Applications

Large tonnage cooling loads with central chiller plants in areas of medium to high electric rates.

• Hospitals
• Hotels
• Institutions
• High Rise Office Buildings
• Industrial Process Cooling
• Industrial Space Cooling

Overview

Engine-driven chillers are generally described as 'electric chillers with the motor removed and an engine installed.' Of course, there is more to it than that, but it's a good starting point. Engine systems cost at least 50% more than high-efficiency electric systems. Installation costs are also higher due to the need to handle exhaust, noise and engine heat. If electric costs are high enough, engines can be an attractive economic option.

Exhaust is handled by locating the units where they can be correctly vented. Noise is handled with sound attenuation. Engine heat is generally handled by increasing the size of the cooling tower. None of these are major barriers, other than the additional costs.

The efficiency of engine-driven systems are measured in C.O.P. = Coefficient Of Performance, which is a value of BTUs IN / BTUs OUT. Water cooled engine-driven systems have COPs of 1.5 to 1.9, which is measured by the Gas BTUs in to run the engine, over the Cooling BTUs produced.

Most engine-driven systems use screw compressors, as they respond well to variable speed, and have good turn-down ratios, which can improve engine efficiency under part load conditions. Larger tonnage systems use centrifugal chillers that are the most efficient with large loads run under high load-factor conditions.

Operations

Engines are good at following varying loads, so they work well in shoulder seasons when only a small amount of cooling is required. This can also result in reduced peak electric demand charges, as electric chillers remain off, instead of setting the monthly electric demand for only a few hours use. However, because of their higher first cost, it is generally necessary to run engine-drive chillers for as many hours as possible to get a payback.

Most facilities with engine-driven chillers have a 'hybrid plant'. This is where BOTH engine and electric chillers are installed, and optimized so that the best chiller/ mix of chillers are running when they are in their economic 'sweet spot'. Engines will be used during on-peak electric times and when loads are light, and electric will be used off-peak. This also reduces over-all first costs as it is very expensive to purchase engine units for every ton needed, even though it may only run a few hours per year. Less expensive electric units can be purchased by buying a little less efficient of a unit.

Maintenance is always an issue. Most facilities with large tonnage chillers purchase annual maintenance agreements and do not touch their own equipment. Engine-driven units are no different, although the cost of the maintenance agreement will be a little higher, as it must cover the engine in addition to the chiller, tower and any other covered equipment. Simply factor the higher cost into the operating cost analysis and don't let it be an issue. ALL large equipment MUST be maintained, gas or electric, it doesn't matter.

Manufacturers

The following ESC Members have engine-driven chiller products:

Tecogen

Trane

York

Case Studies

Knickerbocker Hotel

Children's Hospital

One Parkway

Go to the Cooling Consortium Web Site

www.gasairconditioning.org

Sources: Energy TechPro