400 amp service -- what is required?

[eepete]

Part of this is the inspectors tell you what you need, but it seemed close. This is an all electric house, let's look at the loads:

3 10KW resistive electric backup for heat pumps: 120 amps
1 five ton and 2 three ton heat pumps: 9KW, 37 amps
2 water heaters (2.5KW each): 20 amps
Cooktop: 20 amps
Dual oven and small oven: 27 amps
Central Vac: 4 amps
Septic Pump: 3 amps

So I'm at 231 amps and still have lights and small appliances left. Now I'll grant you that this would be the holiday throw-down of all time to have all these things going at once, but that's kinda what worst case engineering is all about. And when I build my outbuilding, there will be more power for that too.
Note also that taking two resistive-electric heat pump strips and placing them before the transfer switch makes this worst case load be about 151 amps. Then generator is 45KW --> 180 amps so I have 30 amps left for lights, TVs and computers. It all works out and none one has to think to live in the place- just the way I like it.

 

[MossRoad]

Part of this is the inspectors tell you what you need, but it seemed close. This is an all electric house, let's look at the loads:

3 10KW resistive electric backup for heat pumps: 120 amps
1 five ton and 2 three ton heat pumps: 9KW, 37 amps
2 water heaters (2.5KW each): 20 amps
Cooktop: 20 amps
Dual oven and small oven: 27 amps
Central Vac: 4 amps
Septic Pump: 3 amps

So I'm at 231 amps and still have lights and small appliances left. Now I'll grant you that this would be the holiday throw-down of all time to have all these things going at once, but that's kinda what worst case engineering is all about. And when I build my outbuilding, there will be more power for that too.
Note also that taking two resistive-electric heat pump strips and placing them before the transfer switch makes this worst case load be about 151 amps. Then generator is 45KW --> 180 amps so I have 30 amps left for lights, TVs and computers. It all works out and none one has to think to live in the place- just the way I like it.

Good grief you could fry some serious bacon with that load!

Thanks for the add-up of the loads. I had no idea.

 

[roamerr]

My 36 x 40 garage has a seperate 200 amp service. Now that is overkill but since it is 400 ft from the house I figured go ahead with 200 amp. I mainly needed 50 amp for an RV and then a little more for lights and a compressor. I do not weld but who knows -- I might wanna try it someday.

 

[roamerr]

eepete -- You just need to ad one those on demand electric hot water heaters. I heard 120 to 140 amps for those alone... not for me....

 

[eepete]

@roamerr: The geothermal heat pumps have the water heater feature on them. So we have two 80 gallon tanks. One for the master bedroom zone, one for the main house. We keep the main house at 110 degrees, the master at 120. For 5 months out of the year (heavy cooling cycles), the hot water is free (ok, it's really "pre-paid" with the electric bill). During the winter, the heat pumps can maintain the tanks but not increase the temperature. In the transitional seasons (like we're in now) is when the hot water heaters run the most. This also has an odd side effect of a fairly consistent electric bill.

You point is with merit, though. Who knows what might get added down the road (big air compressor, welding stuff, on demand hot water at some future shop).

@MossRoad: The average draw is less than 25 amps, but it is interesting the difference between average and worst case. I did fire everything up at once before move in and it was all happy. I love sleeping well at night. Off topic but the house also has fire sprinklers in it so it's a really deep sleep.

I've started a project today (just broke ground with my new box blade) that will tie into all this discussion. Should be in the project section in a bit.

 

[ultrarunner]

Part of this is the inspectors tell you what you need, but it seemed close. This is an all electric house, let's look at the loads:

3 10KW resistive electric backup for heat pumps: 120 amps
1 five ton and 2 three ton heat pumps: 9KW, 37 amps
2 water heaters (2.5KW each): 20 amps
Cooktop: 20 amps
Dual oven and small oven: 27 amps
Central Vac: 4 amps
Septic Pump: 3 amps

So I'm at 231 amps and still have lights and small appliances left. Now I'll grant you that this would be the holiday throw-down of all time to have all these things going at once, but that's kinda what worst case engineering is all about. And when I build my outbuilding, there will be more power for that too.
Note also that taking two resistive-electric heat pump strips and placing them before the transfer switch makes this worst case load be about 151 amps. Then generator is 45KW --> 180 amps so I have 30 amps left for lights, TVs and computers. It all works out and none one has to think to live in the place- just the way I like it.

