dslreports logo
site
 
    All Forums Hot Topics Gallery
spc

spacer




how-to block ads


Search Topic:
uniqs
9321
share rss forum feed

pandora
Premium
join:2001-06-01
Outland
kudos:2
Reviews:
·ooma
·Google Voice
·Comcast
·Future Nine Corp..
reply to nunya

Re: Decent 20-30 KW standby generator

said by nunya:

Wasn't there just another thread about this same thing? You already have the Generac ATS, so you need to look at Guardian, Generac, Siemens, or Centurion.

Yes I have 2 Generac 200 amp ATS switches on a soon to be installed 400 amp service.
--
"If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." - Milton Friedman"

Mr Matt

join:2008-01-29
Eustis, FL
kudos:1
Reviews:
·Millenicom
·Embarq Now Centu..
·Comcast
·CenturyLink
reply to pandora

I would expect that the power required by both of your heat pumps running in the defrost mode simultaneously would be 24 KW or approximately 100 Amps or 50 Amps each. The maximum continuous power from a 20 KW generator is 83 Amps. If you want to be able to use most of your appliances at the same time, you should consider at least a 36 KW Generator, which will provide 150 Amps @ 240 Volts. Since you are having a 400 Amp service installed, for the difference in price I would consider a 48 KW generator.


pandora
Premium
join:2001-06-01
Outland
kudos:2
Reviews:
·ooma
·Google Voice
·Comcast
·Future Nine Corp..
reply to TheMG

said by TheMG:

I agree with Cowboyro.

You'd be much better off using the propane to heat the house directly.

No chimney, no flue, no way to vent propane at this time from inside the house (other than cooktops).
--
"If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." - Milton Friedman"

pandora
Premium
join:2001-06-01
Outland
kudos:2
Reviews:
·ooma
·Google Voice
·Comcast
·Future Nine Corp..
reply to Mr Matt

said by Mr Matt:

I would expect that the power required by both of your heat pumps running in the defrost mode simultaneously would be 24 KW or approximately 100 Amps or 50 Amps each. The maximum continuous power from a 20 KW generator is 83 Amps. If you want to be able to use most of your appliances at the same time, you should consider at least a 36 KW Generator, which will provide 150 Amps @ 240 Volts. Since you are having a 400 Amp service installed, for the difference in price I would consider a 48 KW generator.

I think 30 KW is about it for an above ground 1,000 gallon propane tank in terms of gas flow to drive the generator.

As to defrost, I tend to doubt that much power is required.
--
"If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." - Milton Friedman"

TheMG
Premium
join:2007-09-04
Canada
kudos:3
Reviews:
·NorthWest Tel
reply to pandora

said by pandora:

No chimney, no flue, no way to vent propane at this time from inside the house (other than cooktops).

Modern high efficiency furnaces don't require a chimney. The flue is essentially just a couple of plastic pipes. Ours just runs straight out the side wall of the house nearest the furnace.

The furnace would install in your existing ductwork, assuming you have ductwork in place already.

averagedude

join:2002-01-30
San Diego, CA
Reviews:
·Cox HSI

Click for full size
concentric vent sample
I have to agree with TheMG on this.
Todays furnaces use PVC piping for the combustion air exhaust and intake.
You can run the pipes through the roof or exterior side wall.
Most (if not all) offer a Concentric Vent kit that pipes both combustion air and exhaust in to one pipe so there is only one penetration through the wall or roof.
You can even paint out the pipe to hide it.

Edit
In addition, because the combustion air is piped it, you don't have to worry about combustion air louvers or the furnace using warm room air for combustion air.


nunya
Premium,MVM
join:2000-12-23
O Fallon, MO
kudos:12
Reviews:
·Charter
·voip.ms
·surpasshosting
reply to pandora

We just went through this in another recent thread, and the OP tends to believe that the defrost heaters aren't necessary even though I tried to explain otherwise:

»Anyone have a suggestion for standby whole home generator?
--
If someone refers to herself / himself as a "guru", they probably aren't.


Mr Matt

join:2008-01-29
Eustis, FL
kudos:1
Reviews:
·Millenicom
·Embarq Now Centu..
·Comcast
·CenturyLink
reply to pandora

What is the name plate amps on the condenser and air handler of your heat pumps. Your heat strips already draw about 18 Amps at 240 Volts. Each condenser will probably draw about 25 Amps and each air handler exclusive of your heat strips 5 Amps. When in the defrost mode your current requirement should be around 48 Amps per heat pump. Contact your HVAC contractor and confirm.

