Piping and Energy Efficiency In Chillers

The materials and design of the piping have a significant impact on the system pressure drop, which affects pump performance. Many of the decisions made in the piping system design will have an impact on the chiller plant's operating cost every hour the plant runs for the life of the building. From the standpoint of the life cycle, any improvements that can reduce the operating pressure drop should be considered the following:

Material for a pipe. The friction factors of various materials vary.

Pipe dimensioning. The pressure drop increases as the piping size decrease. This must be balanced against the capital cost and taken into account over the system's lifetime.

Fittings are a type of fitting. Fittings should be kept to a minimum.

The word for today is valves. Valves represent significant pressure drops and can be expensive. Isolation and balancing valves should be placed strategically.

Insulation on the piping reduces heat gain into the chilled water. This has a multiplicative effect. For starters, any cooling effect lost due to heat gain adds to the load on the chiller plant. Second, in most cases, the chilled water setpoint must be lowered to provide the correct supply water temperature at the load in order to account for the resulting temperature rise. This raises the lift on the chillers and reduces their efficiency.

-piping systems, ASHRAE 90.1-2001 specifies the following:

Piping must be insulated in accordance with ASHRAE Standard 90.1 Table 6.2.4.1.3.

Among the exceptions are:

Insulation is installed at the factory.

Systems that operate between 60°F and 105°F.

The hydronic system should be proportionally balanced first to minimize throttling losses, and then the impeller should be trimmed or the speed adjusted to meet the requirements to be followed.

Pumps with motors less than 10 hp are an exception.

When throttling produces no more than 5% of nameplate horsepower or 3 hp, whichever is less.

It is not permitted to use three pipe systems with a common return for heating and cooling. (6.3.2.2.1) Two pipe changeover systems are acceptable if the following conditions are met: (6.3.2.2.2) Controls limit changeovers based on a 15°F ambient dry bulb deadband.

The system will run in a single mode for at least 4 hours.

Reset controls reduce the changeover temperature to 30°F or less.

Systems with a total pump nameplate horsepower greater than 10 hp must be variable flow capable of modulation down to 50%. (6.3.4)