Trane SYS-APM001-EN manual Misconceptions about Low-Flow Rates, System Design Options

System Design Options

Figure 23. Annual system operating costs (absorption chillers)

$40,000
$35,000
$30,000
$25,000
$20,000
$15,000
$10,000
$5,000
$-
4.45 gpm/ton	3.60 gpm/ton	3.09 gpm/ton

Condenser Water Flow

Kelly and Chan10 compare the operational costs of chilled-water system designs in site locations. Their summary states:

In conclusion, there are times you can ’have your cake and eat it too.’ In most cases, larger ΔTs and the associated lower flow rates will not only save installation cost but will usually save energy over the course of the year. This is especially true if a portion of the first cost savings is reinvested in more efficient chillers. With the same cost chillers, at worst, the annual operating cost with the lower flows will be about equal to “standard” flows but still at a lower first cost.

Misconceptions about Low-Flow Rates

Some common misconceptions about low-flow systems include:

1Low flow is only good for long piping runs

2Low flow only works well for specific manufacturers’ chillers

3Low flow can only be applied to new chilled-water systems

Let’s discuss each of these three misconceptions.

Misconception 1—Low flow is only good for long piping runs.

One way to examine this claim is to use our previous example, but to concentrate on the condenser-water side. We’ll start with the example covered on pages 30-32.Using the same chiller, but a smaller cooling tower

SYS-APM001-EN Chiller System Design and Control 39