Hey guys,
I maintain generators for a living, so I know a thing or two about them, but everything I work on is 60kw and larger, and all diesel three phase systems. I know little about home units, but due to me always being out of the house when the worst weather hits I would love a fully automatic system that my wife doesn't have to worry about. We tend to lose power during these big storms for several days, and I am tired of it. I want the system to be fully automatic for my piece of mind as well.
We deal with a local generator company for supplies and such from time to time, and they told me they could give the friend rate on some whole house units from Kohler. The thing is their friend price for a 14kw or 20kw is still thousands higher than the deals I see online. I am not sure the specs of the ones they are offering are the same as the discount dealers online, but my guess is they are.
On top of these concerns I have about price I spoke with a friend that has a older Generac water cooled 25kw genset that he swears by. The biggest advantage I see is that the water cooled units are basically what I work on every day (only not diesel), and turn at a much more normal 1800 rpm instead of the air cooled units that turn 3600 rpm. This lower speed to me seems like it is easier on the system all together, and has to be way less noisy. The disadvantage is the higher price (significantly higher), and I suppose more complicated unit due to maybe more failure points like the cooling system.
FYI I have amp clamped my incoming service and it looks like with almost every light on in the house, all 4 burners on high on the stove, oven on,well pump on,washer,dryer,boiler, a dehumidifier, and 2 window air conditioners on results in about 90 amps, so roughly 21kw. Now I understand I will never have all of this stuff going at once, but I think I should at a minimum look at the 20kw sizes in a genset. Am I off on that?
Can you guys steer my in any direction? Oh yeah by the way I am planning on running on LP gas for this genset. There is Natural gas on my street but not at my house, and the LP runs true for the genset kw rating while natural gas causes a derating of the kw output.
Thanks,
Chris
Most generator dealers should be able to provide you with a worksheet for calculating the size generator required. Nothing wrong with a 20kW unit but I suspect you could get by with considerably less. One way to do it is to install a subpanel that handles just the emergency loads (well pump, heat or a/c, a few outlet and light circuits, etc.) and just power those loads with the generator.
This article shows how to set up a subpanel for a generator; it's based on a portable unit with a manual transfer switch but you can see how it would work the same with a permanent generator and automatic transfer switch. http://ne.mara.net/generator/pm_gen_install.pdf
Water cooled and 1800 rpm are both good things to have, but for the total amount of time a home generator is typically run they aren't absolutely necessary (although an 1800 rpm unit will most likely be quieter.)
Kohler and Generac are reputable brands, another one I like for small generators is Cummins/Onan. One thing to consider about ordering from an online source is you aren't going to get same level of service you'll get from your local dealer.
Thanks Stuart. I know all about transfer switches and other means of doing this as I do work on them all the time, and I am a licensed electrician. I don't however know much about the residential side of these systems as far as what is the best bang for my buck. The idea of fully automated is what I really want even though I know I could do it cheaper otherwise, but I don't want to have my wife messing with anything when I am not there which is pretty much always when the bad weather hits.
I have a friend with a natural gas Generac on their house. It's setup with a fully automatic transfer switch, and it cycles its self on once per month for a few minutes whether its needed or not, as preventative maintenance.
They've been very happy with it, and I believe the cost was about $7k a few years ago when they had it installed.
Mongo's Onan 7200 has saved us much discomfort several times, once for 10 days after a severe storm.
petegossett wrote:
I have a friend with a natural gas Generac on their house. It's setup with a fully automatic transfer switch, and it cycles its self on once per month for a few minutes whether its needed or not, as preventative maintenance.
They've been very happy with it, and I believe the cost was about $7k a few years ago when they had it installed.
Do you know if it is of the water or air cooled variety? KW rating?
In reply to Mazdax605:
I'm not sure on either(I'll ask though), but it's a 5500 sq-ft Victorian home, so I'm guessing it puts out some power. I know it's probably 6-8' long and 4' high or so.
I know two people with Onans (they bought them together). They are water cooled and 20k watt rated working on propane. I am not 100% sure, but I believe they have a 250 gallon tank that is good for a week of use.
From what I understood, this was the most efficient and water cooled means they are quiet. They both power a ~3200 sq feet house fully, but they have gas kitchen stove/oven and one of them has a solar water heater.
I have spent time at their house when the generator was running and it is extremely quiet. It runs automatically once a week.
At work there is a water cooled Cummins. Its propane with a 500 gallon tank. Its a V8 engine and its loud when running, but I believe its rated at 45-55k watts.
Looks like you are basing your wattage on 240 volts.
You know what iceracer I am basing my wattage on 240. I should do the calculations on 120 volts because I was only clamping one leg of the service. That calculation comes out at a much more reasonable 11kw or so. You know even us professionals make mistakes from time to time.
