Washer/dryer

[Trivet]

It all depends on how much your park charges per kWh of electricity versus the cost of a gallon of propane.

Both produce the same amount of heat to run the refrigerator's cooling system, so the one that costs less depends on how much you pay for each source.  Joe Peterson (Escapees co-founder) suggested a 20:1 ratio to determine whether electricity or propane produces the least expensive heat, i.e. electricity at 15 cents per kWh equals propane at $3 a gallon.

Hmm...this doesn't match my real-world experience with a gas/electric refrigerator. 

I have a 4-door Norcold 1200 refrigerator.  It uses about 1/2 gallon of propane per day.  If on electric, it uses about 6.5 kwh/day.

In your example of propane at $3/gallon and electricity at 15 cents/kwh, which you said should produce equal costs for running a given appliance, running my refrigerator on propane would cost $1.50 per day ($3 x .5 gallons) and on electric it would cost $1.00 per day ($.15 x 6.5 kwh). 

 

[Lou Schneider]

Like I said, 20:1 is only a round number approximation and is useful for estimating the overall cost of using propane vs. electricity to create heat, taking into account the relative efficiencies of all appliances in the RV.  The actual BTU ratio for 1 gallon of propane to 1 kWh of electricity is 27:1.

Both the water heater and furnace will have ratios lower than theoretical.  In both cases the electric heating elements are enclosed inside the heated area (the water heater electrode is in the water, an electric heater is inside the living area) so all of electricity's energy is delivered to the load

Both have externally vented flames, so some of the flame's heat goes out the exhaust, lowering the propane to electric ratio.

I suppose the refrigerator's efficiency will edge closer to the theoretical ratio because the gas flame and the electric heating element are adjacent to one another, both are inside the flame plenum so each sends roughly the same amount of waste heat out the flue.  This means for this specific appliance, the break even cost ratio could approach the theoretical 27:1.

FWIW, a gas dryer has it's flame in the same location as an electric dryer's heating element with both sending heat out the exhaust, so it's relative cost ratio should also approximate the theoretical 27:1.

Thanks for the correction!

 

[Trivet]

I suppose the refrigerator's efficiency will edge closer to the theoretical ratio because the gas flame and the electric heating element are adjacent to one another, both are inside the flame plenum so each sends roughly the same amount of waste heat out the flue.  This means for this specific appliance, the break even cost ratio could approach the theoretical 27:1.

Actually, it's the opposite.  The numbers for my refrigerator have a break-even cost ratio of 13:1.

I understand how the 27:1 theoretical ratio was arrived at (by comparing BTUs of a gallon of propane to a kilowatt hour of electricity).  Do you know how the 20:1 ratio was arrived at?  I'm beginning to wonder about the methodology behind the 20:1.

 

[Lou Schneider]

I suspect it was just a nice round number a bit less than the theoretical efficiency to allow for waste heat out the exhaust.  The situation was when Escapees started their park system they found people were automatically run all their stuff on electricity, which raised the operating costs.  So they started charging for electricity and this led to questions about the relative cost of using electricity or propane as a heat source.

 

[kdbgoat]

Maybe this will help everyone:

http://suhresgas.com/propane_vs_electric.htm

 

[Ernie n Tara]

All of the above ignores the variables of actual propane use. I'd expect that the actual efficiency of propane use varies with air flow (insects in the flu) for example and certainly the jets will vary in size as well as gas pressure. An electric element will be much more consistent between refrigerators. The net difference could easily be 50% even within a single design let alone between manufacturers.

Ernie

 

[Lou Schneider]

Maybe this will help everyone:

http://suhresgas.com/propane_vs_electric.htm

Nice calculator, although to get an accurate cost-per-hour the BTUs and the heat efficiency for each appliance has to be adjusted to a more realistic value for RV use.  For example, few RVs have a 100,000 BTU furnace.

Assuming 75% efficiency for a propane heat (25% of the heat lost out the exhaust) and 100% for electric heat gives Joe Peterson's 20:1 cost ratio.

Back to the original subject, there's only a 10% efficiency penalty for gas heat vs. electric in a gas dryer.

 

[kdbgoat]

Nice calculator, although to get an accurate cost-per-hour the BTUs and the heat efficiency for each appliance has to be adjusted to a more realistic value for RV use.  For example, few RVs have a 100,000 BTU furnaces.

The calculator is made to be adjusted as needed.