Power Reliability

Hospitals and other critical cooling applications will often consider absorption and/or engine-driven chillers to mitigate the consequences of an electrical outage. In fact, one of the common rationales for absorption is that it downsizes the emergency generator required, and can often be fired with in-place boiler capacity. This logic may well be correct but it should be compared to several other alternative design strategies including:

1. Thermal storage: Today's operating room suites are often better served with 38°F water to provide desired space temperatures. This water can be produced with an ice-based thermal storage system that can also provide emergency cooling during an electrical outage.

2. Emergency generators: Emergency generators are relatively inexpensive and shouldn't be dismissed out of hand. In addition, many of today's electric utilities are interested in contracting with customers to operate this equipment at times when the utilities are peaking. This reduces the utility's own generation requirements (commonly called curtailable power agreements).

3. Equipment retrofit: Always check the economics of replacing inefficient existing equipment. There may be a viable opportunity to upgrade to a more efficient cooling alternative. For example, an existing 300 ton electric chiller operating at 0.9 kW/ton can be replaced with a 450 ton electric chiller operating at 0.6 kW/ton. With the same energy consumption, the system would gain another 150 tons of cooling capacity at no added operating cost!