Looks like you've done your homework... I have one place that is all electric... never worked on anything there. Next time I will have to look and see what my service is...

 

[roamerr]

eepete -- I like your details on the Geothermal. My parents built a new house 3 yrs ago and installed Geothermal. I never understood how the water heater worked until you described it. They are running $200 a month average for all electric 3000 sq ft home electric bill. Not too bad.

 

[eepete]

We're averaging $260 per month heating and cooling about 6000 sq. feet where about 1500 is effectively shut of via dampers (so that would be 4500 actively heated and cooled). The project I broke ground on today is a 7.7 KW solar array, the hope is to cut the average monthly bill to $100 to $120.

As for the geothermal hot water, think of it this way. The heat pump compresses the freon to produce about 140 degree freon. Before the main heat exchanger with the ground temperature water, there is a smaller heat exchange that is on a pump that circulates water to your hot water tank. The drain plug at the bottom of the hot water tank is removed and becomes the other connection to the tank (the 1st is the hot water outlet). Water is pumped and the temperature of the water coming back from the tank is monitored. When that hits 125 degrees, the pump shuts off for some amount of time. In this way, your hot water is free if there is sufficient cooling activity. The main heat exchanger is after this small one. It gets rid of the heat into the 60 to 65 degree ground. There is a closed loop system with water in it and the water lines are buried horizontally at 5 and 7 feet deep. So even when it's 95 degrees out the whole thing works like an air exchange heat pump on a 65 degree day. The temperature of the water leaving the exchange is only about 2-3 degrees warmer than what went in.

During the winter, you get 135 degree freon (the ground is a bit cooler since you've been sucking heat out of it). The same system is used, but the pump that pumps from that small heat exchanger for the hot water heater system runs at a much slower speed (it's a two speed pump). So some of the heat is available for the hot water heater. This is how it can maintain temperature, but cant really increase it a whole lot. This is done because you are trying to heat your house at the same time.

Since freon made heat is 3 times as efficient as resistive electric, even though you are taking some of your heat for the house it is still a win. Hope this addition "how it works" is of interest...

Pete

 

[theboman]

Part of this is the inspectors tell you what you need, but it seemed close. This is an all electric house, let's look at the loads:

3 10KW resistive electric backup for heat pumps: 120 amps
1 five ton and 2 three ton heat pumps: 9KW, 37 amps
2 water heaters (2.5KW each): 20 amps
Cooktop: 20 amps
Dual oven and small oven: 27 amps
Central Vac: 4 amps
Septic Pump: 3 amps

So I'm at 231 amps and still have lights and small appliances left. Now I'll grant you that this would be the holiday throw-down of all time to have all these things going at once, but that's kinda what worst case engineering is all about. And when I build my outbuilding, there will be more power for that too.
Note also that taking two resistive-electric heat pump strips and placing them before the transfer switch makes this worst case load be about 151 amps. Then generator is 45KW --> 180 amps so I have 30 amps left for lights, TVs and computers. It all works out and none one has to think to live in the place- just the way I like it.

You won't use electric heat backups and the heat pump at the same time..... More insulation and then more. MOVE if its that cold!

 

[roamerr]

I like your reply Pete. My parents were under the impression that the geothermal provided pretty much all of the hot water as long as it was running. I think their water heater tank is only 50 gallons. Their lines are 600 ft at about 5 to 7 feet also. I believe they were expecting a much lower bill than they have but they are still satisfied. I do like the geothermal system zoning and lack of noise.

I chose heat pumps for my new home mainly because I felt I could not justify the extra $15000 for the Geothermal. I assumed the Geothermal would use less amps at peak but I guess that is not correct...