clean

Most engine driven chillers installed today operate on pipeline natural gas, however, they can run on a variety of low to no carbon energy sources such as biogas, RNG, or hydrogen. Currently with the fuel mix in the US, the same fuel is powering nearly all electric chillers. How is it that electric chillers are running on pipeline natural gas as well? Ultimately, due to the limited amount of renewable or non-emitting electric generating resources that provide the baseload of our grid today.  Wind, solar, nuclear, and hydro power are only able to meet a portion of our nation’s energy needs annually, and we are using the maximum amount of renewable energy we can currently harvest. So what do we use to adapt to the changes in electrical demand seen by the grid?

The US relies on natural gas as the marginal resource to meet increased demands on the grid that cause electricity use to exceed that of our clean non-emitting resources generating capacity. For example, when cooling systems are turned on because it’s hot, there isn’t any more wind, solar, nuclear, or hydro to turn on to meet the insatiable demands of electric cooling equipment. Natural gas powerplants must step in to provide that added power, ranging typically from 20-40% of additional capacity need. These natural gas powerplants are inherently inefficient and not a very good use of a finite resource as they operate at low efficiencies, typically 40-50% at best, plus an additional 5-7% is lost during transmission and distribution, then electric motors are typically only 95% efficient-in other words it takes a lot of natural gas to get the electricity flowing into your electric chiller.

With engine-driven chillers, there isn’t a need for far away powerplants to send electricity inefficiently. Think of it as a mini-powerplant on the chiller except the energy is directly used in the same location it’s needed, and the thermal energy byproduct is also captured and used. As a result, the overall system efficiency is upwards of 85%. This boost in efficiency while utilizing the same fuel results in an average of 200 tons of scope 2 carbon emissions reduced annually per engine.

Engine-Driven Chillers Offer Many Benefits

Engine-driven chillers offer a high efficiency and practical alternative to traditional electric chillers. These chillers use the principles of combined heat and power (CHP) by providing both cooling and heating, enhancing a facility’s energy efficiency. When considering the complete energy production and distribution process, engine-driven chillers often match or outperform electric chillers, especially given the inefficiencies and higher costs associated with the electrical grid.

Though the initial cost of engine-driven chillers may be higher, their reduced reliance on costly electricity and efficient use of waste heat makes them cost-effective over time. Maintenance requirements are manageable, with about 16 hours of preventive maintenance annually, comparable to electric chillers. Engine-driven chillers also demonstrate high resiliency from grid outages. With the ability to run on cleaner, low-carbon fuels such as biogas, renewable natural gas (RNG), and hydrogen, there can aligning with your sustainability goals. Engine-driven chillers also achieve up to 85% overall system efficiency, optimizing natural resource use and significantly reducing carbon emissions compared to electric options.

In summary, engine-driven chillers provide a reliable, efficient cooling solution that meets modern energy efficiency and sustainability standards. This makes them a valuable asset in hotels, hospitals, universities, indoor agriculture, manufacturing processes, data centers, ice rinks, breweries, and if you don’t have enough power.