Three Letters Re: Natural Gas Powered Generators in a Disaster–Their Compressors, and Yours

JWR,
Thank you for letting your readers know about [public utility] natural gas system compressor stations. I, for one, was was blissfully ignorant about them, and had just assumed that natural gas was “always on.” So, now knowing that, I can now see that a tri-fuel generator that can quickly be changed to propane or gasoline would be best. Thanks also for mentioning the capacity limits of generators. That I was aware of, but I hadn’t ever looked at the specs on my GE refrigerator/freezer. Now I can see that I need to do a “load budget”, to determine what I can leave plugged in, and not bog down my generator. (It is a 3 KW, and all those lights in the house add up a load, real quick.) – Curtis N.

Mr. R. –
Regarding residential refrigerators and generators – I’ve tested a few, using a Kill-A-Watt and the Belkin Insight Tester and a test rig I built to use a clamp-on type multimeter. I’ve measured startup demands – locked rotor current (LRC) – and run current on the last 2 refrigerators I’ve bought, and on several owned by friends. I found that LRC averages between 1200 and 1400 watts, depending on size and design. That’s about 10-12 amps (NEC – National Electrical Code – specifies that circuits be sized to use no more than 80% of the circuit’s maximum capacity, so a nominal 15 amp circuit should never have to carry more than 12 amps, which is why refrigerators are on dedicated 15 amp circuits). The formula, BTW, is AMPS = WATTS divided by VOLTS. Or, WATTS = AMPS x VOLTS. Use actual measured figures for computation. For example, the utility-supplied voltage in my current house is consistently between 120.2 and 120.4 volts. My Honda EU3000i generator varies between about 114 and 122 volts depending on load.

Run current on every fridge I’ve tested – ranging from 18 cu ft to 26 cu ft – settles in well under 200 watts after 2-3 minutes. My old Amana 25 cu ft side-by-side consumed only 141 watts after 3 minutes, my new Samsung 26 cu ft consumes 155 running watts.

Fridge tip – outfit called ACU-RITE makes a wireless fridge and freezer thermometer, about $30 at Amazon.com. Put one of the sensors in the fridge, the other in the freezer, the display unit has a magnet to stick on the outside.  I suggest sensor placement near the warmest part of each. Experiment to find where that is. I tested my old Amana by setting the freezer control to “coldest” (which turned out to be -14 F) and adjusted the fridge to 33-34 F on the top shelf without freezing stuff below that shelf. Give the fridge 18-24 hours between setting changes to stabilize internal temperature. I then unplugged the unit and monitored temps. Without the doors being opened I found that the fridge rose to 46F in just under 6 hours, and when plugged back in took not quite 3 hours to get below 40F after cresting at 49F. The freezer never went above +5 F. On this basis I figured I could put the generator on other tasks for 5 hours at a time.

I experimented with [supplemental] external insulation, from blankets and quilts to rigid foam. Best results were with 2″ thick polyisocyanurate sheets (Dow calls their version “Tuff-R”) which have an R value of about 6.5 per inch. Using an infrared thermometer I found the weak spot in fridges is the door seals followed by the door itself, so I cut the side and top panels to overlap the door edges. To insulate the doors you’ll have to remove the handles. Securing it with duct tape, and sealing the sheet edge joints with duct tape, insulating the back (above the opening for the compressor and related hardware), both sides, top and doors, I got another 3 hours after unplugging before fridge temps rose to 45-46F. – Nosmo

Mr. Rawles,
I don’t know where you got your information that the ‘norm’ for natural gas pipeline compressor stations is electric powered. As a former pipeline CEO of a large pipeline system and still a consultant to the industry (therefore I believe that I have some basis in fact) I would suggest at least on the inter and intra state pipeline transmission systems as well as the majority of gathering systems the compressor stations are powered by natural gas (taken from the pipeline that they are compressing). Only in recent years has there been any real shift to electric drive compressors and those are typically only in areas of the country that are EPA challenged, i.e. they are considered ‘non-attainment’ areas regarding air quality and as such permits for new equipment is difficult to obtain if they are gas fired.
 
[The EMP and grid failure risk that] is relevant is most of the control systems [for natural gas pipelines] are run on grid-supplied power and the vast amount of these controls are digital in some form or fashion these days. Thanks, T.C. in Texas

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