Standby generator setup

[Greg1707]

A company with an office in a two story townhouse is interested in a standby generator. There are no range, dryer or resistance heat. There is just lighting, desktop computers, fax etc. and a heat pump.

The townhouse has a 125 amp service with the disconnect in the meter can. The disconnect feeds a panel in the basement. The basement panel feeds a panel on the first floor and a panel on the second floor.
So, we have a 125 amp service with three panels on three floors!
Is there an option other than installing a 30kw generator (very expensive!) with a 125 amp transfer switch ahead of the basement panel to power the entire townhouse.

 

[360Youth]

Generator will be sized according to calculated load. Your ATS will be sized according to service equipment. You can have a 125amp switch with 20kw generator if that is all you need.

 

[hillbilly1]

You will also need to consider the startup load of the heat pump. Being a heat pump, it may also have resistance heating built into the air handler as a backup, or emergency heat. If so, this can be load shedded if needed.

 

[weressl]

A company with an office in a two story townhouse is interested in a standby generator. There are no range, dryer or resistance heat. There is just lighting, desktop computers, fax etc. and a heat pump.

The townhouse has a 125 amp service with the disconnect in the meter can. The disconnect feeds a panel in the basement. The basement panel feeds a panel on the first floor and a panel on the second floor.
So, we have a 125 amp service with three panels on three floors!
Is there an option other than installing a 30kw generator (very expensive!) with a 125 amp transfer switch ahead of the basement panel to power the entire townhouse.

Get either and engineer to asses the load, or a generator manufacturers rep to do it. (The later also has free download programs, but of course they leave lot of fat in for the laymen user.)

 

[tufts46argled]

Load

Load

It's all about load management. How many tons is the a/c? That is your biggest load, especially start up. Rule of thumb 2.5 times tonage equal starting KW. We install 2 to 3 generators a month. Managing the load is the trick to using smaller generators. If it's a heat pump you can drop out the heat strips, which can be a huge load. We also leave out electric ovens, and some times the dryer. As I said earlier Load Management!

 

[hurk27]

As others have said it will depend upon the connected load, and how much load can be expected at any one time, Generac will have a surge rating that will compensate for AC starting, but not for resistance loads, so if this is a gas heated town home, with gas dryer, gas hot water heater, and range, and a 2 ton AC unit and maybe one extra freezer, I would say a 15kw with a non-service rated auto transfer switch in a R-3 enclosure would do just fine, but if you have more electric loads than this you will need to do a very good load calculations, I believe loads that won't come back on automatically after power is back on from the generator can be left out, as long as the homeowner is aware that they cant run these loads, Electric heat is a biggie as with electric water heater, and a electric tank-less water heaters can even push a 125 amp service over its limit, so these are things to watch out for.

I do many installs but lucky for me almost all houses in this area are all gas, so most will just need a 15 to 20 kw.

 

[hurk27]

Guess I missed the

There are no range, dryer or resistance heat. There is just lighting, desktop computers, fax etc. and a heat pump.

in the OP

Check the loads of the printers and fax machines if laser, they can pull a Lot of wattage, also see what the amperage of the heat pump is, I'm a little surprised as with your location that the heat pump has no strip heaters?

Water heater electric?

but checking these can make the calculation much easier, lighting will depend upon how much is on at any one point in time, if they all will be on then you should include all of them, computers for the most part don't pull that much unless they are some big and bad game machines lol like the one I'm on right now, the power supply is 1200 watts and it heats the room up.