Generator install, sizing, location

[techman]

The shed is at an angle to the house. It is about 25' to the corner of the attached garage and about 40' to the house. Overall the conduit run is about 50'. I ran 6 ga wire from the shed for the generator. If you look closely at the picture of the genset you can see the exhaust running out and through the wall (it is the shiny pipe behind the control panel). With this setup I can run the generator with the door closed, but in warmer weather I open the door. Winter I just leave it closed.

The service light was added to the panel. It is a neon light, one side grounded to the panel. The other leg has an additional 10k resistor (to act as a fusible element just in case). I have a porcelain standoff insulator, about 2" long, with a spring (from a ball point pen) attached to the end with a screw, and connected to the other leg of the lamp. The length is such that the spring contacts the main lug on the breaker. Simple system to make contact and safe, as there is a lot of clear area around the lug.

I have since upgraded the system. I built a small circuit (yes I am an engineer) that uses a wrap of insulated around the incoming power cable. The circuit picks up the electrostatic field from the AC voltage and triggers a relay. There is also some logic in the circuit. If power loss is detected, it drives another relay (HVAC heat contactor) that automatically will disconnect the hot water heater. There is a switch on the control to bypass and turn on the hot water heater if needed to reheat the water. If the utility power comes back on, the logic will sound a small alarm beeper if the generator is providing power. This is an annunciator for me (or the wife) that the power is back and the utility can be switched on, and the genset shut off. It only beeps if utility power and generator power are present.

Paul

 

[techman]

Paul, your strategy is about what I was figuring we would do -- I just need to work out the start/run load for our geothermal system to see if it's even in the cards. Otherwise a 14kW unit will be more than enough.

So how far is your shed from the main home, and what wiring gauge did you run? Did you add an exhaust pipe running out of the shed, or just leave a door open?

The interlock we have is very similar to what you show, but it's a GE part made for the GE panel. As shown, it prevents you from engaging the generator feed breaker when the main (grid) breaker is on, and vice versa. Nice and simple.

I had been planning on a Kubota generator (since I have a Kubota tractor and trust them) but that same company now sells Isuzu units that have notably better fuel economy, so I am thinking Isuzu now....

I believe that the fuel consumption between Isuzu and Kubota are nearly the same. I chose a Kubota for the same reason that my tractor is a kubota and filters, etc will be common between the two.

Paul

 

[s219]

I got the specs for my geothermal system, and it's not in the cards for a generator. The system has a run load of 6kW, but the compressor start load, based on the "locked rotor amperage (LRA)" spec given, is a whopping 27kW. So I definitely won't be able to run that with any generator size I consider reasonable to accommodate with a modest fuel tank. We'll probably have to invest in a couple AC window units to cover our butts if we ever have an outage in extreme hot weather (I do have a wall unit in my workshop, but my wife wasn't amused when I suggested we could sleep in there).

I can't get specs for my well pump since it's 250 feet down, but it's on a 20A 240V breaker so it's most likely a 1.0-1.5 HP pump. The water heater is 4.5kW. When I calculate everything, it looks like a 12-14kW generator would do the trick, or a 21kW if I want a lot of margin. The 21kW unit will give me about 1 less day of run time from a 60 gal tank compared to the 12-14kW models for the same load level.

The Isuzu units at generatorsales.com consume 40-90% of the fuel of the Kubotas when comparing across the board, so they can really increase run time quite a bit from a tank of diesel. For instance, comparing 12kW models, the Isuzus consume 0.48 gal/hr at 50% load, compared to the Kubota at 1.0 gal/hr. That's over double the run time.

 

[techman]

Don't over read the LRA current on the heat pumps. All compressors have an inrush which is greater than running, but a surge of 2 to 3 times FLA is within the capability of most well made (not asian import) generators. As I stated, I can start my 2 ton geo unit with the second 2 ton unit running with my 10KW genset. Also likely that one of my three refrig/freezer is running as well. I also have an associate that runs his conventional 3 ton heat pump with a 6KW generac. Heavier units (more spinning mass) typical of these diesel units results in higher surge capacity, with a conservative design generator head. I am sure that a 12 KW will start your geo units.

