# Furnace fan motor run directly by natural gas combustion ? Why not?

H

#### HVAC Guy

Jan 1, 1970
0
What is the state of the art of natural-gas powered motors?

I'm talking about something that can replace the typical 1/4 or 1/3 hp
electric fan motor in a residential forced-air natural gas furnace.

If such a natural-gas combustion motor did exist, then you could have
a residential heating solution that would be independant of main
utility power and hence could operate during a power blackout.

Related question: What about AC compressor motors run by natural gas
combustion?

Wouldn't the use of a natural-gas powered AC compressor motor reduce
the electrical load in the summer?

So, what is the current situation regarding small natural-gas powered
motors and their use in HVAC systems as a replacement to electric
motors?

A

#### Arnold Walker

Jan 1, 1970
0
HVAC Guy said:
What is the state of the art of natural-gas powered motors?

I'm talking about something that can replace the typical 1/4 or 1/3 hp
electric fan motor in a residential forced-air natural gas furnace.

If such a natural-gas combustion motor did exist, then you could have
a residential heating solution that would be independant of main
utility power and hence could operate during a power blackout.

Related question: What about AC compressor motors run by natural gas
combustion?

Wouldn't the use of a natural-gas powered AC compressor motor reduce
the electrical load in the summer?

So, what is the current situation regarding small natural-gas powered
motors and their use in HVAC systems as a replacement to electric
motors?
Yes ,they are called gas turbines....model jet engines are not cheap.
But folks are buying them to fly model planes at 300-400mph or plane or
powering helicopters.
Even seen some who used a jet engine to heat a boiler system.
Can't remember the web site but a company even had a wood powered jet made
from turbochargers.

H

#### HVAC Guy

Jan 1, 1970
0
Arnold said:
Yes ,they are called gas turbines....

I was thinking more along the lines of a piston-operated combustion
motor - not a turbine.

V

#### Vaughn Simon

Jan 1, 1970
0
HVAC Guy said:
So, what is the current situation regarding small natural-gas powered
motors and their use in HVAC systems as a replacement to electric
motors?

I don't have a direct answer to your question, but there is the Honda micro
CHP system which produces hot water and electricity from natural gas. So far, I
believe they are marketed mostly in Japan.

http://www.hondanews.com/CatID5065?mid=2005042628647&mime=asc

Vaughn

H

#### HVAC Guy

Jan 1, 1970
0
beemerwacker said:
There are a lot of internal combustion engines that run on natural
gas. Wouldn't a natural gas powered generator be a better option?
That way power is provided to the entire home as well as the
furnace.

The loss in converting NG to AC and then using AC to power a
mechanical process (ie furnace fan) is not very attractive.

Since NG is being piped to a furnace already, and since furnaces
already have a waste (combustion) stack, and since the waste heat from
a NG-powered fan could be used by the furnace to help in heating the
air, I would think it's a no-brainer that a fan run directly by NG
combustion would be great for a furnace. Assuming it's quiet.

The problem with a gas powered generator for home use is that it would
have to be sized quite large to be able to handle 5 to 10 kw on a
continuous basis if you really wanted to cut yourself from the grid.
If there is a 10 kw NG generator rated for continuous residential use
that will last for 10+ years, then tell me where I can get one.

When are we (in North America) going to see a totally NG-powered
residential HVAC solution?

Why are we not seeing it by now?

H

#### HVAC Guy

Jan 1, 1970
0
Vaughn said:
I don't have a direct answer to your question, but there is the
Honda micro CHP system which produces hot water and electricity
from natural gas.

I think it's a shame that there is no direct solution to use NG
combustion to drive furnace fans and AC compressors.

Using NG to drive a generator and then use that electricity to run an
electric furnace motor and/or electric AC compressor is a waste.

V

#### Vaughn Simon

Jan 1, 1970
0
HVAC Guy said:
If there is a 10 kw NG generator rated for continuous residential use
that will last for 10+ years, then tell me where I can get one.

Why would you want to do that? I have a little 4KW Onan NG genny for
standby house power. I figure that fuel would cost me about $700 per month if ran it 24/7. My normal electric bill is about$100. End of story.

If you had a use for all of the waste heat, the story might be different; but
probably not when you consider maintenance, depreciation on the equipment, and
cost of capital. The grid is the best bargain you will ever get.

Vaughn

H

#### HVAC Guy

Jan 1, 1970
0
Anthony said:
I imagine that the loss of reliability in switching to an internal
combustion engine for the furnace fan would not be very attractive
either.

