Generator won't run heat pump

[kert]

Sunday after 2 tornadoes hit my area, my only problem was no electricity. I feel very lucky; there was major damage just a mile or 2 away. I fired up my generator for the first time. I fired up the generator and turned off the major power draws (4500W water heater, geo-thermal heat pump). I turned the water heater on and the generator bogged briefly and the lights dimmed briefly while the generator reacted, but everything ran fine. I then turned the water heater off and tried my heat pump, but when the compressor would kick on, the generator couldn't react to the draw fast enough to prevent the heat pump from kicking back off due to low voltage.

Has anybody else had similar experienced similar problems? I am pretty sure my 5000W generator should be capable of running the heat pump if it can get past the initial voltage dip. Any ideas? Maybe a much heavier flywheel on the generator.

 

[zmaxmotorsports]

That generator is good for roughly 20a and change,without knowing the specs on your heat pump Im gonna guess its probably pulling closer to 25-30a when that compressortries to start up cold.
Maybe a generator putting out closer to 7200w would work better,but even thats just the heat pump load Im figuring at start up any other combined loads would put you in the same boat your currently in.

 

[Autorotica]

Let me preface my suggestion with...Im not a sparky...

What about adding capacitors to the system to help support the inrush and not pull the voltage down too low?

Chris

 

[charged355]

Does the compressor have soft start? I don't know squat about geothermal heat systems but I know a thing or two about generators. I did a minute of research on this system and it looks like your heat pump + compressor might be to much for the generator depending on size of the system. Below is the random tid bit I found on these systems.

I pulled up the electrical data for Climatemaster Tranquility 27 series geothermal heat pumps as an example as follows:

2 Ton (26K BTU) = 10.3 compressor amps, = 4.0 loop pump amps, = 3.9 fan amps
3 Ton (38K BTU) = 16.7 compressor amps, = 4.0 loop pump amps, = 3.9 fan amps
4 Ton (49K BTU) = 21.2 compressor amps, = 4.0 loop pump amps, = 6.9 fan amps
5 Ton (64K BTU) = 25.6 compressor amps, = 4.0 loop pump amps, = 6.9 fan amps
6 Ton (72K BTU) = 27.2 compressor amps, = 4.0 loop pump amps, = 6.9 fan amps

These are running amp ratings at rated voltage of 230 VAC.

The 2 ton unit requires a circuit wiring/breaker/fuse rated MIN/MAX of 22A/30A
The 3 ton unit requires a circuit wiring/breaker/fuse rated MIN/MAX of 30A/45A
The 4 ton unit requires a circuit wiring/breaker/fuse rated MIN/MAX of 38A/50A
The 5 ton unit requires a circuit wiring/breaker/fuse rated MIN/MAX of 44A/60A
The 6 ton unit requires a circuit wiring/breaker/fuse rated MIN/MAX of 46A/70A

If you were using a unit for radiant floor heat only, you would replace the fan amps listed above with the amp load for the radiant heat circulating pump which would likely be similar to the amps used for the fan. As an example using the 3 ton heat pump specs above, total system running load would be 16.7A + 4.0A + 3.9A = 24.6A @ 230 VAC = 5.7 KW.

Note that the above running loads do not take into consideration the starting amps required for the compressor. The 3 ton compressor above has a starting load of 82 Amps. This can be significantly reduced if your compressor has soft start capability.

 

[kert]

I did a little research myself. 3 Tons of heating capacity is 10500W. If I figure a COP of 3 which seems to be the pessimistic number that geothermal opponents like to use (MFG rating is about 5), I should be looking at 3500W which is well under 5000W. Like I said, it seemed like the heat pump kicked off before the generator could react to the load. I was able to run the water heater, 3/4HP well pump, 600W halogen lamp, and several misc. lights with no issue all at once. With everything else turned off, the heat pump would pump a few times, the generator would barely start to load before the heat pump would kick back off.

I may see if I can find a friend with a 7000W or so generator and try that before I buy anything bigger. I definetely don't want to buy another generator that doesn't do my job.

 

[zmaxmotorsports]

If the oil in the compressor is cold it will be like cranking over a cummins with a cordless drill.

 

[theoldwizard1]

1. What is the peak power of your generator ?
2. What is the make and model # of the heat pump ?
3. Look for the specification plate on the heat pump or look up the specs on the manufacturers web site.
4. Call the manufacturer and see what they have to say.

A bigger flywheel would help, but it would cost you a lot of fuel to keep it spinning all of the time.

Big capacitors would work, but mega/super capacitors are polarized, meaning they won't work in an AC circuit. You could not afford enough AC capacitors to be effective.