As for the consumption, I can't believe that the Kubota is half the efficiency of the Isuzu, despite the data shown. If you look at the Isuzu 3CD1BD compared to the Kubota D1305-E3B, both 27-29 HP, they are both burn within a few percent of 0.37 lb/HP/hr (220gm/KW/hr) in fuel consumption. Since both use the same Mecc Alte generator head, the consumption is the same. You can find the engine data on engine manufacturers web sites.

I think your estimate of a 12-14 KW is more than comfortable as a backup.

paul

 

[s219]

Well, I'd much rather the Kubota just because I own and like the brand, so let me research the Isuzu fuel numbers more. For the larger generators, they are close. On the smaller side, it seems like the Isuzus spec a lot better on paper.

Thanks for the input on the LRA number and inrush -- that is good to hear. Changes my outlook considerably.

EDIT: My geo unit pushes 29,500-48,150 BTUH over the whole range of heating/cooling, so that's about 3-4 tons.

 

[techman]

Well, I'd much rather the Kubota just because I own and like the brand, so let me research the Isuzu fuel numbers more. For the larger generators, they are close. On the smaller side, it seems like the Isuzus spec a lot better on paper.

Thanks for the input on the LRA number and inrush -- that is good to hear. Changes my outlook considerably.

Look at: Isuzu Diesel Engines - Series for Isuzu and Kubota Engine Division for kubota. You need to compare 1800 RPM numbers, which is slightly off the chart for Kubota. Also to convert lb/HP/hr to gm/KW/hr, multiply by 0.69 (lb/2.2=KG, 0.746 KW/HP).

Paul

 

[buickanddeere]

Don't purchase for a ample a 10KW generator and expect it to run 10KW 24/7. That max rating is on the ragged edge of the generator. In particular in hot weather.
Of course a diesel engine's lb fuel per HP per hour drops as the engine is progressively loaded heavier.
Sizing for 80% is a good rule of thumb.
Another factor is load balance between Line 1 and Line 2. A 10KW generator can be overloaded with a 6KW load.

 

[techman]

Don't purchase for a ample a 10KW generator and expect it to run 10KW 24/7. That max rating is on the ragged edge of the generator. In particular in hot weather.
Of course a diesel engine's lb fuel per HP per hour drops as the engine is progressively loaded heavier.
Sizing for 80% is a good rule of thumb.
Another factor is load balance between Line 1 and Line 2. A 10KW generator can be overloaded with a 6KW load.

Your points are well taken. Consider that most "big" loads are 240 volt, so they will be balanced on the legs. Most 120 volt loads are relatively. light by comparison. As for the overall capacity, I know that my house averages about 2 KW/hr in the summer and 3 KW/hr in the winter. This corresponds to 20% to 30% of the capacity of my 10 KW genset. I think it would be unusual for a residence to use anything like 10 KW steady state.

Paul

 

[s219]

I did find I can add a "soft start" module to the geothermal compressor to cut the start load by 75%, so that is a good safety net if we have issues running the system off a generator. 12-14kW is looking better and better.

 

[dstig1]

T
I have since upgraded the system. I built a small circuit (yes I am an engineer) that uses a wrap of insulated around the incoming power cable. The circuit picks up the electrostatic field from the AC voltage and triggers a relay. There is also some logic in the circuit. If power loss is detected, it drives another relay (HVAC heat contactor) that automatically will disconnect the hot water heater. There is a switch on the control to bypass and turn on the hot water heater if needed to reheat the water. If the utility power comes back on, the logic will sound a small alarm beeper if the generator is providing power. This is an annunciator for me (or the wife) that the power is back and the utility can be switched on, and the genset shut off. It only beeps if utility power and generator power are present.

Paul

That is really cool. Any pics or another thread showing that?