The last thing you will want to do is purchase a generator that cannot carry the offered load. I would not recommend guessing because the information is already on the specification plates on your air handler and condenser. My 3.5 ton condenser requires 20 Amps my air handler requires 5 amps and my 4.8 KW heat strip requires 20 Amps for a total of 45 Amps while in the defrost mode. My 2.5 ton condenser requires 40 Amps while in the defrost mode.



cowboyro
Premium
join:2000-10-11
Shelton, CT
reply to pandora

said by pandora:

As to defrost, I tend to doubt that much power is required.

It's whatever heat pumps+strips+air handler require.
From the specs you gave it will be around 10kW *each*.
You may be able to block the strips if you are willing to cope with ice-cold air being blown at full blast for few minutes (trust me I have tested with aux heat off), but it is very unpleasant. For all practical purposes it's like having the A/C on.

pandora
Premium
join:2001-06-01
Outland
kudos:2
Reviews:
·ooma
·Google Voice
·Comcast
·Future Nine Corp..
reply to nunya

said by nunya:

We just went through this in another recent thread, and the OP tends to believe that the defrost heaters aren't necessary even though I tried to explain otherwise:

»Anyone have a suggestion for standby whole home generator?

When I review the Goodman literature, I see the maximum sustained wattage listed as about 4KW per unit in heat mode. Start up wattage is a bit higher.

I believe defrost is done via reversing the heating units, during that time the air handlers will not blow cool air into the house.
--
"If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." - Milton Friedman"

pandora
Premium
join:2001-06-01
Outland
kudos:2
Reviews:
·ooma
·Google Voice
·Comcast
·Future Nine Corp..
reply to Mr Matt

said by Mr Matt:

What is the name plate amps on the condenser and air handler of your heat pumps. Your heat strips already draw about 18 Amps at 240 Volts. Each condenser will probably draw about 25 Amps and each air handler exclusive of your heat strips 5 Amps. When in the defrost mode your current requirement should be around 48 Amps per heat pump. Contact your HVAC contractor and confirm.

The last thing you will want to do is purchase a generator that cannot carry the offered load. I would not recommend guessing because the information is already on the specification plates on your air handler and condenser. My 3.5 ton condenser requires 20 Amps my air handler requires 5 amps and my 4.8 KW heat strip requires 20 Amps for a total of 45 Amps while in the defrost mode. My 2.5 ton condenser requires 40 Amps while in the defrost mode.

Heat strips can't be used on any generator solution I can afford. They are 20KW a piece, and I'd need a 55-60 KW unit. Not affordable. Heat strips are for auxiliary heat only.

The heat pump is a Goodman DSZC18048 condenser, with a CHPF4860D6 Horizton Cased A Coil 4-5 Ton, a MBVC2000AA Modular Blower, a TX5N4A 3-5 ton TXV, R410A, a F200E1037 HoneyWell Media Air Cleaner. F200 Series. 20'' x 25'' and a HKR-20C Slide in Electric Heat Strip 20KW with Breaker.

When the generator is on, emergency heat will be turned off as it is 20 KW (the size of the generator).

The heat pumps are rated to provide power down to -10F.
--
"If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." - Milton Friedman"

pandora
Premium
join:2001-06-01
Outland
kudos:2
Reviews:
·ooma
·Google Voice
·Comcast
·Future Nine Corp..
reply to cowboyro

said by cowboyro:

said by pandora:

As to defrost, I tend to doubt that much power is required.

It's whatever heat pumps+strips+air handler require.
From the specs you gave it will be around 10kW *each*.
You may be able to block the strips if you are willing to cope with ice-cold air being blown at full blast for few minutes (trust me I have tested with aux heat off), but it is very unpleasant. For all practical purposes it's like having the A/C on.

The Generac DLM permits me to turn off the auxiliary heat (and even the heat pumps) as needed based on load. Heat pumps are set to priority 1, strips to 2. The auxiliary heat will not be available during any defrost cycle while using the generator.

However, the air handlers will not blow cold air. There is a plugboard where a minimum temperature from the heat pump can be set when in heat pump mode, if the heat pump doesn't provide sufficient heat, the air handler will turn off until it does.
--
"If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." - Milton Friedman"


cowboyro
Premium
join:2000-10-11
Shelton, CT

1 edit

said by pandora:

However, the air handlers will not blow cold air. There is a plugboard where a minimum temperature from the heat pump can be set when in heat pump mode, if the heat pump doesn't provide sufficient heat, the air handler will turn off until it does.

You really need to understand how it works. If the coils in the air handler can't suck heat from the house the outdoor coils will never defrost. You are defrosting the outdoor coils using heat from the house.
Refrigerant enters the evaporator, it super-cools and absorbs heat from the air. It is then going in the compressor at indoor air temperature and super-heated through compression, releasing the heat. If it cannot absorb heat it cannot release heat. Without air flow the evaporator *WILL* freeze. Frozen coils can lead to compressor damage.