 

[crazy wheel]

Just a WAG, Probably need closer to a 15,000 watt generator to start the compressor, without damaging the compressor

 

[Highbeam]

Your genset is too small, obviously. The compressor has a surge at startup that can easily be double the running amps. During that surge your genset won't be able to keep up and voltage will fall. Your very smart compressor senses the voltage drop and cuts out to avoid damage from the low voltage situation.

Your water heater is 4500 watts but is a nice resistive load that is very easy for a genset to handle. No surge on a heater load.

A 5000 watt genset is typically a cheap contractor portable genset with minimal flywheel, minimal reserve, and barely capable of 5000 watts while consuming vast quantities of gasoline and making lots of noise.

Get a woodstove skip the heat pump. It will be cheaper, better, and you won't have to find gasoline at a rate of 1 gallon per hour.

 

[kd3pc]

even with softstart or incremental starters, you will need at 7500, to run just the heat pump. and the genny will need a lot of fuel to do so. at least gal/hour if not more.

10K is usually the smallest that "backup" will be happy with. That gets you in pretty expensive things pretty quickly, and if you live in area that is ethanol only, they chances of the genny actually running WHEN YOU NEED it, is actually close to none.

If you really want to get it right, spend the money on a diesel or NG unit, more efficient and more likely to work when you need it.

 

[frankzlt1]

That portable is too small to handle the lock rotor amperage start up from your heat pump.

 

[Jefflitzy]

20 kw to run a heat pump properly. Anything smaller you will have issuses

 

[oilslick]

even with softstart or incremental starters, you will need at 7500, to run just the heat pump. and the genny will need a lot of fuel to do so. at least gal/hour if not more.

10K is usually the smallest that "backup" will be happy with. That gets you in pretty expensive things pretty quickly, and if you live in area that is ethanol only, they chances of the genny actually running WHEN YOU NEED it, is actually close to none.

If you really want to get it right, spend the money on a diesel or NG unit, more efficient and more likely to work when you need it.

I hate reality, I wish you hadn't reminded me of my last few nights of listening to my 11hp Briggs sing its horrible song while it slurped all my emergency gas up, I am considering a Honda on propane.

 

[BillK]

I don't understand why you guys would rather trust a bunch of guys on an internet forum rather than a generator manufacturer. Here is a link to the Generac web site load calculator.

http://www.generac.com/Residential/Sizer/

I just put in some quick info for my 2500 sq ft house and Maryland zip code and it came up with 15KW-17KW just to back up a heat pump and well pump.

Looks like your 5KW unit is nowhere close to being up to the task.

 

[CNGsaves]

Wrong tool for the job . . . . sorry it's just too small.

Also hope that OP didn't have tornado damage . . . . nothing worse than seeing the news with swath of wiped out houses.

To skimp by, just use your 5Kw genset for true emergency power items - - - - refrigerator, freezer, hot water heater just long enough to take showers, sump pump, lights, etc. For your heating, a temporary solution would be Big Buddy heater that is 18K Btu running on 20 lb BBQ bottle of propane . . . or of course a fireplace if your house has one !!

If you want whole house backup power (ie "Standby" power), then you "need" big standby genset like Kohler or Generac powered with it's own directly piped propane or natural gas - - - like 18 Kw to 25 Kw range. These cost pretty good chunk of change beyond your little 5Kw gasser genset.

IDEA: Any military buddies in area who could haul over a MEP-003a is 10Kw running or MEP-004a which is 15Kw that run on diesel?? These easily run on 125% overload and I'm certain a MEP-004a would run your whole house. See SteelSoldiers website and in particular Sewerzuk who is guru on gensets and also a GJ member.

OP for your safety, I hope genset has proper interconnection with main panel like an interlock breaker . . . . or automatic transfer switch. Do NOT take any shortcuts and risk your safety, or your family, or PoCo employees who might get injured with improper backfeed. Good luck.

 

[theoldwizard1]

According to this table, a 3 ton A/C-Heat Pump takes 75A @ 240V to start.

But 75A @ 240V is 18kW, not the 9kW listed in the same table !

I would definitely borrow/rent a 7000 or 10,000 watt generator and try it before I bought one !!

 

[toyotadriver]

Do you own a tractor with PTO and 3pt hitch? If so, you can get a PTO generator. You should be able to get around 10kw or so with a 20-25 hp tractor.

If you have a bigger tractor, you can get even more KWs from it as long as you buy a big enough PTO generator.

I wouldn't want to run my tractor for a long time to generate power because I don't want to rack up hours just making electricity. But, it's a handy source for a large amount of power for short durations.