Natural gas generators are becoming more commonly used in commercial applications due to:
concerns about the environmental impact of diesel generators,
need for onsite diesel fuel storage, and
overall fuel costs.
One of the keys to optimum gaseous generator performance is that the gas/fuel reaches the generator at the appropriate volume and pressure.
When problems with gaseous generators occur, the problems typically occur in the pipelines that direct the natural gas from the utility to the genset. Following are five of the most common sizing and installation issues that interfere with proper performance of a gaseous generator.
A note of caution, only qualified electricians and contractors should attempt installation.
1. Step-Down Regulator is Not Installed in the Proper Location
When installing a gaseous generator at a new site, the generator is typically connected to local utility natural gas lines. Local fuel/gas codes dictate the maximum pressure under which natural gas can be delivered to a site or structure. The supply pressure from the utility meter/regulator is usually not the same as that required by the genset, so a separate primary or step-down regulator is needed to provide the correct pressure and volume of fuel to the genset.
From the primary or step-down regulator, gas flows through a flexible fuel line to the generator connection point, which is the unit mounted regulator.
What often occurs is that the step-down regulator is placed too close to the unit mount regulator. Typically, a minimum of 10 feet of pipeline is required. If the pipeline is too short, it may lead to hard starting, rough running, inability to carry load and erratic operation of the genset. (See diagram below.)
2. Pipe Diameter Size is Not Correct
When determining the appropriate pipe diameter size, the length of the piping as well as the number and type of fittings in the piping system must be taken into account. All pipe fittings (elbows, tees, couplings, unions, etc.) create a pressure loss. The more severe the elbow or turn (90 degrees versus 45 degrees), the greater the pressure loss due to the inherent resistance coefficient. Each pressure loss must be taken into account to ensure that the adequate diameter pipe is selected to maintain proper pressure to the generator. A system with several 90 degree elbows will likely require a larger diameter pipe versus a system with a straighter pathway to the generator.
3. Gas Supply Flow Does not Adequately Account for Overall System Demand
It’s vital that engineers and contractors understand the draws of the equipment being operated and the total amount of load on the system. The generator may be powering furnaces, dryers, refrigerated equipment, pumps, emergency lighting, etc. You need to understand the system, its configuration and various loads so that the piping is sized to provide adequate flow and pressure for initial loads as well as peak loads. Also, best practices for pipe and regulator sizing are to have a fuel flow delivery rating at least 10% greater than the 100% rated kW fuel consumption.
4. Debris in the Pipeline
When installing a natural gas pipeline, debris such as welding slag, pipe dope, Teflon, and more can be collected in the pipe. Debris may reduce the pressure of the gas reaching the generator, so the pipes must be cleaned prior to startup or performance testing.
The pipelines should be cleaned periodically for optimum performance of the system. Debris that enters the regulator and fuel train can cause engine instability, premature wear and even engine catastrophic damage.
5. Excess Moisture in the Pipeline
Excess moisture in the pipe can also adversely affect pressure and volume. Installing a drip leg to remove water and condensate from the gas flow is key. Proper size and location of the drip leg(s) is also critical. (Refer to Diagram 6-1 of the Generac Installation Guideline manual.)
The drip leg(s) should be cleaned periodically for optimum performance of the system.
General Information on Pipe Sizing
There are a wealth of handbooks and information on the Internet available to assist in proper pipe sizing and configuration. Generac offers an” Installation Guide for Stationery Industrial Generators” to assist with proper sizing and installation, as well as our innovative, and recently upgraded software program, Power Design Pro™. Pipe sizing information can be found in the Mechanical Design section of the software. (See below.)
Note: In order to access the pipe sizing area of Power Design Pro™, users must first configure the generator.
Finally, you may want to consult with your local AHJ or your local Generac dealer/distributor for information about proper pipe sizing.