Archive for December, 2008

Flux Fusion Energy Costs: Electricity versus Gas

Tuesday, December 23rd, 2008

When comparing the benefits of electric powered fusion units versus gas fired units, one factor that is often overlooked is the running costs. Obviously the costs go beyond just the raw price of the gas and electricity, but here we will just focus on the cost of electricity consumption of the KATANAX K2 Electric Fluxer versus that of a typical 3 or 4 unit gas burner.

The K2 electric unit:
The instrument takes about 15 minutes to heat up to a hold temperature of 1000oC. At a power of 2750W (i.e. the max power) we have a ramp-up energy of 2750 W x 15 min / (60 min / hr) = 688 W/hr = 0.688 kWh (maintaining the holding temperature of 1000oC uses 1.38 kWh).

The typical “oxide” fusion method lasts 20 minutes from start to finish and uses 2065W of energy.
2065W x 20 min / (60 min) = 688 W/hr = 0.688 kW/hr (same as heat-up)

There are three different ways one can use the instrument and each has a different energy usage:

    1.  Start from cold state then run only one fusion:

Energy = (ramp-up) + (fusion cycle) = 0.688 + 0.688 = 1.38kWh per fusion

    1. Continuous fusions:

24/7:Daily = (average power) x (hours per day) = 2065W x 24 = 50 kW per day

    1. Instrument always on, but fuses only a fraction “f” of the time:

Power = (f %) x (average fusion power) + (1-f %) x (standby power)
Daily eg: fusion 30% (f=30%) avg power = 1577 W; Daily=1577W x 24h=38kWh

The typical gas unit:
For this discussion we will focus only on consumption/cost of gas.

From internet information it appears the maximum gas consumption is approximately 19L of propane gas per minute.  The expansion ratio of LPG is approx 250:1, therefore 1 liter of LPG yields 250L of propane gas.
At a consumption rate of 19 L/min (maximum), 1 liquid liter of LPG will last 250/19 = 13 minutes, meaning the unit uses about 5 liters of liquid LPG per hour.

For comparison to the three cases above:

    1. Not applicable for gas units
    2. Continuous fusions, 24/7

(Liters per hour) x (hours in day) = 5 x 24 = 120L/day

    1. Fusions only a fraction “f” of a day

(Liters per hour) x (hours in day) x (f /100)
Example: fusions 30% of the day (f=30%) = 5 x 24 x 0.3 = 36L/day

The calculations for the gas unit are not as concise as for the electric unit, as the average consumption of gas in an approximation.

The Relative Costs:

Obviously the costs of LPG and electricity vary all round the world and are dependent on the time of year, economic factors, etc.  The costs below, for the discussion here, were from recent UK rates.

Case 2, Continuous fusions:

  • Electrical unit uses 50kW per day.  In the UK a domestic kW costs approx 12p, therefore the total cost would be 50 x £0.12 = £6.00
  • LPG unit uses 120L per day.  In the UK LPG costs 55p/L so the total cost would be 120 x £0.55 = £66.00

Case 3,  30% of time spent doing fusions:

  • Electrical unit uses 38kW/h per day.  1 kW costs approx 12p in the UK, so the total cost would be 38 x £0.12 = £4.56.
  • LPG unit uses 36L/day.  LPG costs 55p/L in the UK, so the total cost would be 36 x £0.55 = £19.80

I would stress again that these calculations use a number of assumptions and therefore are not completely accurate.  However it appears that the energy costs are approximately 4 to 10 times higher for a gas burner unit compared to the electric the K2 unit.