Chiller Clearances vs Efficiency

Airflow restrictions can impact chiller unit placement decisions

Chiller Clearances vs. Efficiency

Making the Most of Air-Cooled Chiller Efficiency

Introduction
In most installations, the chiller is the single largest energy-consuming component of an entire facility. For that reason, decreasing a chiller’s efficiency even slightly can result in a significant impact on energy costs, not to mention long-term maintenance and reliability. In air-cooled chillers, one of the largest contributors to efficiency – or the lack thereof – is proper airflow.

Johnson Controls has established guidelines for the placement of YORK® air-cooled chillers when next to each other or next to walls, while still allowing adequate airflow to the units. When chillers are used in situations that result in restricted airflow due to close spacing, multiple chiller units or other obstructions, increased power consumption and loss of capacity may occur. This article, and a more in-depth application guide which you can request, will summarize the effects of these restrictions to help inform decisions regarding chiller unit placement.

Recommended Clearances
While exact clearances can vary by model, for our example, we will use the factory-recommended minimum clearances for a YORK® YVAA chiller. These include side to wall: 6 ft (1.8 m), rear to wall: 6 ft (1.8 m), control panel end to wall: 4 ft (1.2 m), top: no obstructions and finally, the distance between adjacent units: 10 ft (3 m).

Case Study Findings
Several factors can affect the capacity and power requirements of an air-cooled chiller. However, for purposes of this study, we limited the variables to include the specific obstructions outlined below. The tests were conducted on YORK® YVAA VSD screw and YORK® YLAA scroll chillers. The results for both units were similar, with the effects of the obstructions increasing on units with higher fan counts.

Chillers placed side by side

The recommended minimum clearance for two, air-cooled chillers placed next to each other is 10 ft. While closer placement is possible, the capacity was decreased by more than 2.5% and the power requirement increased by nearly 3% for units six feet apart and having up to 26 fans.

Three or more chillers in a row

As before, the recommended minimum clearance in this configuration is 10 ft. With three units close together, the derating is larger than in CASE 1. Here, the capacity was decreased by 3.5% while the power requirement increased by more than 4.0% for units six feet apart and having up to 26 fans.

Open area of a fence surrounding a single chiller

Customers wanting to conceal the chiller with a thin wall or fence may do so without any negligible derating to capacity or increase in power required, providing the wall does not exceed the height of the chiller.

A single chiller surrounded by a solid wall

Installation of a chiller inside of a pit, or with thick walls around it that are taller than the chiller, will cause lower capacity and higher power consumption. In our testing, the capacity was decreased by more than 4.5% and the power requirement increased by more than 6.0% for units having up to 26 fans with a surrounding wall height of 12 feet placed at a distance six feet away.

Results Summary

A part from thin fencing that does not exceed the height of the chiller, obstructions to the recommended chiller minimum clearances resulted in measurable decreases in capacity and increases in power requirements across the board. While a few-percent reduction in performance may not seem significant, the effects should be considered over the life of the unit. In addition, total cost of ownership considerations may include additional system wear, decreased serviceability and other factors not tested here.

Any potential benefits derived from a deviation from minimum factory clearances should be carefully weighed versus the performance decreases outlined here in.