One doesn't have to power the entire home in an emergency.

Both items (reliability and minimal electrical generation) could be
served by this unit:

http://www.hondanews.com/CatID5065?mid=2005042628647&mime=asc

http://www.appliancedesign.com/CDA/Archives/945ab419cca38010VgnVCM100000f932a8c0____

http://findarticles.com/p/articles/mi_m0FZX/is_8_71/ai_n15341475

"The tightly packaged Honda MCHP system is built around a
single-cylinder vertical crankshaft gas engine that Honda developed
specifically for this use. The engine, which can operate on natural
gas or propane, drives a newly developed 27-pole generator"

"The goal is to operate the engine, with its modest heat output, close
to 100% of the time throughout the heating season in order to maximize
electricity production."

So there ya go. A single cylinder gas engine designed for continuous
use, mainly to drive a 1 kw generator. Heat recovery from the engine
is used directly to heat a home or building, and the electricity would
presumably be used to run the air-handling fan with some left over for
(probably) lighting.

Now if they could build a smaller gas-powered motor to directly turn
the fan and maybe a 100 watt generator to power it's own electronic
controls, then they'd have something.

A

#### AJH

Jan 1, 1970
0
I think it's a shame that there is no direct solution to use NG
combustion to drive furnace fans and AC compressors.

There is the possibility using thermoelectric generators but their
conversion efficiency is poor. On the small scale there are a couple
of stoves that use them for the combustion fans and I think Dellpoint
offer one for a pellet stove but it seems not available outside

AJH

A

#### AJH

Jan 1, 1970
0
If such a natural-gas combustion motor did exist, then you could have
a residential heating solution that would be independant of main
utility power and hence could operate during a power blackout.

The whispergen stand alone product should manage to do this if the
parasitic electrical loads were less than 1kW and 10% of the thermal
output.

AJH

H

#### HVAC Guy

Jan 1, 1970
0
It is one of the laws of the universe that, generally, a turbine
thermodynamic cycle is only about 36% efficient.

First item, I don't think we'll be spinning a furnace fan at 10,000
rpm, so we're not talking about turbines here.

More like a piston.

Second thing, we're probably talking very low displacement. We're
only trying to generate 1/4 to 1/2 horsepower.

1 HP = 750 watts, so 1/3 hp = 243 watts

1 BTU per hour = 0.3 watts, 243 watts = 810 btu's per hour

Assuming a 15% efficiency, then we need 5400 btu's per hour. Natural
gas has about 1200 btu's per cubic foot. So we need 4.5 cubic feed of
NG per hour.

I'm currently paying $2.45 (CDN) per cubic meter (which includes a variety of taxes and charges besides the actual cost for the natural gas).$2.45 CDN = $2.07 US =$1.05 GBP.

1 cubic meter = 34.3 cubic feet = $2.45. 4.5 cubic feet = 0.131 cubic meters =$0.32 per hour.

Since most small electric motors are typically 50% efficient, our
original 243 watts needs to double to 500 watts for the actual
electrical energy required. That is actually a bit on the low side -
this web site:

http://www.dbkpowergenerators.com/Sizing Generators.htm

puts the actual wattage needed for 1/3 hp to be more than 700 watts.
So I'll assumne 600 watts.

I'm paying 11.2 cents (CDN) per kwatt-hour (all taxes and other
charges included). For comparison, 11.2 (CDN) = 4.8 (pence?) = 9.5
cents (US).

600 watts = 0.6 kwatt = 6.72 cents per hour.

So, a small NG-powered motor with a theoretical efficiency of 15%
would cost 32 cents per hour to operate, vs 6.7 cents per hour for a
comparible electric motor.

But if the waste heat from the motor were input into a heat exchanger,
perhaps as a return-air pre-heater for the furnace, then the cost of
operation might make this more attractive. Such a motor with
waste-heat capture could be used as the sole heat source during the
low-demand months of the heating season, with the main furnace burners
operating during the middle of the season.

A

#### Arnold Walker

Jan 1, 1970
0
HVAC Guy said:
First item, I don't think we'll be spinning a furnace fan at 10,000
rpm, so we're not talking about turbines here.
First off if you use a turbine it would replace a Becket gun burner.
Second off when we used turbines for that purpose the boiler did 85% boiler
efficiency.
The jet is your gun burner.....granted the heating system your have is lower
than 3,000,000btu
and has more space for a firebox than we had on the boiler.But 100 to 300
pound thrust drone jets fit the ticket as a alternative to a
standard gun burner for the system, we were using them on.And as war surplus
item was price competitive with a Beckett.

