Hi. Will a 3-ton horizontal closed loop Tranquility 27 with ClimaDry start and run on a 15 KW stand-by Guardian generator? 10 KW electric strips will be excluded. I need to have about 5 KW power for the rest of the house. Thanks and Regards, Masoud

You probably should ask the Climate Master Dealer

Off the top of my head it sounds marginal.

CM dealer may have a good answer, or not, depending on his / her prior experience sizing generators to heat pumps. Start-up current can be found on unit nameplate - right where it says LRA (Locked Rotor Amps) You need to compare the LRA to the generator's surge rating. I noticed that in the case of my two stage Envision, which I believe shares same compressor models as Tranq 27s, that the LRA is 10 or so amps HIGHER than for a single stage unit of same nominal tonnage - so much for the idea I had that a unit starting on low stage would draw fewer amps. I believe my LRA is 82, which may well exactly match your 3 ton Tranq 27...as a matter of fact, I have a Tranq 27 spec guide and sure enough an 038 has an LRA of 82.

The Guardian / Generac folks may be a better source of advice.

My 1800 RPM Generac 25 KW spec sheet lists 43 Locked Rotor KVA at a 35% voltage dip. I believe that figure is intended to shed light on electric motor starting ability. It may translate to LRA as follows: 43 *(1000/240) = 179.2 LRA at a 35% voltage dip, which may be acceptable for startup surge.

Here's a free, back-of-an-envelope calc for your proposed situation: Suppose your generator has an LRA KVA proportional to mine: (15/25 * 43) = 25.8. From that deduct 6 KVA (5 KW and an allowance for power factor), leaving 19.8 KVA. 19.8 * (1000/240) = 82.5 LRA

That brings us back to my first 2 words - sounds marginal!

Disclaimer - though a degreed electrical engineer I have no practical experience in these matters and am thus a bit out over my skis with the foregoing. The assumption of proportional KVA is suspect as my 1800 RPM generator has a lot more rotational mass than the more typical 3600 RPM units of the same power rating. I think, but am not sure that a generator gets its surge rating partially from the angular momentum of its rotating mass. In addition, my assumption that the published 35% voltage dip Locked Rotor KVA has anything to do with compressor LRA is pure speculation.

The problem with a marginal installation during an extended outage is that the compressor and all the rest of the power electronics are repeatedly subject to the voltage sag - every time the compressor starts - several times per hour. That's not good for the unit or anything else running on the generator at the time.

My advice to buyers of generators is go big or don't bother - the net worth of the electrical stuff in a typical house these days isn't worth the risk of cheaping out on a standby generator

My electrician has been comfortable employing the true 15K generators on your unit......However, some of the generators from generac are rated 15/12K depending on gas, the climadry adds to the draw (though don't know the numbers off the top of my head) and should probably be disabled, without your installers blessing you are doing a dangerous dance with the warranties, we are of course uninformed as to how you arrived at the 5K requirement for the rest of the house (and not all K are alike....ie what else has a heavier start-up draw that might come on at the same time...wells-freezers-hot tubs you don't want frozen....). We truely make the decision on a case by case basis. On a bid for a 13Ksf house recently the homeowner decided not to go geo as his generator would have been the size of a bus (sure glad I measured my time carefully in the bid process), if I hadn't brought it up, they wouldn't have thought of it, but it is an important concern on some of our aging grids.
Call your guys, if they are not available, call the manufacturer of the heat pump and the generator. I'd like to tell you you're fine, but your stakes are awfully high for speculation.
Good luck,
Joe

Even with 25 KW and not much else running there is a brief but severe dip as indicated by house lights when my heat pump starts.

My standby system is whole house, but we must manually switch into the generator the panel containing what I consider big discretionary loads (Range, Dryer, Water Heater). Wife knows how to do this and not to run more than one of those at a time with generator running.

The manager of the electrical supply house tells me he hesitates to recommend a generator less than 35 KW for homeowners down here who want a seamless, brainless whole house setup. Virtually every house down here has 1 or more central air units.

Dewayne, Engineer, and Joe, I thank you for the help.
Regards, Masoud

Update. The power was out for two days last week. My 3 ton Tranquility was powered by a 15 KW Guardian generator (surge amp 107) without any noticeable problems. Aux heat, electric water heater, dryer, dishwasher, and stove are not connected to the generator. Propane cost of the homemade power was around $210. Moving the family, a guest, two parrots, two cats, and a fifty-gal fish tank to a hotel would have been more troublesome.

When the heat pump (compressor LRA 82) started and stopped lights slightly dimmed for a moment, but not significantly worse than when powered by the grid. The lights flickered more when the well pump (LRA 41) came on, regardless of the heat pump being on or off.

At the time when the generator was installed five years ago, its largest load was a 2.5 ton central air conditioner, which it handled well. Concerned about the adequacy of this generator for powering the new geo system, among other resources, I consulted with a Guardian dealer. He suggested installing a hard start kit on the compressor. After a call to Climatemaster's technical support staff and consulting with my geo installer, this suggestion was not recommended. Although, I have seen the suggested use of a hard start kit in Climatemaster / NextEnergy's troubleshooting and other heat pump manufacturers' literature for reducing the flickering of lights to an acceptable level.

Not willing to replace the generator with a larger more expensive one, my alternative plan was to place the 10 KW aux / emergency electric strips on the generator, or simply try to get by, by buying five 1500 w inexpensive electric heaters.

Regards, Masoud

Glad it worked for you. $210 to run the generator for 2 days? Quite a hit!!

Glad it worked as well.

Another example of field experience / data meshing with theory. I wonder if my CFL lights dip more / faster than incandescents, making a dip 'feel' worse.

When I ran my earlier back-of-envelope calculation I included your stated requirement for 5 KW for balance-of-house loads, but you wrote that you excluded many of those loads, so I guess you did not burden the generator with most of the additional 5 KW - good move - easier on your compressor.

Ditto your point that propane is expensive, but uprooting a houseful of folks and pets is even more so.

My design scenario is for Jacksonville to finally get a Cat 3 or so hurricane (hasn't had one since a Cat 2 in 1964) resulting in 2-4 weeks without power and zero propane availability for that duration. I want to be able to spare a few amps for my 75+ year old neighbor. That and oversizing is what we engineers do, sometimes to a fault.

We take the grid's surge ability so much for granted - My house's average load is well below 2 KW, but it takes a generator 10 times that to ride out an outage.