Bob4
Account deleted

join:2012-07-22
New Jersey
reply to TheMG

I think the cleaner power comment might have been with regards to frequency regulation. Someone at work had trouble with his furnace shutting down because the frequency would dip every time his air handler turned on.


Mr Matt

join:2008-01-29
Eustis, FL
kudos:1
Reviews:
·Millenicom
·Embarq Now Centu..
·Comcast
·CenturyLink
reply to pandora

You might want to consider doing what my brother in law did for emergency heat. He has a cottage where the power occasionally fails for several days. The cottage was originally heated by electric baseboard heaters. That was not satisfactory during a power failure so he installed a direct vent propane heater which uses a millivolt thermostat that does not require AC power. When he is out of the cottage he uses the propane heater. The heaters were not expensive and can provide a lot of heat rather than using your heat pumps during a power failure. Consider one or more units like this one:

»www.amazon.com/Home-Comfort-DV21···01AH8K68


pandora
Premium
join:2001-06-01
Outland
kudos:2
Reviews:
·ooma
·Google Voice
·Comcast
·Future Nine Corp..

said by Mr Matt:

You might want to consider doing what my brother in law did for emergency heat. He has a cottage where the power occasionally fails for several days. The cottage was originally heated by electric baseboard heaters. That was not satisfactory during a power failure so he installed a direct vent propane heater which uses a millivolt thermostat that does not require AC power. When he is out of the cottage he uses the propane heater. The heaters were not expensive and can provide a lot of heat rather than using your heat pumps during a power failure. Consider one or more units like this one:

»www.amazon.com/Home-Comfort-DV21···01AH8K68

That could work. I'll have to see what happens over time.
--
"If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." - Milton Friedman"

pandora
Premium
join:2001-06-01
Outland
kudos:2
Reviews:
·ooma
·Google Voice
·Comcast
·Future Nine Corp..
reply to pandora

A 20 KW Generac model 5887 was just shipped from Amazon (sold by Amazon). I'm told via email it will arrive Wednesday November 14.
--
"If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." - Milton Friedman"



tmh

@verizon.net
reply to pandora

said by pandora:

Two 4 ton heat pumps are my ONLY heat source. Both must be able to operate.

Since you already have propane, would it not be simpler (and cost less) to put in a 48k BTU heating stove (or two)? These will work both with and without power.

After Sandy, a 40k BTU stove in my basement kept temperatures in the mid 60's on the main level. That's with the valve midway (I estimate about 30k BTU). The power was off overnight. It was in the 30s outside.

ncbill
Premium
join:2007-01-23
Winston Salem, NC
Reviews:
·AT&T Southeast
reply to Mr Matt

The OP has just essentially doubled his house size IIRC.

Even multiple through-the-wall heaters likely won't be enough to keep his large home comfortable.

I would still urge the OP to swap his current air handler for one with a propane furnace - maybe just the downstairs (heat rises).

I'm sure his local HVAC would have no problem pulling a gas line to the handler and putting in the vent pipe (PVC, as noted) through the nearest outside wall.

said by Mr Matt:

You might want to consider doing what my brother in law did for emergency heat. He has a cottage where the power occasionally fails for several days. The cottage was originally heated by electric baseboard heaters. That was not satisfactory during a power failure so he installed a direct vent propane heater which uses a millivolt thermostat that does not require AC power. When he is out of the cottage he uses the propane heater. The heaters were not expensive and can provide a lot of heat rather than using your heat pumps during a power failure. Consider one or more units like this one:

»www.amazon.com/Home-Comfort-DV21···01AH8K68


TheMG
Premium
join:2007-09-04
Canada
kudos:3
Reviews:
·NorthWest Tel

1 recommendation

said by ncbill:

I would still urge the OP to swap his current air handler for one with a propane furnace

I don't know why the OP is so against that. It is perhaps the easiest and most effective solution.

As I said, he's going to be burning through propane very quickly with that large generator running the heatpumps.

I did some quick math, and if it is correct, the OP's heatpumps at optimum advertised efficiency would consume 4kW to produce 72,000BTU.

Generator he purchased running at 1/2 load will be consuming 1.86 gallon of LPG per hour (manufacturer does not give specs for lesser loads, but presumably the OP will have some other electrical loads beyond the heat pumps operating in the house).

A 90% efficiency propane furnace will consume about 0.84 gallon per hour to produce those same BTUs of heat output. That's less than half!!!!

And that's the BEST CASE SCENARIO. Still need to take into account that the large generator still consumes a lot of fuel even under light loads when the heatpumps aren't running, also that the heatpump is less efficient as outside temperature decreases, the heat strips for defrosting, etc, etc.