H

#### HVAC Guy

Jan 1, 1970
0
Arnold said:
First off if you use a turbine it would replace a Becket gun burner.

What's a "becket gun burner". All I can find on the internet are
references to Becket oil burners.
The jet is your gun burner... But 100 to 300 pound thrust drone
jets fit the ticket as a alternative to a standard gun burner
for the system, we were using them on.

What -

I'm going to mount a jet engine in place of my burners and heat
exchanger and blow combusted gas through my house?

A

#### Arnold Walker

Jan 1, 1970
0
HVAC Guy said:
What's a "becket gun burner". All I can find on the internet are
references to Becket oil burners.
Two terms one name, Becket also offers gas burners.
Gun burners are a type of burner that uses a blower to throw the flame like
a flamethrower.
See them also in large commerical gas ovens......resturant and industrial.
What -

I'm going to mount a jet engine in place of my burners and heat
exchanger and blow combusted gas through my house?
No mention of replacing heat exchanger.....common logic would normally tell
you that anyway.
For same reason you don't run combusted burner gases thru the house.
The jet also has a generator to run the ignition and aux. like that duct
blower you forgot to mention.
Or in my case, boiler feedpump.....jets also can vary flame level more than
most gun burners ,that run
only two or three speeds.

H

#### HVAC Guy

Jan 1, 1970
0
Arnold said:
Gun burners are a type of burner that uses a blower to throw the
flame like a flamethrower.
See them also in large commerical gas ovens...
...resturant and industrial.

We're talking residential furncace here, so no "gun burner".
No mention of replacing heat exchanger...

Well then what's circulating house-hold air through the exchanger?

the electric fan motor with an NG-powered blower motor so that we'd
have a furnace that's not dependant on utility AC power.

S

#### Steve Spence

Jan 1, 1970
0
HVAC said:
We're talking residential furncace here, so no "gun burner".

most residential furnaces I have seen use beckett "gun" burners.

C

#### clare at snyder.on.ca

Jan 1, 1970
0
most residential furnaces I have seen use beckett "gun" burners.
Most residential OIL furnaces use gun burners - most gas use
atmospheric burners.

S

#### Steve Spence

Jan 1, 1970
0
clare said:
Most residential OIL furnaces use gun burners - most gas use
atmospheric burners.

We don't see too many gas furnaces here in the north east. We do convert
a fair number of oil furnaces to run on biodiesel and veggie oil.

G

#### [email protected]

Jan 1, 1970
0
When are we (in North America) going to see a totally NG-powered
residential HVAC solution?

Why are we not seeing it by now?

One of the big problems with any sort of energy conversion is the bigger
it is, the more efficient it can be made. You're lucky to get 25%
efficiency out of a small piston engine. Large diesel engines for various
uses can be found that will get over 40%. Something so small to run just
a furnace blower will likely be in the 15% to 20% efficiency or so, not
counting heat recovery.

Then, you have to start thinking about maintenance. Electric motors can
run forever with little or no maintenance, but that is not the case with
combustion engines of any sort. At the very least the oil in them needs
to be changed regularly, no matter how large or small they are. It really
would be quite a headache in the long run to have to do that.

About the best that is out there on the market right now are cogeneration
facilities. Some college campuses have replaced their heating boilers
with NG fired gas turbines. These generate electricity and the hot
exhaust gases are used to generate steam that the old system used to
provide directly from the boilers. Such facilities can get 80% efficiency
when considering all uses of the energy.

Here in Portland, Ore. one of the new buildings near downtown has such a
facility that provides electricity, hot water, heating and cooling. They
are only economical on a fairly large scale, and require a maintenance
crew to change oil and keep them running, but they are out there.

E

#### EXT

Jan 1, 1970
0
What you are looking for apparently is a 1/4 to 1/3 horsepower piston engine
to drive the blower in the furnace! I suppose one could take one of the tiny
4 stroke Honda piston engines and work out some sort of conversion to
natural gas and jury rig it up to the blower. The engine would have to be
outside of the furnace compartment so that gas doesn't leak into the air
flow and to keep the fan from changing the intake air pressures. It would be
noisy and have to be hand started everytime the blower was needed and need
an exhaust line to keep the CO2 down.

I think generator is simpler and offer some power for the electronics and
possibly some other equipment.

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